Embedded IDT Transducer Structure for Acoustic Waves Above 3 GHz
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Solution Overview
Problem
Surface acoustic wave (SAW) devices are limited to operating frequencies below 3 GHz due to the constraints of electrode stability and lithography technology, with higher frequencies requiring advanced lithography and facing challenges in miniaturization and electric losses.
Innovation Solution
A transducer structure with embedded inter-digitated comb electrodes in a piezoelectric layer, where the acoustic impedance of the electrodes is less than that of the piezoelectric layer, allowing for the excitation of a shear wave mode confined within the electrodes, enabling higher phase velocities and operation beyond 3 GHz using standard I-line lithography.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If standard I-line lithography is used for manufacturing, then manufacturing precision and ease of manufacture are maintained, but operating frequency is limited to below 3 GHz
Solution Approach 1:
The patent changes the acoustic impedance parameter by selecting electrode materials with lower acoustic impedance than the piezoelectric substrate. This parameter change enables the excitation of shear wave modes that are confined within the electrodes, allowing the device to operate at frequencies above 3 GHz while maintaining compatibility with standard I-line lithography manufacturing processes
Solution Approach 2:
The patent employs a composite structure consisting of a piezoelectric substrate combined with electrode materials of specifically selected lower acoustic impedance. This composite material approach creates a layered system where the impedance contrast between layers enables confinement of shear waves within the electrodes, achieving high-frequency operation without requiring advanced lithography
2Speed
If electrode dimensions are miniaturized for higher frequencies, then operating frequency increases, but electrode stability and manufacturing feasibility deteriorate
Solution Approach 1:
By changing the acoustic impedance parameter through material selection, the patent achieves higher phase velocities (exceeding 4000 m/s) without miniaturizing the electrode dimensions. The lower acoustic impedance of the electrode materials relative to the piezoelectric substrate enables shear wave confinement, which increases phase velocity while maintaining electrode stability and compatibility with standard manufacturing
3Reliability
If piezoelectric substrates with high coupling are used, then electromechanical coupling improves, but temperature sensitivity increases
Solution Approach 1:
The patent changes the acoustic impedance parameter by selecting specific electrode materials with lower acoustic impedance than the piezoelectric substrate. This material parameter change enables shear wave mode confinement within the electrodes, achieving high electromechanical coupling (exceeding 5%) while the choice of piezoelectric substrate can be optimized for temperature 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
This configuration enables SAW devices to operate at frequencies above 3 GHz with improved stability and reduced electric losses, while maintaining manufacturing feasibility with existing lithography tools, and achieves higher phase velocities and electromechanical coupling.
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
An inter-digitated transducer (IDT) comprises opposing 'electrode combs' with inter-digitated metal fingers disposed on a piezoelectric substrate. 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.