Design and characterization of very small MOSFETs for low temperature operation

Operation of computer circuitry at cryogenic temperatures is an attractive means of obtaining improvements in speed, power, reliability and other device characteristics. Bipolar devices are generally considered to be unusable at such low temperatures as a consequence of enhanced recombination in the base region. In the present work, the operation of polysilicon gated MOSFET devices has been studied both experimentally and theorecti-cally at temperatures ranging from room temperature down to liquid nitrogen temperature. Excellent agreement was found between experimental device characteristics and the predictions of a two-dimensional simulation model, indicating that device operation is well understood and predictable over this entire temperature range. The major advantages of sharper turn-on and higher mobility found at lower temperatures are described and discussed.