具有可變電感的CMOS MEMS加速度計

Abstract

本論文使用CMOS-MEMS製程設計一個具有感測電感的電感式加速度計，此加速度計使用彈簧來當作振盪器的電感並搭配MIM電容形成一個LC振盪器，當給加速度的時候，彈簧會因質量塊受力而有位移並造成電感值改變，當電感值改變的時候，LC振盪器的頻率也會跟著改變，而振盪器的頻率變化會跟加速度成正比，故可以利用頻率輸出的變化去偵測加速度值。此感測器在1G加速度時，預計會有千分之四的電感值變化，而對應的振盪器會有3.9MHz的頻率變化。

本論文設計兩個晶片，Sample I為1P6M 0.18um製程，而Sample II為1P5M 0.18um製程，由於時間因素與機台考量，Sample II沒有做後製程，故只量測電路部份。Sample II的電路有正常工作，振盪器的頻率為2.7GHz，混頻器的輸出為33MHz；而Sample I有量測機械特性，機械共振頻率為2.4kHz，但由於Sample I的電路沒有正常工作，故Sample I重新跑模擬並檢討原因。

In this thesis, an inductive sensing accelerometer was fabricated by CMOS MEMS process. This accelerometer use this spring as the oscillator inductors and MIM capacitors with the formation of an LC oscillator. The inductance value is changed due to the spring mass displacement and force causing by external acceleration. With changing in inductance value, LC oscillator frequency will also change. The change in the oscillator frequency will be proportional to the acceleration. It is capable for detecting acceleration by detecting different output frequencies. A 4/1000 change for inductance value is expected under 1g acceleration corresponding to oscillator frequency change of 3.3MHz.

In this thesis, two device were designed and fabricated. Sample 1 was fabricated by 1P6M 0.18um process, and Sample 2 was 1P5M 0.18um process. Due to limited time and maintenance of facilities, post processes were not finished for Sample 2. Only part of the measurement for circuit have been done for Sample 2. For Sample 2, the circuit was working and an oscillator frequency of 2.7GHz was measured. The mixer output of Sample 2 was 33MHz. The mechanical properties measurement on Sample 1 has been done, the mechanical resonance frequency of 2.4kHz was measured. However, the circuit for Sample 1 was not working. A re-simulation for Sample 1 in later chapters has been done for discussing the failed reason.