Elastic Wave Resonator Stack for Higher-Order Mode Suppression
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Solution Overview
Problem
Elastic wave devices using silicon substrates face significant higher-order mode responses due to the crystal orientation state of the silicon substrate, which existing technologies have not effectively addressed.
Innovation Solution
The elastic wave device incorporates a silicon support substrate with a piezoelectric LiTaO3 film and an interdigital transducer electrode, where the higher-order mode acoustic velocity is set equal to or greater than the acoustic velocity through the silicon substrate, and the film thickness of the LiTaO3 film is optimized within specific ranges to reduce higher-order mode responses, along with the use of a dielectric silicon oxide film to further minimize these modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a silicon substrate is used as support substrate, then the device can be manufactured with existing silicon processing technologies, but higher-order mode responses become significant depending on crystal orientation
Solution Approach 1:
The patent changes the physical parameters of the silicon substrate by specifying precise crystal orientation ranges ((30°, 60°, 0°) to (60°, 30°, 0°)) to control acoustic wave propagation characteristics. This parameter optimization reduces higher-order mode responses while maintaining compatibility with existing silicon manufacturing processes
Solution Approach 2:
The patent creates a composite structure by stacking multiple layers including silicon substrate, dielectric films (SiO2, Si3N4), and metal films (Al, Mo, W) with specific thickness ratios. This composite configuration allows simultaneous achievement of manufacturability and suppression of harmful higher-order modes through controlled acoustic impedance matching
2Reliability
If the film thickness of the piezoelectric film is increased to improve main mode response, then the Q factor improves, but higher-order mode responses become more significant
Solution Approach 1:
The patent optimizes the thickness parameter of the piezoelectric film to specific ranges (0.1λ to 0.5λ for LiTaO3, 0.05λ to 0.3λ for LiNbO3) where λ is the acoustic wavelength. This precise parameter control achieves high Q factor for the main mode while keeping higher-order mode responses suppressed
Solution Approach 2:
The patent applies different thickness ratios for different layers in the stack: piezoelectric film thickness ratio (tf/tsub) of 0.05 to 0.5, dielectric film thickness ratio (td/tsub) of 0.1 to 0.6, creating locally optimized quality characteristics that balance main mode enhancement with higher-order mode suppression
3Object-generated harmful factors
If the crystal orientation of silicon substrate is changed to reduce higher-order mode responses, then the harmful factors are reduced, but the acoustic velocity and Q factor may be affected
Solution Approach 1:
The patent identifies optimal crystal orientation parameter ranges ((30°, 60°, 0°) to (60°, 30°, 0°)) that simultaneously achieve two objectives: reducing higher-order mode responses and maintaining high Q factor for the main acoustic mode. This dual optimization is accomplished through careful selection of the crystal cut angles
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 effectively reduces or prevents higher-order mode responses, improves the Q factor of the main mode, and reduces the absolute value of the temperature coefficient of the resonant frequency, enhancing the performance of high-frequency front-end circuits and communication devices.
Implementation Method 1
a piezoelectric film disposed directly or indirectly on the support substrate
Implementation Method 2
a higher-order mode acoustic velocity of propagation through the piezoelectric film
Data Source
AI summary
An elastic wave device includes a support substrate made of silicon, a piezoelectric film disposed directly or indirectly on the support substrate, and an interdigital transducer electrode disposed on one surface of the piezoelectric film. A higher-order mode acoustic velocity of propagation through the piezoelectric film is equal or substantially equal to an acoustic velocity Vsi=(V1)1/2 of propagation through silicon or higher than the acoustic velocity Vsi, where Vsi is specified by V1 among solutions V1, V2, and V3 with respect to x derived from Ax3+Bx2+Cx+D=0.