Silicon monolithic millimeter wave integrated oscillators

Despite considerable research effort on three terminal devices, there is currently no possibility of replacing IMPATT diodes if powerful oscillator operation in the MM-wave range is required. The development of monolithically integrated silicon IMPATT oscillators is a logical development if the difficulties and frequently unreproducible impedance matching of discrete IMPATTs for waveguide operation are considered. In the fabrication approach, the IMPATT structure is embedded in semiinsulating polycrystalline Si. This poly-Si can be deposited simultaneously with the mono-Si layers necessary for device operation during the so-called `differential epitaxy´. A favourable method for this differential epitaxy of silicon is molecular beam epitaxy (MBE). For this concept highly doped n⁺-substrates are used. The double drift IMPATT diode layers are deposited over a patterned SiO₂ film. A three layer mono-Si zone embedded in poly-Si results. Metallic contacts are evaporated and the p⁺-poly-Si layer is removed because of its poor isolation. The poly-Si and top contact are covered with an Au metallisation so that the diode can be matched to a disc resonator in order to make the whole structure act as an oscillator