High-Frequency Surface Acoustic Wave Resonator with Diamond/AlN/IDT/AlN/Diamond Multilayer Structure

At a Glance

Metadata	Details
Publication Date	2022-08-28
Journal	Sensors
Authors	Lei Liang, Bo Dong, Yuxuan Hu, Yisong Lei, Zhizhong Wang
Institutions	Shenzhen Technology University
Citations	15
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Frequency Diamond SAW Resonators

This document analyzes the research paper “High-Frequency Surface Acoustic Wave Resonator with Diamond/AlN/IDT/AlN/Diamond Multilayer Structure” to provide technical specifications and align the findings with 6CCVD’s advanced Material Processing Chemical Vapor Deposition (MPCVD) diamond capabilities.

Executive Summary

The research successfully demonstrates a novel, high-performance Surface Acoustic Wave (SAW) resonator utilizing a sandwiched Interdigital Transducer (IDT) structure integrated within diamond and Aluminum Nitride (AlN) layers. This design leverages the superior acoustic properties of diamond to achieve exceptional performance metrics, directly addressing the industry demand for high-frequency, high-stability SAW devices.

Novel Structure: Diamond/AlN/IDT/AlN/Diamond multilayer structure on a Si substrate, utilizing a sandwiched IDT configuration.
High Frequency: Achieved an operational frequency up to 6.15 GHz in the M2 (Love Wave) mode, suitable for Ultra-High Frequency (UHF) applications.
Exceptional Phase Velocity: The incorporation of diamond films resulted in a significantly high phase velocity (v_p) of 12,470 m/s.
High Coupling Coefficient: Optimized geometric parameters yielded a strong electromechanical coupling coefficient (K²) of 5.53%.
Thermal Stability: Demonstrated excellent temperature stability with a low Temperature Coefficient of Frequency (TCF) of -6.3 ppm/°C.
Material Requirement: The performance relies critically on high-quality, thin-film diamond layers, a core specialty of 6CCVD’s MPCVD production.

Technical Specifications

The following table summarizes the key performance metrics and optimized geometric parameters extracted from the simulation results (M2 mode optimization).

Parameter	Value	Unit	Context
Operation Frequency (f_r)	6.15	GHz	Optimized M2 Mode Resonance
Phase Velocity (v_p)	12,470	m/s	Optimized M2 Mode
Electromechanical Coupling (K²)	5.53	%	Measure of acoustoelectric conversion efficiency
TCF	-6.3	ppm/°C	Temperature stability at 25 °C
Acoustic Wavelength (λ)	2.0	µm	Defined IDT Periodicity (2 µm)
Optimized AlN Thickness (h_AlN)	0.9λ (1.8)	µm	Critical ratio for high K² and low dispersion
Optimized Al Electrode Thickness (h_Al)	0.075λ (0.15)	µm	Optimized for high K²
Diamond Layer Thickness (h_dia)	0.5λ (1.0)	µm	Initial simulation parameter
Substrate Material	Si	N/A	Base material for layered structure
IDT Metal	Aluminum (Al)	N/A	Simulated electrode material

Key Methodologies

The research utilized Finite Element Method (FEM) simulation to model and optimize the multilayer SAW resonator structure. The critical steps focused on defining precise geometric ratios and applying appropriate boundary conditions to accurately predict high-frequency performance.

Modeling Software: Structural mechanics module of COMSOL Multiphysics software was used for simulation and solving the sandwich structure SAW resonator.
Unit Cell Definition: A periodic unit structure model was adopted to simulate the propagation characteristics, reducing computation time while maintaining accuracy.
Geometric Parameters: The acoustic wavelength (λ) was set to 2 µm. The cross-finger width (a) and cross-finger gap (b) were both set to 0.25λ.
Material Parameters: Material constants for AlN, Diamond, Al, and Si (including elastic constants, piezoelectric constants, relative dielectric constants, and density) were sourced and implemented (Table 3).
Loss Modeling: Mechanical (ŋ_CE) and dielectric (ŋ_εS) losses were included for the AlN piezoelectric layer, set at 0.010.
Boundary Conditions: Periodic boundary conditions were applied to the lateral faces. The lower boundary (Si/PML interface) was set as a fixed constraint. One electrode was set to 1 V, and the other was grounded.
Optimization Strategy: The ratios h_AlN/λ and h_Al/λ were systematically varied to identify the optimal geometry that maximized K² and v_p while minimizing dispersion in the high-frequency M2 mode.

6CCVD Solutions & Capabilities

The successful replication and advancement of this high-frequency diamond SAW resonator design depend entirely on the availability of high-quality, precisely controlled diamond thin films and advanced fabrication support. 6CCVD is uniquely positioned to supply the necessary materials and engineering services.

Applicable Materials

The high phase velocity (v_p) achieved in this research is directly attributable to the use of diamond. 6CCVD offers the necessary high-purity MPCVD diamond materials:

Optical Grade Single Crystal Diamond (SCD): Recommended for the highest acoustic performance and lowest internal loss, ensuring maximum v_p and quality factor (Q).
Acoustic Grade Polycrystalline Diamond (PCD): Suitable for large-area devices (up to 125 mm diameter) where high thermal conductivity and high v_p are required, offering a cost-effective path to scaling.

Customization Potential

The optimization process in the paper relies on achieving specific, thin-film thicknesses (e.g., 1.0 µm diamond, 1.8 µm AlN). 6CCVD’s capabilities directly address these critical requirements:

Research Requirement	6CCVD Capability	Engineering Advantage
Precise Film Thickness (0.1 µm to 1.8 µm range)	SCD/PCD Thickness Control: 0.1 µm to 500 µm.	We guarantee precise thickness control necessary to hit the optimal h_dia/λ and h_AlN/λ ratios for high K² and low TCF.
Large-Area Scaling	Custom Dimensions: Plates/wafers up to 125 mm (PCD).	Enables the transition from simulated unit cells to manufacturable, inch-size wafers for industrial SAW production.
IDT Metalization (Al used in simulation)	In-House Metalization: Au, Pt, Pd, Ti, W, Cu.	While Al was simulated, 6CCVD provides custom deposition of high-adhesion, low-resistance metal stacks (e.g., Ti/Pt/Au) to optimize IDT performance and reliability.
Surface Quality (Minimizing scattering loss)	Advanced Polishing: Ra < 1 nm (SCD) and Ra < 5 nm (Inch-size PCD).	Ultra-smooth surfaces are critical for minimizing acoustic scattering losses at GHz frequencies, enhancing device Q-factor.

Engineering Support

6CCVD’s in-house PhD team specializes in the material science of MPCVD diamond for advanced electronic and acoustic applications. We offer comprehensive support for projects targeting high-frequency SAW devices, including:

Material Selection: Guidance on choosing between SCD and PCD based on required acoustic loss, thermal management, and wafer size.
Integration Consultation: Assistance in defining optimal diamond film specifications (thickness, doping, surface orientation) for integration with piezoelectric layers like AlN.
Custom Fabrication: Providing laser cutting and precise dimensional control for complex resonator and filter geometries.

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

View Original Abstract

A high-frequency surface acoustic wave (SAW) resonator, based on sandwiched interdigital transducer (IDT), is presented. The resonator has the structure of diamond/AlN/IDT/AlN/diamond, with Si as the substrate. The results show that its phase velocity and electromechanical coupling coefficient are both significantly improved, compared with that of the traditional interdigital transduce-free surface structure. The M2 mode of the sandwiched structure can excite an operation frequency up to 6.15 GHz, with an electromechanical coupling coefficient of 5.53%, phase velocity of 12,470 m/s, and temperature coefficient of frequency of −6.3 ppm/°C. This structure provides a new ideal for the design of high-performance and high-frequency SAW devices.

Tech Support

Original Source

DOI: https://doi.org/10.3390/s22176479

References

2013 - Surface acoustic wave microfluidics [Crossref]
1991 - Advanced channelization for RF, microwave, and millimeterwave applications [Crossref]
1973 - Propagation of acoustic surface waves in multilayers: A matrix description [Crossref]
2013 - Simulation on effects of electrical loading due to interdigital transducers in surface acoustic wave resonator [Crossref]
2017 - Enhanced performance of 17.7 GHz SAW devices based on AlN/diamond/Si layered structure with embedded nanotransducer [Crossref]
2021 - Structure with thin SiOx/SiNx bilayer and Al electrodes for high-frequency, large-coupling, and low-cost surface acoustic wave devices [Crossref]
2019 - High-velocity non-attenuated acoustic waves in LiTaO3/quartz layered substrates for high frequency resonators [Crossref]
2019 - Ultra high frequency acoustic wave propagation in fully polymer based surface acoustic wave device [Crossref]
2020 - 3D layout of interdigital transducers for high frequency surface acoustic wave devices [Crossref]
2019 - High-frequency V-doped ZnO/SiC surface acoustic wave devices with enhanced electromechanical coupling coefficient [Crossref]