Probing the work function of a gate metal with a top-gate ZnO-thin-film transistor with a polymer dielectric

We report on the fabrication and application of top-gate ZnO thin-film transistors (TFTs) with a poly-4-vinylphenol (PVP) gate dielectric layer formed on n-ZnO by spin casting. Al, Au, and NiOx top-gate metals patterned on the PVP of a top-gate TFT by thermal evaporation exhibited different threshold voltages (V-t) and saturation currents. This provides us with an all-electrical way to measure the work function of an unknown new electrode (NiOx) based on those of two reference electrodes (Al and Au). Our data show that the work function of semitransparent conductive NiOx is similar to 5.1 eV, which is larger than the value (4.95 eV) determined from capacitance-voltage (C-V) curves. We conclude that our top-gate ZnO-TFT is a unique test bed for confirming and validating the C-V results for the work function measurement of any metal electrodes.