高G值壓阻式微型加速度感測器之設計與性能分析

Structure Design And Performance Analysis Of High-G Piezoresistive Micro-Accelerometer

唐興(Hsin Tang)

指導教授 ： 翁宗賢

國立臺灣大學/工學院/應用力學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.00924

摘要

微型加速度感測器是一種體積小，並且可將加速度轉換成類比訊號輸出的感測元件。近十年來半導體製程技術突飛猛進，靠著與積體電路的高製程相容率，連帶著使微型感測器的製造成本降低，同時也提高了可靠度及加速度的量測範圍，成為微機電系統中發展最快，最早被商品化的產品。藉由不同設計的量測範圍，微型加速度計被廣泛使用在我們的生活周遭，舉凡從航太科技、軍用武器，到日常生活常見的汽車、手機、電視遊樂器，均可見到微型加速度計的應用。
本文以微機電製程技術(MEMS)研製微型加速度感測器，可以運作於0至10,000G的衝擊變化環境下，連續感測載體所承受的加速度，並輸出類比電訊號。為求降低研究成本，首先依據文獻與理論完成三種懸臂樑尺寸的微型加速度感測器的機械構型設計：80μm、100μm、120μm。選用壓阻器為加速度感測元件，並運用數值模擬軟體來分析在給定的高G值衝擊加速度條件下，各構件所承受的應力與電壓輸出變化；考量結構的應力變化範圍與自然頻率，調整細部微調構件的設計，以確保組件不會損壞，並有效提升輸出訊號敏感度。
經數值模擬驗證所設計的加速度感測器在加速度為10,000G的衝擊環境下，結構所受最大應力可達120MPa，尚未達矽的降伏應力，而電壓變化可達mV等級，再藉由後續的放大電路可使敏感度符合預期。偵測器結構的第一共振頻為76kHz，遠高於輸入波的主頻頻率4.8kHz，避開輸入波可能引起的共振與失真。
接著以半導體微機電系統製程研製所設計的微加速度感測器，根據整體的製程規劃，設計與委製所需的光罩，再以微奈米機電製程技術進行試製，成功製作出所設計的微型加速度感測器，最後經切割與封裝。加速度感測器採用離心測試台進行測試，以提供0至10,000G的穩定離心加速度，在旋轉台上以無線射頻即時傳輸模組來輸出加速度偵測器在固定加速度時的穩態訊號，建立系統的響應參數。實驗結果顯示本文研製的加速度偵測器在測試加速度範圍0~4500G下敏感度最高可達1.92μV/V/G，其中懸臂樑尺寸為120μm的設計敏感度也可達到1.54μV/V/G。
由於加速度偵測器是以半導體製程研製，可以批次作業量產，不但品質均一，且單位成本將遠低於以機械加工方式製作的產品。再者，由於速度偵測器的體積小，質量輕，因此可縮減系統引信的尺寸與重量，且更耐衝擊。

關鍵字

加速度偵測器 ； 微機電製程 ； 高G衝擊模擬 ； 動態響應

並列摘要

Micro-accelerometer is a tiny sensing component which can convert as well as output acceleration into analog signals. Over the past decade, the technique of semiconductor process has been greatly improved. Since the MEMS processing is compatible with the CMOS manufacturing, the cost of producing micro sensors thus has been reduced; withal, the micro sensors have turned to be more reliable, and the measuring range of acceleration has widened. Hence, micro-accelerometers have become the first commoditized products that grow the rapidest in MEMS. With different measuring range of various designs, micro-accelerometers have been applied widely in daily life, ranging from aerospace technology and military weapons to vehicles, cell phones, and video games of everyday life. The application of micro-accelerometer is everywhere.
In this thesis, micro-accelerometer that is developed by MEMS process can be operated from 0 to 10,000 G impact. This micro-accelerometer can continuously sense the acceleration which the carrier undergoes and simultaneously output analog signals. In order to reduce research costs, three kinds of micro-accelerometer are designed with different sizes of cantilever beams: 80μm, 100μm, and 120μm in accordance to documents and theories. First, piezoresistor is selected as the component to sense acceleration and use the software for numerical simulation to analyze, on condition that given the same high G shock acceleration, observe the change of stress and output voltage that each structural element. Considering both the range of change and the usual frequency of structural stress, adjust the design of detailed fine-tuning, ensuring the components will not be damaged and will effectively gain sensitivity towards output signals.
The micro-accelerometer that is designed based on the former numerical simulation can endure 120MPa at most which is yet reaching the yield strength of silicon. The change of voltage could be up to mV level, and subsequently, the amplifier enables the sensitivity to meet the anticipation. The first resonant frequency of the sensor structure is 76kHz. Since the first resonant frequency is much higher than the main frequency 4.8kHz of input wave, it avoids the possibility of the input wave causing resonance and distortion.
The micro-accelerometer designed by MEMS manufacturing process and mask made based on the whole manufacturing process, use micro-nanometer process technology for electromechanical trial. Eventually, after segmentation and packaging, the designed micro-acceleration sensor is successfully made. These sensors will be arranged on a centrifugal machine which can produce a steady acceleration ranged from 0 to 10,000G by adjusting the spin rate of a turning table where the sensor is mounted. The steady acceleration allows calibrations of linearity and sensitivity of the devices. Experimental results show that the sensitivity of the accelerometer is up to 1.92μV/V/G between0~ 4500G,even the sensitivity of design that size of cantilever beam is 120μm can be reached 1.54μV/V/G.
Since the accelerometer are made by semiconductor process, the production could be divided into several times. Consequently, the quality is equal, and the cost per unit is much lower than the products that are made in the way of machining. Moreover, due to the small capacity and the lightness of the acceleration sensor, the size as well as weight of fuse can be shrunk and becomes more resistant to impact.

並列關鍵字

Piezoresistive accelerometer ； MEMS ； high G impact ； dynamic response.

參考文獻

[1] Charles S. Smith, Piezoresistance Effect in Geruianium and Silicon, Physical Review, vol. 94, Issue 1, pp. 42-49.

[3] Wilfinger, R.J.; Bardell, P.H.; Chhabra, D.S. The resonistor a frequency selective device utilizing the mechanical resonance of a substrate. IBM J. 1968,12

[4] Roylance, L.M., Angell, J.B., A batch-fabricated silicon accelerometer, Electron Devices, IEEE Transactions on(Volume:26 ,Issue: 12)

[5] Kanda, Y, A Graphical Representation of the Piezoresistance Coefficients in Silicon, Electron Devices, IEEE Transactions on(Volume:29 ,Issue: 1)

[6] Shaoqun Shen, Jlan Chen and Mmhang Bao, Analysis on twin-mass structure for a piezoresistive accelerometer, Sensors and Actuators A, 34 (1992) 101~ 107