Buried Electrodes Research Articles

Damping of the longitudinal streak in the boundary layer by ‘plasma panel’ actuator

The group of microdischarges in surface DBD can be used as a virtual roughness element. Localization of the discharge along the electrode span can be performed on the ‘plasma panel’ principle by sectioning the buried electrode and individually controlling sections potential. The paper describes the study of the details of such actuator operation. Data presented include the flowfield induced by discharge and the analysis of the controllability of the created disturbances in a subsonic boundary layer. In the final part of the paper, the control of the low-velocity streak, an object widely present in transitionary and turbulent flows, by an adaptive plasma actuator, is demonstrated.

Long-Range Charge Extraction in Back-Contact Perovskite Architectures via Suppressed Recombination

Summary Metal-halide perovskites are promising solution-processable semiconductors for efficient solar cells with unexpectedly high diffusion ranges of photogenerated charges. Here, we study charge extraction and recombination in metal-halide perovskite back-contact devices, which provide a powerful experimental platform to resolve electron- or hole-only transport phenomena. We prepare polycrystalline films of perovskite semiconductors over laterally separated electron- and hole-selective materials of SnO2 and NiOx. Upon illumination, electrons (holes) generated over SnO2 (NiOx) rapidly transfer to the buried collection electrode, leaving holes (electrons) to diffuse laterally as majority carriers in the perovskite layer. Under these conditions, we find recombination is strongly suppressed. Resulting surface recombination velocities are below 2 cm s−1, approaching values of high-quality silicon. We find diffusion lengths exceed 12 μm, an order of magnitude higher than reported in vertically stacked architectures. We fabricate back-contact solar cells with short-circuit currents as high as 18.4 mA cm−2, reaching 70% external quantum efficiency.

Buried graphene electrode heater for a polymer waveguide thermo-optic device.

We propose the use of graphene as the electrode heater material for a polymer waveguide thermo-optic (TO) device. Because a graphene electrode can be buried in a polymer waveguide without introducing a significant loss to the transverse magnetic polarized light, we can do away with the buffer layer that is required in a conventional TO device to isolate the metal electrode heater from the waveguide and, hence, reduce the driving electric power of the device. To demonstrate the principle, we fabricate and compare two polymer waveguide TO mode switches based on the configuration of a balanced Mach-Zehnder interferometer, which are identical except that one uses a buried graphene electrode and the other uses an aluminum electrode deposited on the waveguide surface. Our experimental device that uses a graphene electrode has a switching power almost four times lower and also responds faster. The use of buried graphene electrodes is an effective approach to reducing the power consumption of TO devices.

Temperature Cross-Sensitivity of AlN-Based Flexural Plate Wave Sensors

In this paper, we investigate the temperature cross-sensitivity of aluminum nitride (AlN)-based flexural plate wave devices for sensing applications in contact with liquids. In our improved device topology, the interdigital transducers are designed as a buried electrode, and thus, are electrically shielded, enabling full immersion of the sensor into the liquid. The fabricated devices showed a mass sensitivity of 240 cm2/g for loading with deionized water which is in good agreement with the theoretical predictions. The temperature coefficient of frequency (TCF) was evaluated for devices with initially compressive and tensile stressed AlN layers. Devices with compressive film stress exhibited a TCF of −62 ppm/K to −28 ppm/K, while the devices with tensile film stress showed an increased TCF of −391 ppm/K to −72 ppm/K. It is shown that variations in in-plane tension are mainly accountable for the increased TCF, while the lower TCF is primarily caused by material softening.

IRCG inversion of buried electrode resistivity data from an electrically conducting layered medium

Electric potential resulting from the injection of direct current into the ground can be used to explore the earth’s structure. We propose to use an iteratively regularized inversion algorithm for the interpretation of buried electrode resistivity data gathered from a horizontally stratified layered earth. Two types of ground structures are used to investigate the electrical conductivity profiles. An iterative regularization scheme using the nonlinear conjugate gradient technique is applied to estimate the model parameters of conductivity variation. A suitable value of the regularization parameter is determined by using the well known L–curve criterion. The final inverted models obtained are in excellent qualitative agreement with the true models when using synthetic data. A comparison of inversion results obtained from our scheme and the Levenberg–Marquardt method on test data sets clearly demonstrates an edge over the other stated scheme as far as the robustness is concerned.

60‐4: Mechanically Robust High‐Performance Flexible Oxide TFTs with Imbedded Buried CNT Electrode for Bendable Displays

We demonstrate highly robust flexible a‐IGZO thin‐film transistors (TFTs) with imbedded carbon nano‐tube (CNT) buried electrode (BE) in between polyimide (PI) substrate. The excellent mechanical durability of flexible TFTs on thin wrinkle‐free and the self‐standing PI substrate with imbedded CNT BE has been demonstrated. The strain on the TFT can be reduced by the imbedded CNT electrode which is calculated from the 3D‐TCAD simulation.

Buried MoO x/Ag Electrode Enables High-Efficiency Organic/Silicon Heterojunction Solar Cells with a High Fill Factor.

Silicon (Si)/organic heterojunction solar cells based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and n-type Si have attracted wide interests because they promise cost-effectiveness and high-efficiency. However, the limited conductivity of PEDOT:PSS leads to an inefficient hole transport efficiency for the heterojunction device. Therefore, a high dense top-contact metal grid electrode is required to assure the efficient charge collection efficiency. Unfortunately, the large metal grid coverage ratio electrode would lead to undesirable optical loss. Here, we develop a strategy to balance PEDOT:PSS conductivity and grid optical transmittance via a buried molybdenum oxide/silver grid electrode. In addition, the grid electrode coverage ratio is optimized to reduce its light shading effect. The buried electrode dramatically reduces the device series resistance, which leads to a higher fill factor (FF). With the optimized buried electrode, a record FF of 80% is achieved for flat Si/PEDOT:PSS heterojunction devices. With further enhancement adhesion between the PEDOT:PSS film and Si substrate by a chemical cross-linkable silance, a power conversion efficiency of 16.3% for organic/textured Si heterojunction devices is achieved. Our results provide a path to overcome the inferior organic semiconductor property to enhance the organic/Si heterojunction solar cell.

Direct-Write Laser Greyscale Lithography for Multi-Layer Lead Zirconate Titanate Thin Films.

Direct-write laser greyscale lithography has been used to facilitate a single step patterning technique for multi-layer lead zirconate titanate (PZT) thin films. A 2.55 μm thick photoresist was patterned with a direct-write laser. The intensity of the laser was varied to create both tiered and sloped structures that are subsequently transferred into multi-layer PZT(52/48) stacks using a single Ar ion mill etch. Traditional processing requires a separate photolithography step and an ion mill etch for each layer of the substrate, which can be costly and time consuming. The novel process allows access to buried electrode layers in the multi-layer stack in a single photolithography step. The greyscale process was demonstrated on three 150 mm diameter Si substrates configured with a 0.5 μm thick SiO2 elastic layer, a base electrode of Pt/TiO2, and a stack of four PZT(52/48) thin films of either 0.25 μm thickness per layer or 0.50 μm thickness per layer, and using either Pt or IrO2 electrodes above and below each layer. Stacked capacitor structures were patterned and results will be reported on the ferroelectric and electromechanical properties using various wiring configurations and compared to comparable single layer PZT configurations.

Imaging mass spectrometry tackles interfacial challenges in electrochemistry

Summary Electrochemistry has played a significant role in many research fields. Owing to its sensitivity and selectivity, in situ electroanalysis has been widely used as a fast and economical means for achieving outstanding results. Although many spectroscopic techniques have been used in electrochemistry, the challenges to capture short-lived intermediate species as a result of electron transfer in the buried solid electrode and electrolyte solution interface remains a grand challenge. In situ imaging mass spectrometry (IMS) recently has been extended to capture transient species in electrochemistry. This review intends to summarize newest development of IMS and its applications in advancing fundamental electrochemistry.

Photo-physical properties of He-related color centers in diamond

Diamond is a promising platform for the development of technological applications in quantum optics and photonics. The quest for color centers with optimal photo-physical properties has led in recent years to the search for novel impurity-related defects in this material. Here, we report on a systematic investigation of the photo-physical properties of two He-related (HR) emission lines at 535.2 nm and 559.7 nm (as measured at a temperature of 25 K) created in three different diamond substrates upon implantation with 1.3 MeV He+ ions and subsequent annealing. The spectral features of the HR centers were studied in an “optical grade” diamond substrate as a function of several physical parameters, namely, the measurement temperature, the excitation wavelength, and the intensity of external electric fields. The emission lifetimes of the 535.2 nm and 559.7 nm lines were also measured by means of time-gated photoluminescence measurements. The Stark shifting of the HR centers under the application of an external electrical field was observed in a CVD diamond film equipped with buried graphitic electrodes, suggesting the lack of inversion symmetry in the defects' structure. Furthermore, the photoluminescence mapping under 405 nm excitation of a “detector grade” diamond sample implanted at a He+ ion fluence of 1 × 1010 cm−2 enabled us to identify the spectral features of both the HR emission lines from the same localized optical spots. The reported results provide an insight into the structure of He-related defects in diamond and their possible utilization in practical applications.

AlN/Pt/LN structure for SAW sensors capable of operating at high temperature

There is a need for wireless sensors able to operate in the intermediate temperature range (ITR) between 300 °C and 600 °C. Surface acoustic wave (SAW) sensors are promising candidates to solve this issue. However, existing SAW sensors most often fail in the ITR, due to the quick degradation of the sensor housing in extreme conditions. A promising way to circumvent the issue is to use “package-less” devices, where the acoustic waves are guided in a multilayered structure where they are intrinsically protected from adverse environmental effects. We present here an innovative multilayered structure that fulfills all the basic requirements, to achieve a wireless and “package-less” SAW Sensor for the ITR. The structure is made of a thin AlN layer deposited on top of a Y + 128°LN substrate and equipped with buried Pt electrodes. Numerical simulations of the acoustic waves propagating in SAW resonators built on this structure reveal the existence of a useful Rayleigh-type SAW that propagates at the AlN/LN interface with a velocity up to 4500 m/s and a high electromechanical coupling k2=5.6%, without leakage into the substrate. The existence of this mode is due to specific properties of the Y + 128°LN cut, which are analyzed in detail in this paper. The performances of an optimized AlN/Pt/LN structure are also compared to the ones of previously suggested “package-less” structures, including AlN/ZnO/Sapphire. It is shown that better device characteristics can be expected from the AlN/Pt/LN structure in the ITR.

Thin CVD diamond film detector for slow neutrons with buried graphitic electrode

We fabricated neutron detectors based on thin epitaxial CVD diamond films grown on single crystal diamond substrates, with a buried graphitic electrode produced by ion implantation and annealing. The spectra of 5.5 MeV alpha particles were measured with ≈3.5% energy resolution, and, based on the features of those spectra, a precise assessment of the film thickness was able achieved. A 10 μm thick detector was tested for 252Cf neutron and γ-radiation source, using 10B and 6Li isotopes as converters. Due to the small film thickness the contribution from the γ-quanta background to the spectra was restricted by energies below 200 keV, and could be easily discriminated from the neutron related signals. The performance of the detectors was tested for 5.5 MeV α-particles at fluences up to 109cm−2, and no detrimental polarization effect was observed for the best sample.

Pulsed Polarization-Based NOx Sensors of YSZ Films Produced by the Aerosol Deposition Method and by Screen-Printing.

The pulsed polarization technique on solid electrolytes is based on alternating potential pulses interrupted by self-discharge pauses. Since even small concentrations of nitrogen oxides (NOx) in the ppm range significantly change the polarization and discharge behavior, pulsed polarization sensors are well suited to measure low amounts of NOx. In contrast to all previous investigations, planar pulsed polarization sensors were built using an electrolyte thick film and platinum interdigital electrodes on alumina substrates. Two different sensor layouts were investigated, the first with buried Pt electrodes under the electrolyte and the second one with conventional overlying Pt electrodes. Electrolyte thick films were either formed by aerosol deposition or by screen-printing, therefore exhibiting a dense or porous microstructure, respectively. For screen-printed electrolytes, the influence of the electrolyte resistance on the NOx sensing ability was investigated as well. Sensors with buried electrodes showed little to no response even at higher NOx concentrations, in good agreement with the intended sensor mechanism. Electrolyte films with overlying electrodes, however, allowed the quantitative detection of NOx. In particular, aerosol deposited electrolytes exhibited high sensitivities with a sensor output signal ΔU of 50 mV and 75 mV for 3 ppm of NO and NO2, respectively. For screen-printed electrolytes, a clear trend indicated a decrease in sensitivity with increased electrolyte resistance.

Impact of surface roughness on Dielectrophoretically assisted concentration of microorganisms over PCB based platforms.

This article presents a PCB based microfluidic platform for performing a dielectrophoretic capture of live microorganisms over inter-digitated electrodes buried under layers of different surface roughness values. Although dielectrophoresis has been extensively studied earlier over silicon and polymer surfaces with printed electrodes the issue of surface roughness particularly in case of buried electrodes has been seldom investigated. We have addressed this issue through a layer of spin coated PDMS (of various surface roughness) that is used to cover the printed electrodes over a printed circuit board. The roughness in the PDMS layer is generally defined by the roughness of the FR4 base which houses the printed electrodes as well as other structures. Possibilities arising out of COMSOL simulations have been well validated experimentally in this work.

A graphene barristor using nitrogen profile controlled ZnO Schottky contacts.

We have successfully demonstrated a graphene-ZnO:N Schottky barristor. The barrier height between graphene and ZnO:N could be modulated by a buried gate electrode in the range of 0.5-0.73 eV, and an on-off ratio of up to 107 was achieved. By using a nitrogen-doped ZnO film as a Schottky contact material, the stability problem of previously reported graphene barristors could be greatly alleviated and a facile route to build a top-down processed graphene barristor was realized with a very low heat cycle. This device will be instrumental when implementing logic functions in systems requiring high-performance logic devices fabricated with a low temperature fabrication process such as back-end integrated logic devices or flexible devices on soft substrates.

Sensitivity analysis of the electrostatic force distance curve using Sobol’s method and design of experiments

Previous studies have demonstrated that the electrostatic force distance curve (EFDC) is a relevant way of probing injected charge in 3D. However, the EFDC needs a thorough investigation to be accurately analyzed and to provide information about charge localization. Interpreting the EFDC in terms of charge distribution is not straightforward from an experimental point of view. In this paper, a sensitivity analysis of the EFDC is studied using buried electrodes as a first approximation. In particular, the influence of input factors such as the electrode width, depth and applied potential are investigated. To reach this goal, the EFDC is fitted to a law described by four parameters, called logistic law, and the influence of the electrode parameters on the law parameters has been investigated. Then, two methods are applied—Sobol’s method and the factorial design of experiment—to quantify the effect of each factor on each parameter of the logistic law. Complementary results are obtained from both methods, demonstrating that the EFDC is not the result of the superposition of the contribution of each electrode parameter, but that it exhibits a strong contribution from electrode parameter interaction. Furthermore, thanks to these results, a matricial model has been developed to predict EFDCs for any combination of electrode characteristics. A good correlation is observed with the experiments, and this is promising for charge investigation using an EFDC.

Improving resistivity survey resolution at sites with limited spatial extent using buried electrode arrays

Electrical resistivity tomography (ERT) surveys are widely used in geological, environmental and engineering studies. However, the effectiveness of surface ERT surveys is limited by decreasing resolution with depth and near the ends of the survey line. Increasing the array length will increase depth of investigation, but may not be possible at urban sites where access is limited. One novel method of addressing these limitations while maintaining lateral coverage is to install an array of deep electrodes. Referred to here as the Multi-Electrode Resistivity Implant Technique (MERIT), self-driving pointed electrodes are implanted at depth below each surface electrode in an array, using direct-push technology. Optimal sequences of readings have been identified with the “Compare R” method of Wilkinson. Numerical, laboratory, and field case studies are applied to examine the effectiveness of the MERIT method, particularly for use in covered karst terrain. In the field case studies, resistivity images are compared against subsurface structure defined from borings, GPR surveys, and knowledge of prior land use. In karst terrain where limestone has a clay overburden, traditional surface resistivity methods suffer from lack of current penetration through the shallow clay layer. In these settings, the MERIT method is found to improve resolution of features between the surface and buried array, as well as increasing depth of penetration and enhancing imaging capabilities at the array ends. The method functions similar to a cross-borehole array between horizontal boreholes, and suffers from limitations common to borehole arrays. Inversion artifacts are common at depths close to the buried array, and because some readings involve high geometric factors, inversions are more susceptible to noise than traditional surface arrays. Results are improved by using errors from reciprocal measurements to weight the data during the inversion.

Estimation of Saturated Hydraulic Conductivity during Infiltration Test with the Aid of ERT and Level‐Set Method

Core Ideas A new technique for estimating the saturated hydraulic conductivity is developed. It uses a combination of hydrogeophysical and numerical methods. Electrical resistivity tomography and the instantaneous profile method are used. The technique is validated using simple and complex numerical hydrogeological models. Many hydrogeological and geophysical tools have been developed to determine subsoil properties, but they are often limited by sparse datasets and by the portability of the method from one site to another and often underestimate the complexity of the medium. We present a saturated hydraulic conductivity (Ks) estimation scheme, named the KES method, based on hydrogeophysical and numerical methods. The targeted medium of investigation is an unsaturated and heterogeneous soil. Estimation of Ks is accomplished by estimating the position of the wetting front and the distribution and velocity of flow lines during an infiltration test. Using numerical modeling, Ks is determined by minimizing the velocity difference between the measured flow lines and the modeled flow lines. Surface and buried electrodes are used as part of the electrical resistivity survey in determining the position of the wetting front. An instantaneous profile method is used to determine the water retention curve of the medium. The KES method has been tested and validated using data produced from simple and more complex geological models from published case studies. We obtained good reconstruction of the saturated hydraulic conductivity. We have found that the estimated value of Ks in log scale has a mean error <2.5%. Error increases along the boundaries of different hydrofacies.

High-speed electro-optic switch using buried electrode structure in polymer Mach–Zehnder waveguide

A low-cost and high-speed electro-optic (EO) switch using the guest–host EO material Disperse Red 1/Polymethyl Methacrylate (DR1/PMMA) was designed and fabricated. The DR1/PMMA material presented a low processing cost, an excellent photostability and a large EO coefficient of 13.1 pm/V. To improve the performance of the switch, the in-plane buried electrode structure was introduced in the polymer Mach–Zehnder waveguide to improve the poling and modulating efficiency. The characteristic parameters of the waveguide and the electrodes were carefully designed and the fabrication process was strictly controlled. Under 1550 nm, the insertion loss of the device was 12.7 dB. The measured switching rise time and fall time of the switch were 50.00 ns and 54.29 ns, respectively.

The active modulation of drug release by an ionic field effect transistor for an ultra-low power implantable nanofluidic system.

We report an electro-nanofluidic membrane for tunable, ultra-low power drug delivery employing an ionic field effect transistor. Therapeutic release from a drug reservoir was successfully modulated, with high energy efficiency, by actively adjusting the surface charge of slit-nanochannels 50, 110, and 160 nm in size, by the polarization of a buried gate electrode and the consequent variation of the electrical double layer in the nanochannel. We demonstrated control over the transport of ionic species, including two relevant hypertension drugs, atenolol and perindopril, that could benefit from such modulation. By leveraging concentration-driven diffusion, we achieve a 2 to 3 order of magnitude reduction in power consumption as compared to other electrokinetic phenomena. The application of a small gate potential (±5 V) in close proximity (150 nm) of 50 nm nanochannels generated a sufficiently strong electric field, which doubled or blocked the ionic flux depending on the polarity of the voltage applied. These compelling findings can lead to next generation, more reliable, smaller, and longer lasting drug delivery implants with ultra-low power consumption.