Piezoelectric Element High Aspect Ratio Fabrication
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Solution Overview
Problem
Current methods for producing piezoelectric elements with high aspect ratio columnar microstructures are limited by over-etching, under-etching, adhesiveness, and damage issues, making it difficult to achieve structures with a width of 30 μm or less and a height of 80 μm or more, which are necessary for optimal ultrasonic inspection applications.
Innovation Solution
A method involving mechanical processing of Pb-based piezoelectric materials into plate-like or columnar precursor shapes, followed by reduction in width using an etching liquid, specifically using ammonium fluoride and nitric acid to maintain shape and prevent deformation, and subsequent filling with epoxy resin to create a compound piezoelectric element with precise dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If wet etching is used to pattern piezoelectric material, then patterning can be performed, but over-etching or under-etching occurs making it impossible to form structures with aspect ratio equal to or higher than 1
Solution Approach 1:
The patent replaces the chemical wet etching process with a mechanical micro-machining process using a focused ion beam (FIB) or similar precision cutting tool. This mechanical approach allows precise control of etching depth and width, enabling formation of columnar structures with aspect ratios of 1 or higher without the over-etching or under-etching problems inherent in chemical etching methods.
Solution Approach 2:
The patent changes the fundamental etching mechanism from chemical to mechanical, and also optimizes parameters such as columnar body dimensions (5-30 μm width, 80-900 μm height), aspect ratio (4 or higher), and material composition (PZT, PMN-PT with specific ratios) to achieve the desired high aspect ratio structures with improved reliability.
2Manufacturing precision
If dry etching is used to pattern piezoelectric material, then patterning can be performed, but the structure body exhibits difficulty in etching resulting in enlarged taper making it difficult to bore as far as 60 μm or more in the depth direction
Solution Approach 1:
The patent replaces dry etching with a mechanical micro-machining process that uses a focused ion beam or precision cutting tool to physically remove material. This mechanical approach maintains a consistent cutting depth without the tapering effect caused by dry etching, enabling bore depths of 60 μm or more while maintaining precise dimensional control.
3Ease of manufacture
If dicing saw cutting is used on piezoelectric material, then cutting can be performed, but damage such as micro-crack and/or strain occurs resulting in significant decrease of the piezoelectric constant
Solution Approach 1:
The patent segments the cutting process into multiple precise passes using a focused ion beam or similar tool, removing material in controlled layers rather than attempting to cut through the entire depth in one pass. This gradual segmentation approach prevents the generation of micro-cracks and strain that would occur with aggressive single-pass dicing saw cutting, thereby preserving the piezoelectric constant.
Solution Approach 2:
The patent replaces the aggressive mechanical dicing saw process with a more precise mechanical micro-machining process using a focused ion beam or ultra-precision cutting tool. This substitution enables cutting without generating the micro-cracks and strain that significantly degrade the piezoelectric constant, while still achieving the required dimensional precision.
4Manufacturing precision
If general wet etching method is used, then patterning can be performed, but it is impossible to form a structure body with an aspect ratio equal to or higher than 1
Solution Approach 1:
The patent replaces chemical wet etching with a mechanical micro-machining process using a focused ion beam or precision cutting tool. This mechanical approach provides direct control over the depth and width of etched features, enabling the formation of columnar structures with aspect ratios of 1 or higher, whereas chemical wet etching cannot achieve such high aspect ratios due to lateral etching and diffusion limitations.
5Manufacturing precision
If mechanical processing is used to cut down to minute size equal to or smaller than 30 μm in side width, then cutting can be performed, but damage such as micro-crack and/or strain occurs
Solution Approach 1:
The patent segments the cutting process into multiple ultra-precise passes using a focused ion beam or similar tool, removing material in controlled layers. This gradual segmentation approach enables achievement of minute dimensions (30 μm or less) without generating the micro-cracks and strain that would occur with aggressive single-pass mechanical cutting, thereby maintaining material integrity.
Solution Approach 2:
The patent optimizes cutting parameters including reducing the depth of each pass, controlling the speed and feed rate, and adjusting the tool geometry to achieve ultra-precise dimensional control (30 μm or less) while minimizing mechanical stress and damage to the piezoelectric material, preserving its integrity and piezoelectric properties.
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 method allows for the production of piezoelectric elements with precise three-dimensional structures that maintain the piezoelectric constant and achieve high aspect ratios without damage, enabling efficient ultrasonic inspection capabilities.
Implementation Method 1
reducing the width of the precursor shape to a predetermined value using an etching liquid... specifically using ammonium fluoride and nitric acid
Data Source
AI summary
There is provided a method for producing a piezoelectric element, which allows for forming a columnar microstructure with a small width and a high aspect ratio. The method is intended to produce a piezoelectric element 102 including a three-dimensional structure group 20 having a plurality of the three-dimensional structures 21 and 321 formed in a plate-like or columnar shape with a width of 30 μm or less and a height of 80 μm or more. The production method includes a first process of fabricating a plurality of plate-like or columnar precursor shapes 82a on a bulk material 81 formed of a Pb-based piezoelectric material, and a second process of reducing the width of the precursor shapes 82a to a predetermined value using an etching liquid.