AlN/ZnO/Si Structure Combining Surface Acoustic Waves and Waveguiding Layer Acoustic Wave

Transcription

1 Presented at the COMSOL Conerence 2010 Paris AlN/ZnO/Si Structure Combining Surace Acoustic Waves and Waveguiding Layer Acoustic Wave O. Legrani*, O. Elmazria*, S. Zhgoon +, L. Le Brizoual#, A. Bartasyte*, * Institut Jean Lamour (IJL), CNRS-Nancy University, Vandoeuvre lès Nancy, France + Moscow Power Engineering Institute, 14, Krasnokazarmennaja, Moscow, Russia # Institut des Matériaux Jean Rouxel (IMN), Université Nantes, CNRS, Nantes, France 1

2 Summary Introduction Motivation and approach Model Results > ZnO/Si structure > AlN/ZnO/Si structure: thickness inluence Conclusion/Outlook 2

3 Introduction Description and principle: Surace Acoustic Wave (SAW) = Interdigital Transducer (IDTs) + Piezoelectric layer + Gap ~ V - λ V SAW Piezoelectric substrate ( Hz ) = V SAW ( m / λ ( m ) s ) 3

4 Introduction Advantages o SAW devices: > Small size > Sensitive to the environments variations (temperature, pressure, atmosphere composition ) > Passive Wireless sensing without embedded electronics Wireless + harsh environments 4

5 What s wrong? Motivation and approach SAW devices are very sensitive to environmental variations (oxidation, humidity...) Need o protection package Packaging limits the extreme miniaturization o devices Solution: Realization o Waveguiding Layer Acoustic Wave (WLAW) devices 5

6 Motivation and approach WLAW device description: High acoustic velocity Low acoustic velocity AlN ZnO IDTs Isolation depends on: - Choices o Materials - Film thickness - Wavelength λ. High acoustic velocity Si (100) Substrate Semi- Modeling by sotware 2D COMSOL Multiphysics K. Bhattacharjee et al., IEEE, 135 (2007) L. Le Brizoual et al., IEEE 57, 1818 (2010) 6

7 Model AlN ZnO Si (100) Substrate Semi- Built-in 2D Structural Mechanics Module & Piezo plane Stress Physical constants o materials given by literature* λ = 8 µm -> or the modeling, only need λ/2 (symetric structure, save calculation time) Triangle mesh Periodic boundary conditions λ/2 K. Tsubouchi et al., IEEE Ultrasonics Symposium, 375 (1981) G. Carlotti et al., Appl. Phys. Lett 51, 1889 (1987) 7

8 Model Important properties o WLAW devices: > Phase velocity V => eigenrequency V = * λ > Electromechanical coupling K 2 => curves o Admittance modulus 100 Typical admitance modulus response 10 r k 2 = π 2 r a tg π 2 a a r * Y 1 0,1 0,01 a r : resonance requency a : anti-resonance requency 420,0M 450,0M 480,0M 510,0M 540,0M Frequency (Hz) D. ROYER, Ondes elastiques dans les solides, tome 2 8

9 Model Important properties o WLAW devices: > Phase velocity V => eigenrequency V = * λ > Electromechanical coupling K 2 => Curves o admittance modulus k 2 π = 2 r a π tg 2 a > Conditions o wave coninement => cross-section o acoustic ield distribution along Y-axis a r * Distance Y-axis 9

10 Results K 2 (%) Simple ZnO/Si structure - Si assumed semi-ininite - 1µm < h ZnO < 10µm 4,0 mode 0 3,5 mode 1 mode 2 3,0 2,5 2,0 1,5 1,0 0,5 Best perormance - 1 st mode increase up to a maximum value - 0 th and 2 nd increase and stabilize at high h ZnO - Good agreement with previous works* - Best perormance is obtained or 1.5 < kh ZnO < 4.5 0, kh ZnO * G. Carlotti et al., IEEE ultrasonics symposium, 295 (1987) * L. Le Brizoual et al., Ultrasonics 45, 100 (2006) 10

11 AlN/ZnO/Si structure Results AlN thickness - 1µm < h AlN 12 µm - ZnO thickness ixed at 5 µm 3,0 2,5 h ZnO = 5 µm mode 0 mode 1 mode h ZnO = 5µm mode 0 mode 1 mode 2 K 2 (%) 2,0 1,5 1,0 velocity (m/s) ,5 0, kh AlN kh AlN > Large impact o AlN thickness on the structure perormance 11

12 AlN/ZnO/Si structure Results AlN thickness and wave coninement Distance (m) 7,0x10-5 6,0x10-5 5,0x10-5 4,0x10-5 ZnO=5µm Variation o AlN thickness, h ZnO =5µm, λ=8µm 0 µm 2 µm 4 µm 6 µm 8 µm AlN 10 µm 12 µm 63,0µ 3,0x10-5 Silicon substrate 0,0 0,2 0,4 0,6 0,8 1,0 Normalized Y displacement (arb.u.) Distance (m) 60,0µ 57,0µ 54,0µ 0,00 0,05 0,10 0,15 0,20 Normalized Y displacement (arb.u.) 12

13 AlN/ZnO/Si structure Results Thickness o ZnO h AlN = 12µm, 1µm < h ZnO 5µm 2,5 2,0 K 2 (% %) 1,5 1,0 0,5 0, ZnO thickness (µm) - h ZnO inluence on wave coninement 1 µm 2 µm 4 µm 5 µm - Best K 2 value or hzno ~ 3-7 µm Variation o acoustic ield distribution 13

14 Conclusion An eicient AlN/ZnO/Si structure has been optimized beore experiments The eects o AlN and ZnO thicknesses on structure have been demonstrated Experimental tests have been realized and conirmed the results obtained by modelling 6000 simulation COMSOL expérimental insitu 5500 velocity (m/s) mode1 lambda=10 micron Outlook: - Inluence o IDTs position in the structure - Other Substrates - Inluence o temperature (TCF) - More experimental tests AlN (µm) 14

15 Thank you or your attention 15

16 [1] R.Stonely, Elastic waves at the surace o separation o two solids, Roy. Soc. Proc. London, Series A, 106 (1924), pp [2] K. Sezawa and K. Kanai, Discontinuity in dispersion curves o Rayleigh waves, Bull. Earthquake Res. Inst., vo1. 13, pp , March [3] C. Maereld and P.Tournois, Pure shear elastic surace wave guided by the interace o two semi-ininite media, Appl. Phys. Lett., vol. 19, pp , [4] K. Yamanouchi, K. Iwahashi, and K. Shibayama, Piezoelectric Acoustic Boundary Waves Propagating Along the Interace Between SiO2 and LiTaO3. IEEE Trans. On Sonics and Ultrasonics, vol. SU-25, N 6, 1978, pp [5] T. Yamashita, K. Hashimoto, and M. Yamaguchi, Highly piezoelectric shear-horizontal-type boundary waves, Jpn. J. Appl. Phys., vol. 36, part 1, pp , [6] M. Yamaguchi, T. Yamashita, K. Hashimoto, and T. Omori, Highly piezoelectric boundary baves in Si/SiO 2 /LiNbO 3 structure, 1998 IEEE International Frequency Control Symposium, pp [7] H. Kando, D. Yamamoto, H. Tochishita, and M. Kadota, RF ilter using boundary acoustic wave, Japanese J. o Appl. Phys., vol. 45, No. 5B, pp , [8] S. Ballandras, V. Laude, H. Majjad, W.Daniau, D. Gachon, and E. Courjon, Prediction and Measurement o Boundary Waves at the Interace Between LiNbO3 and Silicon, Third Int. Symposium on Acoustic Wave Devices or Future Mobile Communication Systems, Chiba University, Japan, [9] K. Bhattacharjee, A. Shvetsov, and S. Zhgoon, Packageless SAW Devices with Isolated Layer Acoustic Waves (ILAW) and Waveguiding Layer Acoustic Waves (WLAW), Proc. o TimeNav'07 Conerence, Geneva, [10] R.Takayama, H.Nakanishi, Y.Iwasaki, T.Sakuragawa, and K.Fujii, US-PCS SAW Duplexer using high-q SAW resonator with SiO2 coat or stabilizing temperature characteristics, Proc. o UFFC IEEE Int. Joint Conerence, pp , [11] K. Yamanouchi, K. Iwahashi, and K. Shibayama, Temperature dependence o Rayleigh waves and piezoelectric leaky surace waves in rotated Y-cut LiTaO3 and SiO2/LiTaO3 structures, Wave Electronics, vol. 3, pp, , [12] T. E. Parker and H. Wichansky, Temperature compensated surace-acoustic-wave devices with Si02 overlays, J. Appl. Phys. vol. 50, pp , [13] F. S. Hickernell, H. D. Knuth, R. C. Dablemont, and T. S. Hickernell, The Surace Acoustic Wave Propagation Characteristics o 64' Y-X LiNbO, and 36' Y-X LiTaO, Substrates with Thin-Film Si02, 1995 IEEE Utrasonics Symposium, pp