The Research On Integrated PH-ISFET Biosensor

On the base of all kinds of sensors development toward miniaturiation, integration, and intellligentization, it has become the research focus in this field to integrate ion sensitive units with signal read-out circuits. Because Ion-Sensitive-Field-Transistors (ISFETs) are similar with Metal-Qxide-Semiconductor-Field-Transistors (MOSFETs) in architecture and CMOS technology has gotten rapid development and become the main technology in semiconductor industry,it can be realized to integrate ISFET with its signal process circuit using the CMOS technology.Base on the site-binding model,two kinds of clear physical models (surface site adsorption model and surface site recombination center model) have been presented firstly. Using both models,the author has investigated the microscopic process of H dissociation-association on the electroly-insulator interface of this pH-ISFET sensor respectively,and has also developed their analytical expression between the charge and potential of the E-I interface.From the property of MOSFET,this paper presents the mechanism of pH-ISFET in detail and according to the site bind theories of electrochemistry, the author developed a more general and user-friendly SPICE model for the ISFET device with the use of MOSFET device model in SPICE;With simulation, the behaviour of this macromodel has been agreed with those results obtained by experiment measurement.However,technological steps usually employed for making ISFET's special gate are not compatible with standard CMOS process,which uses polysilicon gate to define self-aligned source and drain transistor regions. To overcome the restraint, pH-ISFET of "sandwich" configuration has been presented in this paper and the results of theory analysis are consistent with those experiment datas ,which shows high accuracy and stability.To implement ISFET sensor monolithically on the same chip together with the interface electronics,the previous circuits all neglect the influence of "silicon substrate body effect" on measurement; This paper presents a method integrating the ISFET and signal process circuit realized in an standard CMOS technology;The simulation results show that "complementary ISFET/MOSFET pair" can eliminate "temperature drift"and "body effect",which proves that this is a more suitable readout circuit for ISFET integration. With the layout editor,the drawings of the circuit and sensor unit abide the all technology rules and keep consistent with the schematics and the results of post simulation show excellent performance.