CMOS-compatible Platform Research Articles

Distributed Bragg reflector based ASE noise removal pump wavelength filters for futuristic chip-scale quantum photonic circuits.

This article reports a novel design of a compact tunable resonance filter with a highly extinguished and ultra-broad out-of-band rejection for on-chip amplified spontaneous noise suppression from pump lasers highly demanding for generating pure/entangled photon pairs via χ(3) process in a CMOS compatible silicon photonics technology platform. The proposed device is designed with two identically apodized distributed grating structures for guided Fabry-Perot resonant transmissions in a silicon-on-insulator rib waveguide structure. The device design parameters are optimized by theoretical simulation for a low insertion loss singly-resonant transmission peak at a desired wavelength. We observed that a device length of as low as ∼ 35 µm exhibits a rejection band as large as ∼ 60 nm with an extinction of ∼ 40 dB with respect to the resonant wavelength peak at λr ∼ 1550 nm (FWHM ∼ 80 pm, IL ∼ 2 dB). The experimental results have been shown to be closely matching to our theoretical simulation and modeling results in terms of its stop bandwidth and resonance wavelength for noise suppressed pump laser wavelength filtering. As expected from the theoretical prediction, the trend pertaining to the trade-off between passive insertion loss and Q-value of the resonances has been observed depending on the device parameters. The thermo-optic tuning characteristics of resonant wavelengths have been obtained by integrating microheaters. The resonance peak could be tuned at a rate of 96 pm per mW of consumed thermal power. Noise associated with an amplified pump wavelength (λP ∼ 1550 nm) has been shown to be suppressed (∼ 40-dB), up to the detector noise floor.

Generation of entangled photon pairs from a silicon bichromatic photonic crystal cavity

Integrated quantum photonics leverages the on-chip generation of nonclassical states of light to realize key functionalities of quantum devices. Typically, the generation of such nonclassical states relies on whispering gallery mode resonators, such as integrated optical micro-rings, which enhance the efficiency of the underlying spontaneous nonlinear processes. While these kinds of resonators excel in maximizing either the temporal confinement or the spatial overlap between different resonant modes, they are usually associated with large mode volumes, imposing an intrinsic limitation on the efficiency and footprint of the device. Here, we engineer a source of time-energy entangled photon pairs based on a silicon photonic crystal cavity, implemented in a fully CMOS-compatible platform. In this device, resonantly enhanced spontaneous four-wave mixing converts pump photon pairs into signal/idler photon pairs under the energy-conserving condition in the telecommunication C-band. The design of the resonator is based on an effective bichromatic confinement potential, allowing it to achieve up to nine close-to-equally spaced modes in frequency, while preserving small mode volumes, and the whole chip, including grating couplers and access waveguides, is fabricated in a single run on a silicon-on-insulator platform. Besides demonstrating efficient photon pair generation, we also implement a Franson-type interference experiment, demonstrating entanglement between signal and idler photons with a Bell inequality violation exceeding five standard deviations. The high generation efficiency combined with the small device footprint in a CMOS-compatible integrated structure opens a pathway toward the implementation of compact quantum light sources in all-silicon photonic platforms.

Investigation of dynamic ron stability and hot electrons reliability in normally-off AlGaN/GaN power HEMTs

The current collapse and hot electron effect of 100 V normally-off GaN power HEMTs are investigated. The 100 V GaN-on-Si power HEMTs are fabricated on an industrial 200 mm Si CMOS compatible technology platform. The double pulse test (DPT) and the dynamic high temperature operating life (DHTOL) test are implemented to verify the dynamic on-resistance (dynamic Ron) stability. Wafer level hot electron reliability test is performed to investigate the effect of high electric field and high current on GaN power HEMT. It is proved that the dynamic Ron stability of 100 V GaN power HEMT is qualified (Ron/Rini, static < 1.2) when the drain-source off-state voltage (Vdsoff) is less than 80 V. It is shown that the dynamic Ron degradation of GaN device is recoverable by means of annealing. Hot electrons reliability is dominated by the high electric field at drain edge and the high current which is source injected electrons flowing to the drain. It is demonstrated that the Vth drift and Ron degradation are extraordinary serious under semi on-state stress condition with Vdsoff = 60 V.

Reliable micro-transfer printing method for heterogeneous integration of lithium niobate and semiconductor thin films

High-speed Pockels modulation and second-order nonlinearities are key components in optical systems, but CMOS-compatible platforms like silicon and silicon nitride lack these capabilities. Micro-transfer printing of thin-film lithium niobate offers a solution, but suspending large areas of thin films for long interaction lengths and high-Q resonators is challenging, resulting in a low transfer yield. We present a new source preparation method that enables reliable transfer printing of thin-film lithium niobate. We demonstrate its versatility by successfully applying it to gallium phosphide and silicon, and provide an estimate of the transfer yield by subsequently printing 25 lithium niobate films without fail.

A Novel Evaluation Methodology for the Reliability and Lifetime of 200 mm E-Mode GaN-on-Si Power HEMTs

In this paper, a novel evaluation methodology for the reliability and lifetime of E-mode AlGaN/GaN HEMTs has been proposed. A practical example of reliability evaluation is presented for commercial 100V E-mode GaN-on-Si power HEMTs, which are fabricated on an industrial 200mm Si CMOS compatible technology platform. Firstly, wafer-level reliability test (WLRT), Joint Electron Device Engineering Council (JEDEC) qualification and dynamic high temperature operating life (DHTOL) test of 200mm GaN-on-Si power HEMTs for mass production have been carried out. Secondly, the relationships of WLRT with JEDEC and DHTOL have been found, therefore, a fast evaluation method for the reliability of commercial 100V E-mode GaN-on-Si power devices has been established. Finally, DHTOL and switching accelerated lifetime test (SALT) have been carried out to demonstrate the validity of the fast evaluation method. In summary, it is proved that the novel evaluation methodology can better screen the robust GaN power devices, and greatly simplify the reliability testing flow of commercial 200mm GaN-on-Si power devices for mass production.

Engineered second-order nonlinearity in silicon nitride

The lack of a bulk second-order nonlinearity (χ(2)) in silicon nitride (Si3N4) keeps this low-loss, CMOS-compatible platform from key active functions such as Pockels electro-optic (EO) modulation and efficient second harmonic generation (SHG). We demonstrate a successful induction of χ(2) in Si3N4 through electrical poling with an externally-applied field to align the Si-N bonds. This alignment breaks the centrosymmetry of Si3N4, and enables the bulk χ(2). The sample is heated to over 500°C to facilitate the poling. The comparison between the EO responses of poled and non-poled Si3N4, measured using a Si3N4 micro-ring modulator, shows at least a 25X enhancement in the r33 EO component. The maximum χ(2) we obtain through poling is 0.30pm/V. We observe a remarkable improvement in the speed of the measured EO responses from 3 GHz to 15 GHz (3 dB bandwidth) after the poling, which confirms the χ(2) nature of the EO response induced by poling. This work paves the way for high-speed active functions on the Si3N4 platform.

Soliton formation and spectral translation into visible on CMOS-compatible 4H-silicon-carbide-on-insulator platform

Recent advancements in integrated soliton microcombs open the route to a wide range of chip-based communication, sensing, and metrology applications. The technology translation from laboratory demonstrations to real-world applications requires the fabrication process of photonics chips to be fully CMOS-compatible, such that the manufacturing can take advantage of the ongoing evolution of semiconductor technology at reduced cost and with high volume. Silicon nitride has become the leading CMOS platform for integrated soliton devices, however, it is an insulator and lacks intrinsic second-order nonlinearity for electro-optic modulation. Other materials have emerged such as AlN, LiNbO3, AlGaAs and GaP that exhibit simultaneous second- and third-order nonlinearities. Here, we show that silicon carbide (SiC) -- already commercially deployed in nearly ubiquitous electrical power devices such as RF electronics, MOSFET, and MEMS due to its wide bandgap properties, excellent mechanical properties, piezoelectricity and chemical inertia -- is a new competitive CMOS-compatible platform for nonlinear photonics. High-quality-factor microresonators (Q = 4 × 106) are fabricated on 4H-SiC-on-insulator thin films, where a single soliton microcomb is generated. In addition, we observe wide spectral translation of chaotic microcombs from near-infrared to visible due to the second-order nonlinearity of SiC. Our work highlights the prospects of SiC for future low-loss integrated nonlinear and quantum photonics that could harness electro-opto-mechanical interactions on a monolithic platform.

Precise Deposition of Carbon Nanotube Bundles by Inkjet-Printing on a CMOS-Compatible Platform.

Carbon nanotubes (CNTs) are ultimately small structures, attractive for future nanoelectronics. CNT-bundles on Si nanostructures can offer an alternative pathway to build hybrid CMOS-compatible devices. To develop a simple method of using such CNT-bundles as transistor channels, we fabricated semiconductor single-walled CNT field-effect transistors using inkjet printing on a CMOS-compatible platform. We investigated a method of producing stable CNT solutions without surfactants, allowing for CNT debundling and dispersion. An inkjet-printing system disperses CNT-networks with ultimately low density (down to discrete CNT-bundles) in Al source-drain gaps of transistors. Despite the small number of networks and random positions, such CNT-bundles provide paths to the flow current. For enhanced controllability, we also demonstrate the manipulation of CNT-networks using an AFM technique.

Platicon microcomb generation using laser self-injection locking

The past decade has witnessed major advances in the development and system-level applications of photonic integrated microcombs, that are coherent, broadband optical frequency combs with repetition rates in the millimeter-wave to terahertz domain. Most of these advances are based on harnessing of dissipative Kerr solitons (DKS) in microresonators with anomalous group velocity dispersion (GVD). However, microcombs can also be generated with normal GVD using localized structures that are referred to as dark pulses, switching waves or platicons. Compared with DKS microcombs that require specific designs and fabrication techniques for dispersion engineering, platicon microcombs can be readily built using CMOS-compatible platforms such as thin-film (i.e., thickness below 300 nm) silicon nitride with normal GVD. Here, we use laser self-injection locking to demonstrate a fully integrated platicon microcomb operating at a microwave K-band repetition rate. A distributed feedback (DFB) laser edge-coupled to a Si3N4 chip is self-injection-locked to a high-Q ( > 107) microresonator with high confinement waveguides, and directly excites platicons without sophisticated active control. We demonstrate multi-platicon states and switching, perform optical feedback phase study and characterize the phase noise of the K-band platicon repetition rate and the pump laser. Laser self-injection-locked platicons could facilitate the wide adoption of microcombs as a building block in photonic integrated circuits via commercial foundry service.

Observation of Ultrashort Laser Pulse Evolution in a Silicon Photonic Crystal Waveguide

Using the sum frequency generation cross-correlation frequency-resolved optical gating (SFG-XFROG) measurement setup, we observed the soliton evolution of low energy pulse in an Si photonic crystal waveguide, and it exhibited the pulse broadening, blue shift, and evident pulse acceleration. The soliton evolution was also investigated by nonlinear Schrödinger equation (NLSE) modelling simulation, and the simulated results agreed well with the experimental measurements. The effects of waveguide length on the pulse evolution were analyzed; the results showed that the pulse width changed periodically with increasing waveguide length. The results further the understanding of the ultra-fast nonlinear dynamics of solitons in silicon waveguides, and are helpful to soliton-based functional elements on CMOS-compatible platforms.

Silicon Nanoantenna Mix Arrays for a Trifecta of Quantum Emitter Enhancements.

Dielectric nanostructures have demonstrated optical antenna effects due to Mie resonances. Previous work has exhibited enhancements in absorption, emission rates and directionality with practical limitations. In this paper, we present a Si mix antenna array to achieve a trifecta enhancement of ∼1200-fold with a Purcell factor of ∼47. The antenna design incorporates ∼10 nm gaps, within which fluorescent molecules strongly absorb the pump laser energy through a resonant mode. In the emission process, the antenna array increases the radiative decay rates of the fluorescence molecules via a Purcell effect and provides directional emission through a separate mode. This work could lead to novel CMOS-compatible platforms to enhance fluorescence for biological and chemical applications.

Metasurface-based subtractive color filter fabricated on a 12-inch glass wafer using a CMOS platform

Optical color filters are widely applied in many areas including display, imaging, sensing, holography, energy harvest, and measurement. Traditional dye-based color filters have drawbacks such as environmental hazards and instability under high temperature and ultraviolet radiation. With advances in nanotechnology, structural color filters, which are based on the interaction of light with designed nanostructures, are able to overcome the drawbacks. Also, it is possible to fabricate structural color filters using standard complementary metal-oxide-semiconductor (CMOS) fabrication facilities with low cost and high volume. In this work, metasurface-based subtractive color filters (SCFs) are demonstrated on 12-inch (300-mm) glass wafers using a CMOS-compatible fabrication process. In order to make the transmissive-type SCF on a transparent glass wafer, an in-house developed layer transfer process is used to solve the glass wafer handling issue in fabrication tools. Three different heights of embedded silicon nanopillars (110, 170, and 230 nm) are found to support magnetic dipole resonances. With pillar height and pitch variation, SCFs with different displayed colors are achieved. Based on the resonance wavelength, the displayed color of the metasurface is verified within the red-yellow-blue color wheel. The simulation and measurement results are compared and discussed. The work provides an alternative design for high efficiency color filters on a CMOS-compatible platform, and paves the way towards mass-producible large-area metasurfaces.

Four-wave mixing in high-Q tellurium-oxide-coated silicon nitride microring resonators

We report the first-time observation, to the best of our knowledge, of four-wave mixing (FWM) in hybrid tellurium oxide coated silicon nitride ring resonators with internal Q factors of 1.7 × 105 to 1.0 × 106. We show oscillation at NIR wavelengths ranging from 1020 nm to 2530 nm under 1590 nm pumping. The FWM process has been investigated for TeO2-coated Si3N4 ring resonators with a 600 µm radius and FWM is observed for threshold launched pump powers as low as 25 mW with normal group velocity dispersion (GVD). With the potential for engineering of the GVD to the anomalous regime, a phase-matched and more efficient FWM process can be realized, which can pave the way for broadband frequency comb generation in this platform. These results suggest further promise of higher performance and lower threshold power nonlinear devices on a low-loss CMOS compatible platform with the possibility of co-integration of active functionalities due to high solubility of rare earth dopants in tellurium oxide.

(Plenary) The Revival of Compound Semiconductors and How They Will Change the World in a 5G/6G Era

Compound semiconductor devices have always intrigued the semiconductor industry due to their high intrinsic mobilities and the heterostructure engineering enabled by those materials. While CMOS has been the vehicle pushing the industry to ever smaller devices, better performance and of course reduced cost, the unique properties of compound semiconductor devices are finding renewed interest in an era where an increasing amount of data is being sent around, stored and analyzed. While several applications like photonics, high-power electronics and image sensors also benefit from enabling a variety of III-V materials and devices, specifically, in the RF Front-End Modules of 5G radio chips [1], these materials allow to address the challenges related to speed, efficiency and output power needed for this next generation wireless communication standard. And while 5G is in full deployment, with first addressing the sub-6GHz frequency bands and in a later phase the mm-wave frequency bands, first publications are already appearing on 6G, where even higher frequencies (beyond > 100GHz) will be targeted [2].GaN [3] and InP-based devices [4] have a clear performance advantage over Si CMOS and SiGe HBT/BICMOS, but their lower integration potential, still restricted to smaller size substrates and lab-like processing today, is one of the key limitations for adopting those technologies for high-volume 5G and 6G applications. Upscaling those devices to a 200mm/300mm Si platform will be a first step to improve yield and maturity and increase complexity. In a second phase, upscaling and maturing these technologies will allow to co-integrate these devices, usually quite dissimilar to CMOS, with advanced Si technology nodes and provide a fully integrated heterogeneous system.In this talk, we will review the status and progress toward integrating these devices on a CMOS-compatible platform.

A Non-Mechanical Multi-Wavelength Integrated Photonic Beam Steering System

In this work we experimentally demonstrate a fully packaged one-dimensional beam steering system that is based on a fully CMOS compatible silicon photonics platform. This configuration enables multi-wavelength operation and is suitable for short-wavelength infrared (SWIR) applications from light detection and ranging (LIDAR) to telecommunication and sensing applications. The switching fabric in this system employs a 1x9 array of add/drop ring resonators that are fed by a common waveguide through a single etch input grating. The switching fabric re-directs the resonance wavelengths at each drop waveguide to the output facet at the edge of the chip and into free space. The divergent beams that exit the waveguides along the output facet are then collimated and magnified using an array of micro-lenses (pitch = 750 μm, Diameter = 700 μm) in addition to a two lens afocal system in order to enhance the fill factor and diminish any blind zones between adjacent beams. Each one of these drop waveguides is used to address portion of the steering aperture. Combined together they enable steering across the entire aperture. Multi-wavelength operation is obtained by placing individual titanium tungsten alloy (TiW) heaters on top of each ring resonator to enable wavelength tuning.

A Complete Si Photonics Platform Embedding Ultra-Low Loss Waveguides for O- and C-Band

We report ultra-low propagation losses in silicon sub-micrometric waveguides on a 200 mm CMOS compatible photonics platform. We show median losses in C-band (O-band) as low as 0.1 dB/cm and 0.7 dB/cm (0.14 dB/cm and 1.1 dB/cm) in monomode rib and strip waveguides, respectively, thanks to a H2 smoothing annealing. In addition to the significant loss reduction, we show that the performance characteristic of the main passive and active components of the photonics platform are preserved or even improved by the smoothing process.

High-temperature silicon thermal diode and switch

A thermal rectifier/diode is a nonreciprocal element or system that enables preferential heat transport in one direction. In this work we demonstrate a single-material thermal diode operating at high temperatures. The diode is made of nanostructured silicon membranes exhibiting spatially and temperature-dependent thermal conductivity and, therefore, falling into the category of spatially asymmetric, nonlinear nonreciprocal systems. We used an all-optical state-of-the-art experimental technique to prove rectification along rigorous criteria of the phenomenon. Using sub-milliwatt power we achieve rectification of about 14%. In addition, we demonstrate air-triggered thermal switching and passive cooling. Our findings provide a CMOS-compatible platform for heat rectification and applications in energy harvesting, thermal insulation and cooling, as well as sensing and potentially thermal logic. • Single material thermal rectifier/diode is fabricated from thin holey silicon membranes. • The diode operates at 300–1000 K, sub-milliwatt driving power and rectification of about 14%. • The device can operate as air-triggered thermal switch or passive cooler. • The surface-to-volume ratio is the key parameter governing the rectifier performance.

Subwavelength pixelated CMOS color sensors based on anti-Hermitian metasurface

The demand for essential pixel components with ever-decreasing size and enhanced performance is central to current optoelectronic applications, including imaging, sensing, photovoltaics and communications. The size of the pixels, however, are severely limited by the fundamental constraints of lightwave diffraction. Current development using transmissive filters and planar absorbing layers can shrink the pixel size, yet there are two major issues, optical and electrical crosstalk, that need to be addressed when the pixel dimension approaches wavelength scale. All these fundamental constraints preclude the continual reduction of pixel dimensions and enhanced performance. Here we demonstrate subwavelength scale color pixels in a CMOS compatible platform based on anti-Hermitian metasurfaces. In stark contrast to conventional pixels, spectral filtering is achieved through structural color rather than transmissive filters leading to simultaneously high color purity and quantum efficiency. As a result, this subwavelength anti-Hermitian metasurface sensor, over 28,000 pixels, is able to sort three colors over a 100 nm bandwidth in the visible regime, independently of the polarization of normally-incident light. Furthermore, the quantum yield approaches that of commercial silicon photodiodes, with a responsivity exceeding 0.25 A/W for each channel. Our demonstration opens a new door to sub-wavelength pixelated CMOS sensors and promises future high-performance optoelectronic systems.

Energy-Efficient Stochastic Computing with Superparamagnetic Tunnel Junctions

Superparamagnetic tunnel junctions (SMTJs) have emerged as a competitive, realistic nanotechnology to support novel forms of stochastic computation in CMOS-compatible platforms. One of their applications is to generate random bitstreams suitable for use in stochastic computing implementations. We describe a method for digitally programmable bitstream generation based on pre-charge sense amplifiers. This generator is significantly more energy efficient than SMTJ-based bitstream generators that tune probabilities with spin currents and a factor of two more efficient than related CMOS-based implementations. The true randomness of this bitstream generator allows us to use them as the fundamental units of a novel neural network architecture. To take advantage of the potential savings, we codesign the algorithm with the circuit, rather than directly transcribing a classical neural network into hardware. The flexibility of the neural network mathematics allows us to adapt the network to the explicitly energy efficient choices we make at the device level. The result is a convolutional neural network design operating at $\approx$ 150 nJ per inference with 97 % performance on MNIST -- a factor of 1.4 to 7.7 improvement in energy efficiency over comparable proposals in the recent literature.

InGaAs photo field-effect-transistors (PhotoFETs) on half-inch Si wafer using layer transfer technology

InGaAs photo field-effect transistors (PhotoFETs) integrated on a half-inch Si wafer have been demonstrated by means of layer transfer technology. According to the Raman measurement and scanning transmission electron microscopy, the InGaAs layer was transferred onto the half-inch Si wafer without degradation of crystal quality or introduction of strain. The optical performance of InGaAs photoFETs on Si, operating in shortwave infrared (SWIR) region was also investigated. The photoFETs on Si wafer show a responsivity of ∼3 A W−1 at SWIR of 1550 nm with investigated range of bias. These results demonstrate InGaAs layer transfer technology is suitable for SWIR detectors on CMOS compatible platforms for monolithic integration.