The Research On Current-mode Readout Circuit For ISFET Biosensor

Bioelectronic is a crossing subject which relates to Biomedical, Electronic, Engineering and etc., and it has attracted widespread interests around the world and is becoming a hot topic. This work mainly focuses on designing of current-mode read-out circuit for ISFET biosensor. This topic is divided into four sub-topices in this work, they are: ISFET modeling and simulation, low-voltage and low-power current-mode read-out circuit designing research, the designing method of layout which integrates ISFET and readout circuit, and the appication of ISFET biosensor.In the thesis, the classify methods of biosensors are introduced firstly; the development of ISFET layers, readout circuits, fabration and application are reviewed; the problems thich stop the development of ISFET biosensor are summarized. The author presents his own opinions here to solve these problems. The main works are listed as follow:(1) The structures and working theories of ISFET and MOSFET are analyzed and compared. The sensitive characters of Ta2O5 semsitive layer is studied, and then the electrochemistry equations of Ta2O5 are proposed. A behavioral macromodel of ISFET in SPICE is proposed based on 0.35μm 2-Poly-4-Metal integrated circuit technology provided by Chartered, Singapore. The proposed model is much easier to use and modify than tranditional Bio-SPICE model.(2) The output characters of ISFET and the theory of ISFET read-out circuit are studied, and based on this, two types of novel ISFET current-mode read-out circuits are proposed. These circuits can work in low-voltage and low-power mode, and it can be connected with current-mode A/D converter and other current-mode signal processing circuit modules without conversion. It has great value in both theory and application aspects. The proposed circuits are simulated using the SPICE model presented before.(3) The integrated method of ISFET sensor is researched, and an integrated system layout contains ISFET and read-out circuit is designed. It highly integrated the elements of ISFET biosensor and reduced the bulk of system, has great value in application. The application problem of ISFET is studied in this thesis. A novel muti-function ISFET-based electronic capsule system is proposed. This is a promising research topic in both academic and commercial aspects.