一個具有LC差動式振盪器與數位輸出的電容式加速度計

Abstract

現今由於消費性電子產品的蓬勃發展，帶動了整個半導體產業技術不斷的進步，其中越來越多的行動裝置需要整合進各種感測器，也導致微機電感測器的需求越來越大，將微機電製程整合進標準半導體製程中做出的CMOS MEMS感測器有成本低、效能好等優點。本篇論文使用TSMC 0.18μm標準CMOS製程搭配國家晶片系統中心提供的後製程來完成一個微機電加速度計，其使用的是電容式的感測方式，並且整合進了電感與積體電路使其成為一個振盪器，再搭配後端電路使其具有頻率與數位輸出。 本篇的加速度計利用振盪器的電容值會影響震盪頻率的特性，將感測電容結合進振盪器中，利用偵測頻率變化量偵測加速度，這種方法結合了電容式感測與頻率輸出電路，具有電容值不易受溫度影響、後製程較簡單、無須複雜的類比數位轉換器、電路有較高的靈敏度與線性度等優點。量測結果此論文的靈敏度為3.44 MHz/g，解析度為0.4 mg/rtHz，相較於相關文獻此論文的加速度計有更高的靈敏度。

The rapid development of electronics products makes the entire semiconductor technology continue to progress. More and more mobile devices need various sensors, leading to the growing demand for MEMS sensors. The MEMS sensors whose fabrication process is compatible to the standard CMOS process are called CMOS MEMS sensors. The CMOS MEMS sensors have the advantages of low cost and high performance. This thesis used TSMC 0.18μm standard CMOS process and post process supported by National Chip Implementation Center to complete a CMOS MEMS accelerometer. This accelerometer has capacitive sensing mechanism, and integrates the sensing capacitor with an oscillator circuit and the back-end circuit to have a frequency and digital output. The oscillation frequency can be influenced by the sensing capacitor. By detecting the variation of the oscillator output frequency, this accelerometer can define the acceleration value applied on this chip. The combination of capacitive sensing and frequency output has the advantage of capacitor values being less sensitive to temperature, post process being relatively simple, no need of complex analog-digital converters and higher sensitivity and linearity. The measurement result shows that this accelerometer can achieve 3.44 MHz/g sensitivity and 0.4mg/rtHz resolution.