Temperature Dependence Of Voltage Research Articles

The effect of ionization threshold softness on the temperature dependence of the impact ionization coefficient

The effect of the ionization threshold softness on the temperature variation of impact ionization coefficients is examined theoretically. It is found that increasing the softness reduces the temperature dependence of ionization, because temperature induced heating or cooling of the carrier distribution results in a smaller change in the ionization scattering rate sampled. This may explain the wide variation in the temperature dependence of breakdown voltage reported in the literature and the difficulty in modelling accurately the temperature dependence of the ionization process.

Fabrication and characterization of GaInP/GaAs triple barrier resonant tunneling diodes grown by MOCVD

GaInP/GaAs triple barrier resonant tunneling diodes (TBRTDs) grown by metal organic chemical vapor deposition were fabricated. Temperature dependence of current–voltage characteristics was measured from 18.6 to 294.1 K and negative differential resistance was observed up to 167 K. From the temperature dependence of peak voltage, peak current, valley voltage, and valley current, we estimated that the NDR characteristic of the TBRTDs is due to alignment and misalignment of quantum levels of left and right well at energy close to the conduction band bottom.

Fluoro-isothiocyanated Liquid Crystal Materials with High Dielectric Anisotropy and Voltage Holding Ratio

As liquid crystal (LC) materials for TFT-TN display, two-ring and three-ring homologues with 2-fluoroisothiocyanatophenyl and 2,6-difluoroisothiocyanatophenyl with high dielectric anisotropy and birefringence are prepared. In spite of the existence of a high polar –NCS group, the voltage holding ratio (VHR) of NLC mixtures contained in them is sufficiently high for application of active matrix addressing. In this paper, we will explain the voltage holding property of three types of liquid crystal materials included the terminal –NCS group considering their molecular parameters such as the Hückel charge, polarizability and dipole moment and the temperature and frequency dependence of voltage holding ratios are examined.

Heat and power management of a direct-methanol-fuel-cell (DMFC) system

In this paper, we describe the heat and the power management of a direct methanol fuel cell system. The system consists mainly of a direct methanol fuel cell stack, an anode feed loop with a heat exchanger and on the cathode side, a compressor/expander unit. The model calculations are carried out by analytical solutions for both mass and energy flows. The study is based on measurements on laboratory scale single cells to obtain data concerning mass and voltage efficiencies and temperature dependence of the cell power. In particular, we investigated the influence of water vaporization in the cathode on the heat management of a direct-methanol-fuel-cell (DMFC) system. Input parameters were the stack temperature, the cathode pressure and the air flow rate. It is shown that especially at operating temperatures above 90 °C, the combinations of pressure and air flow rate are limited because of heat losses due to vaporization of water in the cathode.

Hafnium oxide gate stack prepared by in situ rapid thermal chemical vapor deposition process for advanced gate dielectrics

A high-quality HfO2 gate stack with equivalent oxide thickness (EOT) of 7.8 Å and a leakage current of Jg=0.5 mA/cm2 @ Vg=−1.0 V has been achieved by an in situ rapid thermal chemical vapor deposition process. It is found that both NH3-based interface layer and N2 postdeposition annealing are very effective in reducing EOT and leakage, and at the same time, improving film qualities. These HfO2 gate stacks show negligible frequency dependence, small hysteresis in capacitance–voltage (C–V) and weak temperature dependence of the leakage current. They also show negligible charge trapping at high voltage stress.

Low-noise visible-blind UV avalanche photodiodes with edge terminated by 2° positive bevel

4H-SiC avalanche photodiodes edge terminated by a 2° positive bevel have been fabricated and characterised. Low leakage current, positive temperature dependence of breakdown voltage, high avalanche gain and very low noise have been achieved.

Relationship between channel mobility and interface state density in SiC metal–oxide–semiconductor field-effect transistor

Temperature dependence of threshold voltage in n-channel SiC metal–oxide–semiconductor field-effect transistors (MOSFETs) was studied. Linear relation was observed between the threshold voltage shift when the temperature varies from −150 to 150 °C and the number of the interface states present within the energy range of 0.2–0.4 eV from the conduction band edge energy Ec. This relationship revealed that the interface state profile near Ec in n-channel SiC MOSFETs can be represented by that in n-type SiC MOS capacitors. The relationship between the channel mobility and the interface state profile also suggested that the interface states within the energy range of 0.2–0.4 eV from Ec have little influence on the channel mobility.

Analysis of Temperature Behavior of the NPT-IGBT's Characteristics

An analytical model for calculating the forward voltage of a conventional NPT-IGBT (Non-Punch Through Insulated Gate Bipolar Transistor) is presented, taking into account decrease of the current densities in the epi layer near the cathode junction. Simulation results of the temperature dependent forward voltage and emitter injection efficiency for an IGBT with blocking capability of 1700 V are shown to support the model developed with temperature dependent mobilities. The present model allows a good agreement with the simulation results within 10% in error.

A cause for highly improved channel mobility of 4H-SiC metal–oxide–semiconductor field-effect transistors on the (112̄0) face

4H-silicon carbide (SiC) metal–oxide–semiconductor field-effect transistors fabricated on both (112̄0) and (0001) faces were characterized at various temperatures. From the temperature dependence of channel mobility, carrier transport in the inversion layer at the SiO2/4H-SiC(112̄0) interface was found to be affected by phonon scattering (μ0∼T−2.2), while that at the SiO2/4H-SiC(0001) interface was thermally activated (μ0∼T2.6) due to the decrease of Coulomb scattering by emission of electrons from acceptor-like interface states. From the temperature dependence of threshold voltage, the density of acceptor-like interface states near the conduction band edge seems to be low at the SiO2/4H-SiC(112̄0) interface, but quite high (>1013 cm−2 eV−1) at the SiO2/4H-SiC(0001) interface. The low density of acceptor-like interface states near the conduction band edge on the (112̄0) face should be the primary cause for the high inversion-channel mobility.

Temperature dependence of output voltage generated by interaction of threshold voltage and mobility of an NMOS transistor

Mutual compensation of mobility and threshold voltage temperature variations may result in a zero temperature coefficient (ZTC) bias point of an NMOS transistor. The conditions under which this effect occurs, stability of this bias point, and the temperature dependence of the output voltage for a diode-connected transistor operating in the vicinity of ZTC point are investigated in this paper. Some possible applications of this effect include temperature sensors with linear dependence of voltage versus temperature, and voltage and current reference circuits. The theory is verified experimentally investigating the temperature behavior of an NMOS transistor realized in 0.35 μm CMOS process. The design and simulation results of simple current and voltage reference circuits for implementation in 0.18 μm CMOS technology are given.

Tunneling study of underdoped and overdoped Bi 2Sr 2CaCu 2O 8

The temperature dependence of the edge peak voltage of a natural-barrier planar tunneling junction of overdoped and underdoped Bi 2Sr 2CaCu 2O 8− x suggests that the superconducting gap closes at the superconducting critical temperature.

Temperature-dependent study of a lattice-matched InP/InGaAlAs heterojunction bipolar transistor

In this work, we report the temperature-dependent characteristics of a new InP/InGaAlAs heterojunction bipolar transistor (HBT). In order to improve the dc performance of conventional InGaAs-based single HBTs, the quaternary In/sub 0.53/Ga/sub 0.34/Al/sub 0.13/As with a wider bandgap is employed as the material for both the base and collector layers. Experimentally, the studied device exhibits a relatively high common-emitter breakdown voltage and low output conductance even at high temperature. Based on the breakdown mechanism of avalanche multiplication, the negative temperature dependence of breakdown voltage is attributed to the positive temperature-dependent impact ionization coefficient. Furthermore, the temperature dependence of current gain is investigated and reported. It is believed that the suppression of hole injection current with decreasing temperature is responsible for the opposite variation of current gains at high current levels.

Coupling between the layers in vortex liquid regime of YBa 2Cu 3O 7−δ single crystals

We have measured the temperature dependence of voltages on both sides of MTG-YBCO single crystals in case of the applied magnetic field up to 7.5T parallel and perpendicular to the c-axis, respectively. The results show that in the dissipative regime the voltage signal on the side of the applied current contacts is more than that on the opposite side. There is a maximum and a minimum in the ratio curves of voltage signals. The layers coupling destroyed by the applied magnetic field was observed. The field of layers-coupling temperature follows the formula HH 0(1-T/T c0) 1.44 consistent with the “irreversibility line”.

Temperature dependent effective ionization coefficient for Si

Analytical expressions for temperature dependence of breakdown voltage and on-resistance of Si p+n diodes are derived successfully by employing the temperature dependent effective ionization coefficient and mobility in Si. The analytical results are compared with numerical simulations. The variation of the on-resistance with temperature is also compared with the one reported previously. Good fits with the numerical results are found for the breakdown voltage within 10% in error for the doping concentration in the range of 10 14–10 17 cm −3.

Temperature dependence of GaN high breakdown voltage diode rectifiers

The temperature dependence of reverse breakdown voltage ( V RB) and forward turn-on voltage ( V F) of GaN Schottky diode rectifiers is reported. The V RB values display a negative temperature coefficient (−0.92 V K −1 for 25–50°C; −0.17 V K −1 for 50−150°C), indicative of surface- or defect-assisted breakdown. The V F values decrease with increasing temperature. The room temperature breakdown voltage is approximately a factor of three lower than the theoretical maximum expected based on avalanche breakdown, and the current performance of GaN rectifiers is comparable to that of Si at the same on-resistance.

Anelastic Creep Phenomena in Thin Metal Plated Cantilevers for MEMS

ABSTRACTDuring the past several years, we have developed high displacement sensitivity tunneling accelerometers using surface micromachining and metal electroplating techniques. These devices consist of a Au tunneling tip fabricated below a 1-2 μm thick metal cantilever beam of electroplated Ni or Au. A thin film of e-beam evaporated Au on the underside of the cantilever serves as the tunneling counter electrode. In operation, a 100mV bias is applied across the tunneling gap. A larger turn-on voltage is also applied between the cantilever and a control electrode, located on the substrate, to deflect the cantilever and maintain a constant tunneling current of 1 or 10 nA. Typical deflections of the end of 100 μm-long and 250 μm-long cantilevers are 0.5μm during operation. We have observed that the turn-on voltage decreases over time for most devices with a larger drop observed for the Au cantilevers. In all cases, the initial decay of the turn-on voltage was almost completely recoverable after the device was turned off for 24 hrs. This decay was not found to be strongly dependent on the magnitude of the tunneling current, but could be significantly reduced by pre-stressing the cantilever before operation. Finally, a vacuum anneal at 100°C influences the measured temperature dependence of the turn-on voltage. The observed effects appear to be consistent with fatigue and creep phenomena in the cantilevers. These effects are reversible at room temperature and are dependent on the stress and temperature history of the devices. A comparison is made between metal plated and all-Si structures.

Temperature dependences of channel mobility and threshold voltage in 4H- and 6H-SiC MOSFETs

ABSTRACTWe have investigated the effect of polytype and oxidation condition on the temperature dependence of channel mobility and threshold voltage in 4H- and 6H-SiC MOSFETs. The behaviors of the channel mobility are apparently different for 4H- and 6H-SiC MOSFETs. In contrast to the polytype effect, dry and wet oxidation samples have almost similar channel mobilities. The variation of the threshold voltage with temperature is proportional to the number of the interface states near the conduction band extracted from n-type MOS capacitors. Therefore, we argue that the distribution of the interface states near the conduction band in p-type SiC MOS structure can be represented by that in n-type SiC MOS structure. Although the oxidation condition varies the distribution of the interface states in the energy range between 0.2 and 0.4 eV from the conduction band, it has little influence on the channel mobility.

Phase slip scaling relationship for the 59 K and 143 K charge-density-waves in NbSe3

Selective area irradiation was used to create irradiated/unmodified/irradiated CDW heterostructures with well-defined interfaces on a single Nbse 3 crystal. The temperature dependence of the extra voltage required for carrier conversion (phase slip voltage, V Ps 0 is extracted from length dependent studies. We find that the temperature dependence of V Ps 0 for the 143 K and 59 K CDW transitions are identical if properly scaled by the transition temperature. The V ps 0 temperature dependence is not thermally activated, but contains an upper and lower temperature branch. The crossover temperature for the two branches is 0.75Tp. For the 59 K CDW we observe a zero-bias resistance anomaly near a single irradiated/unmodified interface. This anomaly abruptly changes with temperature near 44 K suggesting a qualitative change in the phase slip mechanism near 0.75Tp.

Physical and Electro-Optical Properties of New Nematic LC Mixtures for Highly Multiplexed TN-Displays

A set of new, blended nematic liquid crystal mixtures to improve the performance of highly multiplexed TN-displays are presented. The physical and electro-optical properties of new LC mixtures have been investigated, along with the frequency and temperature dependence of threshold voltage about newly developed liquid crystals. The multiplexable mixtures are completely miscible and can be blended, thus leading to new mixtures covering a wide range of threshold voltages 1.2 > V10 > 2.0 V, nematic-isotropic phase transition temperatures 60 > Tc > 100[ddot]C, and/or optical anisotropies 0.13>Δ n>0.18.

Temperature dependence of superstructure and electrical tree initiation voltage of polyethylene

Below the melting point, polyethylene forms a structure in which the crystalline and the amorphous regions exist together. Therefore, polyethylene is not homogeneous. It is thought that generation of a crack by Maxwell stress is one of the tree initiation causes. The crack is generated easier in an unhomogeneous than in a homogeneous structure. Above the melting point, the homogeneity may increase because all crystalline regions melt into the amorphous region. To examine the homogeneity of polyethylene and the relationship to the generation of electrical trees, polyethylene was heated up to 180 °C. The relationship between the superstructure and the electrical tree initiation voltage at various temperatures was examined. © 1999 Scripta Technica, Electr Eng Jpn, 128(3): 24–30, 1999