Al_2o_3 Buffer In A Zno Thin Film Transistor With Poly-4-vinylphenol Dielectric

摘要

We compared the characteristics of bottom-gate ZnO-thin film transistors using poly-4-vinylphenol (PVP) and PVP/Al_2O_3 dielectrics. The PVP dielectric is more hydrophobic than the PVP/Al_2O_3 dielectric and is not useful for TFT devices because of its high leakage current density, but this leakage current density can be significantly reduced by inserting Al_2O_3. We deposited ZnO and Al_2O_3 films by atomic layer deposition (ALD) because it is a low-temperature process. The ZnO-TFTs with either a PVP or a PVP/Al_2O_3 dielectric exhibit typical field-effect transistor characteristics with n-channel properties. The ZnO-TFT containing PVP/Al_2O_3 exhibits clear pinch-off and excellent saturation with an enhanced mode operation. The on/off ratio of 7.9 × 10~4 for the device containing the hybrid dielectric is about three orders of magnitude higher than the ratio of 47 for the device containing PVP. The subthreshold gate swings are 12 V/decade for the TFT containing PVP and 1.2 V/decade for the TFT containing PVP/Al_2O_3. The density of the interface trap state is significantly lower in the device containing PVP/Al_2O_3 than in the ZnO-TFT containing PVP. The saturation mobility was 0.05 and 0.8 cm~2 V~(-1) s~(-1) respectively, in the TFTs containing PVP and PVP/Al_2O_3.