No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Integrated all-photonic non-volatile multi-level memory
Abstract
Implementing on-chip non-volatile photonic memories has been a long-term, yet elusive goal. Photonic data storage would dramatically improve performance in existing computing architectures by reducing the latencies associated with electrical memories and potentially eliminating optoelectronic conversions. Furthermore, multi-level photonic memories with random access would allow for leveraging even greater computational capability. However, photonic memories have thus far been volatile. Here, we demonstrate a robust, non-volatile, all-photonic memory based on phase-change materials. By using optical near-field effects, we realize bit storage of up to eight levels in a single device that readily switches between intermediate states. Our on-chip memory cells feature single-shot readout and switching energies as low as 13.4 pJ at speeds approaching 1 GHz. We show that individual memory elements can be addressed using a wavelength multiplexing scheme. Our multi-level, multi-bit devices provide a pathway towards eliminating the von Neumann bottleneck and portend a new paradigm in all-photonic memory and non-conventional computing.
... This paper offers an overview of various single-bit and multi-bit OPCM cell designs that have been proposed in the literature. As an example, [19] presented an OPCM chip, which utilizes a GST thin film embedded in a silicon nitride ridge waveguide that could store 0 or 1 based on the GST phase. ...
... Several prototypes have been developed in recent years by using GST-based phase change memory cells. For instance, Rios et al [19] demonstrated that PCMs consisting of GST were capable of fast readout and low switching energy consumption. An optically addressing PCM cell was demonstrated by Zhang et al [81] by using a microring resonator and GST material. ...
Unlike Dynamic Random Access Memory (DRAM), Phase Change Memory (PCM) offers higher density, longer data retention, and improved scalability because of its non-volatility and low leakage power. However, Electrically-Addressable PCM (EPCM) has a higher dynamic power and long latency than DRAM. To address these issues, scientists have developed Optically-Addressable PCM (OPCM), which uses 5-level cells instead of 2-level cells in EPCM. A silicon photonic link allows optical signals to reach OPCM cells at a high speed. Hence, OPCM can achieve a higher density while maintaining better performance at multi-level cells and consuming less power per access. However, OPCM is not suitable for general use since the photonic links do not provide an electrical interface to the processor. The aim of this paper is to present a hybrid OPCM architecture based on the use of novel multi-bank clusters with distinctive properties. Electrical-Optical-Electrical conversion (EOE) allows OPCM cells to be randomly accessed by using DRAM-like circuitry. The proposed hybrid design with multi-core processing and OPCM achieves a 2.13x speedup over previous approaches while consuming less Central Processing Unit (CPU) power. It is important to note that the proposed design offers 97 units fewer power-consistent bits than EPCM. In addition, the proposed architecture provides comparable performance and power to DDR4, as well as improved bandwidth density, space efficiency, and versatility. The Gem5 simulator was used to evaluate the design. Based on the outcomes of the analysis, the proposed architecture offers 2.08x and 2.14x better evaluations and density performance than EPCM. Furthermore, the execution time has been reduced by 2.13x, the analysis time by 1.23x, and the composition time by 4.60%.
... (d) wavelength selective photonic switch based on GST 综 述 Fig. 10 Straight waveguide element device structure [43][44][45][46] . Fig. 11 Hybrid element device structure [47][48][49] . ...
... Phase change materials (PCMs) possess a ′ self-holding ′ quality in which no static power is demanded to sustain the previous state once obtained, hence substantially reducing the power consumption for saving the deployment of a continuous power supply [13,14]. When integrated with an SOI platform, PCMs can provide dynamic control of light with a reduced active volume and correspondingly lower power consumption than is possible with SOI alone [15][16][17][18][19][20][21]. Ge 2 Sb 2 Te 5 (GST) is an outstanding compound semiconductor PCM composed of triple elements: germanium (Ge), antimony (Sb), and tellurium (Te), with an extensive range of optical and electrical properties in distinct phase states. ...
A novel non-volatile optical filter with a large bandwidth and extinction ratiotunability is firstly experimentally demonstrated by introducing all-optical phase change of Ge 2 Sb 2 Te 5 (GST). The Si-GST hybrid device promises flexible multi-level regulation of essential parameters of filters in an ultra-compact footprint of 30 µm×13 µm. Ultra-low power consumption is realized on account of the saving of external static power that required in other electric-optic or optic-optic driven filters. The GST is loaded onto two triple-waveguides directional couplers located at the coupling regions of an add-drop microring resonator. By initiating the GST phase transition with pump optical pulses, the transmitted optical power to the cross port of the triple-waveguides coupler is adjustable, hence influencing the coupling efficiency states of the microring filter. Consequently, a tunable on-off extinction ratio from 0.7 dB to 18.2 dB and a tunable bandwidth from 0.6 nm to 3.3 nm are experimentally obtained with the aid of optically manipulating crystallization degree of GST. Our device potentially enabling the realization of high-density photonic integrated circuits especially in dense wavelength division multiplexing
... (a) Schematic of LMI material structure [25] ; (b) when the input power density of nanorod and quantum dot systems changes, the extinction crosssection (left yaxis) and imaginary part of the refractive index (right yaxis) of the system also change [25] ; (c) nonlinear function of transmittance versus input power density when quantum components are placed at different locations on the waveguide [15] ; (d) schematic of endselectivity of surfactants to gold nanomaterials; (e) microscopic image of nanorods and nanospheres dimer [28] Fig. 6 Nonlinear activation function caused by PCM. (a) Nonlinear conversion before and after optical synapses is achieved through PCM on the waveguide [29] ; (b) optical nonlinear activation function implemented by PCM [5] ; (c) neural network achieved by nonlinear processing of multiple sets of input pulses utilizing PCM [5] Fig. 7 SOA nonlinear activation function. (a) SOAbased MZI implements a logic AND gate [32] ; (b) (c) nonlinear relationship among SOA gain, input optical power, and bias current ［35］ ; (d) Sigmoid trigger function neural network combined with XPM and XGM ［36］ ; (e) onchip SOA array neural network [33] [8] ; (c) four line types that can be achieved by the scheme; (d) diagram of the experimental apparatus [38] ; (e) systemgenerated Sigmoid function; (f)(g) schematic after adding graphene and achievable line patterns [39] 封面文章·特邀综述 第 43 卷 第 16 期/2023 年 8 月/光学学报 ...
... In addition, it is worth noting that a photonic counterpart of an electronic crossbar array has been demonstrated 34 . The passive photonic crossbar array uses waveguide directional couplers and crossings as interconnects and phase-change materials (PCMs) as memories (optical transmissions tuned by the non-volatile crystalline state of the PCM 36 ). ...
New developments in hardware-based ‘accelerators’ range from electronic tensor cores and memristor-based arrays to photonic implementations. The goal of these approaches is to handle the exponentially growing computational load of machine learning, which currently requires the doubling of hardware capability approximately every 3.5 months. One solution is increasing the data dimensionality that is processable by such hardware. Although two-dimensional data processing by multiplexing space and wavelength has been previously reported, the use of three-dimensional processing has not yet been implemented in hardware. In this paper, we introduce the radio-frequency modulation of photonic signals to increase parallelization, adding an additional dimension to the data alongside spatially distributed non-volatile memories and wavelength multiplexing. We leverage higher-dimensional processing to configure such a system to an architecture compatible with edge computing frameworks. Our system achieves a parallelism of 100, two orders higher than implementations using only the spatial and wavelength degrees of freedom. We demonstrate this by performing a synchronous convolution of 100 clinical electrocardiogram signals from patients with cardiovascular diseases, and constructing a convolutional neural network capable of identifying patients at sudden death risk with 93.5% accuracy.
... However, PCMs present another degree of freedom for tunability: the possibility to encode multilevel non-volatile states via partial crystallization. Recently, several works exploited this potential of PCMs for devices in waveguides, thin-films or metasurfaces [12][13][14][15][16][17]. Even though it may appear straightforward to prepare a thin-film to a desired level of partial crystallization -after all, one should just bring it to the correct temperature for a given duration -several issues make it a serious challenge to face. ...
We propose and demonstrate a simple method to accurately monitor and program arbitrary states of partial crystallization in phase-change materials (PCMs). The method relies both on the optical absorption in PCMs as well as on the physics of crystallization kinetics. Instead of raising temperature incrementally to increase the fraction of crystallized material, we leverage the time evolution of crystallization at constant temperatures and couple this to a real-time optical monitoring to precisely control the change of phase. We experimentally demonstrate this scheme by encoding a dozen of distinct states of crystallization in two different PCMs: GST and Sb 2 S 3 . We further exploit this ’time-crystallization’ for the in-situ analysis of phase change mechanisms and demonstrate that the physics of crystallization in Sb 2 S 3 is fully described by the so-called Johnson-Mehl-Avrami-Kolmogorov formalism. The presented method not only paves the way towards real-time and model-free programming of non-volatile reconfigurable photonic integrated devices, but also provides crucial insights into the physics of crystallization in PCMs.
... 13,14 In general, electronic systems are currently superior in data processing and storage for the flexibility in terms of electronic operation for different purposes. In contrast, photonics is capable of storing and processing data in an optical manner with unprecedented bandwidth and higher speed; [15][16][17] therefore, photonic computing is thought as one of the best candidates for a future computing system. 18,19 Nowadays, various kinds of photonic computing devices by using different materials, for example, phase-change materials (PCMs), 15,16,20 hybrid perovskites materials, 21 and silicon-based material 22 have widely been demonstrated. ...
Photonic computing has the potential to significantly improve energy efficiency and data processing speed beyond that of von Neumann architecture. Although various optical processing techniques have been developed during recent two decades, the photonic manipulation is still a big challenging due to the bosonic nature of photons. Herein, we propose a ferroelectric field-controlled photonic computing based on the heterostructure of ferroelectric/van der Waals semiconductor. The strong and tunable electrostatic coupling of ferroelectric (PMN-PT) with monolayer WS2 results in a multi-level (24 bits) photoluminescence (PL) output. Furthermore, combining device modeling with experiments, we find that the multi-level PL output is because of the regulation of ferroelectric polarization on the net recombination rate of WS2. The ferroelectric field-controlled multi-level PL output enables us to design an optical arithmetic operation in the PMN-PT/WS2 heterostructure, which provides an attractive solution for photonic information computing.
... Integrated optics is to build up some optical components, such as light-emitting elements, lighttransmitting devices, and receiving elements, on the same substrate/chip in the form of thin films to manufacture a micro-optical system with independent functions. 1 The first problem to be solved in integrated optics is to use thin films to propagate light waves, that is, to utilize thin films as optical waveguides. 2 Relying on the principle of total internal reflection, the waveguide restricts light to propagate in a certain direction. 3 According to the different structures, it can be generally divided into planar and strip waveguides. ...
In this work, the ridge waveguide was formed by the femtosecond laser ablation with a central wavelength of 0.808 μm and a speed of 50 μm/s on the planar Nd³⁺‐doped fluorophosphate glass waveguide that was fabricated by the C³⁺ ion implantation with an energy of 6.0 MeV and a fluence of 1.0×10¹² C³⁺s/mm². The mechanism of the ion‐implanted waveguide was discussed by the Stopping and Range of Ions in Matter 2013. The cross‐section morphology of the ridge waveguide was captured by an optical microscope. Its mode characteristics were analyzed by the end‐face coupling method. The ridge Nd³⁺‐doped fluorophosphate glass waveguides have potential as fundamental structures for many optoelectronic devices including waveguide amplifiers and lasers.
... In general, the flagship phase change material is ternary Ge 2 Sb 2 Te 5 , which is a pseudo-binary chalcogenide material typically comprising Sb 2 Te 3 and GeTe [17][18][19][20][21][22]. In amorphous Ge -Sb-Te (GST) compounds, the atoms are randomly distributed without long-range order and can be sequentially crystallized into an equilibrium hexagonal structure, as illustrated in Figure 1(a) [23]. The crystalline states generally exhibit low electrical resistivity and low transmittance, whereas the amorphous states exhibit high electrical resistivity and high transmittance. ...
Phase-change memory (PCM), recently developed as the storage-class memory in a computer system, is a new non-volatile memory technology. In addition, the applications of PCM in a non-von Neumann computing, such as neuromorphic computing and in-memory computing, are being investigated. Although PCM-based devices have been extensively studied, several concerns regarding the electrical, thermal, and structural dynamics of phase-change devices remain. In this article, aiming at PCM devices, a comprehensive review of PCM materials is provided, including the primary PCM device mechanics that underpin read and write operations, physics-based modeling initiatives and experimental characterization of the many features examined in nanoscale PCM devices. Finally, this review will propose a prognosis on a few unsolved challenges and highlight research areas of further investigation.
... The ability to precisely control the V T of a transistor allows it to be used as a memory element, such as flash memory. In recent years, beyond-binary tunability between the "1" and "0" states has become particularly interesting in post-von Neumann applications, such as neuromorphic computation 1,2 , multi-state memory 3,4 and multiplexed sensing 5 . The capacity to finely tune V T over a wide range is crucial for these applications, as it directly impacts the storage capacity and weight precision of associated devices. ...
The scaling of transistors with thinner channel thicknesses has led to a surge in research on two-dimensional (2D) and quasi-2D semiconductors. However, modulating the threshold voltage ( V T ) in ultrathin transistors is challenging, as traditional doping methods are not readily applicable. In this work, we introduce a optical-thermal method, combining ultraviolet (UV) illumination and oxygen annealing, to achieve broad-range V T tunability in ultrathin In 2 O 3 . This method can achieve both positive and negative V T tuning and is reversible. The modulation of sheet carrier density, which corresponds to V T shift, is comparable to that obtained using other doping and capacitive charging techniques in other ultrathin transistors, including 2D semiconductors. With the controllability of V T , we successfully demonstrate the realization of depletion-load inverter and multi-state logic devices, as well as wafer-scale V T modulation via an automated laser system, showcasing its potential for low-power circuit design and non-von Neumann computing applications.
... Applications of GST films, 52 such as THz and IR modulators and filters, 33 spatial light modulators, 53 memory and logic devices, 54 or even neuromorphic photonic devices, 55 require precise knowledge of their dielectric and optical constants in the THz and IR ranges. The retrieved broadband complex dielectric permittivity of the three GST phases [Fig. ...
Phase-change alloy Ge2Sb2Te5 (GST) forms a favorable material platform for modern optics, photonics, and electronics thanks to a pronounced increase in conductivity with thermally induced phase transitions from amorphous (a-GST) into cubic (c-GST) and then hexagonal (h-GST) crystalline states at the temperatures of ≃150 and ≃300 Co, respectively. Nevertheless, the data on broadband electrodynamic response of distinct GST phases are still missing, which hamper the design and implementation of related devices and technologies. In this paper, a-, c-, and h-GST films on a sapphire substrate are studied using broadband dielectric spectroscopy. For all GST phases, complex dielectric permittivity is retrieved using Drude and Lorentz models in the frequency range of 0.06-50 THz or the wavelength range of ≃5000-6 μm. A contribution from the free charge-carriers conductivity and vibrational modes to the broadband response of an analyte is quantified. In this way, the Drude model allows for estimation of the static (direct current-DC) and dynamic (at 1.0 THz) conductivity values, caused by motions of free charges only, which are as high as σ_DC ≃ 15 and 40 S/cm and σ_1.0THz ≃ 8.8 and 28.6 S/cm for the c-and h-GSTs, respectively. This overall agrees with the results of electrical measurements of GST conductivity using the four-point probe technique. The broadband electrodynamic response models obtained for the three GST phases are important for further research and developments of GST-based devices and technologies.
Published under an exclusive license by AIP Publishing.
A high‐throughput ion beam sputtering system is used to synthesize compositional gradient superlattice‐like (SLL) thin film libraries of Ge–Sb–Te alloys over the entire phase diagram. The optical properties and structural evolution of the Ge–Sb–Te combinatorial SLL thin film are investigated. A systematic screening over the annealing temperature, annealing time, and modulation period has elucidated the critical factors that affect the stability of the metastable phase and optical properties. It is found that amorphous stability and optical constant are highly dependent on the modulation period and chemical composition of the thin film. This data‐driven approach offers new perspectives for accelerating the development of new materials with excellent optical and amorphous stability and for exploring their mechanisms, by greatly expanding the dataset of Ge–Sb–Te alloys with SLL structures through high‐throughput experiments.
Photonic Integrated Circuits (PICs) are revolutionizing the realm of information technology, promising unprecedented speeds and efficiency in data processing and optical communication. However, the nanoscale precision required to fabricate these circuits at scale presents significant challenges, due to the need to maintain consistency across wavelength‐selective components, which necessitates individualized adjustments after fabrication. Harnessing spectral alignment by automated silicon ion implantation, in this work scalable and non‐volatile photonic computational memories are demonstrated in high quality resonant devices. Precise spectral trimming of large‐scale photonic ensembles from few picometers to several nanometres is achieved with long‐term stability and marginal loss penalty. Based on this approach spectrally aligned photonic memory and computing systems for general matrix multiplication are demonstrated, enabling wavelength multiplexed integrated architectures at large scales.
This article is protected by copyright. All rights reserved
Programmable photonic integrated circuits offer exciting opportunities for optoelectronic signal processing, computing and communications in a number of emerging applications in classical and quantum photonics. In this work, we show the array-level demonstration of tunable couplers and phase shifters with capacitive electrostatic microelectromechanical actuators in a recirculating mesh network. The overall fabrication process is compatible with the conventional wafer-level passive silicon photonics platform. Extremely low unit-level standby power consumption of <10 femtowatts and reconfiguration energy of <40 picojoules with <11 V programming voltages offer well-balanced, scalable routes for efficient phase and amplitude modulation of the guided lightwaves with sub-decibel optical losses. The extinction ratios of the continuously tunable directional coupler exceed 30 dB. Full 2π-phase shifting can be achieved with a modulation efficiency of less than 0.075 V cm and a phase-dependent insertion-loss variation of 0.01 dB.
Owing to their unique tunable optical properties, chalcogenide phase change materials are increasingly being investigated for optics and photonics applications. However, in situ characterization of their phase transition characteristics is a capability that remains inaccessible to many researchers. Herein, a multifunctional silicon microheater platform capable of in situ measurement of structural, kinetic, optical, and thermal properties of these materials is introduced. The platform can be fabricated leveraging industry‐standard silicon foundry manufacturing processes. This platform is fully open‐sourced, including complete hardware design and associated software codes.
The burgeoning of artificial intelligence has brought great convenience to people’s lives as large-scale computational models have emerged. Artificial intelligence-related applications, such as autonomous driving, medical diagnosis, and speech recognition, have experienced remarkable progress in recent years; however, such systems require vast amounts of data for accurate inference and reliable performance, presenting challenges in both speed and power consumption. Neuromorphic computing based on photonic integrated circuits (PICs) is currently a subject of interest to achieve high-speed, energy-efficient, and low-latency data processing to alleviate some of these challenges. Herein, we present an overview of the current photonic platforms available, the materials which have the potential to be integrated with PICs to achieve further performance, and recent progress in hybrid devices for neuromorphic computing.
The recent wave of the artificial intelligence (AI) revolution has aroused unprecedented interest in the intelligentialize of human society. As an essential component that bridges the physical world and digital signals, flexible sensors are evolving from a single sensing element to a smarter system, which is capable of highly efficient acquisition, analysis, and even perception of vast, multifaceted data. While challenging from a manual perspective, the development of intelligent flexible sensing has been remarkably facilitated owing to the rapid advances of brain-inspired AI innovations from both the algorithm (machine learning) and the framework (artificial synapses) level. This review presents the recent progress of the emerging AI-driven, intelligent flexible sensing systems. The basic concept of machine learning and artificial synapses are introduced. The new enabling features induced by the fusion of AI and flexible sensing are comprehensively reviewed, which significantly advances the applications such as flexible sensory systems, soft/humanoid robotics, and human activity monitoring. As two of the most profound innovations in the twenty-first century, the deep incorporation of flexible sensing and AI technology holds tremendous potential for creating a smarter world for human beings.
Chalcogenide phase change materials (PCMs) have become one of the most promising material platforms for the Optics and Photonics community. The unparalleled combination of nonvolatility and large optical property modulation promises devices with low‐energy consumption and ultra‐compact form factors. At the core of all these applications lies the difficult task of precisely controlling the glassy amorphous and crystalline domains that compose the PCM microstructure and dictate the optical response. A spatially controllable glassy‐crystalline domain distribution is desired for intermediate optical response (vs. binary response between fully amorphous and crystalline states), and temporally resolved domains are sought after for repeatable reconfiguration. In this perspective, we briefly review the fundamentals of PCM phase transition in various reconfiguring approaches for optical devices. We discuss each method's underpinning mechanisms, design, advantages, and downsides. Finally, we lay out current challenges and future directions in this field.
Programmable photonics play a crucial role in many emerging applications, from optical accelerators for machine learning to quantum information technologies. Conventionally, photonic systems are tuned by mechanisms such as the thermo-optic effect, free carrier dispersion, the electro-optic effect, or micro-mechanical movement. Although these physical effects allow either fast (>100 GHz) or large contrast (>60 dB) switching, their high static power consumption is not optimal for programmability, which requires only infrequent switching and has a long static time. Non-volatile materials, such as phase-change materials, ferroelectrics, vanadium dioxide, and memristive metal oxide materials, can offer an ideal solution thanks to their reversible switching and non-volatile behavior, enabling a truly “set-and-forget” programmable unit with no static power consumption. In recent years, we have indeed witnessed the fast adoption of non-volatile materials in programmable photonic systems, including photonic integrated circuits and free-space meta-optics. Here, we review the recent progress in the field of programmable photonics, based on non-volatile materials. We first discuss the material’s properties, operating mechanisms, and then their potential applications in programmable photonics. Finally, we provide an outlook for future research directions. The review serves as a reference for choosing the ideal material system to realize non-volatile operation for various photonic applications.
We present an adaptive optical neural network based on a large-scale event-driven architecture. In addition to changing the synaptic weights (synaptic plasticity), the optical neural network’s structure can also be reconfigured enabling various functionalities (structural plasticity). Key building blocks are wavelength-addressable artificial neurons with embedded phase-change materials that implement nonlinear activation functions and nonvolatile memory. Using multimode focusing, the activation function features both excitatory and inhibitory responses and shows a reversible switching contrast of 3.2 decibels. We train the neural network to distinguish between English and German text samples via an evolutionary algorithm. We investigate both the synaptic and structural plasticity during the training process. On the basis of this concept, we realize a large-scale network consisting of 736 subnetworks with 16 phase-change material neurons each. Overall, 8398 neurons are functional, highlighting the scalability of the photonic architecture.
Optical phase-change materials are highly promising for emerging applications such as tunable metasurfaces, reconfigurable photonic circuits, and non-von Neumann computing. However, these materials typically require both high melting temperatures and fast quenching rates to reversibly switch between their crystalline and amorphous phases: a significant challenge for large-scale integration. In this work, we use temperature-dependent ellipsometry to study the thermo-optic effect in GST and use these results to demonstrate an experimental technique that leverages the thermo-optic effect in GST to enable both spatial and temporal thermal measurements of two common electro-thermal microheater designs currently used by the phase-change community. Our approach shows excellent agreement between experimental results and numerical simulations and provides a noninvasive method for rapid characterization of electrically programmable phase-change devices.
Optical switches based on phase change materials (PCMs) hold great promise for various photonic applications such as telecommunications, data communication, optical interconnects, and signal processing. Their non-volatile nature as well as rapid switching speeds make them highly desirable for developing advanced and energy-efficient optical communication technologies. Ongoing research efforts in exploring new PCMs, optimizing device designs, and overcoming existing challenges are driving the development of innovative and high-performance optical switches for the next generation of photonics applications. In this study, we design and experimentally demonstrate a novel optical amplitude switch design incorporating PCM antimony trisulfide (Sb 2 S 3 ) based on the Brewster angle phenomenon.
Perovskites field‐effect transistors (PeFETs) have been intensively investigated for their application in detector and synapse. However, synapse based on PeFETs is still very difficult to integrate excellent charge carrier transporting ability, photosensitivity and nonvolatile memory effects into one device, which is very important for developing bionic electronic devices and edge computing. Here, two‐dimensional perovskites were synthesized by incorporating fused π‑conjugated pyrene‐O‐ethyl‐ammonium (POE) ligands and a systematic study was conducted to obtain enhanced performance and reliable PeFETs. The optimized (POE)2SnI4 transistors display the hole mobility over 0.3 cm2V−1s−1, high repeatability and operational stability. Meanwhile, the derived photo memory devices show remarkable photoresponse, with a switching ratio higher than 105, high visible light responsivity (>4×104 A/W), and stable storage‐erase cycles, as well as competitive retention performance (104 s). The photoinduced memory behavior can be benefiting from the insulating nature of quantum‐well in 2D perovskite under dark and its excellent light sensitivity. The excellent photo memory behaviors have been maintained after 40 days in a N2 atmosphere. Finally, a 2D perovskite‐only transistors with a multi‐level memory behavior (16 distinct states) was described by controlling incident light pulse. This work provides broader attention toward 2D perovskite and optoelectronic application.
This article is protected by copyright. All rights reserved
Spiking Neural Networks, also known as third generation Artificial Neural Networks, have widely attracted more attention because of their advantages of behaving more biologically interpretable and being more suitable for hardware implementation. Apart from using traditional synaptic plasticity, neural networks can also be based on threshold plasticity, achieving similar functionality. This can be implemented using e.g. the Bienenstock, Cooper and Munro rule. This is a classical unsupervised learning mechanism in which the threshold is closely related to the output of the post-synaptic neuron. We show in simulations that the threshold characteristics of the nonlinear effects of a microring resonator integrated with Ge 2 Sb 2 Te 5 demonstrate some complex dependencies on the intracavity refractive index, attenuation, and wavelength detuning of the incident optical pulse, and exhibit class II excitability. We also show that we are able to modify the threshold power of the microring resonator by the changes of the refractive index and loss of Ge 2 Sb 2 Te 5, due to transitions between the crystalline and amorphous states. Simulations show that the presented device exhibits both excitatory and inhibitory learning behavior, either lowering or raising the threshold.
Advanced memory technologies are impacting the information era, representing a vibrant research area of huge electronic industry interest. The demand for data storage, computing performance and energy efficiency is increasing exponentially and will exceed the capabilities of current information technologies.
Alternatives to traditional silicon technology and novel memory principles are expected to meet the need of modern data-intensive applications such as “big data” and artificial intelligence (AI). Functional materials or methodologies may find a key role in building novel, high speed and low power consumption computing and data storage systems.
This book covers functional materials and devices in the data storage areas, alongside electronic devices with new possibilities for future computing, from neuromorphic next generation AI to in-memory computing.
Summarizing different memory materials and devices to emphasize the future applications, graduate students and researchers can systematically learn and understand the design, materials characteristics, device operation principles, specialized device applications and mechanisms of the latest reported memory materials and devices.
This study proposes a general strategy for constructing an asymmetric Fabry–Perot structure based on an ultra‐thin composite absorber, Ni/Ge 2 Sb 2 Se 4 Te 1 , to produce reflective full‐color structural colors with high brightness and purity. The composite absorber effectively enhances the strong interference effect of thin film, which can significantly reduce the reflection bandwidth of the target band and the reflectivity of the non‐target band. Under the premise of optimizing the five‐layer base structure, full‐color structural colors can be tuned by only changing the thickness of the LaTiO 3 layer. Using the ion‐assisted electron beam evaporation technique, a simple and efficient film deposition process, six color devices (namely red, orange, yellow, green, blue, and purple) are successfully prepared with reflection peaks exceeding 90%. The chromaticity coordinates of the proposed high‐purity red, green, and blue (RGB) samples are (0.554, 0.339), (0.280, 0.600), and (0.164, 0.075), respectively. These coordinates are fairly close to the standard RGB color coordinates used in liquid crystal displays. This device has a simple structure with a novel material combination and a low production cost, which makes it feasible for mass production using just one coating run process. It has excellent application potential in various fields such as micro‐nano displays, anti‐counterfeiting measures, reflective color filters, and decorations.
Polarizers are used to eliminate the undesired polarization state and maintain the other one. The phase change material Ge 2 Sb 2 Se 4 Te 1 (GSST) has been widely studied for providing reconfigurable function in optical systems. In this paper, based on a silicon waveguide embedded with a GSST, which is able to absorb light by taking advantage of the relatively large imaginary part of its refractive index in the crystalline state, a multifunctional polarizer with transverse electric (TE) and transverse magnetic (TM) passages has been designed. The interconversion between the two types of polarizers relies only on the state switching of GSST. The size of the device is 7.5µm∗4.3µm, and the simulation results showed that the extinction ratio of the TE-pass polarizer is 45.37 dB and the insertion loss is 1.10 dB at the wavelength of 1550 nm, while the extinction ratio (ER) of the TM-pass polarizer is 20.09 dB and the insertion loss (IL) is 1.35 dB. For the TE-pass polarizer, a bandwidth broader than 200 nm is achieved with ER>20dB and IL<2.0dB over the wavelength region from 1450 to 1650 nm and for the TM-pass polarizer, ER>15dB and IL<1.5dB in the wavelength region from 1525 to 1600 nm, with a bandwidth of approximately 75 nm.
Phase Change Materials (PCMs) have demonstrated tremendous potential as a platform for achieving diverse functionalities in active and reconfigurable micro-nanophotonic devices across the electromagnetic spectrum, ranging from terahertz to visible frequencies. This comprehensive roadmap reviews the material and device aspects of PCMs, and their diverse applications in active and reconfigurable micro-nanophotonic devices across the electromagnetic spectrum. It discusses various device configurations and optimization techniques, including deep learning-based metasurface design. The integration of PCMs with Photonic Integrated Circuits and advanced electric-driven PCMs are explored. PCMs hold great promise for multifunctional device development, including applications in non-volatile memory, optical data storage, photonics, energy harvesting, biomedical technology, neuromorphic computing, thermal management, and flexible electronics.
In this work we experimentally demonstrate a Si3N4 Photonic Integrated Circuit which offers Row Decoding and RAM addressing functionalities. The passive integrated structure comprises a MRR-based wavelength filtering bank scheme in a 2x4 configuration, which reveals a suppression ratio in the range of 12-25 dB. The performance of the optical circuit has been evaluated in a system-level testbed, where successful addressing in one RAM row has been achieved. Error-free operation has been accomplished for all cases under study, with the whole Row Decoder system’s performance to offer a total power penalty of 2.5 dB.
Polarization imaging presents advantages in capturing spatial, spectral, and polarization information from target objects across various spectral bands. It can improve the perceptual ability of image sensors and has garnered more applications. Despite its potential, challenges persist in identifying band information from imaged objects and implementing image enhancement using polarization imaging. These challenges often necessitate integrating spectrometers or other components, resulting in increased complexities within image processing systems and hindering device miniaturization trends. Here, we systematically elucidate the characteristics of anisotropic absorption reversal in pucker‐like group IV‐VI semiconductors MX (M = Ge, Sn; X = S, Se) through theoretical predictions and experimental validations. Additionally, the fundamental mechanisms behind anisotropy reversal in different bands are also explored. The polarization‐sensitive photodetector is constructed by utilizing MX as light‐absorbing layer, harnessing polarization‐sensitive photoresponse for virtual imaging. The results indicate that the utilization of polarization reversal photodetectors, without excessively emphasizing anisotropy photocurrent ratios, holds advantages in achieving further multifunctional integration within the device structure while simplifying its configuration, including band information identification and image enhancement. This study provides a comprehensive analysis of polarization reversal mechanisms and presents a promising and reliable approach for achieving dual‐band image band identification and image enhancement without additional auxiliary components.
This article is protected by copyright. All rights reserved
In recent years, with the further ministration of the semiconductor device in integrated circuits, power consumption and data transmission bandwidth have become insurmountable obstacles. As an integrated technology, photonic integrated circuits (PICs) have a promising potential in the post‐Moore era with more advantages in data processing, communication, and diversified sensing applications for their ultra‐high process speed and low power consumption. Silicon photonics is believed to be an encouraging solution to realize PICs because of the mature CMOS process. The past decades have witnessed a huge growth in silicon PICs. However, there is still a demand for the development of silicon PICs to enable powerful chip‐scale systems and new functionalities. In this paper, a review of the photonic components, functional blocks, and emerging applications for PICs is offered. The common photonic components are classified into several sections, including on‐chip light sources, fiber‐to‐chip couplers, photonic resonators, waveguide‐based sensors, on‐chip photodetectors, and modulators. The functional blocks of the PICs mentioned in this review are photonic memories and photonic neural networks. Finally, the paper concludes with emerging applications for further study.
Elemental antimony (Sb) is regarded as a promising candidate to improve the programming consistency and cycling endurance of phase-change memory and neuro-inspired computing devices. Although bulk amorphous Sb crystallizes spontaneously, the stability of the amorphous form can be greatly increased by reducing the thickness of thin films down to several nanometers, either with or without capping layers. Computational and experimental studies have explained the depressed crystallization kinetics caused by capping and interfacial confinement; however, it is unclear why amorphous Sb thin films remain stable even in the absence of capping layers. In this work, we carry out thorough ab initio molecular dynamics (AIMD) simulations to investigate the effects of free surfaces on the crystallization kinetics of amorphous Sb. We reveal a stark contrast in the crystallization behavior between bulk and surface models at 450 K, which stems from deviations from the bulk structural features in the regions approaching the surfaces. The presence of free surfaces intrinsically tends to create a sub-nanometer region where crystallization is suppressed, which impedes the incubation process and thus constrains the nucleation in two dimensions, stabilizing the amorphous phase in thin-film Sb-based memory devices.
The luminescence color of molecule‐based photoactive materials is the key to the applications in lighting and optical communication. Realizing continuous regulation of emission color in molecular systems is highly desirable but still remains a challenge due to the individual emission band of purely organic molecules. Herein, a novel alloy strategy based on molecular co‐crystals is reported. By adjusting the molar ratio of pyrene (Py) and fluorathene (Flu), three types of molecular co‐crystal alloys (MCAs) assemblies are prepared involving Py‐Flu‐OFN‐ x %, Py‐Flu‐TFP‐ x %, Py‐Flu‐TCNB‐ x %. Multiple energy level structure and Förster resonance energy transfer (FRET) process endow materials with tunable full‐spectra emission color in visible region. Impressively, these MCAs and co‐crystals can be successfully applied to low optical loss waveguide and optical logic gate by virtue of all‐color luminescence from blue across green to red, together with smooth surface of one‐dimensional microrods, which show promising applications as continuous light emitters for advance photonics applications.
Recent research in silicon photonic chips has made huge progress in optical computing owing to their high speed, small footprint, and low energy consumption. Here, we employ nanostructured 2×2 optical processors in an optical neural network for implementing a binary classification task efficiently. The proposed optical neural network is composed of five linear layers including ten optical processors in each layer, and nonlinear activation functions. 2×2 optical processors are designed based on digitized meta-structures which have an extremely compact footprint of 1.6×4 μm
<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>
. A brand-new end-to-end design strategy based on Deep Q-Network is proposed to optimize the optical neural network for classifying a generated ring data set with better generalization, robustness, and operability. A high-efficient transfer matrix multiplication method is applied to simplify the calculation process in traditional optical software. Our numerical results illustrate that the maximum and mean accuracy on the testing data set can reach 90.5% and 87.8%, respectively. The demonstrated optical processors with a significantly compact area, and the efficient optimization method exhibit high potential for large-scale integration of whole-passive optical neural network on a photonic chip.
The demand for information processing at ultrahigh speed with large data transmission capacity is continuously rising. Necessary building blocks for on-chip photonic integrated circuits (PICs) are reconfigurable integrated low-loss high-speed modulators and switches. Phase change materials (PCMs) provide unique opportunities for integration into PICs. Here, the investigation of layered gallium monosulfide (GaS) as a novel low-loss PCM from infrared to optical frequencies is pioneered, with high index contrast (n ≈ .) at the optical telecommunication band. The GaS bandgap switches from. ±. eV for the amorphous state to. ±. eV for the crystalline state. It is demonstrated that the reversible GaS amorphous-to-crystalline phase transition can be operated thermally and by picosecond green (nm) laser irradiation. The design of a reconfigurable integrated optical modulator on-chip based on Mach-Zehnder Interferometers (MZI) with the GaS PCM cell deposited on one of the arms for application is presented at the telecommunication wavelength of = nm, where the standard single mode optical fiber exhibits zero chromatic dispersion, and at = nm, where a minimum optical loss of. dB km − is obtained. This opens the route to applications such as reconfigurable modulators, beam steering using phase modulation, and photonic neural networks. The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/. /adom.
Phase change memory (PCM) is an emerging technology that combines the unique properties of phase change materials with the potential for novel memory devices, which can help lead to new computer architectures. Phase change materials store information in their amorphous and crystalline phases, which can be reversibly switched by the application of an external voltage. This article describes the advantages and challenges of PCM. The physical properties of phase change materials that enable data storage are described, and our current knowledge of the phase change processes is summarized. Various designs of PCM devices with their respective advantages and integration challenges are presented. The scaling limits of PCM are addressed, and its performance is compared to competing existing and emerging memory technologies. Finally, potential new applications of phase change devices such as neuromorphic computing and phase change logic are outlined.
Conventional flash memory devices are voltage driven and found to be unsafe for confidential data storage. To ensure the security of the stored data, there is a strong demand for developing novel nonvolatile memory technology for data encryption. Here we show a photonic flash memory device, based on upconversion nanocrystals, which is light driven with a particular narrow width of wavelength in addition to voltage bias. With the help of near-infrared light, we successfully manipulate the multilevel data storage of the flash memory device. These upconverted photonic flash memory devices exhibit high ON/OFF ratio, long retention time and excellent rewritable characteristics.
An optical switch operating at a wavelength of 1.55 μm and showing a 12 dB modulation depth is introduced. The device is implemented in a silicon racetrack resonator using an overcladding layer of the phase change data storage material Ge2Sb2Te5, which exhibits high contrast in its optical properties upon transitions between its crystalline and amorphous structural phases. These transitions are triggered using a pulsed laser diode at λ = 975 nm and used to tune the resonant frequency of the resonator and the resultant modulation depth of the 1.55 μm transmitted light.
The phase transformation dynamics induced in Ge2Sb2Te5 films by picosecond laser pulses were studied using real-time reflectivity measurements. With subnanosecond resolution. Evidence was found that the thermal diffusivity of the substrate plays a crucial role in, determining the ability of. the films to crystallize and amorphize. A film/substrate configuration with optimized heat flow. conditions for ultrafast phase cycling with picosecond laser pulses was designed and produced. In this system; we achieved reversible phase transformations with large optical contrast (>20%) using single laser pulses with a duration of 30 ps within well-defined fluence windows. The amorphization (writing) process is completed within less than 1 ns, whereas, crystallization (erasing) needs approximately 13 ns to be completed. (C) 2004 American Institute of Physics.
Three-dimensional integration may allow for continued improvements in the speed, density and cost of non-volatile memory.
Light is intrinsically very difficult to store in a small space. The ability to trap photons for a long time (photon lifetime, τph) and to slow the propagation of light plays a significant role in quantum information1, 2, 3 and optical processing4, 5, 6. Photonic-crystal cavities with an ultrahigh quality factor (Q) are attracting attention7, 8 because of their extremely small volume; however, high-Q demonstrations have been accomplished only with spectral measurements9, 10, 11. Here we describe time-domain measurements on photonic-crystal cavities with the highest Q among wavelength-scale cavities, and show directly that photons are trapped for one nanosecond. These techniques constitute clear and accurate ways of investigating ultrasmall and long τph systems. We also show that optical pulses are delayed for ~1.45 ns, corresponding to light propagation at ~2×10−5 c the speed of light in a vacuum, which is the slowest for any dielectric slow-light medium. Furthermore, we succeeded in dynamically changing the Q within the τph, which is key to realizing the dynamic control of light12, 13 and photon-trapping memory14.
We propose an all-photonic, non-volatile memory and processing element based
on phase-change thin-films deposited onto nanophotonic waveguides. Using
photonic microring resonators partially covered with Ge2Sb2Te5 (GST)
multi-level memory operation in integrated photonic circuits can be achieved.
GST provides a dramatic change in refractive index upon transition from the
amorphous to crystalline state, which is exploited to reversibly control both
the extinction ratio and resonance wavelength of the microcavity with an
additional gating port in analogy to optical transistors. Our analysis shows
excellent sensitivity to the degree of crystallization inside the GST, thus
providing the basis for non-von Neuman neuromorphic computing.
A comprehensive and thorough review of PCM technologies, including a discussion of material and device issues, is provided in this paper. ABSTRACT | In this paper, recent progress of phase change memory (PCM) is reviewed. The electrical and thermal proper-ties of phase change materials are surveyed with a focus on the scalability of the materials and their impact on device design. Innovations in the device structure, memory cell selector, and strategies for achieving multibit operation and 3-D, multilayer high-density memory arrays are described. The scaling prop-erties of PCM are illustrated with recent experimental results using special device test structures and novel material synthe-sis. Factors affecting the reliability of PCM are discussed.
Phase-change memory (PCM) has emerged as one among the most promising technologies for next-generation non-volatile solid-state memory. Multilevel storage, namely storage of non-binary information in a memory cell, is a key factor for reducing the total cost-per-bit and thus increasing the competiveness of PCM technology in the nonvolatile memory market. In this paper, we present a family of advanced programming schemes for multilevel storage in PCM. The proposed schemes are based on iterative write-and-verify algorithms that exploit the unique programming characteristics of PCM in order to achieve significant improvements in resistance-level packing density, robustness to cell variability, programming latency, energy- per-bit and cell storage capacity. Experimental results from PCM test-arrays are presented to validate the proposed programming schemes. In addition, the reliability issues of multilevel PCM in terms of resistance drift and read noise are discussed.
Ultra-small, low-power, all-optical switching and memory elements, such as all-optical flip-flops, as well as photonic integrated circuits of many such elements, are in great demand for all-optical signal buffering, switching and processing. Silicon-on-insulator is considered to be a promising platform to accommodate such photonic circuits in large-scale configurations. Through heterogeneous integration of InP membranes onto silicon-on-insulator, a single microdisk laser with a diameter of 7.5 µm, coupled to a silicon-on-insulator wire waveguide, is demonstrated here as an all-optical flip-flop working in a continuous-wave regime with an electrical power consumption of a few milliwatts, allowing switching in 60 ps with 1.8 fJ optical energy. The total power consumption and the device size are, to the best of our knowledge, the smallest reported to date at telecom wavelengths. This is also the only electrically pumped, all-optical flip-flop on silicon built upon complementary metal-oxide semiconductor technology.
Phase-change memory technology relies on the electrical and optical properties of certain materials changing substantially when the atomic structure of the material is altered by heating or some other excitation process. For example, switching the composite Ge(2)Sb(2)Te(5) (GST) alloy from its covalently bonded amorphous phase to its resonantly bonded metastable cubic crystalline phase decreases the resistivity by three orders of magnitude, and also increases reflectivity across the visible spectrum. Moreover, phase-change memory based on GST is scalable, and is therefore a candidate to replace Flash memory for non-volatile data storage applications. The energy needed to switch between the two phases depends on the intrinsic properties of the phase-change material and the device architecture; this energy is usually supplied by laser or electrical pulses. The switching energy for GST can be reduced by limiting the movement of the atoms to a single dimension, thus substantially reducing the entropic losses associated with the phase-change process. In particular, aligning the c-axis of a hexagonal Sb(2)Te(3) layer and the 〈111〉 direction of a cubic GeTe layer in a superlattice structure creates a material in which Ge atoms can switch between octahedral sites and lower-coordination sites at the interface of the superlattice layers. Here we demonstrate GeTe/Sb(2)Te(3) interfacial phase-change memory (IPCM) data storage devices with reduced switching energies, improved write-erase cycle lifetimes and faster switching speeds.
The search for a universal memory storage device that combines rapid read and write speeds, high storage density and non-volatility is driving the exploration of new materials in nanostructured form. Phase-change materials, which can be reversibly switched between amorphous and crystalline states, are promising in this respect, but top-down processing of these materials into nanostructures often damages their useful properties. Self-assembled nanowire-based phase-change material memory devices offer an attractive solution owing to their sub-lithographic sizes and unique geometry, coupled with the facile etch-free processes with which they can be fabricated. Here, we explore the effects of nanoscaling on the memory-storage capability of self-assembled Ge2Sb2Te5 nanowires, an important phase-change material. Our measurements of write-current amplitude, switching speed, endurance and data retention time in these devices show that such nanowires are promising building blocks for non-volatile scalable memory and may represent the ultimate size limit in exploring current-induced phase transition in nanoscale systems.
Phase-change materials offer a promising route for the practical realisation of new forms of general-purpose and 'brain-like' computers. An experimental proof-of-principle of such remakable capabilities is presented that includes (i) the reliable execution by a phase-change 'processor' of the four basic arithmetic functions of addition, subtraction, multiplication and division, (ii) the demonstration of an 'integrate and fire' hardware neuron using a single phase-change cell and (iii) the expostion of synaptic-like functionality via the 'memflector', an optical analogue of the memristor.
We survey the current state of phase change memory (PCM), a non-volatile solid-state memory technology built around the large electrical contrast between the highly-resistive amorphous and highly-conductive crystalline states in so-called phase change materials. PCM technology has made rapid progress in a short time, having passed older technologies in terms of both sophisticated demonstrations of scaling to small device dimensions, as well as integrated large-array demonstrators with impressive retention, endurance, performance and yield characteristics. We introduce the physics behind PCM technology, assess how its characteristics match up with various potential applications across the memory-storage hierarchy, and discuss its strengths including scalability and rapid switching speed. We then address challenges for the technology, including the design of PCM cells for low RESET current, the need to control device-to-device variability, and undesirable changes in the phase change material that can be induced by the fabrication procedure. We then turn to issues related to operation of PCM devices, including retention, device-to-device thermal crosstalk, endurance, and bias-polarity effects. Several factors that can be expected to enhance PCM in the future are addressed, including Multi-Level Cell technology for PCM (which offers higher density through the use of intermediate resistance states), the role of coding, and possible routes to an ultra-high density PCM technology. Comment: Review article
Could optical technology offer a solution to the heat generation and bandwidth limitations that the computing industry is starting to face? The benefits of energy-efficient passive components, low crosstalk and parallel processing suggest that the answer may be yes.
Phase-change materials are some of the most promising materials for data-storage applications. They are already used in rewriteable optical data storage and offer great potential as an emerging non-volatile electronic memory. This review looks at the unique property combination that characterizes phase-change materials. The crystalline state often shows an octahedral-like atomic arrangement, frequently accompanied by pronounced lattice distortions and huge vacancy concentrations. This can be attributed to the chemical bonding in phase-change alloys, which is promoted by p-orbitals. From this insight, phase-change alloys with desired properties can be designed. This is demonstrated for the optical properties of phase-change alloys, in particular the contrast between the amorphous and crystalline states. The origin of the fast crystallization kinetics is also discussed.
Photonic signals were efficiently stored in a semiconductor-based memory cell. The incident photons were converted to electron-hole pairs that were locally stored in a quantum well that was laterally modulated by a field-effect tunable electrostatic superlattice. At large superlattice potential amplitudes, these pairs were stored for a time that was at least five orders of magnitude longer than their natural lifetime. At an arbitrarily chosen time, they were released in a short and intense flash of incoherent light, which was triggered by flattening the superlattice amplitude.
Photonic integration has long been pursued, but remains immature compared with electronics. Nanophotonics is expected to change this situation. However, despite the recent success of nanophotonic devices, there has been no demonstration of large-scale integration. Here, we describe the large-scale and dense integration of optical memories in a photonic crystal chip. To achieve this, we introduce a wavelength-addressable serial integration scheme using a simple cavity-optimization rule. We fully exploit the wavelength-division-multiplexing capability, which is the most important advantage of photonics over electronics, and achieve an extremely large wavelength-channel density. This is the first demonstration of the large-scale photonic integration of nanophotonic devices coupled to waveguides in a single chip, and also the first dense wavelength-division-multiplexing nanophotonic devices other than filters. This work paves the way for optical random-access memories and for a large-scale wavelength-division-multiplexing photonic network-on-chip.
An effective solution to enhance the capacity of an optical-interconnect link is utilizing advanced multiplexing technologies, like wavelength-division-multiplexing (WDM), polarization-division multiplexing (PDM), spatial-division multiplexing (SDM), bi-directional multiplexing, etc. On-chip (de)multiplexers are necessary as key components for realizing these multiplexing systems and they are desired to have small footprints due to the limited physical space for on-chip optical interconnects. As silicon photonics has provided a very attractive platform to build ultrasmall photonic integrated devices with CMOS-compatible processes, in this paper we focus on the discussion of silicon-based (de)multiplexers, including WDM filters, PDM devices, and SDM devices. The demand of devices to realize a hybrid multiplexing technology (combining WDM, PDM and SDM) as well as a bidirectional multiplexing technologies are also discussed to achieve Peta-bit optical interconnects.
Inspired by the brain’s structure, we have developed an efficient, scalable, and flexible non–von Neumann architecture that
leverages contemporary silicon technology. To demonstrate, we built a 5.4-billion-transistor chip with 4096 neurosynaptic
cores interconnected via an intrachip network that integrates 1 million programmable spiking neurons and 256 million configurable
synapses. Chips can be tiled in two dimensions via an interchip communication interface, seamlessly scaling the architecture
to a cortexlike sheet of arbitrary size. The architecture is well suited to many applications that use complex neural networks
in real time, for example, multiobject detection and classification. With 400-pixel-by-240-pixel video input at 30 frames
per second, the chip consumes 63 milliwatts.
The development of materials whose refractive index can be optically transformed as desired, such as chalcogenide-based phase-change materials, has revolutionized the media and data storage industries by providing inexpensive, high-speed, portable and reliable platforms able to store vast quantities of data. Phase-change materials switch between two solid states--amorphous and crystalline--in response to a stimulus, such as heat, with an associated change in the physical properties of the material, including optical absorption, electrical conductance and Young's modulus. The initial applications of these materials (particularly the germanium antimony tellurium alloy Ge2Sb2Te5) exploited the reversible change in their optical properties in rewritable optical data storage technologies. More recently, the change in their electrical conductivity has also been extensively studied in the development of non-volatile phase-change memories. Here we show that by combining the optical and electronic property modulation of such materials, display and data visualization applications that go beyond data storage can be created. Using extremely thin phase-change materials and transparent conductors, we demonstrate electrically induced stable colour changes in both reflective and semi-transparent modes. Further, we show how a pixelated approach can be used in displays on both rigid and flexible films. This optoelectronic framework using low-dimensional phase-change materials has many likely applications, such as ultrafast, entirely solid-state displays with nanometre-scale pixels, semi-transparent 'smart' glasses, 'smart' contact lenses and artificial retina devices.
Phase change materials are widely considered for application in non-volatile memories due to their ability to achieve phase transformation in nano-second time scale. However the knowledge of fast crystallization dynamics in these materials are limited due to the lack of fast and accurate temperature control methods. In this work we have developed an experimental methodology that enables ultra-fast characterization of phase-change dynamics on a more technologically relevant melt-quenched amorphous phase using practical PCM device structures. We have extracted the crystallization growth velocity (U) in a functional capped PCM device over eight orders of magnitude (10(-10) m/s < U < 10(-1) m/s) spanning a wide temperature range (415 K < T < 580 K). We also observed direct evidence of non-Arrhenius crystallization behavior in programmed PCM devices at very high heating rates (>10(8) K/s), which reveals the extreme fragility of Ge2Sb2Te5 in its super-cooled liquid phase. Furthermore, these crystallization properties were studied as a function of device programming cycles and the results show degradation in the cell retention properties due to elemental segregation. The above experiments are enabled by the use of an on-chip fast heater and thermometer called as Micro Thermal Stage (MTS) integrated with a vertical phase change memory (PCM) cell. The temperature at the PCM layer can be controlled up to 600 K using MTS and with a thermal time constant of 800 ns leading to heating rates ~ 10(8) K/s that are close to the typical device operating conditions during PCM programming. The MTS allows us to independently control the electrical and thermal aspects of phase transformation (inseparable in a conventional PCM cell) and extract the temperature dependence of key material properties in real PCM devices.
Phase-change materials integrated into nanophotonic circuits provide a flexible way to realize tunable optical components. Relying on the enormous refractive-index contrast between the amorphous and crystalline states, such materials are promising candidates for on-chip photonic memories. Non-volatile memory operation employing arrays of microring resonators is demonstrated as a route toward all-photonic chipscale information processing.
A class of two-terminal passive circuit elements that can also act as
memories could be the building blocks of a form of massively parallel
computation known as memcomputing.
Optical computers will be more interesting if they take advantage of
phenomena that are unique to optics. In this respect, telecommunications
hardware might have something to offer.
Historically, the application of phase-change materials and devices has been limited to the provision of non-volatile memories. Recently, however, the potential has been demonstrated for using phase-change devices as the basis for new forms of brain-like computing, by exploiting their multilevel resistance capability to provide electronic mimics of biological synapses. Here, a different and previously under-explored property that is also intrinsic to phase-change materials and devices, namely accumulation, is exploited to demonstrate that nanometer-scale electronic phase-change devices can also provide a powerful form of arithmetic computing. Complicated arithmetic operations are carried out, including parallel factorization and fractional division, using simple nanoscale phase-change cells that process and store data simultaneously and at the same physical location, promising a most efficient and effective means for implementing beyond von-Neumann computing. This same accumulation property can be used to provide a particularly simple form phase-change integrate-and-fire “neuron”, which, by combining both phase-change synapse and neuron electronic mimics, potentially opens up a route to the realization of all-phase-change neuromorphic processing.
Ultra-compact four-channel wavelength division multiplexing (WDM) devices in add/drop filter and multi-mode interferometer configurations were demonstrated on silicon-on-insulator for future on-chip optical interconnects. Both devices show a crosstalk level ≤-13dB and a footprint ≤0.006mm2.
A rapid and reversible transition between a highly resistive and conductive state effected by an electric field, which we have observed in various types of disordered semiconducting material, is described in detail. The switching parameters and chemical composition of a typical material are presented, and microscopic mechanisms for the conduction phenomena are suggested.
Silicon photonics is currently a very active and progressive area of research, as silicon optical circuits have emerged as the replacement technology for copper-based circuits in communication and broadband networks. The demand for ever improving communications and computing performance continues, and this in turn means that photonic circuits are finding ever increasing application areas. This text provides an important and timely overview of the hot topics in the field, covering the various aspects of the technology that form the research area of silicon photonics. With contributions from some of the worlds leading researchers in silicon photonics, this book collates the latest advances in the technology. Silicon Photonics: the State of the Art opens with a highly informative foreword, and continues to feature: the integrated photonic circuit; silicon photonic waveguides; photonic bandgap waveguides; mechanisms for optical modulation in silicon; silicon based light sources; optical detection technologies for silicon photonics; passive silicon photonic devices; photonic and electronic integration approaches; applications in communications and sensors. Silicon Photonics: the State of the Art covers the essential elements of the entire field that is silicon photonics and is therefore an invaluable text for photonics engineers and professionals working in the fields of optical networks, optical communications, and semiconductor electronics. It is also an informative reference for graduate students studying for PhD in fibre optics, integrated optics, optical networking, microelectronics, or telecommunications.
Phase-change random-access memory (PCRAM) is one of the leading candidates for next-generation data-storage devices, but the
trade-off between crystallization (writing) speed and amorphous-phase stability (data retention) presents a key challenge.
We control the crystallization kinetics of a phase-change material by applying a constant low voltage via prestructural ordering
(incubation) effects. A crystallization speed of 500 picoseconds was achieved, as well as high-speed reversible switching
using 500-picosecond pulses. Ab initio molecular dynamics simulations reveal the phase-change kinetics in PCRAM devices and
the structural origin of the incubation-assisted increase in crystallization speed. This paves the way for achieving a broadly
applicable memory device, capable of nonvolatile operations beyond gigahertz data-transfer rates.
The structure of laser-crystallized thin films of Ge <sub> 2 </sub> Sb <sub>2+x</sub> Te <sub> 5 </sub> (0.0≪x≤1.0) formed by the sputtering method were identified by x-ray diffraction studies to be composed of two phases: one phase is chiefly NaCl type crystal with a lattice constant of about 6 Å and a composition corresponding to Ge <sub> 2 </sub> Sb <sub> 2 </sub> Te <sub> 5 </sub>; the other phase comprises a small amount of an amorphous component such as Sb metal. Results of the Rietveld and the whole-powder-pattern fitting analyses show good agreement when assuming that (i) the 4(a) site is wholly occupied by only Te, (ii) the 4(b) site is randomly occupied by Ge or Sb atoms, and (iii) a little less than 20% of the 4(b) site is always vacant independent of the x value. The above results and the fact that halo noise rises with x increasing from 0.0 to 1.0 indicate a more precise model of crystal structure as follows. That is, Sb atoms added beyond the stoichiometric ratio, Ge <sub> 2 </sub> Sb <sub> 2 </sub> Te <sub> 5 </sub>, never fill up the vacancies of the 4(b) site in the NaCl type structure; the excess Sb atoms will remain in the amorphous state and concentrate, for example, at the grain boundary. The authors conclude that the amounts of the amorphous component produced through the crystallization process predominantly determine the crystallization rates and the critical temperatures of Ge–Sb–Te amorphous films, reportedly that they show a gentle and continuous dependence on the compositional deviation from the GeTe–Sb <sub> 2 </sub> Te <sub> 3 </sub> pse-
udobinary line. © 2000 American Institute of Physics.
An optical gate switch using Ge<sub>2</sub>Sb<sub>2</sub>Te<sub>5</sub> phase-change material integrated with a silicon waveguide is reported. The switch is very small (~2 ¿m) owing to the large difference in absorption coefficient between the crystalline state and the amorphous state. The prototype switch has been fabricated and successfully switched from the transparent on-state to the opaque off-state by laser pulse irradiation. An extinction ratio of more than 12.5 dB was achieved over a wavelength range of 75 nm.
The increasing speed of fibre-optic-based telecommunications has focused attention on high-speed optical processing of digital information. Complex optical processing requires a high-density, high-speed, low-power optical memory that can be integrated with planar semiconductor technology for buffering of decisions and telecommunication data. Recently, ring lasers with extremely small size and low operating power have been made, and we demonstrate here a memory element constructed by interconnecting these microscopic lasers. Our device occupies an area of 18 x 40 microm2 on an InP/InGaAsP photonic integrated circuit, and switches within 20 ps with 5.5 fJ optical switching energy. Simulations show that the element has the potential for much smaller dimensions and switching times. Large numbers of such memory elements can be densely integrated and interconnected on a photonic integrated circuit: fast digital optical information processing systems employing large-scale integration should now be viable.
Non-volatile 'flash' memories are key components of integrated circuits because they retain their data when power is interrupted. Despite their great commercial success, the semiconductor industry is searching for alternative non-volatile memories with improved performance and better opportunities for scaling down the size of memory cells. Here we demonstrate the feasibility of a new semiconductor memory concept. The individual memory cell is based on a narrow line of phase-change material. By sending low-power current pulses through the line, the phase-change material can be programmed reversibly between two distinguishable resistive states on a timescale of nanoseconds. Reducing the dimensions of the phase-change line to the nanometre scale improves the performance in terms of speed and power consumption. These advantages are achieved by the use of a doped-SbTe phase-change material. The simplicity of the concept promises that integration into a logic complementary metal oxide semiconductor (CMOS) process flow might be possible with only a few additional lithographic steps.
The authors also acknowledge support from the DFG and the State of Baden-Württemberg through the DFG-Center for Functional Nanostructures (CFN) within subproject A6.4
- Wirtschaft
Wirtschaft (sdw). H.B. acknowledges support from the John Fell Fund and the EPSRC
(EP/J00541X/2 and EP/J018694/1).The authors also acknowledge support from the DFG
and the State of Baden-Württemberg through the DFG-Center for Functional
Nanostructures (CFN) within subproject A6.4. This work was partly carried out with the
support of the Karlsruhe Nano Micro Facility (KNMF, http://www.knmf.kit.edu), a
Helmholtz Research Infrastructure at Karlsruhe Institute of Technology (KIT, http://www.
kit.edu). The authors thank S. Diewald for assistance with device fabrication and M.
Blaicher for technical assistance with device design.