近年來，電容式溼度計以高分子材料聚亞醯胺，倍受業界及學術界所使用。電氣特性方面，聚亞醯胺提供溼度計優異的靈敏度及線性度；從製程整合的角度，聚亞醯胺固化後經由黃光微影製程，可定義出不同的幾何形貌，抑或是透過點膠的方式，填入結構夾層中，再進行固化。因此，聚亞醯胺具有與CMOS-MEMS平台進行整合的好處，對於需要批量化製造之商品無非是一大優勢。間苯二酚-甲醛與聚亞醯胺同為高分子材料，亦具備與CMOS-MEMS平台整合的條件；在材料性質方面，間苯二酚-甲醛的骨架上具有親水性官能基─羥基，透過超臨界乾燥製備成奈米級孔洞之氣凝膠後，更提升了材料與環境接觸的面積，因而對於環境溼度具有更佳之靈敏度表現。
本研究採用TSMC 0.18 um 1P6M CMOS製程平台，結合後製程金屬濕蝕刻、點膠技術及超臨界乾燥，使氣凝膠成形於垂直平板電容夾層內，實現以間苯二酚-甲醛氣凝膠為感測膜層的CMOS-MEMS 電容式溼度感測器。經一系列之製程與實驗量測結果，凸顯間苯二酚-甲醛氣凝膠的優點，不論在製程整合能力與性能表現上，皆足以與聚亞醯胺材料相比較；本研究主要設計兩種溼度計：Type 1 0.53-um與Type 2 1.91-um電極間距之設計，靈敏度分別為0.591%/%RH 、0.571%/%RH，而反應步階溼度變化20%RH~80%RH的時間為11 s、19 s；與未填入間苯二酚-甲醛氣凝膠之原始結構相比，Type 2元件靈敏度之提升達410.7%RH；Type 1填入間苯二酚-甲醛氣凝膠的溼度計相較PI元件，靈敏度提升209.5%RH。結構設計方面，依循可靠度優化之設計方針─透過氧化矽支柱固定感測間隙，並有效強化薄膜結構主體剛性；此外，融合後製程金屬濕蝕刻之優點，以氧化層包覆感測電極，降低金屬電極與外界環境作用所衍生之問題，確保元件之可靠度。本研究中將溫度計與溼度計作單晶整合，達到環境感測器的目的，並提出針對溼度計作溫度校正的方式。
後續研究上利用溼度計陣列的結構設計，經由準直的反應式離子蝕刻，定義出柱狀之間苯二酚-甲醛氣凝膠，以期達到高靈敏度與低反應時間之訴求。

Currently, state-of-the art humidity sensors that have been used in mobile applications are mostly capacitive-based sensors integrated with electronics monolithically and fabricated with the industrial standard CMOS process to achieve a cost-effective solution for accuracy, performance and reliability. As for the moisture sensitive films, polymer-based and especially polyimide-based sensors have been used predominantly inasmuch as the superior properties over wide humidity range and the compatibility with CMOS platforms. However, based on a great deal of on-going researches, polyimide features slow diffusion constant and have long-term stability problems. As a result, RF-Aerogel, shown great potential in humidity sensing and capability to integrate with CMOS platforms, was adopted herein.
This study presents the design, implementation and characterization of a high-sensitivity capacitive humidity sensor. TSMC 0.18 m CMOS process was used followed by in-house maskless post-processing and pneumatic dispensing of precursors of aerogels to form a vertical parallel-plate (VPP) topology for capacitive sensing. A sensitive material, resorcinol-formaldehyde (RF) organic aerogel, was prepared by the sol-gel method and supercritical fluid (SCF) drying. The low-density RF-aerogels synthesized by this method exhibit high surface areas, high porosities, and mesoporosity, which are beneficial to moisture diffusion and sensing reaction. Despite the sensor response to moisture is non-linear, a minimum sensitivity up to 0.571% capacitance change per percent relative humidity (RH), is achieved. Further measurements show that a response time of 12s and maximum hysteresis of 1.1%RH have been obtained. In addition, a resistive type temperature sensor had been integrated with humidity sensor on the same chip. Furthermore, this study proposed a method to calibrate the temperature-dependent readout of a humidity sensor by means of an on-chip temperature sensor.
For further investigation, a new kind of sensor topology – VPP array is proposed. In the design, VPP ensures sensors’ sensitivity; meanwhile, RF-aerogels are patterned by plasma etching in column shapes so as to shorten the diffusion path of water vapors and thus reduced response time of the sensor. The aim of this study is to design a high-sensitivity and high-speed humidity sensor.

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