Digital Microfluidic Device for Hotspot Cooling in ICS Using Electrowetting on Dielectric

We report the development of a microfluidic device that is the first of its kind to generate uniform arrays of individually addressable cell seeded calcium alginate gels for 3D cell culture using electrowetting on dielectric (EWOD) digital microfluidics (DMF). This is combined with EWOD DMF's multiplexing abilities to demonstrate how a single device is capable of forming cell seeded alginate hydrogels, generating different concentrations of chemicals and delivering these generated chemical concentrations to different alginate gels to observe the effect of chemicals on 3D cultured cells. This lays the foundation for a more efficient and versatile 3D cell culture and chemical screening platform.

Liquid-liquid extraction techniques are one of the major tools in chemical engineering, analytical chemistry, and biology, especially in a system where two immiscible liquids have an interface solutes exchange between the two liquid phases along the interface up to a point where the concentration ratios in the two liquids reach their equilibrium values [1]. Solutes including nucleic acids and proteins of interests can be extracted from one liquid phase to the other immiscible liquid phase as a preparation step for many analytical processes. There are several advantages in miniaturizing the liquid-liquid extraction methods to on-chip level extraction. Usual advantages of miniaturization are the reduction in the sample size and portability. In addition, transport phenomena is faster in Micro-systems than in ordinary size systems, and therefore, one may expect that liquid-liquid extraction takes less time to achieve in miniaturized devices. It is due to shorter diffusion time in micro scale as well as high surface to volume ratio of Microsystems. Electrowetting on dielectric (EWOD) digital microfluidics is an efficient platform to process droplet based analytical processes [2]. Nanoliter (nL) or smaller volume of aqueous liquid droplets can be generated and transported on a chip by EWOD process. In addition to the high surface to volume ratio, high chemical potential can be expected in droplet based extraction when the droplets are in motion. In this paper, we propose to use room temperature ionic liquid (RTIL) as a second liquid phase for extraction, which forms immiscible interface with aqueous solutions. Properties of RTIL can be tailored by choice of cation, anion and substituents. RTIL has been investigated as replacements for the organic solvents and various “task-specific” ionic liquid are being developed which exhibit many attractive properties such as very low vapor pressure, high thermal stability [3]. We recently published EWOD properties of various RTILs toward microfluidic applications [4]. To demonstrate liquid-liquid micro extraction on chip, we fabricated and tested EWOD digital microfluidic devices. Fig. 1 shows (a) top and (b) cross sectional views of EWOD device. Two model extraction systems were tested. One is organic dye extracted from RTIL (1-butyl-3-methylimidazolium bis(trifluoromethanesulfonylimide or BMIMNTf2) to water and the other is iodine (I2) extracted from water to BMIMNTf2. The later model experiment is demonstrated in Fig. 2. Droplets of aqueous solution and BMIMNTf2 solution were generated on chip reservoir then transported for extraction and separated by EWOD actuation. When an aqueous solution and BMIMNTf2 solution join together, they created an interface, since water and BMIMNTf2 are immiscible. Extraction of I2 was done along the interface. After successful extraction, two immiscible liquid phases were separated by EWOD actuation and formed two separate droplets. From the result shown in Fig 2 (g), it is expected that extraction performance at the interface of moving droplet would be enhanced compared to the stationary droplet, because a moving interface prevent the chemical equilibrium, thus more chemical extraction potential can be provided with a moving interface than at a stationary interface. This demonstration is the first step toward total analysis system. The presented result opens the way to on-chip micro extraction, which will be readily integrated with other sample preparation microfluidic components and detection components. Currently, micro extraction systems for larger molecules such as nucleic acids, proteins and biological cells are being developed for further analytical applications.

In this work, circular economy was investigated for commercial indium tin oxide (ITO) thin films deposited on glass substrates obtained from degraded organic light-emitting diodes (OLED). These devices were assembled and polarized at laboratory in a previous work. For each substrate, with geometry 2.5 × 2.5 cm, four OLEDs with active area of 3 × 3 mm were set up. These OLED devices were assembled with ITO as the electrode anode and successive depositions of other materials (layer-by-layer), to form the complete structure. To obtain the recovered ITO, all layers were removed from the samples containing the OLEDs previously mounted, remaining only the ITO thin films, that were cleaned with commercial product together with the received ITO/glass samples. Both samples were compared using some techniques, such as: colorimetry, electrical resistance, and Raman spectroscopy. A methodology with light-emitting diode (LED) device polarized emitting light crossing the ITO thin films was used, and the luminance with chromaticity coordinates was obtained, revealing the good transparency of the thin films. Electrical resistance of recovered ITO revealed five higher orders of magnitude in comparison to the one of received ITO. This fact can be tributed to a poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) layer, causing corrosion of the ITO thin films during the assembly of OLEDs or loss of the field lines created during the electrical measurements by probes of four-point probe. Raman spectroscopy did not show satisfactory results in the chemical composition analyses of the samples, but it indicated good cleaning process of the samples before the analyses.

【This paper has relatively high technical standard and experimental skill. The fabrication of TCO film with high transparency, low resistance and low chromaticity require exact control of several competing factors. This paper has resolved these problems reasonably well, thus recommended for publication. Indium tin oxide(ITO) thin films were by D.C. magnetron roll-to-roll sputter system utilizing ITO and $SiO_2$ targets of ITO and $SiO_2$ . In this experiment, the effect of D.C. power, winding speed, and oxygen flow rate on electrical and optical properties of ITO thin films were investigated from the view point of sheet resistance, transmittance, and chromaticity( $b^*$ ). The deposition of $SiO_2$ was performed with RF power of 400W, Ar gas of 50 sccm and the deposition of ITO, DC power of 600W, Ar gas of 50 sccm, $O^2$ gas of 0.2 sccm, and winding speed of 0.56m/min. High quality ITO thin films without $SiO_2$ layer had chromaticity of 2.87, sheet resistivity of 400 ohm/square, and transmittance of 88% and $SiO_2$ -doped ITO Thin film with chromaticity of 2.01, sheet resistivity of 709 ohm/square, and transmittance of more than 90% were obtained. As a result, $SiO_2$ was coated on PET before deposition of ITO, their chromaticity( $b^*$ ) and transmittance were better than previous results of ITO films. These results show that coating of $SiO_2$ induced arising chromaticity( $b^*$ ) and transmittance. If the thickness of $SiO_2$ is controlled, sheet resistance value of ITO film will be expected to be better for touch screen. A four point probe and spectrophotometer are used to investigate the properties of ITO thin films.】

The transparent flexible plastic antenna was fabricated. Indium tin oxide (ITO) thin film was deposited on flexible plastic substrate at room temperature by radio frequency (RF) magnetron sputtering with a new technique, called gas-timing. By using the X-ray diffraction (XRD) measurement of the ITO thin film grown by this technique, a cubic nanocrystalline structure with predominant (222) orientation was observed. The technique of gas-timing we used, the ITO thin film on flexible substrate was achieved with high transmittance in visible region of 90% and low resistivity. The performance of the new film antenna was studied experimentally with its return loss and radiation patterns.

This paper reports the synthesis of indium tin oxide (ITO) nanoparticles and the effect of annealing temperature on the microstructural and electrical properties of ITO thin films. The synthesized ITO (90:10) nanoparticles are deposited at 29°C using E beam evaporation to form ITO thin films and annealed at 200, 400 and 500°C. The microstructural properties are investigated using XRD and AFM , and electrical properties such as temperature coefficient of resistance (TCR) and gauge factor are investigated using four-probe and four-point beam bending method, respectively. The investigations results reveal an increase in grain size, carrier concentration and gauge factor with an increase in the annealing temperature. The absolute value of TCR is constant at high temperatures for the film annealed at 500°C. The ITO thin film annealed at 500°C shows improved morphological and electrical properties and can be used for the development of sensors operating at high temperature.

This paper reviews the principles, operations, and applications of bubble-based electrowetting-on-dielectric (EWOD). EWOD has proved to be an efficient tool in digital microfluidics that employs discrete droplets, and various applications that use the principles of EWOD have been developed from lab-on-a-chip to optical systems. Similar to its use with droplets, EWOD can also be applied to gaseous bubbles. This review begins with a discussion of the principles of EWOD for a bubble on an electrode covered with a hydrophobic dielectric layer. It then addresses EWOD actuation and the transportation of a bubble in an aqueous medium, along with a physical explanation of bubble motion. The operation of EWOD is then extended to the on-chip creation/elimination and splitting of bubbles. In particular, micro-mixers and pumps are discussed as potential applications of these operations. Unlike droplets, bubbles can be easily oscillated by external excitation, which provides additional functionalities. By integrating EWOD with external excitation, a number of new advanced applications are introduced, including the capture/separation of particles and the propulsion of objects. In these advanced operations, cavitational microstreaming flows and acoustic radiation forces are mainly responsible for the physical mechanisms. This paper also discusses these advanced operations along with their underlying physics. It is expected that in addition to bubble oscillation, other bubble actuation modes will create new functionalities and new potential applications.

An indium tin oxide (ITO) thin film based saturable absorber (SA) is proposed and demonstrated for the operation of Q-switched pulse within the C-band region. The ITO was deposited through DC magnetron sputtering method. The thickness of ITO was 86.40 nm and it was measured using F20 Filmetrics. The deposited fiber ferrule was incorporated in an erbium-doped fiber (EDF) laser cavity for generating a stable Q-switching pulse. The generated output pulses displayed a repetition rate that ranged between 16.74 kHz and 38.03 kHz. The shortest pulse width retrieved was 5.78 µs at the maximum pump power of 165.5mW, while the maximum pulse energy recorded was 12.30 nJ. These results show that ITO has the potential to be used for pulsed laser applications.

Low-molecular weight polydimethylsiloxane, a versatile performance enhancer for the solution processed indium tin oxide transparent electrode

ITO thin films used in PTCDA/Si detector should be made at low temperature for low temperature resistance of substrate. ITO thin films were deposited at low temperature by RF magnetron sputtering. Properties of ITO thin films such as conductivity and transmission measured by 4 point probe and UV spectral photometry respectively. The results show that the sputtering pressure is an important parameter in the deposition of indium tin oxide（ITO） thin films, which affects the properties of ITO films. The optimized parameter for preparation of ITO thin films at low temperature are sputtering pressure 0.45 Pa, sputtering power 45W. Meanwhile, the post-annealing is not necessary.

This paper describes highly efficient in-droplet particle concentrations/separations (over 91% in efficiency), where magnetic particles are concentrated/separated within a droplet by applying a magnetic field and a subsequent EWOD (electro wetting-on-dielectric) actuation physically splits a magnetic particle-rich region into an individual droplet. This in-droplet method will provide a new functionality of separation/concentration for digital (droplet-based) microfluidics, possibly allowing use of many magnetic-particles-based bio assays in digital microfluidics.

Indium tin oxide (In-Sn-O, ITO) system is typical widely used as transparent electrodes for display devices, transparent coatings for solar energy heat mirrors and window films in p-n heterojunction solar cells because of their’s unique properties of a high visible transparency, good electrical conductivity, and excellent adhesion to the substrate, stable chemical property and easy patterning ability. In this paper, preparation and characterization of Indium tin oxide (ITO) thin films were studied by deposited dip coating process onto glass substrate. The mixing of various molar ratio of indium chloride (InCl3) and tin chloride (SnCl2.2H2O), (In:Sn mole ratio , 9:1, 7:3, 1:1), in acetylacetone were used as the starting solution. The suitable In:Sn ratio for one stoichiometry indium tin oxide (In2Sn2O7) compound were studied via hydrolysis process of mixed solution. The result of thermal gravimetric analysis were used to supported and corrected of calcining temperature. The precipitated powders were calcined at 500 0C and 600 0C. The result of XRD spectrum indicated that the calcined 9:1 powders at 6000C was show the highest stoichiometry of indium tin oxide (In2Sn2O7) compound with a polycrystalline cubic structure. The ITO thin films were studied by deposited dip coating process onto glass substrate with 20 layers at 600 0C for 1 hour. The optical properties, band gap energy and microstructure of ITO thin films were investigated by UV-vis spectrophotometer and Scaning Electron Microscope (SEM) respectively. The result of SEM was shown highly homogeneous surface and average grain size 20 nm with 95% transmittance which corresponding to XRD results. The calculated energy gap of ITO film was 3.40 eV.

Thickness dependence of structural and optical properties of indium tin oxide nanofiber thin films prepared by electron beam evaporation onto quartz substrates

A route to increase the efficiency of thin film solar cells is improving the light-trapping capacity by texturing the top Transparent Conductive Oxide (TCO) so that the sunlight reaching the solar absorber scatters into multiple directions. In this study, Indium Tin Oxide (ITO) thin films are treated by infrared sub-picosecond Direct Laser Interference Patterning (DLIP) to modify the surface topography. Surface analysis by scanning electron microscopy and confocal microscopy reveals the presence of periodic microchannels with a spatial period of 5 µm and an average height between 15 and 450 nm decorated with Laser-Induced Periodic Surface Structures (LIPSS) in the direction parallel to the microchannels. A relative increase in the average total and diffuse optical transmittances up to 10.7% and 1900%, respectively, was obtained in the 400–1000 nm spectral range as an outcome of the interaction of white light with the generated micro- and nanostructures. The estimation of Haacke’s figure of merit suggests that the surface modification of ITO with fluence levels near the ablation threshold might enhance the performance of solar cells that employ ITO as a front electrode.

Indium tin oxide (ITO) thin films were deposited by radio frequency (RF) magnetron sputtering onto glass substrates. The transparent and conducting ITO thin films were obtained on externally unheated glass substrate, without any post-heat treatment, and by varying the deposition process parameters such as the working pressure and the RF Power. The effect of the variation of the above deposition parameters on the structural, surface morphology, electrical, and optical properties of the thin films have been studied. A minimum resistivity of 2.36 × 10−4 Ω cm and 80% transmittance with a figure of merit 37.2 × 10−3 Ω−1 is achieved for the thin films grown on externally unheated substrate with 75 W RF power and 0.5 mTorr working pressure.