以微機電製程探討微尺度結構表面接觸角與微滴操控之研究

Abstract

本論文主要目的為使用微機電系統製程製作具有可操控液滴接觸角變化之可逆性及雙穩定性微滴操控系統，此微滴操控系統所採用之方法是以機械方式改變表面之幾何構造，使液滴能隨著表面結構變化而具有不同之接觸角。為了探討液滴接觸角與表面粗糙度的關係，本論文設計了具有孔洞狀與柱狀之微尺度結構表面，並且將量測結果與Cassie’s Formula做比較，所預測的結果與實際接觸角非常符合，在孔洞狀及柱狀結構表面上接觸角則僅有6°及10°差異，此一實驗結果提供了後續之微滴操控系統在設計表面結構上的參考。 微滴操控系統應用靜電式微致動器與接觸角原理，以微機電系統中的面型微加工技術製作而成，此系統設計部分主要可以分為表面結構與微致動器兩部分。表面設計部分以微尺度表面結構接觸角的研究為參考並配合微致動器的幾何設計而成，微致動器部分則以相關設計原則及製程設計，並且輔以有限元素分析軟體進行結構行為分析以及使用靜電力理論求解驅動電壓。製程上則使用五層光罩，以25個操作步驟製作。 此微滴操控系統尚於開發階段，無法即時觀測接觸角在微滴操控系統上的變化，但已可對已完成的微滴操控系統元件進行靜態的液滴接觸角量測與微致動器之結構行為探討。此系統經接觸角量測後，實際值與理論值具有15°的差異，並且可使液滴接觸角具有13°的變化量，與理論值16°則相當接近。微致動器之結構經實驗測試後亦具有足夠強度以抵抗變形。

In this thesis, we develop a reversible and bi-stable droplet-controlling system (RBDCS) to control the contact angle. The device is fabricated by MEMS. The method focuses on changing the surface geometry on which the contact angle can vary mechanically. In order to investigate the relationship between the surface roughness and the contact angle, we fabricate micro-hole and micro-pillar surfaces. The measurements of the contact angle show a very good agreement in comparing with those predicted by Cassie’s formula. The development of the RBDCS aims to combine those theories from electrostatic microactuator and contact angle. The device is fabricated in 25 processes with 5 masks by surface micromachining. The design of RBDCS is divided into two parts. One is the design of the surface, which takes advantage of the above-mentioned study of contact angle on micro-patterned substrates, but is restricted to the design of the microactuator. The other is the design of the microactuator which is restricted to both the rules about RBDCS and the manufacture processes. The design is also analyzed by FEM and the applied voltage is solved by the electrostatic theory. The RBDCS is still under development. It cannot be used to measure the real-time contact angle of droplets. Nevertheless we can statically measure the contact angle of droplets on the surface component of the RBDCS and investigate the structural behaviors. The results indicate the difference in contact angle between the theoretical value and the practical value is fifteen, and the microactuator is strong enough to resist mechanical deformation.