Journal of the Korean Crystal Growth and Crystal Technology (한국결정성장학회지)

The Korea Association of Crystal Growth (한국결정성장학회)
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MgO doping and annealing effect on high temperature electrical resistivity of AlN-Y2O3 ceramics

MgO doping 및 annealing이 AlN-Y2O3 세라믹스의 고온전기저항에 미치는 영향

  • Yu, Dongsu (Icheon Branch, Korea Institution of Ceramic Engineering and Technology) ;
  • Lee, Sung-Min (Icheon Branch, Korea Institution of Ceramic Engineering and Technology) ;
  • Hwang, Kwang-Taek (Icheon Branch, Korea Institution of Ceramic Engineering and Technology) ;
  • Kim, Jong-Young (Icheon Branch, Korea Institution of Ceramic Engineering and Technology) ;
  • Shim, Wooyoung (Department of Advanced Materials Science and Engineering, Yonsei University)
  • 유동수 (한국세라믹기술원 이천분원) ;
  • 이성민 (한국세라믹기술원 이천분원) ;
  • 황광택 (한국세라믹기술원 이천분원) ;
  • 김종영 (한국세라믹기술원 이천분원) ;
  • 심우영 (연세대학교 신소재공학과)
  • Received : 2018.10.01
  • Accepted : 2018.11.26
  • Published : 2018.12.31
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Abstract

High temperature electrical conductivity of Aluminum Nitride (AlN) ceramics sintered with $Y_2O_3$ as a sintering aid has been investigated with respect to various sintering conditions and MgO-dopant. When magnesium oxide is added as a dopant, liquid glass-film and crystalline phases such as spinel, perovskite are formed as second phases, which affects their electrical properties. According to high temperature impedance analysis, MgO doping leads to reduction of activation energy and electrical resistivity due to AlN grains. On the other hand, the activation energy and electrical resistivity due to grain boundary were increased by MgO doping. This is a result of the formation of liquid glass film in the grain boundary, which contains Mg ions, or the elevation of schottky barrier due to the precipitation of Mg in the grain boundary. For the annealed sample of MgO doped AlN, the electrical resistivity and activation energy were increased further compared to MgO doped AlN, which results from diffusion of Mg in the grains from grain boundary as shown in the microstructure.

$Y_2O_3$를 소결조제로 사용한 질화알루미나(AlN)에 다양한 소결조건과 MgO의 도핑이 고온전기전도도의 특성에 대해 미치는 영향에 대해 연구하였다. MgO를 도핑 하였을 때, 2차상으로 스피넬과 페로브스카이트 상이 생성되었고, 이는 전기적 특성에 영향을 끼쳤다. 고온 임피던스를 분석한 결과 MgO의 도핑은 AlN 입내의 활성화 에너지와 전기전도도의 감소를 보이는 반면에, 입계의 경우에는 활성화 에너지와 전기전도도의 증가를 보였다. 이는 저항이 높은 비정질의 액상이 입계에 형성되거나, Mg의 석출에 의하여 쇼트키 장벽이 높아졌기 때문으로 예상된다. MgO가 도핑된 AlN을 어닐링 한 경우에는 어닐링 하지 않은 경우에 비하여, 활성화 에너지와 전기전도도가 더욱 증가하는 것을 볼 수 있었다. 이러한 결과는 $1500^{\circ}C$에서 어닐링을 통하여 미세구조분석에서 보이는 바와 같이 Mg 이온이 입계에서 입내로 확산된 때문으로 예상된다.

Keywords

GJSJBE_2018_v28n6_235_f0001.png 이미지

Fig. 1. X-ray diffraction patterns for the sintered specimens of 1Y (a), 1Y2M (b), and 1Y2M-A (c). For (a), YAG is found beside the AlN main phase. For (b) and (c), YAP and MSP are observed along with AlN.

GJSJBE_2018_v28n6_235_f0002.png 이미지

Fig. 2. TEM images for (a) 1Y, (b) the enlarged image of (a), and (c) grain boundary of (a). TEM images for (d) 1Y2M, (e) the enlarged image of (d), and (f) grain boundary of (d). TEM images for (g) 1Y2M-A, (h) the enlarged image of (g), and (i) grain boundary of (g).

GJSJBE_2018_v28n6_235_f0003.png 이미지

Fig. 3. EDX maping images of (a) 1Y (refer to Fig. 2(b)), (b) 1Y2M (refer to Fig. 2(e)) and (c) 1Y2M-A (refer to Fig. 2(g)).

GJSJBE_2018_v28n6_235_f0004.png 이미지

Fig. 5. Complex impedance spectrum spectra of 1Y ((a), (b)), 1Y2M ((c), (d)), and 1Y2M-A ((e), (f)).

GJSJBE_2018_v28n6_235_f0005.png 이미지

Fig. 6. Grain and grain boundary conductivities with respect to temperature for 1Y, 1Y2M, and 1Y2M-A.

GJSJBE_2018_v28n6_235_f0006.png 이미지

Fig. 4. (a) Temperature and time dependences of the electronic resistivity for 1Y2M-A at 100 V/mm (red: RT, black: 100℃, blue: 200℃, Cyan: 300℃, pink: 400℃, green: 500℃). (b) Electronic conductivity with respect to temperature for 1Y, 1Y2M and 1Y2M-A at 100 V/mm.

Table 1 Subscript (m = g, gb) corresponds to high frequency (grain) and low frequency (grain boundary) contributions in Rm, Qm, Cm, εm, respectively. R: resistance, Q: pseudo-capacitance, n: empirical CPE (constant phase element) parameter. Capacitance (C) and permittivity (ε) values were calculated by equation, C = (Q*R)1/n/R

GJSJBE_2018_v28n6_235_t0001.png 이미지

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