改善EWOD 元件於產生奈升級液滴之研究

Abstract

摘要

電濕潤是藉由氣液介面的表面張力影響來液珠，而使液珠移動，其中優點包含，製造過程簡單、可控制定量的液珠、價格較低可取代微制動器與微混合器等。 本研究先簡化質量守恆方程式與動來守□方程式來當作電濕潤的模擬模式，並利用商用軟體CFD-ACE+來模擬液珠在電濕潤的情況。 而電濕潤元件的組成包含，8個0.48mm X 0.5mm的底部電極（金/鉻）、介電層厚度為3000Å的氮化矽、厚度為1000 Å的鐵福龍層和旋塗厚度1000 Å鐵福龍的氧化銦錫玻璃為上電極。 其實驗量測系統包含，微流體元件、微處理器、控制電路、LCD顯示器、4X4小鍵盤、電源供應器和功率放大器。 幾種不同設計的電極形狀會先在模擬情況下互相比較，總共有16組，將常用的正方形電極改成指插電極，並改變流道高度(20 、35 和70 )、指插電極角的數目與指插電極角的寬度，來探討液珠的壓力與平均速度之變化，其中，液珠的內壓與大氣壓的壓差會隨著流道高度的縮小而變大的情形亦被模擬，也於流道高度為35 的模擬，其結果可以發現指插電極所產生的壓差(240Pa~600Pa)都大於正方形電極(192Pa)。 由於驅動壓力大，有助於液珠的移動與分離，進而抽取出奈升液珠，以便於在生醫上的應用。 最後根據模擬的預測，選取3種的電極設計，並利用微機電技術製造元件來證明模擬的趨勢，其中選取的電極分別為正方形電極，指插電極角數目為2323的排列與5656的排列順序。 對於液珠在流道高度為20 的移動情況下分別作平均速度的比對，其中，在實驗上液珠的平均速度對於排列順序為2323的指插電極為11.36 mm/s，而模擬的平均速度為13.291 mm/s。 對於電極排列順序為5656在實驗與模擬的平均速度分別為11.07 mm/s和11.542 mm/s。 而正方形分別為10.49 mm/s和9.614 mm/s。 最後，在實驗上於應用電壓為100V的交流電下，也成功產生出2.9∼8.5nl的奈升液珠。

ABSTRACT

Electrowetting on dielectric (EWOD) moving fluid driven by surface tension offers some advantages, including simplicity of fabrication, control of minute volumes, low cost, substitution for micro-mixers and others. In this study, The EWOD model based on the reduced forms of the mass and momentum conservation equations is adopted to simulate the fluid dynamics of droplet, and its movement is simulated by a commercial software CFD-ACE+. The EWOD device consists of eight 0.5 x 0.48 mm bottom electrodes (Au/Cr), a dielectric layer of 3000 Å nitride, a Teflon layer of 1000 Å and a piece of indium tin oxide (ITO)-coated glass with 1000 Å Teflon as the top electrode. The measurement system consists of the microfluidic device, microprocessor, electric circuits, LCD module, keypad, power supply and power amplifier. Several simulations using different electrode designs were carried out in advance. The interdigitated electrodes were used to replace common-used square ones to investigate the changes of droplet pressure difference. The varying parameters include the channel height (20 , 35 and 70 ), and the number and width of extended rectangle of interdigitated electrodes. Sixteen simulations were carried out in this thesis. Under the same shape of interdigitated electrode, the phenomenon of increasing pressure difference due to decrease of channel height can be simulated. For simulations of 35 -channel height, the ones with interdigitated electrode can generate the larger pressure differences (310 Pa~680 Pa) than that of square electrode (300 Pa). The increment of pressure difference is helpful to move and cut droplets, and further to create a nano-liter droplet, which can be applied in biomedical applications. The following optimal designs of electrode were according to the best simulation results. Then, they were manufactured by MEMS processes and their performances were certified by EWOD device. Furthermore, the predictions of simulations for droplet of moving, in which the channel height was 20 were compared with experimental results for three designs of electrodes including square electrodes and interdigitated electrodes with arrangements of 2323 and 5656 extended rectangles. It is found that the mean velocity of droplet for interdigitated electrode (2323) was 11.36 mm/s, whereas the corresponding prediction was 13.291 mm/s. For 5656 arrangement, the mean experimental and numerical velocities were 11.07 and 11.542 mm/s, respectively. As to square electrode, they were 10.49 and 9.614 mm/s, separately. Finally, the 2.9nl~8.5nl droplets are successfully created at 100 VAc experimentally.