Zinc Oxide Nanowire Field Effect Transistor Used as a pH Sensor

An ion sensitive field effect transistor can outperform conventional ion-selective electrodes. Thus, a zinc oxide (ZnO) nanowire field effect transistor (NWFET) pH sensor was fabricated and measured. The sensor contained a channel with 1.7 x 10^18 cm^-3 donor concentration and 100 ZnO nanowires in parallel, each with the following dimensions: 10 μm x 120 nm x 20 nm. The active channel is passivated with an 18 nm Al2O3 layer. The device was measured under a controlled environment with and without pH solutions. The pH range was 3–9 with a sensitivity of 2.48 mV to 10.3 mV. The voltage sensitivity translates to a percentage value of 15%. The measurements obtained before and after the pH solution treatment demonstrate the possibility of re-use of the device by rinsing and brushing the sensing layer.