R.P. Smith

2.5-THz GaAs monolithic membrane-diode mixer

A novel GaAs monolithic membrane-diode (MOMED) structure has been developed and implemented as a 2.5 THz Schottky diode mixer.

Submicron scaling of HBTs

The variation of heterojunction bipolar transistor (HBT) bandwidth with scaling is reviewed. High bandwidths are obtained by thinning the base and collector layers, increasing emitter current density, decreasing emitter contact resistivity, and reducing the emitter and collector junction widths. In mesa HBTs, minimum dimensions required for the base contact impose a minimum width for the collector junction, frustrating device scaling. Narrow collector junctions can be obtained by using substrate transfer or collector-undercut processes or, if contact resistivity is greatly reduced, by reducing the width of the base ohmic contacts in a mesa structure. HBTs with submicron collector junctions exhibit extremely high f/sub max/ and high gains in mm-wave ICs. Transferred-substrate HBTs have obtained 21 dB unilateral power gain at 100 GHz. If extrapolated at -20 dB/decade, the power gain cutoff frequency f/sub max/ is 1.1 THz. f/sub max/ will be less than 1 THz if unmodeled electron transport physics produce a >20 dB/decade variation in power gain at frequencies above 110 GHz. Transferred-substrate HBTs have obtained 295 GHz f/sub T/. The substrate transfer process provides microstrip interconnects on a low-/spl epsiv//sub r/ polymer dielectric with a electroplated gold ground plane. Important wiring parasitics, including wiring capacitance, and ground via inductance are substantially reduced. Demonstrated ICs include lumped and distributed amplifiers with bandwidths to 85 GHz and per-stage gain-bandwidth products over 400 GHz, and master-slave latches operating at 75 GHz.

A grid amplifier

A 50-MESFET grid amplifier is reported that has a gain of 11 dB at 3.3 GHz. The grid isolates the input from the output by using vertical polarization for the input beam and horizontal polarization for the transmitted output beam. The grid unit cell is a two-MESFET differential amplifier. A simple calibration procedure allows the gain to be calculated from a relative power measurement. This grid is a hybrid circuit, but the structure is suitable for fabrication as a monolithic wafer-scale integrated circuit, particularly at millimeter wavelengths. >

Monolithic Schottky-collector resonant tunnel diode oscillator arrays to 650 GHz

We report monolithic array oscillators incorporating Schottky-collector resonant tunnel diodes (SRTDs). In the SRTD, a 0.1-/spl mu/m width Schottky collector contact provides a greatly reduced device series resistance, resulting in an estimated 2.2 THz maximum frequency of oscillation. A 64-element oscillator array oscillated at 650 GHz while a 16-element array produced 28 /spl mu/W at 290 GHz.

Submicron transferred-substrate heterojunction bipolar transistors

We report submicron transferred-substrate AlInAs/GaInAs heterojunction bipolar transistors (HBTs). Devices with 0.4-/spl mu/m emitter and 0.4-/spl mu/m collector widths have 17.5 dB unilateral gain at 110 GHz. Extrapolating at -20 dB/decade, the power gain cutoff frequency f/sub max/ is 820 GHz. The high f/sub max/, results from the scaling of HBTs junction widths, from elimination of collector series resistance through the use of a Schottky collector contact, and from partial screening of the collector-base capacitance by the collector space charge.

Bias stabilization for resonant tunnel diode oscillators

While resonant tunnel diodes (RTDs) are useful as submillimeter-wave oscillators, circuit design constraints imposed to suppress parasitic bias circuit oscillations have limited output powers to well below 1 mW. We report a 7-GHz RTD oscillator with a shunt regulator for bias circuit stabilization. With regulation, oscillator power is not limited by stability constraints. Regulation elements are readily integrated with RTDs to construct monolithic RTD oscillator arrays. >

0.1 /spl mu/m Schottky-collector AlAs/GaAs resonant tunneling diodes

The Schottky-collector resonant tunneling diode (RTD) is an RTD with the normal N+ collector and ohmic contact replaced by a Schottky contact, thereby eliminating the associated parasitic resistance. With submicron Schottky contact dimensions, the remaining components of the parasitic series resistance can be greatly reduced, resulting in an increased maximum frequency of oscillation, f/sub max/. AlAs/GaAs Schottky-collector RTDs were fabricated using 0.1 /spl mu/m T-gate technology developed for high electron mobility transistors. From their measured dc and microwave parameters, and including the effect of the quantum well lifetime, f/sub max/=900 GHz is computed.<<ETX>>

Fabrication and performance of planar Schottky diodes with T-gate-like anodes in 200-GHz subharmonically pumped waveguide mixers

A T-gate-like structure has been developed, fabricated, and tested as the anode for millimeter and submillimeter wave Schottky diodes, The low parasitics of the T-anode diodes yield extremely high cutoff frequencies, making the diodes useable at frequencies well beyond 1 THz. The diodes were tested as an antiparallel-pair, integrated monolithically with microstrip circuitry on a quartz substrate, in a subharmonically pumped waveguide mixer. A double sideband noise temperature of 600 K with a conversion loss of 4.7 dB were measured at 200 GHz. This is believed to be the lowest noise temperature ever reported for a room-temperature subharmonically pumped Schottky diode mixer at this frequency.

Generalized scattering matrices for unit cell characterization of grid amplifiers and device de-embedding

Amplifying grid arrays, consisting of periodic unit cells loaded with active devices such as HEMTs, are currently being developed for high frequency quasi-optical use. Motivation for their development includes the inherent advantages of an approach that employs spatial power combining and spatial amplification. Thus, losses between multistage amplifiers are virtually eliminated. Also due to the spatial combining, the phase of the array is determined by the phase of the incident wave which is then amplified by the planar circuit. This eliminates the need for complex phase shifters and the associated lines for independent element control. Other advantages include the existence of graceful degradation when failures occur. Typically, a unit cell of these planar arrays has been analyzed using quasi-static transmission line approaches. This approach is used due to its simplicity and the easy addition of the port locations required by the active devices. The benefit of a grid amplifier design at high frequency is limited by this approach which may ignore strong mutual coupling or surface waves present at higher frequencies. Based on more conventional periodic array analysis, the method described extended the generalized scattering matrix approach to include the port locations of the device. This allows accurate inclusion of the effects of the mutual coupling between elements, the presence of bias lines, ground planes, and superstrates/substrates. In addition this numerically generated scattering matrix can be combined with the conventional scattering matrix of the device to form a composite matrix of a grid amplifier.

Submicron transferred-substrate heterojunction bipolar transistors with greater than 8000 GHz f/sub max/

We report submicron transferred-substrate AlInAs/GaInAs heterojunction bipolar transistors. Devices with 0.4 /spl mu/m emitter and 0.9 /spl mu/m collector widths have 17.5 dB unilateral gain at 110 GHz. Extrapolating at -20 dB/decade, the power gain cut-off frequency f/sub max/ is 820 GHz.