Frequency response of advanced silicon bipolar transistors at low temperature

The high-frequency behavior of advanced bipolar silicon transistors has been measured at temperatures between 83 and 350 K. The cutoff frequency, DC gain, and associated frequency-dependent parameters are reported. Although the transistors are optimized for room-temperature operation, their performance at liquid-nitrogen temperature is not severely degraded. Though decreased, the current gain remains sufficiently high for use in some applications. The cutoff frequency is reduced by about a factor of two. It is suggested that this is primarily due to an increase of the base transit time and that increasing the base doping may improve the low-temperature response. Using the maximum frequency of oscillation to predict circuit switching speed, it appears that small, high-performance transistors suffer a speed degradation at near liquid-nitrogen temperature.>