Design and fabrication of 0.5 micron GaAs Schottky barrier diodes for low-noise terahertz receiver applications

Recent technological advances have made possible the development of heterodyne receivers with high sensitivity and high spectral resolution for frequencies in the range 1,000–3,000 GHz (1–3 THz). These receivers rely on GaAs Schottky barrier mixer diodes to translate the high-frequency signal to a lower frequency where amplification and signal processing are possible. At these frequencies, the diode quality is a major limitation to the performance of the receiver. The design, fabrication and DC evaluation of a diode for this frequency range is presented. A figure-of-merit cut-off frequency of over 10 THz is achieved with a record low zero biased capacitance of 0.5 fF. Results from RF tests are also given.This work has been supported in part by the National Science Foundation under contract ECS-8720850 and the US Army.     

A k-band broadband monolithic distributed frequency multiplier based on nonlinear transmission line

A fabrication technology of GaAs planar Schottky varactor diode (PSVD) is successfully developed and used to design and manufacture GaAs-based monolithic frequency multiplication based on 23-section nonlinear transmission lines (NLTLs) consisting of a coplanar waveguide transmission line and periodically distributed PSVDs. The throughout design and optimization procedure of 23-section monolithic NLTLs for frequency multiplication in the k-band range is based on a large signal equivalent model of PSVD extracted from small-signal S-parameter measurements. This paper reports that the distributed SPVD exhibits a capacitance ratio of 5.4, a normalized capacitance of 0.86 fF/μm2 and a breakdown voltage in excess of 22 V. The integrated 23-section NLTLs fed by 20-dBm input power demonstrates a 26-GHz peak second harmonic output power of 14-dBm with 25.3% conversion efficiency in the second harmonic output frequency range of 6 GHz-26 GHz.     

Millimeter wave frequency multiplier

Conclusions The GaAs Schottky diode mounted in a crossed waveguide structure gives much more efficient conversion than previously used point contact devices, and the power output at the second harmonic is sufficient for use in recently developed cryogenically cooled mixers [10, 11]. The diodes have electrical properties which are similar to conventional mixer diodes and they can be fabricated using similar masks and processing techniques.     

Investigation of high sensitivity radio-frequency readout circuit based on AlGaN/GaN high electron mobility transistor

An Al Ga N/Ga N high electron mobility transistor(HEMT) device is prepared by using a semiconductor nanofabrication process. A reflective radio-frequency(RF) readout circuit is designed and the HEMT device is assembled in an RF circuit through a coplanar waveguide transmission line. A gate capacitor of the HEMT and a surface-mounted inductor on the transmission line are formed to generate LC resonance. By tuning the gate voltage V g, the variations of gate capacitance and conductance of the HEMT are reflected sensitively from the resonance frequency and the magnitude of the RF reflection signal. The aim of the designed RF readout setup is to develop a highly sensitive HEMT-based detector.     

High reliability sputtered Schottky diodes on GaAs

We describe developments to improve reliability and power handling for high frequency applications in whisker-contacted Schottky barrier diode mixers, detectors and multipliers fabricated using sputtered refractory metals and silicides. The lift-off process has been used to fabricate diodes on GaAs with ideality factors of 1.18 and 1.06 for W/GaAs and TiSi_x/GaAs contacts respectively.     

Spin dynamics at low microwave frequencies in crystalline Fe ultrathin film double layers using co-planar transmission lines

Magnetic damping has been studied in magnetic double layers using a network analyzer (NA) with a coplanar transmission line. The magnetic films consisted of ultrathin crystalline films of Fe separated by an Au spacer. The films were deposited on GaAs(0 0 1) substrates using the molecular beam epitaxy (MBE) technique. NA-ferromagnetic resonance (NA-FMR) measurements were carried out along the magnetic hard axis, allowing one to follow the frequency FMR linewidth down to the 1 GHz range of frequencies. It will be shown that the FMR linewidth in the NA-FMR measurements is not entirely described by Gilbert damping. The additional contribution in the frequency linewidth increases with decreasing frequency, and is most likely caused by dipolar fields associated with an inhomogeneous RF field around the coplanar transmission line.     

Fabrication of Al air-bridge on coplanar waveguide

Superconducting coplanar waveguide(CPW) can be widely used as two-dimensional(2 D) resonator, transmission line or feedline, providing an important component for superconducting quantum circuit which is a promising candidate for quantum information processing. Due to the discontinuities and asymmetries in the ground planes, CPW usually exhibits the spurious resonance, which is a common source of decoherence in circuit quantum electrodynamics experiments. To mitigate the spurious resonance, we fabricated superconducting aluminum air-bridges on Nb CPW. The fabricated airbridges are approximately 3 m high and up to 120 m long. Compared with other methods, the fabrication procedures of our air-bridges are simpler, and the air-bridge can withstand strong ultrasound.     

Radio frequency characteristics of Fe-filled carbon nanotube film

The conduction noise suppression in radio frequency region using film type of the Fe-filled carbon nanotubes and its epoxy composite was evaluated on a coplanar waveguide. Fe in carbon nanotubes have shown α-Fe crystalline structure and had a coercivity of 650 Oe. The magnitudes of the signal attenuation of Fe-filled carbon nanotubes on coplanar waveguide were shown in the range of about 10–18 dB/cm at 20 GHz (the stop-band frequency region). The power losses of these films exhibited 65–85% at 20 GHz in the stop-band frequency.     

Hydrogen plasma modification of metal/GaAs interface

GaAs surface modification caused by room-temperature atomic hydrogen treatment in an RF plasma system operated in the reactive ion etching (RIE) mode has been studied by electrical characterization of subsequently fabricated Au/GaAs Schottky barriers. Unlike with reported results for plasma hydrogenation at higher temperatures, the Schottky barrier height on n-GaAs is found to decrease slightly. More interestingly, a pronounced increase in the effective barrier height is seen for p-GaAs. Dopant deactivation close to the surface is also observed for both conductivity types.     

Features of surface acoustic wave propagation in lithium niobate damaged by an electron beam

The propagation of surface acoustic waves (SAWs) in a thin-film aluminum waveguide of Δv/v type fabricated on a 128° Y-X LiNbO₃ plate by lift-off lithography and direct writing by a 20-keV electron beamis studied experimentally. The temperature dependence of the phase of the signal passed through an SAW delayline exhibits steps and hysteresis. The line consists of such a waveguide and two interdigital transducers with acenter frequency of 486 MHz and is exposed to a nitrogen flow. The vapors of water-containing analytes introduced into the nitrogen flow cause anomalous phase changes. These changes are of opposite sign and more thanone order of magnitude greater than the phase changes observed under similar conditions in specimens fabricated by optical lithography. It is concluded that these phenomena offer possibilities for designing SAW humidity sensors with a low threshold of sensitivity.     

Monolithically-integrated optoelectronic circuit for ultrafast sampling of a dual-gate field-effect transistor

An integrated optoelectronic circuit for ultrafast sampling of multi-terminal devices is described. This is achieved using optimized photoconductive switches fabricated from low-temperature-grown GaAs, monolithic integration of the device with the sampling circuit, control of the electromagnetic modes propagating on the coplanar waveguide using microfabricated airbridges, and discrimination of guided and freely-propagating modes using a novel electrooptic sampling method. As an example, the scattering parameters associated with the propagation of a picosecond pulse through one of the gates of a dual-gate heterojunction field-effect transistor are obtained at frequencies up to 300 GHz. The inter-gate capacitance is determined by measuring the electromagnetic transient coupled between the gates.     

具有调制功能的多模干涉型1×3分束器

提出了利用量子约束斯塔克(Stark)效应制作具有调制功能的多模干涉型1×3分束器的设计思想,并详细分析了这种光分束器的工作原理。根据理论计算结果,制作了具有调制功能的多模干涉型1×3分束器。分束器的脊型多模波导长度为275μm,宽度为10μm,波导层采用GaAs/AlGaAs多量子阱结构,厚度约为0.2μm;电极采用共面波导结构。首先用有限差分光束传播法模拟了器件的光波传播特性,然后进行了初步的实验验证。理论模拟和实验结果表明,波长为0.86μm的高斯光束对称入射到多模波导的中心,器件实现了3分束功能;施加3 V的直流偏压,器件的调制深度达90%以上、调制带宽为2 GHz,实现了电吸收调制功能。     

Uhf to Ka band upconverter

A balanced upconverter circuit has been developed in planar transmission line configuration using NEC GaAs beam lead Schottky barrier diodes. RF power output of +1.6 dBm SSB is obtained at Ka-band when up converter is driven by +17 dBm IF and +20 dBm LO signal.     

UHF to Ka band upconverter

A balanced upconverter curcuit has been developed in planar transmission line configuration using NEC GaAs beam lead Schottky barrier diodes. RF power output of +1.6 dBm SSB is obtained at Ka-band when up converter is driven by +17 dBm IF and +20 dBm LO signal.     

砷化镓半导体材料与器件中高频场分布研究的新方法——脉冲电光检测技术

介绍了砷化镓材料和器件中高频电场的分布测量的新方法——谐波混频脉冲电光检测:它的原理、实验装置以及在砷化镓共平面波导中微波驻波场分布测量中应用的结果.在频率高达20.10GHz及开路、短路和50Ω不同的负载条件下测得的结果与理论预计值符合很好.本文最后对方法的灵敏度和空间分辨率进行讨论.     

Polymeric flat focal field arrayed waveguide grating using electron-beam direct wiring

A four-channel 400-GHz spacing flat focal field arrayed waveguide grating (AWG) demultiplexer is designed based on polymeric optical waveguide. The waveguide core-layer material is a newly developed negative tone epoxy Novolak resin (ENR) polymer with ultravoilet (UV) cured resin Norland optical adhesive 61(NOA61) as the cladding layer. The device is fabricated using electron-beam direct writing, which has less processing steps than the reported polymeric AWGs. The experimental result is presented.     

Study and modeling of the transport mechanism in a semi insulating GaAs Schottky diode

The current through a metal–semiconductor junction is mainly due to the majority carriers. Three distinctly different mechanisms exist in a Schottky diode: diffusion of carriers from the semiconductor into the metal, thermionic emission–diffusion (TED) of carriers across the Schottky barrier and quantum–mechanical tunneling through the barrier. The insulating layer converts the MS device in an MIS device and has a strong influence on its current–voltage (I–V) and the parameters of a Schottky barrier from 3.7 to 15 eV. There are several possible reasons for the error that causes a deviation of the ideal behavior of Schottky diodes with and without an interfacial insulator layer. These include the particular distribution of interface states, the series resistance, bias voltage and temperature. The GaAs and its large concentration values of trap centers will participate in an increase of the process of thermionic electrons and holes, which will in turn the IV characteristic of the diode, and an overflow maximum value [NT = 3 × 10²⁰] is obtained. The I–V characteristics of Schottky diodes are in the hypothesis of a parabolic summit.     

Millimeter wave self-mixing oscillators

Self-oscillating mixers in both dielectric and waveguide cavities have veen investigated in the 60 GHz frequency range. The deveces consist of negative resistance diodes of GaAs and InP material coupled to waveguide cavities or high resistivity dielectric cavities such as silicon or Al₂O₃. Experimental measurements show that these devices have a sensitivity in the order of –80 dBm with the intermediate frequency at 60 MHz and an IF bandwidth of 120 MHz. Applications are suggested based on minimum detectable signal and RF power capabilities for systems requiring small size and low cost.     

Electrooptic sampling of low temperature GaAs pulse generators for oscilloscope calibration

Optoelectronic generation of well characterized ultrashort electrical pulses plays an important role in the calibration of fast-sampling oscilloscopes. In this paper the authors describe the National Physical Laboratory (NPL) pulse generator, comprising a femtosecond laser and an ultrafast photoconductive switch which can generate electrical pulses as short as 650 fs. The photoconductive switch consists of a GaAs substrate with a top GaAs layer grown under low temperature conditions to ensure a subpicosecond recombination rate. The technique of electrooptic sampling is used to measure pulses on planar transmission lines, such as coplanar waveguide and coplanar stripline. Good agreement is shown between electrooptic sampling measurement and the modelling of pulse propagation along a coplanar waveguide, enabling one to optimize a design of a calibration test source. The use of a pulse generator to calibrate a 50 GHz sampling oscilloscope is described.