• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.37 no.3
• /
• pp.14-19
• /
• 2000

Free-standing GaN single crystal substrates have been obtained by growing thick GaN epitaxial layers on (0001) sapphire substrates using hydride vapor phase epitaxy (HVPE) method. After growing the GaN thick film of 200 ${\mu}{\textrm}{m}$, a free-standing GaN with a size of 10 mm $\times$10 mm were obtained by mechanical polishing process to remove sapphire substrate. Crack-free GaN substrates have been obtained by GaCl pre-treatment prior to the growth of GaN epitaxial layers. Properties of free-standing GaN substrates have been compared with those of lateral epitaxial overgrowth (LEO) GaN films by double-crystal x-ray diffraction (DC-XRD), cathodoluminescence (CL) and photoluminescence (PL) measurements.

• Journal of Biomedical Engineering Research
• /
• v.18 no.3
• /
• pp.307-313
• /
• 1997

he photoconductive gain mechanism in amorphus silicon devices was investigated in connection with applications to radiation detection. Various device types such as p-i-n, n-i-n and i-i-p-i-n structures were fabricated and tested. Photoconductive gain was measured in two time scales : one for short pulses of visible light(<$1{\mu}sec$) which simulate the transit of energetic charged particles or ${\gamma}$-rays, and the other for rather long pulses of light(1msec) which simulate x-ray exposure in medical imaging, We used two definitions of phtoconductive gain : current gain and charge gain which is an integration of the current gain. We obtained typical charge gains of 3~9 for short pulses and a few hundreds for long pulses at a dark current density level of 10mA/$cm^2$. Various gain results are discussed in terms of the device structure, applied bias and dark current density.

• Journal of the Korean Magnetics Society
• /
• v.5 no.1
• /
• pp.42-47
• /
• 1995

FeN thin films for inductive recording heads were sputter deposited using RF diode sputtering mehtod from a pure iron target onto 7059 glass substrates, and their magnetic properties were measured. The magnetic properties were greatly affected by film thickness, gas pressure, sputter power and flow ratio of $N_{2}$ to Ar. Single layer FeN films with their thickness varied from $1,000\;{\AA}$ to $6,000\;{\AA}$ were doposited. 800 W sputter power, 3 mT gas pressure, $N_{2}$ to Ar flow ratio of 6.6 : 100 were the sputtering conditions. Up to 7 layers of FeN films having total thickness of $6,000\;{\AA}$ were deposited using $SiO_{2}$ of $30\;{\AA}$ thickness as intermediate layers and their coercivity and saturation magnetization were measured. The sputtering conditions were the same as those in the single layer films. Easy axis coercivity of the single layer FeN films gradually decreased as their thickness was increased, but for the films with their thicknesses above $3,000\;{\AA}$, the coercivity changed very little. As the number of the FeN layers were increased, the coercivity decreased We estimated the grain size of FeN films from the FWHM (Full Width at Half Maximum) of X-ray diffraction peaks. The grain size steadily decreased from about $200\;{\AA}$ to $120\;{\AA}$ as the number of layers were increased. Minimum hard axis coercivity of 0.4 Oe was obtained when the number of layers was four. Maximum relative permeability was 2,900 when the number of layers was three. The cut off frequeocy of the multilayer films were above 100 MHz.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.51 no.5
• /
• pp.185-190
• /
• 2002

Capacitor material utilized in the downsizing passive devices and dynamic random access memory(DRAM) requires the physical and electrical properties at given area such as capacitor thickness reduction, relative dielectric constant increase, low leakage current and thermal stability. Common capacitor materials, $SiO_2$, $Si_3N_4$, $SiO_2$/$Si_3N_4$,TaN and et al., used until recently have reached their physical limits in their application to several hundred angstrom scale capacitor. $Ta_2O_{5}$ is known to be a good alternative to the existing materials for the capacitor application because of its high dielectric constant (25 ~35), low leakage current and high breakdown strength. Despite the numerous investigations of $Ta_2O_{5}$ material, there have little been established the clear understanding of the annealing effect on capacitance characteristic and conduction mechanism, design and fabrication for $Ta_2O_{5}$ film capacitor. This study presents the structure-property relationship of reactive-sputtered $Ta_2O_{5}$ MIM capacitor structure processed by annealing in a vacuum. X-ray diffraction patterns skewed the existence of amorphous phase in as-deposited condition and the formation of preferentially oriented-$Ta_2O_{5}$ in 670, $700^{\circ}C$ annealing. On 670, $700^{\circ}C$ annealing under the vacuum, the leakage current decrease and the enhanced temperature-capacitance characteristic stability. and the leakage current behavior is stable irrespective of applied electric field. The results states that keeping $Ta_2O_{5}$ annealed at vacuum gives rise to improvement of electrical characteristics in the capacitor by reducing oxygen-vacancy and the broken bond between Ta and O.

• Korean Journal of Materials Research
• /
• v.25 no.3
• /
• pp.138-143
• /
• 2015

Aluminum nitride, a compound semiconductor, has a Wurtzite structure; good material properties such as high thermal conductivity, great electric conductivity, high dielectric breakdown strength, a wide energy band gap (6.2eV), a fast elastic wave speed; and excellent in thermal and chemical stability. Furthermore, the thermal expansion coefficient of the aluminum nitride is similar to those of Si and GaAs. Due to these characteristics, aluminum nitride can be applied to electric packaging components, dielectric materials, SAW (surface acoustic wave) devices, and photoelectric devices. In this study, we surveyed the crystallization and preferred orientation of AlN thin films with an X-ray diffractometer. To fabricate the AlN thin film, we used the magnetron sputtering method with $N_2$, NH3 and Ar. According to an increase in the partial pressures of $N_2$ and $NH_3$, Al was nitrified and deposited onto a substrate in a molecular form. When AlN was fabricated with $N_2$, it showed a c-axis orientation and tended toward a high orientation with an increase in the temperature. On the other hand, when AlN was fabricated with $NH_3$, it showed a-axis orientation. This result is coincident with the proposed mechanism. We fabricated AlN thin films with an a-axis orientation by controlling the sputtering electric power, $NH_3$ pressure, deposition speed, and substrate temperature. According to the proposed mechanism, we also fabricated AlN thin films which demonstrated high a-axis and c-axis orientations.

• Korean Journal of Materials Research
• /
• v.2 no.2
• /
• pp.110-118
• /
• 1992

When CVD-W films deposited on the reactively sputter-deposited TiN(${\circled1}$), the $NH_3$-RTP (rapid themal processed) TiN(${\circled2}$), and the furnace-annealed TiN submitate (${\circled3}$) by $SiH_4$, reduction, deposition rate is in the order of ${\circled1}>{\circled2}>{\circled3}$ and incubation period of W nucleation is in the order of ${\circled1}{\leq}{\circled2}<{\circled3}$. The longest incubation period of nucleation and lowest deposition rate for the CVD-W on the annealed TiN is due to the incorporation of oxygen from the nitrogen ambient containing some oxygen as contaminant into the TiN film. The higher W deposition rate and the lower incubation period of W nucleation on the RTP-TiN substrate in comparison with those on the sputtered TiN substrate seem to be due to a negative effect of the high compressive stress of the RTP-TiN on the nucleation and growth of W. Also the thickness uniformity of the W film deposited on the TiN substrate by $SiH_4$ reduction turns out to be better than that by $H_2$ reduction.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.22 no.4
• /
• pp.76-83
• /
• 1985

Mo2N/Mo double layer which is to be used for gate of the RMOS (refractory metal oxide semiconductor) and interconnection material has been formed by means of low temperature r.f. reactive sputtering in Ar and N2 mixture. The sheet .esistance of 1 000$\AA$Mo2 N/4000$\AA$Mofilm was about 1.20-1.28 ohms/square, which is about an order of magnitude lower than that of polysilicon film. The workfunction difference naE between MO2N/MO layer and (100) p-Si with 6-9 ohm'cm resistivity obtained from C-V plots was about -0.30ev, and the fixed charge density Qss/q in the oxide was about 2. Ix1011/cm2. To evaluate the signal transfer delay time per inverter stage, an integrated ring oscillator circuit consisting of 45-stage inverters was fabricated using the polysilicon gate NMOS process. The signal transfer delay time per inverter stage obtained in this experiment was about 0.8 nsec

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.02a
• /
• pp.105-105
• /
• 2012

본 논문에서는 전세계적으로 차세대 에너지절감 반도체로 각광을 받고 있는 GaN 소자의 연구개발 동향에 관하여 발표하고자 한다. GaN 반도체는 와이드 밴드갭(Eg=3.4eV)과 고온 안정성($700^{\circ}C$)등 재료적인 특징으로 인하여 고출력 RF 전력증폭기와 고전력용 전력반도체 응용에 큰 장점을 가진다. 고출력용 GaN RF 전력증폭 소자의 전력밀도는 기존 Si-기반 LDMOS 트랜지스터보다 10배 이상 높아 제품의 소형화와 경량화를 통하여 30% 이상의 전력절감이 가능하며, 레이더, 위성등 송수신 트랜시버 모듈에 GaN 전력증폭기를 이용할 경우 기존 GaAs-기반 전력증폭기에 비하여 높은 전력밀도(>x8)와 높은 효율(>20%)로 인하여 모듈 크기를 50% 이상 줄임과 동시에 경량화를 이룰 수 있어 비행기, 위성등 탑재체의 에너지 절감에 크게 기여할 수 있다. 고전력용 GaN 전력 스위칭 소자는 기존 Si-기반 IGBT에 비하여 스위칭 손실과 온-저항 손실이 낮아 30% 이상의 에너지 절감이 가능하다. 뿐만 아니라, 일본 도요타 자동차사의 보고에 의하면 HEV등 전기자동차의 DC-DC 부스터 컨버터나 DC-AC 인버터에 GaN 전력반도체를 적용할 경우 경량화, 변환효율 향상, 전용 냉각시스템을 제거할 수 있어 연료소모를 10% 이상 줄일 수 있어 연간 400불 이상의 에너지 절감 효과를 가진다. 이러한 에너지절감 효과는 미국, 유럽, 일본등 선진국을 중심으로 차세대 GaN 반도체의 신시장 개척과 선진입을 위한 치열한 경쟁 구도의 구동력이 될 것이며, 본 논문을 통하여 GaN 반도체의 연구개발 방향과 상용화의 중요성을 함께 생각해보고자 한다.

• Journal of Conservation Science
• /
• v.2 no.2 s.2
• /
• pp.25-30
• /
• 1993

Materials (refractory, stone) of iron making furnace excavated from Kalcheon were investigated by the scanning electron microscopy(SEM) with an energy dispersive X-ray analysis (EDAX), X-ray fluorescence(XRF), and X-ray diffraction(XRD). Chemical composition of the refractory materials were $SiO_2(68.74\%),\;Al_2O_3(18.40\%),\;CaO(0.42\%),\;MgO(1.04\%)\;and\;K_2O(2.26\%)$ in weight ratio, which were the typical components presented in common clay. The results of chemical analysis for the stone and the glaze coated, alkali ion(K, Na, Ca) components of the glaze contained high concentration than that the stone. It was suggested that this change had a close relationship with the kinds of fuels used.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.7
• /
• pp.1664-1673
• /
• 1994

As a fundamental study on effects of thermal-cycles on residual stress of ceramics/metal joints, residual stresses in $Si_3N_4$/SUS304 joint specimens were measured before and single thermal-cycle by X-ray diffraction method and finite element method(FEM). The residual stress was found to increase after single thermal-cycle, which was agreeable with the results of residual stress measurement by X-ray diffraction method and residual stress analysis by finite element method. After the residual stress measurement, 4-point bending tests were performed. The relationship between the bending strength, the thermal-cycle temperature and hold time was examined. The bending strength was found to decrease with the increase of residual stress in linear relation.