A Study of Dip-Coatable, High-Capacitance Ion Gel Dielectrics for 3D EWOD Device Fabrication.

Carlos Clement,Dongyue Jiang,Si Thio,Sung-Yong Park

doi:10.3390/ma10010041

Abstract

We present a dip-coatable, high-capacitance ion gel dielectric for scalable fabrication of three-dimensional (3D) electrowetting-on-dielectric (EWOD) devices such as an n × n liquid prism array. Due to the formation of a nanometer-thick electric double layer (EDL) capacitor, an ion gel dielectric offers two to three orders higher specific capacitance (c ≈ 10 μF/cm2) than that of conventional dielectrics such as SiO2. However, the previous spin-coating method used for gel layer deposition poses several issues for 3D EWOD device fabrication, particularly when assembling multiple modules. Not only does the spin-coating process require multiple repetitions per module, but the ion gel layer also comes in risks of damage or contamination due to handling errors caused during assembly. In addition, it was observed that the chemical formulation previously used for the spin-coating method causes the surface defects on the dip-coated gel layers and thus leads to poor EWOD performance. In this paper, we alternatively propose a dip-coating method with modified gel solutions to obtain defect-free, functional ion gel layers without the issues arising from the spin-coating method for 3D device fabrication. A dip-coating approach offers a single-step coating solution with the benefits of simplicity, scalability, and high throughput for deposition of high-capacitance gel layers on non-planar EWOD devices. An ion gel solution was prepared by combining the [EMIM][TFSI] ionic liquid and the [P(VDF-HFP)] copolymer at various wt % ratios in acetone solvent. Experimental studies were conducted to fully understand the effects of chemical composition ratios in the gel solution and how varying thicknesses of ion gel and Teflon layers affects EWOD performance. The effectiveness and potentiality of dip-coatable gel layers for 3D EWOD devices have been demonstrated through fabricating 5 × 1 arrayed liquid prisms using a single-step dip-coating method. Each prism module has been individually controlled to achieve spatial beam steering without the need for bulky mechanical moving parts.

Highlights

We present a dip-coatable, high-capacitance ion gel dielectric for scalable fabrication of three-dimensional (3D) electrowetting-on-dielectric (EWOD) devices such as an n × n liquid prism array
For static EWOD studies, indium tin oxide (ITO)-coated substrates were dip-coated at various were mixed at different weight ratios and further diluted in acetone to vary the solution viscosity, withdrawal speeds ranging from 100 to 800 mm/min, after which the samples were left to dry at room which is one of the variables to determine the thicknesses of the dip-coated gel layer [29]
Since an ion gel layer is fabricated by combining an ionic liquid (IL) and a structuring copolymer (CP), itanpresents features of both constituents suchanasionic the high capacitance by copolymer the IL

Summary

Introduction

We present a dip-coatable, high-capacitance ion gel dielectric for scalable fabrication of three-dimensional (3D) electrowetting-on-dielectric (EWOD) devices such as an n × n liquid prism array. The effectiveness and potentiality of dip-coatable gel layers for 3D EWOD devices have been demonstrated through fabricating 5 × 1 arrayed liquid prisms using a single-step dip-coating method. For many practical EWOD applications, the use of high-capacitance dielectrics is critical to induce large surface tension modulation at a given voltage input. To meet this requirement, various dielectrics such as silicon dioxide (SiO2 ), aluminum oxide (Al2 O3 ), and tantalum pentoxide (Ta2 O5 ) have been used [7,8,9,10]. These dielectric materials are fabricated by conventional integrated circuit (IC)

Methods

Results

Conclusion