Investigation of Surface Acoustic Wave Propagation Characteristics in New Multilayer Structure - SiO2/IDT/LiNbO3/Diamond/Si

At a Glance

Metadata	Details
Publication Date	2021-10-21
Journal	Micromachines
Authors	Hanqiang Zhang, Hongliang Wang
Institutions	North University of China
Citations	28
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Performance SAW Filters using CVD Diamond Substrates

This document analyzes the research paper “Investigation of Surface Acoustic Wave Propagation Characteristics in New Multilayer Structure: SiO₂/IDT/LiNbO₃/Diamond/Si” to provide technical specifications and highlight how 6CCVD’s advanced CVD diamond materials and processing capabilities are essential for replicating and advancing this high-frequency Surface Acoustic Wave (SAW) technology.

Executive Summary

The research successfully models a novel multilayer structure utilizing diamond as a high-velocity substrate for next-generation SAW filters, achieving superior performance metrics critical for 5G and beyond.

High Phase Velocity: The diamond layer enabled a high phase velocity (Vp) up to 10 km/s (Sezawa mode), significantly increasing the potential operating frequency (f₀ > 1 GHz, with potential for >10 GHz).
Zero TCF Achieved: The inclusion of the SiO₂ temperature compensation layer resulted in an optimal Temperature Coefficient of Frequency (TCF) of 0 ppm/°C, solving the poor temperature stability issues common in LiNbO₃-based devices.
Enhanced Coupling: A high electromechanical coupling coefficient (k²) of up to 6.47% was achieved, crucial for wideband applications.
Material Advantage: Diamond’s high elastic modulus (1200 GPa) and excellent thermal conductivity allow the device to handle super-high power at high frequencies, surpassing traditional SAW materials.
Process Simplification: The high phase velocity provided by the diamond substrate allows for a larger interdigital transducer (IDT) finger width (λ = 6 µm used), reducing photolithography difficulty and ohmic loss compared to traditional high-frequency designs.

Technical Specifications

The following parameters were extracted from the finite element method (FEM) simulation results for the optimized SiO₂/IDT/LiNbO₃/Diamond/Si structure.

Parameter	Value	Unit	Context
Maximum Phase Velocity (Vp)	10	km/s	Sezawa mode, h₁/a = 0.1
Maximum Coupling Coefficient (k²)	6.47	%	Sezawa mode, h₁/a = 0.4, h₅/a = 0.2
Optimal TCF	0	ppm/°C	Zero temperature coefficient achieved
Center Frequency (f₀)	1023	MHz	Simulated operating frequency
Potential Frequency (f₀)	>10	GHz	Predicted for λ = 1 µm (Sezawa mode)
SAW Wavelength (λ)	6	µm	Designed parameter for simulation
Diamond Elastic Modulus (E)	1200	GPa	Key material property for high Vp
Diamond Density (ρ)	3515	Kg/m³	Material constant used in simulation
LiNbO₃ TCF (Bulk Crystal)	-75	ppm/°C	Improved significantly by multilayer structure

Key Methodologies

The investigation relied on advanced simulation techniques to optimize the layered structure for high-performance SAW devices.

Finite Element Method (FEM) Simulation: COMSOL Multiphysics 5.6 was utilized to model the piezoelectric coupling between the structural domain (stress, strain) and the electrical domain (electric field, displacement).
Multilayer Structure Defined: The model analyzed a SiO₂/IDT/128°YX-LiNbO₃/Diamond/Si stack, focusing on the interaction between the high-velocity diamond substrate and the piezoelectric LiNbO₃ film.
Geometric Parameter Optimization: A 2D unit model was established with a fixed SAW wavelength (λ = 6 µm) and metallization rate (MR = 0.5).
Thickness Ratio Variation: The normalized film thickness ratios (h₁/a for LiNbO₃, h₄/a for IDT metal, and h₅/a for SiO₂) were systematically varied to determine optimal Vp, k², and TCF.
Transient Analysis: Time-domain simulation (50 ns run time) was performed to analyze the propagation state of the acoustic signal and validate the confinement of acoustic energy near the surface, which improves the Q-factor.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-quality CVD diamond materials required to transition this theoretical design into manufacturable, high-performance SAW filters. Our capabilities meet and exceed the stringent material requirements for high-frequency acoustic devices.

Applicable Materials

The core of this high-performance structure is the diamond layer, which requires exceptional purity, stiffness, and thermal properties. 6CCVD recommends the following materials:

Optical Grade Polycrystalline Diamond (PCD): Ideal for large-area, cost-effective substrates. Our PCD wafers offer high stiffness and thermal conductivity, crucial for high-power SAW applications. Available in custom dimensions up to 125mm.
High-Quality Single Crystal Diamond (SCD): For ultimate performance, especially in high-frequency applications where minimal scattering is required. SCD offers superior crystalline quality and uniformity, ensuring optimal acoustic wave propagation.
Custom Substrate Thickness: 6CCVD can supply diamond films (SCD/PCD) in the required thickness range (0.1 µm to 500 µm) or as robust substrates up to 10 mm thick, suitable for integration with the LiNbO₃/Si stack.

Customization Potential

The fabrication of the SiO₂/IDT/LiNbO₃/Diamond/Si structure requires precise material deposition and patterning, all of which 6CCVD supports.

Requirement from Paper	6CCVD Customization Capability	Value Proposition
Diamond Substrate	Custom dimensions up to 125mm (PCD) and precise thickness control (0.1 µm - 500 µm).	Enables scaling from R&D prototypes to commercial wafer sizes.
IDT Metalization	Custom metal deposition services (Au, Pt, Pd, Ti, W, Cu).	While the paper used Al, 6CCVD can deposit high-conductivity metals like Au or Pt for IDTs, minimizing ohmic loss and improving Q-factor.
Surface Finish	Ultra-low roughness polishing: Ra < 1 nm (SCD) and Ra < 5 nm (PCD).	Essential for minimizing acoustic scattering losses and ensuring optimal coupling at GHz frequencies.
Integration Support	Custom laser cutting and shaping services.	Allows for precise device geometry and integration into complex packaging.

Engineering Support

The optimization of the multilayer structure (specifically the thickness ratios h₁/a and h₅/a) is critical to achieving the zero TCF and maximum k².

6CCVD’s in-house PhD team specializes in CVD diamond material science and acoustic applications. We offer consultation services to assist engineers and scientists in:

Material Selection: Determining the optimal diamond grade (SCD vs. PCD) and thickness for specific frequency and power handling requirements.
Interface Engineering: Advising on surface preparation and polishing techniques necessary for high-quality deposition of the piezoelectric (LiNbO₃) and compensation (SiO₂) layers.
Design Extension: Assisting with material specifications for similar high-frequency, wideband SAW filter projects, particularly those targeting the >10 GHz range predicted by the Sezawa mode analysis.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Surface acoustic wave (SAW) devices are widely used in many fields such as mobile communication, phased array radar, and wireless passive sensor systems. With the upgrade of mobile networks, the requirements for the performance of SAW devices have also increased, and high-frequency wideband SAW devices have become an important research topic in communication systems and other application fields. In this paper, a theoretical study for the realization of a layered SAW filter based on a new SiO2/IDT/128°YX-LiNbO3/diamond/silicon layered structure using the modeling software COMSOL Multiphysics is presented. The effects of lithium niobate (LiNbO3), an interdigital transducer (IDT), and SiO2 thin films on the evolution of the phase velocity, electromechanical coupling coefficient (k2), and temperature coefficient of frequency were studied by employing a finite element method simulation. Furthermore, a longitudinal coupling resonator filter was designed. To investigate the SAW characteristics of the filter, a transient analysis was conducted to calculate the electrical potential and particle displacement under the resonance condition and to analyze the frequency response. The study concluded that this new multilayer structure can be applied to design and manufacture a variety of high-frequency and wideband SAW filters with a temperature compensation function, for operation above the GHz range.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi12111286

References

2020 - High-frequency surface acoustic wave resonator with ScAlN/hetero-epitaxial diamond [Crossref]
2021 - High-performance surface acoustic wave devices using composite substrate structures [Crossref]
2000 - Modelling of SAW filter based on ZnO/diamond/Si layered structure including velocity dispersion [Crossref]
2015 - FEM simulation of Rayleigh waves for SAW devices based on ZnO/AlN/Si [Crossref]
2017 - Enhanced performance of 17.7 GHz SAW devices based on AlN/diamond/Si layered structure with embedded nanotransducer [Crossref]
2020 - FEM analysis of piezoelectric film as IDT on the diamond substrate to enhance the quality factor of SAW devices [Crossref]
2013 - Characteristics of surface acoustic waves excited by (1120) zno films deposited on R-sapphire substrates [Crossref]
2020 - Analysis of propagation characteristics of AlN/diamond/Si layered SAW resonator [Crossref]
2007 - Theoretical investigation of surface acoustic wave in the new, three-layered structure: ZnO/AlN/diamond [Crossref]