題 目：應用MEMS微型壓力感測器於風洞實驗之研究
研 究 生：陳丕宇
指 導 教 授：苗君易
共同指導教授：李國賓
本實驗採用微機電技術(Micro-Electric-Mechanical System)以研發高靈敏度與陣列式排列的壓力感測器，期突破由於傳統感測器的空間解析度與靈敏度不足的限制，以便應用於在低速風洞實驗探討鈍形體前緣停滯區流場特性的研究。
本微壓力感測器設計的最主要的考量在於靈敏度和頻率響應，靈敏度的考慮在於能夠偵測到1~10 Pa的壓力擾動量，頻率響應能夠偵測到大於10K Hz，本研究之微壓力感測器的感測原理是利用壓阻材料(複晶矽)因應變而使電阻值的產生變化，透過惠斯登電橋電路的轉換，以得到電壓訊號，其製作方法是利用低壓化學氣相沉積(LPCVD)的表面微細加工技術製作氮化矽(Si3N4)薄膜、複晶矽壓阻及導線的部分，利用乾式蝕刻DRIE(Deep-Reactive-Ion-Etching)和氫氧化鉀(KOH)溼式蝕刻的體型微細加工技術蝕刻背面的矽基材製作感測器薄膜變形區域。
本研究所製作的MEMS微型壓力感測器所量測的壓力值是相對壓力，其線性的壓力量測範圍為-0.3bar到+1.0 bar之內，工作電壓為20V，其壓力靈敏度為 2.5mv/v.bar，由於在多晶矽壓阻摻入的硼離子劑量與設計點不符，以致於感測器對溫度敏感，其溫阻係數(TCR)為-2.14.10^(-3) 。但是此溫度效應可用定電流的放大電路加以修正。

Subject：A Study of Applying MEMS Pressure Sensors in Wind Tunnel Experiment
Student：P. U. Chen
Advisor：J. J. Miau, G. B. Lee
The purpose of this study is to develop a high-sensitivity, array-type micro piezoresistive pressure sensors based on MEMS (Micro-electro-mechanical-system) technologies. The pressure sensor will be superior to its large-scale counterparts in the aspects of spatial resolution and sensitivity. The developed pressure sensors will be employed to investigate the characteristics of flow in the stagnation region at the leading edge of a bluff body.
The sensor should resolve pressure variation of 1~10Pa and have a frequency response higher than 10KHz. The sensing principle of the sensor is based on transformation between strain and electrical resistance, which applies a piezoresistive material to sense the strain of a diaphragm caused by pressure variations and then produce electric signals using a Wheatstone bridge circuit. Namely, low-stress silicon-nitride is chosen as the material of the diaphragm and polycrystalline silicon is chosen as the strain gauge. These materials are deposited using a low-pressure-chemical-vapor-deposition (LPCVD) process. Subsequently, deep-reactive-ion-etching (DRIE) and KOH wet etching procedures are employed, respectively, to backside-etch silicon wafers and form the diaphragm.
The performance of the fabricated MEMS pressure sensor is systematically investigated. The output signals are reasonably linearly with input pressure in range of –0.3 bar to +1.0 bar, while the operation voltage is 20 Volts. The sensitivity of the MEMS pressure sensor is found to be 2.5mv/v.bar . Since doping concentration of boron-doped LPCVD polysilicon does not match the design value, the MEMS pressure sensor is found to be also sensitive to temperature variations. The temperature effect can be expressed in terms of temperature coefficient of resistance (TCR), which is -2.14.10^(-3) . Nevertheless, a constant-current circuit can be employed to alleviate the temperature effect.

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