Properties of a silver bonded diode for parametric amplification

Recently the parametric amplifier has received attention because of its low noise characteristic. One of the authors has designed a new diode which is suited for a parametric amplifier. This diode is a silver bonded diode which is composed of a silver-gallium whisker and n-type germanium. After the whisker is contacted to the germanium crystal, electrical forming is applied to make a silver bonded contact. We measured the impedance variation of the diode as a function of bias voltage at 6Kmc, by use of a coaxial standing wave meter. The barrier capacitance was calculated from this variation, and it agreed with the theoretical value in reverse bias, but in forward bias the capacitance was larger than the theoretical value. The effect is believed to be due to diffusion capacitance. The cut-off frequency of the diode was more than 400Kmc. The factor of barrier capacitance variation, C1/C0, was four times larger than that of other point contact silicon and germanium diodes. It was discovered that electrical forming was the most important factor for the characteristics of the diode. A 6Kmc parametric amplifier using a silver bonded diode was constructed. The bandwidth was 40mc at 20db gain with a noise figure of about 5db.