Annular - A new semiconductor device structure

A new device structure is described which allows fabrication of high voltage, passivated, silicon transistors and other semiconductor devices, which exhibit superior electrical stability. In the annual process, a "worst case" channel is induced during thermal oxidation of the wafer. A highly doped annular ring is implanted in the collector by epitaxy or solid state diffusion, adjacent to and completely surrounding the collector-base junction. Because the ring is of the same conductivity type as the collector, it terminates the channel and allows realization of a breakdown voltage commensurate with that of the collector material, along with very low leakage currents and stable junctions. It is shown, in the non-annular transistor, that the channel is induced in the high resistivity collector region by a positively charged species in the silicon-dioxide, resulting in a large majority carrier channel current which is additive to the normal junction leakage current. A model for the annular structure is developed and the electrical characteristics of devices utilizing this structure are explained. It is also shown that annular transistors exhibit better long-term stability under ionizing irradiation than similar geometries made by other techniques. Examples of PNP transistors produced by the annular process will be discussed, including a 200 volt silicon power transistor.