Journal of the Institute of Electronics Engineers of Korea SD (대한전자공학회논문지SD)

The Institute of Electronics and Information Engineers (대한전자공학회)
권호 표지

Theoretical Analysis of FBARs Filters with Bragg Reflector Layers and Membrane Layer

브래그 반사층 구조와 멤브레인 구조의 체적 탄성파 공진기 필터의 이론적 분석

  • 조문기 (인하대학교 전자재료공학과) ;
  • 윤영섭 (인하대학교 전자재료공학과)
  • Published : 2002.04.01
Download PDF
⟨ Previous Next ⟩

Abstract

In this study, we have analyzed the effects of the membrane layer and the bragg reflector layers on the resonance characteristics through comparing the characteristics of the membrane type FBAR (Film Bulk Acoustic Wave Resonator) and the one type bragg reflector layers with those of the ideal FBAR with top and bottom electrode contacting air by using equivalent circuit technique. It is assumed that ZnO is used for piezoelectric film, $SiO_2$ are used for membrane layer and low acoustic impedance layer, W are used for the high acoustic reflector layer and Al is used for the electrode. Each layer is considered to have a acoustic propagation loss. ABCD parameters are picked out and input impedance is calculated by converting 1-port equivalent circuit to simplified equivalent circuit that ABCD parameters are picked out possible. From the variation of resonance frequency due to the change of thickness of electrode layers, reflector layers and membrane layer it is confirmed that membrane layer and the reflector layer just under the electrode have the greatest effect on the variation of resonance frequency. From the variation of resonance properties, K and electrical Q with the number of layers, K is not much affected by the number of layers but electrical Q increases with the number of layers when the number of layers is less than seven. The electrical Q is saturated when the number of layers is large than six. The electrical Q is dependent of mechanical Q of reflector layers and membrane layer. Both ladder filter and SCF (Stacked Crystal Filters) show higher insertion loss and out-of-band rejection with the increase of the number of resonators. The insertion loss decreases with the increase of the number of reflector layers but the bandwidth is not much affected by the number of reflector layers. Ladder Filter and SCF with membrane layer show the spurious response due to spurious resonance properties. Ladder filter shows better skirt-selectivity characteristics in bandwidth but SCF shows better characteristics in insertion loss.

본 논문에서는 등가회로를 이용하여 브래그 반사층형 FBAR (Film Bulk Acoustic Wave Resonator) 와 membrane 형 FBAR 그리고 상 하부 전극이 공기와 접하는 이상적인 FBAR 의 특성을 서로 비교함으로서 브래그 반사층과 membrane 이 공진 특성에 미치는 영향을 분석하였다. 압전층으로는 ZnO, membrane 층과 낮은 음향적인 임피던스 반사층은 SiO₂, 높은 음향적인 임피던스 반사층으로는 W, 전극층으로는 Al를 가정하였고 각 층은 탄성파 전달 손실을 가정하였다. 1-port 의 등가회로를 ABCD 파라미터를 추출할 수 있는 단순화된 등가회로로 변환하여 ABCD 파라미터를 추출하여 입력임피던스를 계산하였다. 필터 설계에서는 구하여진 파라미터를 산란행렬로 변환하여 필터의 대역폭 및 삽입손실을 구하였다. 전극층, 반사층, membrane 층의 두께 변화에 의한 공진주파수의 변화는 membrane 층과 전극 바로 아래의 반사층의 두께 변화가 가장 큰 영향을 미친다는 결과를 확인하였다. 반사층 구조에서 반사층수에 따른 공진특성과 K/sub eff/와 electrical Q 의 변화에서는 반사층수가 K/sub eff/ 에는 거의 영향을 미치지 않지만 electrical Q 는 층수가 증가할수록 증가하다가 7층 이상에서 포화되었다. 또한 FBAR의 electrical Q 는 membrane 층과 반사층의 mechanical Q 에 의존함을 알 수 있었다. Ladder 필터와 SCF(Stacked Crystal Filters) 모두 공진기의 수가 증가할수록 삽입손실과 out-of-band rejection 이 증가하였고 층수가 증가할수록 삽입손실은 감소하지만 대역폭에는 거의 변화가 없었다. membrane형의 ladder 필터와 SCF 는 불효 공진 특성으로 인한 불효응답특성이 나타났다. 또한 ladder 필터는 보다 우수한 대역폭의 skirt-selectivity 특성을 나타내었으며 SCF 는 대역폭의 삽입손실 측면에서 더 우수하였다.

Keywords

References

  1. K.M. Lakin 'Thin Film Resonator Filters' IEEE Ultrasonics Symposium, pp 895-906, 1999
  2. S. H. Park, B. C. Seo, H. D. Park, and G. W. Yoon, 'Film Bulk Acoustic Resonator Fabrication for Radio Frequency Filter Applications' JJAP. Vol. 39 July 2000, pp. 4115-4119 https://doi.org/10.1143/JJAP.39.4115
  3. K. M. Lakin, K. T. McCarron, and R. E. Rose 'Solidly Mounted Resonators And Filters' IEEE Ultrasonics Symposium, pp 905-908, 1995 https://doi.org/10.1109/ULTSYM.1995.495711
  4. V. P. Kutepovam, D. A. Hall 'Effect of Sputtering parameters on the Growth and Piezoelectirc Properties of Zinc Oxide Thin Films', IEEE Ultrasonics Symposium, pp. 213-217, 1998 https://doi.org/10.1109/ULTSYM.1998.762131
  5. K. M. Lakin, G. R. Kline, and K. T. McCarron. 'High-Q Microwave Acoustic Resonators and Filters' IEEE Trans. on. Microwaves Theory and Techniques, 41(12):2139-2146, December 1993 https://doi.org/10.1109/22.260698
  6. B. A. Auld Acoustic Fields and Waves in Solids: Volume I, Krieger Publishing Company, Malabar, Folida, 2 edition, 1990 pp. 89-91
  7. J. F. Rosenbaum. 'Bulk Acoustic Wave Theory and Devices' Artech House, Inc., Norwood, MA, 1988 pp. 213-218
  8. M. A. Dubois, P. Muralt, H. Matsumoto, V. Plessky. 'Solidly Mounted Resonator Based on Alumimum Nitride Thin Film' IEEE Ultrasonics Symposium, pp. 909-912, 1998 https://doi.org/10.1109/ULTSYM.1998.762291
  9. K. M. Lakin, J. Rosenbaum, S. Horwitz, C. Vale and R. A. Moore 'Film Bulk Wave Resonator Technology' IEEE Ultrasonics Symposium, pp. 529-536, 1990
  10. K. M. Lakin, 'Modeling of thin film resonators and filters' In IEEE MTT-S Digest, 1992, pp. 149-152 https://doi.org/10.1109/MWSYM.1992.187931
  11. H. Kanbara, H. Kobayashi, and K. Nakamura 'Analysis of Piezoelectric Thin Film Resonator with Acoustic Quarter-Wave-Multilayers' JJAP. vol.39 May 2000, pp. 3049-3053 https://doi.org/10.1143/JJAP.39.3049
  12. Qing-Xin Su, Paul Kirby, Eiju Komuro, Massaki Imura, Qi Zhang, Roger Whatmore, 'Thin-Film Bulk Acoustic Resonators and Filters Using ZnO and Lead-Zirconium_Titanate Thin Films' IEEE Trans. on. Microwaves Theory and Techniques, 49(4): 769-778, April 2001 https://doi.org/10.1109/22.915462
  13. W. E. Newell, 'Face-mounted Piezoelectric Resonator', in Proc. IEEE, Vol. 53, June 1965, pp. 575-581 https://doi.org/10.1109/PROC.1965.3925
  14. P. Osbond, C. M. Beck, J. Brierley, M. R. Cox, S. P. Marsh, and N. M. Shorrocks, 'The Influence of ZnO and Electrode Thickness on the Performance of Thin Film Bulk Acoustic Wave Resonators' IEEE Ultrasonics Symposium, pp 911-914, 1999 https://doi.org/10.1109/ULTSYM.1999.849137
  15. S. V. krishnaswamy, J. Fosenbaum, S. Horwitz, C. Vale and R. A. Moore 'Film Bulk Acoustic Wave Resonator Technology' IEEE Ultrasoncis Symposium, pp. 529-536, 1990 https://doi.org/10.1109/ULTSYM.1990.171421