Stacked PIN diode structures for microwave switching

A diode structure consisting of several stacked PIN diodes with tunnel junctions serving as quasi-Ohmic intercontacts is proposed. This structure is preferable if a microwave switch is required to have both high breakdown voltage and very small switching time. In this case a conventional (single-base) PIN switch has too large forward voltage drop across the base at sufficiently high current densities, because the base length is much greater than the bipolar diffusion length. This leads to high electric fields in the base and the development of unwelcome hot-electron effects. The replacement of the long base with several narrow bases connected in series by heavily doped p⁺n⁺ tunnel inserts solves this problem effectively. Direct numerical calculations have shown that this stacked structure exhibits a substantially smaller DC forward voltage drop at the same switching times (or substantially smaller switching times at the same DC forward voltage drops). At the microwave frequency range, the resistance of the stacked structure can be decreased drastically because all the newly formed pn-junctions are shorted by their large capacitances.