RF single electron transistor readout amplifiers for superconducting astronomical detectors of X-ray to sub-mm wavelengths

We have made Radio-Frequency Single-Electron Transistors (RF-SETs) with lar ge input gates, and tested performance and modes of operation with the goal of using such devices as on-chip amplifiers for a variety of high impedanc e cryogenic photodetectors. We achieved approximate to 100 kHz of closed-lo op bandwidth for charge-locked-loop and transimpedance amplifier feedback c onfigurations, and have combined amplifier outputs using a form of waveleng th division multiplexing. With our choice of SET junction resistance, a 0.5 fF input gate capacitance gave a cotunneling-degraded charge noise of 1x10 (-4) e/root Hz, but a fairly low input voltage noise of 30 nV/root Hz.