Optimization of High‐κ HfO ₂ Transistor Dielectrics by Atomic Layer Deposition as an Enabler of Novel Thin‐Film Circuits and Sensors

This study explores the integration of atomic layer deposited (ALD) HfO 2 dielectric films with solution‐processed In 2 O 3 semiconductor channel, thin‐film transistors (TFTs) for a silicon chip‐free temperature sensor label. The inclusion of the HfO 2 high‐κ dielectric permits reduced voltage operation of the sensor label. HfO 2 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 ( ε r ≈ 18.5–18.8) correspond to an equivalent oxide thickness (EOT) of about 3.1 nm, consistent with optimized high‐κ film formation. To enhance drain current, a reduced 7.5 nm HfO 2 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.