Atomic‐layer‐deposited ZnO thin‐film transistors with various gate dielectrics

We have investigated the effects of gate dielectric layers having different microstructures on the crystallographic properties and device performances of atomic‐layer‐deposited (ALD) ZnO thin‐film transistors (TFTs) in a bottom‐gated structure. Among three gate dielectric materials (thermally grown SiO2, ALD‐HfO2, and ALD‐Al2O3), the ALD‐ZnO layer on Al2O3 exhibited the best crystallinity and surface morphology due to the excellent surface roughness and/or hydrophilic surface polarity of the amorphous Al2O3 layer. As a result, it showed the best TFT performance, including field‐effect mobility (∼3.9 cm2/Vs), subthreshold swing (∼1.35 V/decade), and on/off ratio (∼5 × 107).