Fabrication and Characterization of ZnO Based Thin Film Transistors With HfO2 as Dielectric Material

Abstract

HfO2 thin films were prepared using reactive RF magnetron sputtering of a pure hafnium target in argon and oxygen ambient onto heavily doped p++ silicon (100) substrates. ZnO semiconducting thin film channel was deposited using sputtering of a pure metallic zinc target in oxygen ambient over the already deposited dielectric layer and the metallization for contact electrodes was done using thermal evaporation system. The thin film transistors (TFTs) were also fabricated with copper and aluminum as gate material other than heavily doped silicon. Besides TFT, metal-insulator-metal (MIM) and metal-oxide-semiconductor (MOS) structures were also made using HfO2 as oxide dielectric layer. The dielectric layer thickness, along with various growth parameters were studied and optimized using the various electrical characterization results from MOS, MIM and FET devices, to know the limit of oxide thickness that can provide sufficient charge polarization and electric field for channel conduction at lower gate voltages while giving low leakage current for the successful operation of the field-effect transistor (FET) device.