No abstract

We developed an implantable thin film transistor temperature sensor (TFT-TS) to measure temperature changes in the brain. These changes are assumed to be associated with cerebral metabolism and neuronal activity. Two prototype TFT-TSs were designed and tested in-vitro: one with 8 diode-connected single-ended sensors, and the other with 4 pairs of differential-ended sensors in an array configuration. The sensor elements are 25~100 μm in width and 5 μm in length. The TFT-TSs were fabricated based on high-speed ZnO TFT process technology on flexible polyimide substrates (50 μm thick, 500 μm width, 20 mm length). In order to interface external signal electronics, they were directly bonded to a prototype printed circuit board using anisotropic conductive films The prototypes were characterized between 20~40 °C using a surface mounted thermocouple and custom-designed temperature controlled oven. The maximum sensitivity of 40 mV/°C was obtained from the TFT-TS.

We report using a novel, weak oxidant, plasma-enhanced atomic layer deposition (PEALD) process at 200 °C to fabricate stable, high mobility ZnO thin film transistors (TFTs) and fast circuits on glass and polyimide substrates. Weak oxidant PEALD provides a simple, fast deposition process that results in uniform, conformal semiconductor and dielectric layers and enhancement-mode MOSFETs from uncompensated films. Highly conformal PEALD Al 2 O 3 layers provide a high yield dielectric on rough plastic substrates for both PEALD ZnO TFTs and cross-overs. Our PEALD ZnO TFTs have field-effect mobility of >20 cm 2 /V⋅s on polyimide substrates with excellent bias stress stability. TFTs biased continuously for 40,000s showed <50 mV threshold voltage shift. We also report fast PEALD ZnO circuits on polyimide substrates with propagation delay <20 ns/stage for V DD = 18 V. 61.