Improved electric contact of recessed source and drain electrodes for sol–gel-based thin-film transistors consisting of amorphous ZrO2 and IGZO fabricated by microwave-annealing

We investigate the effects of recessed source/drain (S/D) electrodes on the device performance of microwave-induced metal-oxide thin-film transistors (oxide-TFTs) by analyzing their contact resistances. High-performance top-gate-bottom-contact oxide-TFTs consisting of sol–gel-based high-k zirconium dioxide dielectric (ZrO2) and indium-gallium-zinc oxide (IGZO) semiconducting films were developed by employing microwave annealing. Vibration energy induced microwave annealing even at a low temperature (∼120 °C) with a short process time (10 min), which is sufficient to form dense metal–oxygen bonding while suppressing oxygen vacancies as defect states, resulted in high-quality sol–gel-based amorphous ZrO2 and IGZO films. The low-voltage operating oxide-TFTs with recessed S/D electrodes exhibited higher field-effect mobility (∼7.0 cm2 V−1 s−1) than those with elevated S/D electrodes (∼0.15 cm2 V−1 s−1). This result is attributed to the conformable deposition of the channel layer on the planar surface of S/D electrodes, leading to the improved interfacial characteristics. Relatively low effective contact resistance (∼79.7 Ω cm), which was extrapolated from a plot of the width-normalized resistance as a function of the channel length using a transmission line method, in oxide-TFTs with recessed S/D electrodes, is compared to that (∼1480.6 Ω cm) of elevated S/D electrodes. This was in good agreement with the Ohmic contact behavior contact where the low charge injection barrier improved charge transport.