水膠薄膜濕度感測器之設計、製作與測試

Abstract

本研究利用微機電技術，以水膠(HEMA)為感測薄膜材料製作電容式濕度感測器並成功整合本實驗室研發之溫度感測器與電容讀取電路，製造出高靈敏度、高線性度、低成本之電容式濕度感測器。整個系統期望用於冷鏈物流中，監控產品處於各階段時的溫度與濕度，溫度感測器另外可輔助濕度感測器之運作。 水膠之介電係數與相對濕度關係為 ∆ε_s = 0.024 / %RH，相較於Polyimide (∆ε_s=0.0071 / %RH)大了將近3.5倍。換句話說，如果為了達到相同之靈敏度(∆C / %RH)且感測電極高度相同的情況下，以水膠做為感測薄膜能夠使面積縮小3倍。在反應時間上，水膠的反應時間為55秒，比Polyimide大了2倍多，不過在一般的應用中，濕度的變化速度遠大於55秒，因此並不受影響。水膠不能承受高溫(70°C以上)，因此在特殊量測上(高溫環境)仍須使用Polyimide做為感濕材料。 因此，本研究發現了以較低價的材料，水膠，取代現今常用之Polyimide做為濕度感測器，在冷鏈物流的應用上，能夠有效的減少成本、提高濕度感測器之靈敏度。另外，水膠在保存上較Polyimide容易許多也大幅度的簡化了製作過程。

A capacitive humidity sensor based on HEMA film and CMOS temperature sensor combine with readout circuit is implemented by MEMS technology and CMOS Mixed Signal process. The humidity sensor is featured with a great performance of sensitivity and linearity. Also, the cost of HEMA is cheaper than Polyimide widely used for the sensing film of humidity sensor. This system is expected for monitoring the environment temperature and humidity when transporting products in cold chain logistics. The sensitivity (∆ε_s ) of HEMA film is 0.024 / %RH which is 3.5 times than the sensitivity of Polyimide film (0.0071 / %RH). In the other hand, if the sensitivity (∆C / %RH) of humidity sensor based on HEMA film is same as the humidity sensor based on Polyimide film, the area of sensing film will be reduced to one third. Although the response time of HEMA film is 55 sec. which is 2 times than the Polyimide film but the it is sufficient in general applications. Finally, the Polyimide is still used as a sensing film because the HEMA film is not suitable in high temperature ambient. A low cost material (HEMA) is proposed as the sensing material for humidity sensor which is featured with high sensitivity and high linearity. Also, the preservation way of HEMA is easier than Polyimide which will simplify the fabrication process.