SAW Composite Substrate With Intervening Layers for Low Spurious Noise
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Solution Overview
Problem
Surface acoustic wave filters experience noise issues due to energy leakage and reflection at the bonding interface between piezoelectric crystal films and supporting substrates, leading to deteriorated frequency characteristics and increased loss, as well as potential polarization disturbances during the wafer process and heat treatment.
Innovation Solution
A composite substrate with a piezoelectric single crystal thin film and a support substrate, featuring a first intervening layer with an acoustic velocity faster than the piezoelectric single crystal thin film, and a second intervening layer with a slower acoustic velocity, along with an uneven structure at the bonding interface, to trap and reflect elastic waves effectively and maintain polarization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a piezoelectric single crystal substrate is bonded to a supporting substrate to improve temperature characteristics, then temperature stability is improved, but spurious noise and energy leakage occur at the bonding interface
Solution Approach 1:
An intervening layer is introduced between the piezoelectric single crystal thin film and the support substrate to act as an acoustic impedance matching layer. This intermediary prevents direct bonding interface contact, thereby suppressing spurious noise and energy leakage while maintaining the temperature stability benefits of the bonded structure.
Solution Approach 2:
The composite substrate structure combines multiple materials with different acoustic velocities - the piezoelectric single crystal thin film, the intervening layer with specific acoustic velocity characteristics, and the support substrate. This composite structure optimizes both temperature stability and spurious noise suppression by leveraging the complementary properties of each material layer.
2Stability of the object's composition
If the piezoelectric single crystal thin film is thinned to several μm to several tens μm to improve temperature characteristics, then temperature stability is improved, but polarization disturbance occurs during wafer process and heat treatment
Solution Approach 1:
The intervening layer is deposited on the piezoelectric single crystal thin film before bonding to the support substrate, providing protective cushioning during subsequent wafer processing and heat treatment steps. This pre-established protective layer prevents polarization disturbance that would otherwise occur in thinned films during manufacturing processes.
3Object-generated harmful factors
If an uneven structure is formed at the bonding interface to suppress spurious noise, then spurious noise is reduced, but manufacturing complexity increases
Solution Approach 1:
The uneven structure is formed locally only at the bonding interface region where spurious noise generation occurs, rather than throughout the entire substrate. This localized approach suppresses spurious noise effectively while minimizing the increase in manufacturing complexity compared to global structural modifications.
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 solution significantly reduces spurious noise and loss in the passband of surface acoustic wave filters, prevents ripple, and maintains the polarization of the piezoelectric single crystal film, enhancing the overall performance and stability of the composite substrate.
Implementation Method 1
the acoustic velocity of the transverse wave in the first intervening layer is faster than the acoustic velocity of the fast transverse wave in the piezoelectric single crystal thin film
Implementation Method 2
a second intervening layer with a slower acoustic velocity
Data Source
AI summary
A piezoelectric composite substrate for SAW devices with small loss is provided. A composite substrate for a surface acoustic wave device according to one embodiment of the present invention has a piezoelectric single crystal thin film, a support substrate, and a first intervening layer between the piezoelectric single crystal thin film and the support substrate. In the composite substrate, the first intervening layer is in contact with the piezoelectric single crystal thin film, and the acoustic velocity of the transverse wave in the first intervening layer is faster than the acoustic velocity of the fast transverse wave in the piezoelectric single crystal thin film.