InP millimeter wave Schottky barrier mixer diodes for low local oscillator power requirements

A number of system applications at millimeter wavelengths have low local oscillator (LO) power requirements in addition to good noise performance. For instance, the replacement of Klystrons by a combination of solid state sources plus frequency multipliers at millimeter wavelengths has a strict LO power requirement. The barrier height φBis the important diode parameter in that it determines the local oscillator power required to bias the Schottky diode into its non-linear region. Schottky barriers to InP exhibit a low barrier due to the fact that the Fermi level is not pinned in the center of the energy gap. However, the development of reliable Schottky barriers to InP has been hampered by the large leakage current Schottky barriers to InP have exhibited. In the present paper, we report on a low barrier height, low leakage current Schottky barrier to InP. The InP Schottky barrier diodes fabricated have exhibited low noise figure at 36 and 94 GHz and require exceptionally low local oscillator power. The metallization scheme consisted of TiW sputtered at 200 W rf power. These diodes were processed with a 5 µm diameter active area on n-n⁺InP layers. At 36 GHz a noise figure of 6.5-7.0 dB resulted at LO power of .5 mW. At 94 GHz the noise figure of 8.0 dB required a LO power of only 0.75 mW.