Supply voltage design tradeoffs between speed and NMOSFET reliability of half-micrometer BiCMOS gates

Voltage supply scaling for a BiCMOS gate was investigated experimentally and analytically. For half-micrometer technology, the supply voltage design tradeoffs between propagation delay and NMOSFET reliability were studied. It was found that the minimum BiCMOS operating voltage ranges from 2.5 to 3.0 V. This minimum can be explained by the sum of twice the base-emitter potential and the NMOSFET threshold voltage, due to the emitter grounded Bi-MOS structure of the BiCMOS gate. As a result, 3.3-V operation is inherently marginal for BiCMOS gates. On the other hand, NMOS reliability in the BiCMOS gate is drastically improved because effective drain voltage is reduced by the base-emitter potential. Thus, NMOSFETs with a channel length shorter by more than 0.2 μm can be used, and this ensures reliable operation of BiCMOS gates at 5 V. In terms of the tradeoffs between gate speed and NMOS reliability, it is verified that BiCMOS gates offer the highest speed in half-micrometer design