MODELING NONIDEAL BEHAVIORS IN H+-SENSITIVE FETS WITH SPICE

In recent years, much work has been done to characterize ion-selective devices (ISFETs). The response of these devices to pH is commonly explained by considering H+ specific binding sites at the surface of an insulator exposed to an electrolyte. A previous generalized site-binding description is used here to model two specific aspects of the ISFET behaviour, namely: hysteresis in the response to pH, which is not predicted by the 'standard' site-binding theory; partial insensitivity to pH, that is, REFET structures, which are of interest as integrated reference electrodes in differential measurements. The ISFET model is implemented in SPICE and simulation results are given and compared with data reported in the literature.