Embedded IDT Transducer Structure for SAW Devices Above 3 GHz
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing surface acoustic wave (SAW) devices face limitations in operating frequencies due to stability issues with comb electrodes at higher frequencies, requiring advanced lithography and experiencing electric losses, which hinder miniaturization and frequency expansion beyond 3 GHz.
Innovation Solution
A transducer structure with embedded inter-digitated comb electrodes in a piezoelectric layer, utilizing a shear wave mode confined within the electrodes, allowing operation above 3 GHz using standard I-line lithography, and featuring adjustable electro-mechanical coupling and reduced electric losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If standard I-line lithography is used for comb electrodes, then manufacturing cost is reduced, but operating frequency is limited to below 3 GHz due to stability issues
Solution Approach 1:
The patent transitions from surface-level electrode structures to vertically embedded electrodes within the piezoelectric layer. This dimensional change from surface mounting to subsurface embedding enables higher frequency operation (above 3 GHz) while maintaining compatibility with standard I-line lithography processes, thus resolving the contradiction between manufacturing ease and operating frequency.
Solution Approach 2:
The electrodes are nested within grooves formed in the piezoelectric layer, creating a hierarchical structure where conductive elements are embedded within the substrate material. This nesting approach allows standard lithography to define the groove patterns while the embedded electrodes provide enhanced high-frequency performance, combining manufacturing simplicity with advanced operational capabilities.
2Speed
If electrode pitch is reduced for higher frequencies, then operating frequency increases, but manufacturing precision requirements increase
Solution Approach 1:
By embedding electrodes vertically within the piezoelectric layer rather than placing them on the surface, the patent enables reduced electrode pitch for higher frequencies without proportionally increasing manufacturing precision requirements. The vertical embedding provides structural support and electrical isolation that relaxes lateral positioning tolerances.
Solution Approach 2:
The patent changes the structural parameter of electrode placement from surface-level to subsurface embedded configuration. This parameter change enables smaller pitch dimensions for high-frequency operation while the embedding process itself provides the necessary precision, decoupling the pitch reduction from proportional increases in manufacturing difficulty.
3Adaptability or versatility
If piezoelectric substrates like LiNbO3 or LiTaO3 are used, then electromechanical coupling is improved, but temperature sensitivity increases
Solution Approach 1:
The patent applies different properties to different regions: the piezoelectric layer provides high electromechanical coupling where needed for transducer operation, while the underlying base substrate provides thermal stability. This local differentiation allows the device to benefit from both high coupling and low temperature sensitivity simultaneously.
Solution Approach 2:
The patent employs a composite substrate structure combining a piezoelectric layer (LiNbO3 or LiTaO3) with a thermally stable base substrate. This composite approach allows the piezoelectric material to provide high electromechanical coupling (ks² > 1%) while the base substrate constrains thermal expansion and reduces overall temperature sensitivity, resolving the contradiction between coupling performance and thermal stability.
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
Enables SAW devices to operate at frequencies above 3 GHz with improved stability and reduced electric losses, while maintaining manufacturability and temperature stability, achieving bandwidths up to 15% and phase velocities of 10,000 m/s.
Implementation Method 1
one or more inter-digitated transducers (IDTs) are formed over a surface propagating substrate and are used to convert acoustic waves to electrical signals and vice versa by exploiting the piezoelectric effect of the substrate
Implementation Method 2
A Rayleigh surface acoustic wave develops on the substrate by electrically exciting the fingers
Data Source
AI summary
A transducer structure for a surface acoustic device comprises a composite substrate comprising a piezoelectric layer, a pair of inter-digitated comb electrodes, comprising a plurality of electrode means with a pitch p satisfying the Bragg condition, wherein the inter-digitated comb electrodes are embedded in the piezoelectric layer such that, in use, the excitation of a wave propagating mode in the volume of the electrode means is taking place and is the predominant propagating mode of the structure. The present disclosure relates also to an acoustic wave device comprising at least one transducer structure as described above and to a method for fabricating the transducer structure. The present disclosure relates also to the use of the frequency of the bulk wave propagating in the electrode means of the transducer structure in an acoustic wave device to generate contribution at high frequency, in particular, above 3 GHz.