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 Rsrelative to the minimum capacitanceCₘᵢₙ, which is measured at a reverse voltage slightly less than the breakdown voltage. A cutoff frequencyfc = (2ₛCₘᵢₙ)⁻¹is 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.