高線性度與低跨軸敏感度之懸浮壓阻式垂直平板型加速度感測器研發

Development of a vertical-plate-type Microaccelerometer with Suspended Piezoresistors Characterizing High Linearity and Low Cross-axis Sensitivity

甯煜宗(Yu-Tzong Ning)

指導教授 ： 翁宗賢

國立臺灣大學/工學院/應用力學研究所/博士(2015年)

https://doi.org/10.6342/NTU.2015.00902

摘要

本研究藉由電腦輔助工程方法並配合微機電製程設計製造一個壓阻式垂直平板型微加速度感測器。有別於傳統方法-在結構變形最大處內嵌壓阻器，在設計之初即規劃感測器在受到定量慣性加速度場後，於產生最大位移處放置四個相同的懸浮橋式壓阻器，並用佈線方式將各個壓阻器連線組合成惠斯同電橋電路，用於偵測變化量。而特殊壓阻配置方式預期有兩個結果；一者可以有效提升電壓輸出的敏感度，減少在規劃量測範圍及整合測試電路時的限制；二來也可以大幅度減少跨軸敏感度，顯著地提升系統於單一向性的表現。
本文設計感測器其主要核心元件包含有一組固定於兩側的垂直式彈性平板，並在平板中段處加入一個感測質量塊。在質量塊前後，也就是預期位移最大處各放置一組兩個懸浮橋式壓阻元件，每一個壓阻器兩端將分別繫於質量塊端及邊框固定端。利用數值模擬方法偶合結構應力場及壓阻轉換函式來分析最大應力產生位置及其值，避免應力超過安全設計範圍導致損壞情況；另外運用模態分析來計算自然頻率來推估可使用頻寬，最後透過壓阻效應分析所得輸出電訊號可以計算此結構下之預期敏感度。完成設計的感測器結構將利用大量深蝕刻技術製作於SOI晶圓上，並將電路佈局經由微影製程沉積表面與壓阻器匹配。使用直列式封裝(Dual-In-Package)完成測式晶片。接下來再使用可以提供高達3,000G加速度的離心機，結合數位化電路及RF傳輸模組進行測試實驗，遠端接收輸出電壓訊號。
本文所設計之加速度感測器其自然頻率約為232.4kHz，最大可承受加速度為10,000G。經由數次實驗，統計迴歸後得出其敏感度為3.0015μV/Vexc/G，最佳線性度為0.11%FS。而跨軸敏感度的測試結果在上述實驗範圍內其值幾乎低於本實驗電路之精度。利用文獻中提到的最佳表現計算法可以得到優值 (Figure of Merit)為609

關鍵字

高G值加速度感測器 ； 微機電製程 ； 機電整合 ； 離心式加速度測試 ； 高線性度 ； 低跨軸干擾

並列摘要

This research developed a microaccelerometer via Computer-Aid-Design(CAE) and Micro Electro Mechanical Systems(MEMS) with high performance in linearity and cross-axis sensitivity. Unlike the conventional sensing elements which are always embedded at the position of maximum displacement, the present study situated the sensors at the locations where the maximum displacements of the structure are generated in order to raise up the maximal output than the former.
The core elements of accelerometer includes a vertical, double-ended flexural beam, a proof mass integrated at the middle section of the beam, and four suspended piezoresistors fixed at the mass block and across the trenches to the anchor pads. The mass block had maximum displacements of the dynamic structure which would activate the sensors to deliver maximal output. It was simulated by numerical method to analyze how much and where the maximal stress would be. The sensing chip was fabricated on a silicon-on-insulator(SOI) wafer through MEMS processes and installed by Dual-In-Package. The accelerometer was placed on a rate table that provided stable centrifugal acceleration up to approximately 3000 G for quasi-static testing. The output voltage of the accelerometer was digitized and radiofrequency transmitted for remote data acquisition.
The natural frequency was about 232.4 kHz from mode analysis. After numerous experiments, the correlations for the individual runs showed that the accelerometer had a sensitivity of 3.0015 μV/Vexc/G with extraordinary performance. The best linearity of the sensing output was only 0.11% of full scale output (FS, or 59 dB), as deduced from the average standard deviation of all test runs. The average of the maximum reading deviations from the corresponding correlated curves was approximately 0.26% FS. Moreover, the cross-axis sensitivity for the two orthogonal directions nearly vanished in the test range. With the high rigidity of the microstructure, the accelerometer exhibited an ultra high performance factor of 25.8 x 10^6 MHz. The accelerometer possessed exceptional sensitivity, linearity, and repeatability, and extremely low cross-axis interference and noise.

並列關鍵字

High-G accelerometer, High linearity, Low cross-axis sensitivity ； Piezoresistor ； MEMS ； Centrifugal test

參考文獻

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