New Type of Ion-Sensitive Field-Effect Transistor with Sensing Region Separate from Gate-Controlled Region

Abstract

A new type of ISFET is proposed where the proposed ISFET channel is divided into a gate controlled region (Region(gate)) and sensing region (Region(sense)). The ISFET is operated by controlling the gate voltage of the Regiongate with the attached biomolecules on the gate dielectric of the Regionsense. When the gate voltage is applied over the threshold voltage (14n), the channel resistance of the Regiongote sharply decreases and the larger channel resistance of the Regionsense limits the ISFET current. Thus, the on-current (I-on) of the ISFET is controlled by the attached biomolecule charge on the gate dielectric of the Region(sense). Our proposed ISFET has many advantages over conventional ISFETs. From TCAD simulations, the proposed ISFET was found to have higher sensitivity according to pH levels than conventional ISFETs due to the unique limitation of the I-on by the channel resistance change of the Region(sense). Additionally, the field-dependent drift effect can be mitigated, because hydrogen ions or biomolecules in the solution are hardly affected by the gate voltage. Furthermore, the proposed ISFET has uniform Ion change regardless of Vth variation, because only the channel resistance of the Regionse, determines the I-on.