Weijie Wang

Agency for Science, Technology and Research (A*STAR) | A*Star · Institute of Microelectronics

Scandium-doped aluminum nitride (AlScN) has generated great research interest owing to its unique properties. The wurtzite-structure AlScN is compatible with the complementary metal oxide semiconductor (CMOS) process and has improved piezoelectricity compared with undoped aluminum nitride (AlN), making it a promising candidate to be used for next-g...

In this work, a non-idealities aware software-hardware co-design framework for deep neural network (DNN) implemented on memristive crossbar is presented. The device level non-ideal factors such as device conductance variation, nonuniform quantization levels, device-to-device variation and programming failure probability are included in the model. A...

In this letter, we report the KrF excimer laser annealing for achieving high-performance ferroelectric Hf <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> O <sub xmlns:mml="http://www.w3...

Chalcogenide based phase change random access memory (PCRAM) holds great promise for high speed and large data storage applications. This memory is scalable, requires a low switching energy, has a high endurance, has fast switching speed, and is nonvolatile. However, decreasing the switching time whilst increasing the cycle endurance is a key chall...

In this letter, we report analog switching characteristics in an analog resistive random access memory device based on a TiW/Al2O3/Ta2O5/Ta stack. For this device, both oxides were grown by using an atomic layer deposition system and the oxygen vacancies were found to exist at the interface of these oxides by using angle-resolved X-ray Photoelectro...

Electrode materials selection guidelines for oxide-based memory devices are constructed from the combined knowledge of observed device operation characteristics, ab-initio calculations, and nano-material characterization. It is demonstrated that changing the top electrode material from Ge to Cr to Ta in the Ta 2O5-based memory devices resulted in a...

Electrode materials selection guidelines for oxide-based memory devices are constructed from the combined knowledge of observed device operation characteristics, ab-initio calculations, and nano-material characterization. It is demonstrated that changing the top electrode material from Ge to Cr to Ta in the Ta2O5-based memory devices resulted in a...

Of all the advantages exhibited by the RRAM devices, e.g. low power consumption, fast switching speed, and especially the good scalability are particularly striking for high density memory application. However, 3D RRAM still suffer from poor endurance especially during high speed operation which limits its extensive applications. Here, we report th...

Electrical pulse programming provides more practical and precise assessment of the resistive memory performance, and also provides another angle of view on the switching mechanism investigation. This work presents the bipolar switching of the TaO x -based resistive memory devices using electrical pulses. The SET process is almost independent on the...

GeTe phase change material doped with 12 to 22 atomic percent TiO 2 were deposited and characterized. The crystallization of amorphous doped GeTe is inhibited by the incorporation of TiO 2 dopant up to 22 % as depicted by the increasing activation energy. However, only working devices fabricated using 12% of TiO 2 dopant with activation energy of 4...

We present a novel selector made of doped-chalcogenide material. This selector not only achieves low holding voltage (0.2 V) and large on/off ratio (>107), but also exhibits the high oncurrent density (>1.6 MA/cm2) and large hysteresis window (1.2 V). Besides, excellent selector performances with ultra-low offstate leakage current (10 pA), high swi...

Varying ZrO2 doped GeTe phase change material of atomic percent greater than 10% were deposited and characterized. It was discovered that the crystallization of amorphous doped GeTe is suppressed by the incorporation of ZrO2 at lower concentration but the crystallization improves as the concentration increases as depicted by the activation energy f...

Current efforts to overcome such limitations are focused on employing material-optimization, or scaling, approaches, such as the development of nanowire-based, or nanostructured, PCM devices. However, the improvement of performance with these methods is rapidly becoming impossible due to physical and lithographic constraints. Applying multiple elec...

Supplementary

Significance The ever-increasing demand for faster computers is tackled by reducing the size of devices, but this is becoming almost impossible to continue. To improve the speed of computers, a solution is to increase the number of operations performed per device. Numerous operations in phase-change–based “in-memory” logic devices have previously b...

We report new clathrate-based phase-change materials with cage-like structures incorporating Cs and Ba guest atoms, as a means of altering crystallization and amorphization behaviour by controlling 'guest-cage' interactions via intra-complex guest vibrational effects. Both a high resistance to spontaneous crystallization, and long retention of the...

A method for programming a resistive memory cell is provided. The method may include providing a programming signal to the resistive memory cell. The programming signal may include an electrical pulse and a bias pulse coupled with the electrical pulse. The electrical pulse includes an electrical pulse portion, and the bias pulse includes at least t...

Phase-change random access memory (PCRAM) is one of the leading candidates for next-generation, non-volatile electronic data-storage devices, in which data bits are stored in terms of different structural states of a memory material, i.e. either crystalline or amorphous, each having a different electrical resistivity. Switching between these two me...

Phase-change memory (PCM) represents one of the best candidates for a “universal memory”. However, its slow SET speed, high RESET power, and high resistance drift present key challenges towards this ambition. Here, grain-engineered Ge2Sb2Te5 is exploited to control the crystallization kinetics, and electrical properties of PCM. We report 120 % high...

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...

The quest for universal memory is driving the rapid development of memories with superior all-round capabilities in non-volatility, high speed, high endurance and low power. Phase-change materials are highly promising in this respect. However, their contradictory speed and stability properties present a key challenge towards this ambition. We revea...

Supplementary Information

Nanoscale superlattice-like (SLL) dielectric was employed to reduce the power consumption of the Phase-change random access memory (PCRAM) cells. In this study, we have simulated and found that the cells with the SLL dielectric have a higher peak temperature compared to that of the cells with the SiO2 dielectric after constant pulse activation, due...

The reversible switching between the amorphous and crystalline phases of Ge2Sb2Te5 (GST) is investigated with ab initio molecular dynamics. We apply different quench rates (-16 K/ps, -5 K/ps, -2 K/ps, and -0.45 K/ps) and different annealing temperatures (500 K, 600 K, 700 K, and 800 K) to amorphize and crystallize GST respectively. Results show tha...

Phase-change random access memory cells with superlattice-like (SLL) GeTe/Sb(2)Te(3) were demonstrated to have excellent scaling performance in terms of switching speed and operating voltage. In this study, the correlations between the cell size, switching speed and operating voltage of the SLL cells were identified and investigated. We found that...

Phase change materials have been found to be useful for many applications including phase change optical media, phase change memory, and probe storage. In order to increase density, bit size has been continuously shrunk. At the nano-scale, the extreme dimensional and nano-structural constraints and the large proportion of interfaces will cause the...

Superlatticelike (SLL) dielectric comprising of Ge2Sb2Te5 and SiO2 was employed to reduce the power and increase the speed of phase-change random access memories (PCRAMs). In this study, we found that PCRAM cells with SLL dielectric require lower currents and shorter pulse-widths to switch compared to the cells with SiO2 dielectric. As the thicknes...

We have explored a different method to increase the phase switching speed for the nanocell of the non-volatile phase change random memories. The correlation between the nanocell size and the switching speed has been investigated theoretically, and the ultrafast phase switching has been demonstrated experimentally. The ultrafast switching mechanisms...

The reversible and fast phase transitions induced by picosecond electrical pulses are observed in the nanostructured GeSbTe materials, which provide opportunities in the application of high speed nonvolatile random access memory devices. The mechanisms for fast phase transition are discussed based on the investigation of the correlation between pha...

In this paper, phase change random access memory (PCRAM) cells at the nano-scale was studied. A hybrid patterning process integrating with electron beam lithography (EBL) and optical lithography was used to fabricate nano-PCRAM cell. PCRAM cells with different feature sizes ranging from 40 nm to 200 nm have been fabricated and tested by an in-house...

Laser processing has found an important application in the hard disk drive (HDD) industry to fabricate bumps for screen testing of the manufactured magnetic disk media prior to HDD assembly. The flying height of the head slider needs to be calibrated by a specifically designed bump array. With areal density of HDD already exceeds 100Gbits/in2, the...

A near-field scanning optical microscopy (NSOM) and a double-frequency femtosecond laser (400 nm, 100 fs) were applied to push the optical resolution further down to sub-50 nm on thin UV photoresist. A 20-nm feature size can be obtained. It is at a resolution of λ/20 (λ: laser wavelength) and a/2 (a: NSOM probe aperture diameter), respectively. It...

Understanding of the phase change in nano-scale, or so-called nano-phase change, and its related issues are important for its applications on both optical recording and phase change random access memory (PCRAM). Nano-phase change can be classified into thickness-dependent and structure dependent types. For PCRAM device performance, the film thickne...

It is a big challenge to determine ultra-low slider flying height accurately. The standard bump disk method is probably the most reliable and acceptable method so far. One of the key issues to determine slider-flying height with the bump disk method is the complicated slider–bump interaction process and the possible disturbance of the bumps on the...

The phase change memory cells were developed by using a combination system of a femtosecond laser with near-field scanning optical microscopy. The memory cells with feature size varying from 800 nm down to 90 nm were achieved. The cell functional performances were tested, and the scalability of the programming current as a function of the memory ce...

In this work, phase change random access memory (PCRAM) was studied theoretically and experimentally. Phase change materials were deposited and their physical parameters were measured. A simulation and design software for PCRAM was developed based on multidisciplinary theories including electrodynamics, thermal conduction, crystallization kinetics...

In this paper, phase change random access memory (PCRAM) devices with two different geometric configurations were studied. The geometry effect on device functionalities in terms of thermal and electrical properties has been analyzed by simulation and experiments. Based on 0.35μm technology, 128 bits PCRAM array integrating with CMOS as the selectio...

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We report direct laser writing of lithography patterns with a feature width of 205nm on thin photoresist film by combining a double-frequency femtosecond laser and a near-field scanning optical microscope. The obtained feature size is much smaller than the laser wavelength () and the aperture diameter (d) with a resolution of /20 and d/2, respectiv...

The increasing demand for smaller devices as well as research into novel structures for high density data storage has necessitated the use of advanced nanolithography techniques for fabrication in the sub-100 nm regime. In this paper, nanoscale lines with a minimum full width at half maximum of 20 nm have been achieved, demonstrating resolution of...

We have developed the laser nanoprocessing technique by the integration of the ultrafast laser and near-field scanning microscopy (NSOM). The second harmonic femtosecond laser working in the optical near-field with the assistance of NSOM equipment was applied to expose the photosensitive polymer material. The nanopatterns with feature size smaller...

We have explored the optical near-field technology for the fabrication of subwavelength-size binary bit by the combination of the femtosecond laser of the second harmonic output with the near-field scanning optical microscopy (NSOM). The photosensitive polymer material was exposed, and the nanopatterns with feature size smaller than the laser wavel...

The periodic microfringe structures were induced on the front silicon surface by pulsed CO2 laser irradiation with the existence of a painting or coating layer on the bottom surface of silicon substrate. The microfringes were formed under single pulse irradiation due to the laser induced periodic surface structure (LIPSS) effect. The nanodot were s...

Cobalt nanoparticles have been fabricated by laser ablation of metal target at laser wavelengths of 1064 nm and 532 nm. The target was immersed in water during the ablation. Size of the resulted nanoparticles was determined by optical microscope and field emission scanning electron microscope (FESEM). It was observed that the minimum particle was 6...

Femtosecond (fs) laser application in three-dimensional (3D) optical recording is introduced. The laser irradiation on transparent glass and polymer matrix doped with fluorescent material is carried out, which changes the physical or chemical properties of the recording media and records information bits. With the change of the focusing positions i...

Laser deposition of barium ferrite films with varying substrate temperature during film growth has been studied. It is found that both perpendicular and in-plane coercivities increase with peak substrate temperature and reach 5.2kOe. The magnetization hysteresis loops are similar for both magnetic fields applied parallel and perpendicular to the su...

Laser microprocessing has been extensively studies with applications in microelectronics, data storage and photonics. In addition to the fundamental aspects of laser materials interactions, we have investigated various applications of laser microprocessing in different areas. Laser cleaning has been studies systematically both theoretically and exp...

In this paper, we will describe a new method to fabricate optical diffractive gratings on glass surface with direct CW CO2 laser irradiation. A laser beam with linear polarization was focused and scanned on a glass substrate. The interaction of the beam with the material irradiated results in a periodic ridge structure formation on the substrate un...

Laser processing has large potential in the packaging of integrated circuits (IC). It can be used in many applications such as laser cleaning of IC mold tools, laser deflash to remove mold flash form heat sinks and lead wires of IC packages, laser singulation of BGA and CSP, laser reflow of solder ball on GBA, laser marking on packages and on SI wa...

Laser bumps have been formed on the silicon surface with anisotropic patterns induced by the pulsed CO2 laser under the backside effect conditions. The microstructures are formed with periodic patterns, and vary with the laser parameters. The parallel narrow fringes have period around 2 micrometers , and the fringe orientation is in parallel with t...

Laser-induced removal of plate-like particles from solid surfaces has been studied both experimentally and theoretically. A theoretical model has been established by taking into account adhesion force, cleaning force and heat equation. The cleaning condition and threshold can be obtained by comparing adhesion force and cleaning force. The theoretic...

Laser-induced periodic microstructures on the silicon substrate have been studied using a pulsed CO 2 laser under the backside conditions. The microstructures are formed with periodic parallel fringes and circular fringes on the front surface of silicon substrate, when the backside of which is coated with a thin layer of paints or Au. The parallel...

Laser microprocessing has been extensively studies with applications in microelectronics and magnetic data storage. In addition to the fundamental aspects of laser materials interactions, we have investigated various possible applications of laser microprocessing in different areas. Laser cleaning has been studies systematically both theoretically...

We have grown Li-doped ZnO films on silicon (100) using the rf planar magnetron sputtering method. The surface charges induced piezoelectrically by defect and by polarization can be observed by electric force microscopy. The Li-doped ZnO films have been proven to be ferroelectric. The Raman spectra of ZnO and Li-doped ZnO films have been measured....

Recently, scanning probe microscope (SPM) has become a promising technique for nanofabrication. In this paper, we present a novel method of nano-fabrication, namely, nano-fabrication by atomic force microscope (AFM) tips under laser irradiation. The SPM was operated as an AFM@. During imaging and nano-fabrication, the AFM is in constant force mode....

The experimental analysis of dry laser cleaning efficiency is done for certified spherical particle (SiO2, 5.0, 2.5, 1.0 and 0.5 μm) from different substrates (Si, Ge and NiP). The influence of different options (laser wavelength, incident angle, substrate properties, i.e. type of material, surface roughness, etc.) on the cleaning efficiency is pre...

Zinc oxide thin films have been grown on silicon (100) and sapphire (0001) substrates by pulsed laser deposition. The thin films deposited at different processing parameters were evaluated by x-ray diffraction, Raman spectroscopy, and atomic force microscopy (AFM). The influences of substrate temperature and laser fluence on the properties of the d...

Barium ferrite films with high coercivity, large magnetic anisotropy, good crystal orientation and crystallinity with hexagonal symmetry have been prepared on single crystal sapphire substrates by laser in-situ deposition. The structures of these films were characterized by X-ray diffractometry. X-ray diffraction pattern shows a preferential c-axis...

Laser-induced deformation on hard disk surface has been studied. A diode-pumped Q-switched Nd:YVO4 laser was used in the experiment. The sample is a commercial hard disk. Atomic force microscope (AFM) was employed to analyze the surface morphology after laser irradiation. Depending on the laser fluence used, a radial structure with or without a cir...

Laser-induced microtexture has been produced by using an argon-ion-laser-based system to provide low flying height and low stiction between the head and the disk for high recording density. Laser bumps with different profiles, such as dome-like type, crater type, double-rim crater type and elliptical type, etc. have been formed because of the preci...

Pulsed green laser with 532 nm wavelength and 270 ns pulse duration was first used to produce a textured zone on a Ni-P disk substrate. Combining a so-called tip-writing method, typical small bumps of interest with bump diameter around 3 micrometer and with bump height about 10 - 20 nm were successfully created. A dependence of bump height on bump...

Laser buffing of nickel-phosphorous (NiP) surface after mechanic texturing has been investigated. A KrF excimer laser ((lambda) equals 248 nm, (tau) equals 23 ns) was employed in the experiment as an irradiation source. The sample is a mechanic- textured hard disk. Atomic force microscope (AFM) was used to analyze the surface morphologies before an...

Laser-induced deposition of palladium lines on glass from palladium acetate was systematically studied by scanning thermal microscopy and atomic force microscopy. The atomic force microscopy studies provide 3D images of deposited metal lines and fine structures on these metal lines. The scanning thermal microscope (SThM) allows mapping of thermal c...

At the nano-scale, phase change behavior is different from that of bulk. In this paper dimensional nano-phase change effect of GeSbTe was investigated theoretically and experimentally in terms of different film thickness and different material composition. The measured properties in this work include size dependent electrical resistance versus temp...