Self-Aligned Acoustic Holes for Low-Leakage Piezoelectric MEMS Microphones
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Solution Overview
Problem
Existing MEMS devices face challenges in forming acoustic holes with smooth sidewalls and minimizing air leakage, which affects the performance and efficiency of the device.
Innovation Solution
A method involving the formation of alternating electrode and piezoelectric layers, specifically using AlScN layers, where the acoustic hole is etched to maintain a smooth sidewall by exploiting the lattice structure and point defect sites, ensuring the hole is spaced apart from the electrodes, and utilizing controlled etching processes to minimize air leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If the acoustic hole is made smaller to reduce air leakage, then air leakage is reduced, but the manufacturing precision becomes more difficult to achieve
Solution Approach 1:
A sacrificial layer is introduced as an intermediary element between the acoustic hole opening and the final through-hole. The sacrificial layer is deposited conformally and then selectively removed to create the acoustic hole, enabling precise control of the through-hole dimensions and position without directly etching through the membrane. This intermediary approach allows for better manufacturing precision while maintaining small hole dimensions to reduce air leakage.
Solution Approach 2:
The sacrificial layer is deposited and patterned before the acoustic hole is formed. This preliminary action establishes a precise template that guides the subsequent hole formation process, ensuring accurate positioning and dimensional control of the acoustic hole relative to the membrane and electrodes, thereby improving manufacturing precision.
2Ease of manufacture
If conventional etching is used to form the acoustic hole, then the process is simple, but the sidewalls become rough and air leakage increases
Solution Approach 1:
The sacrificial layer serves as a mediator that enables the formation of smooth sidewalled acoustic holes. By depositing the sacrificial layer conformally and then removing it selectively, the process creates clean, smooth sidewalls without requiring complex etching techniques. This maintains ease of manufacture while eliminating the air leakage problem associated with rough sidewalls.
Solution Approach 2:
The conventional mechanical etching process that creates rough sidewalls is replaced with a deposition-removal cycle using the sacrificial layer. Instead of mechanically cutting through the membrane with potentially rough edges, the process uses conformal deposition followed by selective removal, resulting in smooth sidewalls that reduce air leakage while keeping the process relatively simple.
3Device complexity
If the acoustic hole is positioned close to the electrodes, then the device structure is compact, but alignment precision deteriorates
Solution Approach 1:
The sacrificial layer acts as a positioning intermediary that is deposited conformally on the membrane surface. Its thickness and pattern are precisely controlled to define the acoustic hole position relative to the electrodes. This intermediary approach enables accurate alignment even when the hole is positioned close to the electrodes, maintaining both compactness and alignment precision.
Solution Approach 2:
The sacrificial layer is patterned in advance to establish the precise position of the acoustic hole relative to the electrodes. This preliminary positioning step ensures accurate alignment before the actual hole formation, allowing the device to maintain a compact structure with the hole close to the electrodes while achieving high alignment precision.
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 method results in a MEMS device with reduced air leakage and improved signal integrity by maintaining a smooth sidewall and precise alignment of the acoustic hole, enhancing the device's performance and manufacturing efficiency.
Implementation Method 1
a first piezoelectrical layer... a second piezoelectrical layer... a third piezoelectrical layer
Data Source
AI summary
A membrane is formed through processes including depositing a first piezoelectrical layer, depositing a first electrode layer over the first piezoelectrical layer, patterning the first electrode layer to form a first electrode, depositing a second piezoelectrical layer over the first electrode, depositing a second electrode layer over the second piezoelectrical layer, patterning the second electrode layer to form a second electrode, and depositing a third piezoelectrical layer over the second electrode. The third piezoelectrical layer, the second piezoelectrical layer, and the first piezoelectrical layer are etched to form a through-hole. The through-hole is laterally spaced apart from the first electrode and the second electrode. A first contact plug and a second contact plug are then formed to electrically connect to the first electrode and the second electrode, respectively.