Frequency Dependence Of Capacitance Research Articles

Presence of capacitive memory in indium doped TiO2 alloy thin film

A capacitive memory effect has been reported for Indium (In) metal doped titanium dioxide (TiO2) alloy thin film (TF). Two distinct structures of Au/TiO2 TF/n-Si and Au/In doped TiO2 alloy TF/n-Si were fabricated by e-beam deposition technique. An instantaneous source of In was used to dope the TiO2 TF on the Si substrate. The frequency dependent capacitance (C) -voltage (V) and conductance (G) -voltage (V) characteristics were measured to analyze charge trapping behavior of both the devices. The study revealed that the frequency dispersion in the accumulation region decreases more for the undoped device (∼3 nF) compared to doped alloy (∼6.12 nF) device. The maximum memory window of 4.74 V was obtained from the In doped alloy device as compared to the undoped TF device with 1.16 V under sweeping top gate biasing of ±8 V. Large hysteresis in the depletion region was obtained for In doped TiO2 alloy TF device.

Effects of frequency-dependent membrane capacitance on neural excitability

Objective. Models of excitable cells consider the membrane specific capacitance as a ubiquitous and constant parameter. However, experimental measurements show that the membrane capacitance declines with increasing frequency, i.e., exhibits dispersion. We quantified the effects of frequency-dependent membrane capacitance, c(f), on the excitability of cells and nerve fibers across the frequency range from dc to hundreds of kilohertz. Approach. We implemented a model of c(f) using linear circuit elements, and incorporated it into several models of neurons with different channel kinetics: the Hodgkin–Huxley model of an unmyelinated axon, the McIntyre–Richardson–Grill (MRG) of a mammalian myelinated axon, and a model of a cortical neuron from prefrontal cortex (PFC). We calculated thresholds for excitation and kHz frequency conduction block, the conduction velocity, recovery cycle, strength–distance relationship and firing rate. Main results. The impact of c(f) on activation thresholds depended on the stimulation waveform and channel kinetics. We observed no effect using rectangular pulse stimulation, and a reduction for frequencies of 10 kHz and above using sinusoidal signals only for the MRG model. c(f) had minimal impact on the recovery cycle and the strength–distance relationship, whereas the conduction velocity increased by up to 7.9% and 1.7% for myelinated and unmyelinated fibers, respectively. Block thresholds declined moderately when incorporating c(f), the effect was greater at higher frequencies, and the maximum reduction was 11.5%. Finally, c(f) marginally altered the firing pattern of a model of a PFC cell, reducing the median interspike interval by less than 2%. Significance. This is the first comprehensive analysis of the effects of dispersive capacitance on neural excitability, and as the interest on stimulation with kHz signals gains more attention, it defines the regions over which frequency-dependent membrane capacitance, c(f), should be considered.

Multilayer Ge nanocrystals embedded within Al2O3 matrix for high performance floating gate memory devices

Metal-insulator-silicon devices with Ge nanocrystals dispersed in Al2O3 have been studied with a view to exploit them for floating gate memory applications. Multilayer devices comprising of five layers Ge nanocrystals have exhibited superior memory characteristics over the single layer Ge and multilayer Si nanocrystals reported in literature. The effect of interface traps on the memory behavior using frequency dependent capacitance- and conductance-voltage measurements has been investigated. This study has demonstrated an enhanced memory window with superior retention characteristics, owing to the Coulomb blockade effect, due to the introduction of multi-layer nanocrystals in the floating gate.

Trap states in enhancement-mode double heterostructures AlGaN/GaN high electron mobility transistors with different GaN channel layer thicknesses

This is the report on trap states in enhancement-mode AlGaN/GaN/AlGaN double heterostructures high electron mobility transistors by fluorine plasma treatment with different GaN channel layer thicknesses. Compared with the thick GaN channel layer sample, the thin one has smaller 2DEG concentration, lower electron mobility, lower saturation current, and lower peak transconductance, but it has a higher threshold voltage of 1.2 V. Deep level transient spectroscopy measurements are used to obtain the accurate capture cross section of trap states. By frequency dependent capacitance and conductance measurements, the trap state density of (1.98–2.56) × 1012 cm−2 eV−1 is located at ET in a range of (0.37–0.44) eV in the thin sample, while the trap state density of (2.3–2.92) × 1012 cm−2 eV−1 is located at ET in a range of (0.33–0.38) eV in the thick one. It indicates that the trap states in the thin sample are deeper than those in the thick one.

Influence of active layer thickness on contribution of hole and electron trapping to threshold voltage instability in organic field effect transistors

Effect of active layer thickness on threshold voltage stability was studied. Threshold voltage instability was found to be minimum for an optimum thickness of 15nm when operated under normal room light conditions. Influence of active layer thickness on individual contribution of hole and electron trapping effect to hysteresis was estimated. Hole and electron trap concentrations were found to exhibit different pattern of variation with thickness compared to each other. Film with 15nm thickness exhibited minimum hole trapping and maximum electron trapping effect. This could be attributed to reduced grain boundary density and availability of large photogenerated carrier concentration at the dielectric/semiconductor interface. Along with electron trap, hole trap concentrations were also shown to be significantly influenced by photogenerated carrier concentration at the interface. For further increase in thickness, increase in hole trapping and reduction in electron trapping were observed again. This could be attributed to (a) increase in grain boundary density due to volume effect and (b) lesser number of photogenerated carriers at the interface due to limitations in exciton quenching length. Hole and electron trapping effect were suggested to be mutually affecting each other, depending on active layer thickness. Effect of active layer thickness was further confirmed with frequency and voltage dependent capacitance measurements.

Evaluation of Three Terminal Capacitance Standards at CSIR-NPL

The reported work is the part of the establishment of metrological traceability of high frequency impedance standards at CSIR-NPL. The evaluation of three terminal GR 1404 type air capacitance standards of nominal values 100 and 1000 pF has been completed using electrical equivalent circuit model. This involves the measurement of reference capacitance at 1 kHz and residual parameters which are capacitive and inductive in nature. Frequency dependent inductance is estimated using linear curve fit from measured residual inductive parameters. Then frequency dependent capacitance value for capacitance standards has been computed at set of frequencies ranging from 1 kHz to 1 MHz.

Investigation of hole transport in α-NPD using impedance spectroscopy with F4TCNQ as hole-injection layer

The charge carrier transport is studied in N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (α-NPD) with the incorporation of sequentially doped p-type dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) as hole-injection layer in hole-only device structures. The field dependent mobility of the charge carriers is determined using frequency dependent capacitance, conductance and impedance methods by varying the thickness of α-NPD. The Poole–Frenkel zero-field mobility and the Poole–Frenkel coefficient thus obtained for each device in all the three methods is found to be almost constant.

Analysis of negative capacitance and self-heating in organic semiconductor devices

In admittance spectroscopy of organic semiconductor devices, negative capacitance values arise at low frequency and high voltages. This study aims at explaining the influence of self-heating on the frequency-dependent capacitance and demonstrates its impact on steady-state and dynamic experiments. Therefore, a one dimensional numerical drift-diffusion model extended by the heat equation is presented. We calculate the admittance with two approaches: a Fourier method that is applied to time domain data and a numerically efficient sinusoidal steady state analysis (S3A), which is based on the linearization of the equations around the operating point. The simulation results coincide well with the experimental findings from reference [H. Okumoto and T. Tsutsui, Appl. Phys. Express 7, 061601 (2014)] where the negative capacitance effect of an organic device becomes weaker with better cooling of the structure. Linking the frequency- and time-domain with the Fourier approach supports an effortless interpretation of the negative capacitance. Namely, we find that negative capacitance originates from self-heating induced current enhancement.

Potentiality of trap charge effects and SiON induced interface defects in a-Si3N4/SiON based MIS structure for resistive NVM device

Potential application of amorphous silicon nitride (a-Si3N4)/silicon oxy-nitride (SiON) film has been demonstrated as resistive non-volatile memory (NVM) device by studying the Al/Si3N4/SiON/p-Si metal–insulator–semiconductor (MIS) structure. The existence of several deep trap states was revealed by the photoluminescence characterizations. The bipolar resistive switching operation of this device was investigated by current–voltage measurements whereas the trap charge effect was studied in detail by hysteresis behavior of frequency dependent capacitance–voltage characteristics. A memory window of 4.6V was found with the interface trap density being 6.4×1011cm−2eV−1. Excellent charge retention characteristics have been observed for the said MIS structure enabling it to be used as a reliable non-volatile resistive memory device.

Preparation of silver-hydroyapatite/PVA nanocomposites: Giant dielectric material for industrial and clinical applications

Pure hydroxyappatite Ca10(PO4)6(OH)2 (or HAP) was prepared from eggshell and potassium dihydrogen phosphate (KH2PO4) by a simple self-chemical reaction method. The clean eggshell was heated at 800 °C in air giving the source of CaO. Appropriate amount of CaO was dissolved in KH2PO4 solution at 37°C for few days. The PH value decreases with increasing the duration of preparation of HAP. Silver nanoparticles derived from silver nitrate solution using black tea leaf extract had been introduced to hydroxyapatite due to its biocompatibility. The unique size- dependent properties of nanomaterials make them superior and indispensable. In this work, hydroxyapatite-silver nanoparticles/polyvinyl alcohol (PVA) composites with 4 different concentrations of hydroxyapatite (1-4 wt %) were prepared by bio-reduction method. Several techniques like XRD and SEM were used to characterize the prepared samples. Frequency dependent capacitance and conductance of the samples were measured using an impedance analyzer. The results showed a remarkable increase in dielectric permittivity (~5117) with low loss (~0.23) at1000 HZ and room temperature (300K) for 4wt% Hydroxapatie-Silver/PVA nanocomposite. Such nanocomposite might be directly applied in manufacturing clinical devices and also for embedding capacitor applications.

Capacitance and conductance studies on silicon solar cells subjected to 8MeV electron irradiations

The space grade silicon solar cells were irradiated with 8 MeV electrons with doses ranging from 5–100 k Gy. Capacitance and conductance measurements were carried out in order to investigate the anomalous degradation of the cells in the radiation harsh environments and the results are presented in this paper. Detailed and systematic analysis of the frequency-dependent capacitance and conductance measurements were performed to extract the information about the interface trap states. The small increase in density of interface states was observed from the conductance–frequency measurements. The reduction in carrier concentration upon electron irradiation is due to the trapping of charge carriers by the radiation induced trap centres. The Drive Level Capacitance Profiling (DLCP) technique has been applied to study the properties of defects in silicon solar cells. A small variation in responding state densities with measuring frequency was observed and the defect densities are in the range 10 15 –10 16 cm −3 . • Space grade Si solar cells were subjected to 8 MeV electron radiation. • Capacitance and conductance measurements were done before and after irradiation. • Density of interface states and the interface trap time constant is found to increase with increasing electron dose. • The displacement damage formed due to electron is not uniform throughout the active region of c-Si solar cell.

Space charge-induced unusually-high mobility of a solution-processed indium oxide thin film transistor with an ethylene glycol incorporated aluminum oxide gate dielectric

Undecomposed ethylene glycol residuals in solution processed aluminum oxide gate dielectric result in the frequency-dependent capacitance.

Characterization of Interface Charge in NbAlO/AlGaN/GaN MOSHEMT with Different NbAlO Thicknesses

We investigate the influence of interface charge on electrical performance of NbAlO/AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOSHEMTs). Through C—V measurements and simulations, we find that the donor-type interface fixed charge density Qit of 2.2 × 1013 cm−2 exists at the NbAlO/AlGaN interface, which induces the shift of the threshold voltage much more negative. Furthermore, a trap density of approximately 0.43 × 1013–1.14 × 1013 cm−2eV−1 is obtained at the NaAlO/AlGaN interface, which is consistent with the frequency-dependent capacitance and conductance measurement results.

Fabrication and electrical characterization of bamboo fiber-reinforced polypropylene composite

The objective of this research is to characterize the bamboo fiber extracted from bamboo culms and to use these fibers as reinforcement in polypropylene-based composites. In the experiment, the fiber was characterized using wet chemical analysis, scanning electron microscope, and Fourier transform infrared spectroscopy. Chemical analysis showed that bamboo fiber had high amount of holocellulose containing alpha cellulose with compact sclerenchyma sheath. Bamboo fiber showed significant wave length at 3420 cm−1 for –OH stretching, 2921 cm−1 for –CH stretching, and 896 cm−1 for 1,4-β linkage for cellulose units in Fourier transform infrared spectroscopy spectrum. This paper also illustrates the electrical properties of the fabricated composite that consist of bamboo fiber-reinforced polypropylene. At constant temperature (about 30℃), frequency dependence of capacitance, resistivity, and dielectric constant was observed. There were approximately 19.35%, 90.38%, and 66.67% decrease in capacitance, resistance, and dielectric constant, respectively, over a range of frequency from 1 kHz to 10 kHz. This research is focused to use the polymeric composite as an insulating material while observing its electrical properties.

Spectroscopic characterization of a red light-emitting polymer: Anthracene-containing poly(p-arylene-ethynylene)-alt-poly(p-arylene-vinylene)

We report fabrication and characterization of a red polymer light emitting device (PLED) based on poly (p-arylene-ethynylene)-alt-poly(p-arylene-vinylene) (AnE-PVstat). The electroluminescence (EL) spectra peaking at 620nm and the resulting PLED is red in color. To determine both hole and electron mobilities in AnE-PVstat, we used current–voltage (I–V) and impedance spectroscopy (IS) based on capacitance (conductance) versus frequency (C–f) ((G–f)) measurements. We employed a negative differential susceptance (–ΔB) and differential conductance (ωΔG) methods respectively from (C–f) and (G–f) measurements. The electron mobility in AnE-PVstat thin film measured with J–V characteristic and IS are nearly identical, it is high, compared to other organic semiconductors and is closed to 10−3cm2V−1s−1. Frequency dependent capacitance displays a power law dependence “s” which decreases with applied voltage indicating a dominant hopping process.

Capacitance-conductance-frequency characteristics of Au/Ni/n-GaN/undoped GaN Structures

Frequency-dependent capacitance (C) and conductance (G) characteristics of the Au/Ni/n-GaN/undoped GaN device have been investigated in the reverse bias voltage range of 0.00–0.40V. The GaN films have been epitaxially grown by metal organic chemical vapor deposition on c-plane Al2O3 substrate. The measurement frequency (f) ranges from 1.0kHz to 10MHz. The slow and fast interface states with two time constants differing by about two orders of magnitude have been calculated from analysis of the reverse bias C-f and G-f characteristics. The interface state density has values of 1010–1011eV−1cm−2 and time constant has taken the values which change in range of 10−5–10−7s. The phase angle versus bias voltage curves have shown at four different frequencies at the room temperature that the device behaves more capacitive at the reverse bias region rather than the forward bias region at 100 and 200kHz.

Formation of Shallow n-p Junctions in Cz-Si by Low-Energy Implantation of Carbon Ions

I ntroduction Heat treatments of Cz Si in the temperature range between 400 and 1200°С result in the aggregation of supersaturated interstitial oxygen leading to the formation of bulk defects. At low temperatures in the range between 450 and 650°C, the formation of small clusters (O3, O4) leads to shallow thermal donor (TD) centers. The presence of carbon has a considerable influence on thermal donor formation due to the small size of the substitutional carbon atom leading to a tensile stress field around it.It is possible to introduce into the subsurface layer of silicon the atoms of carbon in a wide range of concentrations, and to create a p-n junction in p-type Si. Taking into account the low diffusion coefficient of carbon in silicon and the low temperature of carbon-oxygen TD formation, it is possible to form shallow p-n junctions (<100 nm) by means of implantation of carbon ions.In this study, a low-temperature method is developed for the creation of shallow р-n junctions using carbon ion implantation controlled TD formation. The described approach can be used for different applications, in particular, for photo-converters manufacturing, as low temperatures do e.g. not lead to lifetime degradation of non-equilibrium charge carriers. Experimental (001) Cz Si wafers with oxygen concentration of about 8×1017 сm- 3 are implanted by carbon ions with an energy of 20 keV and doses between 6.0×1012 and 1.3×1015 cm- 2. After implantation, thermal annealing at temperatures between 550 and 750°С is performed during 20 to 300 minutes in argon ambient. Investigations of electro-physical properties of the structures are performed using the admittance method. This method allows to obtain information about the concentration and energy position of levels in the forbidden gap of the semiconductor that are responsible for the observed frequency dependence of capacitance in these structures. The type, size and concentration of structural defects in the investigated silicon samples are investigated using X-ray diffraction and diffuse scattering. Results and discussion It is shown that the concentration of TD's depends on annealing temperature and dose of carbon ions. The maximum concentration (3×1016 cm-3) of TD's is observed after annealing at 650°С and for a carbon dose of 6×1013 cm-2. Annealing at 750°С leads to an annihilation of the TD's.The temperature dependence of CVC's is shown in the figure for high-frequencies of the test signal (3 MHz). This dependency has a clear maximum of capacity in the voltage range from - 6 to 3 V. The existence of this maximum in the CVC indicates that in a certain part of the investigated structure there is an electric charge storage due to the creation of a considerable concentration of TD's near the surface of the p-type substrate. Analysis of the temperature dependence of the capacitance integral within the limits of the voltages, where this peak is observed, had been carried out. The value of the integral that is equal to the peak area under the CVC curve has been calculated, allowing to extract an activation energy for the TD's of 0.012 eV in the temperature interval between 25°С and 160°С.X-ray diffuse dispersion measurements are also performed on the samples containing TD's and reveal that the signal intensity increase correlates with an increase of TD concentration. After annealing at 650°С, the scattering intensity and the related concentration of point defects are at maximum. Annealing at 750°С leads to a decrease of the concentration of interstitial defects and of TD's. The nature of investigated TDs is related to interstitial and oxygen complexes. The implanted carbon is a stimulating factor for the gettering of oxygen, defect nucleation and growth of TD's. Conclusions It is shown that by implantation of carbon ions and subsequent annealing at temperatures between 600 and 700°C in Cz-silicon it is possible to form p-n junctions with breakdown voltages of 100-150 V. The highest breakdown voltages and lowest leakage currents are obtained using an implantation dose of 6×1013 cm-2 followed by annealing at 650°C.

Analysis of interface trap states in InAlN/AlN/GaN heterostructures

Gate-source frequency-dependent capacitance and conductance measurements were performed on the In0.17Al0.83N/AlN/GaN heterostructure field-effect transistor with side-Ohmic contacts to study the characteristics of trap states at the interface between InAlN and GaN. The values of interface trap state density and time constant were determined to be (0.96–3.36) × 1013 cm−2 eV−1 and (0.29–1.61) μs, respectively. We calculated the strain in the InAlN barrier layer under the gate and found that the InAlN barrier layer was compressively strained with the in-plane strain of 1.31%. This is a possible reason for such a high interface trap state density which is not as low as supposed in the lattice-matched heterostructures.

General equivalent circuit derived from capacitance and impedance measurements performed on epitaxial ferroelectric thin films

Voltage and frequency dependent capacitance measurements were performed on epitaxial BaTiO3 and Pb(Zr0.2Ti0.8)O3 thin films deposited on single crystal SrTiO3 substrates with (001) and (111) orientations. The measured capacitors have common bottom SrRuO3 contact and different metals as top electrodes: SrRuO3, Pt, Cu, Al, and Au. The capacitance-voltage characteristics were used to extract information regarding the density of the free carriers and the linear contribution to the static dielectric constant. The frequency dependent impedance was used to develop a suitable equivalent circuit for the epitaxial ferroelectric capacitors. It was found that the frequency dependence of the imaginary part of the impedance can be well simulated, in all cases, using a circuit composed of Schottky-type capacitance related to electrode interfaces, contact resistance, and the R-C parallel connection related to the ferroelectric volume of the film. Values for the components of the equivalent circuit were obtained by fitting the experimental data with the simulated curves. These were then used to extract quantities such as dielectric constant in the ferroelectric volume, the width of the depletion layers, and the apparent built-in potential. It was found that, although the investigated capacitors are of different ferroelectric materials, grown on substrates with different orientations, and having different metals as top electrodes, the values for the capacitance associated with the Schottky contacts and the apparent built-in potential are not very different. The results suggest a strong influence of ferroelectric polarization on the electrode interface properties in the case of epitaxial ferroelectric films.

Frequency-dependent quantum capacitance and plasma wave in monolayer transition metal dichalcogenides

Frequency-dependent quantum capacitance CQ of monolayer transition metal dichalcogenides (TMDs) is computed and compared to that of graphene. It is found that the frequency dependence of CQ in TMDs differs drastically from that of graphene which has a divergent point. The plasma resonance forms when the quantum capacitance is negative and has the same magnitude as the electrostatic capacitance. The calculation shows that the plasma in TMDs depends on the band-structure-limited velocity, band gap, and doping density, which can be controlled via gate biases. The plasma frequencies of TMDs are in the rage of terahertz useful for various applications.