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

Executive Summary

This study presents the design and analysis of novel interdigital transducer (IDT) parallel layouts for high-performance, miniaturized Surface Acoustic Wave (SAW) devices utilizing a LiNbO₃/Diamond/Si multilayer structure.

Core Value Proposition: Achieved high characteristic frequency and electromechanical coupling (K²) while stabilizing performance against fabrication variations, enabling cost-effective miniaturization.
Multilayer Structure: Utilizes LiNbO₃ (piezoelectric), Diamond (high sound velocity/stability), and Si (IC compatibility) to optimize SAW propagation characteristics.
Novel Layouts: Two parallel IDT structures—Stagger Layer and Cross Layer—were designed and compared against the traditional Flat Layer layout using Finite Element Analysis (FEA).
High Performance: The Flat Layer layout achieved an electromechanical coupling coefficient (K²) exceeding 20% at an optimal normalized IDT thickness (h_IDT/λ = 0.1), significantly higher than standard LiNbO₃ single crystal (5.5%).
Fabrication Stability: The Cross-layer layout demonstrated the highest stability; its characteristic frequency (f_c) and coupling coefficient (K_c²) were minimally affected by deviations in positive/negative electrode spacing (S₂).
Miniaturization Path: The stability of the Cross-layer structure allows for reduced electrode spacing and overall lateral device size, offering a new direction for miniaturized, high-reliability SAW devices.

Technical Specifications

Parameter	Value	Unit	Context
Multilayer Stack	LiNbO₃/Diamond/Si	N/A	Structure used for simulation
Electrode Material	Molybdenum (Mo)	N/A	IDT material
Wavelength (λ)	4	µm	Initial simulation parameter
LiNbO₃ Thickness (h_LN)	2	µm	Initial simulation parameter
Diamond Thickness (h_DIA)	2	µm	Initial simulation parameter
Silicon Thickness (h_Si)	12	µm	Substrate layer
IDT Height (h_IDT)	0.2	µm	Initial simulation parameter
IDT Width (d)	1	µm	Initial simulation parameter
Max K² (Flat Layer)	> 20	%	Achieved at normalized thickness h_IDT/λ = 0.1
Max K² (Stagger Layer)	9.35	%	Achieved at h_DIA/λ = 0.1 and h_LN/λ = 0.3
Standard LiNbO₃ K²	5.5	%	Reference value for single crystal
Characteristic Frequency (Flat)	1.042	GHz	First-order mode, initial parameters
Characteristic Frequency (Cross)	1.027	GHz	First-order mode, initial parameters
Frequency Increase (λ reduction)	~0.35	GHz	When λ is reduced from 4 µm to 3 µm
LiNbO₃ Euler Angle	(0, 0, 90)	°	Piezoelectric material orientation

Key Methodologies

Modeling Platform: Finite Element Analysis (FEA) was performed using COMSOL Multiphysics to simulate the propagation characteristics of the SAW devices.
Multilayer Stack Definition: The device was modeled as a LiNbO₃ film layer, a Diamond film layer, and a Silicon (Si) substrate layer. Molybdenum (Mo) was used for the Interdigital Transducers (IDTs).
IDT Layout Variations: Three distinct IDT electrode arrangements were analyzed:
- Flat Layer: Traditional layout, all electrodes on the top surface of the LiNbO₃ film.
- Stagger Layer: Positive and negative electrodes arranged on the top and bottom surfaces of the LiNbO₃ film, respectively.
- Cross Layer: Positive electrodes on the upper surface of the LiNbO₃ film and negative electrodes on the lower surface of the Diamond film layer.
Boundary Conditions: A Perfectly Matched Layer (PML) was placed at the bottom of the Si substrate to absorb wave reflections. Periodical boundary conditions were applied laterally. Electrical excitation was set with 1V on one set of electrodes and 0V (ground) on the opposing set.
Parametric Analysis: The simulation systematically investigated the influence of key normalized parameters on characteristic frequency (f_o) and electromechanical coupling coefficient (K²):
- Normalized LiNbO₃ film thickness (h_LN/λ).
- Normalized Diamond film thickness (h_DIA/λ).
- Normalized IDT electrode thickness (h_IDT/λ).
- Deviation in electrode spacing (S₂) between positive and negative IDTs.

Commercial Applications

The development of stable, high-performance, miniaturized SAW devices using multilayer structures is critical for several high-growth engineering sectors:

5G/6G Wireless Communications: SAW devices are essential components for high-frequency filters and resonators. The high phase velocity provided by the Diamond layer supports higher operating frequencies (GHz range).
Integrated RF Systems: The use of Si substrates ensures compatibility with standard CMOS manufacturing processes, facilitating the integration of high-performance SAW filters directly onto integrated circuits (ICs).
High-Reliability Sensors: The stability of the Cross-layer layout against fabrication tolerances (S₂ deviation) makes this technology ideal for robust sensors (e.g., torque, pressure, temperature) used in harsh environments, such as industrial monitoring and automotive systems.
Miniaturized Electronics: The ability to reduce the lateral size of the device by utilizing parallel IDT layouts addresses the increasing demand for smaller, lighter electronic components in portable and embedded systems.
Automotive and Autonomous Driving: Application in intelligent sensors required for vehicle control and navigation systems, leveraging the robustness and high-frequency capability of the LiNbO₃/Diamond structure.

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