Modeling and design of polythiophene gate electrode ChemFETs for environmental pollutant sensing

Water-borne pollutants such as volatile organic compounds are a serious environmental concern, which has increased the demand for chemical sensing elements. Solid-state sensors based on catalytic gate devices are a subject of current research, however they are restricted in practical applications because of their inability to operate at room temperature. Conducting polymer FETs, which employ a conducting gate polymer, have received much attention due to their unique electronic and optical properties. Polythiophene is chosen as the semi-conductive gate polymer in this work. A functional group attached to the polythiophene is used to detect analytes (i.e., mercury in this work) of interest. The selectivity of the derivitized polythiophene to mercury can be rationalized based on the size of the ring, presence of oxygen and nitrogen donor atoms. In this paper, the modeling and design of a polythiophene gate electrode ChemFET will be discussed. Specifically the model development and resultant device simulations using Silvaco TCAD will be presented. Using this model various current-voltage characteristics of the ChemFET corresponding to parameters such as substrate doping, gate oxide thickness, various gate stacks, and device geometries are presented.