Elastic Wave Device Bulk Wave Cancellation via Bonded Structure
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Solution Overview
Problem
Elastic wave devices face frequency characteristic deterioration due to bulk waves, which is exacerbated by the thinning of piezoelectric substrates, and roughening the substrate surface to mitigate this issue can lead to cracking and further strength reduction.
Innovation Solution
A path difference is created between two components of bulk waves by bonding a structure to the substrate's surface, allowing one component to be reflected and the other to pass through, canceling each other out due to phase differences, thus eliminating the adverse effects on the device characteristic without requiring surface roughening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the undersurface of a piezoelectric substrate is roughened to suppress bulk wave reflection, then frequency characteristic deterioration is reduced, but the substrate becomes easily cracked and flexural strength deteriorates
Solution Approach 1:
The invention divides the bulk wave into two separate components (first and second components) that travel along different paths. The first component reflects off the bonding surface while the second component transmits through it. By controlling the path length difference between these two segmented wave components, they interfere destructively to cancel each other out, eliminating the need for surface roughening and preserving substrate strength.
Solution Approach 2:
The bonding surface acts as an intermediary element that mediates the bulk wave behavior. Instead of directly roughening the surface to suppress reflections, the bonding structure creates controlled phase differences that lead to destructive interference, achieving wave cancellation through the intermediary's path difference mechanism rather than direct surface modification.
2Volume of moving object
If the piezoelectric substrate is reduced in thickness to miniaturize the device, then device size is reduced, but bulk wave effects are increased and the substrate becomes more prone to cracking
Solution Approach 1:
By segmenting the bulk wave into two path components with different lengths, the invention creates destructive interference that cancels bulk wave effects. This allows thin substrates to be used for miniaturization without suffering from enhanced bulk wave reflections, as the segmented paths ensure wave cancellation regardless of substrate thickness.
3Volume of moving object
If the piezoelectric substrate is reduced in thickness to miniaturize the device, then device size is reduced, but the substrate becomes easier to crack
Solution Approach 1:
Instead of the conventional approach of roughening the surface to suppress bulk waves, the invention inverts the approach by using a smooth bonding surface that creates transmitted waves. The path difference mechanism inverts the traditional reflection-based suppression method, allowing thin, strong substrates to be used without compromising frequency characteristics.
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 approach effectively reduces and prevents frequency characteristic deterioration without compromising the substrate's strength, even at thinner thicknesses, by ensuring the bulk waves are canceled before reaching the output, thereby enhancing the device's performance.
Implementation Method 1
a bulk wave that includes unnecessary oscillations generated at the IDT
Implementation Method 2
the first component being reflected from the bonding surface
Implementation Method 3
the second component entering the structure from the bonding surface, propagating in the structure
Implementation Method 4
the first and second components propagating in the same direction in the piezoelectric substrate and cancel each other because of the phase difference between them
Implementation Method 5
An elastic wave device excites a surface acoustic wave or a boundary acoustic wave using a comb-shaped electrode (Interdigital Transducer (IDT)) formed on a piezoelectric substrate having piezoelectricity
Data Source
AI summary
In an elastic wave device that significantly reduces and prevents deterioration of a frequency characteristic without roughening an undersurface of a piezoelectric substrate, a structure is bonded to a surface of a piezoelectric substrate other than a main surface of the piezoelectric substrate on which IDTs are located. The structure is provided so that a path difference is defined between a first component and a second component of a bulk wave that is excited by the IDT and propagates in the piezoelectric substrate toward the bonding surface. The first component of the bulk wave is reflected from the bonding surface. The second component of the bulk wave enters the structure from the bonding surface, propagates in the structure, enters the piezoelectric substrate from the bonding surface, and propagates in the same direction as that of the first component reflected from the bonding surface in the piezoelectric substrate.