High Frequency Conductance Research Articles

Atomic layer deposited HfO2 ultra-thin films on different crystallographic orientation Ge for CMOS applications

The properties of the HfO2 ultra-thin films high-k gate stack deposited on surface passivated (GeON) germanium with three different orientations viz. Ge (100), Ge (110) and Ge (111) for CMOS applications have been studied. The effect of post deposition annealing (PDA) at temperatures 350 °C and 400 °C has been investigated. The high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy and atomic force microscopy were used to study the interfacial, chemical and surface properties of atomic layer deposited-HfO2 ultrathin films, respectively. The high frequency conductance method was applied to evaluate the value of interface trap density (Dit) and the lowest Dit of 6.24 × 1012 cm−2ev−1 was evaluated for (111) orientation annealed at 400 °C than (100) and (110) orientation. The effective barrier height extracted from the Fowler-Nordheim conduction transport is in the range of 0.29–0.70 eV for all samples and shows the significant dependence of the substrate orientations and PDA temperature.

Experimental study on the transition of plasmonic resonance modes in double-ring dimers by conductive junctions in the terahertz regime.

Plasmonic dimers that made from two subwavelength particles have drawn much attention in the recent years, which are quite promising in local field enhancement, sensing, high frequency conductance probing and electron tunneling. In this work, we experimentally investigate the mode transition effect of different plasmonic resonances in double-ring dimers when introducing conductive junction at the dimer gap in the terahertz regime. Without the junction, the dimers support a single dipolar bonding dimer plasmonic (BDP) mode. With the junction of a high conductance, two new resonance modes-a screened BDP (SBDP) mode and a charge transfer plasmonic (CTP) mode emerge. Such effect is proved to be unrelated to the shape of the rings, whether circular, square or triangular. However, the resonance statuses of the specific modes are different. Furthermore, we also experimentally study the controllable mode resonance behavior as the conductivity of the junction gradually changes by using superconducting material, and meanwhile numerically investigate the active mode transition behavior as well as the threshold effect. These results show great potential in applications of plasmonic sensing, spectral modulating and optical switching.

New equivalent-electrical circuit model and a practical measurement method for human body impedance

Human body impedance analysis is an effective tool to extract electrical information from tissues in the human body. This paper presents a new measurement method of impedance using armpit electrode and a new equivalent circuit model for the human body. The lowest impedance was measured by using an LCR meter and six electrodes including armpit electrodes. The electrical equivalent circuit model for the cell consists of resistance R and capacitance C. The R represents electrical resistance of the liquid of the inside and outside of the cell, and the C represents high frequency conductance of the cell membrane. We propose an equivalent circuit model which consists of five parallel high frequency-passing CR circuits. The proposed equivalent circuit represents alpha distribution in the impedance measured at a lower frequency range due to ion current of the outside of the cell, and beta distribution at a high frequency range due to the cell membrane and the liquid inside cell. The calculated values by using the proposed equivalent circuit model were consistent with the measured values for the human body impedance.

A high sensitivity ultralow temperature RF conductance and noise measurement setup

We report on the realization of a high sensitivity RF noise measurement scheme to study small current fluctuations of mesoscopic systems at milli-Kelvin temperatures. The setup relies on the combination of an interferometric amplification scheme and a quarter-wave impedance transformer, allowing the measurement of noise power spectral densities with gigahertz bandwidth up to five orders of magnitude below the amplifier noise floor. We simultaneously measure the high frequency conductance of the sample by derivating a portion of the signal to a microwave homodyne detection. We describe the principle of the setup, as well as its implementation and calibration. Finally, we show that our setup allows to fully characterize a subnanosecond on-demand single electron source. More generally, its sensitivity and bandwidth make it suitable for applications manipulating single charges at GHz frequencies.

Moisturizing Effect on the Stratum Corneum of Skin Lotion Containing Egg Shell and Membrane Powder Evaluated by High Frequency Conductance in Healthy Human Volunteers

Moisturizing Effect on the Stratum Corneum of Skin Lotion Containing Egg Shell and Membrane Powder Evaluated by High Frequency Conductance in Healthy Human Volunteers

Gamma-ray irradiation effects on the interface states of MIS structures

Gamma-ray irradiation effects on the interface states of Au/SiO 2/n-Si (MIS) structures have been determined from capacitance–voltage ( C– V) and conductance–voltage ( G/ ω– V) measurements. The MIS structures were irradiated with gamma-rays at doses up to 100 kGy. The C–V and G/ ω– V characteristics were measured at high frequency (1 MHz) and room temperature before and after 60Co γ-ray irradiation. The obtained results showed that the barrier height ( Φ b) decreases with increasing radiation dose, while the interface states ( N ss) and depletion layer width ( W D) increase with the increase in radiation dose obtained from reverse bias C– V measurements. After γ irradiation, the decrease in capacitance and conductance of MIS structure result in the increase in the semiconductor depletion width. In addition, the voltage dependency of the series resistance ( R s) profile for various radiation doses was obtained from admittance-based measurement method. 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 R s to obtain the real capacitance of MIS structure. Experimental results indicate that the total dose radiation hardness of MIS structures may be limited by the decisive properties of the SiO 2/Si interface to radiation-induced damage.

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.

Admittance of a quantum point contact

The high frequency conductance G of a quantum point contact was studied for f ⩽ 300 MHz . While the real part R ( G ) remains unchanged by frequency we observe a stepwise change of the imaginary part I ( G ) when adding additional conductance channels. The step height Δ I ( G ) is linear in frequency with a positive slope and thus has capacitive character with a Δ C per channel of a few fF.

Scientific characterization of subclinical skin changes by noninvasive biophysical methods for development of more efficacious skincare products

In 1966, after finishing only my first year of a residency program, I went to the US to study for 2.5 years with Dr Albert M. Kligman the analysis of functional properties of various skin changes in vivo using aged skin, various types of dermatitis and topically applied steroid‐induced atrophy as experimental models. Ten years later, I luckily found that measurements of high frequency conductance and capacitance of the skin enable us to evaluate the skin surface hydration state that determines the softness and smoothness of the skin and in particular to detect even subtle skin changes induced by changes in our environmental or by the application of skincare products and cosmetics. Employing such noninvasive biophysical instruments, I have analyzed the functional properties of normal and abnormal skin changes including subclinical skin changes such as atopic xerosis, senile xerosis, scars and effects of various topical and systemic agents. From these studies it became apparent that as long as a certain level of barrier function was retained skin surface hydration is a more important factor for enjoying a good quality of life. We also succeeded in confirming the effect of corneotherapy, the term so pertinently suggested by Dr Kligman for the beneficial effects of skincare products. We could show that their daily application definitely improves the condition of subclinical skin problems. Further progress in such instrumental analysis of skin properties will greatly aid us in the future in selecting a more desirable skincare product on an individual basis.

On the profile of frequency dependent series resistance and surface states in Au/Bi 4Ti 3O 12/SiO 2/n-Si(MFIS) structures

The frequency dependent capacitance–voltage ( C– V) and conductance–voltage ( G/ ω– V) characteristics of the metal–ferroelectric–insulator–semiconductor (Au/Bi 4Ti 3O 12/SiO 2/n-Si) structures (MFIS) were investigated by considering series resistance ( R s) and surface state effects in the frequency range of 1 kHz–5 MHz. The experimental C– V– f and G/ ω– V– f characteristics of MFIS structures show fairly large frequency dispersion especially at low frequencies due to R s and N ss. In addition, the high frequency capacitance ( C m) and conductance ( G m/ ω) values measured under both reverse and forward bias were corrected for the effect of series resistance to obtain the real capacitance of MFIS structures. The R s– V plots exhibit anomalous peaks between inversion and depletion regions at each frequency and peak positions shift towards positive bias with increasing frequency. The C −2– V plot gives a straight line in wide voltage region, indicating that interface states and inversion layer charge cannot follow the ac signal in the depletion region, but especially in the strong inversion and accumulation region. Also, it has been shown that the surface state density decreases exponentially with increasing frequency. The C– V– f and G/w– V– f characteristics confirm that the interface state density ( N ss) and series resistance ( R s) of the MFIS structures are important parameters that strongly influence the electrical properties of MFIS structures.

High-frequency conductance of a thin rectangular metal wire

The high-frequency conductance of a straight metal wire of rectangular cross section is calculated. The case when the transverse dimensions of the wire are several times smaller than its length is considered. The condition of diffuse reflection of electrons from the internal surfaces of the wire are taken as the boundary conditions for the problem. The limiting cases are considered, and the results are discussed.

Functional properties of the stratum corneum in patients with diabetes mellitus: similarities to senile xerosis

Although diabetes mellitus is known to induce many pathophysiological changes in the skin, none of the earlier studies has focused on the state of the stratum corneum (SC) in patients with diabetes. In our previous report on a diabetic mouse model, we described a decreased SC hydration state and abnormalities in the function of the sebaceous gland together with a normally retained barrier function of the SC. To examine the functional changes of the SC in patients with diabetes. The following values were measured in 49 patients with diabetes: fasting plasma glucose (FPG) and haemoglobin A1c (HbA1c); skin surface lipid level on the forehead; and high-frequency conductance (HFC) and transepidermal water loss (TEWL) of the SC of the volar forearm and extensor surface of the lower leg. These functions of the SC were compared in two pairs of patient groups, i.e. between groups with high and low FPG, and between groups with high and low HbA1c. The HFC levels on the extensor leg and volar forearm were significantly lower in the group with high FPG (FPG > 110 mg dL(-1)) than in the group with low FPG (FPG < 110 mg dL(-1)), although TEWL values were almost the same in these two groups. The skin surface lipids on the forehead were significantly lower in the former than in the latter. The HFC did not differ significantly between the group with high HbA1c (HbA1c > 5.8%) and the group with low HbA1c (HbA1c < 5.8%), whereas the TEWL of the volar forearm was slightly lower in the former than in the latter. These new results as well as our earlier results with diabetic mice suggest that patients with diabetes mellitus tend to show a reduced hydration state of the SC together with decreased sebaceous gland activity, without any impairment of the SC barrier function.

Influence of environmental stress on skin tone, color and melanogenesis in Japanese skin

Influence of environmental stress on skin tone, color and melanogenesis in Japanese skin

High frequency conductance of a quantum point contact

We present an experimental study of the AC conductance G AC of an atomic force microscope engraved quantum point contact at high frequency f=160 MHz . In agreement with theoretical predictions the real part R(G AC ) is unchanged from the DC-conductance G DC. The imaginary part I(G AC ) changes for every addition of a new conductance channel.

InP Hot Electron Transistors with a Buried Metal Gate

To apply the ballistic nature of hot electrons, an InP hot electron transistor with a buried metal (BM-HET) is reported. In this device, carriers are extracted from the emitter by an attractive potential originating from an embedded metal grating, and they propagate through intrinsic semiconductor material only. A simple estimation shows a high cutoff frequency and low output conductance. The estimated highest cutoff frequency is approximately 1 THz. Fabricated devices show that the collector current increased with the gate bias. After extraction of the leakage current, a clear saturation of the collector current in common-emitter characteristics was confirmed and the possibility of BM-HET as a candidate for high-speed electron devices was demonstrated.

Gamma and electron dose response of the electrical conductivity of polyaniline based polymer composites

Conducting polymers, also known as “synthetic metals”, have been the subject of wide-spread investigations over the past decade due to their very promising characteristics. It was published earlier that the electrical conductivity of polyaniline (PANI) based polymer composites increases to a significant extent when irradiated to gamma, electron or UV radiation. The aim of the present study was to determine the dose response of PANI samples blended with poly(vinyl chloride) (PVC) and chlorinated poly(propylene) (PPCl) by measuring the high frequency conductance of these blends irradiated to different doses. In order to find the most suitable composition of these blends the concentration of both the PPCl and PVC, and the PANI base were changed, respectively. These samples were then gamma irradiated and the induced electrical conductivity was measured in the frequency range of 1 kHz–1 MHz in order to find the most sensitive evaluation conditions. After selecting both, the most suitable measuring conditions as well as the blend compositions, the dose response of the samples was determined in the dose range of 10–250 kGy. With respect to potential dosimetry application the effects of electron irradiation, irradiation temperature and the stability of the irradiated samples have also been investigated.

Pruritus and Hydration State of Stratum corneum in Hemodialysis Patients

Background: Xerosis is the most frequent cutaneous manifestation in hemodialysis (HD) patients, but the association between dry skin and pruritus remains to be clarified. Since the skin surface hygrometer can detect the changes of water content in the stratum corneum more sensitively, we re-examined the relationship between the severity of pruritus and water content in dialysis patients. Methods: Fifty patients who had been undergoing regular HD were examined for the degree of pruritus by clinical grading. Water contents in the stratum corneum at volar forearm and lower leg were assessed by measurement of high-frequency conductance using a skin surface hygrometer both at pre- and postdialysis. Results: Thirty-seven (74%) of dialysis patients complained of pruritus. High-frequency conductance values were significantly lower in HD patients compared to those of age-matched control subjects (n = 13) both at forearm (35.1 ± 3.0 vs. 73.3 ± 10.4 µS, p < 0.01) and lower leg (14.2 ± 1.1 vs. 52.4 ± 7.5 µS, p < 0.01). There was no relationship between the severity of pruritus and age, gender, HD duration, underlying renal disease, or removing fluid volume. A significant reduction of itching score was found in patients using polysulfone membrane. A single HD session using cellulose triacetate or polysulfone membrane significantly increased water content both at forearm and lower leg (p < 0.05). However, the degree of pruritus did not correlate with the skin water content both at the beginning and the end of HD session, respectively. Conclusion: It follows from these findings that water content in the stratum corneum was reduced in HD patients, but did not correlate with the severity of pruritus.

Characterization of the physical properties of the stratum corneum by a new tactile sensor.

BACKGROUND/AIMS: The physical properties of the stratum corneum (SC) change with its water content, which is regulated by the presence of water solutes (natural moisturizing factors) and lipids in the SC, and are considered to be responsible for the induction of desquamation, skin surface roughness, and fine wrinkles. Recently a new type of tactile sensor developed for evaluating the physical properties of objects has been introduced as a simple, non-invasive method to evaluate them; because the data obtained with this sensor have not yet been characterized in detail, we compared them with other physical parameters of the skin. METHODS: A change in resonant frequency (Deltaf ) was measured under various levels of pressure applied by a tactile sensor placed on the cheeks of 29 women. We also measured high-frequency conductance that reflects the hydration state of the skin surface, water holding capacity of the SC, transepidermal water loss (TEWL), skin flexibility, skin elasticity, amino acid composition of the SC, and desquamation index of the SC at the same time, and evaluated the correlation between Deltaf and other physical parameters. RESULTS: The correlation between Deltaf and high-frequency conductance of the SC, and that between Deltaf and the water holding capacity of the SC were substantially high. Deltaf under high pressure was more closely correlated with the acidic amino acid ratio of the SC. Deltaf also showed a correlation with desquamation index for thickness of the SC as well as with skin elasticity, independent of the applied pressure. CONCLUSIONS: Because Deltaf determined with the tactile sensor correlated with other physical parameters specific to the properties of the SC, such as high frequency conductance of the SC, its water holding capacity, ratio of acidic amino acids, and the desquamation index for thickness, the physical properties of the SC may be adequately evaluated with the measurements of Deltaf.

Noise properties and ac conductance of mesoscopic diffusive conductors with screening

A theory of non-equilibrium (``shot'') noise and high frequency conductance in diffusive mesoscopic conductors with screening is presented. Detailed results are obtained for two simple geometries, for both large and short electron-electron scattering length $l_{ee}$, at frequencies of the order of the inverse Thouless time $1/\tau_T$. The conductance and the noise are found to exhibit significant frequency dependence. For $L \ll l_{ee}$, the high-frequency ($\omega\tau_T \gg 1$) shot noise spectral density $S_I(\omega)$ approaches a finite value between $2eI/3$ and $2eI$, depending on the screening properties of the system, with temperature corrections to $S_I(\omega)$ being linear in $T$. However, when $L \gg l_{ee}$, $S_I(\omega)$ grows as $\omega^{1/4}$ (at T=0), is not upper-bound by $2eI$, and has a temperature-dependent component quadratic in $T$. As a result, measurements of $S_I(\omega, T)$ can be utilized as a probe of the strength of electron-electron scattering.

The conductance analysis of ferroelectric KNbO3 single crystal

The complex impedance of KNbO3 single crystal has been investigated at various frequencies from 10 Hz to 10 MHz and at various temperatures from 30°C to 550 °C. The frequency dependence of the impedance shows the characteristic features of the universal dielectric response and is described by an empirical Jonscher type relaxation function. High-frequency conductance dispersion was observed near the Curie temperature (T c = 430 °C) at the frequency of 1.5 MHz. An equivalent circuit model based two parallel G-C circuits was adopted to describe the conductance relaxation behavior observed below and above T c = 430 °C. The conductance relaxation was found as two types of dispersions. One may be caused by intrinsic polarization, the other by mobile carrier. This is attributed to a circuit element that includes the capacitance associated with the ferroelectric polarization processes.