Parametric Diodes ¿ Design and Fabrication

Solid state diffusion into silicon can be used to produce a rectifying junction. The capacitance of a diode made this way varies with the bias applied to it. The device is designed to be a variable capacitance having a low loss. The unbiased capacitance of a diode depends on the starting material and the diffusion parameters but to reduce the value to one that is useful (a few pF) the area has to be limited. A small area of the junction is isolated by ultrasonic cutting, leaving a plinth or ¿mesa¿. Contact to the mesa is made in an encapsulation suitable for use in a wave-guide. Amongst other uses, the diodes are suitable for low-noise (para metric) amplifiers, frequency multipliers and high-frequency switches.