A Multi-Finger GHz Frequency Doubler Based on Amorphous Indium Gallium Zinc Oxide Thin Film Transistors

This paper presents a multi-finger doubler based on amorphous-indium gallium zinc oxide (a-IGZO) thin film transistors (TFT) operating at GHz frequency. The doubler and the TFTs have been fabricated in-house with chromium (Cr) gate electrodes. We have used the Rensselaer Polytechnic Institute amorphous silicon (RPI-a) TFT DC model and a Null-Bias method extracted AC model for simulation. The device output power, the threshold voltage mismatch, and breakdown characteristics are explained with the help of the model. The device yield reduces as the number of fingers in the TFTs increase. The model helps explain the doubler's non-idealities and compensate for these transistors' low yield. The peak second harmonic conversion gain of the doubler is measured to be -32 dB at a gate overdrive voltage of around 2.8 V for a 500 MHz input signal. This second harmonic output frequency exceeds the TFT's transit and maximum oscillation frequencies.