Monolithic Platform Research Articles

Heterostructured silicon-germanium-silicon p-i-n avalanche photodetectors for chip-integrated optoelectronics -INVITED

Optical photodetectors are at the forefront of photonic research since the rise of integrated optics. Photodetectors are fundamental building blocks for chip-scale optoelectronics, enabling conversion of light into an electrical signal. Such devices play a key role in many surging applications from communication and computation to sensing, biomedicine and health monitoring, to name a few. However, chip integration of optical photodetectors with improved performances is an on-going challenge for mainstream optical communications at near-infrared wavelengths. Here, we present recent advances in heterostructured silicon-germanium-silicon p-i-n photodetectors, enabling high-speed detection on a foundry-compatible monolithic platform.

Unique role of small satellites in empowering spacecraft formation flying missions

Spacecraft formation flying avails unprecedented means of conducting space missions compared to a single conventional large monolithic platform. Chiefly, formation flying enables sparse and synthes...

Nonlinear silicon photonics on CMOS-compatible tellurium oxide

Silicon photonics is coming of age; however, it is still lacking a monolithic platform for optical sources and nonlinear functionalities prompting heterogeneous integration of different materials tailored to different applications. Here we demonstrate tellurium oxide as a complementary metal oxide semiconductor silicon photonics platform for nonlinear functionalities, which is already becoming an established platform for sources and amplifiers. We show broadband supercontinuum generation covering the entire telecom window and show for the first time to our knowledge third-harmonic generation in its integrated embodiment. Together with the now-available lasers and amplifiers on integrated TeO 2 this work paves the way for a monolithic TeO 2 -based nonlinear silicon photonics platform.

(Invited) Capturing Biological Behavior in Nanomagnetic Artificial Neurons and Synapses for Energy-Efficient Neuromorphic Computing

Modeling computer architecture after the human brain is a promising approach to the ever-increasing demands for real-time processing of massive amounts of data. But, the building blocks of the brain, i.e. neurons and synapses, have more detailed behavior than simply how they are connected, and this behavior is central to their computing efficiency. If we want to capture the energy efficiency of such a neuromorphic architecture, we need devices themselves that can capture the behavior of the biological elements.Magnetic materials and devices have many properties similar to the brain that make them attractive candidates as artificial neurons and synapses. We will present our recent work on designing and modeling three-terminal domain wall-magnetic tunnel junctions (DW-MTJs) that can act as both leaky, integrate, and fire neurons with inherent lateral inhibition [1-2] and as synapses with online learning and spike-timing dependent plasticity behavior [3].The DW-MTJ neuron consists of a perpendicularly magnetized wire containing a single DW and an MTJ on top of the wire, shown in Fig. a. When current is applied to the wire, the DW propagates through spin transfer torque (STT) or spin orbit torque (SOT). The MTJ defines the firing point of the neuron: when the DW moves past the junction, the MTJ resistance switches to generate a spiking current at the MTJ output terminal. We will show results of integration, firing, and inherent leaking of the device. When assembled into a crossbar array as shown in Fig. b, 1-10 digit identification is simulated by measuring which of ten neurons reach the firing point first as shown in Fig. c.Lateral inhibition (LI) is an important function in neuromorphic computing, modeled after the biological neuron behavior that a neuron prevents its less active neighbors in the same layer from firing. In most neuromorphic hardware platforms, LI is implemented with external circuitry, thereby decreasing the energy efficiency and increasing the area overhead of such systems. We show that the DW-MTJ neuron has inherent LI via magnetic interactions. We will show results from modeling current- and field-driven DW motion in adjacent DW-MTJ neurons. Figure d shows that with 90 nm spacing between two 50 nm wide DW-MTJs, the slower device’s DW velocity is drastically reduced from 75 m/s to 20 m/s and a LI of 75% is achieved. The results are explained by current-driven DW velocity characteristics in response to external magnetic fields and are quantified by an analytical model based on the Landau-Lifshitz-Gilbert (LLG) equation. We will show results of arrays of DW-MTJs implementing a soft winner-take-all function and application of the effect to image recognition.We will furthermore present simulation results of the DW-MTJ showing synaptic behavior when the MTJ is made long. By constructing a small circuit around the device we implement spike-timing-dependent plasticity (STDP), where the current flowing through the synapse, which will determine its resistive synaptic weight, is determined by the delay between input and output neurons (Fig. e). We will show that the STDP synapses can process time-dependent input data.The results will be compared with other emerging nonvolatile devices for artificial neural networks. The work presented shows that DW-MTJs can provide a monolithic platform for neuromorphic computing circuits, where both synapses and neurons can be made from the same thin film stack, and motivate further study of magnetic devices for neuromorphic computing.SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. References N. Hassan, X. Hu, L. Jiang-Wei, W. H. Brigner, O. G. Akinola, F. Garcia-Sanchez, M. Pasquale, C. H. Bennett, J. A. C. Incorvia & J. S. Friedman. Magnetic domain wall neuron with lateral inhibition. J. Appl. Phys. 124, (2018).C. Cui, O. G. Akinola, N. Hassan, H. Christopher, M. J. Marinella, J. S. Friedman & J. A. C. Incorvia. Maximized Lateral Inhibition in Paired Magnetic Domain Wall Racetracks for Neuromorphic Computing. IOP Nanotechnology (2020).O. G. Akinola, X. Hu, C. H. Bennett, M. Marinella, J. S. Friedman & J. A. C. Incorvia. Three-terminal magnetic tunnel junction synapse circuits showing spike-timing-dependent plasticity. J. Phys. D. Appl. Phys. 52, 49LT01 (2019). Figure 1

Piezocatalytic Foam for Highly Efficient Degradation of Aqueous Organics

Piezoelectric catalysis (piezocatalysis) is a physical/chemical process that utilizes piezoelectric potential for accelerating chemical reactions, in which ubiquitous mechanical energies in nature are used for various catalysis applications, e.g., treating organic water pollutants. Despite the high efficiency achieved by piezocatalytic powders, the particles used tend to diffuse in water systems and are hard to be separated, thus causing secondary pollution. Herein, a free‐standing piezocatalytic foam is designed and fabricated, which is composed of BaTiO3 nanoparticles embedded in the PVDF scaffold. The as‐prepared PVDF–BaTiO3 composite foam demonstrates outstanding piezocatalytic efficiency in removing aqueous organics among state‐of‐the‐art integral piezocatalytic platforms, which lie in the synergy of piezoelectric materials and abundant interconnected pores within the foam. Significantly, PVDF–BaTiO3 foam is further applied for purifying natural water samples, by which the permanganate index of the water sample reduces by nearly 30% after 2 h of treatment. In addition, as a monolithic platform, PVDF–BaTiO3 foam is easy to be collected, with high reuse stability and applicability for treating various pollutants, resulting in dominant advantages over powder‐based systems for practical high‐flux wastewater treatment. Herein, a piezocatalytic platform is provided for the effective degradation of organic pollutants in water, with minimal environmental side effects.

Integrated optical isolators using electrically driven acoustic waves.

We propose and investigate the performance of integrated photonic isolators based on non-reciprocal mode conversion facilitated by unidirectional, traveling acoustic waves. A triply-guided waveguide system on-chip, comprising two optical modes and an electrically-driven acoustic mode, facilitates the non-reciprocal mode conversion and is combined with spatial mode filters to create the isolator. The co-guided and co-traveling arrangement enables isolation with no additional optical loss, without magnetic-optic materials, and with low power consumption. The approach is theoretically evaluated with simulations predicting over 20 dB of isolation and 2.6 dB of insertion loss with a 370 GHz optical bandwidth and 1 cm device length. The isolator uses only 1 mW of electrical drive power, an improvement of 1-3 orders of magnitude over the state of the art. The electronic drive and lack of magneto-optic materials suggest the potential for straightforward integration with drive circuits, including in monolithic CMOS electronic-photonic platforms, enabling a fully contained 'black box' optical isolator with two optical ports and DC electrical power.

Beam shaping for ultra-compact waveguide crossings on monolithic silicon photonics platform.

A beam shaping approach has been implemented to realize high-performance waveguide crossings based on cosine tapers. Devices with a compact footprint of 4.7µm×4.7µm were fabricated on the GLOBALFOUNDRIES 45 nm monolithic silicon photonics platform (45 CLO technology). Fabricated devices are found to be nearly wavelength independent (±0.035dB for 1260nm≤λ≤1360nm) with low insertion loss (∼0.2dB) and crosstalk (-35dB). The measured response of the devices is consistent with the three-dimensional finite-difference time-domain simulation results. The design stability is validated by measuring the device insertion loss on eight chips, which is found to be 0.197±0.017dB at the designed center wavelength of 1310 nm.

Carrier removal and transport in photonic integrated circuit ready InGaAsP/InP substrate: Electrical and transients of charges evaluation

InGaAsP based technologies are more favorable due to its unique monolithic integrated nature. For an efficient electro-optical device structure, there is a keen interest to develop active and passive components to suffice the needs of monolithic platform. Thus, carrier's transport and removal regions are carefully fabricated with low optical and electronic signal loss in order to optimize the signal to noise ratio (SNR) to effectively produce monolithic chip. In this specialized study we have provided an insight about the effective multi-implant ion-assisted carrier removal capability of the highly conductive epitaxially grown InGaAsP/InP device matrix as PIC's substrate. For this multi-implant strategy has been adopted with C+ and Ni+ ions implanted separately. Their dosage's along with ion energies are simulated rigorously before the actual implantations. Post implant measurements of Sheet resistance, mobility, drift driven electric fields, current-voltage, Arrhenius based activation energies, charge based transient analysis and detailed investigations of traps have been performed to study the viability of carrier removal scheme for the stable as well as reversible electrical isolation of this photonic integrated circuit's platform.Trap parameters identified as a result of a specialized charge deep level transient spectroscopy provides an insight about the energy levels and possible evaluation of recombination/generation centers for effective photonic activity within the device regions. The optical loss study has been performed to inspect the optical hindrance levels into the said InGaAsP PIC matrix.

Self-powered monolithic accelerometer using a photonic gate

Abstract Harvesting sustainable energy resources from surrounding environments to power small electronic devices and systems has attracted massive research attention. Herein, we develop a novel technology to harvest light energy to self-power and simultaneously sense mechanical acceleration in a monolithic structure. When the photonic gate is illuminated the operation mode of the device changes from conventional mode to light harvesting and self-powered operation. The light illumination provides a gradient of majority carrier concentration on the top semiconductor layer, generating a lateral photovoltage, which is the output voltage of the sensor. Under acceleration, the mechanical inertial force induces stress in the sensor material leading to the change of mobility of the charge carriers, which shifts their diffusion rate, and hence changes the gradient of the majority carriers and the lateral photovoltage. The sensitivity at 480 lx light illumination was measured to be 107 μ V / g , while it was approximately 30 μ V / g under the ambient light illumination without any electrical power source. In addition, the acceleration sensitivity is tunable by controlling parameters of the photonic gate such as light power, light spot position and light wavelength. The integration of sensing and powering functions into a monolithic platform proposed in this work eliminates the requirement of external power sources and offers potential solutions for wireless, independent, remote, and battery-free sensing devices and systems.

Solid-state ion recognition strategy using 2D hexagonal mesophase silica monolithic platform: a smart two-in-one approach for rapid and selective sensing of Cd2+ and Hg2+ ions.

Thepossibility of a multifunctional and reversible solid-state colorimetric sensor is describedfor the identification and quantification of ultra-trace Cd2+ and Hg2+ ions, using a honeycomb-structured mesoporous silica monolith conjoined with an indigenous chromoionophoric probe, i.e., 4-hexyl-6-((5-mercapto-1,3,4-thiadiazol-2-yl)diazenyl)benzene-1,3-diol (HMTAR). The amphiphilic probe is characterized using NMR, FT-IR, HR-MS, and CHNS elemental analysis. The structural and surface properties of the monolithic template have been characterized using p-XRD, XPS, TEM-SAED, SEM-EDAX, FT-IR, TG-DTA, and N2 isotherm analysis. The unique structural features and distinct analytical properties of the solid-state sensor proffer a strong response in selectively signaling the target analytes. The probe (HMTAR) exhibits a 1:1 stoichiometric binding ratio with the target ions (Cd2+ & Hg2+), with a visual color change from pale orange to dark red for Cd2+ (525nm, λmax), and topurple for Hg2+ (530nm, λmax), respectively, in the pH range 7.0-8.0. The influence of variousanalytical criteria such as pH, temperature, response kinetics, critical probe concentration, sensor quantity, matrix tolerance, linear response range, reusability, the limit of detection (LOD), and quantification (LOQ) has been investigatedto validate the sensor performance. The proposed method displays a linear signal response in the concentration range 5-100μg/L, with a LOD value of 2.67 and 2.90μg/L, for Cd2+ and Hg2+, respectively. The real-world efficacy of the sensor material has been tested with real and synthetic water samples with a significant recovery value of ≥ 99.2%, to authenticate its data reliability and reproducibility (RSD ≤ 3.53%). Graphical abstract.

Monolithic quartz platform for cellular contact guidance

Abstract

SciKit-Surgery: compact libraries for surgical navigation

PurposeThis paper introduces the SciKit-Surgery libraries, designed to enable rapid development of clinical applications for image-guided interventions. SciKit-Surgery implements a family of compact, orthogonal, libraries accompanied by robust testing, documentation, and quality control. SciKit-Surgery libraries can be rapidly assembled into testable clinical applications and subsequently translated to production software without the need for software reimplementation. The aim is to support translation from single surgeon trials to multicentre trials in under 2 years.MethodsAt the time of publication, there were 13 SciKit-Surgery libraries provide functionality for visualisation and augmented reality in surgery, together with hardware interfaces for video, tracking, and ultrasound sources. The libraries are stand-alone, open source, and provide Python interfaces. This design approach enables fast development of robust applications and subsequent translation. The paper compares the libraries with existing platforms and uses two example applications to show how SciKit-Surgery libraries can be used in practice.ResultsUsing the number of lines of code and the occurrence of cross-dependencies as proxy measurements of code complexity, two example applications using SciKit-Surgery libraries are analysed. The SciKit-Surgery libraries demonstrate ability to support rapid development of testable clinical applications. By maintaining stricter orthogonality between libraries, the number, and complexity of dependencies can be reduced. The SciKit-Surgery libraries also demonstrate the potential to support wider dissemination of novel research.ConclusionThe SciKit-Surgery libraries utilise the modularity of the Python language and the standard data types of the NumPy package to provide an easy-to-use, well-tested, and extensible set of tools for the development of applications for image-guided interventions. The example application built on SciKit-Surgery has a simpler dependency structure than the same application built using a monolithic platform, making ongoing clinical translation more feasible.

Towards the Development of a 3-D Biochip for the Detection of Hepatitis C Virus.

The early diagnostics of hepatitis C virus (HCV) infections is currently one of the most highly demanded medical tasks. This study is devoted to the development of biochips (microarrays) that can be applied for the detection of HCV. The analytical platforms of suggested devices were based on macroporous poly(glycidyl methacrylate-co-di(ethylene glycol) dimethacrylate) monolithic material. The biochips were obtained by the covalent immobilization of specific probes spotted onto the surface of macroporous monolithic platforms. Using the developed biochips, different variants of bioassay were investigated. This study was carried out using hepatitis C virus-mimetic particles (VMPs) representing polymer nanoparticles with a size close to HCV and bearing surface virus antigen (E2 protein). At the first step, the main parameters of bioassay were optimized. Additionally, the dissociation constants were calculated for the pairs “ligand–receptor” and “antigen–antibody” formed at the surface of biochips. As a result of this study, the analysis of VMPs in model buffer solution and human blood plasma was carried out in a format of direct and “sandwich” approaches. It was found that bioassay efficacy appeared to be similar for both the model medium and real biological fluid. Finally, limit of detection (LOD), limit of quantification (LOQ), spot-to-spot and biochip-to-biochip reproducibility for the developed systems were evaluated.

Wafer-scale 4H-silicon carbide-on-insulator (4H–SiCOI) platform for nonlinear integrated optical devices

4H-silicon carbide-on-insulator (4H–SiCOI) serves as a novel and high efficient integration platform for nonlinear optics and quantum photonics. The realization of wafer-scale fabrication of single-crystalline semi-insulating 4H–SiC film on Si (100) substrate using the ion-cutting and layer transferring technique was demonstrated in this work. The thermodynamics of 4H–SiC surface blistering is investigated via observing the blistering phenomenon with a series of implanted fluences and annealing temperatures. Surface tomography and the depth dependent film quality of the 4H–SiC have been extensively studied by employing scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Moreover, X-ray diffraction (XRD) was carried out and the diffraction spectrum reveals a narrow peak with a full width at half maximum (FWHM) of 75.6 arcsec, indicating a good maintenance of the single-crystalline phase for the prepared thin film of 4H–SiC as compared to its bulk counterpart. With the single-crystalline 4H–SiCOI, we have successfully fabricated a micro-ring resonator with a quality factor as high as 6.6 × 104. The reported 4H–SiCOI wafer provides a feasible monolithic platform for integrated photonic applications.

Hybrid integrated quantum photonic circuits.

Recent developments in chip-based photonic quantum circuits has radically impacted quantum information processing. However, it is challenging for monolithic photonic platforms to meet the stringent demands of most quantum applications. Hybrid platforms combining different photonic technologies in a single functional unit have great potential to overcome the limitations of monolithic photonic circuits. Our review summarizes the progress of hybrid quantum photonics integration, discusses important design considerations including optical connectivity and operation conditions, then highlights several successful realizations of key physical resources for building a quantum-teleporter. We conclude by discussing the roadmap for realizing future advanced large-scale hybrid devices, beyond the solid state platform, which hold great potential for quantum information applications.

Mid-infrared dual-comb spectroscopy with room-temperature bi-functional interband cascade lasers and detectors

Interband cascade (IC) laser structures offer attractive potential for operation at room temperature as both broadband coherent sources of mid-infrared light and fast photodetectors. This makes the realization of extremely compact spectrometers on a monolithic platform possible, and even dual-comb spectroscopy (DCS) configurations. IC comb devices are perfect candidates for this configuration, since they develop near-THz-wide optical frequency comb spectra from a millimeter-sized cavity, using a multi-stage structure that can also function as a very fast photodetector. In this work, we leverage IC photodetectors with a gigahertz bandwidth to demonstrate a self-contained, free-running, room-temperature DCS system in the mid-infrared. The DCS system used detection by the same bi-functional IC device structure to measure 1,1-difluoroethane over ∼600 GHz of optical coverage around 3.6 µm. These results show that the IC platform is suitable for full integration as a broadband, high-resolution on-chip spectrometer in a future chemical sensing system.

Monolithic microfluidic platform for exerting gradients of compression on cell-laden hydrogels, and application to a model of the articular cartilage

Movement is essential to our quality of life, and regulates cell behavior via mechanical stimulation. Here, we report a monolithic microfluidic platform, in which engineered tissues composed of cells in a hydrogel are exposed to gradients of mechanical compression. Mechanical stimulation is applied through the deflection of a thin polydimethylsiloxane (PDMS) vertical membrane. The device design and all actuation parameters were optimized in this work to produce physiologically relevant compression on a cartilage model (strain of 5–12 %), as well as gradients of compression ranging from healthy to hyper-physiological conditions in the same device, as evidenced by the measured gradients in cell deformation. While this work focuses on mechanical compression of engineered tissues, we also demonstrated that our platform allowed creating more sophisticated multi-modal stimulation patterns. As the membrane is actuated by three independently addressed yet connected pressurized chambers, a variety of programmable deflection patterns and various cell stimulation modalities can easily be created by tuning the pressure applied in the different chambers (positive vs. negative, and amplitude). Advantageously, the fabrication of this monolithic platform is straightforward, with a single-step process. Moreover, the vertical membrane configuration allows for real-time imaging of cells encapsulated in the hydrogel matrix. The herein reported platform is highly versatile and of great interest to model other types of tissues, which also experience complex mechanical actuation patterns in vivo.

Plasmonic monolithic lithium niobate directional coupler switches

Lithium niobate (LN) has been the material of choice for electro-optic modulators owing to its excellent physical properties. While conventional LN electro-optic modulators continue to be the workhorse of the modern optoelectronics, they are becoming progressively too bulky, expensive, and power-hungry to fully serve the needs of this industry. Here, we demonstrate plasmonic electro-optic directional coupler switches consisting of two closely spaced nm-thin gold nanostripes on LN substrates that guide both coupled electromagnetic modes and electrical signals that control their coupling, thereby enabling ultra-compact switching and modulation functionalities. Extreme confinement and good spatial overlap of both slow-plasmon modes and electrostatic fields created by the nanostripes allow us to achieve a 90% modulation depth with 20-μm-long switches characterized by a broadband electro-optic modulation efficiency of 0.3 V cm. Our monolithic LN plasmonic platform enables a wide range of cost-effective optical communication applications that demand μm-scale footprints, ultrafast operation and high environmental stability.

Terahertz photonic integrated circuit for frequency tuning and power modulation

The quantum cascade laser is a powerful solid-state source of terahertz-frequency radiation. However, integrating multiple photonic functions into a monolithic platform in this frequency range is non-trivial due to the scaling of photonic structures for the long terahertz wavelengths and the low frequency tuning coefficients of the quantum cascade lasers. Here, we have designed a simple terahertz-frequency photonic integrated circuit by coupling a racetrack resonator with a ridge laser in the longitudinal direction to design a notch filter. The transmission properties of this filter structure are dependent on the phase matching and losses in the coupled racetrack and results in a comb of stopband frequencies. We have optimized the comb separation by carefully selecting the cavity dimensions of the racetrack resonator to suppress longitudinal modes in the ridge laser enabling single-mode emission. The emission frequencies and output power from laser are controlled through appropriate control of drive currents to the ridge and the racetrack resonator. The emission frequency is electrically tuned over ∼81 GHz exploiting Stark shift of the gain as a function of drive current at the ridge laser, coinciding with an output power variation of ∼27% of the peak power (at a heat sink temperature of 50 K). The output power from the ridge also varied by ∼30% and the frequency was tuned by a further 10 GHz when the driving conditions at the ridge laser are invariant and the current at the racetrack resonator was varied. To our best knowledge, this is the first report of a frequency engineering, tuning and power modulation of terahertz-frequency quantum cascade lasers using a photonic integrated circuit.

4H-silicon-carbide-on-insulator for integrated quantum and nonlinear photonics

Optical quantum information processing will require highly efficient photonic circuits to connect quantum nodes on-chip and across long distances. This entails the efficient integration of optically addressable qubits into photonic circuits, as well as quantum frequency conversion to the telecommunications band. 4H-silicon carbide (4H-SiC) offers unique potential for on-chip quantum photonics, as it hosts a variety of promising colour centres and has a strong second-order optical nonlinearity. Here, we demonstrate within a single, monolithic platform the strong enhancement of emission from a colour centre and efficient optical frequency conversion. We develop a fabrication process for thin films of 4H-SiC, which are compatible with industry-standard, CMOS nanofabrication. This work provides a viable route towards industry-compatible, scalable colour-centre-based quantum technologies, including the monolithic generation and frequency conversion of quantum light on-chip. Monolithic photonics devices based on SiC are fabricated by a wafer bonding and thinning technique. The strong enhancement of single-photon emission from a colour centre and optical frequency conversion with an efficiency of 360% W−1 are demonstrated.