Extending the high-frequency limit of a single-electron transistor by on-chip impedance transformation

We have fabricated an aluminum single-electron transistor (SET) and characterized it at frequencies up to 700 kHz. The relatively high frequency was achieved by reducing the capacitance at the SET output. The SET was bonded to an InP high-electron-mobility transistor (HEMT), and biased through a small (<100 mu m) on-chip resistor made of 150 tunnel junctions in series. The output voltage swing of the SET decreases with increasing HEMT current because of heating. Thus, the gain of the HEMT was limited and therefore the noise performance of the system was limited to 3x10(-4)e/root Hz at 10 kHz.