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6CCVD Research

SAW Resonators and Filters Based on Sc0.43Al0.57N on Single Crystal and Polycrystalline Diamond

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2022-06-30
JournalMicromachines
AuthorsMiguel Sinusía Lozano, Laura Fernández-García, D. López‐Romero, Oliver A. Williams, G.F. Iriarte
InstitutionsUniversitat PolitĂšcnica de ValĂšncia, Institute of Micro and Nanotechnology
Citations8
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”
  • 5G Technology Enablement: High-frequency Surface Acoustic Wave (SAW) filters were successfully fabricated using Sc0.43Al0.57N/Diamond heterostructures, achieving operating frequencies above 4.7 GHz and bandwidths up to 189 MHz.
  • High Electromechanical Coupling: Resonators exhibited high effective electromechanical coupling coefficients (K2eff), reaching 3.72% for the Sezawa mode (2.05 GHz) on Single Crystal Diamond (SCD).
  • Diamond Substrate Advantage: The use of diamond substrates (PCD and SCD) leveraged high acoustic wave propagation velocity, enabling efficient Sezawa mode propagation at high frequencies.
  • Crystal Quality Impact: Devices fabricated on SCD showed significantly lower insertion losses (IL as low as -2.5 dB) and improved conductance baselines compared to Polycrystalline Diamond (PCD), confirming that grain boundaries degrade electrical response.
  • Synthesis Method: Highly c-axis oriented Sc0.43Al0.57N thin films were synthesized using reactive pulsed DC magnetron sputtering without intentional substrate heating, validating a scalable, low-thermal-budget process.
  • High Q-Factor: The Rayleigh mode on SCD achieved a high series quality factor (Qs) of 251, demonstrating excellent resonance performance.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Piezoelectric Film CompositionSc0.43Al0.57N-Synthesized via pulsed DC sputtering
Piezoelectric Film Thickness (Resonator)2000nmIDT wavelength (λ) = 2.8 ”m
Piezoelectric Film Thickness (Filter)850nmIDT wavelength (λ) = 1.2 ”m
Filter Center Frequency (Sezawa, SCD)4.90GHzHighest frequency mode reported
Filter Bandwidth (-3 dB, Sezawa, PCD)189MHzWide bandwidth for 5G applications
K2eff (Sezawa Mode, SCD)3.72%Effective coupling coefficient (2.05 GHz)
K2eff (Rayleigh Mode, PCD)3.19%Effective coupling coefficient (1.22 GHz)
Q-Factor (Rayleigh Mode, SCD)251-Series resonance quality factor (Qs)
Insertion Loss (Filter, SCD)-2.5dBRayleigh mode maximum gain
Propagation Velocity (Sezawa, SCD)5725m/sCalculated effective velocity (Veff)
ScAlN c-axis Orientation (FWHM)Below 3°Confirmed high crystal quality via XRD 0002 ω-Ξ scans
Substrate Roughness (RRMS)Below 2nmPCD and SCD substrates

Key Methodologies

Section titled “Key Methodologies”
  1. Substrate Preparation: Polycrystalline Diamond (PCD) on 500-”m Si (001) and Single Crystal Diamond (SCD) (111) were cleaned using a two-solvent method (acetone at 60 °C, followed by methanol sonication for 5 min each).
  2. ScAlN Synthesis (Reactive Magnetron Sputtering): Sc0.43Al0.57N thin films were grown using a home-built system with a Sc0.6Al0.4 target (45 mm distance). No intentional substrate heating was applied.
  3. Sputtering Parameters: A pulsed DC generator (ENI RPG50) was used (pulse width 1616 ns). The gas admixture ratio (N2/(N2 + Ar)) was set to 25%, and the process pressure was maintained at 0.40 Pa.
  4. Structural Analysis: X-ray diffraction (XRD) confirmed high c-axis orientation (FWHM < 3°). Rutherford Backscattering Spectroscopy (RBS) confirmed the target Sc concentration of 43%.
  5. IDT Fabrication (E-beam Lithography): Interdigital Transducers (IDT) were patterned using a standard lift-off process and a Crestec CABL-9500C e-beam system. An organic anti-static layer (Espacer 300Z) was used to prevent charge accumulation on the insulating diamond substrates.
  6. Metallization Stack: A 5-nm Cr adhesion layer was deposited, followed by Au electrodes (thickness varied from 65 nm to 130 nm depending on the device type).
  7. Electrical Testing: Devices were characterized using an Agilent N5230 A Vector Network Analyzer (VNA) with 300-”m pitch GSG probes, employing a standard Short, Open, Load, Through (SOLT) 50 Ω calibration.

Commercial Applications

Section titled “Commercial Applications”
  • 5G/6G RF Front-Ends: The high operating frequencies (up to 4.9 GHz) and wide bandwidths (up to 189 MHz) position these ScAlN/Diamond filters as high-performance components for next-generation mobile communication systems.
  • High-Power RF Devices: Polycrystalline piezoelectric thin films offer superior thermal stability and power handling capabilities compared to traditional materials, making them suitable for high-power base station filters.
  • Harsh Environment Sensors: The inherent thermal, chemical stability, and high stiffness of the ScAlN/Diamond compound are highly advantageous for developing stable SAW sensors operating under extreme temperature or chemical conditions.
  • Cost-Effective MEMS Manufacturing: Utilizing polycrystalline thin films and standard clean room fabrication techniques provides a cost-effective MEMS solution for high-volume production of high-performance filters.
  • Acoustic Wave Delay Lines: The high propagation velocity enabled by the diamond substrate is crucial for applications requiring precise, high-speed signal processing and delay lines.
View Original Abstract

The massive data transfer rates of nowadays mobile communication technologies demand devices not only with outstanding electric performances but with example stability in a wide range of conditions. Surface acoustic wave (SAW) devices provide a high Q-factor and properties inherent to the employed materials: thermal and chemical stability or low propagation losses. SAW resonators and filters based on Sc0.43Al0.57N synthetized by reactive magnetron sputtering on single crystal and polycrystalline diamond substrates were fabricated and evaluated. Our SAW resonators showed high electromechanical coupling coefficients for Rayleigh and Sezawa modes, propagating at 1.2 GHz and 2.3 GHz, respectively. Finally, SAW filters were fabricated on Sc0.43Al0.57N/diamond heterostructures, with working frequencies above 4.7 GHz and ~200 MHz bandwidths, confirming that these devices are promising candidates in developing 5G technology.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 1972 - Elastic Wave Propagation in Thin Layers [Crossref]
  2. 1991 - Surface Acoustic Wave Devices and Their Signal Processing Applications [Crossref]
  3. 2019 - The 2019 surface acoustic waves roadmap [Crossref]
  4. 2010 - The influence of sputter deposition parameters on piezoelectric and mechanical properties of AlN thin films [Crossref]
  5. 2012 - Thermal conductivity of aluminium nitride thin films prepared by reactive magnetron sputtering [Crossref]
  6. 2009 - Enhancement of Piezoelectric Response in Scandium Aluminum Nitride Alloy Thin Films Prepared by Dual Reactive Cosputtering [Crossref]
  7. 2010 - Origin of the Anomalous Piezoelectric Response in WurtziteScxAl1−xNAlloys [Crossref]

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