Low-Voltage Operation of Ring Oscillators Based on Room-Temperature-Deposited Amorphous Zinc-Tin-Oxide Channel MESFETs

Abstract

Schottky diode FET logic (SDFL) ring oscillator circuits comprising metal-semiconductor field-effect transistors (MESFETs) based on amorphous zinc-tin-oxide (ZTO) n-channels are presented. The ZTO channel layers are deposited entirely at room temperature by long-throw magnetron sputtering. Best MESFETs exhibit on/off current ratios as high as 8.6 orders of magnitude, a sub-threshold swing as low as 250 mV dec−1, and a maximum transconductance of 205 µS. Corresponding inverters show peakge gain magnitude (pgm) values of 83 with uncertainty levels as low as 0.5 V at an operating voltage of 5 V. Single stage delay times down to 277 ns are measured for three-stage ring oscillators, corresponding to oscillation frequencies as high as 451 kHz. Oscillations are observed at operating voltages as low as 3 V. These results prove the feasibility of room-temperature-deposited, amorphous semiconducting oxide based integrated circuits with SDFL layout. The presented approach provides more efficient as well as fail-safe device fabrication and similar oscillation frequencies at significantly lower operating voltages compared to conventional, high-temperature processed logic circuits based on insulating gates.