Planar GaAs Mixer Diodes for Millimeter Wave MMIC´s

A new fabrication process for planar GaAs mixer diodes operating in the millimeter wave range of frequencies is presented. This technology, which is fully compatible with MESFET fabrication on the same chip, combines the advantages of selective ion implantation for the n⁺ contact regions and epitaxial growth for the active n-layer. With Si implantation n⁺ - layer sheet resistances of down to 16 n/c have been achieved using a rapid thermal anneal. Schottky diodes with Al and Ti Schottky contacts have been fabricated with different contact areas and configurations. Diode resistances of 8 n and junction capacitances of around 20 fF were obtained for a contact area of 1.5 × 6 ¿m². n-factors were typically 1.15 for Ti and 1.3 for Al Schottky contacts. RE performance was tested in a hybrid mixer configuration with an oscillator frequency of 35 GHz. Conversion losses of 6 or 5.5 dB and noise figures of 5 or 4.5 dB have been determined for Al or Ti Schottky diodes, respectively.