Changes In Electrical Characteristics Research Articles

Polymer-based microsensor for soil moisture measurement

A moisture microsensor based on poly(3,4-ethylenedioxythiophene–poly(styrene-sulfonate) (PEDOT–PSS) conductive polymer is developed and presented in this paper. The change in electrical characteristics of the PEDOT–PSS polymer film is used to determine its sensitivity and working mechanism when exposed to different levels of moisture content. The output characteristics, the change in electrical sheet resistance of the PEDOT–PSS film versus the percentage change in relative humidity (%RH), show that the conductivity of the film decreases when it is exposed to increasing levels of moisture content. The moisture sensors thus fabricated based on the PEDOT–PSS thin film were used to detect the gravimetric water content present in highly plastic (CH) soil samples (Buckshot Clay) for geological and geotechnical engineering applications. The Fourier transform infrared spectroscopy (FT-IR) study of the PEDOT–PSS film on a glass substrate showed the incorporation of OH molecules in the film when it was exposed to moisture environment. This incorporation of OH molecules caused the change in resistance of the PEDOT–PSS film when exposed to moisture content. The change in the output resistance of the sensor device was observed to be from 2.5 to 4.0 M ohm when exposed to soil samples with 15–35% change in gravimetric water content.

Sudden Change of Electrical Characteristics at Lasing Threshold of a Semiconductor Laser

Accurate forward electrical characteristics of multiquantum-well (MQW) lasers have been measured using ac admittance measurements together with dc I-V plot. The synchronous step offsets of apparent conductance, apparent capacitance, junction voltage, series resistance, and ideality factor at the onset of lasing were observed for the first time. With this effect, the lasing threshold can be deduced immediately by the LCR Meter. It is also found that the junction voltage jumps abruptly to a saturated value at the onset of lasing, and the starting and end points of jumping exactly correspond to the maximum of the second derivative of lasing power with respect to current and the kink point of the first derivative, respectively. All of the phenomena may help to verify and improve existing semiconductor laser models. In addition, negative capacitance effect in LDs was observed

Effects of molecular oxygen and ozone on polythiophene-based thin-film transistors

The effects of exposure of polymeric thin-film transistors (TFTs) to the ambient atmosphere, oxygen, and ozone were investigated. The off-state current increased and the threshold voltage became more positive for TFTs made with several thiophene-based polymers when exposed to the ambient. Exposure to purified air did not change the characteristics of TFTs. Exposure to ozone caused similar changes as exposure to the ambient. Density functional calculations showed that ozone forms a complex with polythiophene, that is, a shallow acceptor. These results suggest that ozone in the ambient can cause changes in electrical characteristics of polythiophene-based TFTs rather than oxygen.

Changes in Electrical Characteristics of ZnO Thin Films Due to Environmental Factors

The impact of light and controlled gas ambient on the electrical characteristics of ZnO:P grown by pulsed laser deposition (PLD) is investigated with temperature-dependent Hall-effect and photo-Hall-effect using above-bandgap light. Exposure to blue/ultraviolet (UV) light results in long-lived persistent photoconductivity (PPC) effects dominated by electron conduction. However, these persistent effects can be largely reversed by exposing the sample to a controlled ambient of dry O2 gas. These O2-induced changes in the electronic properties persist in vacuum up to at least 400 K. Exposure to dry N2 gas following blue/UV light has no effect on the observed PPC characteristics. The implications of these effects on the preparation of p-type ZnO will be discussed.

Cu-Ni/Cu/Cu-Ni 積層材料の抵抗特性

Resistive materials with resistivity (ρ) of 10.3 to 25.1×10-8 Ωm and temperature coefficient of resistance (TCR) of 540 to 2800×10-6 K-1 were successfully fabricated by using the stacking and rolling of metallic sheets of Cu and Cu-Ni. The Cu-Ni/Cu/Cu-Ni sandwich structure showed changes of electrical characteristics with the conditions of heat treatment. The TCR values of the specimens decreased with increase of diffusion layer thickness at the interface of Cu and Cu-Ni layers by heat treatment. This process allows the electrical characteristics to be controlled as required, and the preparation of a precise resistor for current detection.

Modified Rare Earth Semiconductor Oxide As a New Nucleotide Probe

Recent rapid developments in biological analysis, medical diagnosis, pharmaceutical industry, and environmental control fuel the urgent need for recognition of particular DNA sequences from samples. Currently, DNA detection techniques use radiochemical, enzymatic, fluorescent, or electrochemiluminescent methods; however, these techniques require costly labeled DNA and highly skilled and cumbersome procedure, which prohibit any in-situ monitoring. Here, we report that hybridization of surface-immobilized single-stranded oligonucleotide on praseodymium oxide (evaluated as a biosensor surface for the first time) with complimentary strands in solution provokes a significant shift of electrical impedance curve. This shift is attributed to a change in electrical characteristics through modification of surface charge of the underlying modified praseodymium oxide upon hybridization with the complementary oligonucelotide strand. On the other hand, using a noncomplementary single strand in solution does not create an equivalent change in the impedance value. This result clearly suggests that a new and simple electrochemical technique based on the change in electrical properties of the modified praseodymium oxide semiconductor surface upon recognition and transduction of a biological event without using labeled species is revealed.

An investigation on air stability of copper phthalocyanine-based organic thin-film transistors and device encapsulation

The device performances of copper phthalocyanine (CuPc)-based organic thin-film transistors (OTFTs) in main components of air were studied. We found that the device stored in O2 humidified by water exhibited the changes of electric characteristics including positive-shifted threshold voltage and lower Ion/Ioff but unchanged mobility, which was similar to the device exposed to room air. These changes are attributed to O2 doping to copper phthalocyanine thin film assisted by water. Furthermore, a cross-linked polyvinyl alcohol film was used as encapsulation layer to prevent the permeation of O2 and water, which resulted in excellent stability even when devices were placed in air for over a year. Therefore, current studies will push the development of OTFTs for practical applications.

Effects of humidity on unencapsulated poly(thiophene) thin-film transistors

The effects of humidity on unencapsulated polymeric thin-film transistors (TFTs) of poly[5,5’-bis(3-dodecyl-2-thienyl)-2,2’-bithiophene] (PQT-12) were investigated. The field effect mobility of PQT-12 TFTs decreases and the rate of trapping of charge carriers increases under increasing humidity. The amount of water absorbed by the PQT-12 films was measured using a quartz crystal microbalance. Thin films of PQT-12 absorb comparable amounts of water to the carrier concentration in TFTs under routine operating conditions (humidity of 30% relative humidity and gate voltage of −30V); the changes in electrical characteristics under humid atmospheres are attributed to the interaction of absorbed water with the carriers in the film.

Environmental sensitivity of Au diodes on n-AlGaN

With growing interest in AlGaN for ultraviolet detectors and high-power/high-temperature electronic devices, the problem of forming high-quality Schottky contacts to this semiconductor has become increasingly important. It was shown that wet-chemical surface pretreatments affect the as-deposited diode characteristics for Au/n-AlGaN Schottky diodes. However, these diodes improve over the course of days when exposed to air at room temperature, exhibiting reduced leakage currents, enhanced barrier heights, and reduced ideality factors. Exposure to oxygen, with an enhanced effect in the presence of water vapor, is responsible for the environmental aging. The environmental aging was found to occur regardless of the source of AlGaN, surface preparation, and metal deposition technique. It was determined that high asdeposited reverse currents were due to current transport beneath the contact area, rather than across the semiconductor surface. Two findings further suggested that the change in electrical characteristics was due to a phenomenon occurring at the metal/semiconductor interface. First, metal thickness played a key role in the rate of change of the electrical characteristics, with thicker contacts being more impervious to surrounding gas species at room temperature. Second, a metal that readily forms an oxide, Ni, exhibited little environmental aging, while noble metals, such as Au and Pt, showed dramatic effects. Mild anneals revealed that the environmental change was partially reversible, which suggests the passivation of electrically active defects at the metal/semiconductor interface as the cause of the altered diode behavior. Taken together, the data indicate that oxidizing species diffuse through noble metal contacts to the metal/semiconductor interface and passivate electrically active defects, which may be reactivated upon mild anneals in N2.

Fast array analysis using a combination of FDTD and matrix manipulation techniques

In many cases, antenna array design and modelling are performed by the finite difference time domain (FDTD) method. The method is robust but very demanding in computer memory and CPU power. The authors present a new method that allows otherwise impractical FDTD simulations to produce valid results with no great dissipation of computer power. This is achieved with a combined effort of reduced full-wave simulations and matrix manipulations in the proposed array geometry. With the new scheme, the computational limitations of the conventional FDTD analysis are surpassed and the scope of the analysis itself is broadened; changes in electrical characteristics of an array, such as beam scanning, do not necessitate new simulation runs.

Photostimulated Changes of Electrical Characteristics of Ag/CdTe Thin Film Structures

AbstractElectrical, optical and structural properties of Ag/CdTe structures exposed to thermal (in dark) and photoannealing (under illumination) have been studied. The effective diffusion coefficie nt of Ag in CdTe films have been estimated from resistance versus duration of annealing curves. In the range of 280-420°C the effective coefficient of thermal diffusion (Dt) and photodiffusion (Dph) are described as Dt= 1.9x105exp (-1.60/kT) and Dph =8.7x103exp(-1.36/kT). The acceleration of Ag diffusion under illumination was tentatively attributed to photoionization of Ag increasing the interstitial flux of silver. Ag/CdTe structures exposed to annealing were characterized by X-ray diffraction (XRD), I-V, C-V, conductivity-temperature and optical transmission measurements. In XRD patterns of annealed Ag/CdTe structures, besides the intensive (111) peak of cubic CdTe, the weak peaks of Ag2Te phase are also present. The temperature dependence of conductivity of annealed Ag/CdTe structures showed the energy levels 0.13 eV.

Role of Liquid Phase in PTCR Characteristics of (Ba0.7Sr0.3)TiO3 Ceramics

The role of liquid phase in the enhancement of the PTCR (positive temperature coefficient of resistance) effect in (Ba 0.7 Sr 0.3 )TiO 3 (BST) with the addition of AST (4Al 2 O 3 . 9SiO 2 .3TiO 2 ) is investigated in this paper. The AST-BST samples were characterized with optical microscopy, transmission electron microscopy, energy-dispersive spectroscopy, and impedance spectroscopy. Microscopic observations showed that slower cooling might facilitate the precipitation of the (Ba,Sr)TiO 3 phase from the liquid phase on matrix grains since the amount of liquid phase was reduced with a decreasing cooling rate. Impedance spectroscopy indicated that this variation accompanied the change in the intrinsic properties of grain boundaries, which could not be explained by well-known oxidation effects. With the aid of a brick-layer model and high-resolution transmission electron microscopy (HRTEM), it appeared that the change in electrical characteristics of grain boundaries with decreasing cooling rate originated from the precipitation of (Ba,Sr)TiO 3 . Finally, the effect of precipitated (Ba,Sr)TiO 3 on the PTCR characteristics is discussed in terms of the acceptor-state density and the polarization state at grain boundaries.

Influence of Si3N4 passivation on surface trapping in SiC metal-semiconductor field-effect transistors

The SiC metal-semiconductor field-effect transistors (MESFETs) have been reported to have current instability and strong dispersion caused by trapping phenomena at the surface and in the substrate, which degrade direct-current (DC) and radio-frequency (RF) performance. This paper illustrates the change in electrical characteristics of SiC MESFETs after Si3N4 passivation. Because of a reduction of surface trapping effects, Si3N4 passivation can diminish current collapse under pulsed DC conditions, increasing the RF power performance. The reduction of surface trapping effects is verified by the change in the ratio of the drain current to the gate current under pinch-off conditions.

EST(Emitter Switched Thyristor) 소자의 트랜치 전극에 의한 특성 변화 연구

EST(Emitter Switched Thyristor) 소자의 트랜치 전극에 의한 특성 변화 연구

Electrophysical Characteristics of the Laser-Glazed Surface Layer in Aluminum Oxide Ceramics

Results of a study of the laser-glazed surface of aluminum oxide substrates are reported. The laser glazing causes compositional and structural transformations in the subsurface layer, which results in a substantial change in electrical characteristics of the components.

Peculiar features in the electrical characteristics of CuPc based diodes

We have investigated electrical properties of copper phthalocyanine (CuPc) thin films by means of current–voltage (I–V), capacitance–voltage (C–V) and charge deep-level transient spectroscopy (Q-DLTS) measurements. CuPc films were deposited on indium tin oxide (ITO) via organic molecular beam deposition (OMBD) at room temperature followed by Ag evaporation through a shadow mask, resulting in contacts of different sizes of dots. The measurements were carried out in situ at a pressure below 8×10−10mbar. No noticeable changes of electrical characteristics have been found after storing the devices for a few days under these conditions. Diodes of 330nm CuPc sandwiched between ITO and Ag show very low reverse currents with hysteresis-like characteristics for short delay times, which are the times between two consecutive voltage steps in an I–V measurement. Especially the bias at which current passes through zero is drastically affected by the sweep voltage direction. Almost identical curves in both directions can only be achieved using an extremely long delay time of 100s. It was found that the offset voltages for delay times of 5 and 100s are −0.85 and −0.1V for up-sweep and 0.14 and 0V for down-sweep voltage directions, respectively. This effect is likely due to the presence of deep traps which require a large time constant for charging and discharging in response to a change of the external voltage. The forward current, on the other hand, is virtually not affected, increasing initially over many orders of magnitude in a narrow voltage range and then increasing at a reduced slope. This behaviour is not stable when a high external voltage is applied. Q-DLTS measurements show presence of traps with time constants exceeding 50ms at ambient temperature.

Age-related changes in cyclic voltammetry and potentiodynamic studies of normal human dentine.

Impedance spectroscopy is one of the non-destructive techniques used by researchers to measure electrical resistance of biological tissues and ceramics. The purpose of this study is to investigate the voltage-current (V-I) characteristics of sound human dentine from young and old teeth, using cyclic voltammetry and potentiodynamic techniques. Dentine samples were prepared from freshly extracted sound third molars. After electrical measurements, dentine samples were characterized using scanning electron microscopy (SEM). Cyclic voltammetric measurements showed that variation of current through sample as a function of applied voltage is linear for dry samples of both age groups. However, for wet samples V-I characteristic were found to be different. The resistivity of dry young dentine is greater than that of old dentine in dry environment, whereas, it was found to be opposite for wet dentine samples. Using the same voltage sweep in potentiodynamic measurements dry samples display similar traces to controls suggesting that the dry dentine acts as an insulator. The number of dentinal tubules and their diameter has been found to decrease with increasing age. We propose that these changes determine the changes in electrical characteristics of sound human dentine. In spite of increasing use of electrical techniques to understand electrical properties of teeth, it is clear from this study that local structural variations and environment have a marked influence. Therefore, this baseline data needs to be considered in any future study or clinical application.

Downhole GPR for high-resolution analysis of material properties near Fairbanks, Alaska

Abstract In August 2000, we used cross-borehole ground penetrating radar (GPR) measurements to investigate sites on Fort Wainwright, Alaska, and east of the Cold Regions Research and Engineering Laboratory (CRREL) permafrost tunnel near Fox, Alaska. The sites are characterized by perennially frozen soils characteristic of much of interior Alaska. The purpose of this investigation was to define variations in GPR signal velocity and attenuation that may be indicative of hydrocarbon contamination and to determine if downhole GPR methods could detect petroleum contaminants. To acquire background information for comparison, we conducted detailed investigations in non-contaminated areas to define general conditions before we profiled at the Fort Wainwright Tank Farm where extensive contamination has been documented. Results showed that cross-borehole GPR is a useful tool for detecting changes in electrical characteristics in permafrost and contaminated environments. Bulk electrical properties (velocity and attenuation) were observed to vary systematically between frozen and unfrozen materials, and produced distinct signal responses to frozen/unfrozen sediments, bedrock and massive ground ice. There is considerable overlap in both velocity and attenuation for soils and rock. Fine-grained silts exhibit higher attenuation (9–10 dB m −1 ) than coarser sand and gravel (1.5–2 dB m −1 ). Bedrock values are intermediate (2–7 dB m −1 ). Unfrozen sediment and rock exhibit velocities between 0.05 m ns −1 and 0.1 m ns −1 and attenuation ranges from 4 dB m −1 to 11 dB m −1 at 100 Mhz while frozen materials are between the velocities of 0.1 m ns −1 and 0.18 m ns −1 and 1.5 dB m −1 and 10 dB m −1 at −0.3 °C. The general trend is for frozen materials to have higher velocities than their unsaturated or saturated counterparts. Preliminary results where petroleum contamination was pervasive show that the attenuation decreases from 6 dB m −1 to 7 dB m −1 in uncontaminated schist to 4 dB m −1 in the hydrocarbon-contaminated schist. Additional measurements are required to determine that the observed decrease in attenuation is primarily related to petroleum contamination.

Electrical and dielectric properties of (Ba 0.5Sr 0.5)TiO 3 thin films prepared by a hydroxide–alkoxide precursor-based sol–gel method

Thin films of barium strontium titanate with composition (Ba 0.5Sr 0.5)TiO 3 were prepared by a sol–gel method using Ba-, Sr-hydroxides, titanium(IV) isopropoxide as source materials and 2-methoxyethanol as the solvent. Well-crystallised films were obtained at relatively low temperatures. We observed grain growth accompanied with increase in the dielectric constant as the annealing temperature increased. The films prepared from this method and annealed at 800 °C showed high dielectric constant of 650. Typical leakage current density of the film annealed at 700 °C is 0.8×10 −6 at 75 kV cm –1. The change in electrical characteristics of the films has been correlated to their microstructure, which revealed that the concentration change affected the film porosity and grain size distribution. The results indicate that the microstructure could be tailored by changing the precursor solution concentration.

Change in electrical characteristics of poly(p-phenylene vinylene)-based self-assembled devices by addition of ionic salt to poly(sodium 4-styrenesulfonate)

A systematic study was performed on the effect of added salt on the effective conjugation lengths poly(p-phenylene vinylene)s (PPVs) formed by heat-treatment of PPV precursors in self-assembled films based on the layer-by-layer deposition between PPV and poly(sodium 4-styrenesulfonate) (PSS). It was demonstrated that the increased adsorbed amount of negatively charged PSS layer by adding NaCl salt to the PSS solution caused a blue spectral shift in electroluminescence and at the same time yielded a high turn-on voltage. The changes of electrical properties of PPV in the self-assembled films were mainly attributed to the restricted growth of conjugation bond length of PPVs induced by the increase of binding sites with the adsorbing PSS and the subsequent formation of sulfonic ester group during the thermal elimination reaction. Consequently, it is shown that the electrical properties of PPV can be simply tuned by the variation of physical parameters for the fabrication of self-assembled films without a change of PPV chemistry.