CMOS Integrated Sensing Chip For PH Value And Cell Membrane Potential

A monolithic chip processing method is reported, which includes the cell membrane potential sensor, pH sensor and mixed-signal circuits using 0.6μm double poly double mental (DPDM) N well standard CMOS process.The major contents and contributions of this dissertation could be summarized as follows:1. A new array sensor chip for recording cell membrane potential is designed based on standard CMOS process. It consists of 8 X 8 active sensor array, reference voltage, analog multiplexer, output buffers and digital controlling circuits. The electrode array of group enhances the electrode density and improves the parallel processing ability of circuits. The active sensor unit is the optimization of electrode extracellular recording and FET on-site amplification, and could linearly amplify signals with peak-to-peak valued from 100μV to 20mV.2. A multi-floating gate field effect transistor pH sensing unit is reported here based on the standard CMOS process, and the silicon nitride passivation layer is used as the hydrogen sensitive membrane. The electrolyte-insulator interfacial potential equation simulated with MATLAB is obtained from the site-binding model and the Gouy-Chapman-Stern theory. The threshold model of MFGFET is built from conventional open-gate FET sensitive theory. A pH sensing macro-model is developed. The model can be used as an IC part and allows simulation with the on-chip readout interface.3. PMOS transistor is used as the pH sensor, which can avoid the body effect. The pH sensor on-chip controlling circuits keep the source drain voltage and source drain current of the MFGFET constant. The linear range of source voltage reaches to 4.6V and this greatly satisfy the testing request for different pH value solutions. Exposure to UV lamp with 396nm wavelength can erase the charge trapped on the floating gate, which can increase the threshold voltage, improve the hysteresis characteristic and can adjust the linear range of gate voltage in solution effectively. Pattern mode noise in the circuits is reduced through a differential output between the ion-sensitive MFGFET and a reference MFGFET, also the temperature characteristic is improved. The testing result shows the pH sensor has an average sensitivity of 35.8 mV/pH from pH 1 to 13.4. The Post-CMOS process, layout optimization and improved package technique enhance the stability of the biosensor in the solution environment.In this paper, the CMOS mixed-signal IC combined with pH sensor and cell membrane potential sensor are researched, which proves the possibility of monolithic biosensor chip. The research paves the way for advanced biosensor systems.