Beam-lead Schottky-barrier diodes for low noise integrated microwave mixers

Abstract

Beam lead technology inherently lends itself to integrated microwave devices. Closely controlled junction geometry leads to uniformity of device characteristics. Specially designed tapered leads for improved microwave matching are easily formed using this technology. High speed bonding is also possible, with automatic equipment. These advantages are obtained with a process sequence which allows the use of a since metal deposition step for both the Schottky barrier and beam lead interconnection system. Molybdenum with a gold overlay is the metallurgical system used to form the barrier and the beam lead interconnections. Typical I-V and 1/C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> -V plots indicate uniformity of barrier height and "n" factor. Values of n are less than 1.1 with the barrier height at 0.61 e.v. Measurements of change in barrier height with temperature up to 500°C show less than 210 mV variation. With the stable moly barrier used, device parameters are a compromise of geometry and epitaxy layer. DC characteristics of these devices give forward current matching of ± 10 mV at 1 ma. The Rs is 10 ohms and the Cj is less than 0.3 pf, giving an RC product less than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3 \times 10_{-12}</tex> sec. Using these devices in a chrome-gold on alumina microstrip integrated mixer, overall single sideband noise figures of 6.5- 7.0 dB were measured, with a 1.5 dB IF noise figure, at 9.4 GHz. Measured noise figure was essentially constant over a range of 1-10 mw of local oscillator power, and the diodes will withstand over 500 mw cw RF power. These values compare favorably with discrete packaged devices. Fabrication in series pairs, matched quads or other configurations can be accomplished with good uniformity.