Uniform current density and high current gain bipolar transistor

Abstract

The present invention discloses method for fabricating, and the structure of, a unique and novel bipolar transistor. The bipolar transistor of the present invention has a substantially uniform current density in base and collector regions. This uniform current density prevents the characteristic early fall-off of bipolar transistor current gain, and improves the forward safe operating area performance. As such, the bipolar transistor of the invention increases current gain at high collector currents, and expands the current and voltage region over which the device may safely operated. The advantages of the present invention are achieved by optimally spacing the neighboring emitters in relation to base thickness and further by maintaining a symmetrical topology by the self-aligned formation of emitters and base contacts. According to the invention, the emitters are optimally spaced so that the current emanating from an emitter would fill base and collector regions beneath and beside the emitter in a fashion to provide a uniform current distribution. As such, the entire base and collector regions below the center of a given emitter conduct the emitter majority carrier current in a substantially uniform manner. Therefore, the current density below each emitter island is substantially uniform and the transistor as a whole can conduct a higher total current. Furthermore, according to the invention, a uniform current flow is established before the carriers move out of the base region. The invented transistor inhibits formation of current filaments and hot spots because the electric field in the collector region is uniform.