lithium niobate / 06 Devices / 6.9
6.9 RF acoustic filters
L1 Phenomenon
A phone picks its radio bands out of the air with tiny acoustic filters; a 2018 count put more than 50 in a mid- to high-tier 4G phone (Microwave Journal, 2018-10-11). Many are surface-acoustic-wave filters on a lithium tantalate or lithium niobate crystal; the comb electrodes set the frequency. LT appears to dominate SAW filters (inference from product pages; no public share figure) inference; bulk-acoustic-wave (BAW) filters use aluminum nitride, not LN inference.
L2 Facts with sources
| Fact | Status | Source |
|---|---|---|
| SAW filters are built on piezoelectric LT or LN substrates; 128-degree Y LN and 36-50-degree rotated Y LT are standard cuts; 4" and 6" wafers | company page | Sumitomo Metal Mining |
| Shin-Etsu's piezo crystal page lists LT only | company page | Shin-Etsu |
| Soitec POI (piezo-on-insulator) is offered as LT (LT6 150 mm, LT8 200 mm) and LN (LN6 150 mm) | company page | Soitec |
| XBAR: 400 nm ZY-LN platelet, resonance about 4,800 MHz, coupling about 25%, resonance Q about 300 | reported | [Plessky et al. 2019] |
| Murata states its high-frequency filters use LiNbO3 | company statement | [Murata Manufacturing Co., Ltd.] |
| Filters per phone: "> 50" in mid/high-tier 4G phones, "> 70" expected with 5G (2018) | trade press | Microwave Journal, 2018-10-11 |
| LT vs LN share of SAW filter volume | N/A: no public quantitative source found | - |
Interdigital transducer and SAW, top view, 14 px per µmsingle-electrode IDT, finger width λ/4
λac 1.989 µmIDT period (pitch) 1.989 µmfinger 0.497 µmv 3978.4 m/s
Cut
λ = v/f. v: free-surface SAW velocity of the cut from the partial-wave solver with the Kushibiki 1999 constants derived (solver: chapter 03). Crests drawn qualitatively; the photoelastic index change follows the strain sign.
Cut
- Acoustic wavelength = IDT period
- 1.989 µm
- Finger width
- 0.497 µm
- SAW velocity
- 3978.4 m/s
Doubling the frequency halves the finger pitch on screen (fixed 18 px per µm). Single-electrode IDT, finger width λ/4; λ = v/f with the free-surface SAW velocity of the cut from the partial-wave solver and the Kushibiki 1999 constants derived (solver: chapter 03). Crests drawn qualitatively; the photoelastic index change follows the strain sign.
L3 Gaps
- Electromechanical coupling k2 and f*Q records for TFLN acoustic resonators are not given here; a mmWave TFLN acoustic review exists Lu 2025.
Sources
| Ref | Title | Link |
|---|---|---|
| Kushibiki et al. 1999 | Accurate measurements of the acoustical physical constants of LiNbO/sub 3/ and LiTaO/sub 3/ single crystals | doi:10.1109/58.796136 |
| Lu 2025 | Recent advances in high-performance millimeter-Wave acoustic resonators and filters using thin-film lithium niobate | doi:10.1016/j.pquantelec.2025.100565 |
| Microwave Journal, 2018-10-11 | Microwave Journal, 2018-10-11 | www.microwavejournal.com/articles/31149-sawbaw-new-market-entrants-offer-new-approaches |
| Murata Manufacturing Co., Ltd. | Murata exhibits at OFC 2026 (news release, 2026-03-10) | corporate.murata.com/en-us/newsroom/news/company/general/2026/0310 |
| Plessky et al. 2019 | 5 GHz laterally‐excited bulk‐wave resonators (XBARs) based on thin platelets of lithium niobate | doi:10.1049/el.2018.7297 |
| Shin-Etsu | Shin-Etsu Chemical, Oxide Single Crystals (LT) | www.shinetsu.co.jp/en/products/electronics-materials/oxide-single-crystals |
| Soitec | Soitec, Connect POI | www.soitec.com/en/products/poi |
| Sumitomo Metal Mining | Sumitomo Metal Mining, LT/LN product page | www.smm.co.jp/en/business/material/products/lithium |