SKM 2021 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 11: Focus Session: Functional Metal Oxides for Novel Applications and Devices
HL 11.5: Invited Talk
Tuesday, September 28, 2021, 15:30–16:00, H4
Integration of 33∘Y-LiNbO3 films with high-frequency BAW resonators — Sondes Boujnah1, Mihaela Ivan2, Vincent Astié3, Samuel Margueron1, Mario Constanza1, Jean-Manuel Decams3, and •Ausrine Bartasyte1 — 1FEMTO-ST Institute, University of Bourgogne Franche-Comté Besançon, France — 2SATT-Sayence, Dijon, France — 3Annealsys, Montpellier, France
The next generation telecommunications require RF filters operating at frequencies of 6-9 GHz. LiNbO3 (LN) films were identified as one of the materials with sufficient electromechanical coupling, K2, for these applications. To attain 6-9 GHz frequencies in bulk acoustic wave (BAW) devices, LN film thickness has to be below 200 nm, which makes challenging their fabrication by popular smart-cut process. This motivates further development of integration of deposited highly-coupled LN films with BAW resonators. Several challenges have to be overcome in the case of LN direct growth on electrodes/mirrors/sacrificial layers used in BAW devices: (i) heterostructure has to be stable chemically/structurally at LN growth temperature/atmosphere, (ii) eliminate interaction between Li2O and SiO2, (iii) bottom electrode with good conductivity.
The aim of this work is to optimize SMR and HBAR structures adapted to high-deposition temperatures, and chemically not interacting with LN thin films. The Bragg mirror with a reflection coefficient of 0.98 and a stopband width of 3.1 GHz, centered at 6 GHz, for the longitudinal mode was designed. Deposition parameters were optimized to fabricate the Bragg reflectors with small roughness, without defaults and good stability and Pt bottom electrode with low resistivity (4µΩ·cm). The SMR resonator based on 125 nm thick 33∘Y-LN film allows attain pure longitudinal mode with K2 as high as 14.5 % at 5.9 GHz. 33∘Y-LN films grown on seed layer/Pt bottom electrode presented single orientation, and dielectric constant close to bulk LN. After electrical poling, the pyroelectric coefficient increased from 11 µC·m−2·K−1 to the value of bulk 33∘Y-LN indicating single domain state of the film. The acoustical performance of BAW devices will be presented, as well.