This paper presents the design, fabrication, and performance of a 77 Ghz monolithic GaAs PIN switch network developed for an automotive collision warning radar. The RF front end of the radar contains three control circuits which were initially realized by a hybrid approach using a duroid circuit and beam lead diodes. These three circuits were successfully integrated into a single 77 Ghz MMIC. The MMIC uses vertical GaAs PIN diodes with a switching cutoff frequency of over 3000 Ghz, attaining low insertion loss and high isolation. Insertion loss is comparable to that obtained with a hybrid circuit, while the isolation improved from a typical level of 16 dB for a single hybrid switch to over 25 dB in the MMIC. The use of GaAs PIN diodes also allowed switching speeds of less than 2ns to be attained, a key requirement for the radar.being realized by a multichip approach, where the best available device technology is used for a specific circuit function. The switching functions required by the pulsed Doppler radar described in this paper are best realized by a monolithic GaAs PIN diode approach. Radar Architecture MMIC SWlTCH CONTROLS

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Unusual negative resistance characteristics were observed in low barrier HMIC (Heterolithic Microwave Integrated Circuit) silicon Schottky diodes with HF (hydrofluoric acid)/IPA (isopropyl alcohol) vapor clean prior to epitaxial growth of silicon. SIMS (secondary ion mass spectroscopy) analysis and the results of the buried layer structure confirmed boron contamination in the substrate/epitaxial layer interface. Consequently the structure turned into a thyristor like p-n-p-n device. A dramatic reduction of boron contamination was found in the wafers with H 2 0/HCl/HF dry only clean prior to growth, which provided positive resistance characteristics. Consequently the mean differential resistance at 10 mA was reduced to about 8.1 . The lower series resistance (5.6-5.9 ) and near 1 ideality factor (1.03-1.06) of the Schottky devices indicated the good quality of the epitaxial layer.

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