Characterization of bipolar transistors for cryogenic temperature sensors in standard CMOS

This paper presents the cryogenic characterization of the bipolar substrate PNPs that are typically employed as sensing elements in CMOS integrated temperature sensors. PNPs realized in a standard 160-nm CMOS technology were characterized over the temperature range from 7 K to 294 K. Although PNP non-idealities, such as finite current gain and parasitic base resistance, deteriorate at lower temperature, device operation similar to room temperature is observed down to 70 K, while operation at lower temperatures is limited by carrier freeze-out in the base region and limited current gain. These results demonstrate the feasibility of temperature sensors in standard CMOS at cryogenic temperature.