Simulation of time-dependent effects of pH-ISFETs

It has been shown that the accuracy of ISFETs is limited by the time-dependent effects which include slow response and drift. The abnormal phenomenon will result in hysteresis. The time-dependent effects of the device can be modeled by mathematical expression. In this paper, we use multi-exponential step-response expression to fit the previous experimental data of total response of various gate insulator such as Ta2O5, Si3N4 and a-Si:H. The curve-fitting employ the method of least squares criteria to extract the time constant and amplitude. The extracted parameters were used to simulate the mechanism of hysteresis. The previous data of pH-response of a-Si:H in our laboratory can be combined with earlier measurements of Ta2O5, Si3N4 surfaces to simulate their hysteresis property at a loop time of 160 min (9600 s). The magnitude of normalized hysteresis width of simulation was found: a-Si:H>Si3N4>Ta2O5.