• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.131-132
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• 2007

An AlGaN/GaN high electron mobility transistor(HEMT) was fabricated and the effect of photoelectrochemical oxidation of AlGaN/GaN surface was investigated. The oxidation of AlGaN surface was done in water at the bias of 10 V under the deep UV light illumination. The sheet resistance of the AlGaN/GaN structure was increased and gate leakage current of the HEMT was decreased by the oxidation. However, the transconductance of the HEMT was not degraded by the oxidation.

• JSTS:Journal of Semiconductor Technology and Science
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• v.3 no.2
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• pp.63-68
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• 2003

The DC and RF characteristics of $In_{0.5}Ga_{0.5}P/In_{0.22}Ga_{0.78}As/GaAs$ p-HEMTs with a gate oxide layer of various thicknesses ($50{\;}{\AA},{\;}300{\;}{\AA}$) were investigated and compared with those of a Schottky-gate p-HEMT without the gate oxide layer. A prominent improvement in the breakdown voltage characteristics were observed for a p-HEMT having a gate oxide layer, which was implemented by using a liquid phase oxidation technique. The on-state breakdown voltage of the p-HEMT having the oxide layer of $50{\;}{\AA}$was ~2.3 times greater than that of a Schottky-gate p-HEMT. However, the p-HEMT having the gate oxide layer of $300{\;}{\AA}$ suffered from a poor gate-control capability due to the drain induced barrier lowering (DIBL) resulting from the thick gate oxide inspite of the lower gate leakage current and the higher on-state breakdown voltage. The results for a primitive p-HEMT having the gate oxide layer without any optimization of the structure and the process indicate the potential of p-HEMT having the gate oxide layer for high-power applications.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.3
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• pp.258-264
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• 2004

In this paper, MMIC double balanced star mixer for 40 ㎓ was implemented on GaAs substrate with backside vias. In the design of the MMIC mixer, the design of balun and diode was required. A novel balun structure using microstrip to CPS was presented. The 40 ㎓ balun was designed based on the design experience of the scale-down balun by 2 ㎓. The balun may be suitable for fabrication in MMIC process with backside via and can easily be applied for DBM(Double Balanced Mixer). A Schottky diode was designed and implemented using p-HEMT process considering the compatability with other high frequency MMIC's fabricated on p-HEMT base process. Finally, the double balanced star mixer was fabricated using the balun and the p=HEMP Schottky diode. The measured performance of mixer shows 30 ㏈ conversion loss at 18 ㏈m LO power. This insufficient performance is caused by the unwanted diode at AlGaAs junction in vertical structure of p-HEMT. If the p-HEMT's gate is recessed to AlGaAs layer, and so the diode is eliminated, the mixer's performances will be improved.

• JSTS:Journal of Semiconductor Technology and Science
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• v.1 no.2
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• pp.111-115
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• 2001

Metamorphic InAlAs/InGaAs HEMT are successfully demonstrated, exhibiting several advantages over conventional P-HEMT on GaAs and LM-HEMT on InP substrate. The strain-relaxed metamorphic structure is grown by MBE on the GaAs substrate with the inverse-step graded InAlAs metamorphic buffer. The device with 40% indium content shows the better characteristics than the device with 53% indium content. The fabricated metamorphic HEMT with $0.2\mu\textrm{m}$T-gate and 40% indium content shows the excellent DC and microwave characteristics of $V_{th}-0.65V,{\;}g_{m,max}=620{\;}mS/mm,{\;}f_T120GHZ{\;}and{\;}f_{max}=210GHZ$.

• Korean Chemical Engineering Research
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• v.48 no.4
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• pp.511-514
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• 2010

Perfluorinated polymer($Cytop^{TM}$) was deposited on selective area of AlGaN/GaN HEMT structure using low cost and simple spin-coating method, and the electrical characteristics of the device was analyzed for application of passivation layer on semiconductors. Gate lag measurement results of $Cytop^{TM}$ passivated and unpassivated HEMT were compared. Passivated device shows improved 65 % pulsed drain current of dc mode value. Rf measurements were also performed. $Cytop^{TM}$ passivated HEMT have similar rf performance to PECVD grown $Si_3N_4$ passivated device. $Cytop^{TM}$ passivation layer may play an important role in mitigating surface state trapping in the region between gate and drain.

• Proceedings of the IEEK Conference
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• 2000.11a
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• pp.353-356
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• 2000

Multi-bias parameter extraction technique for HEMT small signa] equivalent circuits is presented in this paper. The technique in this paper uses S-parameters measured at various bias points in the active region to construct one optimization problem, of which the vector of unknowns contains only a set of bias-independent elements. Tests are peformed on measured S-parameters of a pHEMT at 30 bias points. Results indicate that the calculated S-parameters is similar to the measured data.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.05a
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• pp.79-82
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• 2003

본 논문은 마이크로파발진기의 위상잡음 특성에 영향을 미치는 P-HEMT의 비선형 파라미터를 선정하고, 3개의 비선형 파라미터와 최소 위상잡음을 분석하였다. 분석된 P-HEMT가 저 위상잡음을 가지는 최적의 바이어스 동작점을 선정하여, 선정된 바이어스 동작점에서 두 가지 형태의 발진기를 설계하므로 서 발진기의 물리적 구조에 의한 위상 잡음의 영향을 비교하고 위상잡음의 감소방안을 제시하였으며, 이를 이용하여 ku-대역 위상동기유전체공진 발진기를 설계 제작하였다.

• Proceedings of the KIPE Conference
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• 2018.07a
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• pp.324-325
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• 2018

본 논문에서는 GaN(Gallium Nitride) HEMT를 적용한 300W급 자기유도 방식 무선전력전송 시스템을 설계 및 구현한다. GaN HEMT의 물성적 특성을 고려하여 무선전력전송 시스템을 설계하며 이를 검증하기 위해 300W급 Prototype 무선전력전송 시스템을 구현하고 Simulation과 실험을 통해 논문에서 제시한 설계과정의 타당성을 검증한다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.11
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• pp.1064-1073
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• 2013

In this paper, a compact 370 W high efficiency GaN(Gallium Nitride) HEMT(High Electron Mobility Transistor) power amplifier(PA) using internal harmonic manipulation circuits is presented for cellular and L-band. We employed a new circuit topology for simultaneous high efficiency matching at both fundamental and 2nd harmonic frequency. In order to minimize package size, new 41.8 mm GaN HEMT and two MOS(Metal Oxide Semiconductor) capacitors are internally matched and combined package size $10.16{\times}10.16{\times}1.5Tmm^3$ through package material changes and wire bonded in a new package to improve thermal resistance. When drain biased at 48 V, the developed GaN HEMT power amplifier has achieved over 80 % Drain Efficiency(DE) from 770~870 MHz and 75 % DE at 1,805~1,880 MHz with 370 W peak output power(Psat.). This is the state-of-the-art efficiency and output power of GaN HEMT power amplifier at cellular and L-band to the best of our knowledge.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.5
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• pp.23-36
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• 2004

A computationally efficient and accurate Monte Carlo (MC) simulator of electron beam lithography process has been developed for sub-0.l${\mu}{\textrm}{m}$ T-shaped gate formation in the HEMT devices for millimeter-wave frequencies. For the exposure process by electron to we newly and efficiently modeled the inner-shell electron scattering and its discrete energy loss with an incident electron for multi-layer resists and heterogeneous multi-layer targets in the MC simulation. In order to form the T-gate shape in resist layers, we usually use the different developer for each resist layer to obtain good reproducibility in the fabrication of HEMT devices. To model accurately the real fabrication process of electron beam lithography, we have applied the different developers in trilayer resist system By using this model we have simulated and analyzed 0.l${\mu}{\textrm}{m}$ T-gate fabrication process in the HEMT devices, and showed our simulation results with the SEM observations of the T-shaped gate process.