Sublayer-ratio engineering of RF-sputtered ITO/ZnO nanolaminate channels for enhancement-mode thin-film transistors

Controlling the carrier concentration of oxide thin-film transistors (TFTs) while retaining useful transport and normally-off switching is a persistent materials-processing challenge. Here, 40-nm ITO/ZnO nanolaminate channels were formed by sequential RF magnetron sputtering, and the nominal ITO:ZnO sublayer-thickness ratio was varied at approximately constant total channel thickness to establish a processing–property relationship. Devices with 2:1, 1:1, and 1:2 ratios exhibited threshold voltages of −1.77, −0.46, and +1.37 V, respectively, demonstrating systematic threshold-voltage control with increasing ZnO fraction. X-ray photoelectron spectroscopy and X-ray diffraction of the selected ZnO-rich 1:2 channel indicate a metal–oxygen-dominated bonding environment and limited long-range structural order. The 1:2 TFT achieved a maximum linear-regime field-effect mobility of 26.4 cm 2 V −1 s −1 , a subthreshold swing of 0.434 V dec −1 , an I on / I off ratio of approximately 10 7 , and transfer hysteresis below 0.2 V. Positive and negative gate-bias stress at ±30 V for 3600 s produced threshold-voltage shifts of +0.71 and −1.13 V, respectively. Temperature-dependent measurements from 25 to 175 °C produced an overall threshold-voltage displacement of approximately −1.38 V while preserving distinct gate-controlled switching. These results show that ITO/ZnO sublayer-ratio engineering provides a practical sputter-processing route for tuning the transport–electrostatics balance and achieving enhancement-mode operation in oxide nanolaminate TFTs.