低電壓電潤濕光學折光器之研究

Investigation of low operating voltage for electrowetting optical deflector

陳秀香(Hsiu-Hsiang Chen)

指導教授 ： 傅建中

國立清華大學/工學院/奈米工程與微系統研究所/博士(2011年)

https://doi.org/10.6843/NTHU.2011.00649

摘要

隨著光學和顯示技術的發展，可調變光學偏折器的需求正在增加。可調變光學偏折器在某些應用領域是必要的，例如: 光的方向控制、照明系統、汽車頭燈的掃描、條碼閱讀器，頭戴式顯示器和二維/三維顯示器。此外，可調變光學偏折器可應用在相機，使得在某特定的角度觀看、即時追蹤物體或補償手部的移動。傳統的光學偏折器需要使用到馬達而且體積過大。由於電濕潤光學偏折器具有低功耗（〜毫瓦），加上採用微機電系統（MEMS）技術，元件可以批量複製和減少尺寸大小。未來的光學元件需要與商業電子產品相容。然而目前的電濕潤元件的操作電壓約在數十伏特左右。因此發展低的操作電壓是未來的趨勢。
本研究的目的是在探討不同的方法以實現低的操作電壓。首先，測試兩種含氟聚合物（Teflon®AF1600和Cytop®CTL-809M），用來確認厚度的影響和可潤濕性。第二，測試三種相同厚度的不同介電層（SiO2、Si3N4和Ta2O5），用來確認介電常數的影響。第三，測試三種不同的介面活性劑（sodium dodecyl sulfate (SDS)、Triton X100和Triton X15），用來確認界面表面張力的作用。第四，測試退火對高介電層（Ta2O5和Nb2O5）之介電常數的影響。
在這篇論文中，提出一個電濕潤光學偏折器，用來檢測操作電壓和液體界面傾斜。結果顯示，分別經由高溫爐管在400℃和700℃氧氣氣氛下退火，可得到高介電常數的Nb2O5（25.5）和Ta2O5（18.8）。在此基礎上的結果，測試電濕潤光學偏折器的效能，並在此元件內填充水（含1% sodium dodecyl sulfate (SDS))和油(dodecane）。我們展示了在dodecane/water/Cytop®/Ta2O5 和dodecane/water/Cytop®/Nb2O5系統，水的液面傾斜變化高達70℃，而操作電壓只需11V和9 V。最後，展示了光束通過電濕潤光學偏折器的半月界面與切換頂點角度約±20o。
玻璃基板是經常被應用在微流體通道製作，但它很難被乾刻蝕。在本研究中，我們提出最近在石英基板上製作微結構的研究。三種不同的蝕刻氣體混合物，即SF6/Ar、CF4/Ar和CHF3/Ar，與製程參數，如氬氣流量比、偏壓功率、ICP功率、腔室氣體壓力和氣體總流量作系統性研究。使用SU8光阻層作蝕刻遮罩層以取代金屬遮罩層以避免污染。我們發現，使用CF4/Ar和CHF3/Ar氣體混合物作為乾蝕刻介質時，SU8是一個很好的蝕刻遮罩層。並達到製作深度55μm以及幾乎垂直側壁（86o）的微流道通道。此研究所得到的製程數據，可提供將來研究石英乾式蝕刻的基本參考。

關鍵字

電濕潤 ； 低電壓 ； 光學折光器 ； 介電常數 ； 活性離子蝕刻 ； 石英 ； 微流道 ； SU8光阻

並列摘要

As optics and displays technologies advance, the demand for variable optical deflector is increasing. Variable optical deflector is essential for such applications as beam steering, lighting systems, scanning head-light of cars, bar code readers, heads-up displays and two-dimensional/three-dimensional (2D/3D) display. Moreover, the variable optical deflector could be applied in the cameras to make looking under certain angle, follow objects instantly or compensate for hand moving. The traditional optical deflectors need to use the motor and the volume is too large. As the electrowetting optical deflector (EOD) is low power consumption (~ mW), together with using micro-electro-mechanical systems (MEMS) technology, the devices can be bulk replicating and size reducing. Future optical components need to be compatible with commercial electronics. However, the operating voltage for current electrowetting devices is about tens of volts. Therefore, the development of low operating voltage is the future trend.
The goal of this study was to explore various approaches to achieving a low operating voltage. First, two kinds of fluoropolymers (Teflon®AF1600 and Cytop®CTL-809M) were utilized to confirm the thickness effect and wettability. Second, three different dielectric layers (SiO2, Si3N4, and Ta2O5) with the same thickness were tested to confirm the dielectric constant effect. Third, three different surfactants (sodium dodecyl sulfate (SDS), Triton X100, and Triton X15) were used to confirm the interfacial surface tension effect. Finally, the high dielectric layers (Ta2O5 and Nb2O5) were employed to test the annealing effect on the dielectric constant.
In this dissertation, an EOD was proposed to test the operating voltage and liquid interface tilting. The results show that the high dielectric constants for Nb2O5 (25.5) and Ta2O5 (18.8) were achieved with annealing at 400℃ and 700℃ O2 ambiance in a conventional furnace, respectively. Based on this result, an EOD device filled with the water (containing 1% sodium dodecyl sulfate (SDS)) and dodecane was fabricated and tested. We demonstrate that the contact angle of water can change as much as 70° in dodecane/water/Cytop®/Ta2O5 system (with 11V) and dodecane/water/Cytop®/Nb2O5 system (with 9 V). Finally, the switchable apex angles of ~ ± 20° and deflection of a beam passing through the meniscus of the EOD are presented.
Glass substrate is often applied in the microfluidic channels fabrication; however, it is hard to dry etching. In this research, we present our recent investigations on fabricating the microstructures on the quartz substrate. Three different etching gas mixtures, namely SF6/Ar, CF4/Ar and CHF3/Ar, with process parameters such as Ar flow ratio, bias power, ICP power, chamber gas pressure and gas total flow rate have been studied systematically. The SU-8 layer was applied as the mask layer instead of metal to avoid contamination. We found that the SU-8 is a good alternative mask material when the CF4/Ar and CHF3/Ar gas mixtures are selected as the dry etching media. Micro channel with a depth of 55 μm is fabricated, and a nearly vertical side-wall profile (86o) is achieved. The processed data gathered in this study may offer a good basic reference on the quartz dry etching for future investigation.

並列關鍵字

electrowetting ； low voltage ； optical deflector ； dielectric constant ； reactive ion etching ； quartz ； microfluidic channel ； SU8 photoresist

參考文獻

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[3] Quilliet C and Berge B 2001 Electrowetting: a recent outbreak Current Opinion in Colloid & Interface Science 6 34-9.

[4] Mugele F and Baret J 2005 Electrowetting: from basics to applications J. Phys.: Condens. Matter. 17 R705-74.

[6] Heikenfeld J 2008 Flat Electrowetting Optics and Displays Proc. SPIE Photonics West MOEMS 6887-6904