A Si/SiGe heterojunction bipolar transistor with undoped SiGe spacer for CRYO-BiCMOS circuits

A heterojunction bipolar transistor (HBT) for BiCMOS circuits is described which can operate at liquid nitrogen (LN2) temperature (CRYO-BiCMOS). An HBT which has an n/sup +/-polysilicon/n-type Si epitaxial layer emitter structure on an undoped SiGe/p/sup +/ SiGe base structure, with both SiGe layers having a Ge fraction of 30%, has been developed to maintain the current gain and to reduce the emitter-base turn-on voltage at LN2 temperature. This HBT achieves a high current gain of 124 and a low turn-on voltage of 0.96 V at LN2 temperature. Under the conditions of 3.3 V supply voltage and 83 K, a 0.6 mu m CRYO-BiCMOS two-input NAND gate shows a basic gate delay of 200 ps.<
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