Highly sensitive ion sensor based on the MOSFET–BJT hybrid mode of a gated lateral BJT

In this study, a highly sensitive ion sensor using a gated lateral bipolar junction transistor (BJT) was proposed and evaluated. The proposed device was developed using a semiconductor technology that combined the MOSFET and the BJT structures. We found that the sensitivity of the conventional semiconductor-based sensors has a large dependence on the transconductance of the device. Therefore, a MOSFET–BJT hybrid-mode-operated gated lateral BJT structure ion sensor was developed that has higher transconductance than MOSFET sensor devices. In order to confirm the characteristics of the sensor device, the VG–IE curve, transconductance, and current gain performance were evaluated and compared between the MOSFET mode and MOSFET–BJT hybrid mode. Then, ion detection experiments were performed using pH buffer solutions. The evaluation results indicated that the sensitivity of the MOSFET–BJT hybrid mode can be controlled by altering the base current and is higher (21.77 μA/pH) than the sensitivity of the MOSFET mode, which is similar to the conventional MOSFET-structure-based ISFET (17.56 μA/pH). Further, this study proved that in the MOSFET–BJT hybrid mode, the proposed device has higher transconductance and current gain characteristics.