Zinc Oxide와 갈륨이 도핑 된 Zinc Oxide를 이용하여 Radio Frequency Magnetron Sputtering 방법에 의해 상온에서 제작된 박막 트랜지스터의 특성 평가

전훈하,노경석,김도현,최원봉,전민현,Jeon, Hoon-Ha,Verma, Ved Prakash,Noh, Kyoung-Seok,Kim, Do-Hyun,Choi, Won-Bong,Jeon, Min-Hyon 한국진공학회 2007 Applied Science and Convergence Technology Vol.16 No.5

본 논문에서는 zinc oxide (ZnO)와 gallium이 도핑 된 zinc oxide (GZO)를 이용하여 radio frequency (RF) magnetron sputtering 방법에 의해 상온에서 제작된 bottom-gate 박막 트랜지스터의 특성을 평가하고 분석하였다. 게이트 절연층 물질로서 새로운 물질을 사용하지 않고 열적 성장된 $SiO_2$를 사용하여 게이트 누설 전류를 수 pA 수준까지 줄일 수 있었다. ZnO와 GZO 박막의 표면 제곱평균제곱근은 각각 1.07 nm, 1.65 nm로 측정되었다. 그리고 ZnO 박막은 80% 이상, GZO 박막은 75% 이상의 투과도를 가지고 있었고, 박막의 두께에 따라 투과도가 달라졌다. 또한 두 시료 모두 (002) 방위로 잘 정렬된 wurtzite 구조를 가지고 있었다. 제작된 ZnO 박막 트랜지스터는 2.5 V의 문턱 전압, $0.027\;cm^2/(V{\cdot}s)$의 전계효과 이동도, 104의 on/off ratio, 1.7 V/decade의 gate voltage swing 값들을 가지고 있었고, enhancement 모드 특성을 가지고 있었다. 반면에 GZO 박막 트랜지스터의 경우에는 -3.4 V의 문턱 전압, $0.023\;cm^2/(V{\cdot}s)$의 전계효과 이동도, $2{\times}10^4$의 on/off ratio, 3.3 V/decade의 gate voltage swing 값들을 가지고 있었고, depletion 모드 특성을 가지고 있었다. 우리는 기존의 ZnO와 1wt%의 Ga이 도핑된 ZnO를 이용하여 두 가지 모드의 트랜지스터 특성을 보이는 박막 트랜지스터를 성공적으로 제작하고 분석하였다. In this paper we present a bottom-gate type of zinc oxide (ZnO) and Gallium (Ga) doped zinc oxide (GZO) based thin film transistors (TFTs) through applying a radio frequency (RF) magnetron sputtering method at room temperature. The gate leakage current can be reduced up to several ph by applying $SiO_2$ thermally grown instead of using new gate oxide materials. The root mean square (RMS) values of the ZnO and GZO film surface were measured as 1.07 nm and 1.65 nm, respectively. Also, the transmittances of the ZnO and GZO film were more than 80% and 75%, respectively, and they were changed as their film thickness. The ZnO and GZO film had a wurtzite structure that was arranged well as a (002) orientation. The ZnO TFT had a threshold voltage of 2.5 V, a field effect mobility of $0.027\;cm^2/(V{\cdot}s)$, a on/off ratio of $10^4$, a gate voltage swing of 17 V/decade and it operated in a enhancement mode. In case of the GZO TFT, it operated in a depletion mode with a threshold voltage of -3.4 V, a field effect mobility of $0.023\;cm^2/(V{\cdot}s)$, a on/off ratio of $2{\times}10^4$ and a gate voltage swing of 3.3 V/decade. We successfully demonstrated that the TFTs with the enhancement and depletion mode type can be fabricated by using pure ZnO and 1wt% Ga-doped ZnO.

RF magnetron sputtering 법으로 증착된 GZO와 ZnO 박막의 광학적 특성

황보수정,전훈하,김금채,이지수,김도현,최원봉,전민현,HwangBoe, S.J.,Jeon, H.H.,Kim, G.C.,Lee, J.S.,Kim, D.H.,Choi, W.B.,Jeon, M.H. 한국진공학회 2007 Applied Science and Convergence Technology Vol.16 No.6

상온에서 RF magnetron sputtering 을 이용하여 10nm에서 50nm 의 두께를 가지는 ZnO와 GZO 를 유리 기판위에 증착하여 두 물질 간의 구조적 특성과 광학적 특성을 평가하였다. 구조적인 특성은 투과전자현미경 (TEM) 과 주사전자현미경 (SEM)을 통해 이루어졌다. 광학적 특성 평가는 spectrophotometer를 이용하여 UV-VIS-NIR 영역에 관한 투과도를 측정하였다. ZnO의 결정크기가 GZO보다 상대적으로 더 크게나왔으며 이는 결정 경계면에서 발생하는 광산란을 줄임으로서 투과도의 향상을 가져왔다. 투과 전 영역에서 ZnO의 투과도가 더 높게 나왔으며, 특히 50nm 박막의 경우 ZnO의 투과도가 GZO 보다 20% 이상 더 뛰어난 것을 확인 할 수 있었다. Zinc oxide (ZnO) and Ga doped zinc oxide (GZO) with different thickness in range of 10nm to 100nm are prepared on glass substrate by RF magnetron sputtering at room temperature. The structural and optical properties of the thin films is evaluated. The structural properties of ZnO and GZO are investigated by Tunneling Electron Microscopy (TEM) and scanning electron microscopy (SEM). Optical properties are also investigated by UV-VIS-NIR spectrophotometer (200$\sim$1400nm). The much larger grain size of ZnO compared to GZO decreased the light scattering at the grain boundary and improved the transmittance. The transmittance of ZnO is higher than that of GZO through all of the ranges of wavelengths. In case of over 50nm, we found that the transmittance of ZnO is 20% higher than that of GZO.

Influence of Grain Size and Room-Temperature Sputtering Condition on Optical and Electrical Properties of Undoped and Ga-Doped ZnO Thin Films

김도현,전민현,전훈하,임재영,문주호,이성휘,Ved Prakash Verma,최원봉 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.III

The optical and the electrical properties of undoped zinc-oxide (ZnO) thin lms of various thicknesseswerecomparedwiththoseofGa-doped(GZO)thinlms. Transparent,high-qualityundoped ZnO and GZO lms were deposited successfully using radio-frequency (RF) sputtering at room temperature. The lms were polycrystalline with a hexagonal structure and a strongly preferred orientation along the c-axis. The lms had an average optical transmission >85 % in the visible partoftheelectromagneticspectrum. TheundopedZnOthinlmsweremoretransparentthanthe GZO thin lms. The ZnO thin-lm transistors (TFTs) were operated in the enhancement mode withathresholdvoltageof2.5V.Incontrary,theGa-dopedZnOTFTswereoperatedinadepletion mode with a threshold voltage of {3.4 V. We successfully demonstrated undoped and the Ga-doped ZnO TFTs by using conventional SiO2 gate insulators at room temperature. We postulate that undoped ZnO lms, which have not been treated to improve the optical properties, can be used, instead of doped ZnO lms, in transparent devices for next generation optoelectronic devices. The optical and the electrical properties of undoped zinc-oxide (ZnO) thin films of various thicknesses were compared with those of Ga-doped (GZO) thin films. Transparent, high-quality undoped ZnO and GZO films were deposited successfully using radio-frequency (RF) sputtering at room temperature. The films were polycrystalline with a hexagonal structure and a strongly preferred orientation along the $c$-axis. The films had an average optical transmission $>$85 \% in the visible part of the electromagnetic spectrum. The undoped ZnO thin films were more transparent than the GZO thin films. The ZnO thin-film transistors (TFTs) were operated in the enhancement mode with a threshold voltage of 2.5 V. In contrary, the Ga-doped ZnO TFTs were operated in a depletion mode with a threshold voltage of --3.4 V. We successfully demonstrated undoped and the Ga-doped ZnO TFTs by using conventional SiO$_2$ gate insulators at room temperature. We postulate that undoped ZnO films, which have not been treated to improve the optical properties, can be used, instead of doped ZnO films, in transparent devices for next generation optoelectronic devices.

RF 마그네트론 스퍼터링 법으로 유리 기판 위에 성장 시킨 Ga 도핑된 ZnO 박막의 열처리에 따른 구조적, 광학적 특성 평가

이지수,김금채,전훈하,황보수정,김도현,성창모,전민현,Lee, J.S.,Kim, G.C.,Jeon, H.H.,HwangBoe, S.J.,Kim, D.H.,Seong, C.M.,Jeon, M.H. 한국진공학회 2008 Applied Science and Convergence Technology Vol.17 No.1

본 연구에서는 상온에서 RF 마그네트론 스퍼터링 법으로 유리 기판위에 증착된 Ga 도핑 된 다결정 ZnO 박막의 특성을 개선하기 위하여 적정 열처리 조건을 분석하였다. 먼저 박막 성장 후 박막의 특성을 분석하였고 각각 $400{\sim}600^{\circ}C$에서 30분, 60분간 질소 분위기에서 열처리를 한 후 구조적, 광학적 특성을 평가하였다. XRD와 FE-SEM을 사용하여 열처리온도 변화에 따른 결정입자의 크기의 변화를 관찰하였다. 그 결과 성장된 결정의 크기의 증가와 박막의 결정성이 향상되었음을 확인할 수 있었으며 그로 인해 박막 특성을 중시하는 투명 전도막의 투과도의 향상 또한 확인할 수 있었다. 결론적으로, 본 실험을 통하여 ZnO 성장 후 적절한 열처리를 수행함으로서 GZO 박막을 사용하여 제작된 소자의 특성을 개선할 수 있으리라 판단된다. We have investigated the effect of annealing on the structural and optical properties of polycrystalline Ga doped ZnO (GZO) films grown on glass substrates by RF-magnetron sputter at room temperature. The structural and optical properties of as-grown GZO films were characterized and then samples were annealed at $400{\sim}600^{\circ}C$ in $N_2$ ambient for 30, 60 minutes, respectively. The field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were used to measure the grain size and the crystalline quality of the films. We found that the crystalline quality was improved and the grain size tends to be increased. The optical properties of GZO thin films were analyzed by UV-VIS-NIR spectrophotometers. It is found that optical properties of thin films are increased by annealing and can be used for transparent electrode application. We believe that the appropriate post-growth heat treatment could be contributed to the improvement of GZO-based devices.