Dielectric Layer Interface Research Articles

Numerical investigation on nucleate bubble departure by electrowetting-on-dielectric in battery cooling plates

A thermal management system is necessary to control battery operating temperature in electric vehicles (EV). Typically, the most common way to dissipate heat from the battery pack is to use the cooling plate. The cooling medium in the cooling plate removes the excess heat from the battery pack through boiling heat transfer. This paper proposes an electrowetting-on-dielectric (EWOD) method to enhance the bubble departure in nucleate boiling heat transfer in a cooling plate. In order to investigate the bubble splitting due to the EWOD effect, theoretical models are developed to solve for the electrophoretic force, dielectrophoretic force, and electrostrictive force. The theoretical model coupled a phase field method with an electric conservation model, where the body force acts as an external force due to the electric field. Our preliminary simulation results demonstrated that the EWOD effect can change the apparent contact angle when applied to a certain electric field. The free charge density displays at the dielectric layer interface with water and at the bubble’s interface near the triple contact point. Then two types of simulation case were investigated to apply the voltage in the battery cooling plates. In the first case, a pair of parallel discs are used as the electrodes at the bottom and top of the region. In the second case, the voltage is applied at the top of the nucleate bubble in a rod electrode. The various behavior of bubble dynamics were compared and discussed to indicate the optimized case for enhancing the nucleate bubble departure in the EV battery cooling plates.

Highly stretchable and robust textile-based capacitive mechanical sensor for human motion detection

Mechanically stretchable capacitive sensors are extremely promising for applications in continuous health-monitoring. Typical capacitive sensors, made from polymer and thin metal film supporters, lack interfacial adhesion or chemical bonding and have intrinsically low stretchability. Moreover, the performance of most sensors is critically affected by the conformity mismatch at the electrode and dielectric layer interface during high mechanical deformation. Many mechanical sensors have limited practical applications due to significant hysteresis, low sensitivity, and lack of reproducibility. Herein, we develop a textile-based capacitive mechanical sensor by utilizing titanium carbide-based MXene (Ti3C2Tx) to fabricate conductive textiles and a composite film of polystyrene (PS) fibers and ecoflex silicone as a dielectric layer. Ti3C2Tx showed strong bonding with the fabric owing to its rich surface chemistry, hydrophilicity, and large surface area. The MXene-coated fabric and integration of the composite film make the sensor mechanically stretchable, thus improving its sensitivity, response time, and stability. The sensor showed negligible hysteresis (∼0.2) and demonstrated a high sensitivity of 1.11 when stretched to 100 % elongation and 13.02 kPa−1 when squeezed at a pressureof 200 kPa and excellent cyclic stability (1000 cycles). The sensor was further utilized for the detection of human motion when specificbody movements were performed.

Analytic solution of the radiative transfer equation for the analysis of the efficiency and spatial resolution of a granular X-ray scintillator

In this study, we discussed the efficiency and spatial resolution of a granular X-ray scintillator using an analytic solution of the radiative transfer equation (RTE). A conventional X-ray scintillator employs a large high-density charge-coupled device (CCD) in direct contact with thin phosphor layers to remove imaging optics. To analyze the performance of the scintillator using the CCD, we derive the analytic solution of the RTE in order to calculate light propagation in a double-layer structure without imaging optics. The analytic solution calculates multiple light sources and scatterings in the phosphor layer as well as refraction in the dielectric-layer interface between the phosphor layer and the CCD. For the calculations, we introduced the scattering phase function, including the backward scattering due to micron-sized phosphor particles, and included the geometrical relations of the refraction at the interface. We analyzed the performance of the scintillator with respect to various scintillator design parameters, such as the size of phosphor particles, the thickness of the phosphor layer, and the thickness and refractive index of the dielectric interlayer. We confirmed the analytic calculation by comparing the results with those obtained using a Monte Carlo (MC) simulation tool. The results are in good agreement, with small differences of 1% and 3% on average for the total efficiency and spatial resolution of the scintillator, respectively.

The stability of tin silicon oxide thin-film transistors with different annealing temperatures

The influence of annealing temperature on the electrical properties of tin silicon oxide (TSO) thin-film transistors (TFTs) and the corresponding bias stress stability have been investigated. With increasing annealing temperature, the TSO films present a structure which is closer to crystallization, and it is conducive to the improvement of the mobility of TSO TFTs. Meanwhile, the positive bias stress (PBS) stability of TSO TFTs is ameliorated due to the decreasing traps at the interface of dielectric layer and channel layer. The threshold voltage shifts in opposite direction after being stressed under negative bias stress (NBS), which is due to the competition between electrons captured by defects related to oxygen vacancies in the channel layer and water molecule adsorption on the back channel.

Interfacial Energy Alignment at the ITO/Ultra-Thin Electron Selective Dielectric Layer Interface and Its Effect on the Efficiency of Bulk-Heterojunction Organic Solar Cells.

We have investigated the photovoltaic properties of an inverted bulk heterojunction (BHJ) cell in a device with an indium-tin-oxide (ITO)/electron selective layer (ESL)/P3HT:PCBM active layer/MoOx/Ag multilayered structure. The insertion of only single layer of poly(diallyl-dimethyl-ammonium chloride) (PDDA) cationic polymer film (or poly(ethyleneimine) (PEI) polymeric interfacial dipole layer) and titanium oxide nanosheet (TN) films as an ESL effectively improved cell performance. Abnormal S-shaped curves were observed in the inverted BHJ cells owing to the contact resistance across the ITO/active layer interface and the ITO/PDDA/TN/active layer interface. The series resistance across the ITO/ESL interface in the inverted BHJ cell was successfully reduced using an interfacial layer with a positively charged surface potential with respect to ITO base electrode. The positive dipole in PEI and the electronic charge phenomena at the electrophoretic deposited TN (ED-TN) films on ITO contributed to the reduction of the contact resistance at the electrode interface. The surface potential measurement revealed that the energy alignment by the transfer of electronic charges from the ED-TN to the base electrodes. The insertion of the ESL with a large positive surface potential reduced the potential barrier for the electron injection at ITO/TN interface and it improved the photovoltaic properties of the inverted cell with an ITO/TN/active layer/MoOx/Ag structure.

P‐13: High Performance Ink‐Jet‐Printed TFTs on Solution Wetting Polymer Gate Dielectric Layer

AbstractWe have demonstrated high performance C60 thin‐film transistors by inkjet‐printing technology. C60 inks was jetted onto a polymer or self‐assembled monolayers gate dielectric layer, then vacuum‐dried to form uniform thin films. Inkjet‐printed C60 thin‐film transistors on a polymer gate dielectric layer showed an electron mobility of 1.6 cm2/Vs in operating voltage of 5 V. These results are attributed to high uniformity of vacuum‐dried C60 thin films and low charge trap density between C60 thin films and gate dielectric layer interface.

Effects of Dielectric-Layer Composition on Growth of Self-Formed Ti-Rich Barrier Layers in Cu(1 at%Ti)/Low-k Samples

In our previous studies, Ti atoms in Cu(Ti) alloy films were found to segregate at the film surface and the interface between Cu(Ti) alloy films and dielectric layers after annealing in Ar atmosphere at elevated temperatures. Such self-formed Ti-rich interface layers can act as a diffusion barrier layer. This technique was called ‘‘self-formation of the diffusion barrier,’’ which is attractive for the fabrication of ultra-large scale integrated interconnects. In the present study, we investigated the growth of Ti-rich barrier layers in Cu(Ti)/dielectric-layer samples wit ha low Ti content (1 at%) after annealing in ultra high vacuum (UHV). Ti atoms were found to segregate only to the Cu(Ti)/dielectric-layer interface under annealing in UHV. The microstructures were analyzed by transmission electron microscopy and Rutherford backscattering spectrometry, and correlated with the electrical properties of the Cu(Ti) films. It was concluded that Ti-rich interface layers were formed in all the Cu(Ti)/dielectric-layer samples. The Ti-rich interface layers were identified to consist of TiC or TiSi in addition to Ti oxides. The growth of the Ti-rich interface layers consisting of TiC was faster than those consisting of TiSi. Similarly, the resistivities of Cu(Ti)/dielectric-layer samples in which the TiC formation was observed were quickly reduced and those in which the TiSi formation was observed were gradually reduced. Compositions of the self-formed Ti-rich interface layers were concluded to be determined by the C concentration in the dielectric layers rather than by the enthalpy of formation. The growth of the self-formed Ti-rich interface layers consisting of TiC may be controlled by C diffusion in the Ti-rich interface layer. The composition of the dielectric layers was concluded to play an important role on the growth of the Ti-rich interface layers. [doi:10.2320/matertrans.MAW200809]