ZnO Thin Film Transistor Ring Oscillators with sub 75 nsec Propagation Delay

We have fabricated simple circuits, including ring oscillators, using ZnO thin films deposited by low temperature (200degC) atmospheric pressure chemical vapor deposition. Bottom gate TFTs with aluminum source and drain contacts typically had field effect mobility >15 cm²/Vs. Seven stage ring oscillators operated at frequency as high as 1 MHz for a supply voltage of 32 V, corresponding to a propagation delay less than 75 nsec/stage. These circuits also had propagation delay less than 150 ns/stage at a supply voltage of 18 V. To our knowledge, these are the fastest ZnO circuits reported to date.