Piezoelectric Micromachined Ultrasonic Transducer Supporting Pillar Design
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Solution Overview
Problem
Piezoelectric micromachined ultrasonic transducers and arrays face deformation and collapse issues due to vacuum attraction during the vacuumizing process, leading to abnormal operation and reduced manufacturing yield, especially when the thickness and size of the elements are reduced.
Innovation Solution
A piezoelectric micromachined ultrasonic transducer design that includes a silicon substrate, a first protective layer with a cavity, a supporting pillar, a piezoelectric composite film, and a second protective layer, where the supporting pillar provides rigidity to prevent deformation and collapse by maintaining a specific distance and ratio, and is made of materials like amorphous silicon or tetraethoxysilane, with communicating holes and metal layers for electrical connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the thickness and size of the piezoelectric element are reduced, then the device becomes more compact and integrated, but the element becomes more susceptible to deformation and collapse due to vacuum attraction
Solution Approach 1:
The cavity is divided into multiple regions by introducing supporting pillars that segment the vacuum space. This segmentation provides localized structural support to the piezoelectric element, preventing global deformation while maintaining the compact design. The pillars create smaller vacuum compartments that reduce the overall vacuum attraction force on any single region of the piezoelectric element.
Solution Approach 2:
Supporting pillars are introduced as intermediary structures between the piezoelectric element and the cavity walls. These pillars act as mediators that bear the vacuum attraction force, transferring it from the piezoelectric element to the substrate. The pillars serve as mechanical intermediaries that protect the piezoelectric element from direct vacuum-induced stress while allowing the compact structure to function.
2Strength
If supporting structures are added to prevent deformation, then structural integrity is improved, but device complexity increases
Solution Approach 1:
The supporting pillars are designed with optimized dimensions (width of 3-10 μm and height-to-distance ratio of 1/70 to 1/200) that provide necessary mechanical support while maintaining a thin-film profile. This allows the structure to remain relatively simple and planar, avoiding complex three-dimensional support mechanisms. The pillars act as thin-film reinforcement elements that prevent deformation without significantly increasing overall device complexity.
Solution Approach 2:
The supporting pillars utilize specific geometric parameters (width ratio of 3-10 μm, height-to-distance ratio of 1/70 to 1/200) that optimize the balance between structural support and device simplicity. By carefully controlling these parameters, the pillars provide adequate mechanical strength while maintaining a compact, low-complexity structure that integrates easily with the piezoelectric element and cavity design.
3Volume of moving object
If the piezoelectric element is made thinner for integration, then manufacturing precision requirements increase due to vulnerability to vacuum attraction
Solution Approach 1:
The supporting pillars are formed in the cavity before the piezoelectric element is fully assembled and vacuumized. This preliminary placement of support structures ensures that the pillars are already in position to counteract vacuum attraction forces during the critical vacuumizing process. The pre-formed pillars provide immediate structural protection, allowing thinner piezoelectric elements to be manufactured with relaxed precision requirements since the support mechanism is already in place before vacuum-induced deformation can occur.
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 design enhances the structural integrity and manufacturing yield of the transducers, maintaining their function while reducing the influence of vacuum attraction, and increases sound pressure even at reduced volumes.
Implementation Method 1
a piezoelectric composite film arranged on the first protective layer, wherein a vertical projection of the piezoelectric composite film partially overlaps with the cavity, and a part of the bottom of the piezoelectric composite film is in contact with the supporting pillar
Data Source
AI summary
A piezoelectric micromachined ultrasonic transducer includes a silicon substrate, a first protective layer, a supporting pillar, a piezoelectric composite film and a second protective layer. The supporting pillar is in the cavity of the first protective layer, the non-supporting pillar regions in the cavity communicates with each other. The shortest distance between a wall of the first protective layer and the supporting pillar is a first distance. The piezoelectric composite film is provided with at least two communicating holes, and the communicating holes penetrate the piezoelectric composite film and are communicated with the cavity. The second protective layer fills the two communicating holes to close the cavity. The distance between the two communicating holes is greater than twice of the first distance, and a ratio of a height of the supporting pillar to the first distance is 1/70 to 1/200, and a width of the supporting pillar is 3-10 um.