Jean Bruston

Fabrication of 200 to 2700 GHz multiplier devices using GaAs and metal membranes

Multiplier device fabrication techniques have been developed to enable robust implementation of monolithic circuits well into the THz frequency range. To minimize the dielectric loading of the waveguides, some circuits are realized entirely on a 3 /spl mu/m thick GaAs membrane with metal beamleads acting as RF probes and DC contact points. Other designs retain some thicker GaAs as a support and handling structure, allowing a membrane of bare metal or thin GaAs to be suspended across an input or output waveguide. Extensive use is made of selective etches, both reactive ion (RIE) and wet chemical, to maintain critical dimensions. Electron beam (e-beam) lithography provides the small contact areas required at the highest frequencies. Planar multiplier circuits for 200 GHz to 2700 GHz have been demonstrated using a variety of metal and GaAs membrane configurations made available by these fabrication techniques.

Performance of a 1.2 THz frequency tripler using a GaAs frameless membrane monolithic circuit

The first ever planar Schottky diode multiplier working over a THz will be presented in this paper. A tunerless 1.2 THz waveguide frequency tripler has been designed, fabricated and tested. The frequency multiplier consists of a 3 micron-thick GaAs frameless-membrane monolithic circuit, mounted in a split waveguide-block, which includes a built-in Picket-Potter horn. The 1.2 THz membrane tripler is driven by a 400 GHz solid-state chain composed of HEMT based power amplifiers followed by two tunerless planar diode frequency doublers. At room temperature, output power up to 80 microwatts was measured at 1126 GHz with a peak-efficiency of 0.9% and a 3 dB bandwidth of about 3.5%. The output power of the multiplier chain increased dramatically with a decrease of the ambient temperature-up to 195 microwatts was measured at 120 K. When further cooled to 50 K the chain delivers power levels as high as 250 microwatts. To the best of our knowledge, this is the first demonstration of a fully planar multiplier chain at these frequencies, along with performance that supercedes current state-of-the-art performance of whisker-contacted sources.

MMIC power amplifiers as local oscillator drivers for FIRST

The Heterodyne Instrument for the Far-Infrared and Sub- millimeter Telescope requires local oscillators well into the terahertz frequency range. The mechanism to realize the local oscillators will involve synthesizers, active multiplier chains (AMCs) with output frequencies from 71 - 112.5 GHz, power amplifiers to amplify the AMC signals, and chains of Schottky diode multipliers to achieve terahertz frequencies. We will present the latest state-of-the-art results on 70 - 115 GHz Monolithic Millimeter-wave Integrated Circuit power amplifier technology.

Development of 200 GHz to 2.7 THz multiplier chains for submillimeter-wave heterodyne receivers

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.

Development of millimeter and submillimeter-wave local oscillator circuits for a space telescope

FIRST (Far InfraRed and Submillimeter Telescope) is a European science mission that will perform photometry and spectroscopy in the 80 - 670 micrometers range. The proposed heterodyne instrument for FIRST is a seven-channel receiver, which combines the high spectral resolving capability (0.3 - 300 km/s) of the radio heterodyne technique with the low noise detection offered by superconductor-insulator- superconductor and hot electron bolometer 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.

2.7 THz waveguide tripler using monolithic membrane diodes

The description and performance of an 850 to 2550 GHz waveguide tripler is presented. The tripler utilizes GaAs monolithic membrane diodes (MOMED) in single and antiparallel pairs. Output power of/spl ap/0.1 /spl mu/W is reported.