Metal emitter structures in a class of developmental InP-based high-speed heterojunction bipolar transistors (HBTs) have been redesigned to have T-shaped cross sections. T-cross-section metal features have been widely used in Schottky diodes and high-electron-mobility transistors, but not in HBTs. As explained, the purpose served by the present T cross-sectional shapes is to increase fabrication yields beyond those achievable with the prior cross-sectional shapes.

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.

High bandwidths are obtained with heterojunction bipolar transistors 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 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 max and high gains in mm-wave ICs. Logic gate delays are primarily set by depletion-layer charging times, and neither fτ nor f max is indicative of logic speed. For high speed logic, epitaxial layers must be thinned, emitter and collector junction widths reduced, current density increased, and emitter parasitic resistance decreased. 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 max is 1.1 THz. Transferred-substrate HBTs have obtained 295 GHz f τ . Demonstrated ICs include lumped and distributed amplifiers with bandwidths to 85 GHz, 66 GHz master-slave flip-flops, and 18 GHz clock rate Δ-Σ ADCs.

A novel semiconductor fabrication process has been developed at the Jet Propulsion Laboratory for realizing millimeter and submillimeter-wave monolithic integrated circuits. The process enables integration of the active devices, Schottky diodes, with planar metallic transmission lines. To reduce the RF losses in the passive circuitry, the semiconductor substrate under the transmission lines is etched away, leaving the metal suspended in air and held only by its edges on a semiconductor frame. The frame also allows the circuit to be handled and mounted easily, and makes the whole structure more robust. Moreover, this technology allows for the diodes to be positioned precisely with respect to the circuitry and can be scaled for higher frequency applications. Metallic beam-leads are used extensively on the structure to provide mechanical ‘handles’ as well as current paths for both DC grounding and diode biasing. To demonstrate the utility of this technology, broadband balanced planar doublers based on the concepts in [1] have been designed in the 200 and 400 GHz range. Extensive simulations were performed to optimize the diodes and design the circuits around our existing device fabrication process. The 368-424 GHz circuits were measured and achieve 15% peak efficiency at 369 GHz. The 3-db bandwidth of the fix-tuned doubler is around 9%. The maximum output power measured is around 6 mW and drops down to 1mW at 424 GHz. This represents the highest frequency waveguide based planar doubler to date known to the authors.

Several astrophysics and Earth observation space missions planned for the near future will require submillimeter-wave heterodyne radiometers for spectral line observations. One of these, the Far InfraRed and Submillimeter Telescope will perform high-sensitivity, high-resolution spectroscopy in the 400 to 2700 GHz range with a seven channel super- conducting heterodyne receiver complement. The local oscillators for all these channels will be constructed around state-of-the-art GaAs power amplifiers in the 71 to 115 GHz range, followed by planar Schottky diode multiplier chains. The Jet Propulsion Laboratory is responsible for developing the multiplier chains for the 1.2, 1.7, and 2.7 THz bands. This paper will focus on the designs and technologies being developed to enhance the current state- of-the-art, which is based on discrete planar or whisker contacted GaAs Schottky diode chips mounted in waveguide blocks. We are proposing a number of new planar integrated circuit and device topologies to implement multipliers at these high frequencies. Approaches include substrateless, framed and frameless GaAs membrane circuitry with single, and multiple planar integrated Schottky diodes. Circuits discussed include 200 and 400 GHz doublers, a 1.2 THz tripler and a 2.4 THz doubler. Progress to date, with the implications of this technology development for future Earth and space science instruments, is presented.

With appropriate device structures, bined lithographi and epitaxial scaling of HBTs,RTDs and S hottky diodes results in rapid in reases in device bandwidths.0.1 ¹m InGaAs RTDs have os illated at 650 GHz,Submi ron heterojunction bipolar sistors (HBTs)fabri ated with substrate transfer pro-esses have obtained 21 dB unilateral power gain at 100 GHz;if extrapolated at -20 dB/decade,this corresponds to a 1.1 THz power-gain uto ®frequency.HBT current-gain uto ®frequencies as high as 300 GHz have been obtained.

The OH radical is an important player in known ozone depletion cycles; however, due to its location in the atmosphere, it must be studied from either a balloon or spaceborne platform. For long-term mapping over large portions of the Earth, a spaceborne platform is the most desirable. NASA's Earth Observing System Microwave Limb Sounder instrument is to house a 2.5 THz Schottky-diode receiver for such measurements. The authors describe the design, fabrication, and testing of the engineering model receiver front end. This is the precursor to the first terahertz heterodyne receiver to be flown in space

This paper describes a dual-polarized rectenna capable of producing a 50-V output voltage that can be used for driving mechanical actuators. This study demonstrates a circuit topology that allows the output of multiple rectenna elements to be combined in order to step up the output voltage. In this paper, an independent rectifying circuit is used for each of two orthogonal polarizations. By proper combination, the output voltage is doubled over that of the single polarization case. Such panels are being explored for use on the next-generation space telescope to eliminate wiring between actuators and provide for true mechanical isolation.

Using substrate transfer processes, we have fabricated heterojunction bipolar transistors with submicrometer emitter-base and collector-base junctions, minimizing RC parasitics and increasing f/sub max/ to 500 GHz. The process also provides a microstrip wiring environment on a low-/spl epsiv//sub r/ dielectric substrate. First design iterations of emitter-coupled-logic master-slave flip-flops exhibit 48 GHz maximum clock frequency when connected as static frequency dividers. Baseband amplifiers have been demonstrated with bandwidths up to 85 GHz.

New developments in higher performance planar diode balanced doublers are reported. These include higher output power, higher efficiency, wider bandwidth, and simpler, more reliable construction. An output power of 80 mW was produced at 140 GHz using a new planar diode array designed to handle very high power. An efficiency of 25% was achieved at 270 GHz with 14 mW output. A wideband doubler has been designed which is extremely simple and easy to assemble, using a new planar diode with on-chip matching. All of these new designs are mechanically improved and should survive cooling to 80K. On those devices where tests have been made, the efficiency at 80 K improves by 30-36% relative to the room temperature value. Introduction In work reported last year [1], a wideband fixed-tuned balanced doubler was described using planar diodes with typically 26% efficiency over the band 130-165 GHz. This doubler used an array of four diodes and worked best at 120 mW input power. In this new work, the same basic doubler circuit has been duplicated and improved in a number of ways. A new six diode array has been used in the doubler, and while not tested over any bandwidth, has produced a record high power. A similar circuit has been used with a four diode array in the 270-340 GHz band and works well, with very high efficiencies at 270 and 330 GHz. A cascaded pair of these doublers has been tested over a 5% bandwidth with good results. The general layout of a planar balanced doubler is shown in Figure 1. Output Planar Coax DC Bias diode Matching Filter Section Figure 1. Balanced doubler using planar diode array, in a generic form. This circuit shows the essential elements and does not represent any real circuit.

Using e-beam lithography and combined reactive-ion and wet-chemical etches, we have fabricated transferred-substrate heterojunction bipolar transistors (HBTs) with 0.2 μm emitter and 0.6 μm collector widths and a measured DC current gain of 14. Devices with 0.4 μm emitter and 1.0 μm collector widths obtain record 500 GHz f/sub max/ value.

Using substrate transfer processes, we have fabricated heterojunction bipolar transistors with submicron emitter-base and collector-base junctions, minimizing RC parasitics and increasing f(max) to 500 GHz. The process also provides a microstrip wiring environment on a low-epsilon(r) dielectric substrate. Demonstrated small-scale ICs in the process include lumped and distribute amplifiers with bandwidths to 85 Hz, 48 GHz static frequency dividers, and 50GHz AGC/limiting amplifiers. (C) 1999 Elsevier Science Ltd. All rights reserved.

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.

Using substrate transfer processes, we have fabricated heterojunction bipolar transistors with submicron emitter-base and collector-base junctions, minimizing RC parasitics and increasing f/sub max/ to 820 GHz, the highest reported for any transistor. The process also provides a microstrip wiring environment on low-/spl epsiv//sub r/ dielectric substrate. Demonstrated small-scale ICs in the process include lumped and distributed amplifiers with bandwidths to 85 GHz, 48 GHz static frequency dividers, and 50 GHz AGC/limiting amplifiers.

A novel GaAs monolithic membrane-diode (MOMED) structure has been developed and implemented as a 2.5-THz Schottky diode mixer, The mixer blends conventional machined metallic waveguide with micromachined monolithic GaAs circuitry to form, for the first time, a robust, easily fabricated, and assembled room-temperature planar diode receiver at frequencies above 2 THz, Measurements of receiver performance, in air, yield a T-receiver of 16 500-K double sideband (DSB) at 8.4-GHz intermediate frequency (IF) using a 150-K commercial Miteq amplifier. The receiver conversion loss (diplexer through IF amplifier input) measures 16.9 dB in air, yielding a derived "front-end" noise temperature below 9000-K DSB at 2514 GHz, Using a CO2-pumped methanol far-infrared laser as a local oscillator at 2522 GHz, injected via a Martin-Puplett diplexer, the required power is approximate to 5 mW for optimum pumping and can be reduced to less than 3 mW with a 15% increase in receiver noise, Although demonstrated as a simple submillimeter-wave mixer, the all-GaAs membrane structure that has been developed is suited to a wide variety of low-loss high-frequency radio-frequency circuits.

FIRST (Far InfraRed and Submillimetre Telescope) is a European science mission that will perform photometry and spectroscopy in the 80-670 mu m range. The proposed heterodyne instrument for FIRST is a seven-channel receiver, which combines the high spectral resolving capability (0.3-300km/s) of the radio heterodyne technique with the low noise detection offered by Superconductor-Insulator-Superconductor (SIS) and Hot Electron Bolometer (HEB) mixers. It is designed to provide almost continuous frequency coverage from 480-2700 GHz. The Jet Propulsion Laboratory is responsible for developing and implementing the local oscillator sources for the 1200-2700 GHz mixers. The present state-of-the-art approach for millimeter-wave multipliers, based on waveguide blocks and discretely mounted devices, becomes harder and harder to implement as the frequency range is extended beyond 300 GHz. This talk will focus on the technology that is being developed to enhance and extend planar integrated Schottky devices and circuits to meet mission local oscillator requirements. The baseline approach is to use GaAs power amplifiers from 71 to 115 GHz followed by a series of planar Schottky diode varactor multiplier stages to generate the required LO signal. The circuits have to be robust, relatively easy to assemble, and must provide broad fix-tuned bandwidth. A number of new technology initiatives being implemented to achieve these goals will be discussed. Approaches include quartz-based and substrate-less diode circuitry and integrated GaAs membrane technology. Recent results and progress-to-date will be presented.

Using substrate transfer processes, we have fabricated heterojunction bipolar transistors with submicron emitter- base and collector-base junctions, minimizing RC parasitics and increasing fmax to 500 GHz. The process also provides a microstrip wiring environment on a low- ϵr dielectric substrate. Demonstrated small-scale ICs in the process include lumped and distributedamplifiers with bandwidths to 85 GHz, 48 GHz static frequency dividers, and 50GHz AGC / limiting amplifiers.

The authors report on the design, analysis and performance of an all GaAs MMIC multiplier for use at submillimeter wavelengths. A novel method for coupling power in and out of the MMIC chip via a broadband photoetched ridge-waveguide-to-microstrip transition has been developed and used for this implementation. Measurements on the first iteration chipset, which implements a Schottky varactor diode doubler to 320 GHz, show a conversion efficiency of 2.8% at an input power level of 15 mW. This performance is shown to be extremely well predicted by commercially available circuit simulators: HP MDS and Ansoft Maxwell. A second iteration chipset, based upon the excellent agreement between the numeric simulator and measurements on the existing circuit, is nearly complete and is expected to yield even better performance.