Research On ISFET Sensor And Related Materials

Ion-Sensitive Field Effect Transistor(ISFET) is normally used as a sensitive device to detect the biological and chemical signals. The ISFET-based biochemical sensor with great performance in small size, low cost and strong specificity, which can easily be integrated and realize the nondestructive and durable measurement for the application in many fields, such as food safety, biological medicine, environmental monitoring, military, aeronautics, agricultural machinery, industrial control, judicial expertise etc. In this thesis, based on the application characteristics in the pH detection, the ISFET with a ferroelectric material layer is studied by simulation and the influence of ferroelectric material like the BFO(BiFeO3) thin film is also investigated.Firstly, based on the basic principles and theoretical models of the ISFET for pH detection, the simulation models for the electrolyte-insulator-semiconductor system are studied. The simulation methods of the electrochemical and device behaviors for the ISFET are separated, which can propose a behavioral macromodel for the ISFET device simulation by Silvaco simulation software.Besides, in order to beat the Nernst limit of the ISFET for pH detection, the Dual-Gate thin-film transistor(TFT) structure is used. By using the ferroelectric material with electric hysteresis loop properties and high dielectric constant as gate dielectric layer, and the amorphous Indium Gallium Zinc Oxide(a-IGZO) with high electron mobility as the semiconductor layer, the ISFET with high sensitivity for pH detection is obtained, called Fe ISFET for short. In order to study the effect of ferroelectric material on the FeISFET, the ferroelectric materials with different values of coercive electric field, polarization intensity and dielectric constant of ferroelectric material are used in the design of FelSFET. The simulation results show that the higher detection sensitivity of the FeISFET can be obtained when the ferroelectric material has a smaller coercive electric field, a larger polarization intensity and a higher dielectric constant.What is more, based on the study of the optimization methods for the ferroelectric material applied in FeISFET, BFO is selected as a main research object to gain the larger polarization, smaller coercive electric field and nondecreasing dielectric constant. The leakage mechanism of the BFO thin film with PZT seeding layer is studied systematically. It can be found that the FeISFET with La-doped BFO thin flim deposited on a PZT seed layer has a high detection sensitivity of 755 mV/pH. The study on the characteristic and mechanism of BFO thin film applied in Fe ISFET device has an important significance for improving the overall performance of Fe ISFET.