Piezoelectric Plate Fabrication Using Sacrificial Layer Transfer
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Solution Overview
Problem
Current methods for fabricating piezoelectric structures, such as PZT, require high sintering temperatures incompatible with low-cost substrates like glass or plastic, limiting their use in ultrasonic sensors and energy harvesters due to sensitivity issues and inability to form individual electrical devices from these structures.
Innovation Solution
A method involving the formation of PZT or other piezoelectric materials on a growth substrate with top and bottom metal electrodes, using a sacrificial layer and template layer to create polygon-shaped structures that can be annealed at high temperatures and separated for use in various applications, including ultrasonic sensors and ferroelectric memory arrays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ceramic piezoelectric materials (PZT) are used to achieve high piezoelectric coefficient, then sensitivity is improved, but sintering temperature becomes too high for low-cost substrates like glass or plastic
Solution Approach 1:
The fabrication process is segmented into two independent stages: (1) forming PZT disks on a sacrificial substrate that can withstand high sintering temperatures, and (2) transferring the sintered disks to the final low-cost substrate. This segmentation allows each stage to use materials and processes optimized for its specific requirements, resolving the temperature incompatibility issue.
Solution Approach 2:
A sacrificial substrate (such as platinum foil or ceramic tile) serves as an intermediary carrier that temporarily holds the PZT material during high-temperature sintering. This intermediary absorbs the thermal stress and allows the PZT to be formed under optimal conditions, after which it is removed and the PZT disks are transferred to the final substrate.
2Reliability
If PZT disks are formed on a continuous planar bottom electrode, then sintering can be performed under optimized conditions, but the structure has very limited use and cannot be separated into individual electrical devices
Solution Approach 1:
The PZT disks are extracted from the continuous planar electrode structure by etching away the electrode material between adjacent disks. This extraction process creates individually addressable electrical devices while preserving the benefits of batch sintering, as the disks remain on the substrate during processing and are only separated after sintering is complete.
Solution Approach 2:
The bottom electrode is formed as a continuous planar layer before sintering, providing mechanical support and electrical connection during the high-temperature process. After sintering is complete, the electrode is selectively patterned to create individual device structures. This preliminary action allows optimized sintering while enabling subsequent device separation.
3Temperature
If polymer-based piezoelectric material is used to be compatible with low-cost substrates, then temperature compatibility is improved, but piezoelectric coefficient becomes 25 times lower than ceramic materials
Solution Approach 1:
The process segments the temperature requirements by using a sacrificial substrate that can withstand high temperatures for PZT sintering, while the final application substrate (glass or plastic) only needs to withstand the lower temperatures of the transfer and assembly processes. This allows ceramic PZT to be used without requiring the final substrate to be temperature-resistant.
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
Enables the fabrication of high-sensitivity piezoelectric structures compatible with low-cost substrates, enhancing the sensitivity of ultrasonic sensors and enabling their use in diverse applications like touchscreen sensors and health monitors.
Implementation Method 1
the sintering process can be carried out using optimized conditions for forming the PZT material (e.g., sintering at 650° C. for several hours)
Implementation Method 2
After removing the template layer and annealing, the polygon-shaped structures are separated from the sacrificial layer. With the proper choice of growth substrate material, the annealing can be performed at a relatively high temperature.
Data Source
AI summary
A method is provided for fabricating piezoelectric plates. A sacrificial layer is formed overlying a growth substrate. A template layer, with openings exposing sacrificial layer surfaces, is formed over the sacrificial layer. An adhesion layer/first electrode stack is selectively deposited in the openings overlying the sacrificial layer surfaces, and a piezoelectric material formed in the openings overlying the stack. Then, a second electrode is formed overlying the piezoelectric material. Using the second electrode as a hardmask, the piezoelectric material is etched to form polygon-shaped structures, such as disks, attached to the sacrificial layer surfaces. After removing the template layer and annealing, the polygon-shaped structures are separated from the sacrificial layer. With the proper choice of growth substrate material, the annealing can be performed at a relatively high temperature.