High-low Frequency Capacitance Research Articles

Quality Improvements of Titanium Oxide/Gallium Arsenide MOS Capacitors by Post-Metallization Annealing and Sulfur-Treatment

The characteristics of post-metallization annealed TiO2 with various thicknesses on (NH4)2S-treated GaAs were investigated. The electrical characteristics of TiO2 films grown on (NH4)2S-treated GaAs were improved due to the removal of native oxide. The post-metallization annealing treatment can further passivate the grain boundary of TiO2 film and interface of TiO2/GaAs. With both treatments, the leakage current densities of thick TiO2 (77nm)/GaAs are 1.4 × 10-7 and 2.3 × 10-5 A/cm2 at ± 1.5 MV/cm, and that of thin TiO2 (7.5 nm) are 1.7 × 10-6 and 4.5 × 10-5 A/cm2 at ± 2 V (2.7 MV/cm). The dielectric constant and equivalent oxide thickness can reach 52 and 0.53 nm, respectively. The lowest interface state density is 3.8 × 1012 cm-2eV-1 by the high-low frequency capacitance method.

Electrochemical impedance of poly(9-tosyl-9 H-carbazole-co-pyrrole) electrocoated carbon fiber

In this paper, copolymer of 9-tosyl-9 H-carbazole (TCz) and pyrrole (Py) comonomers were electrochemically deposited onto carbon fiber micro electrode (CFME) as an active electrode material. An electrochemical impedance study on the prepared electrodes is reported. Poly(TCz-co-Py)/CFME is characterized by cyclic voltammetry (CV), Fourier transform infrared reflectance-attenuated total reflection spectroscopy (FTIR-ATR), scanning electron microscopy–energy dispersive X-ray analysis (SEM–EDX), and electrochemical impedance spectroscopy (EIS). Capacitive behaviors of modified CFMEs were defined via Nyquist, Bode-magnitude and Bode-phase plots. An examination is made of which equivalent circuits of R( C( R( Q( RW)))) and R( C( R( Q( RW))))( CR) used for modeling the system. The effect of monomer ratio (mole fraction, X TCz = n TCz/ n TCz + n Py) on the formation of copolymer is reported in 0.1 M sodium perchlorate (NaClO 4)/acetonitrile (ACN) solution. The inclusion of TCz in the copolymer structure was also confirmed by FTIR-ATR, SEM, and CV measurements. The highest low frequency capacitance ( C LF = 22.7 for R( C( R( Q( RW)))) and C LF = 22.6 mF cm −2 for R( C( R( Q( RW))))( CR)) were obtained for X TCz = 0.91.

A Comparative study of redox parameters and electrochemical impedance spectroscopy of polycarbazole derivatives on carbon fiber microelectrode

In this study, N-Carbazole and its derivatives (N-Vinylcarbazole, N-Ethylcarbazole, N-Vinylbenzylcarbazole, and N-Benzylcarbazole) were electrochemically polymerized on carbon fiber microelectrodes (diameter ∼7 µm) by cyclic voltammetry within a potential range from 0.0 to 1.4 V. Redox parameters, Scanning electron microscopic (SEM) images were determined and also capacitance behaviors of polymers were examined via electrochemical impedance spectroscopy (EIS). EIS measurements of polycarbazole derivatives were given comparatively. The existence of a capacitance behavior is shown by Nyquist, Bode magnitude, Bode-phase, Admittance plots relationship. Although the highest low frequency capacitance (CLF=12901 µA cm−2) and maximum phase angle of 81.9 ° at a frequency of 1 Hz were obtained for N-Vinylbenzylcarbazole, the lowest anodic and cathodic potential difference (ΔE=0.04 V) and double layer capacitance (C dl =0.11 µA cm−2) were indicated in 0.1 M LiClO4/PC.

Electrochemical Copolymerization of 3,4-Ethylenedioxythiophene and N-Phenylsulfonyl Pyrrole: Morphologic, Spectroscopic, Electrochemical Characterizations

In this paper, we demonstrate the electrochemical synthesis of a copolymer of -phenylsulfonyl pyrrole (PSP) with 3,4-ethylenedioxythiophene (EDOT) as thin films on single carbon fiber microelectrodes. The deposition conditions on carbon fiber and the influence of monomer concentrations on the copolymerization were shown, as well as the electrochemistry of the resulting copolymers. The inclusion of PSP in the copolymer structure was also confirmed by Fourier transform IR–attenuated total reflectance spectroscopy, where the highest low frequency capacitance was obtained for the mole fraction of PSP 0.86. Poly(EDOT-co-PSP) exhibits high capacitances compared to that of poly(3,4-ethylenedioxythiophene), which was shown by electrical impedance spectroscopy and equivalent circuit modeling (ECM). values obtained from the ECM indicates the porosity of the electrode, which almost remains constant as for . Charge-transfer resistance shows an increasing trend with PSP inclusion into the copolymer due to the partial destruction of conjugation. The double layer capacitance has also shown a similar behavior. Both of these parameters have exhibited an almost linear relationship with the thickness of the film. The film resistance was between 0.88 and . According to the calculations from the ECM, the inclusion of PSP in copolymer improved the capacitance and diffusion properties.

On the temperature dependent profile of interface states and series resistance characteristics in (Ni/Au)/Al 0.22Ga 0.78N/AlN/GaN heterostructures

The bias dependent series resistance ( R s ) and density distribution profile of interface states ( N ss ) of (Ni/Au)/Al 0.22Ga 0.78N/AlN/GaN heterostructure have been investigated by admittance measurements in a wide temperature range of 80–400 K. Experimental results show that both the values of capacitance ( C) and conductance ( G/ ω) were found to be strongly temperature and applied bias voltage dependent. The capacitance–voltage ( C– V) plots give a peak especially at high temperatures in the depletion region and disappear at low temperatures. When the temperature was increased both the values of C and G/ ω reduced. This decrease of capacitance can be understood if the dielectric constant of interfacial layer decreases with increasing temperature. Such temperature dependent behavior of C and G/ ω also can be attributed to the thermal restructuring and reordering of the interface states. The downward curvatures in C– V plots have been attributed to the R s of heterostructure and R s may cause a large deviation in C– V and G/ ω– V data. Therefore, the entire C– V and G/ ω– V measurements were corrected for the effect of R s . Also, the value of R s increases with increasing temperature. The density distribution profile of N ss was obtained from high–low frequency capacitance method. In addition, the temperature dependent ac conductivity ( σ ac ) data obtained between 275 and 400 K show a linear behavior and was fitted to the Arrhenius plot. The E a values were obtained from the slope of ln σ vs 1/ T plots to be −58.5, −59.7, −60.4 and −60.6 meV for the applied biases of −4, −3, −2 and −1 V, respectively.

Analysis of electrical characteristics of Au/SiO 2/n-Si (MOS) capacitors using the high–low frequency capacitance and conductance methods

The purpose of this paper is to analyze electrical characteristics in Au/SiO 2/n-Si (MOS) capacitors by using the high–low frequency ( C HF– C LF) capacitance and conductance methods. The capacitance–voltage ( C– V) and conductance–voltage ( G/ω– V) measurements have been carried out in the frequency range of 1 kHz–10 MHz and bias voltage range of (−12 V) to (12 V) at room temperature. It was found that both C and G/ω of the MOS capacitor were quite sensitive to frequency at relatively low frequencies, and decrease with increasing frequency. The increase in capacitance especially at low frequencies is resulting from the presence of interface states at Si/SiO 2 interface. Therefore, the interfacial states can more easily follow an ac signal at low frequencies, consequently, which contributes to the improvement of electrical properties of MOS capacitor. The interface states density ( N ss) have been determined by taking into account the surface potential as a function of applied bias. The energy density distribution profile of N ss was obtained from C HF– C LF capacitance method and gives a peak at about the mid-gap of Si. In addition, the high frequency (1 MHz) capacitance and conductance values measured under both reverse and forward bias have been corrected for the effect of series resistance ( R s) to obtain the real capacitance of MOS capacitors. The frequency dependent C– V and G/ω– V characteristics confirm that the N ss and R s of the MOS capacitors are important parameters that strongly influence the electrical properties of MOS capacitors.

Interface characterization and current conduction in HfO 2-gated MOS capacitors

Metal-oxide-semiconductor (MOS) capacitors incorporating hafnium dioxide (HfO 2) dielectrics were fabricated and investigated. In this work, the electrical and interfacial properties were characterized based on capacitance–voltage ( C– V) and current–voltage ( I– V) measurements. Thereafter the current conduction mechanism, electron effective mass ( m*), mean density of interface traps per unit area and energy ( D ¯ it ), energy distribution of interface traps density and near-interface oxide traps density ( N NIOT) were studied in details. The characterization reveals that the dominant conduction mechanism in the region of high temperature and high field is Schottky emission. The mean density of interface traps per unit area and energy is about 6.3 × 10 12 cm −2 eV −1 by using high–low frequency capacitance method. The maximum D it is about 7.76 × 10 12 cm −2 eV −1 located at 0.27 eV above the valence band.

On the energy distribution of interface states and their relaxation time and capture cross section profiles in Al/SiO 2/p-Si (MIS) Schottky diodes

The energy distribution profile of the interface states ( N ss) and their relaxation time ( τ) and capture cross section ( σ p) of metal–insulator–semiconductor (Al/SiO 2/p-Si) Schottky diodes have been investigated by using the high–low frequency capacitance and conductance methods. The capacitance–voltage ( C– V) and conductance–voltage ( G/ω– V) characteristics of these devices were investigated by considering series resistance ( R s) effects in a wide frequency range (5 kHz–1 MHz.). It is shown that the capacitance of the Al/SiO 2/p-Si Schottky diode decreases with increasing frequency. The increase in capacitance especially at low frequencies results form the presence of interface states at Si/SiO 2 interface. The energy distributions of the interface states and their relaxation time have been determined in the energy range of (0.362- E v)–(0.512- E v) eV by taking into account the surface potential as a function of applied bias obtained from the measurable C– V curve (500 Hz) at the lowest frequency. The values of the interface state density ( N ss) ranges from 2.34 × 10 12 to 2.91 × 10 12 eV −1/cm 2, and the relaxation time ( τ) ranges from 1.05 × 10 −6 to 1.58 × 10 −4 s, showing an exponential rise with bias from the top of the valance band towards the mid-gap.

Hafnium oxide thin films deposited by high pressure reactive sputtering in atmosphere formed with different Ar/O 2 ratios

The physical and electrical properties of hafnium oxide (HfO 2) thin films deposited by high pressure reactive sputtering (HPRS) have been studied as a function of the Ar/O 2 ratio in the sputtering gas mixture. Transmission electron microscopy shows that the HfO 2 films are polycrystalline, except the films deposited in pure Ar, which are amorphous. According to heavy ion elastic recoil detection analysis, the films deposited without using O 2 are stoichiometric, which means that the composition of the HfO 2 target is conserved in the deposition films. The use of O 2 for reactive sputtering results in slightly oxygen-rich films. Metal-Oxide-Semiconductor (MOS) devices were fabricated to determine the deposited HfO 2 dielectric constant and the trap density at the HfO 2/Si interface ( D it) using the high–low frequency capacitance method. Poor capacitance–voltage ( CV) characteristics and high values of D it are observed in the polycrystalline HfO 2 films. However, a great improvement of the electrical properties was observed in the amorphous HfO 2 films, showing dielectric constant values close to 17 and a minimum D it of 2×10 11 eV −1 cm −2.

Au/SnO2/n-Si (MOS) structures response to radiation and frequency

Metal–insulator–semiconductor (MOS) structures with insulator layer thickness of 290Å were irradiated using a 60Co (γ-ray) source and relationships of electrical properties of irradiated MOS structures to process-induced surface defects have been investigated both before and after γ-irradiation. The density of surface state distribution profiles of the sample Au/SnO2/n-Si (MOS) structures obtained from high–low frequency capacitance technique in depletion and weak inversion both before and after irradiation. The measurement capacitance and conductance are corrected for series resistance. Series resistance (Rs) of MOS structures were found both as function of voltage, frequency and radiation dose. The C(f)–V and G(f)–V curves have been found to be strongly influenced by the presence of a dominant radiation-induced defects. Results indicate interface-trap formation at high dose rates (irradiations) is reduced due to positive charge build-up in the semiconductor/insulator interfacial region (due to the trapping of holes) that reduces the flow rate of subsequent holes and protons from the bulk of the insulator to the Si/SnO2 interface. The series resistance decreases with increasing dose rate and frequency the radiation-induced flat-band voltage shift in 1 V. Results indicate the radiation-induced threshold voltage shift (ΔVT) strongly dependence on radiation dose rate and frequency.

Influence of electron cyclotron resonance nitrogen plasma exposure on the electrical characteristics of SiNx:H/InP structures

We have studied the influence of nitrogen plasma exposure of the InP surface on the electrical characteristics of electron cyclotron resonance deposited Al/SiNx:H/InP devices. Nitrogen plasma exposure was performed just before the SiNx:H deposition without vacuum breaking. A 30 s plasma treatment at low microwave power (60 W) sharply reduces the minimum of the interface trap density, from 4×1012 to 1.6×1012 eV−1 cm−2 (obtained by the high–low frequency capacitance method). We explain this reduction due to the formation of P–N and/or In–P–N complexes at the InP surface during the plasma-exposure step. These bonds are broken thermally after a rapid thermal annealing of the device. The minimum of the interface trap density, obtained at the optimum plasma exposure conditions, is among the lowest ones reported in the literature and similar to those obtained with more complicated processing technologies of the SiNx:H/InP structure. This is a clear indication that plasma exposure in N2 atmosphere seems to be a valuable and simple surface conditioning method.

A simple approach to the capacitance technique for determination of interface state density of a metal–semiconductor contact

In this study we attempt to interpret the experimentally observed nonideal Al–pSi Schottky diode I– V and C– V characteristics. The expressions for the capacitance–voltage relationship at low frequency and high frequency are derived considering two non idealities, namely interface states and series resistance. After extracting the diode parameters from the I– V and C– V characteristics, theoretical plots for the high frequency and low frequency capacitance are obtained using the expressions derived. A comparison of the latter with available experimental plots reveals that the expressions for the low frequency and high frequency capacitance derived here are simpler, more accurate and closer to experimental results than those used in the past. The variation of interface state density with the applied bias voltage is obtained from the low frequency and high frequency C– V plots by using the capacitance technique. To examine the validity of the present approach, the value of density of interface states is compared with that obtained by the multifrequency admittance method. It is observed that there is good agreement between the results obtained by both methods.

Accurate measurement of trivalent silicon interface trap density using small signal steady-state methods

The high–low-frequency capacitance method for determining the interface trap density is widely used in studying the effects of ionizing radiation on thermally grown SiO2, and in verifying the trivalent silicon interface traps first discovered in electron paramagnetic resonance studies. It is shown that the high–low-frequency capacitance method gives fictitious interface trap density peaks because of the departure of the 1-MHz high-frequency capacitance from the ideal high-frequency capacitance. This method gives accurate values of the interface trap density near the center of the silicon band gap, but for a given high frequency, the range of band-gap energy over which accurate values are obtained decreases with increasing interface trap density. Interface trap density is obtained over a band-gap energy range with an accuracy that is independent of interface trap density from a comparison of the measured and calculated slopes of gate bias versus equilibrium band-bending curves using the Q-C (charge-capacitance) method. The accuracy of this method is verified using the conductance method. This work shows that it is not likely that interface traps are trivalent silicon defects superimposed on a U-shaped background interface trap distribution of unknown identity.