LiNbO3 thin films, deposited by DLI-CVD, for high-frequency BAW devices

The development of wide-band RF filters operating at high frequency is urgently needed for the implementation of the 5th generation (5G) communication infrastructure. LiNbO3 is a promising material for integration into bulk acoustic wave (BAW) resonators/filters adapted to high-frequency applications owing to its high piezoelectric properties. However, integrating this material typically involves ion-slicing/polishing techniques of single crystals, which pose challenges for thickness homogeneity and thus industrial-scale production.

In this thesis, we investigated the integration of highly-coupled 32.8°Y-LiNbO3 thin films grown by DLI-CVD in BAW resonators. We initially focused on optimizing the growth of pure phase LiNbO3 with (01-12) textured growth on a LaNiO3 seed layer. We then assessed the ferroelectric, pyroelectric, and piezoelectric properties of the grown LN films, obtaining values of P_s = 52 μC/cm², pi = 60 μC/m². K and e_(31,f) = -2.81 C/m², which are comparable to those of LN single crystal.

Next, we optimized the fabrication process for integration into a basic HBAR structure to evaluate the performance of the grown films. The HBARs demonstrated a k_eff² up to 22.4 % at a resonance frequency of 5.6 GHz. For integrating the grown films into SMRs, we first optimized the growth and studied the thermal stability of the ZnO/Pt Bragg reflector. This reflector was then used to fabricate 32.8°Y-LN based SMRs. Electrical characterization of the fabricated SMRs showed resonances at frequencies in the range of 5.2-5.7 GHz, indicating great potential for high-frequency RF filtering applications.

BAW resonators, thin films, CVD, structural properties, piezoelectricity

Confidential thesis until 03/10/2034.