Diffused silicon nonlinear capacitors

Diffused silicon nonlinear capacitors have been fabricated by solid-state diffusion. The resulting graded p-n junction is a planar structure which permits low series resistance R
s
relative to the minimum capacitance
C_{\min}
, which is measured at a reverse voltage slightly less than the breakdown voltage. A cutoff frequency
f_{c} = (2\piR_{s}C_{\min})^{-1}
is used as a figure of merit; values up to 150 kmc have been obtained. These "varactor" diodes may be used as UHF and microwave amplifiers and as harmonic generators. The noise figures of the UHF amplifiers are better than the best noise figures obtainable by present electron-tube techniques. These diodes are also efficient harmonic generators.