- 學位論文
CMOS電容式壓力感測器與讀出電路設計
CMOS Capacitive Pressure Sensor and Readout Circuit Design
摘要
本論文主要的目的是研究CMOS相容電容式壓力感測器的製作與設計其讀出電路系統，並驗證讀出電路中電容對頻率轉換器的輸出方波週期與外接電容成正比，以及讀出電路的數位輸出與外接電容呈線性關係。在感測器製作方面，採用表面微細加工方式形成密閉腔，利用第二層和第四層金屬層作為電極板，第三層金屬層為蝕刻層。 整體架構包含一個電容式壓力感測器、其感測電容匹配且不隨壓力變化的參考電容、兩個電容對頻率轉換器與十二位元向上／向下計數器，在前半個週期進行對參考電容轉換頻率，並將其頻率做向上計數。在後半個週期，對受壓力改變之感測電容做向下計數，將電容差轉換成頻率差與向上計數時間（與向下計數時間相等）的乘積。最後，計數器的輸出呈現電容式壓力感測器所承受多少壓力。 讀出電路系統使用0.18μm 1P6M CMOS製程實現，工作電壓操作3V，功率消耗6mW。在頻率對電容特性曲線上，得到晶片內部電容轉頻率電路的靈敏度為1.796 [ μs / pF ]，線性度為99.94%。在12位元數位輸出對電容特性曲線上，針對電容式壓力感測器受壓力而增加0pF～2pF，其2pF的變化量，在轉換時間為0.1s，晶片數位輸出的靈敏度為275 [ code / pF ]，解析度達到3.6fF，線性度為99.95%。
並列摘要
The aim of this thesis is to fabricate CMOS-compatible capacitive pressure sensors and design its readout circuit. The capacitor to frequency converter and readout circuit is tested and it is linear. The sensors use surface micromachining to form an airtight cavity. The sensing capacitor of the capacitive pressure sensors is composed wtih the fourth metal and second metal layer. The third metal layer serves as the sacrificial layer. The whole structure consisted of a sensor capacitor, a reference capacitor, two capacitor to frequency converters and a 12 bit up／down counter. In the first half cycle, the capacitance of the reference capacitor was converted into frequency and counted its frequency upwardly. In the latter half cycle, counting downwardly for the frequency of stressed sensor capacitor. The readout circuit converted capacitor difference into the product of frequency difference and the time of counting upwardly（be the same as the time counting downwardly）. The output of counter represents the pressure on the capacitive pressure sensor. The readout system has been implemented with 0.18μm 1P6M CMOS technology. With 3V power supply, the power consumption is 6mW. The sensitivity of frequency to capacitor curve is 1.796 [ μs / pF ] and the linearity of the curve is 99.94%. The sensitivity is 275 [ code / pF ], resolution is 3.6fF and linearity is 99.95% for 12 bit digital output to capacitor curve under the conditions of 0.1s converting time and 0pF～2pF capacitance increase of the capacitive pressure sensor.