• Journal of the Korean Vacuum Society
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• v.15 no.5
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• pp.534-540
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• 2006

Thin films of $V_2O_3$, $VO_2$, and $V_2O_5$ were obtained from a single precursor solution through post-annealing processes under different annealing conditions. As annealed in air, the deposited films became $V_2O_5$ with orthorhombic crystal structure, while they were $V_2O_3$ and $VO_2$ with rhombohedral and monoclinic crystal structure as annealed in vacuums with base pressure of $1{\times}10^{-6}$ Torr and with 10 mTorr $O_2$ pressure, respectively. Electrical and optical measurements indicated that the $V_2O_5$ and $VO_2$ films are semiconducting, while the $V_2O_3$ films are metallic at room temperature. Chromium doping in $VO_2$ resulted in a decrease of the resistivity and changed the conduction type from n-type to p-type. 10% Cr-doped $VO_2$ films were found to have orthorhombic crystal structure, which is different from that of the undoped $VO_2$. Spectral features in the optical absorption spectra of all the films were interpreted as the transitions involving O 2p and V 3d bands. The crystal-field splittings between $t_{2g}$ and $e_g$ states of the V 3d bands are estimated to be about 1.5 and 1.0 eV for $V_2O_5$ and $VO_2$, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.6
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• pp.278-282
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• 2010

The doping effect of thulium on electrical properties and degradation behavior in barium titanate ceramics ($BaTiO_3$) was investigated in terms of generations of core-shell structure and micro-chemical changes through highly accelerated degradation test. The dielectric specimens of pellet type and multi-layered sheets were prepared by using $BaTiO_3$ with undoped and doped with 1 mol% $Tm_2O_3$. The $BaTiO_3$ ceramics doped with 1 mol% $Tm_2O_3$ had 40% higher dielectric constant (${\varepsilon}$ = 2700) than that of the undoped $BaTiO_3$ specimen at curie temperature and met X7R specification. According to the result of highly accelerated degradation test conducted at $150^{\circ}C$, 70 V, and 24 hr, the oxygen diffusion was declined in dielectrics doped with 1 mol% $Tm_2O_3$. The $Tm^{3+}$ ion substituted selectively Ba site and Ti site and contributed to the generation of the core-shell structure. Oxygen vacancies occurred by substitution for Ti site could reduce excess oxygen that reacted to the Ni electrode.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.430-430
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• 2008

Using multi plasma enhanced chemical vapor deposition system (Multi-PECVD), p-a-Si:H deposition layer as a $p^+$ region which was annealed by laser (Q-switched fiber laser, $\lambda$ = 1064 nm) on an n-type single crystalline Si (100) plane circle wafer was prepared as new doping method for single crystalline interdigitated back contact (IBC) solar cells. As lots of earlier studies implemented, most cases dealt with the excimer (excited dimer) laserannealing or crystallization of boron with the ultraviolet wavelength range and $10^{-9}$ sec pulse duration. In this study, the Q-switched fiber laser which has higher power, longer wavelength of infrared range ($\lambda$ = 1064 nm) and longer pulse duration of $10^{-8}$ sec than excimer laser was introduced for uniformly deposited p-a-Si:H layer to be annealed and to make sheet resistance expectable as an important process for IBC solar cell $p^+$ layer on a polished n-type Si circle wafer. A $525{\mu}m$ thick n-type Si semiconductor circle wafer of (100) plane which was dipped in a buffered hydrofluoric acid solution for 30 seconds was mounted on the Multi-PECVD system for p-a-Si:H deposition layer with the ratio of $SiH_4:H_2:B_2H_6$ = 30:120:30, at $200^{\circ}C$, 50 W power, 0.2 Torr pressure for 20 minutes. 15 mm $\times$ 15 mm size laser cut samples were annealed by fiber laser with different sets of power levels and frequencies. By comparing the results of lifetime measurement and sheet resistance relation, the laser condition set of 50 mm/s of mark speed, 160 kHz of period, 21 % of power level with continuous wave mode of scanner lens showed the features of small difference of lifetime and lowering sheet resistance than before the fiber laser treatment with not much surface damages. Diode level device was made to confirm these experimental results by measuring C-V, I-V characteristics. Uniform and expectable boron doped layer can play an important role to predict the efficiency during the fabricating process of IBC solar cells.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.32-32
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• 2008

Microstructure and positive temperature coefficient of resistivity (PTCR) characteristics of $0.9BaTiO_3-0.1(Bi_{0.5}Na_{0.5})TiO_3$ [BaBiNT] ceramics doped with $Nb_2O_5$ were investigated in order to develop the Pb-free high Curie temperature ($T_c$)(>$160^{\circ}C$) PTC thermistor. The BaBiNT ceramics showed a tetragonal perovskite structure, irrespective of the added amount of $Nb_2O_5$. They also have a homogeneous microstructure. The resistivity of BaBiNT ceramics was gradually decreased by doping $Nb_2O_5$, which might be due to $Nb^{+5}$ ions substituting for $Ti^{+4}$ sites. The PTCR characteristics of BaBiNT ceramics appeared when the amount of doped $Nb_2O_5$ exceeded 0.0025mol%. Moreover, the abrupt grain growth was observed for the 0.03mol% $Nb_2O_5$added BaBiNT ceramics. It showed an especially high $T_c$ of approximately $172^{\circ}C$ and good PTCR characteristics of a high $\rho_{max}/\rho_{min}$ ratio ($2.96\times10^3$), a high resistivity temperature factor (11.40/$^{\circ}C$) along with a relatively low resistivity ($3.5\times10^4\Omega{\cdot}cm$).

• Journal of the Microelectronics and Packaging Society
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• v.15 no.2
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• pp.23-28
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• 2008

To improve the external quantum efficiency by means of the optimization of the polymer light emitting diodes(PLEDs) structure, the PLED with ITO/PEDOT:PSS/(PFO)/PFO:MEH-PPV/LiF/Al structure were fabricated and investigated the electrical and optical properties for the prepared devices. ITO(indium tin oxide) and PEDOT:PSS [poly (3,4-ethylenedioxythiophene): poly(styrene sulfolnate)] were used as transparent anode film and hole transport materials, respectively. PFO[poly(9,9-dioctylfluorene)] and MEHPPV[poly(2-methoxy-5(2-ethylhe xoxy)-1,4-phenylenevinyle)] were used as the light emitting host and dopant materials. The doping concentration of MEH-PPV was 9wt% with thickness of about $400{\AA}$. We investigated the dependence of the PFO thickness ranging from $200{\AA}$ to $300{\AA}$ on the electrical, optical properties of PLEDs. Among prepared PLED devices with different PFO thicknesses, the highest value of the luminance was obtained for the PLED device with $250{\AA}$ in thickness. As a result, the current density and luminance ware found to be about $400mA/cm^2$ and $1500cd/m^2$ at 13V, respectively. In addition, the luminance and current efficiency of PLED device with double emitting layer (PFO/PFO:MEH-PPV) were improved about 3 times compared with the one with single emitting layer (PFO:MEH-PPV).

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.1
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• pp.6-13
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• 2010

In this study, Ga-doped ZnO (GZO) thin films have been fabricated on Eagle 2000 glass substrates at various substrate temperatures $100{\sim}400^{\circ}C$ and thin film thickness by RF magnetron sputtering in order to investigate the structural, electrical, and optical properties of the GZO thin films. It is observed that all the thin films exhibit c-axis orientation and a (002) diffraction peak only. The GZO thin films, which were deposited at $T=300^{\circ}C$ and 400 nm, shows the highest (002) orientation, and the full width at half maximum (FWHM) of the (002) diffraction peak is $0.4^{\circ}$. AFM analysis shows that the formation of relatively smooth thin films are obtained. The lowest resistivity ($8.01{\times}10^{-4}\;{\Omega}cm$) and the highest carrier concentration ($3.59{\times}10^{20}\;cm^{-3}$) are obtained in the GZO thin films deposited at $T=300^{\circ}C$ and 400 nm. The optical transmittance in the visible region is approximately 80 %, regardless of process conditions. The optical band-gap shows the slight blue-shift with increase in doping which can be explained by the Burstein-Moss effect.

• Applied Chemistry for Engineering
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• v.8 no.2
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• pp.172-178
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• 1997

Polyaniline(PANI)-stearic acid(SA) composite monolayer was formed at the air-water interface. The stearic acid as a surfactant was used to promote PANI monolayer formation. Uniform PANI-SA monolayer assemblies with Y type and transfer ratio of ca. 1 were fabricated using the Langmuir-Blodgett(LB) technique. The PANI-SA composite LB films with high electrical conductivity of $10^{-1}{\sim}10^{-2}S/cm$ were obtained by doping of HCl or $I_2$, and their conductivity revealed essentially close value as that of conventional PAHI-HCl complex. Especially, iodine is found to be the most promising dopant, since it gives a remarkable stability for the application as a polymer electrode in the MIM molecular device consisted of acceptor, sensitizer, and donor. The structure and physical properties of PANI-SA LB films were investigated through the near-ir UV, FT-IR, and Cyclic voltammetry.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.52-52
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• 2008

The positive temperature coefficient of resistivity (PTCR) effect in (1-x)$BaTiO_3$ - $x(Bi_{0.5}K_{0.5})TiO_3$ doped with $Nb_2O_5$ was investigated. $(Bi_{1/2}K_{1/2})TiO_3$ (BKT) is more environment-friendly than $PbTiO_3$ in order to use in PTC thermistors. The incorporation of 1 mol% BKT to $BaTiO_3$ increased the Curie temperature (Tc) to $148^{\circ}C$. Doping of $Nb_2O_5$ to $Ba_{0.99}(Bi_{0.5}K_{0.5})_{0.01}TiO_3$ (BaBKT) ceramic has enhanced its PTCR effects. For the sample containing 0.025 mol% $Nb_2O_5$, it showed good PTCR properties; low resistivity at room temperature (${\rho}_r$) of 30 $\Omega{\cdot}cm$, a high PTCR intensity of approximately $3.3\times10^3$, implying the ratio of maximum resistivity to minimum resistivity (${\rho}_{max}/{\rho}_{min}$) in the measured temperature range, and a large resistivity temperature factor (a) of 13.7%/$^{\circ}C$ along with a high Curie temperature (Tc) of $167^{\circ}C$. In addition, the cooling rate of the samples during the sintering process had an influence on their PTCR behavior. All the samples showed the best ${\rho}_{max}/{\rho}_{min}$ ratio when they have cooled down at a rate of $600^{\circ}C$/min.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.9
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• pp.723-727
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• 2011

0.935Ba$TiO_3$-0.065($Bi_{0.5}Na_{0.5}$)$TiO_3+xmol%MnO_2$ (BBNTM-x) ceramics with $0{\leq}x{\leq}0.05$ were fabricated with muffled sintering by a modified synthesis process. Their microstructure and enhanced positive temperature coefficient of resistivity (PTCR) characteristics were systematically investigated in order to obtain lead-free high TC PTCR thermistors. All specimens showed a perovskite structure with a tetragonal symmetry and no secondary phase was observed. Grain growth was achieved when the doped MnO2 was increased above 0.02 mol%. This is due to the effect of positive Mn ion doping as an acceptor compensating a Ba vacancy occurred by the higher donor dopant concentration of $Bi^{3+}$ ion. Especially, enhanced PTCR characteristics of the extremely low ${\rho}_{RT}$ of $9\;{\Omega}{\cdot}cm$, PTCR jump of $5.1{\times}10^3$, ${\alpha}$ of 15.5%/$^{\circ}C$ and high $T_C$ of $167^{\circ}C$ were achieved for the BBNTM-0.04 ceramics.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.279-279
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• 2007

비휘발성 메모리 Fe-RAM은 빠른 정보처리 속도와 전원공급이 차단되었을 때도 계속 정보를 유지할 수 있는 비휘발성 특징과 더불어 저전압, 저전력 구동의 장점이 있어서, 차세대 메모리로 많은 주목을 받고 있다. FeRAM에 사용되는 강유전체는 주로 Pb(Zr,Ti)$O_3$가 적용되었는데, 최근에는 비납계 강유전체의 연구도 활발히 이루어지고 있다. 이러한 비납계 강유전체 중에서 가장 특성이 우수한 물질은 $(Bi,La)_4Ti_3O_{12}$ (BLT) 이다. 그런데 BLT는 결정 방향에 따른 강한 이방성의 강유전 특성을 나타내기 때문에 BLT 박막을 이용하여 Fe-RAM 소자 등을 제작하기 위해서는 결정의 방향성을 세심하게 제어하는 것이 매우 중요하다. 지금까지 연구된 BLT 박막의 방향성 조절결과를 보면, BLT 박막을 스핀 코팅 법 (spin coating method)으로 증착하고, 핵생성 열처리 단계를 조절하여 무작위 방향성을 갖는 박막을 제조하는 방법이 일반적이었다. 그런데 이러한 스핀 코팅법에서의 핵생성 단계의 제어는 공정 조건 확보가 너무 어려운 단점이 있다. 이러한 어려움을 극복할 수 있는 대안은 스퍼터링 증착법(sputtering deposition method), PLD (pulsed laser deposition)법 등과 같은 PVD (physical vapor deposition) 법의 증착방법을 적용하는 것이다. PVD 법으로 증착하는 경우에는 이미 박막 내에 무수한 결정핵이 존재하기 때문에 핵생성 단계가 필요가 없게 된다. PVD 증착법의 적용을 위해서는 타겟의 제조 및 평가 실험이 선행되어야 한다. 그런데 벌크 BLT 재료의 소결공정 조건과 전기적 특성에 관한 연구 결과는 거의 발표가 되지 않고 있다. 본 실험에서는 $Bi_2O_3,\;TiO_2,\;La_2O_3,\;Nb_2O_5\;and\;Al_2O_3$ 분말들을 이용하여 최적의 조성을 구하기 위하여 $Nb^{+5}$ 와 $Al^{+3}$을 $Ti^{+4}$ 자리에 소량 치환시켜 제조하였다. 혼합된 분말을 하소 후 pellet 형태로 성형하여 소결을 실시하였다. 시편을 1mm 두께로 연마하고, 양면에 silver 전극을 인쇄하여 전기적 특성을 측정하였다. 측정결과 $Ti^{+4}$ 자리에 $Nb^{+5}$를 치환하여 제조한 시편에서 $2P_r{\sim}31\;{\mu}c/cm^2$정도의 매우 우수한 특성을 얻었다.