High-Performance ISFET pH Sensor with HfO2 Sensing Film Using Post-CMOS Processing

In this letter, we develop an ion-sensitive field-effect transistor (ISFET) using a commercial CMOS and low temperature atomic layer deposition (ALD) processes. The ISFET has a floating gate structure and utilizes the hafnium oxide deposited on the aluminum pad as a pH-sensitive film. A surface preparation step is introduced before the hafnium oxide deposition to ensure a clean and more reproducible interface between the surface of the floating gate and the deposited oxide. The ISFET device incorporating an HfO2 sensing film deposited using O2 plasma enhanced process at 150 °C has a high pH sensitivity of 56 mV/pH, a good linearity in the pH range from 3 to 7.4, and exhibits high stability of HfO2 layer and low values of voltage drift after pH cycling. The developed ISFET has a number of advantages over ISFETs manufactured using unmodified CMOS process and can be used for creation of high-performance sensing devices.