Thin-Membrane MEMS Transducer Packaging for Flat Acoustic Coupling
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Solution Overview
Problem
Current manufacturing methods for MEMS devices, particularly ultrasonic transducers, face challenges such as reduced flexibility due to the use of a single technology for both driving and receiving circuits, limited testing capabilities before completion, and issues with cavity filling in transducer membranes, which affect the performance and efficiency of acoustic wave transmission and reception.
Innovation Solution
A method involving the formation of a layered structure with a planar membrane surface, where transducer devices are coupled to a supporting structure using FOWLP technology, allowing for mechanical and electrical coupling, and the removal of the substrate to expose the membrane surface, enabling uniform thickness and flatness without cavities or depressions, and facilitating integration with ASICs and redistribution structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single technology is used for both driving and receiving circuits, then device complexity is reduced, but manufacturing flexibility and performance are degraded
Solution Approach 1:
The patent divides the manufacturing process into separate segments: the transducer array is manufactured on a first substrate, while the driving and receiving circuits are manufactured separately on a second substrate using FOWLP technology. This segmentation allows each component to be optimized independently, resolving the contradiction between device complexity and manufacturing flexibility.
Solution Approach 2:
The second substrate is designed to accommodate multiple functions: it integrates both driving circuits for transmitting acoustic waves and receiving circuits for detecting echo signals, along with redistribution structures for electrical connections. This multi-functional design allows a single substrate to handle diverse circuit requirements, improving manufacturing flexibility without proportionally increasing device complexity.
2Reliability
If transducers are located close to electronic circuitry, then signal amplification performance is improved, but the number of connections and channel management complexity increases
Solution Approach 1:
The patent merges the driving circuits and receiving circuits onto a single second substrate, along with their associated electrical connections. This consolidation reduces the overall number of separate connection management tasks compared to having distributed circuits, while maintaining close proximity between transducers and their corresponding circuitry for optimal signal amplification performance.
Solution Approach 2:
The second substrate acts as an intermediary structure that integrates multiple circuits and their connections. It provides a centralized platform with redistribution structures that manage the electrical connections between transducers and circuits, simplifying the complexity of managing thousands of individual connections while maintaining close proximity for signal amplification.
3Reliability
If cavities are formed in the membrane for coupling material, then acoustic coupling is improved, but manufacturing complexity and filling reliability are degraded
Solution Approach 1:
The patent extracts the coupling material function from the membrane structure itself. Instead of forming cavities within the membrane to hold coupling material, the coupling material is applied as a separate layer on the membrane surface. This eliminates the complexity of cavity formation and filling while maintaining effective acoustic coupling between the transducers and the external medium.
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 enhances the flexibility and performance of MEMS devices by allowing for uniform membrane thickness, improved coupling efficiency, and efficient integration with signal-processing circuitry, thereby improving the amplification and spatial control of acoustic signals.
Implementation Method 1
a piezoelectric layer (64) formed on the first electrode (62)
Implementation Method 2
The transducer thus functions both as acoustic emitter and as acoustic receiver
Data Source
AI summary
A method for manufacturing a MEMS device includes forming a first solid body by forming, on a substrate, a layered structure having a thickness of a value comprised between 4 and 10 μm, with the layered structure having a first surface that is uniformly flat or planar throughout the extension thereof that faces the substrate. The method further includes forming, on a second surface of the layered structure opposite to the first surface in a direction, multiple transducer devices. The method then proceeds with coupling the first solid body to a supporting structure, and completely removing the substrate to expose said uniformly flat or planar surface.