7.4 Sound on a crystal

LiNbO₃ is piezoelectric: squeeze it and charge appears, apply a voltage and it deforms. In 1965 Bell Labs measured how elastic waves travel through it [Spencer et al. 1965 rec]. The same year Richard White and Fred Voltmer at Berkeley invented the interdigital transducer, two interleaved metal combs that launch and catch sound waves along a crystal surface. Their first device was on quartz, not lithium niobate [White & Voltmer 1965 rec; White & Voltmer 1965 rec].

At Tohoku University in Sendai, Kazuhiko Yamanouchi and Kimio Shibayama found a cut of LiNbO₃ with large surface-wave coupling (64 degree rotated Y, 1972) and then a cut that removes a spurious wave (127.86 degree rotated Y, X-propagating, 1976) [Yamanouchi & Shibayama 1972 rec; Shibayama et al. 1976 rec]. Sumitomo Metal Mining lists 128 degree rotated Y LN wafers for SAW filters [Sumitomo Metal Mining rec]. Surface acoustic wave (SAW) filters became practical in television receivers around 1980 and in radio-frequency filters on rotated-cut LN and LT in the late 1980s [Kadota 2011 S]. Murata acquired XBAR's developer, Resonant, in 2022 [Murata 2022 rec].

IDT. White and Voltmer: “direct piezoelectric surface wave transduction by a spatially-periodic electrode on the plane surface of a piezoelectric plate”; 1000 A aluminum on a quartz bar; 15 and 45 Mc [White & Voltmer 1965 rec]. The synchronous frequency of an IDT is f0 = v / p, with p the electrode period (one finger pair).

Cuts. Yamanouchi and Shibayama (1972): leaky SAW along X on 64 degree rotated Y-cut, K² = 0.113, attenuation 0.036 dB per wavelength on a free surface and zero when metallized; the Rayleigh wave on 130 degree Y-cut X-propagation has larger K² than Y-cut Z-propagation [Yamanouchi & Shibayama 1972 rec]. Shibayama et al. (1976): a 127.86 degree rotated Y-cut X-propagating plate suppresses the slower shear wave, the most obstructive spurious component, while keeping large coupling [Shibayama et al. 1976 rec].

Industry. Kadota (Murata), writing in 2011: TV SAW filters practical about 1980; RF filters on 40-70 degree YX-LN and LT practical from the late 1980s; SiO₂/Cu/YX-LN Love-wave duplexer practical 2003; SiO₂/Au/YX-LN boundary-wave GSM receive filter 2005 [Kadota 2011 S]. Shin-Etsu lists LT development in 1984 [Shin-Etsu 2026 rec]. Sumitomo Metal Mining was studying LN substrates for Ti:LN optics by 1989 [Fujiwara et al. 1989a rec] and in 2014 planned to expand LT/LN SAW substrate output from 120k to 210k wafers per month [Sumitomo Metal Mining 2014 S]. Soitec contracted volume piezoelectric-on-insulator wafers (thin LT on oxide on Si) for Qualcomm filters in 2020 [eeNews 2020 S].

The 1965 IDT was on quartz; SAW filters on LN date from the 1970s cuts above.

References

1. E. G. Spencer et al., Applied Physics Letters 7 67-69 (1965). ELASTIC WAVE PROPAGATION IN LITHIUM NIOBATE. Issued 1965-08-01. doi:10.1063/1.1754303
2. White & Voltmer, Applied Physics Letters 7 314-316 (1965). DIRECT PIEZOELECTRIC COUPLING TO SURFACE ELASTIC WAVES. Issued 1965-12-15. doi:10.1063/1.1754276
3. R. M. White & F. W. Voltmer, Electronics Research Laboratory, University of California, Berkeley (1965). Direct piezoelectric coupling to surface elastic waves (ERL Technical Memorandum M-132). Issued 1965-10-12. www2.eecs.berkeley.edu/Pubs/TechRpts/1965/ERL-m-132.pdf
4. Kazuhiko Yamanouchi & Kimio Shibayama, Journal of Applied Physics 43 856-862 (1972). Propagation and Amplification of Rayleigh Waves and Piezoelectric Leaky Surface Waves in LiNbO3. Issued 1972-03-01. doi:10.1063/1.1661294
5. Shibayama et al., Proceedings of the IEEE 64 595-597 (1976). Optimum cut for rotated Y-cut LiNbO3crystal used as the substrate of acoustic-surface-wave filters. Issued 1976. doi:10.1109/proc.1976.10181
6. Sumitomo Metal Mining. LT/LN single-crystal wafers (product page). www.smm.co.jp/en/business/material/products/lithium/
7. Michio Kadota, Journal of the Acoustical Society of Japan 67 494-495 (2011). Surface acoustic wave devices (in Japanese). Issued 2011. acoustics.jp/cms/wp_asj/wp-content/uploads/2019/03/6710onkochish…
8. Murata completes acquisition of Resonant (2022). Murata completes acquisition of Resonant. Issued 2022-03-29. corporate.murata.com/newsroom/news/company/general/2022/0329
9. Shin-Etsu Chemical corporate history (2026). Shin-Etsu Chemical corporate history. Issued 2026. www.shinetsu.co.jp/jp/company/history/
10. T. Fujiwara et al., Applied Physics Letters 54 975-977 (1989). Wavelength dependence of photorefractive effect in Ti-indiffused LiNbO3 waveguides. Issued 1989-03-13. doi:10.1063/1.101421
11. Sumitomo Metal Mining TSE disclosure on LT/LN substrate expansion (2014). Sumitomo Metal Mining TSE disclosure on LT/LN substrate expansion. Issued 2014-12-18. www2.jpx.co.jp/disc/57130/140120141218095422.pdf
12. eeNews Europe (2020). Qualcomm adopts Soitec POI wafers for SAW filters. Issued 2020-07-07. www.eenewseurope.com/en/qualcomm-adopts-soitec-poi-wafers-for-sa…
13. Kushibiki et al., IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 46 1315 (1999). Accurate measurements of the acoustical physical constants of LiNbO3 and LiTaO3 single crystals. Issued 1999. doi:10.1109/58.796136