Analysis of the Effects of Parameters on the Performance of Resonators Based on a ZnO/SiO2/Diamond Structure

At a Glance

Metadata	Details
Publication Date	2024-01-19
Journal	Applied Sciences
Authors	Gang Cao, Hongliang Wang, Peng Zhang
Institutions	North University of China
Citations	1
Analysis	Full AI Review Included

Technical Documentation & Analysis: ZnO/SiO₂/Diamond SAW Resonators

6CCVD Reference Document: 2024-SAW-0874 Target Application: High-Frequency Surface Acoustic Wave (SAW) Devices for 5G Communications

Executive Summary

This research validates a novel multilayer structure (IDT/ZnO/SiO₂/Diamond) for high-performance SAW resonators, achieving critical metrics necessary for 5G applications. 6CCVD specializes in providing the foundational MPCVD diamond substrates required for this advanced technology.

Structure Validation: Systematic analysis confirms the viability of the ZnO/SiO₂/Diamond stack for high-frequency SAW devices, leveraging diamond’s superior acoustic and thermal properties.
Performance Achievement: The optimized structure successfully excites the Sezawa wave mode, yielding a high characteristic frequency (2446 MHz) and high acoustic velocity ($v_p$) of 4892 m/s.
Enhanced Coupling: The electromechanical coupling coefficient ($k^2$) reached 4.9% for the Sezawa mode, representing a 753% improvement over the Rayleigh mode in the same structure.
Temperature Stability: The inclusion of the SiO₂ temperature complementary layer successfully achieved a Temperature Coefficient of Frequency (TCF) close to 0 ppm/°C, ensuring stable operation in communication environments.
Material Necessity: Diamond substrates are confirmed as essential for achieving high sound velocity and providing the high thermal conductivity required to improve device power tolerance.
6CCVD Value Proposition: 6CCVD offers high-quality MPCVD Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) substrates, custom dimensions (up to 125mm), and ultra-low roughness polishing (Ra < 1nm) critical for replicating and scaling this high-performance device architecture.

Technical Specifications

The following hard data points were extracted from the simulation results for the optimized Sezawa mode resonator structure (where $\lambda$ = 2 µm).

Parameter	Value	Unit	Context
Substrate Material	Diamond	N/A	Essential for high $v_p$ and thermal management
Target Wavelength ($\lambda$)	2.0	µm	SAW Device Design Parameter
ZnO Film Thickness (h1)	0.8 (0.4 $\lambda$)	µm	Piezoelectric Layer
SiO₂ Film Thickness (h2)	0.4 (0.2 $\lambda$)	µm	Temperature Compensation Layer
Al Electrode Thickness (h3)	0.16 (0.08 $\lambda$)	µm	Interdigital Transducer (IDT)
Metallization Rate (MR)	50	%	IDT Design
Sezawa Mode Characteristic Frequency ($f_0$)	2446	MHz	High-Frequency Operation
Sezawa Mode Acoustic Velocity ($v_p$)	4892	m/s	1.7 times that of Rayleigh mode
Sezawa Mode Coupling Coefficient ($k^2$)	4.9	%	High Electromechanical Coupling
Temperature Coefficient of Frequency (TCF)	Close to 0	ppm/°C	Crucial for frequency stability
Optimal IDT Pairs ($N_t$)	130	Pairs	Optimized for high Q factor
Optimal Aperture Width (W)	40 $\lambda$ (80 µm)	µm	Optimized for high Q factor

Key Methodologies

The research utilized advanced simulation techniques to model and optimize the multilayer SAW structure.

Modeling Software: 3D Finite Element Method (FEM) modeling was performed using COMSOL 6.1 software.
Structure Definition: The model consisted of an IDT (Al)/ZnO/SiO₂/Diamond stack. The diamond substrate depth was fixed at 4 $\lambda$, with a Perfectly Matched Layer (PML) of 1 $\lambda$ at the bottom to prevent boundary reflection.
Material Parameters: Comprehensive material parameters (Elastic constants, relative dielectric constants, mass density, and their respective Temperature Coefficients) for Al, ZnO, SiO₂, and Diamond were used, sourced from the COMSOL database.
Geometric Optimization: The study systematically varied the normalized thicknesses of the ZnO piezoelectric film (h1/$\lambda$) and the SiO₂$ layer (h2/$\lambda$) to determine the optimal ratios that maximize $k^2$ and $v_p$ while achieving zero TCF.
Electrode Loading Analysis: The impact of the metallic IDT thickness (h3/$\lambda$) was investigated to balance mass loading effects against coupling efficiency.
Resonator Performance Analysis: The final design was analyzed by simulating the admittance (Y11 parameter) of a single-port resonator, varying the number of IDT pairs ($N_t$) and the acoustic aperture width (W) to optimize the Quality Factor (Q).

6CCVD Solutions & Capabilities

This research confirms that diamond is the enabling substrate for next-generation, high-frequency, temperature-stable SAW devices. 6CCVD is uniquely positioned to supply the high-quality MPCVD diamond materials and customization services required to transition this simulation into a manufacturable product.

Applicable Materials

To replicate and extend this research, the following 6CCVD materials are recommended:

Optical Grade Polycrystalline Diamond (PCD): Recommended for large-area, cost-effective manufacturing feasibility studies. PCD offers high acoustic velocity and excellent thermal conductivity (up to 2000 W/mK), crucial for high-power SAW devices.
High-Purity Single Crystal Diamond (SCD): Recommended for ultimate performance where maximum sound speed and lowest surface roughness are required. SCD offers superior crystalline consistency for optimal thin-film deposition.
Substrate Thickness: 6CCVD can provide diamond substrates up to 10mm thick, ensuring mechanical stability and infinite acoustic impedance modeling for the 4 $\lambda$ depth used in the simulation.

Customization Potential

The success of this multilayer structure relies on precise material integration and geometry. 6CCVD offers critical customization capabilities:

| Research Requirement | 6CCVD Customization Service | Specification Match | | :--- | :--- | :--- | | Large-Scale Production | Custom Dimensions & Wafer Size | Plates/wafers up to 125mm (PCD), supporting commercial scaling. | | Surface Quality for Thin Films | Ultra-Precision Polishing | Achievable roughness: Ra < 1nm (SCD) or Ra < 5nm (Inch-size PCD), ensuring optimal ZnO/SiO₂ layer growth. | | IDT Material Exploration | Custom Metalization Services | While Al was used, 6CCVD offers in-house deposition of Ti, Pt, Au, Pd, W, and Cu. Researchers can explore multi-layer metal stacks (e.g., Ti/Pt/Au) for improved adhesion, lower resistance, or enhanced power handling. | | Precise Layer Thickness | SCD/PCD Thickness Control | SCD and PCD layers available from 0.1µm to 500µm (for thin-film diamond) or up to 10mm (for bulk substrates). |

Engineering Support

The optimization process detailed in the paper (balancing h1/$\lambda$, h2/$\lambda$, and h3/$\lambda$) requires deep material knowledge. 6CCVD’s in-house PhD team can assist with material selection for similar High-Frequency SAW Filter and Sensor projects, ensuring the chosen diamond substrate properties (e.g., orientation, thermal grade) align perfectly with the simulation parameters.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We offer global shipping (DDU default, DDP available) to support your research worldwide.

View Original Abstract

With the development of communications technology, surface acoustic wave (SAW) and bulk acoustic wave (BAW) devices have become hotspots of the competitive research in the frequency band above GHz. It imposes higher requirements on the operating frequency, temperature coefficient of frequency (TCF), and electromechanical coupling coefficient (k2) of SAW devices. In this work, we reported on a novel ZnO/SiO2/diamond-layered resonator structure and systematically investigated its propagation characteristics by using finite element methods. A comparative study and analysis of k2 and acoustic velocity (vp) for both the excited Rayleigh mode and the Sezawa mode were conducted. By selecting the appropriate ZnO piezoelectric film, SiO2, and electrode thickness, the Sezawa mode was chosen as the main mode, effectively improving both k2 and vp. It was observed that the k2 of the Sezawa mode is 7.5 times that of the excited Rayleigh mode and nearly 5 times that of piezoelectric single-crystal ZnO; vp is 1.7 times that of the excited Rayleigh mode and nearly 1.5 times that of piezoelectric single-crystal ZnO. Furthermore, the proposed multilayer structure achieves a TCF close to 0 while maintaining a substantial k2. In practical applications, increasing the thickness of SiO2 can compensate for the device’s TCF reduction caused by the interdigital transducer (IDT). Finally, this study explored the impact of increasing the aperture width and IDT pairs on the performance of the single-port resonator, revealing the changing patterns of quality factor (Q) values. The results reported here show that the structure has great promise for the fabrication of high-frequency and low-TCF SAW devices.

Tech Support

Original Source

DOI: https://doi.org/10.3390/app14020874

References

2015 - A Snapshot in Time: The Future in Filters for Cell Phones [Crossref]
2020 - Epitaxial Aluminum Scandium Nitride Super High Frequency Acoustic Resonators [Crossref]
2020 - Ultra-Large-Coupling and Spurious-Free SH 0 Plate Acoustic Wave Resonators Based on Thin LiNbO3 [Crossref]
2023 - Investigation on the Temperature Coefficient of Frequency Performance of LiNbO3 on Quartz and Glass Surface Acoustic Wave Resonators [Crossref]
2018 - Improved Resistance to Electromigration and Acoustomigration of Al Interdigital Transducers by Ni Underlayer [Crossref]
2018 - Three-Dimensional Finite Element Simulation of Love Mode Surface Acoustic Wave in Layered Structures Including ZnO Piezoelectric Film and Diamond Substrate [Crossref]
2000 - Modelling of SAW Filter Based on ZnO/Diamond/Si Layered Structure Including Velocity Dispersion [Crossref]
2021 - Wideband and Low-Loss Surface Acoustic Wave Filter Based on 15° YX-LiNbO₃/SiO₂/Si Structure [Crossref]