Silicon-on-insulator Research Articles

Monolithic integrated chip of AWG and PD for an FBG interrogation system

To advance the development of a compact and highly integrated fiber Bragg grating (FBG) interrogation system, to the best of our knowledge, this paper is the first to present the design and fabrication of a monolithic integration chip based on silicon-on-insulator (SOI), which is specifically intended for application in fiber grating sensing interrogation systems. By considering the impact of coupling structure dimensions on coupling efficiency as well as the effect of the photodetector (PD) parameters on the optical absorption efficiency of the device, we refine the structure of the monolithic integrated chip for arrayed waveguide grating (AWG) and PD. The test results reveal that the coupling loss between AWG and PD is -2.4 dB. The monolithic integrated interrogation chip achieves an interrogation accuracy of approximately 6.79 pm within a dynamic range of 1.56 nm, accompanied by a wavelength resolution of 1 pm. This exceptional performance highlights the potential of the monolithic integrated chip to enhance the integration of AWG-based fiber grating interrogation systems.

Slow-light-enhanced Brillouin scattering with integrated Bragg grating.

Advancements in photonic integration technology have enabled the effective excitation of simulated Brillouin scattering (SBS) on a single chip, boosting Brillouin-based applications such as microwave photonic signal processing, narrow-linewidth lasers, and optical sensing. However, on-chip circuits still require large pump power and centimeter-scale waveguide length to achieve a considerable Brillouin gain, making them both power-inefficient and challenging for integration. Here, we exploit the slow-light effect to significantly enhance SBS, presenting the first, to the best of our knowledge, demonstration of a slow-light Brillouin-active waveguide on the silicon-on-insulator (SOI) platform. By integrating a Bragg grating with a suspended ridge waveguide, a 2.1-fold enhancement of the forward Brillouin gain coefficient is observed in a 1.25 mm device. Furthermore, this device shows a Brillouin gain coefficient of 1,693 m-1W-1 and a mechanical quality factor of 1,080. The short waveguide length reduces susceptibility to inhomogeneous broadening, enabling the simultaneous achievement of a high Brillouin gain coefficient and a high mechanical quality factor. This approach introduces an additional dimension to enhance acousto-optic interaction efficiency in the SOI platform and holds significant potential for microwave photonic filters and high spatial resolution sensing.

Thermal Boundary Conductance of Direct Bonded Aluminum Nitride to Silicon Interfaces.

Heat accumulation and self-heating have become key issues in microelectronics owing to the ever-decreasing size of components and the move toward three-dimensional structures. A significant challenge for solving these issues is thermally isolating materials, such as silicon dioxide (SiO2), which are commonly used in microelectronics. The silicon-on-insulator (SOI) structure is a great demonstrator of the limitations of SiO2 as the low thermal conductivity insulator prevents heat dissipation through the bottom of a device built on a SOI wafer. Replacing SiO2 with a more thermally conductive material could yield immediate results for improved heat dissipation of SOI structures. However, the introduction of alternate materials creates unknown interfaces, which can have a large impact on the overall thermal conductivity of the structure. In this work, we studied a direct bonded AlN-to-SOI wafer (AlN-SOI) by measuring the thermal conductivity of AlN and the thermal boundary conductance (TBC) of silicon (Si)/AlN and Si/SiO2/aluminum-oxygen-nitrogen (AlON)/AlN interfaces, the latter of which were formed during plasma-activated bonding. The results show that the AlN-SOI possesses superior thermal properties to those of a traditional SOI wafer, with the thermal conductivity of AlN measured at roughly 40 W m-1 K-1 and the TBC of both interfaces at roughly 100 MW m-2 K-1. These results show that AlN-SOI is a very promising structure for improving heat dissipation in future microelectronics.

Leaky-integrate-fire neuron based on vertically extended drain Si[formula omitted]Ge[formula omitted] source TFET: Ultra-energy-efficient and high speed design

This article investigates the performance of a vertically extended drain double gate Si1−x Gex source tunnel field effect transistor (VD-DG-Si1−x Gex S-TFET) as a leaky integrate-and-fire (LIF) neuron. The proposed VD-DG-Si1−x Gex S-TFET structure has been designed and optimized by deploying the commercially available Silvaco TCAD. The LIF neuron using VD-DG-Si1−x Gex S-TFET requires a low spiking threshold voltage (i.e. 0.20 V) which is 5x, 3x, 5x, 1.3x, 1.55x, 7.5x, and 1.44x times less in comparison to MOSFET, Bulk FinFET, phase change device, SOI MOSFET, DG-JLFET, silicon nanowire, and DL-TFET silicon neuron. The proposed device based neuron demonstrates the least spiking energy (177 ZJ) reported to date which is 18192 times less as compared to BTBT based PDSOI MOSFET neuron. The threshold value of current is achieved at 0.20 V drain voltage which is 15x, 14x, 10x, and 1.5x less as compared to FinFET, PD-SOI MOSFET, LBIMOS, and DL-TFET, respectively. Moreover, the effects of gate metal work function, germanium mole fraction, and temperature on the spike current variations have also been investigated. Here, impact ionization is a key method for generating a neuron spike due to holes accumulated in the potential well of VD-DG-Si1−xGex S-TFET. In addition, a LIF neuron based on VD-DG-Si0.5Ge0.5 S-TFET device exhibits a 9 THz spiking frequency which is approximately 12 times higher than real nerves present in the human body. This work shows a remarkable reduction in the power consumption and the proposed device neuron is a potential start-up solution for a large scale spiking neural networks (SNN) implementation because of its better performance and compact circuitry.

Multimodule microwave assembly for fast readout and charge-noise characterization of silicon quantum dots

Fast measurements of quantum devices is useful in areas such as quantum sensing, quantum computing, and nanodevice quality analysis. Here, we develop a superconductor-semiconductor multimodule microwave assembly to demonstrate charge-state readout at the state of the art. The assembly consist of a superconducting readout resonator interfaced to a silicon-on-insulator (SOI) chiplet containing quantum dots (QDs) in a high-κ nanowire transistor. The superconducting chiplet contains resonant and coupling elements as well as LC filters that, when interfaced with the silicon chip, result in a resonant frequency f=2.12 GHz, a loaded quality factor Q=850, and a resonator impedance Z=470Ω. Combined with the large gate lever arms of SOI technology, we achieve a minimum integration time for single and double QD transitions of 2.77 and 13.5 ns, respectively. We utilize the assembly to measure charge noise over 9 decades of frequency up to 500 kHz and find a 1/f dependence across the whole frequency spectrum as well as a charge-noise level of 4μeV/Hz at 1 Hz. The modular microwave circuitry presented here can be directly utilized in conjunction with other quantum devices to improve the readout performance as well as enable large bandwidth noise spectroscopy, all without the complexity of superconductor-semiconductor monolithic fabrication. Published by the American Physical Society 2024

Integrated Electro‐Optic Frequency Combs: Theory and Current Progress

AbstractOptical frequency combs (OFCs) have evolved into one of the most active areas of photonics, underpinning advancements in both fundamental science and commercial contexts. Electro‐optic modulation for OFC generation offers excellent versatility, stability, and phase coherence. With the rapid progress in micro‐nano fabrication techniques, electro‐optic frequency combs (EOFCs) have been realized on many integrated platforms, including silicon on insulator (SOI), indium phosphide (InP), and lithium niobate on insulator (LNOI). These compact, low‐cost, and energy‐efficient EOFCs support a wide range of applications. In this study, we review the theory for the generation of integrated EOFCs, summarize the demonstrations on the main integrated platforms, present applications, and envision the development directions of integrated EOFCs in view of materials, devices, and applications.

Design and demonstration of high efficiency perfectly vertical grating couplers with a random structure.

Utilizing an automated optimization method, we propose a perfectly vertical grating coupler (PVGC) characterized by random structure, superior performance, simplified fabrication process, and increased minimum feature size (MFS). Within the range of MFS from 60 to 180 nm, the optimized PVGC exhibited a simulated coupling efficiency of approximately -2.0 dB at 1550 nm with a 34 nm 1-dB bandwidth. Experimental results for the PVGCs fabricated by electron beam lithography (EBL) demonstrated coupling efficiencies ranging from -2.5 to -2.8 dB with a 32 nm 1-dB bandwidth while maintaining high manufacturing tolerances. This represents the most outstanding experimental outcome to date regarding the coupling performance of a PVGC fabricated on a 220 nm silicon on insulator (SOI), without requiring any complex processes as reported in the existing literature.

Suitability of applying ultrathin SOI‐based PIN diodes to photodetection of UV wavelength

AbstractThis work intends to investigate the impact of silicon layer thickness and substrate biasing on the UV photodetection efficiency of PIN diodes fabricated with ultra‐thin body and buried oxide (UTBB silicon‐on‐insulator [SOI]) technology, aiming to verify their behaviour on an ultimate commercial technology. UV photodetectors are applied in different fields, such as environmental and biomedical ones, and their implementation in UTBB SOI could enable the design of mixed circuits where data acquisition and processing could be made in the same chip, enhancing systems’ performance. It is shown that a 20‐nm‐thick silicon layer can be applied for UV photodetection and enhanced generated current is obtained when substrate bias is set to guarantee a depletion regime in the entire active layer.

Design and analysis of Si photonic NaCl sensors based on suspended microdisk resonators

In this paper, two optical refractive index sensors, respectively based on a suspended microdisk resonator (SMDR) and a sub-wavelength Bragg grating suspended microdisk resonator (SWG-SMDR) have been designed on a silicon on insulator (SOI) platform, and their optical and sensing performances have been analyzed using the three-dimensional finite-difference time-domain method. It has been shown that the Bragg grating increases the optical confinement factor in the sensing region and, consequently, improves the light–matter interaction and sensitivity. Considering concentrations of 0 to 25% for the NaCl dissolved in the deionized water, the enhanced sensitivity and FOM of the SWG-SMDR sensor with the miniaturized optimal geometrical dimensions are 163.77 nm RIU−1 and 10.81 RIU−1, respectively. This compact optical sensor enhances the sensitivity and FOM by combining effects of the Bragg grating and suspension configuration in improving the light–matter interaction.

Hybrid Graphene–Silicon Arrayed Waveguide Gratings for On-Chip Signal–Frequency Conversion

We present the design and simulations of a novel integrated device concept enabling a frequency conversion of a broad signal. The solution is based on a hybrid silicon–graphene photonic chip, which could be used for controlled spectrometry in low-cost devices. The device is based on a silicon-on-insulator (SOI) platform on which an arrayed waveguide grating (AWG) is designed for operation at the center wavelength of λ = 1800 nm. The AWG is spectrally separating one broad input signal to thirty-two-output channels with a channel spacing of 2.72 nm. The output signals are well separated and uniform with the extinction ratio and the standard deviation of 10.00 dB and 0.04, respectively. The 3 dB channel width is 1.34 nm, which is suitable for sensing applications with significant accuracy. After spacial and spectral separation, each output signal is then converted to one signal at 1480 nm wavelength through a graphene-based saturable absorber scheme. Therefore, the device allows the detection of each separated signal with a simple near-infrared camera on which the outputs are imaged using conventional optics, leading to a classical pixel/wavelength correspondence. Crossed-waveguide couplers are designed to combine the controlling signal at 1480 nm to each channel waveguide of the AWG. The combination of the signals saturates the graphene layer at the output waveguides, allowing the pass of the controlling wavelength. This device can be applied as a spectrometer in environmental sensing and monitoring with high efficiency and low cost.

Effect of overheat and direct flow loading on the MEMS bistable flow sensor

We present the findings from an experimental study of a MEMS flow sensor in which an initially curved, double-clamped bistable microbeam is the primary sensing element. Our research explores how the overheat ratio, direct flow loading, and turbulence-induced vibration affect the sequential snap-through (ST) buckling and snap-back (SB) release of an electrostatically actuated beam heated by an electric current. The sensor is fabricated from highly doped single-crystal silicon using a silicon-on-insulator (SOI) wafer. Positioned at the chip’s edge, the microbeam is exposed to airflow, enabling concurrent dynamic response measurements with a laser Doppler vibrometer and a video camera.Our research demonstrates that the overheat ratio can be significantly lower for this sensing principle than conventional thermal sensing elements, pointing to the potential for substantial energy savings. We also emphasize the significant impact of flow angles and vibrations on the critical ST and SB voltages, which are vital for the flow sensor’s output. Additionally, we introduce the first direct experimental observation of the beam profile’s time history during the snap-through/snap-back transition.The potential impact of this research lies in developing more robust MEMS flow sensors with enhanced sensitivity and a better understanding of their response to environmental factors, which could have broader applications in fields such as aerospace, environmental monitoring, and industrial process control.

Ultra-compact and efficient photonic waveguide bends with different configurations designed by topology optimization

Transporting light signals over the corners and sharp bends imposes high optical loss and distortion on the mode profiles. Usually, bends with larger radii are used in circuits to minimize the loss over transmission, resulting in a severe limitation in integration density. In this paper, we propose novel topology-optimized optimized L-bend and U-bend structures designed for a 220 nm silicon-on-insulator (SOI) platform. Optimized L-bends with footprints of 2.5 µm × 2.5 µm, 1.5 µm × 1.5 µm, and 1 µm × 1 µm show maximum insertion losses of only 0.07 dB, 0.26 dB, and 0.78 dB, respectively. For optimized U-bends with footprints of 3 µm × 3.6 µm, 2.5 µm × 2.5 µm, and 1.5 µm × 1.5 µm, the maximum insertion losses are 0.07 dB, 0.21 dB, and 3.16 dB. These optimized bends reduce the maximum insertion loss by over 50% compared to un-optimized arc-type bends across a broad wavelength range of 1450–1650 nm. Experimental verification of a meander line with 16 optimized U-bends (3 µm × 3.6 µm) demonstrates an averaged insertion loss of 1.23 dB in the wavelength range of 1520–1580 nm, agreeing with simulated results and indicating a high potential of loss reduction with optimized bends.

Defect control for high efficiency antimony selenosulfide solar cells by interface Engineering of buried monoatomic aluminum oxide layer

Antimony selenosulfide (Sb2(S,Se)3) reveals excellent optoelectronic characteristics, positioning it as a propitious light-absorbing substance with potential applications in photovoltaic technology. However, a multitude of deep-level defects significantly limit the efficiency of Sb2(S,Se)3 solar cells. In this study, the density of the surface and deep-level defects was reduced by adding a monoatomic Al2O3 layer on the surface of CdS film. Compared to the as-deposited film, highly [hk1]-oriented Sb2(S,Se)3 film having significantly enhanced charge separation was obtained. The addition of a monoatomic Al2O3 layer effectively modified the energy band structure by increasing the valence band maximum and more intrinsic Sb2(S,Se)3 film between n-type CdS layers and p-type spiro. This contributed to increased carrier collection and reduced carrier recombination. Ultimately, 9.39 % efficiency of the device were obtained as a result of the optimized orientation and reduced defects. Consequently, this research demonstrates an effective method for optimizing crystallographic orientation and minimizing defect density, thereby maximizing the efficiency of Sb2(S,Se)3 solar cells.

Optimization of Grating Coupler over Single-Mode Silicon-on-Insulator Waveguide to Reach < 1 dB Loss through Deep-Learning-Based Inverse Design

Grating couplers are essential components in silicon photonics that facilitate the coupling of light between waveguides and fibers. Optimization of the grating couplers to reach <1 dB loss when coupling to single-mode fibers (SMFs) has been reported in the literature, but this was based on silicon-on-insulator (SOI) waveguides supporting multi-modes. In this paper, using a deep-learning model combined with an inverse-design process, we achieve <1 dB losses for grating couplers implemented over single-mode SOI waveguides, i.e., a maximum efficiency of 80.5% (−0.94 dB) for gratings constrained with e-beam (EB) lithography critical dimension (CD), and a maximum efficiency of 77.9% (−1.09 dB) for gratings constrained with deep ultraviolet (DUV) lithography CD. To verify these results, we apply covariance matrix adaptation evolution strategy (CMA-ES) and find that while CMA-ES yields slightly better results, i.e., 82.7% (−0.83 dB) and 78.9% (−1.03 dB) considering e-beam and DUV, respectively, the spatial structures generated by CMA-ES are nearly identical to the spatial structures generated by the deep-learning model combined with the inverse-design process. This suggests that our approach can achieve a representative low-loss structure, and may be used to improve the performance of other types of nanophotonic devices in the future.

Demonstration of a low loss, highly stable and re-useable edge coupler for high heralding efficiency and low g(2)(0) SOI correlated photon pair sources.

We report a stable, low loss method for coupling light from silicon-on-insulator (SOI) photonic chips into optical fibers. The technique is realized using an on-chip tapered waveguide and a cleaved small core optical fiber. The on-chip taper is monolithic and does not require a patterned cladding, thus simplifying the chip fabrication process. The optical fiber segment is composed of a centimeter-long small core fiber (UHNA7) which is spliced to SMF-28 fiber with less than -0.1 dB loss. We observe an overall coupling loss of -0.64 dB with this design. The chip edge and fiber tip can be butt coupled without damaging the on-chip taper or fiber. Friction between the surfaces maintains alignment leading to an observation of ±0.1 dB coupling fluctuation during a ten-day continuous measurement without use of any adhesive. This technique minimizes the potential for generating Raman noise in the fiber, and has good stability compared to coupling strategies based on longer UHNA fibers or fragile lensed fibers. We also applied the edge coupler on a correlated photon pair source and observed a raw coincidence count rate of 1.21 million cps and raw heralding efficiency of 21.3%. We achieved an auto correlation function g H(2)(0) as low as 0.0004 at the low pump power regime.

Enhanced BSA Detection Precision: Leveraging High-Performance Dual-Gate Ion-Sensitive Field-Effect-Transistor Scheme and Surface-Treated Sensing Membranes.

Bovine serum albumin (BSA) is commonly incorporated in vaccines to improve stability. However, owing to potential allergic reactions in humans, the World Health Organization (WHO) mandates strict adherence to a BSA limit (≤50 ng/vaccine). BSA detection with conventional techniques is time-consuming and requires specialized equipment. Efficient alternatives such as the ion-sensitive field-effect transistor (ISFET), despite rapid detection, affordability, and portability, do not detect BSA at low concentrations because of inherent sensitivity limitations. This study proposes a silicon-on-insulator (SOI) substrate-based dual-gate (DG) ISFET platform to overcome these limitations. The capacitive coupling DG structure significantly enhances sensitivity without requiring external circuits, owing to its inherent amplification effect. The extended-gate (EG) structure separates the transducer unit for electrical signal processing from the sensing unit for biological detection, preventing chemical damage to the transducer, accommodating a variety of biological analytes, and affording easy replaceability. Vapor-phase surface treatment with (3-Aminopropyl) triethoxysilane (APTES) and the incorporation of a SnO2 sensing membrane ensure high BSA detection efficiency and sensitivity (144.19 mV/log [BSA]). This DG-FET-based biosensor possesses a simple structure and detects BSA at low concentrations rapidly. Envisioned as an effective on-site diagnostic tool for various analytes including BSA, this platform addresses prior limitations in biosensing and shows promise for practical applications.

An SOI-based post-fabrication process for compliant MEMS devices

Fabricating compliant microelectromechanical system (MEMS) devices is challenging because they are easily damaged during fabrication. This paper presents a fabrication process based on the silicon-on-insulator (SOI) wafer for compliant MEMS devices. In the fabrication process, tethers were used to enhance the strength of the compliant devices during fabrication and finally melted with an electric current to release the device after fabrication. We discover that the power supply mode and voltage value are very critical for low-resistance tether melting. The fabrication results show that the yield rate of the compliant microgripper increased from 44% to 100%, which is a significant improvement compared with conventional processes. The successful fabrication of the microgripper proved that the proposed SOI-based post-fabrication process is feasible and can be used to fabricate different kinds of compliant devices.

Excitation of hybrid modes in plasmonic nanoantennas coupled with GeSiSn/Si multiple quantum wells for the photoresponse enhancement in the short-wave infrared range

Hybrid structures represented by a plasmonic nanoantenna array located on the surface of GeSiSn/Si multiple quantum wells (MQWs) grown on a silicon-on-insulator (SOI) substrate by molecular-beam epitaxy were developed for applications in the short-wave infrared range. Using numerical modeling methods, the electromagnetic characteristics of metasurfaces based on aluminum nanoantennas located on the surface of GeSiSn/Si nanoheterostructures were studied. It is shown that the spectral and spatial overlap of localized plasmons in nanoantennas and waveguide modes in the semiconductor film leads to the formation of hybrid modes with a Fano-type resonance profile. The possibility of significant photoluminescence (PL) enhancement of GeSiSn/Si MQWs through the use of hybrid plasmonic structures is demonstrated. The PL enhancement reached to 250 % at the wavelength of 1.9 μm, coinciding with the maximum of the reflectance spectrum for the hybrid structure. Based on the hybrid system, represented by the plasmonic nanoantenna array on the top part of GeSiSn/Si MQWs, p-i-n photodiodes were fabricated. The photocurrent enhancement was approximately 7 times at wavelengths of 1.73 µm and 1.8 µm. The excitation of separately localized plasmons and waveguide modes is demonstrated, and their hybridization is also studied.

Algorithmically calibrated optical switch with high-extinction-ratio and low-polarization-dependence on 3-μm-thick SOI platform

Crosstalk, calibration complexity, and polarization dependence obstacle the precision of optical networks such as microwave photonics beamforming networks (MPBNs). The optical switch presented in this work, boasting high tolerance and polarization insensitivity, utilizes multimode interferometers (MMIs), a thermo-optical phase shifter, and variable optical attenuators (VOAs) on the 3 μm-thick silicon-on-insulator (SOI) platform. The switch exhibits extinction ratio (ER) exceeding 32.5 dB within 140 nm bandwidth, with maximum ER of 50 dB, accompanied by 0.4 dB loss, and features switching speed of 16 μs/21 μs In 10-layer networks, the VOA-assist golden-section algorithm enables optimal calibration within 170 iterations, serving as fundamental component for establishing precise optical networks.

A polymer trench filling based silicon isolation technique and its application to two-axis scanning comb-drive micromirrors

Electrostatic micromirrors can be widely used in LiDAR, displays, AR/VR and medical imaging. Electrically insulated silicon enabled by trenches filled with thermal oxide and polysilicon is commonly used for 2-axis electrostatic comb-drive scanning mirrors made on SOI (silicon-on-insulator) wafers. These trenches provide both electrical isolation and mechanical stability. However, this method has drawbacks such as high deposition temperature, voids, and high residual stress. In this work, a polymer filling method is proposed to form electrical insulation trenches in the silicon device layer of SOI wafers. Only low-temperature processes are used in this method and the silicon trenches can be fully filled up reliably. Furthermore, the filling polymer not only relieves residual stresses but also significantly increases the shock resistance of the micromirrors made with this method. In particular, Benzocyclobutene (BCB) is employed and a process has been developed to effectively fill deep silicon trenches. Using this method, two-axis electrostatic micromirrors have been successfully fabricated and tested. Experimental results show that the BCB-filled trenches demonstrate excellent electrical insulation performance and mechanical stability and the fabricated 2-axis mirrors can achieve a large field of view of 60°×40° and stand high impact over 2500 g.