Subthreshold Operation of a Monolithically Integrated Strained-Si Current Mirror at Low Temperatures

The dc operation of a simple current mirror built with two monolithically integrated strained-Si (s-Si) MOSFETs operating in the subthreshold region is studied as a function of temperature. At room temperature, the log-log current relationship is linear over 4 dec. The consumed power is approximately 100 muW at 300 K but only 1 nW at 160 K. The cost of this reduction in power is a reduced linear log-log current range. Reducing the temperature further increases the threshold voltage, obstructing operation below 160 K. A comparison is made with the Si control circuit, highlighting the improved linearity and the threshold voltage stability in the s-Si circuit. The estimated cutoff frequency of the subthreshold strained-Si current mirror at 300 K is 50 MHz, compared to 10 kHz for the Si MOSFETs