Ku-Band Alscn-on-Diamond SAW Resonators with Phase Velocity Above 8600 M/S
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-06-29 |
| Authors | Tzu-Hsuan Hsu, Kapil Saha, Jack J. Kramer, Omar Barrera, Paolo Simoni |
| Institutions | Northeastern University, The University of Texas at Austin |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Core Innovation: Demonstration of a Sezawa mode Surface Acoustic Wave (SAW) resonator platform utilizing Aluminum Scandium Nitride (AlScN) thin film deposited on a polycrystalline Chemical Vapor Deposition (CVD) Diamond substrate.
- High Velocity Achievement: Achieved an exceptional Sezawa mode phase velocity (vp) of 8671 m/s at 12.9 GHz, significantly outperforming high-velocity substrates like SiC and sapphire by over 20%.
- Performance Metrics: The prototype resonator exhibited a high maximum Bode-Q (Qmax) of 408 and an electromechanical coupling coefficient (k2eff) of 2.1% in the Ku-band.
- Frequency Scalability: The platform successfully demonstrated operation across the entire X-band (8-12 GHz) and Ku-band (12-18 GHz), highlighting its potential for frequency up-scaling.
- Thermal Robustness: Robust power handling capabilities were experimentally validated up to 12.5 dBm, attributed to the diamond substrateâs superior thermal conductivity (>1500 W/(mK)), which mitigates self-heating effects.
- Design Advantage: The use of diamond enables effective acoustic confinement without requiring heavy metal electrode loading, promoting better frequency scalability and power handling compared to conventional platforms.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Operating Frequency (Sezawa) | 12.9 | GHz | Peak performance resonator |
| Phase Velocity (vp) | 8671 | m/s | Sezawa mode, Ku-band operation |
| Maximum Bode-Q (Qmax) | 408 | - | Extracted using Bode formula |
| Electromechanical Coupling (k2eff) | 2.1 | % | Sezawa mode |
| Power Handling | > 12.5 | dBm | Experimentally validated incident power |
| Piezoelectric Film | 200 nm Al0.7Sc0.3N | ”m | Sputtered thin film |
| Substrate Material | Polycrystalline CVD Diamond | - | 300 ”m thick |
| Electrode Material/Thickness | 50 nm Al | nm | Minimal phase velocity loading |
| Frequency Range Demonstrated | 8 to 18 | GHz | Spans entire X-band and Ku-band |
| Diamond Thermal Conductivity | > 1500 | W/(mK) | Key for thermal management |
| Normalized Thickness (h/λ) | 0.3 | - | Ratio of AlScN thickness to wavelength |
| Diamond Surface Roughness (Ra) | < 20 | nm | Required for satisfactory AlScN crystal quality |
| AlScN Crystallinity (RC) | 3.42 | ° | X-Ray Diffraction FWHM |
Key Methodologies
Section titled âKey Methodologiesâ- Substrate Selection and Preparation: Utilized 300 ”m polycrystalline CVD diamond substrates featuring a low surface roughness (Ra < 20 nm) to ensure high-quality subsequent film deposition.
- Piezoelectric Film Deposition: A 200 nm thick Al0.7Sc0.3N thin film was deposited via sputtering.
- Crystallinity Verification: The quality of the wurtzite crystal structure in the AlScN film was confirmed using X-ray Diffraction (XRD) rocking curve measurement, yielding a full width at half maximum (FWHM) RC angle of 3.42°.
- Resonator Fabrication: 50 nm Aluminum (Al) electrodes were patterned to form the Interdigital Transducers (IDTs) and reflective gratings (e.g., 160 electrode pairs, 120 reflective gratings).
- Design Validation (Simulation): Finite Element Simulations (FEM) were conducted on the unit cell to analyze modal behavior, confirming the deep penetration and confinement of the Sezawa mode within the heteroacoustic waveguide structure.
- Electrical Characterization: Frequency response measurements were performed using a Keysight P5028A Vector Network Analyzer (VNA) and an MPI TS150 GSG prober under ambient conditions, following standard SOLT calibration.
- Power Handling Test: The device was repeatedly tested with incident power (Pin) ranging from -7.5 dBm up to 12.5 dBm to validate thermal stability and power endurance, observing no significant performance degradation.
Commercial Applications
Section titled âCommercial Applicationsâ- 6G Wireless Communication (FR3 Bands): Direct application in the emerging 6G frequency spectrum (Ku-band, 12-18 GHz) for high-performance RF filtering and front-end signal processing.
- High-Frequency RF Filters: Enables the development of highly scalable, low-loss Surface Acoustic Wave (SAW) filters operating at frequencies above 10 GHz, where conventional Rayleigh mode resonators struggle.
- High-Power RF Modules: The exceptional thermal conductivity of the diamond substrate (greater than 1500 W/(mK)) makes this platform ideal for thermally demanding wireless applications, improving device reliability and lifetime by mitigating self-heating.
- Miniaturization of Acoustic Devices: The ultra-high phase velocity (8671 m/s) allows for larger feature sizes (wavelengths) compared to other high-velocity substrates (like SiC) for the same operating frequency, simplifying fabrication and promoting miniaturization.
- Advanced Signal Processing: Potential use in systems requiring wide frequency tunability across both X-band and Ku-band, enabled by varying the normalized thickness ratio (h/λ).
View Original Abstract
In this work, an Aluminum Scandium Nitride (AlScN) on Diamond Sezawa-mode surface acoustic wave (SAW) platform for RF filtering at Ku-band (12-18 GHz) is demonstrated. Thanks to the high acoustic velocity and low-loss diamond substrate, the prototype resonator at 12.9 GHz achieves a high phase velocity ($v_p$) of 8671 m/s, a maximum Bode-$Q$ of 408, and coupling coefficient ($k_{\mathrm{eff}}^2$) of 2.1%, outperforming high-velocity substrates such as SiC and sapphire by more than 20% in velocity. Resonators spanning 8-18 GHz are presented. The platformâs high power handling above 12.5 dBm is also experimentally validated.