Piezoelectric Pump Residual Stress Management
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Solution Overview
Problem
Piezoelectric thin films in vibrating devices, such as piezoelectric pumps, are prone to breakage due to residual stress gradients and tensile stress during vibration, leading to potential fluid conveyance issues.
Innovation Solution
A piezoelectric pump design incorporating a piezoelectric part with balanced residual stresses through the use of first and second bonding parts, which apply and receive compressive residual stress, preventing warping and crack formation, and ensuring efficient fluid conveyance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a piezoelectric thin film is used in a vibrating device, then the device can achieve vibration and fluid conveyance, but the piezoelectric thin film is prone to breakage due to tensile stress during vibration
Solution Approach 1:
The patent applies a compressive residual stress to the piezoelectric layer in advance through thermal processing (cooling after bonding to a substrate with higher thermal expansion coefficient). This preliminary compressive stress counteracts the tensile stress that occurs during vibration, preventing crack formation and layer separation while maintaining the piezoelectric layer's integrity during operation
Solution Approach 2:
The patent changes the stress state parameter of the piezoelectric layer from purely tensile or stress-free to having a controlled compressive residual stress component. By adjusting the thermal expansion coefficient difference between the piezoelectric layer and substrate, and controlling the cooling process, the compressive residual stress is optimized to prevent breakage during vibration while maintaining functional performance
2Reliability
If a compressive residual stress is applied to the piezoelectric thin film to prevent breakage, then the reliability improves, but the piezoelectric layer may warp due to residual stress gradients
Solution Approach 1:
The patent applies different residual stress conditions to different regions of the piezoelectric structure. The piezoelectric layer is designed to have a compressive residual stress that is sufficiently strong to prevent surface crack formation, while the overall structure (including substrate and electrode layers) is configured to balance the stress distribution and prevent excessive warping. This local optimization allows the surface to remain intact while maintaining acceptable global flatness
3Reliability
If the piezoelectric layer is bonded to a substrate with higher thermal expansion coefficient to create compressive residual stress, then breakage is prevented, but manufacturing complexity increases due to thermal processing requirements
Solution Approach 1:
The patent utilizes the thermal expansion coefficient difference between the piezoelectric layer and substrate as the mechanism to generate compressive residual stress. By selecting a substrate material with a higher thermal expansion coefficient than the piezoelectric layer and performing a controlled cooling process after bonding, the substrate contracts more than the piezoelectric layer, inducing the desired compressive stress. This approach converts a manufacturing complexity (thermal processing) into a reliable and controllable process that achieves the desired stress state
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 balanced residual stresses suppress warping and reduce the risk of piezoelectric layer breakage, maintaining fluid conveyance efficiency even under vibration, with minimal deformation due to temperature variations.
Implementation Method 1
The piezoelectric thin film is formed on a substrate having a higher coefficient of linear expansion than that of the piezoelectric thin film in a heated environment. Then, when the piezoelectric thin film is cooled, the substrate contracts by a larger amount than the amount by which the piezoelectric thin film contracts. As a result, a residual stress in the compressive direction is applied to the piezoelectric thin film.
Implementation Method 2
a piezoelectric pump which conveys fluid by causing a vibrating plate which forms a wall surface of a pump chamber to vibrate using the piezoelectric part
Data Source
Figure 1(A)~1(B)
Figure 2(A)~3
Figure 4~5
AI summary
Warping of a piezoelectric layer is eliminated, and even if a tensile stress is applied to the piezoelectric layer due to vibration, a risk that the piezoelectric layer will break is reduced. A piezoelectric pump (100) includes a piezoelectric element (54), an intermediate plate (53), and a vibrating plate (51). The piezoelectric element (54) has a flat-plate-like shape. The intermediate plate (53) is bonded to a principal surface of the piezoelectric element (54) and applies a residual stress in a compressive direction to the piezoelectric element (54). The vibrating plate (51) is bonded to the intermediate plate (53) such that the vibrating plate (51) faces a principal surface of the piezoelectric element (54) and receives a residual stress in a compressive direction from the intermediate plate (53). In addition, the vibrating plate (51) forms a portion of a wall surface of a pump chamber (41) having an open hole (31). A fluid passage is formed in the piezoelectric pump (100). The fluid passage communicates with the outside of the chamber at one end thereof, and communicates with the pump chamber (41) through the open hole (31) at the other end.