CMUT Microarray BCB Bonding for Precision Fabrication
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Solution Overview
Problem
Existing processes for fabricating capacitive micromachined ultrasonic transducers (CMUTs) require precise manufacturing tolerances, limiting the widespread adoption of CMUT sensor arrays in commercial applications.
Innovation Solution
The use of benzocyclobutene (BCB) as a structural component and adhesive in the manufacturing of CMUTs, allowing for the creation of three-dimensional microarray modules with improved reliability and simplified production methods, including partial curing and full curing at reduced temperatures to minimize heat stress and achieve precise bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional CMUT fabrication processes are used, then manufacturing precision is maintained, but device complexity and production difficulty increase
Solution Approach 1:
The patent combines multiple functions into the BCB layer: it serves as both the structural support layer and the adhesive bonding layer between wafers. This merging eliminates the need for separate structural and adhesive layers, simplifying the fabrication process while maintaining manufacturing precision.
Solution Approach 2:
The BCB material is used universally for multiple purposes: as a structural component providing mechanical support, as an adhesive bonding agent joining wafers, and as a material that can be selectively cured to enable precise assembly. This multi-functionality reduces the number of different materials and processes needed.
2Strength
If conventional bonding processes are used, then bonding strength is achieved, but heat stress increases
Solution Approach 1:
The BCB layer is partially cured before wafer assembly, creating a tacky state that enables bonding at lower temperatures. This preliminary curing action allows the adhesive to be activated before the final high-temperature cure, reducing the peak heat stress experienced during assembly.
Solution Approach 2:
The curing process is divided into multiple stages: initial partial curing to enable bonding, assembly, then final complete curing. This periodic curing approach allows bonding to occur at lower temperatures while still achieving full bonding strength through the subsequent complete cure cycle.
3Reliability
If precise manufacturing tolerances are required, then manufacturing reliability improves, but production cost and complexity increase
Solution Approach 1:
The patent changes the curing parameter of the BCB layer from a single-state to a multi-state system (partially cured vs. fully cured). This parameter change enables the material to exhibit different properties at different stages: tacky and conformable when partially cured for easy assembly, then rigid and strong when fully cured for reliable operation.
Solution Approach 2:
The BCB layer functions as a composite material system combining organic polymer properties with controlled cross-linking. The partial curing creates a composite state with both uncured (flexible, adhesive) and cured (rigid, strong) regions, enabling both ease of manufacture and high reliability.
4Shape
If multi-layer wafer assembly is performed, then three-dimensional structure is achieved, but alignment precision becomes more difficult to maintain
Solution Approach 1:
The BCB layer is applied and partially cured before final wafer assembly, creating a self-aligning adhesive interface. This preliminary adhesive layer allows components to be positioned and held in place before final bonding, maintaining alignment precision during the multi-layer assembly process.
Solution Approach 2:
The partially cured BCB layer acts as an intermediary between wafers during assembly, providing a conformable, self-adjusting bonding interface that accommodates minor misalignments while maintaining precise final positioning. The tacky state of partially cured BCB allows for self-correction of alignment errors.
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 enables the reliable and efficient manufacturing of CMUT microarray modules with precise geometries, such as hyperbolic paraboloid configurations, suitable for various sensor applications, including vehicle blind-spot monitoring and autonomous driving, by providing improved bonding strength and reduced thermal stress.
Implementation Method 1
allowing for improved bonding and reduced heat stress through partial curing and full curing at lower temperatures
Implementation Method 2
incorporates benzocyclobutene (BCB) as a structural component... The BCB layers are then fully cured and bonded to each other
Data Source
AI summary
A sensor assembly including one or more capacitive micromachined ultrasonic transducer (CMUT) microarray modules which are provided with a number of individual transducers. The transducers include silicon device and backing layers joined by a fused benzocyclobutene (BCB) layer which defines the transducer air gap, and which are arranged to simulate or orient individual transducers in a hyperbolic paraboloid geometry. The transducers/sensor are arranged in a matrix and are activatable to emit and receive reflected beam signals at a frequency of between about 100 to 170 kHz.