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 near-threshold 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 field-induced mobility reduction. The same trends have been obtained for the pH-sensitivity expressed as partial I_text D/partial text 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.
- Bipolar junction transistor (BJT)
- MOS devices