使用低功耗振盪器讀出電路之高靈敏度CMOS MEMS壓力感測系統;Design of a Highly Sensitive CMOS MEMS Pressure Sensing System with Low-Power Oscillator-Based Readout Circuits

[[abstract]]本論文實現一個以CMOS MEMS製作的電容式與壓阻式壓力感測器系統，將兩種感測器整合為單一結構，以PDMS包覆感測器結構，電容陣列結構作為壓阻感測器薄膜覆蓋區域，透過電容施壓牽動邊緣的壓阻感測器，使感測電容與壓阻可以同時變化，藉此提高感測器的靈敏度。此壓力感測系統將感測器與感測電路完全整合於同一晶片，以標準CMOS製程TSMC 0.35?m 2P4M製作完成，晶片面積為2.5?mm?^2。感測元件透過乾蝕刻與濕蝕刻完成感測器的整合，感測電路採用弛張振盪器為基礎的週期調變電容數位轉換器，弛張振盪器將感測訊號轉換為正比於頻率的輸出訊號，利用弛張振盪器本身低功耗的特性，降低整體電路的功率消耗。電容式與壓阻式壓力感測器透過弛張振盪器RC時間常數與時間長度成正比的關係，當電容與壓阻同時改變時，得到更明顯的RC時間變化。感測弛張震盪器頻率操作在1.02MHz，靈敏度為200Hz/fF，整個晶片的功率消耗為122uW。 The thesis presented a capacitive and piezoresistive pressure sensor system fabricated by CMOS MEMS method. The capacitive and piezoresistive sensor are integrated in a single structure. The capacitive array is used as piezoresistive sensor film, which cover by PDMS. By operating two sensors together, sensitivity can be increased. The pressure sensor and the sensing circuit is integrated in a single chip by standard CMOS process of TSMC 0.35μm 2P4M and the area of whole chip is 2.5?mm?^2. The sensor can be fabricated by post process of dry etching and wet etching method. The sensing circuit adopted relaxation oscillator followed by period modulation capacitance-to-digital converter. The relaxation oscillator transfers sensing signal proportional to frequency output signal. The total power is reduced through the low power characteristic of relaxation oscillator. The more obvious RC time constant changes can obtained when capacitive and piezoresistive changes together. As a result, the relaxation oscillator operating in 1.02MHz and the sensitivity of the oscillator is 200Hz/fF. The total power of the whole chip is 122uW