Piezoelectric Element Stress Relaxation Metal Layer
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Solution Overview
Problem
Piezoelectric elements in ultrasonic transducers are prone to cracking and burnout due to stress concentration at the boundary between active and inactive parts, leading to performance degradation, especially when water infiltrates the cracks caused by stress concentration.
Innovation Solution
A piezoelectric element configuration with a metal layer and insulating layer disposed over the extending part of the piezoelectric layer, which relaxes stress and enhances water resistance by preventing short circuits between electrodes, using materials like Pt, Ir, Ti, Zr, Au, Ni, NiCr, and insulating materials like Al2O3, TaOx, HfOx, and SiO2.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the piezoelectric layer is disposed to straddle the overlapping part beyond the outer peripheral edge of the second electrode layer, then the active area is increased, but stress concentration causes cracks in the piezoelectric film
Solution Approach 1:
A metal layer is introduced as an intermediary component between the piezoelectric layer and the second electrode layer. This metal layer serves as a stress-absorbing intermediary that prevents direct stress transmission to the piezoelectric film at the boundary region, thereby preventing cracks while allowing the piezoelectric layer to extend beyond the electrode perimeter for increased active area.
Solution Approach 2:
The metal layer is positioned in advance at the boundary region where stress concentration is expected to occur. This layer acts as a pre-established cushioning structure that absorbs and distributes stress before it can concentrate on the piezoelectric film, preventing crack formation before it happens.
2Area of stationary object
If the piezoelectric layer extends beyond the second electrode layer, then the active area is increased, but water infiltration causes burnout
Solution Approach 1:
The metal layer acts as an intermediary protective barrier that extends beyond the second electrode layer, covering the exposed piezoelectric layer. This intermediary structure prevents direct contact between water and the piezoelectric material, eliminating the burnout risk while preserving the extended active area.
Solution Approach 2:
The metal layer serves as a sacrificial protective element that can be easily applied and provides reliable water protection. By placing this protective layer over the extended piezoelectric region, the system gains water resistance without compromising the extended active area.
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 configuration effectively prevents cracks and burnout of the piezoelectric film, maintaining the performance and water resistance of the piezoelectric element by distributing stress and isolating the electrodes.
Implementation Method 1
the piezoelectric element is constituted by a lower electrode, a piezoelectric film, and an upper electrode stacked on one another... the area where the lower electrode, the piezoelectric film, and the upper electrode overlap each other is an area (hereinafter also referred to as an active part) to be deformed in response to application of a voltage between the electrodes
Implementation Method 2
the metal layer and the insulating layer are disposed from the second electrode layer to the extending part of the piezoelectric element main body in the plan view... due to the elasticity of the metal layer, the stress in the piezoelectric layer can be relaxed
Data Source
AI summary
A piezoelectric element includes a piezoelectric element main body as a laminated body of a first electrode layer, a piezoelectric layer disposed on the first electrode layer, and a second electrode layer disposed on the piezoelectric layer, and a metal layer disposed on the second electrode layer via an insulating layer, the piezoelectric layer extends from an inner side of at least a part of an overlapping part of an outer peripheral edge of the second electrode layer overlapping an outer peripheral edge of the piezoelectric element main body to an outer side, and the metal layer and the insulating layer extend from an inner side of at least a part of the overlapping part to an outer side to overlap the piezoelectric layer on an outer side of an outer peripheral edge of the second electrode layer.