Oxide Capacitance Research Articles

Biocompatible and capacitive PDA-Ov-Co3O4@CC anode augmented exoelectrogens enrichment and extracellular electron transfer in microbial fuel cells

Metal oxides rich in oxygen vacancies (Ov) possess excellent intrinsic conductivity, variable valence metal center and high capacitance, which were potential candidates as microbial fuel cells anode. However, their high bacterial toxicity greatly hindered the activity of biofilm. To solve this issue, in this work, polydopamine (PDA) covered capacitive Ov doped Co3O4 nanosheets were designed and successfully grown on carbon cloth (CC). The introduction of Ov significantly promoted the charge storage, the net charge and the accumulated charge were 217.1 and 2680.3 C/m2, respectively, surpassed Co3O4 anode without Ov. In addition, Ov also decreased the charge-transfer resistance (Rct), effectively accelerating EET. The Rct of PDA/Ov-Co3O4@CC was 29.51 Ω, lower than CC (382.10 Ω). The cover of PDA prevented the direct contact between metal ions and microorganisms, greatly enhanced the bacterial viability. The power density of MFCs with PDA/Ov-Co3O4@CC anode was 2.77 W/m2, 1.45 times higher than that of bare CC (1.90 W/m2). In addition, PDA/Ov-Co3O4@CC anode displayed excellent coulombic efficiency and daily COD removal amount (23.5 % and 147.6 mg/L/d), higher than the control groups. The community analysis showed the abundance of Geobacter on PDA/Ov-Co3O4@CC anode was 91 %, higher than other anodes. Present study developed a facile and effective PDA coating strategy to simultaneously enhance the biocompatibility and capacitance of Ov-rich metal oxides, which will be a promising method for the preparation of high performance MFCs anode.

Mapping Ferroelectric Fields Reveals the Origins of the Coercivity Distribution.

Better techniques for imaging ferroelectric polarization would aid the development of new ferroelectrics and the refinement of old ones. Here we show how scanning transmission electron microscope (STEM) electron beam-induced current (EBIC) imaging reveals ferroelectric polarization with obvious, simply interpretable contrast. Planar imaging of an entire ferroelectric hafnium zirconium oxide (Hf0.5Zr0.5O2, HZO) capacitor shows an EBIC response that is linearly related to the polarization determined in situ with the positive-up, negative-down (PUND) method. The contrast is easily calibrated in MV/cm. The underlying mechanism is magnification-independent, operating equally well on micrometer-sized devices and individual nanoscale domains. Coercive-field mapping reveals that individual domains are biased "positive" and "negative", as opposed to being "easy" and "hard" to switch. The remanent background E-fields generating this bias can be isolated and mapped. Coupled with STEM's native capabilities for structural identification, STEM EBIC imaging provides a revolutionary tool for characterizing ferroelectric materials and devices.

Phase Transformations Driving Biaxial Stress Reduction During Wake‐Up of Ferroelectric Hafnium Zirconium Oxide Thin Films

AbstractBiaxial stress is identified to play an important role in the polar orthorhombic phase stability in hafnium oxide‐based ferroelectric thin films. However, the stress state during various stages of wake‐up has not yet been quantified. In this work, the stress evolution with field cycling in hafnium zirconium oxide capacitors is evaluated. The remanent polarization of a 20 nm thick hafnium zirconium oxide thin film increases from 9.80 to 15.0 µC cm−2 following 106 field cycles. This increase in remanent polarization is accompanied by a decrease in relative permittivity that indicates that a phase transformation has occurred. The presence of a phase transformation is supported by nano‐Fourier transform infrared spectroscopy measurements and scanning transmission electron microscopy that show an increase in ferroelectric phase content following wake‐up. The stress of individual devices field cycled between pristine and 106 cycles is quantified using the sin2(ψ) technique, and the biaxial stress is observed to decrease from 4.3 ± 0.2 to 3.2 ± 0.3 GPa. The decrease in stress is attributed, in part, to a phase transformation from the antipolar Pbca phase to the ferroelectric Pca21 phase. This work provides new insight into the mechanisms controlling and/or accompanying polarization wake‐up in hafnium oxide‐based ferroelectrics.

Investigations of 4H‐SiC trench MOSFET with integrated high‐K deep trench and gate dielectric

AbstractThis paper proposes and investigates a novel 4H‐SiC trench MOSFET (TMOS) with integrated high‐K deep trench and gate dielectric (INHK‐TMOS). The integrated high‐K (INHK) consists of a high‐K gate dielectric and an extended high‐K deep trench dielectric in the drift region. Firstly, the high‐K gate dielectric together with the metal‐forming high‐K metal gate structure, which increases the gate oxide capacitance (COX), reduces the threshold voltage (VTH) and the specific on‐resistance (Ron,sp). Secondly, the extended high‐K deep trench dielectric not only modulates the electric field in the drift region by introducing a new electric field peak at the bottom of the high‐K deep trench dielectric, thereby enhancing the breakdown voltage (BV), but also improves the doping concentration (ND) of the drift region by the assist depletion effect of the high‐K dielectric, further optimizing the forward conduction characteristics. Simulation results demonstrate that when compared to the conventional TMOS, the INHK‐TMOS using HfO2 exhibits a 52.6% reduction in VTH, a 52.1% reduction in Ron,sp, a 20.3% increasement in BV and a 202.3% improvement in figure of merit.

Sensitivity estimation of biosensor in a tapered cavity MOSHEMT

The present research provides a comprehensive investigation of the structural modification at the cavity under the gate (CUG) on the metal oxide semiconductor high electron mobility transistor (MOSHEMT)-based biosensor by projecting its basic figures of merit (FOMs). The effect of a tapering dielectric on the sensitivity of the biosensor has not been extensively investigated in many research efforts. Therefore, to account for the larger binding surface, the current study considers a wide range of permittivity of the biomolecules from 1 to 10, using the dielectric modulation technique in the tapered cavity. Various cavities are analysed to enhance the sensitivity. The findings indicate that the presence of biomolecules causes a considerable fluctuation in the drain current, threshold voltage, on-current, off-current, channel potential, and oxide capacitance. It has also been estimated how various fill percentages and charged and neutral biomolecules affect the device’s sensitivity. The tapered dielectric MOSHEMT offered an on-current sensitivity and threshold voltage sensitivity of 1.25 and 0.889 for neutral biomolecule (k = 8) and 0.562 and 2.23 for positively charged biomolecule respectively. Thus, tapering of the oxide does offer better sensitivities that can be exploited for biosensing applications.

Enhanced electrochemical properties of cobalt oxide nanoparticle electrode modified with low concentration of cationic surfactant

Metal oxides are proficient electrode materials for supercapacitors because of their physiochemical properties, especially their wide range of oxidation states that facilitate charge transfer in redox reactions and compatibility with electrolytes. Their performances can be further improved by adding surfactants, which also help with controlled synthesis, inhibit aggregation, and alter surface characteristics. The functional groups present in the surfactant molecule can undergo chemical bonding with the surface of the metal oxide, thereby modifying their surface chemistry and electronic characteristics. Recent research has focused on increasing the specific capacitance of cobalt oxide owing to its large surface area and size. The surfactants help to control the surface modification as a size-reducing agent and improve the electrochemical properties. Herein, A facile co-precipitation method is employed in synthesising cobalt oxide without cationic surfactant cetyltrimethylammonium bromide (CTAB) and with different concentrations of CTAB, followed by calcination. Herein, we compare the electrochemical properties with varying concentrations of surfactant-assisted Co3O4. The modified Co3O4 electrode with a low surfactant concentration (CO 1) exhibits a highly specific capacitance of 531F/g at 5 mV/s with a potential window of 0.7 V. The CO 1 electrode is suitable for supercapacitor devices with a specific capacitance of 296F/g at 0.8 A/g. Moreover, the asymmetric supercapacitor composed of CO1//AC demonstrated a remarkable energy density of 46.2 Wh/Kg and a robust power density of 800 W/kg. These results indicate that the hierarchical porous structure accelerates electron and ion movement, lowers charge transfer resistance, and improves hybrid electrode capacitive properties.

Fabrication of a supporting kapok‑carbon/rGO electrode via self-assembly with enhanced capacitance

To address the limitations associated with biomass mass transfer and improve the capacitance of graphene oxide (GO), a supporting Kapok Fiber carbon/reduced GO (CKF/rGO) electrode was constructed via an effective combination of CKF and GO. The carbon electrode (CKF-800/rGO-1:1) fabricated by mixing GO with CKF-800 in a 1:1 ratio showed a specific capacitance of 721.6 mF·cm−2 at a current density of 0.5 mA·cm−2. Moreover, the capacitance retention rate of this film was 95.71 % after 5000 cycles at a current density of 10 mA·cm−2. The use of GO as a stable support system, combined with the kapok carbon's large surface area and a unique tubular transmission channel for carbon electrodes, contributed to this result. Furthermore, the combination prevents agglomeration and restacking between graphene layers, ensuring effective electron and ion transport and providing a CKF/rGO composite carbon-supported electrode with excellent electrochemical properties. Therefore, CKF-800/rGO-1:1 represents a promising material for use as a supporting biomass-based carbon electrode.

Molten Salt Approach for Co3O4 Synthesis as a Charge Storage Electrode

A versatile molten salt method was targeted to fabricate the cobalt oxide (Co3O4) nanospheres as 
 charge storage electrodes. The Co3O4 nanospheres were prepared in KNO3 molten salt in only one step 
 within 5 minutes. The nanospheres were with an average size distribution of almost 80-130 nm. The 
 specific capacitance of cobalt oxide was found to be 285 F/g at 10 mV/s and 171 F/g at 0.5 A /g in 6 M 
 KOH and the Trasatti method was used to understand the outer and inner surface capacitive 
 contributions. The material possessed a moderate rate capability (63.1% at 5 A/g) and had good cyclic 
 stability (90.5% after 1200 cycles). This experimental study does not require any solvent usage and thus 
 can provide a green and continuous approach for the preparation of various transition metal oxides 
 with good electrochemical properties in the energy storage field.

Deep Neural Network Predicts Ti‐6Al‐4V Dissolution State Using Near‐Field Impedance Spectra

AbstractRetrieval studies document Ti‐6Al‐4V selective dissolution within crevices of total hip replacement devices. A gap persists in the fundamental understanding of Ti‐6Al‐4V crevice corrosion in vivo and its impact on local impedance. Previous studies use nearfield electrochemical impedance spectroscopy (nEIS) for characterization of retrieved CoCrMo surfaces and phase angle symmetry‐based EIS (sbEIS) for rapid data acquisition. In this study, these methods are combined with a deep neural network to characterize the local impedance changes after selective dissolution. It is hypothesized that structural changes occurring during dissolution will manifest as property changes to the oxide film capacitance. First, after sustained cathodic activation, the Ti‐6Al‐4V β phase selectively dissolves from the surface. Next, nEIS acquires n = 100 control and n = 105 dissolved spectra. Over dissolved regions, oxide capacitance significantly increases (Log10Q = ‐4.17 versus ‐4.78 (Scm−2(s)α), p = 0.000). Using single frequency EIS (5000 Hz), a capacitance‐based scanning impedance microscopy method identifies dissolved regions within seconds. Finally, Bode phase plots of the 205 control and dissolved nEIS spectra are input into a deep neural network. After training with n = 180 spectra, the model predicts the surface state for n = 25 previously unseen nEIS spectra with 96% accuracy.

Snubber Branch Design and Development of Solid-State DC Circuit Breaker

This research proposes a solid-state DC circuit breaker for low voltage DC system based on reverse-blocking IGCT. The circuit breaker topology gets easier as a result of reverse-blocking IGCTs' ability to withstand reverse voltage. To further enhance the breaking process, we develop a snubber branch with metal oxide varistors (MOV) and capacitance. The advantages and disadvantages of three distinct snubber branches-the no-snubber, the resistance-capacitance (RC), and the MOV-C snubber branch-are then contrasted. In addition to suppressing high-frequency oscillation caught by the parasitic MOV parameters, the structure with MOV-C snubber branch also blocks low frequency harmonics brought on by RC snubber branch. Moreover, this structure can slow down the rate at which the voltage rises during the breaking process. Comparatively speaking to the RC snubber branch and no-snubber branch structures, it is more appropriate for solid-state DC circuit breakers. Finally, a solid-state DC circuit breaker prototype based on RB-IGCT and MOV-C branch has been created. The maximum overvoltage is 1.5kV, and the rated voltage is 750V. The maximum breaking current is 10kA, and the rated current can be 2kA.

Mechanism of oxygen vacancies migration in BaTiO3‐BiMeO3: Experimental investigations and first principles studies

AbstractBaTiO3‐based compounds are recognized as the most common dielectric material used in multilayer ceramic capacitors (MLCCs), among which, BaTiO3‐BiMeO3 is extensively investigated to improve the thermal stability and extend the service life of MLCCs, which are strongly dependent on the conductivity at high temperatures. Despite numerous efforts have been made, the mechanism of oxygen vacancy conduction, which makes the major contributions to the conduction mechanism of BaTiO3‐based compounds at high temperatures below 450°C, is still unclear. In this paper, BaTiO3, 0.88BaTiO3‐0.12Bi(Zn2/3Nb1/3)O3, 0.88BaTiO3‐0.12Bi(Mg2/3Nb1/3)O3, and 0.88BaTiO3‐0.12Bi(Mg2/3Ta1/3)O3 ceramics have been prepared by solid‐state reaction method, and their electrical and dielectric properties have been studied in detail. Meanwhile, first principles were applied to study the mechanisms of the increase of electrical resistivity and the decrease of dielectric loss. It is found that B‐site dopants (Zn, Mg, Nb, and Ta) are effective in reducing the conductivity by inhibiting the migration of oxygen vacancies, which is a kinetics process with an increase of energy barrier. Notably, the greater ability of Zn to inhibit oxygen vacancies migration is a combination of thermodynamics (a strong ability to trap oxygen vacancies) and kinetics (an effect of block the migrating defects in the lattice). This work reveals a new insight into the mechanism of oxygen vacancies migration in BaTiO3‐based perovskite compounds, which makes BaTiO3‐BiMeO3 prospective in designing efficient and durable medium‐temperature solid oxide capacitor devices.

Sources of error and methods to improve accuracy in interface state density analysis using quasi-static capacitance–voltage measurements in wide bandgap semiconductors

Characterizing interface trap states in commercial wide bandgap devices using frequency-based measurements requires unconventionally high probing frequencies to account for both fast and slow traps associated with wide bandgap materials. The C−ψS technique has been suggested as a viable quasi-static method for determining the interface trap state densities in wide bandgap systems, but the results are shown to be susceptible to errors in the analysis procedure. This work explores the primary sources of errors present in the C−ψS technique using an analytical model that describes the apparent response for wide bandgap MOS capacitor devices. Measurement noise is shown to greatly impact the linear fitting routine of the 1/CS∗2 vs ψS plot to calibrate the additive constant in the surface potential/gate voltage relationship, and an inexact knowledge of the oxide capacitance is also shown to impede interface trap state analysis near the band edge. In addition, a slight nonlinearity that is typically present throughout the 1/CS∗2 vs ψS plot hinders the accurate estimation of interface trap densities, which is demonstrated for a fabricated n-SiC MOS capacitor device. Methods are suggested to improve quasi-static analysis, including a novel method to determine an approximate integration constant without relying on a linear fitting routine.

Self-assembled carbon wrapped manganese cobaltite nano-composite with promising electrochemical performance for symmetric and asymmetric supercapacitor device

The growing energy requirements of modern society have led to an intensive search for advanced supercapacitor (SC) electrode materials. Binary transition metal oxides with excellent supercapacitive performance are among the most promising materials. However, the phase transformation of these metal oxides during repeated charging/discharging is a major concern, which depletes their cyclic performance. Coating metal oxides with carbon can provide structural stability to the metal oxide, thereby increasing their cyclic life. In addition, the highly conductive carbon enhances the capacitance of metal oxides by allowing the effective transfer of charges from MnCo2O4 to the current collector. In this study, self-assembled carbon-wrapped MnCo2O4 composite has been prepared through a two-step process involving hydrothermal and solution-mixing processes. The structural/electrochemical performances of the composites have been investigated. The optimized composite offered a maximum capacitance of 626.8 Fg−1 withholding 98 % of capacitance for 6000 cycles. Furthermore, the electrochemical performance of the composite has also been tested in an all-redox symmetric SC (SSC) as well asymmetric (ASC) configuration. In the symmetric cell, 30.2 Whkg−1 of energy is reported for 1.6 kWkg−1 of power. The asymmetric cell with the optimized composite as a cathode and MnO2/Activated carbon as an anode was fabricated. The ASC displayed 45.5 Whkg−1 of energy corresponding to 10 kWkg−1. Three SSCs/ASCs in series illuminated a panel of 39 red-LEDs for 9 and 15 min, respectively. The results suggest the promising performance of such composites for hybrid supercapacitors. Thus, the fabrication of all-redox-type SSCs/ASCs can be a futuristic approach for hybrid storage systems.

First-principles study of quantum capacitance of transition metal oxides and nitrogen functionalized graphene as electrode materials for supercapacitor

Graphene, with many advantages, is considered an active electrode material for the supercapacitors. However, its actual utilization performance is limited by its low specific capacitance caused by the poor quantum capacitance. In this article, we explored the effects of transition metal oxides (TMOs = MnO, FeO, CoO, NiO, CuO and ZnO) on the geometric structure, electronic properties, quantum capacitance (CQ) and surface storage charge (Q) of graphene-based materials using first-principles method. The findings of this article illustrate the TMOs could stably adsorb on the surface of graphene-based materials, making the systems exhibit metallic characteristic with conducive electron transfer. Around the Fermi level, introducing the electronic states of TMOs makes the modified graphene reveal a considerable CQ and Q in the negative applied voltages, especially the NiO-G system. Furthermore, the TMOs and nitrogen atoms co-modified graphene can further increase the quantum capacitance value, and the selection of electrode materials can be controlled by the N modification. The interesting results can provide a straightforward and effective strategy for designing the selection graphene-based material electrodes applied in high-energy supercapacitor.

Band-structure based electrostatics model for ultra-thin-body double-gate silicon-on-insulator MOS devices

The effect of quantum confinement has become significant in terms of its impact on the scalability and electrostatics of ultra-thin-body double-gate MOSFETs. In this paper, we present a simplified model to account for the effect of quantum confinement, considering the contribution of the ground-state and the first excited state of the conduction band, on the electron carrier concentration, which when incorporated into the 1-D Poisson’s equation, enables the determination of the electrostatic potential. We establish the accuracy of the proposed model, over a wide range of process and electrical parameters, through aggressively benchmarking the electrostatics parameters obtained from the proposed model with results from the sp 3 d 5 tight-binding method (TBM), over a wide range of device temperatures. Furthermore, a simplified model for the integrated channel charge density is shown in the form of a diffusion layer charge where the thickness and potential of this layer, while being gate voltage dependent, enables the channel charge density obtained from the model to agree well with results from TBM. Through this physics based and accurate model for the integrated charge, a simplified understanding of the gate capacitance is shown as a series combination of the diffusion layer capacitance, strong-inversion capacitance and oxide capacitance, which includes the effects of structural confinement as well as charge confinement at low and high gate voltages, respectively.

Design and Performance Analysis of Negative Capacitance Effect in the Charge Plasma-Based Junction-Less Vertical TFET Structure

In this paper, a negative capacitance (NC) effect in series with normal oxide capacitance is first time introduced to design negative capacitance charge plasma-based junction less vertical TFET structure (NC-CP-JL-VTFET). The introduced negative capacitance enhances the overall gate capacitance and hence gate capacitive coupling and thus renders high current capabilities with reduced sub-threshold slope and threshold voltage. With the use of negative capacitance along with oxide capacitance, it has been seen that the same drain current is achieved at lower gate voltage as compared to without use of negative capacitance and since the voltage scaling is done considerably, the dynamic power dissipation in circuit application can be reduced significantly. To generate the negative capacitance during the device operation; ferroelectric material [Formula: see text](VDF-TrFE) poly(vinylidene fluoride-trifluoro ethylene) is used in stack with SiO2 gate oxide. Various performance parameters of the designed structure such as electron–hole concentration in the tunneling junction, electric field, surface potential, electron–hole quasi-Fermi variation, and drain current variation are investigated and compared with the results of without considering the ferroelectric material in the gate oxide. The variation of the ferroelectric thickness on the device performance is also investigated. The investigation exhibits significant improvement in the drain current and in the other parameters as well. These improvements are seen because of higher capacitive coupling and these effects are further responsible for more energy band bending which in turn govern high electron tunneling. Due to the existence of negative capacitance, the peak value of the electric field gets doubled while the surface potential increases 44% from the normal structure.

Unravelling the Supercapacitive Potential of Zn-Ni-Co Mixed Transition Metal Oxide

Objective: A promising Zn-Ni-Co mixed transition metal oxide was successfully synthesized by means of the sol-gel route and its super capacitive behavior was studied. Methods: The structural, morphology, and functional groups were deduced via XRD, SEM, EDX, and FTIR analysis. The super capacitive performance of the hybrid and ternary mixed transition metal oxides was executed through a three-electrode system, in a 2M KOH electrolyte. Results: The specific capacitance of Zn-Ni-Co O was reckoned to be 415 Fg-1 at 50 mVs-1, thrice as much as the specific capacitance of ZnCo2O4 hybrid transition metal oxide (139 Fg-1). The synergistic effects benefited from multiple metal constituents and low activation energy for electron transportation plays an important role in boosting the electrochemical performance. Conclusion: The obtained results proved that Zn-Ni-Co O ternary composite has a promising future as an alternative for supercapacitor electrodes.

Toward Low‐Power Cryogenic Metal‐Oxide Semiconductor Field‐Effect Transistors

Herein, cryogenic field‐effect transistors (FETs) are discussed. In particular, the saturation of the subthreshold swing due to band tailing is studied. It is shown with simulations and experiments that engineering of the oxide‐channel interfaces and a strong increase of the gate oxide capacitance are effective in improving the switching behavior of the device. The implication of scaling the oxide capacitance on the power consumption of cryogenic devices is investigated, too. Furthermore, an alternative for conventional doping in cryogenic transistors is discussed. Based on synchrotron X‐Ray absorption spectroscopy at total fluorescence (XAS‐TFY) and ultraviolet photoemission spectroscopy (UPS) measurements, it is shown experimentally that in true nanoscale devices, a simple coating yields a shift of the conduction band that is equivalent to a very high dopant concentration. As a result, nanoscale cryogenic steep slope FETs with strongly improved electrical characteristics become feasible.

Evolution of High Dielectric Permittivity in Low-Temperature Solution Combustion-Processed Phase-Pure High Entropy Oxide (CoMnNiFeCr)O for Thin Film Transistors

An investigation of dielectric permittivity on the sintered high entropy oxide (HEO) capacitor composed of Co, Cr, Fe, Mn, and Ni (i.e., (CoCrFeMnNi)O) developed using solution combustion synthesis is performed. Stabilization of the phase in HEO is extremely important as it has a direct influence on the properties. In order to explore phase stabilization, in-depth studies of thermal, structural, morphological, and compositional analyses are carried out. The optimized processing parameters are further implemented on depositing (CoCrFeMnNi)O dielectric thin films followed by a thin film transistor. Irrespective of the reaction medium, the precursors undergo combustion at a low temperature below 250 °C, resulting in amorphous HEO. Upon crystallization at 500 °C, no secondary impurity oxides were detected and phase-stabilized to a spinel structure (Fd3m). A homogeneous distribution of all five cations without any segregation and a completely disordered occupancy of the cations were displayed by the bulk and thin films of HEOs. The spinel (CoCrFeMnNi)O exhibited high permittivity, with values approximately 7.3 × 102 (in bulk) and 3 × 101 (in a thin film), measured at 1 kHz owing to the entropy stabilization effect of HEO. Due to their high permittivity and low leakage current density (∼10–8 A/cm2), the (CoMnNiFeCr)O thin film was integrated into thin film transistors (TFTs) with molybdenum disulfide-channel. TFTs showed a field effect mobility of 8.8 cm2 V–1 s–1, an on–off ratio of approximately 105, a threshold voltage of −1.5 V, and a subthreshold swing of 0.38 V/dec. The low voltage operation (<5 V) of these TFTs makes solution combustion-derived HEO (CoMnNiFeCr)O a potential candidate in microelectronics and optoelectronics applications.

Tunable Multilevel Gate Oxide Capacitance and Flat‐Band Voltage Shift Characteristics by Filament Formation in Double‐Floating‐Gate Metal–Oxide–Semiconductor Capacitors (Adv. Electron. Mater. 4/2023)

Metal–Oxide–Semiconductors In article number 2201110 by Tae-Sik Yoon and coworkers, a tunable multilevel gate oxide capacitance and flat-band voltage shift characteristics in double-floating-gate metal-oxidesemiconductor capacitors are demonstrated as operating with both conducting filament formation and electrical charging in the gate stack, depending on the constituent materials and device geometries. It paves the way for the potential application to non-volatile memory and programmable logic devices.