Acoustic Wave Resonator Piezoelectric Layer Thickness Control
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Solution Overview
Problem
Surface acoustic wave devices with laminated structures of high and low acoustic velocity films and a piezoelectric film suffer from high-order mode generation in higher frequency bands, which changes with temperature, leading to ripple effects in pass bands, particularly in high-frequency side filters connected to antennas.
Innovation Solution
The acoustic wave device incorporates a series of acoustic wave resonators with a piezoelectric layer, an IDT electrode, and a high acoustic velocity member, where the thickness of the piezoelectric layer is limited to 3.5λ or less, and includes a dielectric film between the piezoelectric layer and the IDT electrode in some resonators, while others do not, to manage the cut-angle and mass per unit length of electrode fingers, reducing temperature-induced frequency changes of high-order modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a laminated structure of high acoustic velocity film, low acoustic velocity film, and piezoelectric film is used to increase Q factor, then the Q factor is improved, but high-order modes are generated in higher frequency bands that change with temperature causing ripple in pass bands
Solution Approach 1:
The patent changes the thickness parameter of the piezoelectric layer to 3.5λ or less, which fundamentally alters the acoustic wave propagation characteristics and eliminates the generation of high-order modes that are sensitive to temperature changes, thereby resolving the frequency stability issue while maintaining the Q factor benefit
Solution Approach 2:
The patent extracts or removes the problematic high-order modes by controlling the piezoelectric layer thickness to 3.5λ or less, preventing these modes from being generated in the first place, thus eliminating the temperature-induced frequency drift and ripple effects in the pass bands
2Reliability
If the piezoelectric layer thickness is increased to improve Q factor, then the Q factor is improved, but high-order modes are generated that deteriorate pass band characteristics
Solution Approach 1:
The patent establishes a critical threshold parameter for the piezoelectric layer thickness (3.5λ or less) that simultaneously optimizes both Q factor and pass band characteristics by preventing high-order mode generation, thus resolving the contradiction between improving Q factor and maintaining manufacturing precision
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 significantly reduces or prevents the deterioration of pass band characteristics and high-order mode changes due to temperature, enhancing the stability and performance of acoustic wave devices, multiplexers, and communication devices by minimizing frequency fluctuations.
Implementation Method 1
Each of the first acoustic wave resonator and the second acoustic wave resonator includes a piezoelectric layer, an interdigital transducer (IDT) electrode
Implementation Method 2
In the high acoustic velocity member, an acoustic velocity of a bulk wave propagating through is higher than an acoustic velocity of an acoustic wave propagating through the piezoelectric layer
Data Source
AI summary
In an acoustic wave device, an antenna end resonator that is electrically closest to a first terminal is a first acoustic wave resonator. In each of the first acoustic wave resonator and a second acoustic wave resonator, a thickness of a piezoelectric layer is about 3.5λ or less when a wavelength of an acoustic wave is denoted as λ. The first acoustic wave resonator and the second acoustic wave resonator satisfy at least one of a first condition, a second condition, and a third condition. The first condition is a condition that the first acoustic wave resonator further includes a dielectric film provided between the piezoelectric layer and an interdigital transducer electrode, and the second acoustic wave resonator does not include the dielectric film.