Dynamic input capacitance of single-electron transistors and the effect oncharge-sensitive electrometers

We examine the "input capacitance," C-SETT, of a single-electron tunneling (SET) transistor. We note that this quantity is crucial in quantifying the sensitivity of a SET transistor used as a charge electrometer. Further, we point out that C-SETT is not the same as the "gate capacitance," C-G, usual ly taken to be e/Delta V-G, where Delta V-G is the period of the oscillatio n in current versus gate voltage. While C-G is indeed the average value of C-SETT over one period, C-SETT can in fact differ substantially from that v alue, depending on the applied voltages. This has important consequences fo r maximizing the sensitivity of SET charge electrometers when a large stray capacitance is present. (C) 2000 American Institute of Physics. [S0021-897 9(00)07812-9].