Design and Analysis of Interdigital Electrode Parallel Layout of Multilayer SAW Devices

At a Glance

Metadata	Details
Publication Date	2024-01-01
Journal	IEEE Access
Authors	X.Y. Meng, Zhipeng Li
Institutions	Northeast Forestry University, Changzhou Institute of Technology
Citations	3
Analysis	Full AI Review Included

Technical Documentation & Analysis: Multilayer SAW Devices Utilizing MPCVD Diamond

Executive Summary

This research successfully demonstrates the design and analysis of high-performance, miniaturized Surface Acoustic Wave (SAW) devices utilizing a LiNbO₃/Diamond/Si multilayer structure. The findings validate the critical role of high-quality diamond films in achieving superior acoustic performance, directly aligning with 6CCVD’s core capabilities in advanced MPCVD diamond materials.

Core Achievement: Successful excitation of SAW in a LiNbO₃/Diamond/Si multilayer stack, achieving characteristic frequencies up to 1.042 GHz.
Diamond’s Role: MPCVD Diamond serves as the crucial growth layer, providing high sound velocity, structural stability, and high-temperature resistance necessary for optimal SAW propagation.
Miniaturization: The study introduces parallel Interdigital Transducer (IDT) layouts (Stagger and Cross-layer) that effectively reduce the lateral size of the SAW device.
Performance Metrics: Optimization of IDT thickness (h_IDT/λ = 0.1) resulted in exceptionally high electromechanical coupling coefficients (K²) exceeding 20% for the flat layer structure.
Process Stability: The Cross-layer IDT structure exhibited superior stability against micro-level deviations in electrode spacing (S₂), simplifying manufacturing control compared to traditional layouts.
Material Requirement: Replicating this high-frequency, high-performance device requires ultra-precise, high-purity MPCVD diamond films with controlled thickness in the micron range (2 µm used in this study).

Technical Specifications

The following parameters were extracted from the finite element analysis (FEA) modeling and results sections of the paper:

Parameter	Value	Unit	Context
Wavelength (λ)	4	µm	Global defined parameter
Diamond Thickness (h_DIA)	2	µm	Critical growth layer thickness
LiNbO₃ Thickness (h_LN)	2	µm	Piezoelectric film thickness
Silicon Substrate Thickness (h_Si)	12	µm	Base substrate thickness
IDT Electrode Height (h_IDT)	0.2	µm	Molybdenum (Mo) electrode thickness
IDT Electrode Width (d)	1	µm	Interdigital electrode width
Electrode Spacing 1 (S₁)	0.5	µm	Distance between electrodes
Characteristic Frequency (Flat Layer)	1.042	GHz	Initial structural parameters (f_F)
Characteristic Frequency (Stagger Layer)	1.012	GHz	Initial structural parameters (f_S)
Characteristic Frequency (Cross Layer)	1.027	GHz	Initial structural parameters (f_C)
Maximum K² (Flat Layer)	> 20	%	Achieved at h_IDT/λ = 0.1
Maximum K² (Stagger Layer)	9.35	%	Achieved at h_DIA/λ = 0.1, h_LN/λ = 0.3

Key Methodologies

The experiment utilized Finite Element Analysis (FEA) via COMSOL Multiphysics to model and analyze the performance of the multilayer SAW structure under varying geometric and layout conditions.

Multilayer Stack Definition: The core structure was defined as LiNbO₃ (Piezoelectric Film) / Diamond (Growth Layer) / Si (Substrate).
Material Selection Rationale: Diamond was chosen for its high sound velocity and structural stability, while LiNbO₃ was selected for its high electromechanical coupling coefficient.
IDT Layout Variation: Three Molybdenum (Mo) Interdigital Transducer (IDT) electrode layouts were modeled:
- Flat Layer Layout (Traditional)
- Stagger Layer Layout (Parallel)
- Cross Layer Layout (Parallel)
Boundary Conditions:
- A Perfectly Matched Layer (PML) was placed at the bottom of the Si substrate to absorb wave reflection.
- Electrical excitation was applied to the electrodes (1V and 0V).
- Periodic boundary conditions were applied to the side walls (Γ_L1, Γ_R1, etc.).
Optimization Parameters: The simulation parametrically scanned the influence of:
- Wavelength (λ) reduction (4 µm down to 3 µm).
- Normalized LiNbO₃ thickness (h_LN/λ).
- Normalized Diamond thickness (h_DIA/λ).
- Normalized IDT electrode thickness (h_IDT/λ).
- Electrode spacing deviation (S₂).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-specification MPCVD diamond materials and custom processing required to manufacture or advance the multilayer SAW devices described in this research.

Applicable Materials

The performance of this high-frequency SAW device is fundamentally dependent on the quality and acoustic properties of the diamond layer.

Research Requirement	6CCVD Material Solution	Technical Justification
High Sound Velocity & Stability	Electronic Grade SCD (Single Crystal Diamond)	SCD offers the highest purity and lowest defect density, ensuring minimal acoustic loss and maximum structural stability for optimal SAW propagation.
Precise Micron Thickness	SCD or PCD Films (0.1 µm - 500 µm)	The paper requires a 2 µm diamond film. 6CCVD provides unparalleled thickness control (± 1 µm or better) across this range, critical for maintaining the precise h_DIA/λ ratio.
Large Area Substrates	Optical/Electronic Grade PCD	For scaling up to commercial production, 6CCVD offers PCD plates/wafers up to 125mm in diameter, enabling large-area device fabrication on Si substrates.

Customization Potential

The successful implementation of the IDT structures (especially the miniaturized parallel layouts) requires highly precise material preparation and micro-patterning capabilities, which 6CCVD provides in-house.

Thickness Control: 6CCVD guarantees SCD and PCD film thicknesses from 0.1 µm up to 500 µm, allowing researchers to precisely tune the normalized thickness ratios (h_LN/λ and h_DIA/λ) identified as critical for optimizing K² and frequency.
Custom Metalization: The paper utilized Molybdenum (Mo) electrodes. 6CCVD offers internal metalization services including Au, Pt, Pd, Ti, W, and Cu. We can assist researchers in selecting alternative metal stacks (e.g., Ti/Pt/Au) that may offer superior adhesion or lower resistivity for high-frequency IDTs, and apply these layers with high precision.
Surface Finish: The interface quality between the LiNbO₃ film and the diamond layer is crucial. 6CCVD provides ultra-smooth polishing services, achieving surface roughness of Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, ensuring minimal scattering loss at the acoustic interface.
Substrate Integration: 6CCVD can supply the required diamond films grown directly on or bonded to custom Si substrates (up to 10mm thick) to facilitate the multilayer stack fabrication process.

Engineering Support

6CCVD’s in-house PhD engineering team specializes in the material science of acoustic and electronic diamond applications. We can assist researchers and engineers working on similar High-Frequency SAW Device projects by:

Material Optimization: Consulting on the optimal diamond grade (SCD vs. PCD) based on required operating frequency, power handling, and substrate size.
Acoustic Modeling Input: Providing precise material parameters (density, sound velocity, elastic constants) for FEA simulations like those performed in COMSOL.
Interface Engineering: Advising on surface preparation and metalization schemes to ensure robust adhesion and optimal electromechanical coupling for complex IDT layouts.

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

View Original Abstract

To obtain high-frequency SAW devices, the interdigital transducer electrodes are prepared narrower and the electrode spacing is smaller, which leads to higher cost and lower reliability of high-frequency SAW devices. In this paper, two other interdigital electrode parallel layout structures are designed based on the traditional IDT flat layer layout structure, and the influence of the three different IDT electrode layout structures on the SAW device of LiNbO3/Diamond/Si multilayer structure is studied by COMSOL Multiphysics. The results show that the designed multi-layer structure SAW device can successfully excite SAW with superior performance, and the parallel layout structure of the interdigital electrode can reduce the lateral size of SAW device, which provides a new idea and direction for the miniaturization of the SAW devices.

Tech Support

Original Source

DOI: https://doi.org/10.1109/access.2024.3380370

References

2020 - Research on the optimal design and application of wideband TIDT structure