Experimental Insights of ScAlN-Based Switchable Resonator and Filter: Operation and Reliability

This paper explores the performance and reliability of ScAlN-based switchable film bulk acoustic resonators (FBARs) and filters. These devices are designed to operate in two frequency bands, 3 GHz and 6 GHz, by leveraging a ferroelectric material (Sc0.3Al0.7N) for frequency switching. The work aims to address challenges related to polarization configurations, switching reliability, and endurance in ferroelectric-based BAW devices.

Key Findings:

1. Switchable Frequency Operation: The paper introduces Sc0.3Al0.7N-based bilayer FBARs and filters capable of switching between 3 GHz and 6 GHz bands. Four polarization configurations were tested to optimize performance, revealing that switching the ScAlN layer enables the desired frequency shift. A new 2-step switching method is proposed to reduce the operational complexity of ladder filters, achieving seamless switching between the two frequency bands.

2. Resonator and Filter Performance: The fabricated devices were tested for their coupling efficiency (k2_eff) and fractional bandwidth (FBW), with the 3 GHz passband exhibiting an FBW of approximately 15% and the 6 GHz passband at 8%. The filters demonstrated low insertion loss (~0.91 dB) for the 3 GHz passband, and the first-ever demonstration of 6 GHz and X-band filtering using ScAlN-based technology was achieved.

3. Endurance and Reliability: Endurance tests revealed three primary failure mechanisms: electrical breakdown, mechanical cracking, and ferroelectric fatigue. The study also explores methods to extend device lifespan, such as a dynamic pulse-amplitude cycling scheme that enhanced endurance up to 10^7 cycles. The results showed that, with optimized pulse conditions, the devices could maintain performance for a significantly higher number of cycles compared to previous studies.

4. Cycling Behavior and Performance: The research also examined how the remnant polarization (Pr) and coupling coefficient (k2_eff) evolve over repeated cycling. It was found that after 10^4 cycles, a dynamic pulsing scheme significantly improved the devices' endurance, allowing them to reach 10^7 cycles without major failure. However, the coupling coefficient and remnant polarization exhibited a gradual decline after approximately 10^5 cycles.

5. Failure Mechanisms: The paper identifies mechanical cracking as a significant issue, especially for the top layers of the Sc0.3Al0.7N films, which exhibit higher current increases due to defect nucleation. This highlights the need for careful material selection and design to minimize these issues.

In conclusion, the paper provides insights into the operation and reliability of ScAlN-based switchable FBARs and filters, offering solutions for improving the endurance and switching capabilities of these devices. The findings contribute to the development of high-performance, reconfigurable acoustic resonators and filters suitable for future communication systems, such as 5G and beyond.