Optimization of High-κ HfO2 Transistor Dielectrics by Atomic Layer Deposition as an Enabler of Novel Thin-Film Circuits and Sensors

ABSTRACT This study explores the integration of atomic layer deposited (ALD) HfO2 dielectric films with solution-processed In2O3 semiconductor channel, thin-film transistors (TFTs) for a silicon chip-free temperature sensor label. The inclusion of the HfO2 high-? dielectric permits reduced voltage operation of the sensor label. HfO2 films are deposited by atomic layer deposition (ALD) at three different hot source temperatures (80°C, 90°C, 100°C), with XPS revealing improved stoichiometry and O/Hf ratios of 1.75, 1.92, and 1.95, respectively, as temperature increases. MOSCAP measurements show improved oxide/semiconductor interface with higher deposition temperatures. The extracted dielectric constants (εr ≈ 18.5?18.8) correspond to an equivalent oxide thickness (EOT) of about 3.1 nm, consistent with optimized high-? film formation. To enhance drain current, a reduced 7.5 nm HfO2 film thickness is used, achieving higher current but reducing yield by 30% due to increased leakage probability in ultrathin films. A voltage divider circuit is developed to integrate an electrochemical thermal sensor, TFT, and an irreversible visual indicator (IVI), allowing for temperature monitoring with a resistivity change of three orders of magnitude at 8°C. The circuit is powered by a 60 mF supercapacitor array providing approximately 0.21 J of available energy, resulting in IVI activation within 40 min at measured activation currents of 20 µA. The system demonstrates potential for low-voltage, energy-efficient, silicon-free sensor labels in applications such as food safety and healthcare monitoring.