Hyungkeun Ahn

An analytical model for high electron mobility transistors

In this paper we present a new model for HEMTs which is based on a single analytical function that describes the electron concentrations in the two dimensional electron gas and in the AlGaAs layer. Besides accounting for the AlGaAs conduction, the model includes the effect of mobility degradation, channel length modulation in the saturation region and the series resistances R/sub S/ and R/sub D/. The model results in closed form expressions for the current, transconductance, output conductance and gate capacitance. Finally, the theoretical predictions of the model are compared with the experimental data and shown to be in good agreement over a wide range of bias conditions. >

A thermal model for insulated gate bipolar transistor module

A thermal resistor-capacitor (RC) model is introduced for the power insulated gate bipolar transistor (IGBT) modules used in a three-phase inverter. The parameters of the model are extracted from the experimental data for the transient thermal impedance from-junction-to-case Z/sub jc/ and case-to-ambient Z/sub ca/. The accuracy of the RC model is verified by comparing its predictions with those resulting from the three-dimensional finite element method simulation. The parameter extraction algorithm is easy to adapt to other types of power modules in an industrial application environment.

A parameter extraction algorithm for an IGBT behavioral model

We propose a new extraction algorithm for the parameters of an insulated gate bipolar transistor dynamic behavioral model. The algorithm relies on the availability of experimental data from the manufacturers and uses Matlab optimization toolbox to extract the parameters automatically. The theoretical predictions of the algorithm are compared with both the experimental and the simulation data that use alternative extraction methods and are found to be in excellent agreement.

Design and fabrication of piezoelectric ceramic transformers for the LCD backlight

This paper describes a type of piezoelectric transformer with improved design principles. It consists of a thin rectangular piezoelectric ceramic plate having two input electrodes and one output electrode. The length of each input and output electrode is nearly one third of piezoelectric transformer itself. In the driving section, the ceramic plate is poled in the thickness direction reversely with each other, and has electrodes on both main faces. The electric input near its fundamental resonance frequency is applied to the driving section in parallel and the output voltage from the generating section is connected to the resistor load. Its equivalent circuit is derived from the Masons model. The frequency characteristics near the resonance frequency under no load have been investigated. Moreover, using this piezoelectric transformer, we measured the LCD backlight characteristics.

Synthesis and photopolymerization of propenyl ether and epoxy functionalized siloxanes

Abstract The reactive precursors, 1-allyloxy-4(1-propenoxy)butane and allyl-epoxy-ester, were synthesized. The synthesis of propenyl ether and epoxy functionalized siloxanes has been achieved by the controlled, rhodium-catalyzed, chemoselective hydrosilation of allyl ether with various H-functional siloxanes. It was shown that the hydrosilation proceeds exclusively at the allyl ether group of allyloxy-propenoxybutane without participation at the propenyl ether group. The photoinduced cationic polymerization of these monomers was studied and found to be all highly reactive.

A /spl plusmn/ 1.5 V high frequency four quadrant current multiplier

This paper presents a four quadrant current multiplier based on the square-law characteristic of a MOS transistor operating in the saturation region. The current multiplier consists of four quadratic cells using only NMOS transistors. The circuit operates using the supply voltages of /spl plusmn/1.5 V and with the quiescent current of 25 /spl mu/A. The nonlinearity is 0.36% when the input current is the same as the bias current and reduced to only 0.1% when the input current is reduced by half. The cut-off frequency is 413 MHz with a total harmonic distortion less than 0.15% (at 1 MHz). The power dissipation is 0.45 mW.

A TRANSIENT MODEL FOR INSULATED GATE BIPOLAR TRANSISTORS (IGBTs)

In this paper, we present a physics-based model for the non punch-through (NPT) insulated gate bipolar transistor (IGBT) during transient turn off period. The steady state part of the model is derived from the solution of the ambipolar diffusion equation in the drift region of the NPT IGBT. The transient component of the model is based on the availability of a newly developed expression for the excess carrier concentration in the base. The transient voltage and current are obtained both numerically and analytically from this model. The theoretical predictions of both approaches are compared with experimental data and found to be in good agreement.

Inverse modeling and its application in the design of high electron mobility transistors

An inverse modeling technique is introduced to determine the structural and physical parameters of HEMT from the desired data for maximum transconductance. The technique is based on the availability of analytical expressions describing the electron carrier concentration, the current, the transconductance, the capacitances and the unity current gain frequency of a HEMT. Empirical formulae are obtained that relate the maximum transconductance to the doped AlGaAs thickness, spacer layer thickness, dopant density and aluminum mole fraction. The technique is applied to the design of a HEMT and shows good agreement with the experimental data. >

D.C. characteristic of MESFETs at High Temperatures

Abstract The ability of GaAs MESFET to operate over a wide temperature range requires accurate models to simulate the temperature dependence of various device parameters. In this paper, a new analytical model for the threshold voltage of MESFETs operating beyond 250°C is introduced. The model takes into account the effect of the gate leakage current on threshold voltage and is used successfully to overcome the shortcomings of existing models in the literature in matching the experimental data at temperatures higher than 250°C. The model is used to predict the drain current dependence on temperature in both the subthreshold and saturation region.

Correlation between Reverse Voltage Characteristics and Bypass Diode Operation with Different Shading Conditions for c-Si Photovoltaic Module Package

A photovoltaic (PV) system generates electricity by installing a solar energy array; therefore, the photovoltaic system can be easily exposed to external factors, which include environmental factors such as temperature, humidity, and radiation. These factors—as well as shading, in particular—lead to power degradation. When there is an output loss in the solar cell of a PV module package, the output loss is partly controlled by the bypass diode. As solar cells become highly efficient, the characteristics of series resistance and parallel resistance improve, and the characteristics of reverse voltage change. A bypass diode is connected in parallel to the string that is connected in series to the PV module. Ideally, the bypass diode operates when the voltage is -0.6[V] around. This study examines the bypass diode operating time for different types of crystalline solar cells. It compares the reverse voltage characteristics between the single solar cell and polycrystalline solar cell. Special modules were produced for the experiment. The shading rate of the solar cell in the specially made solar energy module was raised by 5% each time to confirm that the bypass diode was operating. The operation of the bypass diode is affected not only by the reverse voltage but also by the forward bias. This tendency was verified as the number of strings increased.