Fabrication and performance study of BST/Teflon nanocomposite thin film for low voltage electrowetting devices

Mirzaei

et al. 2020

Sci Rep

Herein, we report the electrowetting-on-dielectric (eWoD) characteristics of Zno nanorods (nRs) prepared via the hydrothermal method with different initial Zn 2+ concentrations (0.03, 0.07, and 0.1 M). Diameter of the resultant ZnO NRs were 50, 70 and 85 nm, respectively. Contact angle (CA) measurements showed that the Teflon-coated ZnO NRs with diameters of 85 nm prepared from the 0.1 M solution had the highest CA (137°). During the EWOD studies, on the application of a voltage of 250 V, the water CA decreased to 78°, which demonstrates the potential application of this material in EWOD electronics. Furthermore, we explained the relationship between the applied voltage and CA based on the substrate nanostructures and our newly developed NR-on-film wetting model. In addition, we further validated our model by introducing the homo-composite dielectric structure, which is a composite of thin layered ZnO/Teflon and nano-roded ZnO/Teflon. Electrowetting (EW) is defined as the decrease in contact angle (CA) when a sufficiently large driving voltage is applied to the interface of solid/liquid. In direct EW, a voltage is used between a liquid and an electrode. Charges and dipoles redistribute at the interface between the liquid and solid, which changes the surface tension, leading to a decrease in the CA of the liquid droplets. However, direct EW can electrolyze the liquid before any change in the water contact angle (WCA), which limits its application 1. To overcome this issue, electrowetting-on-dielectric (EWOD) can be used. In this technique, a dielectric material is sandwiched between the liquid of interest and the underlying electrode (Fig. 1). EWOD is very effective for significantly changing the CA, because the dielectric layer effectively blocks the process of charge transfer at the liquid/electrode interface, which eliminates unwanted electrolysis 2. Therefore, EWOD is used to facilitate EW on solids, for practical applications. Although EWOD devices permit a large CA change, they generally need a high driving voltage. The dielectric layer blocks the transfer of electrons, while sustaining high voltage at the interface, which results in an electric double layer (EDL) formation in the presence of the applied voltage. When a hydrophobic dielectric material is used, the large initial WCA can result in a large change in the WCA 3. The advantages of EWOD include low power consumption, large WCA change, and fast response. It is therefore promising for diverse applications, including lab-on-chips 4 , liquid lenses 5 , optical waveguides 6 , electronic displays 7, 8 , microprism arrays 9 , and smart microbatteries 10. SiO 2 is a highly popular material for EWOD studies 11 because of its excellent compatibility with the microelectronic industry. In our previous study 12 , we investigated the EWOD properties of electrospray-deposited SiO 2 layers and found that the WCA of the optimal SiO 2 layer underwent a hydrophobic-to-hydrophilic transition under a driving voltage of 150 V in air. A novel EWOD mechanism, wherein the ...

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Electrowetting-on-dielectric characteristics of ZnO nanorods

Mirzaei

et al. 2020

Sci Rep

“…Recently, the fabrication of electrowetting devices driven by low voltages has received considerable attention. There have been many reports regarding the use of inorganic materials having high dielectric constants, but substances such as barium strontium titanate (BST) [4] and bismuth zinc niobate…”

Section: Introductionmentioning

confidence: 99%

The Effect of the Terminal Functional Groups on Fluoropolymer on Electrowetting Device Performance

Oishi

Araki²,

Goto

et al. 2019

Technologies

Electrowetting on dielectric (EWOD) devices were fabricated using two hydrophobic organic fluoropolymers, comprising CYTOP (a product name) having different chemical structures only at the terminal functional groups. These devices were subsequently characterized by applying a range of direct current (DC) voltages. The data demonstrated that the EWOD performance was dramatically improved upon incorporating a CYTOP polymer having highly polar terminal functional groups, as compared to a polymer having terminal groups with lower polarity. The new finding about the positive effect of highly polar terminal functional groups on the enhancement of EWOD was exhibited through various careful experiments, changing only the quantitative amount of polar terminal functional groups while keeping other factors constant (thickness, substrate, etc.).

“…A safe design for multilayer insulator should be such that the electric field is distributed uniformly. But, many characteristics, like leakage current [29], contact angle change [23] and scanning Kelvin probe [30], are measured to monitor and analyse degradation in the EWOD system. However, in [23,29,30], the nature of the failure modes for single-layer insulator and multilayer insulator was not clearly discussed.…”

Section: Introductionmentioning

confidence: 99%

Failure modes analysis of electrofluidic display under thermal ageing

et al. 2018

Dielectric failure as well as optical switching failure in electrofluidic display (EFD) are still a bottleneck for sufficient device lifetime. In this study, a dielectric redundancy-designed multilayer insulator of ParyleneC/AF1600X was applied in an EFD device. The reliability performance was systematically studied by tracking the applied voltage-dependent leakage current and capacitance changes (I–V and C–V curves) with thermal ageing time. The multilayer insulator shows a more stable performance in leakage current compared to a single-layer insulator. The failure modes during operation underlying the single-layer and the multilayer dielectric appear to be different as exemplified by microscopic images. The single-layer AFX shows significant detachment. In addition, by quantitatively analysing the C–V curves with ageing time, we find that for the single AFX device, the dominant failure mode is ‘no-opening’ of the pixels. For the multilayer device, the dominant failure mode is ‘no-closing’ of the pixels. This study provides tools for distinguishing the basic failure modes of an EFD device and demonstrates a quantitative method for evaluating the reliability performance of the device under thermal ageing.