Tsuyoshi Horikawa

• Ph.D.
• Specially Appointed Professor at Institute of Science Toyko

A 300-mm silicon photonics platform for a large-scale device integration was developed, leveraging 40-nm complementary metal-oxide-semiconductor (CMOS) technology. Through fabrication using this technology platform, wire waveguides were obtained with low propagation losses for the C-band (0.4 dB/cm) and O-band (1.3 dB/cm). Several types of waveleng...

Low-propagation-loss silicon wire waveguides are key components of optical integrated circuits. In this paper, we clarified, through assessment of the relationship between waveguide loss and fabrication technology that high-resolution lithography and an adjusted lithography process window are important for low-loss waveguides. The silicon wire wave...

We experimentally investigate the impacts of fabrication error in Si wire-waveguides on the spectral variation of 5th-order coupled resonator optical waveguides (CROWs). In the fabrication of these waveguide devices, 40-nmnode CMOS technology with ArF immersion lithography was used. The characterization of the CROWs was done by using an automatic o...

Thin films of (Ba0.65Sr0.35)TiO3 (BST) have been prepared by an rf-sputtering method at substrate temperatures of 500 to 700°C. The dielectric constant of these films ranges from 190 to 700 at room temperature. This value changes with the grain size rather than the film thickness. The dielectric constant of about 300 and leakage current density of...

The dielectric relaxation of (Ba0.5Sr0.5)TiO3 thin films with high electric resistivity is investigated. The films are deposited by an rf-magnetron sputtering method in an atmosphere of argon and oxygen. The dielectric dispersion of the films is measured in the frequency range of 10-2-106 Hz. It is found that the dielectric constant ε slightly decr...

This study presents an efficient testing process for characterizing silicon photonic integrated circuits. This process utilizes a coupling structure that integrates grating couplers and spot-size converters for efficient testing both at the chip and wafer levels, respectively. By leveraging wafer-level testing to estimate the characteristics of fin...

We, for the first time, formulated the behavior of multiple reflections in waveguides with distributed reflections and demonstrated the precise extraction of reflection coefficients in silicon waveguides from OFDR reflection-distance profiles.

The realization of a high dynamic extinction ratio (ER) and optical modulation amplitude (OMA) while keeping the optical and radio-frequency (RF) signal losses low is a major issue for carrier-depletion Mach–Zehnder (MZ) silicon optical modulators. However, there is still room to improve modulator performance by applying the information gained from...

Grating couplers (GC) on silicon-on-insulator (SOI) have an excellent interconnectivity between photonic integrated circuit (PIC) device and fibers. Traditional theory-first hand-turning design method by sweep parameters is time-consuming to perform. In contrast, the target-first inverse design optimization algorithm enables obtaining the best solu...

We demonstrate a membrane photonic integrated circuit (MPIC) that includes a membrane distributed feedback (DFB) laser and a p-i-n photodiode with a buried-ridge-waveguide (BRW) on a Si substrate, using a-Si nanofilm-assisted room-temperature surface activated bonding (SAB) for on-chip optical interconnection. The BRW structure enhanced the lateral...

Characteristic variations caused by nonuniformities in the fabrication process are inevitable in Mach–Zehnder (MZ) silicon optical modulators. However, it is unknown how inter-arm imbalance in phase shifters that have a voltage dependence impacts device performance with respect to the optical modulation amplitude (OMA) and chirp parameter in a push...

Crosstalk among channels in wavelength division multiplexing (WDM) filters must be suppressed to enhance receiver sensitivity in direct-detection-based optical communication systems. We present a systematic method to identify the maximum crosstalk and upper limit of the transmission spectrum bandwidth of a highly multi-staged Mach-Zehnder interfere...

Testing of active photonic devices is totally different from testing of pure electronics; in particular, reduction of testing time in silicon photonics has been a significant issue. In this study, a compact behavioral model of optical phase shifters is constructed for carrier-depletion Mach–Zehnder (MZ) silicon modulators in the push-pull regime. T...

We report phase behaviors in silicon-wire multistage delayed interferometric (MDI) wavelength-division multiplexing (WDM) optical filters on a 300-mm silicon-on-insulator (SOI) wafer. In order to achieve spectrally uniform filter response and make clear the main factor for influencing spectral shape and uniformity across the SOI wafer, we fabricate...

We proposed novel 16λ demultiplexer based on cascaded connection of silicon-nanowire waveguide type delayed interferometric filters and arrayed waveguide gratings, and experimentally verified 100-GHz-spaced bandpass filtering operation with nearly identical insertion loss (<6dB) and low crosstalk (<-19.5dB to <-34.6dB for a single channel, <-12.7dB...

We have developed a highly-miniaturized Si photonic transceiver module named "Optical I/O Core" for use in on-board and co-packaged optics. In an optical I/O structure called "optical pin", a laser diode and a driver IC are mounted on a 5 mm × 5 mm photonic integrated circuit. The data rate is 25 Gbps and the transmission media is a multimode fiber...

Optical I/O core based on silicon photonics technology and optical/electrical assembly was developed as a fingertip-size optical module with high bandwidth density, low power consumption, and high temperature operation. The advantages of the optical I/O core, including hybrid integration of quantum dot laser diode and optical pin, allow us to achie...

We experimentally demonstrated a post-integrated dual-core spot-size converter (SSC) that had a coupling end with a 10-μm diameter at the edge of an Si-photonics chip. Although there was an extra loss increase as a result of post-integration, it can be reduced and, thus, the SSC is a promising candidate for practical use. The large coupling end ena...

Optical transmitter and receiver ICs, each with a footprint of 25 mm2, were fabricated using a silicon photonics platform based on 40-nm-node CMOS technology. High-speed transmissions of data at 300 Gbps were demonstrated. The wire-type waveguide (WG) in the transmitter IC had a width of 350 nm and height of 200 nm, and in the completed optical IC,...

In the fabrication of photonics integrated circuits using silicon photonics technology, dimension control for silicon waveguide is a critical issue to ensure the reproducibility of circuit performance. In this paper, a method to extract fabrication deviations in the waveguide from refractive index change in silicon microring resonators (MRRs) is ex...

The selective area growth of the Si capping layer on Ge was investigated to reduce the leakage current of photodetectors. Using dichlorosilane as a Si precursor, we found that the leakage current was affected by the growth temperature and thickness of the Si capping layer, and that a relatively low growth temperature of 670 °C was effective for bot...

We studied a high speed and high efficiency of vertically-illuminated p-i-n Ge photodetector (Ge-PD) with Ge thickness of around 500 nm and 1800 nm. In case of 500 nm thick Ge layer, we proposed the Ge-PD of the concentric p-i-n electrode structure of Si under the Ge mesa. In case of 1800 nm thick Ge layer, we developed a vertical p-i-n structure o...

We propose a model to consistently interpret the resonant wavelength and group index variation behaviour in numbers of microring resonators, based on fabrication deviation analysis, and demonstrated that the model precisely derives fabrication variations for waveguides in 300-mm wafer processes.

Optical functionality integration on a single chip using silicon photonics technology provides a solution to overcome bandwidth bottleneck both in data transmission among LSIs and in long haul communication. In this paper, we describe the features of optical interconnection circuits using silicon photonics technology, and discuss about their device...

A 300-mm-wafer silicon photonics with fine fabrication accuracy and uniformity provides large-scale photonic integrated circuits with low power consumption and operation flexibility, and provides us key photonic devices in an ultra-low-energy optical path network.

Silicon is a very useful material not only for electrical LSI’s but also for photonic IC’s. Si photonics application basically comes from optical properties of Si, that is, the absorption coefficient of Si is very small between 1.2-1.6 μm wavelengths and the refractive index of Si is higher than silica. Si photonics IC‘s are expected to overcome th...

Infrared light detection capability of a hydrogenated amorphous silicon waveguide with a vertically stacked pin structure by utilising defect absorption, i.e. transition between dangling bond defect and extended states is demonstrated. The responsivities for a 0.6 mm-long device are ∼6.2 and ∼0.22 mA/W at 1300 and 1550 nm wavelength, respectively.

In a method of manufacturing an optical device including an optical waveguide having a core, a cladding and a light input/output part through which a light beam is input or output, a substrate is prepared which is provided with a uniform thickness of single-crystalline film having its constituent atoms forming a diamond lattice structure and its su...

We developed a high-speed and high-efficiency MOS-capacitor-type Si optical modulator (Si-MOD) by applying a low optical loss and a low resistivity of a polycrystalline silicon (poly-Si) gate with large grains. To achieve a low resistivity of a poly-Si film, a P-doped poly-Si film based on Si2H6 solid-phase crystallization (SPC) was developed, whic...

In order to provide solutions to two bottlenecks about memory volume of main memory and bandwidth of interconnect in the computing system, researches for memory cell technology with high-k materials and optical integrated circuit with silicon waveguide devices were done. Regarding memory cell technology with high-k materials, the comprehensive rese...

The Si photonics platform for 300mm SOI wafers has been built up for optical multi-applications. The performance of main optical waveguide devices has been demonstrated. State-of-the-art propagation loss values are obtained for optical waveguides of multi-thickness SOI structures in this platform. The propagation loss is less than 0.5dB/cm at 1.55μ...

PROBLEM TO BE SOLVED: To provide a manufacturing method of an optical element made of Si optical waveguide, which simplifies manufacturing steps and suppresses variations in dimensions, and to provide an optical element manufactured by the manufacturing method. SOLUTION: There is provided a manufacturing method of an optical element having an optic...

The dimension control technology for silicon photonics devices based on 40-nm-node CMOS technology are reviewed. By using ArF immersion lithography in the fabrication technology, the high-level reproducihility in resonant wavelength of demultiplexers (σλ. <1 nm) was achieved, as well as extremely low propagation loss <0.5 dB/cm in silicon wire wave...

We have fabricated lateral MOSFETs on heteroepitaxial 3C-SiC films included high density of defects. Electrical characteristics of 3C-SiC MOSFETs and their temperature dependence were measured to discuss effects of defects on the electrical characteristics. A field effect mobility of 156 cm²/Vs was obtained at room temperature. After applying a dra...

To implement a large-scale integration of superconducting quantum bits (qubits), we have investigated a process of fabricating submicrometer Al/AlOx/Al trilayer Josephson junctions. Moreover, on the basis of this process, we developed a means of fabricating different kinds of superconducting qubits. Superconducting qubits require not only small jun...

A 300mm Si photonics platform has been established for optical multi-applications. For device fabrication process, the advanced CMOS technology can lead to the performance improvement of optical devices. State-of-the-art propagation loss values are obtained for optical waveguides of multi-thickness SOI structures in this platform and discussed them...

Precise dimension control technology for the fabrication of silicon photonics devices was established. The dimension control technology consists of the devices fabrication using 40-nm-node CMOS technology and in-line process monitoring by optical wafer-level probing system. As the results of process optimization in waveguide formation, superior dim...

We previously proposed a photonics-electronics convergence system to solve bandwidth bottleneck problems among large-scale integrations (LSIs) and demonstrated a high bandwidth density with silicon optical interposers at room temperature. For practical applications, the interposers should be usable under hightemperature conditions or rapid temperat...

We previously proposed a photonics-electronics convergence system to solve bandwidth bottlenecks among large scale integrations (LSIs) and demonstrated a high bandwidth density with silicon optical interposers at room temperature. For practical applications, interposers should be usable under high temperature conditions and rapid temperature change...

We developed a 25-Gb/s silicon modulator with 9.83-dB·V αVπL, which is smallest of those operated at 25 Gb/s and higher. We used forward-biased diode operations, which enables small VπL with moderately doped low-loss waveguides.

We demonstrated a 25-Gbps error-free data link on a silicon optical interposer. The experimental results verified that our interposer is compatible with high-performance FPGAs, and transmitter pre-emphasis and receiver equalization reduced bit error rate of the optical data link.

We demonstrated athermal silicon optical interposers integrated with quantum dot lasers at 1.3 μm, achieving a bandwidth density of 15 Tbps/cm2 with a channel line rate of 12.5 Gbps operating up to 125 °C without any bias adjustment.

Interposers for inter-chip interconnects should perform stably under high-temperature conditions and rapid temperature change due to the heat generated by mounted large-scale integration (LSI) chips. Athermal silicon optical interposers integrated with quantum dot lasers and other temperature-insensitive components on a single silicon substrate are...

World-record low propagation losses for single-mode silicon waveguides with TE-polarization were demonstrated. As the results of precise width control, the deviation of 1.8nm was confirmed for the resonance peaks of a ring-resonator on a 300mm-SOI.

We report good phase controllability and high production yield in Si-nanowire-based multistage delayed Mach–Zehnder interferometer-type optical multiplexers/demultiplexers (MUX/DeMUX) fabricated by an ArF-immersion lithography process on a 300 mm silicon-on-insulator (SOI) wafer. Three kinds of devices fabricated in this work exhibit clear waveleng...

One of the most serious challenges facing exponential performance growth in the information industry is the bandwidth bottleneck in interchip interconnects. We propose a photonics–electronics convergence system in response to this issue. To demonstrate the feasibility of the system, we fabricated a silicon optical interposer integrated with arrayed...

In this study, we investigated the effect of the Ge LT layer thickness in HT/LT 2-step Ge growth on the I-V characteristics. Even the ultrathin 5-nm-thick LT layer could lower the dark current caused by the defects due to the effective defect termination between Ge/Si interfaces.

To realize an over 10-Tbit/s bandwidth optical interconnection, a 1000-channel light source was demonstrated by using novel spot-size converters with a SiOx slab layer for a wide fabrication margin and by optimization done in consideration of the thermal interference between each channel in an LD array and also between the LD array chips for low po...

The carbonization mechanism of Si(100) substrates was examined under a pressure of approximately 10−2 Pa. The results indicate that the concentration of carbon on the surface determined the growth mechanism of the carbonized layer. At the initial stage, the carbonized layer forms by epitaxial growth at a pressure lower than 1.1 × 10−2 Pa (p0). At a...

We report good phase controllability and high production yield in Si-wire delayed interferometer-type demultiplexers fabricated by 300-mm wafer-scale ArF-immersion lithography technologies. The results are promising for utilization in high-density WDM interconnects.

An over 1000-channel hybrid integrated light source has been demonstrated by novel spot-size converters with a SiOx slab layer and by optimization considering thermal interference of multiple LD arrays for low power consumption.

We present flatband, low-loss and low-crosstalk characteristics of Si-nanowire-based 5th-order coupled resonator optical waveguides (CROW) fabricated by ArF-immersion lithography process on a 300-mm silicon-on-insulator (SOI) wafer. We theoretically specified why phase controllability over Si-nanowire waveguides is prerequisite to attain desired sp...

The carbonized layer for a buffer layer strongly influences the crystalline quality of the 3C-SiC epitaxial films on the Si substrates. The growth mechanism of the carbonized layer strongly depended on the process conditions. The surface of silicon substrate was carbonized under the pressure of 7.8 × 10⁻³ Pa or 7.8 × 10⁻² Pa in this research. Under...

One of the most serious challenges facing the exponential performance growth in the information industry is a bandwidth bottleneck in inter-chip interconnects. Optical interconnects with silicon photonics have been expected to solve the problem because of the intrinsic properties of optical signals and the industrial advantages of silicon for use i...

We have proposed a photonics-electronics convergence system to solve a bandwidth bottleneck in inter-chip interconnects. We demonstrated silicon optical interposers fully integrated with optical components with high bandwidth density of 30 Tbps/cm2.

We report superior spectral characteristics of silicon-nanowire-based 5th-order coupled resonator optical waveguides (CROW) fabricated by 193-nm ArF-immersion lithography process on a 300-mm silicon-on-insulator wafer. We theoretically analyze spectral characteristics, considering random phase errors caused by micro fabrication process. It will be...

We developed PIN-diode-based silicon Mach-Zehnder modulators, which have side-wall-gratings in the phase-shifter sections. Such passive waveguides with gratings were fabricated using ArF immersion lithography, which showed a small scattering loss of 0.4 dB/mm. We extensively investigated the forward-biased operation of the modulators by using equiv...

A Si wire arrayed waveguide grating designed to reduce the noise and transmission peak width and avoid systematic phase error generated at the curved waveguides is reported. A slab waveguide structure to remove stray light is used. 200 GHz spacing 16 channel devices were fabricated by ArF immersion. An improved crosstalk of ??23 dB was obtained.

Waveguide integrated MSM (metal-semiconductor-metal) Germanium (Ge) photodetectors (PDs) with a SiGe capping layer were exploited for silicon photonics integration. Under optimized epitaxial growth conditions, the capping layer passivated the Ge surface, resulting in sufficiently low dark current of the PDs. In addition, the PDs exhibited a narrowe...

Silicon optical interposers for inter-chip interconnects, integrated with lasers, optical splitters, modulators, waveguides and photodetectors on a single silicon substrate were demonstrated. They were optically complete and closed systems. We achieved 20-Gbps error-free data transmission and a 30-Tbps/cm2 bandwidth density using these interposers.

This paper describes recent progress in silicon photonics integration technology and related developments in interconnect and telecom applications.

We developed a high speed and high efficiency Si optical modulator (Si-MOD) with a metal-oxide-semiconductor (MOS) junction by applying the low optical loss and low resistivity of the poly-Si gate. We designed the optimum Si-MOD structure and demonstrated a very high modulation efficiency of 0.28-0.30 Vcm, which is one of the most efficient in Si-M...

We developed a pin-diode silicon microring modulator that used side-wall grating waveguides. Modulator exhibits 0.28- V·cm-VπL at 25 GHz in forward-biased operation mode. We achieved 50-Gb/s operation at a driving voltage of 1.96 volts-peak-to-peak (Vpp).

We have investigated characteristics uniformity of Si-wire waveguide devices formed on 300 mm SOI wafers by using ArF immersion lithography process. Very low dispersion of group indices within wafers was confirmed from measurements of asymmetric Mach-Zhender interferometers.

We demonstrate silicon optical interposers for inter-chip interconnects, integrating lasers, optical splitters, modulators, waveguides and photodetectors on a single silicon substrate. Innovative challenge of quantum dot lasers for silicon photonics application is also discussed.

One of the most serious challenges facing the exponential performance growth in the information industry is a bandwidth bottleneck in inter-chip interconnects. We therefore propose a photonics-electronics convergence system with a silicon optical interposer. We examined integration between photonics and electronics and integration between light sou...

By integrating compact and high-speed silicon modulators and germanium photodiodes with light sources, we demonstrated a silicon optical interposer for inter-chip interconnects with a bandwidth density of 6.6 Tbps/cm2.

We achieved 50-Gb/s operation of a ring-resonator-based silicon modulator for the first time. The pin-diode phase shifter, which consists of a side-wall-grating waveguide, was loaded into the ring resonator. The forward-biased operation mode was applied, which exhibited a VπL as small as 0.28 V·cm at 25 GHz. The driving voltage and optical insertio...

We studied Si waveguide-integrated metal-semiconductor-metal (MSM) and p-i-n-type Ge photodiodes (Ge-PDs), using a Si-capping layer. As for an MSM Ge-PD, the Schottky barrier height was increased up to 0.44 V by applying a 8-20 nm Si-capping layer, and a very low dark current density of approximately 0.4 nA/mu m(2) was achieved with a high responsi...

An Si wire array waveguide grating wavelength demultiplexer fabricated using immersion ArF lithography is reported. The tilt directions of the input and output star couplers are aligned in the same direction to avoid phase error generated at the curved waveguides. A 16 channel device with 200 GHz wavelength spacing was fabricated.

The formation mechanism of a carbonized layer was investigated under low-pressure and low-temperature process conditions. The initial carbonized layer under those conditions was formed epitaxially using the silicon atoms sublimated from substrate and the carbon atoms of the gas source. This result is suggested from the consideration of pit formatio...

High-density optical interposers integrated with complete optical components on single silicon substrate by using silicon photonics were demonstrated. Error-free data transmission at 12.5-Gbps and high bandwidth density of 6.6-Tbps/cm2 were achieved with the optical interposers.

Silicon optical interposers for inter-chip interconnects, integrated with lasers, an optical splitter, optical modulators and germanium photodetectors on a single silicon substrate were demonstrated. A 12.5-Gbps error-free data transmission and 6.6-Tbps/cm2 transmission density were achieved.

We report on a high speed silicon-waveguide-integrated PIN Ge photodetector of 45 GHz bandwidth, and a high efficiency of 0.3 V·cm silicon optical modulator with a metal-oxide-semiconductor (MOS) junction by applying the low optical loss and high conductivity poly-silicon gate. These OE/EO devices enable low drive voltage of around 1V, which would...

We report the Si wire AWG without systematic phase error generated at the curved waveguides. A 200GHz spacing 16 channel devices were fabricated by ArF immersion and EB lithography and the results are compared.