A novel beam lead GaAs Schottky-barrier diode fabricated by using thick polyimide film

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Abstract
A novel beam lead GaAs Schottky-barrier mixer diode with high performance has been developed for use in super high frequency (SHF) receiving system. The parasitic capacitance of the diode has been reduced to 0.03 pF by using thick polyimide insulating film formed by improved etching techniques. The series resistance has been lowered to 0.5 Ω by a liquid-phase double epitaxial method of growing an n-n++active layer on an n+wafer. The total diode capacitance at zero bias has been lowered to 0.15 pF using a 10-µm junction diameter. An n factor of less than 1.10 was obtained. The calculated cutoff frequency including parasitic capacitance exceeds 2000 GHz. Several reliability tests including temperature cycling in high humidity show good results. In an SHF downconverter consisting of a waveguide which contains a planar circuit, the diode was attached to the planar circuit by means of an intermediate plate, despite the small diode dimensions of 0.75 mm by 0.22 mm. An overall noise figure (NF) as low as 4.3 dB, and conversion loss as low as 3.0 dB were achieved at 12 GHz (IF range of 290-470 MHz and IF amplifier NF of 1.5 dB). These values are shown to be satisfactory for application to a low-noise receiving system for satellite TV broadcasting.

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