Control Strategies for Solution-Processed ZTO-Based Thin-Film Transistors Tailored Toward Volatile Organic Compound Detection

The remote detection of volatile organic compounds (VOCs) in human breath by chemiresistive gas sensors can assist in the non-invasive diagnosis and prevention of life-threatening medical conditions. Solution-processed transparent oxide thin-film transistors (TFTs) are growing examples of chemiresistive gas sensors as they offer thermal stability, cost-effective fabrication, and enhanced sensitivity towards VOCs. We tailor the electrical performance of ZTO-based TFTs by adopting a simple design strategy for an improved chemiresistive response, which involves layering ZTO and ZnO films. The ZTO-ZTO TFT treated at 500 °C achieves near-zero threshold voltage (V_th = 2.20 V) and excellent switching properties (I_on/off = 10⁷) while maintaining high mobility (μ_eff = 9.49 cm²V^-1s^-1). This produces high responsivity toward acetone and isopropanol (IPA) vapours at room temperature and low-voltage operation. The off-current and switching property of the ZTO-ZTO TFT exposed to IPA are maintained, which leads to a peak responsivity approximately five times greater than exposure to acetone. We lastly consider the interrelation between high oxygen vacancy content (V_O = 31.2 %) and gas sensing performance. Deeper compositional and structural analysis allows for precise control over thickness and chemical environment of the multilayer films. This report demonstrates that the sequential deposition and thermal treatment of ZTO and ZnO layers is an effective method to improve the electrical and chemiresistive properties of amorphous metal oxide TFTs, paving the way for a detailed sensing study in the future.