Thermal Endurance of Suspended Thin-Film Lithium Niobate up to 800 ◦C

The paper investigates the thermal endurance of suspended thin-film lithium niobate (LN) platforms, specifically focusing on their performance as acoustic resonators at high temperatures (550°C to 800°C). The study primarily explores the structural integrity and performance changes of these devices after multiple annealing rounds at increasing temperatures.

Key points from the paper include:

1. Material Selection & Design: Thin-film LN is chosen for its high electromechanical coupling, desirable for high-temperature applications. Platinum electrodes with a titanium adhesion layer are used, chosen for their durability at elevated temperatures.

2. Thermal Endurance: The resonators are tested by subjecting them to annealing temperatures from 250°C to 800°C. The devices show good performance up to 550°C, with minimal changes in resonant frequency and quality factor (Q).

3. Temperature Range of 550°C to 800°C: Significant damage occurs beyond 550°C. At temperatures above 600°C, structural damage such as cracks in LN, delamination, and loss of electrical conductivity in platinum electrodes is observed.

4. Material Quality: The study notes that after annealing at high temperatures, LN experiences phase transitions (formation of LiNb3O8) that degrade its quality. The metal layers also show increased resistivity due to thermal effects.

5. Device Performance: Resonant frequencies generally shift upwards with increasing temperature, and quality factors (Q) increase for some modes before dropping due to metal degradation and structural damage. Devices fail to operate after 800°C.

The research concludes that while the thin-film LN platform shows potential for use in MEMS and other high-temperature applications, further optimization of the design and materials is needed to improve its performance at extreme temperatures.