Active solid-state devices (e.g. – transistors – solid-state diode – Bipolar transistor structure – With enlarged emitter area
Patent
1994-02-17
1994-12-20
Hille, Rolf
Active solid-state devices (e.g., transistors, solid-state diode
Bipolar transistor structure
With enlarged emitter area
257538, 257578, 257581, H01L 2972
Patent
active
053748441
ABSTRACT:
A transistor structure incorporates a polysilicon layer which is doped with N-type dopants and is used as an emitter ballast resistor in an array of NPN transistors. In one embodiment, the polysilicon layer is also used as a diffusion source to form N-type emitter regions within a deep and high resistivity P-well, which acts as a relatively high value base ballast resistor for the transistor. In another embodiment, a standard base is used, contributing little base ballast resistance. A buried collector region carries collector current. Preferably, the emitter regions are formed as oblong strips. P-type base contact regions, also generally formed as oblong strips, are formed in the surface of this P-well parallel to the emitter regions. The dimensions of the base contact regions may be varied in order to achieve a constant base-emitter voltage along the entire length of each emitter strip. An emitter metal layer overlies the polysilicon layer and contacts the polysilicon layer through openings in an insulating layer. The resulting three dimensional structure in one embodiment thus incorporates a stacked collector region, base ballast resistor, base region, emitter regions, emitter ballast resistors, and emitter metal layer. In another embodiment, the same three dimensional structure results except that there is no base ballast resistor. Dimensions of the emitter metal layer and other metal layers may be adjusted so that the transistor structure has a trapezoidal shape and requires less silicon real estate.
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Hille Rolf
Micrel Inc.
Ostrowski David
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