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

The Korea Association of Crystal Growth (한국결정성장학회)
권호 표지
DOI QR코드

DOI QR Code

Thermal gradient for LiTaO3 single crystal growth: A simulation study

LiTaO3 단결정 성장을 위한 열 구배 시뮬레이션 연구

  • Joon-Hyuk Kang (Department of Optical Lens Research center, Korea Photonics Technology Institute) ;
  • Won-Bae Sohn (Department of Optical Lens Research center, Korea Photonics Technology Institute) ;
  • Su-Jong Jeon (Department of Optical Lens Research center, Korea Photonics Technology Institute) ;
  • Jin-Hyeok Kim (Optoelectronics Convergence Research Center and Department of Materials Science and Engineering, Chonnam National University) ;
  • Seon Hoon Kim (Department of Optical Lens Research center, Korea Photonics Technology Institute)
  • 강준혁 (한국광기술원 광학렌즈소재연구센터) ;
  • 손원배 (한국광기술원 광학렌즈소재연구센터) ;
  • 전수종 (한국광기술원 광학렌즈소재연구센터) ;
  • 김진혁 (전남대학교 광전자융합기술연구소 신소재공학과) ;
  • 김선훈 (한국광기술원 광학렌즈소재연구센터)
  • Received : 2024.09.12
  • Accepted : 2024.10.04
  • Published : 2024.10.31
Download PDF
⟨ Previous Next ⟩

Abstract

LiTaO3 (Lithium Tantalate) single crystals are widely used in Surface Acoustic Wave (SAW) filters due to their excellent piezoelectric and optical properties. High-quality LiTaO3 single crystals were preferably grown by czochralski methods for RF Saw filter applications. However, if the growth conditions are not optimized, internal cracks and defects which degrade piezoelectric performance tend to occur. To solve these problems, we should consider temperature gradient and thermal insulation to decrease thermal stress. In this study, an iridium cover was added above the iridium crucible to decrease temperature gradients and improve thermal insulation. The simulation results indicated that the temperature in the cen tral region of the melt in creased by up to 8.6 K in the vertical direction an d up to 6.4 K in the radial direction . The addition of the iridium cover resulted in increases in both the maximum and minimum temperatures. In the vertical direction, the maximum temperature increased by 6.4 K and the minimum temperature by 8.5 K. In the horizontal direction, the maximum temperature increased by 2.6 K, and the minimum temperature rose by 2.2 K after applying the cover. The temperature gradient was also reduced with the addition of the iridium cover. The vertical temperature gradient decreased by approximately 39 %, while the radial temperature gradient decreased by 50 %. These results indicate that the iridium cover improves the thermal insulation and reduces the temperature gradient in the furnace.

LiTaO3 단결정은 우수한 압전 및 광학 특성으로 인해 표면 탄성표면파(SAW) 필터에 널리 사용되고 있다. 고품질 LiTaO3 단결정은 RF SAW 필터에 사용되기 위하여 주로 초크랄스키 성장 공법을 통해 제작된다. 그러나 단결정 성장 조건이 최적화되지 않으면 열 응력으로 인해 내부 결함 및 크랙이 발생한다. 이를 해결하기 위해서는 열 응력을 줄이기 위한 온도 구배 및 단열 조건을 고려해야 한다. 본 연구에서는 단열 특성 개선 및 온도 구배 감소를 위해 이리듐 도가니 위에 이리듐 덮개를 추가한 구조에 대해 열 구배 시뮬레이션을 수행하였다. 이리듐 덮개가 있는 경우에서, 이리듐 덮개가 없는 경우와 비교하여, 용융액 중앙 영역의 온도는 수직 방향에서 최대 8.6 K, 수평 방향에서 최대 6.4 K 증가하였다. 그리고 수직 방향에서 최대 온도는 6.4 K, 최소 온도는 8.5 K 증가하였고, 수평 방향에서는 최대 온도가 2.6 K, 최소 온도가 2.2 K 증가하였다. 또한, 이리듐 덮개 추가로 인한 온도 구배 감소를 확인하였다. 수직 방향 온도 구배는 약 39 % 감소하였고, 수평 방향 온도 구배는 50 % 감소하였다. 즉, 이리듐 덮개 적용함으로써 Furnace 내의 단열 특성이 개선되고 온도 구배가 감소됨을 확인하였다.

Keywords

Acknowledgement

이 논문은 과학기술정보통신부의 재원으로 한국연구재단(NRF)의 지원을 받아 수행된 연구임(No. 2022M3H4A3051764).

References

  1. S. Kumaragurubaran, S. Takekawa, M. Nakamura and K. Kitamura, "Growth of 4-in diameter near-stoichiometric lithium tantalate single crystals", J. Cryst. Growth. 285 (2005) 88.
  2. M.E. Lines, E. Malcolm, A.M. Glass and M. Alastair, "Principles and applications of ferroelectrics and related materials", 1st ed., Lines, Malcolm E., et al., Vol. 2 (Oxford university press, 2001) p. 24.
  3. Chen, Pu, Guangxi Li and Zhiyuan Zhu, "Development and application of SAW filter", Micromachines 13 (2022) 656.
  4. Eiichiro Nishimura, Katsuhiko Okano, Junji Lida and Keigo Hoshikawa, "LiTaO3 single crystal growth by the vertical Bridgman technique", Cryst. Res. Technol. 53 (2018) 1800044.
  5. Hui Zhang, Lili Zheng and Haiasheng Fang, "Hot zone design for controlled growth to mitigate cracking in laser crystal growth", J. Cryst. Growth. 318 (2011) 695.
  6. J.C. Brice, "The cracking of czochralski-grown crystals", J. Cryst. Growth. 42 (1977) 427.
  7. S. Narayanaswamy and C.T. Tsai, "Dislocation reduction in GaAs crystal grown from the czochralski process", J. Mater. Process. Technol. 55 (1995) 278.
  8. D. Furrer and S.L. Semiatin, "Metals process simulation", Valencia, Juan J. and Peter N. Quested, Vol. 22B (ASM international, 2010) p. 18.
  9. S.A. Krat, A.S. Popkov, Yu.M. Gasparyan, A.A. Pisarev, Peter Fiflis, Matthew Szott, Micheal Christenson, Kishor Kalathiparambil and David N. Ruzic, "Wetting properties of liquid lithium on lithium compounds", Fusion Eng. Des. 117 (2017) 199.
  10. D. Roshchupkin, R. Fakhrtdinov, B. Redkin, V. Karandashev, V. Khvostikov, A. Mololkin, O. Siminko and A. Zabelin, "Growth of ferroelectric lithium niobate tantalate LiNb(1-x)TaxO3 crystals", J. Cryst. Growth. 621 (2023) 127377.
  11. Ming Wu, Wenhan Zhao, Lijun Liu, Yang Yang, Wencheng Ma and Yuan Wang, "Effects of crucible cover on heat transfer during sapphire crystal growth by heat exchanger method", J. Cryst. Growth. 404 (2014) 130.
  12. Dan Wu, Ning Xia, Keke Ma, Jiabin Wang, Cheng Li, Zhu Jin, Hui Zhang and Deren Yang, "Numerical simulation of β-Ga2O3 single crystal growth by czochralski method with an insulation lid", Crystals 12 (2022) 1715.
  13. I.M. Buckley-golder and C.J. Humphreys, "A theoretical study of temperature distributions during czochralski crystal growth", Philos. Mag. A. 39 (1979) 41.
  14. J.H. Jeong and I.S. Kang, "Optimization of the crystal surface temperature distribution in the single-crystal growth process by the czochralski method", J. Comput. Phys. 177 (2002) 284.