FBAR Etching Resistance Layer for Air Gap Formation
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Solution Overview
Problem
Conventional film bulk acoustic resonators (FBARs) face challenges in manufacturing, particularly with the air gap type, where the etching process can damage the resonance part, making it difficult to form the air gap without harming the device and complicating the manufacturing process.
Innovation Solution
Incorporating an etching resistance layer, preferably made of a high etching selectivity material like chrome or aluminum nitride, between the substrate and the resonance part to limit the etching depth and prevent damage during the air gap formation, using a dry etching method with a mask having rounded corners to shape the air gap effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an air gap type FBAR is manufactured by etching the substrate to form an air gap, then the resonance part can be isolated from the substrate, but the etching process may damage the resonance part
Solution Approach 1:
A mask layer is formed on the substrate before the etching process to define the etching region and protect the resonance part. The mask layer is deposited and patterned in advance, creating a protective barrier that prevents etching damage to the resonance part while allowing the air gap to be formed in the desired location.
Solution Approach 2:
The mask layer acts as an intermediary between the etching process and the resonance part. It mediates the interaction by allowing the etching to proceed in controlled regions while blocking the etchant from reaching the resonance part, thus enabling air gap formation without damage.
2Manufacturing precision
If a sacrificial layer is used to form the air gap, then the air gap can be precisely formed, but the manufacturing process becomes complex
Solution Approach 1:
The invention extracts the protective function from a separate sacrificial layer and integrates it into a mask layer that is deposited directly on the substrate. This eliminates the need for additional sacrificial layer deposition and removal steps, simplifying the manufacturing process while maintaining precise air gap formation.
Solution Approach 2:
The mask layer combines multiple functions: it serves as both the patterning mask for defining the air gap region and as a protective layer during etching. By merging these functions into a single layer deposited directly on the substrate, the process complexity is reduced compared to using separate sacrificial and mask layers.
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 approach allows for the formation of an air gap without damaging the resonance part, simplifying the manufacturing process and improving the resonance characteristics of the FBAR by controlling the etching depth and shape, enabling the production of filters with uniform frequency response.
Implementation Method 1
A principle of operation of the FBAR, is that electric energy applied to an electrode introduces an electric field varying in time in the piezoelectric layer. The electric field generates a Bulk Acoustic Wave in the same direction as a vibration direction of the resonance part in the piezoelectric layer, to produce resonance.
Implementation Method 2
a step of etching a lower part of the substrate to form an air gap
Data Source
AI summary
A film bulk acoustic resonator (FBAR) including a substrate having an etched air gap therethrough; a resonance part having a first electrode, a piezoelectric film and a second electrode which are laminated in turn above the air gap; and an etching resistance layer disposed between the air gap and the resonance part to limit an etching depth in forming the air gap, thereby preventing damage to the resonance part.