The addition of active, nonlinear, and nonreciprocal functionalities to passive piezoelectric acoustic wave technologies could enable all-acoustic and therefore ultra-compact radiofrequency signal processors. Toward this goal, we present a heterogeneously integrated acoustoelectric material platform consisting of a 50 nm indium gallium arsenide epitaxial semiconductor film in direct contact with a 41° YX lithium niobate piezoelectric substrate. We then demonstrate three of the main components of an all-acoustic radiofrequency signal processor: passive delay line filters, amplifiers, and circulators. Heterogeneous integration allows for simultaneous, independent optimization of the piezoelectric-acoustic and electronic properties, leading to the highest performing surface acoustic wave amplifiers ever developed in terms of gain per unit length and DC power dissipation, as well as the first-ever demonstrated acoustoelectric circulator with an isolation of 46 dB with a pulsed DC bias. Finally, we describe how the remaining components of an all-acoustic radiofrequency signal processor are an extension of this work.
Here, the design, fabrication, and characterization of an actively tunable long-wave infrared detector, made possible through direct integration of a graphene-enabled metasurface with a conventional type-II superlattice infrared detector, are reported. This structure allows for post-fabrication tuning of the detector spectral response through voltage-induced modification of the carrier density within graphene and, therefore, its plasmonic response. These changes modify the transmittance through the metasurface, which is fabricated monolithically atop the detector, allowing for spectral control of light reaching the detector. Importantly, this structure provides a fabrication-controlled alignment of the metasurface filter to the detector pixel and is entirely solid-state. Using single pixel devices, relative changes in the spectral response exceeding 8% have been realized. These proof-of-concept devices present a path toward solid-state hyperspectral imaging with independent pixel-to-pixel spectral control through a voltage-actuated dynamic response.
Radio frequency (RF) devices are becoming more multi-band, increasing the number of filters and other front-end components while simultaneously pushing towards reduced cost, size, weight, and power (CSWaP). One approach to reducing CSWaP is to augment the achievable functionalities of electromechanical/acoustic filtering chips to include "active" and nonlinear functionalities, such as gain and mixing. The acoustoelectric (AE) effect could enable such active acoustic wave devices. We have examined the AE effect with a leaky surface acoustic wave (LSAW) in a monolithic structure of epitaxial indium gallium arsenide (In GaAs) on lithium niobate (LiNb0 3 ). This lead to experimentally demonstrated state-of-the-art SAW amplifier performance in terms of gain per acoustic wavelength, reduced power consumption, and increased power efficiency. We quantitatively compare the amplifier performance to previous notable works and discuss the outlook of active acoustic wave components using this material platform. Ultimately, this could lead to smaller, higher-performance RF signal processors for communications applications.
Active surface acoustic wave components have the potential to transform RF front ends by consolidating functionalities that currently occur across multiple chip technologies, leading to reduced insertion loss from converting back and forth between acoustic and electronic domains in addition to improved size and power efficiency. This letter demonstrates a significant advance in these active devices with a compact, high-gain, and low-power leaky surface acoustic wave amplifier based on the acoustoelectric effect. Devices use an acoustically thin semi-insulating InGaAs surface film on a YX lithium niobate substrate to achieve exceptionally high acoustoelectric interaction strength via an epitaxial In0.53Ga0.47As(P)/InP quaternary layer structure and wafer-scale bonding. We demonstrate 1.9 dB of gain per acoustic wavelength and power consumption of 90 mW for 30 dB of electronic gain. Despite the strong intrinsic leaky propagation loss, 5 dB of terminal gain is obtained for a semiconductor that is only 338 μm long due to state-of-the-art heterogenous integration and an improved material platform.
This paper demonstrates a monolithic surface acoustic wave amplifier fabricated by state-of-the-art heterogenous integration of a IH-V InGaAs-based epitaxial material stack and LiNb03. Due to the superior properties of the materials employed, we observe electron gain and also non-reciprocal gain in excess of 30dB with reduced power consumption. Additionally, we present a framework for performance optimization as a function of material parameters for a targeted gain. This platform enables further advances in active and non-reciprocal piezoelectric acoustic devices.
Al0.26Ga0.74N/GaN on SiC lateral Schottky diodes were fabricated with variable anode-to-cathode spacing and were analyzed for blocking and on-state device performance. On-chip normally-on High Electron Mobility Transistor (HEMT) structures were also fabricated for a comparison of blocking characteristics. The Schottky diode displayed an ideality factor of 1.59 with a Ni/AlGaN zero bias barrier height of 1.18 eV and a flat band barrier height of 1.59 eV. For anode-to-cathode spacings between 10 and 100 μm, an increase in median breakdown voltages from 529 V to 8519 V and median specific on-resistance (Ron-sp) from 1.5 to 60.7 mΩ cm2 was observed with an increase in spacing. The highest performing diode had a lateral figure of merit of 1.37 GW/cm2 corresponding to a breakdown voltage upwards of 9 kV and a Ron-sp of 59 mΩ cm2. This corresponds to the highest Schottky diode breakdown voltage reported thus far with an Al0.26Ga0.74N/GaN lateral structure.
The design, fabrication, and performance of InGaAs and InGaP/GaAs microcells are presented. These cells are integrated with a Si wafer providing a path for insertion in hybrid concentrated photovoltaic modules. Comparisons are made between bonded cells and cells fabricated on their native wafer. The bonded cells showed no evidence of degradation in spite of the integration process that involved significant processing including the removal of the III-V substrate.