• Journal of the Korean institute of surface engineering
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• v.41 no.4
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• pp.142-146
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• 2008

Trivalent ions(Ga, Al, In) doped ZnO films were deposited by DC magnetron sputtering on non-alkali glass substrate at substrate temperature of $300^{\circ}C$. We used the different three types of high density($95%{\sim}$) ceramic sintered disks(doped with $Ga_2O_3$; 6.65 wt%, $Al_2O_3$; 3.0 wt%, $In_2O_3$; 9.54 wt%). This study examined the effect of different dopants(Ga, Al, In) on the electrical, structural, and optical properties of the films. The lowest resistivity of $5.14{\times}10^{-4}{\Omega}cm$ and the highest optical band gap of 3.74 eV were obtained by Ga doped ZnO(GZO) film. All the films had a preferred orientation along the(002) direction, indicating that the growth orientation has a c-axis perpendicular to the substrate surface. The average transmittance of the films was more than 85% in the visible range.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.11a
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• pp.27.1-27.1
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• 2009

In recent years, ZnO nanostructures have drawn considerable attentions for the development of futuristic electronic devices due to their superior structural and optical properties. As the growth of ZnO nanowires by MOCVD is a bottom-up technique, the nature of substrates has a vital role for the dimension and alignment of the nanowires. However, in the pursuit of next generation ZnO based nanodevices, it would be highly preferred if well-ordered ZnO nanowires could be obtained on various substrates like sapphire, silicon, glass etc. Vertically aligned nanowires were grown on A and C-plane sapphire substrates, where as nanopencils were obtained on R-plane sapphire substrates. In addition, C-axis oriented vertical nanowires were also found using an interfacial layer(aluminum nitride film) on silicon substrates. On the other hand, long nanowires were found on Ga-doped ZnO film on glass substrates. Structural and optical properties of the ZnO nanowires on various substrates were also investigated.

• JSTS:Journal of Semiconductor Technology and Science
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• v.11 no.3
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• pp.153-161
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• 2011

In this work, we report the physics-based SPICE model of amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) and demonstrate the SPICE simulation of amorphous InGaZnO (a-IGZO) TFT inverter by using Verilog-A. As key physical parameter, subgap density-of-states (DOS) is extracted and used for calculating the electric potential, carrier density, and mobility along the depth direction of active thin-film. It is confirmed that the proposed DOS-based SPICE model can successfully reproduce the voltage transfer characteristic of a-IGZO inverter as well as the measured I-V characteristics of a-IGZO TFTs within the average error of 6% at $V_{DD}$=20 V.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.40-40
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• 2008

$InGaZnO_4$ based thin film transistors (TFTs) are of interest for large area and low cost electronics. The TFTs have strong potential for application in flat panel displays and portable electronics due to their high field effect mobility, high on/off current ratios, and high optical transparency. The application of such room temperature processed transistors, however, is often limited by the operation voltage and long-tenn stability. Therefore, attaining an optimum thickness is necessary. We investigated the thickness dependence of a room temperature grown $MgO_{0.3}BST_{0.7}$ composite gate dielectric and an $InGaZnO_4$ (IGZO) active semiconductor on the electrical characteristics of thin film transistors fabricated on a polyethylene terephthalate (PET) substrate. The TFT characteristics were changed markedly with variation of the gate dielectric and semiconductor thickness. The optimum gate dielectric and active semiconductor thickness were 300 nm and 30 nm, respectively. The TFT showed low operating voltage of less than 4 V, field effect mobility of 21.34 cm2/$V{\cdot}s$, an on/off ratio of $8.27\times10^6$, threshold voltage of 2.2 V, and a subthreshold swing of 0.42 V/dec.

• Korean Journal of Materials Research
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• v.21 no.4
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• pp.202-206
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• 2011

We have investigated the structural and electrical properties of Ga-doped ZnO (GZO) thin films deposited by an RF magnetron sputtering at various RF powers from 50 to 90W. All the GZO thin films are grown as a hexagonal wurtzite phase with highly c-axis preferred parameters. The structural and electrical properties are strongly related to the RF power. The grain size increases as the RF power increases since the columnar growth of GZO thin film is enhanced at an elevated RF power. This result means that the crystallinity of GZO is improved as the RF power increases. The resistivity of GZO rapidly decreases as the RF power increases up to 70 W and saturates to 90W. In contrast, the electron concentration of GZO increases as the RF power increases up to 70 W and saturates to 90W. GZO thin film shows the lowest resistivity of $2.2{\times}10^{-4}{\Omega}cm$ and the highest electron concentration of $1.7{\times}10^{21}cm^{-3}$ at 90W. The mobility of GZO increases as the RF power increases since the grain boundary scattering decreases due to the reduced density of the grain boundary at a high RF power. The transmittance of GZO thin films in the visible range is above 90%. GZO is a feasible transparent electrode for application as a transparent electrode for thin film solar cells.

• Journal of Sensor Science and Technology
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• v.11 no.1
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• pp.60-65
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• 2002

$ZnGa_2O_4$ thin film phosphors have been deposited using a pulsed laser deposition method on Si(100) substrates at a substrate temperature of $550^{\circ}C$ with oxygen pressures of 100mTorr, and subsequently to investigate their photoluminescence characteristics after post-annealed at $600^{\circ}C$ and $700^{\circ}C$. As a result for X-ray diffraction, $Ga_2O_3$ shape appeared with increasing annealing temperature. The luminescent spectra show a broad band extending from 350 to 600nm peaking at 460nm. A post-annealing treatment of $ZnGa_2O_4$ thin films led to the different shape of luminescent intensity and grain size.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.177-177
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• 2013

디스플레이 화소 스위치 소자로 수소화된 비정질 실리콘 박막 트랜지스터를 금속 산화물 반도체 박막 트랜지스터(thin film transistor, TFT)로 대체하기 위한 연구가 활발히 진행되고 있다. 금속 산화물 중에서 박막 트랜지스터의 활성층으로 응용이 가능한 가장 대표적인 물질은 인듐(In), 갈륨(Ga), 아연(Zn), 산소(O) 화합물인 InGaZnO이다. InGaZnO TFT의 전기적 특성은 비정질 실리콘보다 우수한 것으로 확인이 되었지만, 소자의 신뢰성은 아직까지 해결해야 할 문제로 남아있다. 본 연구에서는 InGaZnO TFT를 제작하여 게이트 바이어스와 빛을 소자에 동시에 인가했을 때 발생하는 소자의 열화현상을 분석하였다. 다양한 채널 폭과 길이를 갖는 InGaZnO TFT를 제작하고 동시에 활성층의 구조를 두가지로 제작하였다. 첫번째는 활성층의 폭이 소오스/드레인 전극 폭보다 넓은 구조(active wide, AW)이고 두번째는 활성층의 폭이 소오스/드레인 전극 폭보다 좁은 구조(active narrow, AN) 구조이다. 이들 소자에 대해 +20 V의 게이트 바이어스와 빛을 동시에 인가하여 10000초 후의 소자 특성을 초기 특성과 비교하였을 때는 열화가 거의 발생하지 않았다. 반면 -20 V의 게이트 바이어스와 빛을 동시에 인가하여 10000초 후의 소자 특성을 초기 특성과 비교하면 전달특성 곡선이 음의 게이트 전압 방향으로 이동함과 동시에 문턱전압이하의 동작 영역에서 전달특성 곡선의 hump가 발생하였다. 이 hump 특성은 AW 구조의 소자와 AN 구조의 소자에서 나타나는 정도가 다름을 확인하였다. 이러한 열화 현상의 원인으로 음의 게이트 바이어스와 빛이 동시에 인가될 경우 InGaZnO 박막 내에는 활성층 내에 캐리어 밀도를 증가시키는 donor type의 defect가 발생하는 것으로 추정할 수 있었다. 추가적으로 활성층의 테두리 영역에서는 이러한 defect의 발생이 더 많이 발생함을 알 수 있었다. 따라서, 활성층의 테두리 영역이 소오스/드레인 전극과 직접 연결이 되는 AN 구조에서는 hump의 발생정도가 AW 구조보다 더 심하게 발생한 것으로 분석되었다.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.524-526
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• 2009

The effects of In and Ga contents on characteristics of InGaZnO (IGZO) films grown by a sol-gel method and their thin film transistors (TFTs) have been investigated. Excess In incorporation into IGZO enhances the field effect mobilities of the TFTs due to the increase in conducting path ways, and decreases the grain size and the surface roughness of the films because more $InO_2^-$ ions induce cubic stacking faults with IGZO. Ga incorporation into results in decrease in carrier concentration of films and off-current of TFTs since Ga ion forms stronger chemical bonds with oxygen than Zn and In ions, acting as a carrier killer.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.89-89
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• 2011

a-GIZO(비정질 Ga-In-Zn-O)박막은 유연하며 광학적으로 투명하고 높은 전자의 이동도를 갖는 반도체적 특성을 갖기 때문에 차세대 display분야에서 TFT(Thin-Film-Transistor)의 high speed active-matrix layer로써 각광을 받고 있다. 이 물질의 표면은 환경 및 표면처리에 매우 민감하며 [1,2], 이 표면에 metal이 증착되는 경우에도, 선행 연구에 의하면, 다양한 chemical state가 나타남을 알 수 있었다. 이것은 metal의 증착에 따라 metal과 a-GIZO 사이의 contact 저항이 달라짐을 의미한다. 우리는 a-GIZO 박막 위에 Au를 단계적으로 증착시키면서, Au coverage 증가에 따른 core-level과 valence에서의 x-ray photoelectron spectra의 변화를 살펴봄으로써 a-GIZO박막과 Au의 계면에서 일어나는 chemical state의 변화를 알 수 있었다. 특히, Au deposition의 전 처리과정으로써 Ne ion sputtering을 두 단계로 다르게 하여 a-GIZO의 표면환경에 따른 Au 증착의 영향을 살펴보았다.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.49 no.2
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• pp.15-22
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• 2012

A low power consumption scan driver using depletion-mode n-type InGaZnO thin-film transistors is proposed. The proposed circuit uses 2 clock signals and generates the non-overlap output signals without the additional masking signals and circuits. The power consumption of the proposed circuit is decreased by reducing the number of the clock signals and short circuit current. The simulation results show that the proposed circuit operates successfully when the threshold voltage of TFT is varied from -3.0V to 1.0V. The proposed scan driver consumes 4.89mW when the positive and negative supply voltage is 15V and -5V, respectively, and the operating frequency is 46KHz on the XGA resolution panel.