• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.8
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• pp.667-674
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• 2000

The stability of ZnO-Pr$_{6}$/O$_{11}$-CoO-Er$_{2}$/O$_3$based varistors was investigated with Er$_{2}$/O$_3$additive content of the range 0.0 to 2.0 mol%. All varistors sintered at 130$0^{\circ}C$ exhibited the thermal runaway within short times even under weak d.c. stress. As a result these varistors were completely degraded. On the contrary the stability of varistors sintered at 135$0^{\circ}C$ was far better than that of 130$0^{\circ}C$. In particular the varistors added with 0.5mol% Er$_{2}$/O$_3$ which the nonlinear exponent is 34.83 and the leakage current is 7.38 $mutextrm{A}$ showed a excellent stability which the variation rate of the varistors voltage the nonlinear coefficient and the leakage current is below 1%, 2%, and 3.5% respectively even under more severe d.c. stress such as (0.80 V$_{1mA}$9$0^{\circ}C$/12h)+(0.85 V$_{1mA}$115$^{\circ}C$/12h)+(0.90 V$_{1mA}$12$0^{\circ}C$12h) Consequently it is estimated that the ZnO-0.5 mol% Pr$_{6}$/O sub 11/-1.0 mol% CoO-0.5 mol% Er$_{2}$/O sub 3/ based varistors will be used to develop the advanced Pr$_{6}$/O$_{11}$-1.0 mol% CoO-0.5 mol% Er$_{2}$/O$_{3}$ based varistors will be used to develop the advanced Pr$_{6}$/O$_{11}$-based ZnO varistors having the high performance and stability in future. future.ure. future.

• Proceedings of the Ginseng society Conference
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• 2002.10a
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• pp.392-400
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• 2002

We have previously found that the saponins but not other components in the ginseng reduce the secretion of catecholamines (CAs) from bovine adrenal chromaffin cells, a model of sympathetic nerves, evoked by acetylcholine (ACh) due to the blockade of $Na^+$ influx through nicotinic ACh receptor-operated cation channels, and it has been concluded that the inhibitory effect may be associated with the anti-stress action of ginseng. However, the saponins, which showed the great reduction of the CA secretion, were mainly the protopanaxiatriols. The protopanaxadiol and oleanolic acid saponins had a little or little such effect. Recent studies demonstrated that the oligosaccharides connected to the hydroxyl groups of the aglycones of the saponins are in turn hydrolyzed by gastric acid and enzymes in the intestinal bacteria when the ginseng is orally administrated. In this study, the effects of their major 6 kinds of metabolites on the secretion of CAs were investigated. All metabolites (M1, 2, 3 and 5 derived from the protopanaxadiols, and M4 and 11 from the protopanaxiatriols) reduced the ACh-evoked secretion from the cells. In the metabolites, the M4 inhibition was the most potent ($IC_{50}({\mu}M):M4(9)$ < M2 (18) < M3 (19) < M1l (22) < M5 (36) < MI (38)). Although M4 also reduced the CA secretion induced by high $K^+$, a stimulation activating voltage-sensitive $Ca^{2+}$ channels, the inhibitory effect was much less than that on the ACh-evoked secretion. M4 inhibited the ACh-induced $Na^+$ influx into the cells in a concentration-dependent manner similar to that of the inhibition of the ACh-evoked secretion. When the cells were washed by the incubation buffer after the preincubation of the cells with M4 and then incubated without M4 in the presence of ACh, the M4 inhibition was not completely abolished. On the other hand, its inhibition was maintained even by increasing the external ACh concentration. These results indicate that the saponins are metabolized to the more active substances in the digestive tract and the metabolites attenuate the secretion of CAs from bovine adrenal chromaffin cells stimulated by ACh due to the noncompetitive blockade of the ACh-induced $Na^+$ influx into the cells. These findings may further explain the anti-stress action of ginseng.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.6
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• pp.360-364
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• 2015

Electronic systems based on solid state devices have changed to be more complicated and miniaturized as the electronic systems developed. If the electronic systems are exposed to HPEM (high power electromagnetics), the systems will be destroyed by the coupling effects of electromagnetic waves. Because the HPEM has fast rise time and high voltage of the pulse, the semiconductors are vulnerable to external stress factor such as the coupled electromagnetic pulse. Therefore, we will discuss about malfunction behavior and DFR (destruction failure rate) of the semiconductor caused by amplitude and repetition rate of the pulse. For this experiment, the pulses were injected into the pins of general purpose IC due to the fact that pulse injection test enables the phenomenon after the HPEM is coupled to power cables. These pulses were produced by pulse generator and their characteristics are 2.1 [ns] of pulse width, 1.1 [ns] of pulse rise time and 30, 60, 120 [Hz] of pulse repetition rate. The injected pulses have changed frequency, period and duty ratio of output generated by Timer IC. Also, as the pulse repetition rate increases the breakdown threshold point of the timer IC was reduced.

• Journal of the Korean institute of surface engineering
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• v.48 no.2
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• pp.33-37
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• 2015

High efficiency LED device is being concerned due to its high heat loss, and such heat loss will cause a shorter lifespan and lower efficiency. Since there is a demand for the materials that can release heat quickly into the external air, the organic insulating layer was required to be replaced with high thermal conductive materials such as metal or ceramics. Through anodizing the upper layer of Al, the Breakdown Voltage of 3kV was obtained by using an uniform thickness of $60{\mu}M$ aluminum oxide($Al_2O_3$) and was carried out to determine the optimum process conditions when thermal cracking does not occur. Two Ni layers were formed above the layer of $Al_2O_3$ by sputtering deposition and electroplating process, and saccharin was added for the purpose of minimizing the remain stress in electroplating process. The results presented that the 3-layer film including the Ni layer has an adhesive force of 10N and the thermal conductivity for heat dissipation is achieved by 150W/mK level, and leads to improvement about 7 times or above in thermal conductivity, as opposed to the organic insulation layer.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.5
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• pp.291-294
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• 2015

Recently, ZnO based oxide TFTs used in the flexible and transparent display devices are widely studied. To apply to OLED display switching devices, electrical performance and stability are important issues. In this study, to improve these electrical properties, we fabricated TFTs having Al doped Zinc Oxide (AZO) layer inserted between the gate insulator and ZnO layer. The AZO and ZnO layers are deposited by Atomic layer deposition (ALD) method. I-V transfer characteristics and stability of the suggested devices are investigated under the positive gate bias condition while the channel defects are also analyzed by the photoluminescence spectrum. The TFTs with AZO layer show lower threshold voltage ($V_{th}$) and superior sub-threshold slop. In the case of $V_{th}$ shift after positive gate bias stress, the stability is also better than that of ZnO channel TFTs. This improvement is thought to be caused by the reduced defect density in AZO/ZnO stack devices, which can be confirmed by the photoluminescence spectrum analysis results where the defect related deep level emission of AZO is lower than that of ZnO layer.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.267.1-267.1
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• 2016

본 연구에서는 nematic 액정의 종류 중 하나인 5CB (4-Cyano-4'-pentylbiphenyl) 물질을 박막 트랜지스터 (TFT)의 passivation 층으로 사용했을 때 그 전기적 특성향상을 확인하였다. RF-magnetron sputtering법으로 증착된 비정질 InGaZnO 박막을 활성층으로 사용한 TFT를 제작하여 그 활성층 위에 drop형식으로 passivation 하였다. 그 결과, drain current (I_DS)가 약 10배 정도 증가하고, linear region(V_D=0.5V)에서 mobility와 subthreshold slope(SS)이 각각 6.7에서 12.2, 0.3에서 0.2로 향상되는 것이 보였다. 이것은 gate bias가 인가되었을 때 freedericksz 전이를 통한 액정의 배향과 이때 형성된 dipole 형성에 의한 것으로 보이며, 이러한 LC의 배향은 편광현미경을 통하여 표면과 수직으로 배향한다는 사실을 확인 할 수 있었고 이 LC-passivation된 a-IGZO TFT의 전기적 특성의 향상에 대한 mechanism을 제시하였다. 그리고 배향한 LC가 가지는 dipole에 의해 bias stress 상황에서 독특한 electron trapping과 recovery의 증폭효과가 나타났다. V_G=+20V의 positive gate bias stress를 1000s동안 가했을 때, passivation되지 않은 a-IGZO TFT의 경우 +4V의 threshold voltage shift(${\Delta}V$_TH)가 발생되었고, 바로 -20V의 negative gate bias를 30s간 가해주었을 때 -2.5V의 ${\Delta}V$_TH가 발생하였다. 반면 LC-passivation된 a-IGZO TFT의 경우 각각 +5V와 -4V의 ${\Delta}V$_TH로 더 큰 변화를 가져왔다. 이러한 LC에 의한 electron trapping/recovery 증폭효과에 대한 model을 제시하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.289.2-289.2
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• 2016

In-Ga-Zn-O(IGZO) receive great attention as a channel material for thin film transistors(TFTs) as next-generation display panel backplanes due to its superior electrical and physical properties such as a high mobility, low off-current, high sub-threshold slope, flexibility, and optical transparency. For the purpose of fabricating high performance IGZO TFTs, a thermal recovery process above a temperature of $300^{\circ}C$ is required for recovery or rearrangement of the ionic bonding structure. However diffused metal atoms from source/drain(S/D) electrodes increase the channel conductivity through the oxidation of diffused atoms and reduction of $In_2O_3$ during the thermal recovery process. Threshold voltage ($V_{TH}$) shift, one of the electrical instability, restricts actual applications of IGZO TFTs. Therefore, additional investigation of the electrical stability of IGZO TFTs is required. In this paper, we demonstrate the effect of Ti diffusion and modulation of interface traps by carrying out an annealing process on IGZO. In order to investigate the effect of diffused Ti atoms from the S/D electrode, we use secondary ion mass spectroscopy (SIMS), X-ray photoelectron spectroscopy, HSC chemistry simulation, and electrical measurements. By thermal annealing process, we demonstrate VTH shift as a function of the channel length and the gate stress. Furthermore, we enhance the electrical stability of the IGZO TFTs through a second thermal annealing process performed at temperature $50^{\circ}C$ lower than the first annealing step to diffuse Ti atoms in the lateral direction with minimal effects on the channel conductivity.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.265.2-265.2
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• 2016

Oxide thin film transistors (TFTs) have attracted considerable interest for gate diver and pixel switching devices of the active matrix (AM) liquid crystal display (LCD) and organic light emitting diode (OLED) display because of their high field effect mobility, transparency in visible light region, and low temperature processing below $300^{\circ}C$. Recently, oxide TFTs with polycrystalline In-Ga-O(IGO) channel layer reported by Ebata. et. al. showed a amazing field effect mobility of $39.1cm^2/Vs$. The reason having high field effect mobility of IGO TFTs is because $In_2O_3$ has a bixbyite structure in which linear chains of edge sharing InO6 octahedral are isotropic. In this work, we investigated the characteristics and the effects of oxygen partial pressure significantly changed the IGO thin-films and IGO TFTs transfer characteristics. IGO thin-film were fabricated by rf-magnetron sputtering with different oxygen partial pressure ($O_2/(Ar+O_2)$, $Po_2$)ratios. IGO thin film Varies depending on the oxygen partial pressure of 0.1%, 1%, 3%, 5%, 10% have been some significant changes in the electrical characteristics. Also the IGO TFTs VTH value conspicuously shifted in the positive direction, from -8 to 11V as the $Po_2$ increased from 1% to 10%. At $Po_2$ was 5%, IGO TFTs showed a high drain current on/off ratio of ${\sim}10^8$, a field-effect mobility of $84cm^2/Vs$, a threshold voltage of 1.5V, and a subthreshold slpe(SS) of 0.2V/decade from log(IDS) vs VGS.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.12
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• pp.174-181
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• 2004

Ultra precision positioning mechanism has widely been used on semiconductor manufacturing equipments, optical spectrum analyzer and cell manipulations. Ultra precision positioning mechanism is consisted of several actuators, sensors, guides and control systems. Its efficiency depends on each performance of components. The object of this study is to design, analysis and manufacture all of the inchworm linear motor system, which is one of the equipments embodied in ultra precision positioning mechanism. Inchworm linear motor system is consisted of a controller system and an inchworm linear motor, and its driving form is similar to a motion of spanworm. A design and manufacture of inchworm linear motor, which is consisted of three PZT actuators, a rod, two columns and a guide plate, are performed. Minimizing the von-Mises stress of the hinge using Taguchi method and simulation by FEM software optimizes the structural design in a column of flexure hinge. The designed columns and guide plates are manufactured by a W-EDM and NC-milling. A controller system, which is an apparatus to drive inchworm linear motor, can easily adjust driving conditions by varying resonance frequency and input-output voltage of actuators and amplifiers. The performance of manufactured inchworm linear motor system is verified and valuated. In the future, inchworm linear motor system will be used to make a more precision positioning by reinforcing a sensor and feedback system.

• Transactions on Electrical and Electronic Materials
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• v.15 no.6
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• pp.328-332
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• 2014

Thin film transistors (TFTs) with an amorphous silicon zinc tin oxide (a-2SZTO) channel layer have been fabricated using an RF magnetron sputtering system. The effect of the change of excitation electron on the variation of the total interfacial trap states of a-2SZTO systems was investigated depending on sputtering power, since the interfacial state could be changed by changing sputtering power. It is well known that Si can effectively reduce the generation of the oxygen vacancies. However, The a-2SZTO systems of ZTO doped with 2 wt% Si could be degraded because the Si peripheral electron belonging to a p-orbital affects the amorphous zinc tin oxide (a-ZTO) TFTs of the s-orbital overlap structure. We fabricated amorphous 2 wt% Si-doped ZnSnO (a-2SZTO) TFTs using an RF magnetron sputtering system. The a-2SZTO TFTs show an improvement of the electrical property with increasing power. The a-2SZTO TFTs fabricated at a power of 30 W showed many of the total interfacial trap states. The a-2SZTO TFTs at a power of 30 W showed poor electrical property. However, at 50 W power, the total interfacial trap states showed improvement. In addition, the improved total interfacial states affected the thermal stress of a-2SZTO TFTs. Therefore, a-2SZTO TFTs fabricated at 50 W power showed a relatively small shift of threshold voltage. Similarly, the activation energy of a-2SZTO TFTs fabricated at 50 W power exhibits a relatively large falling rate (0.0475 eV/V) with a relatively high activation energy, which means that the a-2SZTO TFTs fabricated at 50 W power has a relatively lower trap density than other power cases. As a result, the electrical characteristics of a-2SZTO TFTs fabricated at a sputtering power of 50 W are enhanced. The TFTs fabricated by rf sputter should be carefully optimized to provide better stability for a-2SZTO in terms of the sputtering power, which is closely related to the interfacial trap states.