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Keywords:

  • atomic layer deposition;
  • gate dielectrics;
  • high-k dielectrics;
  • thin film transistors;
  • ZnO

Abstract

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).