Improved Sensitivity and Stability for SnO2 Ion-Sensitive Field-Effect Transistor-Based pH Sensor by Electrical Double Layer Gate and Al2O3 Sensitive Film

Hydrogen ion sensor (pH sensor) with high sensitivity and good stability has great potential in modern life, medicine, industry, and other fields. As a core of the pH sensor, an ion-sensitive field-effect transistor (ISFET) based on SnO2 is paired with a high selectivity Al2O3 inorganic insulating film, which enhances its pH sensitivity. In the presence of a voltage applied to the extended gate, the gate and channel act as capacitance plates, and the sensor is equivalent to an electrical double layer (EDL). The hydrogen ions in solution alter the solution capacitance, which changes the capacitance of the solid dielectric layer, regulating the source-drain current. As a result of this work, the sensitivity of the ISFET-based pH sensor with extended gate increased 15.8x to 25.33 nA/pH.V when VGS is 300 mV, compared to a SnO2-based sensor without the extended gate. Also, the stability of the sensor has been greatly improved, as well as the response time of 0.2 s. Our research provides an effective strategy for high-performance ISFET-based pH sensor, and the concept of using the pH-ISFET with an extended gate for direct quantification of pH values in solutions provides a dependable method for industrial applications.

Automated summary

Hydrogen ion sensors (pH sensors) with high sensitivity and stability have great potential in various fields. In this research, an ion-sensitive field-effect transistor (ISFET) based on SnO2 and paired with a high selectivity Al2O3 inorganic insulating film was used to enhance pH sensitivity. The study showed that the sensitivity of the ISFET-based pH sensor with an extended gate was significantly increased compared to a sensor without an extended gate, and the stability and response time were greatly improved.