微泵元件研究設計：薄膜致動器及無閥門微泵腔壁結構

Abstract

微機電系統和傳統機械加工的不同，除了在於元件尺寸範圍的明顯差異之外，在元 件的製造方面是利用半導體相關製程技術結合機械結構設計理念而成。本論文研究目的 在於研製出可應用在微泵元件的熱動式薄膜致動器及高深寬比無閥門微泵腔壁結構。 首先，薄膜致動器原理是採用不同材料（例如：鋁，二氧化矽）之間熱膨脹係數差 異大及楊氏模數小的特性，在加溫的過程中樑結構因彎曲形變輸出大位移及力量進而推 動薄膜作用。薄膜致動器的結構是由四層薄膜，包括二氧化矽（薄膜層），多晶矽（加 熱電阻層），二氧化矽及鋁（複合樑），共經過四道光罩蝕刻而成。利用有限元素軟體 ANSYS 5.1分析單一樑及薄膜整體結構撓曲量及應力分佈和溫度的關係，除了做為實際 致動輸入能量的參考和比較之外，我們亦分析設計並製造出不同複合樑形狀結構，經過 測試致動器薄膜面積1000×1000μm2在輸入功率6.98W時最大薄膜撓曲量為117μm，當 致動頻率最大在30至40赫時，可保持5至10μm的撓曲量。 另外在微泵腔壁結構部份，傳統的微泵腔壁結構是由兩個被動閥門及連接於腔室的 薄膜致動器所組成，經由薄膜的振動造成腔室內體積的改變使液體通過入口閥流向出口 閥。閥門經常開關必定會引起一些破壞，如閥門開關前後所受的高 壓力差、磨耗、疲勞等。此外，這類閥門結構更需要較為複雜的製程配合。因此我們改 良成新式的微小擴散╱噴射型導流道取代舊有泵腔室的開關閥門，設計並製造出無閥門 微泵腔壁結構，經過入口部份的圓角修改及出口部份突起的長條結構設計，由理論可證 實在每一個進排水循環中，此新設計可以達到極大淨排水量的效果。 因應高深寬比無閥門微泵腔室結構(i.e. 100 μm∼300 μm)可容納較大的體積改 變量的需求，我們可以利用一般UV或X光LIGA製程製作此種高深寬比泵腔室結構。在此 我們使用的光阻劑AZ-4620（使用UV光源），經過多重塗布步驟，使光阻劑鋪在晶片上 的厚度可控制達到22μm，全部泵腔壁及導流道微結構只需要經過一道曝光顯影即可完 成。此外，將光阻厚膜結構經過電鍍及背面深腐蝕等步驟，我們亦製造完成X光光罩。 此光景利用在LIGA製程中，便可製造出高深寬比達100μm至300μm的微泵腔室結構，相 較於國外X光光罩的複雜製作方式，我們可自行以較容易且低成本的半導體相關製程技 術完成此光罩製作。

A micro membrane vibrator consisting of four bimorph cantilever beams and a membrane is designed, fabricated, and tested here. In order to increase Z-axis displacement, four kinds of the bimorph cantilever beams attached to the membrane are designed. Due to the discrepancy of thermal expansion coefficients between different layers, the membrane moves with temperature change. The four-layer structure including SiO2-polysilicon-insulated SiO2-aluminum is fabricated with four masks. Additionally, backside etching is performed to fabricate membrane structures. The numerical finite element program ANSYS 51 is used to simulate the behavior of different designed membrane vibrators. The maximum Z-axis displacement of the 1000μm×1000μm micro membrane vibrator is 93μm at temperature 200℃ in simulation. According to experiment results, the maximum Z-axis displacement is 117μm when input power is 6.98 W. The maximum working frequency is 30∼40 Hz with the amplitude 5∼10μm. Fabrications are improved continuously in order to have better performance. Testing results are presented to compare with the finite element analysis. The conventional chamber structure of a micropump consists of two passive check valves connected to an oscillating diaphragm which creates a chamber volume change. Because the movable check valves may cause many problems such as a high pressure drop across the valves, wear, fatigue of the movable parts, and more complicated fabrication processes, thus in the chamber structures of valveless micropump, we design a new version of the micromachined diffuser/nozzle elements which are used to direct flow into and out of pump chambers. By referring to the previous research, we design two new parts including rounded inlet and reentrant outlet. By means of this special design on shapes of the flow channels, a high net volume flow can be predicted to reach in a pumping cycle. The thicker chamber structures (i.e. 100μm∼300μm) are possible to induce larger volume stroke. Exposure sources of X-ray and UV light are adopted to fabricate the high-aspect-ratio pump chamber structures. In order to fabricate the thicker structures, the different photoresists including PMMA (the X-ray photoresist) and AZ-4620 (the UV photoresist) are utilized. By in-situ polymerization casting process and the multiple spinning method, these photoresists can be coated thickly between 20μm and 300μm. Through UV and X-ray LIGA techniques, the whole micropump chamber structures including the inlet/outlet flow microchannels can be fabricated with only one mask step.