• JSTS:Journal of Semiconductor Technology and Science
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• v.17 no.2
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• pp.239-244
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• 2017

We experimentally investigate the physical mechanism for asymmetrical degradation in amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) under simultaneous gate and drain bias stresses. The transfer curves exhibit an asymmetrical negative shift after the application of gate-to-source ($V_{GS}$) and drain-to-source ($V_{DS}$) bias stresses of ($V_{GS}=24V$, $V_{DS}=15.9V$) and ($V_{GS}=22V$, $V_{DS}=20V$), but the asymmetrical degradation is more significant after the bias stress ($V_{GS}$, $V_{DS}$) of (22 V, 20 V) nevertheless the vertical electric field at the source is higher under the bias stress ($V_{GS}$, $V_{DS}$) of (24 V, 15.9 V) than (22 V, 20 V). By using the modified external load resistance method, we extract the source contact resistance ($R_S$) and the voltage drop at $R_S$ ($V_{S,\;drop}$) in the fabricated a-IGZO TFT under both bias stresses. A significantly higher RS and $V_{S,\;drop}$ are extracted under the bias stress ($V_{GS}$, $V_{DS}$) of (22 V, 20V) than (24 V, 15.9 V), which implies that the high horizontal electric field across the source contact due to the large voltage drop at the reverse biased Schottky junction is the dominant physical mechanism causing the asymmetrical degradation of a-IGZO TFTs under simultaneous gate and drain bias stresses.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.4
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• pp.257-261
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• 2014

Carbon nanotubes (CNT) has the excellent physical characteristics in the sensor, medicine, manufacturing and energy fields, and it has been studied in those fields for the several years. We fabricated the NOx gas sensors of MOS-FET type using the MWCNT. The fabricated sensor was used to detect the NOx gas for the variation of $V_{gs}$ (gate-source voltage) with the ambient temperature. The gas sensor absorbed the NOx gas molecules showed the decrease of resistance, and the sensitivity of sensor was reduced by the NOx gas molecules accumulated on the MWCNT surface. Furthermore, when the voltage ($V_{gs}$) was applied to the gas sensor, the term of the decrease in resistance was increased. On the other hand, the sensor sensitivity for the injection of NOx gas was the highest value at the ambient temperature of $40^{\circ}C$. We also obtained the adsorption energy ($40^{\circ}C$) using the Arrhenius plots by the reduction of resistance due to the $V_{gs}$ voltage variations. As a result, we obtained that the adsorption energy also was increased with the increasement of the applied $V_{gs}$ voltages.

• Proceedings of the KIEE Conference
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• 1987.07a
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• pp.775-778
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• 1987

Double-diffused metal oxide power semiconductor field effect transistors are used extensively in recent years in various circuit applications. The temperature variation of the drain current at a fixed bais shows both positive and negative resistance characteristics depending on the gate threhold voltage and gate-to source bias voltage. In this study, the decision method of the internal temperature measurement by $V_{GS}$ and $V_{DS}$ are presented.

• Transactions on Electrical and Electronic Materials
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• v.10 no.6
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• pp.193-195
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• 2009

This paper aims to develop a low gate source voltage ($V_{gs}$) N-LDMOS element that is fully operational at a CMOS Logic Gate voltage (3.3 or 5 V) realized using the 0.35 μm BCDMOS process. The basic structure of the N-LDMOS element presented here has a Low $V_{gs}$ LDMOS structure to which the thickness of a logic gate oxide is applied. Additional modification has been carried out in order to obtain features of an improved breakdown voltage and a specific on resistance ($R_{sp}$). A N-LDMOS element can be developed with improved features of breakdown voltage and specific on resistance, which is an important criterion for power elements by means of using a proper structure and appropriate process modification. In this paper, the structure has been made to withstand the excessive electrical field on the drain side by applying the double gate oxide structure to the channel area, to improve the specific on resistance in addition to providing a sufficient breakdown voltage margin. It is shown that the resulting modified N-LDMOS structure with the feature of the specific on resistance is improved by 31%, and so it is expected that optimized power efficiencies and the size-effectiveness can be obtained.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.10
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• pp.668-672
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• 2014

Carbon nanotubes(CNT) has chemical stability and great sensitivity characteristics. In particular, the gas sensor required characteristics such as rapid, selectivity and sensitivity sensor. Therefore, CNT are ideal materials to gas sensor. So, we fabricated the NOx gas sensors of MOS-FET type using the MWCNT (multi-walled carbon nanotube). The fabricated sensor was used to detect the NOx gas for the variation of $V_{gs}$(gate-source voltage) and electrode changed electrode spacing=30, 60, 90[${\mu}m$]. The gas sensor absorbed with the NOx gas molecules showed the decrease of resistance, and the sensitivity of sensor was increased by magnification of electrode spacing. Furthermore, when the voltage($V_{gs}$) was applied to the gas sensor, the decrease in resistance was increased. On the other hand, the sensor sensitivity for the injection of NOx gas was the highest value at the electrode spacing $90[{\mu}m]$. We also obtained the adsorption energy($U_a$) using the Arrhenius plots by the reduction of resistance due to the voltage variations. As a result, we obtained that the adsorption energy was increased with the increment of the applied voltages.

• JSTS:Journal of Semiconductor Technology and Science
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• v.7 no.3
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• pp.196-208
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• 2007

An analytical model is proposed for an optically controlled Metal Semiconductor Field Effect Transistor (MESFET), known as Optical Field Effect Transistor (OPFET) considering the diffusion fabrication process. The electrical parameters such as threshold voltage, drain-source current, gate capacitances and switching response have been determined for the dark and various illuminated conditions. The Photovoltaic effect due to photogenerated carriers under illumination is shown to modulate the channel cross-section, which in turn significantly changes the threshold voltage, drainsource current, the gate capacitances and the device switching speed. The threshold voltage $V_T$ is reduced under optical illumination condition, which leads the device to change the device property from enhancement mode to depletion mode depending on photon impurity flux density. The resulting I-V characteristics show that the drain-source current IDS for different gate-source voltage $V_{gs}$ is significantly increased with optical illumination for photon flux densities of ${\Phi}=10^{15}\;and\;10^{17}/cm^2s$ compared to the dark condition. Further more, the drain-source current as a function of drain-source voltage $V_{DS}$ is evaluated to find the I-V characteristics for various pinch-off voltages $V_P$ for optimization of impurity flux density $Q_{Diff}$ by diffusion process. The resulting I-V characteristics also show that the diffusion process introduces less process-induced damage compared to ion implantation, which suffers from current reduction due to a large number of defects introduced by the ion implantation process. Further the results show significant increase in gate-source capacitance $C_{gs}$ and gate-drain capacitance $C_{gd}$ for optical illuminations, where the photo-induced voltage has a significant role on gate capacitances. The switching time ${\tau}$ of the OPFET device is computed for dark and illumination conditions. The switching time ${\tau}$ is greatly reduced by optical illumination and is also a function of device active layer thickness and corresponding impurity flux density $Q_{Diff}$. Thus it is shown that the diffusion process shows great potential for improvement of optoelectronic devices in quantum efficiency and other performance areas.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.4
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• pp.274-280
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• 2001

This paper presents transconductance (g$\_$m/( characteristics of GaAs MESFET's at high temperatures ranging from room temperature to 350$\^{C}$. GaAs MESFET of 0.3x750[㎛] gate dimension has been used to obtain the experimental data. Gate to source voltage(V$\_$GS/) has been controlled to obtain the temperature dependent characteristics for maximum transconductance g$\_$mmax/ of the device. Furthermore g$\_$mmax/ and expected g$\_$m/ have been traced with temperatures ranging from room temperature to 350$\^{C}$ also by compensating for C$\_$GS/ to maintain the optimum operation of the device. From the results, V$\_$GS/decreases as the operating temperature increases for optimum operation of the transconductance. Finally V$\_$GS/ has been optimized to trace g$\_$mmax/ and enhances the decreased g$\_$m/ with different temperatures.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.52 no.5
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• pp.290-294
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• 2003

Using a backpropagation neural network (BPNN), a high power semiconductor device was empirically modeled. The device modeled is a n-LDMOSFET and its electrical characteristics were measured with a HP4156A and a Tektronix curve tracer 370A. The drain-source current $(I_{DS})$ was measured over the drain-source voltage $(V_{DS})$ ranging between 1 V to 200 V at each gate-source voltage $(V_{GS}).$ For each $V_{GS},$ the BPNN was trained with 100 training data, and the trained model was tested with another 100 test data not pertaining to the training data. The prediction accuracy of each $V_{GS}$ model was optimized as a function of training factors, including training tolerance, number of hidden neurons, initial weight distribution, and two gradients of activation functions. Predictions from optimized models were highly consistent with actual measurements.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.271-272
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• 2007

Displacement current $(I_{dis})$ and drain-to-source current $(I_{DS})$ are evaluated using the simultaneous measurements of source $(I_S)$ and drain $(I_D)$ currents during the application of a constant drain voltage and a triangular-wave gate voltage $(V_{GS})$ to top-contact pentacene thin-film transistors.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.11
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• pp.895-900
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• 2000

In this paper, C-V characteristics based on the structure of GaAs MESFET’s has been proposed with wide range of applied voltages and temperatures. Small signal capacitance; gate-source and gate-drain capacitances are represented by analytical expressions which are classified into two different regions; linear and saturation regions with bias voltages. The expression contains two variables; the built-in voltage( $V_{vi}$ )and the depletion width(W). Submicron gate length MESFETs has been selected to prove the validity of the theoretical perdiction and shows good agreement with the experimental data over the wide range of applied voltages.