Coplanar Electrode Structure Research Articles

Experimental and theoretical investigation of frequency-dependent and conductivity-dependent threshold actuation voltage of electrowetting-on-dielectric and liquid dielectrophoresis on a one-plate device

Actuation voltage is critical in microfluidic manipulation using electrowetting-on-dielectric (EWOD) and liquid dielectrophoresis (LDEP). Compared to parallel electrode devices, the liquid manipulation of coplanar electrodes requires a higher actuation voltage due to its structure. This study derives an equation related to the threshold actuation voltage and all important parameters (droplet volume, fluid permittivity, fluid conductivity, applied frequency, surface tension, thickness and permittivity of dielectric materials, and electrode width). The equation is also used to analyze and explain frequency-dependent, and conductivity-dependent threshold actuation voltage on a coplanar electrode structure in the experiment. Three water-based solutions with different electrical conductivities (3 *10−4-10−2 S/m) were tested for the threshold voltage of liquid actuation using a wide range of signal frequencies (0.1–100 kHz). The theoretical and experimental data reveal that our model can successfully explain the effects of conductivity and frequency on liquid actuation. In addition, the effects of EWOD and LDEP on the threshold actuation voltage of microfluidics on a one-plate device are also discussed with the model and experiment. This study covers a common range for important parameters (applied frequency, and fluid conductivity) related to the actuation voltage in microfluidic actuation on a coplanar electrode structure. The theory and experimental data can be used to predict the applied voltage of EWOD and LDEP for a broad range of buffers and organic solvents.

Nanoscale Channel Gate-Tunable Diodes Obtained by Asymmetric Contact and Adhesion Lithography on Fluoropolymers.

Adhesion lithography offers to fabrication of coplanar asymmetric nanogap electrodes with a low-cost and facile process. In this study, a gate-tunable diode with coplanar asymmetric nanogap is fabricated using adhesion lithography. A fluoropolymer material is introduced to the adhesion lithography process to ensure a manufacturing patterning process yield as high as 96.7%. The asymmetric electrodes formed a built-in potential, leading to rectifying behavior. The coplanar electrode structure allowed the use of a gate electrode in vertical contact with the channel, resulting in gate-tunable diode characteristics. The nanoscale channel induced a high current density (3.38×10-7 A∙cm-1 ), providing a high rectification ratio (1.67×105 A∙A-1 ). This rectifier diode is confirmed to operate with pulsed input signals and suggests the gate-tunability of nanogap diodes.

Floating-Electrode-Enabled Impedance Cytometry for Single-Cell 3D Localization

As a label-free, low-cost, and noninvasive tool, impedance measurement has been widely used in single-cell characterization analysis. However, due to the tiny volume of cells, the uncertainty of the spatial position in the microchannel will bring measurement errors in single-cell electrical parameters. To overcome the issue, we designed a novel microdevice configured with a coplanar differential electrode structure to accurately resolve the spatial position of single cells without constraining techniques such as additional sheath fluids or narrow microchannels. The device precisely localizes single cells by measuring the induced current generated by the combined action of the floating electrode and the differential electrodes when single cells flow through the electrode-sensing area. The device was experimentally validated by measuring 6 μm yeast cells and 10 μm particles, achieving spatial localization with a resolution down to 2.1 μm (about 5.3% of the channel width) in lateral direction and 1.2 μm (about 5.9% of the channel height) in the vertical direction at a flow rate of 1.2 μL/min. In addition, by comparing measurement of yeast cells and particles, it was demonstrated that the device not only localizes the single cells or particles but also simultaneously characterizes their status properties such as velocity and size. The device offers a competitive electrode configuration in impedance cytometry with the advantages of simple structure, low cost, and high throughput, promising cell localization and thus electrical characterization.

Self-Aligned Organic Metal–Semiconductor Field-Effect Transistor

We propose the design and fabrication of a coplanar electrode structure for an organic metal–semiconductor field-effect transistor (OMESFET), with the gate electrode self-aligned between the source and drain electrodes. We first used nanoimprint lithography (NIL) to define a channel area of the device on a patterned metal, and then used chemical wet etching to create the source and drain electrodes by removing the metal in the channel area. After the wet etching, the gate electrode was deposited in the channel area. The organic semiconductor was then deposited to cover the patterned electrodes. The rectifying response and the device characteristics prove that the self-aligned device is a functional OMESFET. In this experiment, we also demonstrated that the self-aligned OMESFET has lower driving voltages and smaller subthreshold swing (SS) than that of a conventional organic metal–insulator–semiconductor field-effect transistor (OMISFET). Compared with the most common OMESFET structure, this self-aligned coplanar structure effectively eliminates the overlapping area between the gate and source/drain electrodes commonly seen in currently reported OMESFETs, which means that this self-aligned device structure reduces the parasitic capacitance, theoretically allowing the transistor to have a higher cutoff frequency. These features render our proposed OMESFET devices more favorable for low-power and high-frequency organic circuit applications.

Dynamic/static mechanical stimulation double responses and self-powered “green” electronic skin based on electrode potential difference

• Self-powered electronic skin based on electrode potential difference can respond to dynamic/static mechanical stimulation. • The device can be prepared by simple, efficient and low-cost screen printing. • The use of water-soluble and biodegradable materials enables devices to be environmentally friendly during manufacturing and disposal. Low-power or self-powered electronic skin (e-skin) is considered an important research area, as it reduces the requirements for stable energy sources in electronic systems. However, most reported self-powered e-skins can only detect dynamic mechanical stimuli, but cannot detect ubiquitous static mechanical stimuli, resulting in a significant amount of information loss. In this paper, we report a self-powered e-skin based on electrode potential difference that can detect dynamic/static mechanical stimuli with sensitivity and response time of 399 mV/kPa and 85 ms, respectively. In this device, the mechanical stimulus is converted into a voltage signal by regulating the impedance of the electrode/electrolyte interface. In the process of preparing the device, a “green” electrode ink was prepared using a water-soluble, biodegradable polymer as the binder of the active material. Owing to the printability of the ink, a patterned electrode can be formed on a flexible substrate using low-cost screen-printing technology. Finally, we designed a co-planar shared electrode structure, which effectively reduced the complexity of the circuit layout. This new device has been successfully used for information acquisition of objects and detection of physiological signals, and we believe it has significant implications for the future development of e-skins.

Efficient silicon and side-cladding waveguide modulator with electro-optic polymer.

Efficient electro-optic (EO) modulation can be generated in the hybrid silicon modulator with EO polymer in the form of an in-plane coplanar waveguide and electrode structure. Strong confinement of the optical field in the hybrid structure is critical to performing efficient electric poling and modulation of the EO polymer. The waveguide consists of silica-based side claddings and an EO core for increasing the integral of the optical field and the overlap interaction between the optical field and the modulated electric field within the EO polymer. We discuss in detail the volume resistivity dependence of the efficiency of electric poling and modulation for various side-cladding materials. In a Mach-Zehnder interferometer modulator, the measured half-wave-voltage length product (VπL) is 1.9 V·cm at an optical communication wavelength of 1,550 nm under the TE optical mode operation. The high-speed signaling of the device is demonstrated by generating on-off-keying transmission at signal rates up to 52 Gbit/s with a Q factor of 6.1 at a drive voltage of 2.0 Vpp.

Breakdown Behavior of GaAs PCSS with a Backside-Light-Triggered Coplanar Electrode Structure

The competitive relationship between the surface flashover of the coplanar electrodes and the body current channel was investigated. Breakdown behavior of GaAs photo-conductive semiconductor switch (PCSS) with a backside-light-receiving coplanar electrode structure was studied in this paper. GaAs PCSS was triggered by the laser pulse with an extrinsic absorption wavelength of 1064 nm. Special insulating construction was designed for GaAs PCSS, while the surface of the electrodes was encapsulated with transparent insulating adhesive. Our first set of experiments was at a bias voltage of 8 kV, and the surface flashover breakdown of GaAs PCSS was observed with 10 Hz triggering laser pulse. In the second experiment, at a bias voltage of 6 kV, the body current channel breakdown appeared on the backside of the GaAs PCSS. Compared with these results, the existence of a competitive relationship between the surface flashover breakdown and the body current channel breakdown of the GaAs PCSS was confirmed. When the bias voltage is set within a certain range (just reaching avalanche mode), GaAs PCSS with a backside-light-receiving coplanar electrode structure will undergo the body current channel breakdown. This finding is also consistent with the simulation results.

Coplanar electrode directly modulated lasers with different cavity length

AbstractA ridge‐waveguide (RW) directly modulated laser (DML) with a coplanar electrode structure is proposed and measured in this paper. Since utilizing the coplanar electrode can significantly reduce parasitic capacitance, the frequency responses of DMLs exhibit a quite low roll‐off. Shortening the cavity length L is attractive to enhance the high‐speed performance of DMLs, but it will increase the mirror loss and the chip resistance at the same time. We analyzed the static and dynamic characteristics of 200‐μm, 250‐μm, and 300‐μm lasers experimentally and theoretically to investigate the impact of L on the coplanar‐electrode DML. Shortening the cavity length can improve the relaxation oscillation frequency fr effectively. The 200‐μm DML achieves a bandwidth of 15.3 GHz. The fr is the most important limiting factor for the laser to obtain a wide bandwidth. Decreasing L and increasing the differential gain are promising for the further improvement of fr. However, shortening L causes a more severe thermal effect and the deterioration of the linearity. This trade‐off must be considered in the future study.

Coplanar Electrode Polymer Modulators Incorporating Fluorinated Polyimide Backbone Electro-Optic Polymer

High-speed coherent optical communication has been expanding to handle the ever-increasing data traffic, and the large modulation bandwidth of electro-optic (EO) polymer modulators has been especially appreciated. However, to be useful in optical communication, the EO polymer device should address several issues, such as thermal stability, photo-oxidation, and bias drift. In this work, as a part of the experiments to address these challenges, an EO polymer with a fluorinated polyimide backbone is utilized to create EO polymer modulators with improved thermal stability. A coplanar electrode structure is introduced to enhance the poling efficiency and reduce the bias drift.

Ion migration of MAPbBr3 single crystal devices with coplanar and sandwich electrode structures

Organolead halide perovskites (OHPs) have attracted great attention as a promising candidate for optoelectronic applications. However, a series of abnormal photoelectric properties such as slow photo response, large hysteresis in current−voltage curves caused by ion migration, deteriorated the reliability of OHPs-based devices. In this paper, we have fabricated CH3NH3PbBr3 (MAPbBr3) single crystal devices with coplanar and sandwich electrode structure and studied their ion migration phenomenon. Devices with coplanar structure exhibits a more stable temporal response curves, and a much larger ion activation energy (418 meV) than sandwich structure devices (88 meV). The results suggested that compared to sandwich structure devices, ion transport in coplanar structure devices is more diffcult, which indicates that ion migration in perovskites can be adjusted by changing the electron transport channels.

Liquid Crystal Based Rib Waveguide

We report electrically controlled liquid-crystal-core rib waveguide on fused silica substrate, in which the modal characteristics of waveguide can be tuned over a wide range of wavelengths. The coplanar electrode structure is proposed for controlling the LC molecules direction in the waveguide. Electrically controlled refractive index contrast and profile of waveguide is used for single and dual mode operations of the waveguide. We experimentally demonstrate transition from single mode to dual mode operation by externally applied voltage. In single mode regime the externally applied voltage has been used to tune the mode field diameter of the modes from 11.6 to 9.2 μm along the horizontal direction and 7.8 to 6.4 μm along the vertical direction. In the dual mode regime, long period waveguide grating (LPWG) based mode converter has been numerically demonstrated, and more than 99.9% power conversion from TE00 mode to TE01 mode has been obtained. Further, we show electrically tunable wavelength filters using LPWG in an LC core rib waveguide. We have obtained a tuning range of 140 nm for such electrically tunable wavelength filters. The proposed liquid crystal based rib waveguide has the possibility of on-chip low-cost fabrication.

Evaluation of shear piezoelectric coefficient d15 of piezoelectric ceramics by using piezoelectric cantilever beam in dynamic resonance

ABSTRACTA novel method for characterization on the shear piezoelectric coefficient of piezoelectric ceramics was proposed. A shear-mode piezoelectric cantilever with coplanar electrode structure was fabricated via arranging two PZT-51 elements poled opposite in series connection, and a principle model based on Timoshenko beam theory was proposed to establish the relationship between peak-to-peak output voltage and frequency. The measured values are in good agreement with the results simulated by finite element method (FEM) with maximum relative error less than 4.5%. It is reliable and convenient for the proposed method to characterize the shear piezoelectric coefficient of piezoelectric ceramics.

Electrical Behavior of X-Ray Detector Based on PbI2Crystal With Coplanar Electrode Structure

In this work, we report on the results of the electrical behavior of coplanar electrode structure X-ray detector based on PbI2 crystal. The detector with coplanar electrode similar to the Van der Pauw structure instead of conventional planar structure can partly reduce the influence of trapping effect to charge carrier transport along the $c$ -axis. According to the configuration, four operating modes of the detector were thoroughly studied. Several novel results, such as the negative polarity dark current and photocurrent under zero bias voltage, orientation polarization, short relaxation time of steady-state surface leakage current and fast photocurrent response are obtained by this kind of coplanar structure configuration. The detector has the potential to be developed as a solid state X-ray dosimeter in the medical radiation environment, providing a high sensitivity and good adaptability under positive or negative bias voltage.

Characterization of coplanar electrode structures for microfluidic-based impedance spectroscopy

Impedance spectroscopy has the potential for label-free integrated electrochemical detection in microfluidic lab-on-a-chip applications. Its capability to identify and discern between surface and bulk processes in solid–liquid systems finds particular use for the detection of biorecognition events or conductivity measurements. The electrochemical transducer can be in the form of interdigitated electrode structures to increase sensitivity. Experimental work was performed to characterize two different transducer designs. Applications included the monitoring of protein films on contact-less interdigitated electrode structures and conductivity detection of droplets on insulated two-electrode structures. The use of electrode passivation eliminated electrode degradation. Experimental results were compared to theoretical analytical models, and were found to closely correlate with one another. The analytical models were used to design the transducer for optimal conductivity detection. The results inform the current research efforts for the development of in-line impedance spectroscopy in digital microfluidics and confirm the use of simple analytical models for the first-order estimation of the frequency response of interdigitated electrode structures.

Top gate ZnO−Al2O3 thin film transistors fabricated using a chemical bath deposition technique

ZnO thin films were prepared by a simple chemical bath deposition technique using an inorganic solution mixture of ZnCl2 and NH3 on glass substrates and then were used as the active material in thin film transistors (TFTs). The TFTs were fabricated in a top gate coplanar electrode structure with high-k Al2O3 as the gate insulator and Al as the source, drain and gate electrodes. The TFTs were annealed in air at 500 °C for 1 h. The TFTs with a 50 μm channel length exhibited a high field-effect mobility of 0.45 cm2/(V·s) and a low threshold voltage of 1.8 V. The sub-threshold swing and drain current ON-OFF ratio were found to be 0.6 V/dec and 106, respectively.

ZnO TFTs prepared by chemical bath deposition technique with high‐k La2O3 gate dielectric annealed in ambient atmosphere

In this paper, the electrical properties of top‐gated thin‐film transistors with low‐cost chemical bath deposition (CBD) of ZnO as active material and a high‐k rare‐earth oxide La2O3 as gate dielectric have been reported. The source‐drain and gate electrodes and dielectric layers are fabricated by thermal evaporation techniques in high vacuum of the order of 10−6 Torr in a coplanar electrode structure. The channel length of the TFT is of 50 μm. The fabricated TFTs are annealed at 500 °C in air. The TFTs exhibit a field effect mobility 0.58 (cm2 V−1 s−1). Use of a high dielectric constant (high‐k) gate insulator reduces the threshold voltage and subthreshold swing of the TFTs. The TFTs exhibit a low threshold voltage of 4 V. The calculated values of gain–bandwidth product and subthreshold swing are also evaluated and presented. The ON/OFF ratio of the TFT is found to be 106.

Evaluation of electromechanical coupling parameters of piezoelectric materials by using piezoelectric cantilever with coplanar electrode structure in quasi-stasis

Based on Timoshenko beam theory, a principle model is proposed to establish the relationship between electric charge and excitation acceleration, and in quasi-stasis we apply the direct piezoelectric effect of multilayer cantilever with coplanar electrode structure to evaluate the piezoelectric strain coefficient d15 and electromechanical coupling coefficient k15. They are measured as 678 pC/N and 0.74 for the commercial piezoelectric ceramic lead zirconate titanate (PZT-51) bulk specimen and 656 pC/N and 0.63 for the lead magnesium niobate (PMN) bulk specimen, and they are in agreement with the calibration and simulation values. The maximum of relative errors is less than 4.2%, so the proposed method is reliable and convenient.

AC Complex Impedance Study on the Resistive Humidity Sensors with Ammonium Salt-Containing Polyelectrolyte using a Different Electrode Pattern

We examined the effect of electrode fingers and gaps of coplanar interdigitated electrode (IDE) structures to characterize the ammonium salt-containing polyelectrolyte film of resistance-based humidity sensors. IDEs designed for this purpose were flexible gold electrodes deposited on a polyimide substrate using a printing process because the geometry presents a potential for tunable sensitivity over other electrode designs. The basic design of the sensors consisted of IDEs with a different number of electrode fingers such as 3, 4, and 5 and gap sizes of 310, 360, 410, and <TEX>$460{\mu}m$</TEX>. Details of the AC complex impedance characteristics such as the Nyquist plot, Bode plot, and activation energy based on electrode construction were investigated.

원통형 방전소자의 방전특성 연구

In this paper, the discharge characteristics of ac-type cylindrical discharge devices with diameters (D) in the 50～400μm range have been investigated numerically. The cylindrical devices have much lower breakdown voltages compared to the coplanar electrode structures. The breakdown voltage of the cylindrical structures increases with the decrease of diameters in 50～100μm range. In 100～200μm range, however, the breakdown voltage decreases slightly with the decrease of diameters. Also, as the diameter gets smaller, the electron heating efficiency is greatly improved.

Thermally deposited Ag-doped CdS thin film transistors with high-k rare-earth oxide Nd2O3 as gate dielectric

The performance of thermally deposited CdS thin film transistors doped with Ag has been reported. Ag-doped CdS thin films have been prepared using chemical method. High dielectric constant rare earth oxide Nd2O3 has been used as gate insulator. The thin film trasistors are fabricated in coplanar electrode structure on ultrasonically cleaned glass substrates with a channel length of 50 μm. The thin film transistors exhibit a high mobility of 4.3 cm2 V−1 s−1 and low threshold voltage of 1 V. The ON-OFF ratio of the thin film transistors is found as 105. The TFTs also exhibit good transconductance and gain band-width product of 1.15 × 10−3 mho and 71 kHz respectively.