Research On The CMOS Compatible Integrated Micro-capacitive Sensor

Based on capacitor principle, capacitive sensors can translate changes in environmental parameters into varies capacitance, and then into voltages, currents, frequencies or other signals for easily measuring. Using the principle, capacitive sensors are applied to acceleration sensors, humidity sensors, pressure sensors, gas sensors, biosensors, chemical sensors and other sensors. With the rapid development of microelectronics and micro-electro mechanical systems, capacitive sensors have been miniaturized and intelligent.In this thesis, a CMOS compatible integrated micro-capacitive sensor with comb electrodes is researched. The sensitive capacitor and readout circuit are integrated on the same chip using post-CMOS technology, which are easy to reduce the scale and costs, and improve performance.The capacitive sensor with comb electrodes can increase the sensitive capacitance and improve the sensitivity of the sensor, which is compatible with CMOS technology. The change of the sensitive capacitance is theoretically deduced using conformal transformation. Its analytic model is built and simulated by Ansys. Based on the model, the relation between the change of parameters and the change in capacitance is analyzed easily. Simulation result shows that the theoretical model we have gotten is right. Therefore, there is some instruction to the sensor fabrication and test.Based on the analysis of some readout circuits, a capacitor-voltage converter circuit is proposed using standard CMOS process. Differential switched-capacitor circuit converts the sensitive capacitance signal into the voltage signal. The output voltages change with varies the sensitive capacitance through amplification and filter. The readout circuit removes the effect of the amplifier offset and the bias voltage, and decreases the influence of charge injection and clock feed through using the error storage capacitor, CMOS switches and multiple clocks.The readout circuit is simulated by Spectre of Cadence software and TSMC0.18μm CMOS process. The results show that the output voltage changes from OV to1V, when the capacitance changes from1OpF to11pF. The sensitivity of the converter is10mV/10fF. The simulation results of the operation amplifier that the open-loop gain is72dB, the phase margin is65°, the unity gain bandwidth is7MHz, the input common-mode range is-3-2.3V, the output dynamic range is-2.9V-2.9V, the slew rate is8.1V/us, the common mode rejection ratio85dB, the power supply rejection ratio is99.3dB and96.4dB, and the power consumption is1.47mW.The layout of the readout circuit is designed through Virtuoso XL. And the post-processing process of the micro-capacitive sensor is researched. The results show that the structure is compatible with standard CMOS processes.Therefore, the main contributions of the thesis include:(1) deducing the change of the sensitive capacitor in favor of predicting and analyzing the capacitance variation;(2) proposing and designing the CMOS capacitor-voltage readout circuit for integrated micro-capacitive sensor applications;(3) researching the post-processing process of the integrated micro-capacitive sensor using post-CMOS technology.