Ion-Sensitive Gated Bipolar Transistor

In this article, we study the ion-sensitive gated bipolar transistor (ISBiT) by forward biasing the source-body diode of the ion-sensitive field-effect transistor (ISFET). Based on theory, extensive TCAD device simulations, and experiments, it is shown that the ISBiT operates at lower gate-voltages with a higher transconductance (g
_m
) than the ISFET both in subthreshold and nearthreshold modes. In addition, overall maximum g
_m
's have been obtained for the former when operating in saturation mode. However, in the linear superthreshold operation mode, the ISBiT shows lower g
_m
's because of the fieldinduced mobility reduction. The same trends have been obtained for the pH-sensitivity expressed as ∂I4/∂pH, since it is linearly dependent on the g
_m
, as predicted by the theory. Basically, the ISBiT offers more tunability, hence, freedom in the sensor system.