Composite SAW Substrates With Shear Waves for Stable RFID Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing surface acoustic wave (SAW) tag devices using bulk Lithium Niobate substrates are limited by an electromechanical coupling coefficient of 6% and high temperature drift, which restricts their application to temperature measurement and limits interrogation distance.
Innovation Solution
A composite substrate is used for SAW tag devices, comprising a base substrate and a piezoelectric layer with a specific crystallographic orientation that enables the propagation of shear waves, enhancing temperature stability and electromechanical coupling coefficient up to 20%, thus extending application to mechanical parameter measurement and increasing interrogation distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If Rayleigh waves are used in bulk Lithium Niobate substrates, then the device can operate at 2.45 GHz frequency band, but the electromechanical coupling coefficient is limited to 6% which restricts interrogation distance
Solution Approach 1:
The patent employs a composite substrate structure consisting of a piezoelectric layer (Lithium Niobate or Lithium Tantalate) deposited on a base substrate (Silicon, Sapphire, or Diamond). This composite configuration enables shear wave propagation which achieves electromechanical coupling coefficients of 20% or more, representing a 3-4 fold improvement over conventional bulk substrates and thereby extending the interrogation distance significantly.
2Adaptability or versatility
If bulk Lithium Niobate substrates are used, then the device structure is simple, but the temperature drift is strong with TCD of about 70 ppm/K which limits sensor application versatility
Solution Approach 1:
The composite substrate combines a piezoelectric layer with a base substrate having different thermal properties. This structure enables the use of shear waves which exhibit superior temperature stability with TCD values of 30 ppm/K or less, compared to 70 ppm/K for bulk substrates. The composite structure thus extends the device's applicability to various sensor measurements beyond temperature.
Solution Approach 2:
The patent changes the wave propagation mode from Rayleigh waves to shear waves by modifying the substrate structure. This parameter change fundamentally alters the temperature coefficient of delay, reducing it from 70 ppm/K to 30 ppm/K or less, thereby improving temperature stability and enabling broader sensor applications.
3Reliability
If shear wave propagation is enabled through specific crystallographic orientation, then temperature stability improves and electromechanical coupling increases, but the substrate structure becomes more complex
Solution Approach 1:
The patent uses a composite substrate with a piezoelectric layer deposited on a base substrate, where the piezoelectric layer is oriented to support shear wave propagation. This approach achieves high electromechanical coupling (20% or more) and improved temperature stability (TCD ≤ 30 ppm/K) while maintaining compatibility with standard semiconductor fabrication processes, thus managing structural complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The use of a composite substrate with shear wave propagation improves temperature stability and increases the electromechanical coupling coefficient, enabling SAW tag devices to measure mechanical parameters like force and pressure, while also extending the interrogation distance.
Implementation Method 1
a piezoelectric layer with a specific crystallographic orientation that enables the propagation of shear waves
Implementation Method 2
at least one transducer structure provided over the substrate comprising inter-digitated comb electrodes
Data Source
AI summary
A surface acoustic wave tag device is disclosed, comprising: an acoustic wave propagating substrate, at least one transducer structure comprising inter-digitated comb electrodes, and at least one reflecting means, the reflecting means comprising at least one reflector, wherein the acoustic wave propagation substrate is a composite substrate comprising a base substrate and a piezoelectric layer, wherein the crystallographic orientation of the piezoelectric layer with respect to the base substrate is such that the propagation of a shear wave inside the piezoelectric layer and in the direction of propagation corresponding to the acoustic wave is enabled. A physical quantity determining device and a fabrication method of such surface acoustic wave tag device are also disclosed.