Cost-Effective Frequency Scaling of Acoustic Devices from Sub-6 GHz to X-Band on Pizeo-on-SiC

This paper demonstrates a cost-effective solution for scaling the frequency of surface acoustic wave (SAW) devices from sub-6 GHz to X-band using a monolithic lithium niobate/4H-silicon carbide (LN/SiC) heterostructure. The approach leverages three distinct acoustic modes—shear horizontal SAW (SH-SAW), longitudinal leaky SAW (LLSAW), and high-order shear vertical (SV) modes—enabling the integration of multi-band functionality on a single platform.

The key findings of this study are as follows:

1. Wide Frequency Range: The devices fabricated span a broad frequency range from 3 GHz to 12 GHz, covering essential 5G NR bands (n77, n79), Wi-Fi 6/6E channels, and extending into the X-band. This broad frequency coverage is achieved without compromises in performance, demonstrating the scalability of SAW devices on the LN/SiC platform.

2. Efficient Fabrication: The SAW resonators and filters were fabricated using a single-mask KrF photolithography process, widely used in the SAW industry, on high-quality LN/SiC wafers. This simplified fabrication process enables scalable production of these devices for a wide range of applications.

3. Acoustic Mode Selection and Performance: The three acoustic modes were selectively excited on the LN/SiC heterostructure by choosing specific angles of cut and propagation directions for the lithium niobate. The SH-SAW, LLSAW, and high-order SV modes exhibit distinct phase velocities and coupling coefficients, making them suitable for different frequency ranges. The SH-SAW mode is ideal for frequencies below 5 GHz, LLSAW is suited for higher frequencies with substantial bandwidth, and the high-order SV mode is capable of reaching X-band frequencies with high phase velocity.

4. Device Characteristics: The fabricated devices show competitive performance, with measured insertion losses as low as 0.73 dB for the SH-SAW filter targeting the n79 band. The LLSAW filter for Wi-Fi 6/6E demonstrated near full-band coverage, and the first 11.6 GHz filter for X-band applications was realized using this platform.

5. Thermal and Reliability Testing: The devices also demonstrated excellent temperature stability and high-performance metrics in terms of frequency and bandwidth, even under escalating temperatures from -25°C to 85°C. This thermal stability, coupled with the absence of spurious modes, further enhances the feasibility of using these devices in diverse communication scenarios.

In conclusion, this study provides a practical pathway for cost-effective and scalable frequency scaling of SAW devices, offering a robust solution for multi-band RF front-ends in next-generation communication technologies, including 5G and beyond.