• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.9
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• pp.49-54
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• 2008

In this paper, the power added efficiency(PAE) of class F power amplifier is improved by applying a new Photonic Bandgap (PBG) structure on the output of amplifier. The proposed spiral PBG structure is a two-dimensional (2-D) periodic lattice patterned on a dielectric slab that does not require nonplanar fabrication process. This structure bas higher suppression performance at second harmonic. Also, It has a sharp skirt property. This new PBG structure can be applied with class F power amplifier for efficiency improvement. We obtained the PAE of 73.62 % for CDMA applications, and the PAE performance is improved as much as 6.2 % compared with that of a conventional class F power amplifier.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.8
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• pp.1544-1551
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• 2007

A start-up circuit of the bandgap reference voltage generator of cascode current mirror type with wide operating voltage range and enhanced power-up characteristics is proposed in the paper. It is confirmed by simulation that the newly proposed start-up circuit does not affect the operation of the bandgap reference voltage generatory even though the supply voltage(VDDA) is higher and has more stable power-up characteristic than the conventional start-up circuit. Test chips are designed and fabricated with $0.18{\mu}m$ tripple well CMOS process and their test has been completed. The mean value of measured the reference voltage(Vref) is 738mV and The three sigma value($3{\sigma}$) is 29.88mV.

• Journal of IKEEE
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• v.11 no.4
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• pp.265-271
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• 2007

A new type of photonic bandgap(PBG) structures that consist of arrays of spiral metal patches is proposed in this paper. Reflection phases and radiation of these PBG structures are simulated by high frequency structure simulator(HFSS) to characterize their performance. The simulation results show that the resonant frequency of the proposed PBG structures gets significantly lower than those of the PBG structures with square metal patches, but that the radiation is nearly the same for both of the PBG structures. Analysis on reflection phases reveals that the lowering of the resonant frequency is associated with the increase in capacitance.

• Proceedings of the IEEK Conference
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• 2003.07b
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• pp.1093-1096
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• 2003

본 논문에서는, CMOS APS Image Sensor 내에 포함되어 회로의 면적을 줄인 새롭게 제안된 CMOS Bandgap Reference Bias Generator (BGR)를 온도 및 방사능에 대한 응답을 실험하였다. 제안된 BGR 회로의 설계 목표는 V/sub DD/는 2.5V이상이고, V/sub ref/는 0.75V ± 0.5mV 마진을 가지게 하는 것이다. 제안된 BGR회로는 Level Shifter를 갖는 Differential OP-amp단과 Feedback-Loop를 가지는 Cascode Current Mirror를 사용하여 저전압에서도 동작을 가능하게 하였으며, 높은 출력저항 특성을 가지도록 하였다. 제안된 BGR회로는 하이닉스 0.18㎛ ( triple well two-poly five-metal ) CMOS 공정을 이용하여 Test Chip을 제작하였다. 온도의 변화와 Co-60 노출조건 하에서 Total ionization dose (TID) effect된 BGR회로의 V/sub ref/를 측정하여, 이를 평가하였다. 온도에 대한 반응은, 25℃ 일 때의 V/sub ref/에 대해, 각각 45 ℃에서 0.128%. 70℃에서 0.768% 변화하였다. 그리고 온도가 25℃일 때 50krad와 100krad의 방사능을 조사 하였을 경우, V/sub ref/는 각각 2.466%, 그리고 4.612% 변화하였다.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.188-191
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• 2009

A high efficiency deep blue phosphorescent organic light-emitting diode (PHOLED) was developed using a new wide triplet bandgap host material (PPO1) with a phenylcarbazole and a phosphine oxide unit. The wide triplet bandgap host material was synthesized by a phosphornation reaction of 2-bromo-Nphenylcarbazole with chlorodiphenylphosphine. A deep blue emitting phosphorescent dopant, tris((3,5-difluoro-4-cyanophenyl)pyridine)iridium (FCNIr), was doped into the PPO1 host and a high quantum efficiency of 17.1 % and a current efficiency of 19.5 cd/A with a color coordinate of (0.14,0.15) were achieved in the blue PHOLED. The quantum efficiency of the deep blue PHOLED was better than any other quantum efficiency value reported up to now.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.2 s.117
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• pp.199-205
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• 2007

In this paper, a novel hexagonal-shaped electromagnetic bandgap(EBG) power plane for the suppression of the ground bounce noise(GBN) in high-speed circuits is proposed. The proposed structure consists of hexagonal-shaped unit cells and detoured bridges connecting the unit cells. The hexagonal-shaped unit cells could omni-directionally suppress the GBN in digital circuits. The fabricated power plane's omni-directional -30 dB suppression bandwidth is from 330 MHz to 5.6 GHz. Then the proposed structure suppresses electromagnetic interference(EMI) caused by the GBN within the stopband. As a result, the proposed structure is expected to be conducive solving EMI problem in high-speed circuits.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.9
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• pp.35-43
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• 2002

In this paper, microstrip ring with a narrow gap is characterized and used as a tunable microwave bandgap (MBG) structure. The center frequency of MBG is mainly determined by the mean circumference of the ring and coincides with odd mode resonance frequency of the ring resonator. The stop band formation by the proposed microstip MBG ring is due to the reflection of electromagnetic waves at the narrow gap introduced in the ring, and the reactive component mounted on the gap makes the stop band vary according to its value. The mounting of capacitor (inductor) is observed to decrease (increase) the center frequency of the stop band. The varactor-mounted microstrip MBG ring is expected to be useful in microwave switches and microwave amplifier circuits.

• Korean Journal of Optics and Photonics
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• v.16 no.3
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• pp.261-265
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• 2005

The large and polarization-independent photonic bandgap (PBG) is very useful to the application to various optical devices. Until present, it has been known that the PBG for a triangular lattice remains the largest both in the E- and H-polarized modes. However, we proposed a new structure with a larger polarization-independent PBG, by analyzing and systemizing the PBG opening trends as the structural changes. This optimal structure for maximum bandgap has more increased gap-midgap ratio $(\Delta\omega/\omega)$ of about $30\%$ than the triangular lattice.

• Current Photovoltaic Research
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• v.4 no.3
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• pp.114-118
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• 2016

$Cu_{1.8}Zn_{1.2}(Sn_{1-x}Ge_x)S_4$ (CZTGeS) nanocrystals were mechanochemically synthesized from elemental precursor powders without using any organic solvents and any additives. The composition of CZTGeS nanocrystals were systematically varied with different Ge mole fraction (x) from 0.1 to 0.9. The XRD, Raman spectroscopy, high-resolution TEM, and diffuse reflectance studies show that the as-synthesized CZTGeS nanocrystals exhibited consistent changes in various structural and optical properties as a function of x, such as lattice parameters, wave numbers for $A_1$ Raman vibration mode, interplanar distances (d-spacing), and optical bandgap energies. The bandgap energy of the synthesized CZTGeS nanocrystals gradually increases from 1.40 to 1.61 eV with increasing x from 0.1 to 0.9, demonstrating that Ge-doping is useful means to tune the bandgap of mechanochemically synthesized nanocrystals-based kesterite thin-film solar cells. The preliminary solar cell performance is presented with an efficiency of 3.66%.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.9
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• pp.576-580
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• 2016

Single-layered transition metal dichalcogenides (TMDs) exhibit more interesting physical properties than those of bulk TMDs owing to the indirect to direct bandgap transition occurring due to quantum confinement. In this research, we demonstrate that layer-by-layer laser etching of molybdenum diselenide ($MoSe_2$) flakes could be controlled by varying the parameters employed in laser irradiation (time, intensity, interval, etc.). We observed a dramatic increase in the photoluminescence (PL) intensity (1.54 eV peak) after etching the samples, indicating that the removal of several layers of $MoSe_2$ led to a change from indirect to direct bandgap. The laser-etched $MoSe_2$ exhibited the single $MoSe_2$ Raman vibration modes at ${\sim}239.4cm^{-1}$ and ${\sim}295cm^{-1}$, associated to out-of-plane $A_{1g}$ and in-plane ${E^1}_{2g}$ Raman modes, respectively. These results indicate that controlling the number of $MoSe_2$ layers by laser etching method could be employed for optimizing the performance of nano-electronic devices.