Evaluation of Single-Electron Transistor as Nanoscale Thermometer for a Cryogenic Radiation Detector

Abstract

We have proposed a position-sensitive radiation detector, which is a microcalorimeter that uses single-electron transistors (SETs) as its electrical circuit to readout the temperature changes of an absorber, which are due to the energy deposition caused by incident radiation. In order to demonstrate the principle of the detector, we used numerical calculations with the orthodox theory to estimate the required performance of the SETs. Our results indicate that several SETs with different dynamic temperature ranges are necessary to span the entire temperature range found within the detector. Moreover, we fabricated a nanometer-scale tunneling junction using electron-beam lithography with a bilayer resist and a two-angle shadow evaporation technique. The current-voltage characteristics of the fabricated tunneling junction agree with Simmons’ theory. In addition, a current modulation of about 10 pA by the gate voltage was successfully observed at 4.4 K. Comparisons with numerical calculations estimated that the total capacitance of the SET is 180 aF. Thus, the SET should be able to operate as a thermometer from 0.8 K to 2.2 K. Although we could not observe the decreased conductance around the zero bias voltage at 4.4 K, the decreased conductance should be observed if the SET is cooled below 2.4 K.