Dual-Gate Oxide Ion-Sensitive Thin-Film Transistor for Panel-Scale Manufacturing of High Resolution and High Sensitivity Biochips

This work proposes a dual-gate (DG) ion-sensitive thin-film transistor (ISTFT) design with enhanced pH sensitivity and excellent robustness against process variation for high-resolution biochips, which is fully compatible with the standard inverted staggered structure indium gallium zinc oxide (IGZO) thin-film transistor (TFT) processes. The top gate (TG) connected to the extended-gate sensing electrode is formed directly onto the etch stop layer (ESL), having a larger capacitance to the channel than that of the bottom gate (BG). With the capacitance coupling effect, the device has a potential amplification coefficient of 2.5 and, in turn, achieves pH sensitivity of 83.4 mV/pH, which is beyond the Nernst limit. TCAD simulations and experimental measurements confirm that the amplification factor of the DG structure remains stable despite variations in TG dimensions, demonstrating strong robustness and scalability. The structure, therefore, enables the design of a high-resolution ISTFT array by leveraging a one-TFT (1-T) active pixel. Finally, a biochip consisting of a $12\times 12$ ISTFT array [250 pixels-per-inch (ppi)] with exceptional thermal and operational durability is demonstrated, proving the scalability of the proposed device design for panel-level mass production.