CMUT Cavity Diameter Control via Segmented Sacrificial Layers
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Solution Overview
Problem
Existing methods for producing capacitive micromachined ultrasonic transducers face challenges in accurately controlling the cavity diameter and vibration membrane thickness, leading to reduced design flexibility and potential performance variations due to the trade-off between sacrificial layer thickness and membrane thickness.
Innovation Solution
A method involving a two-layer sacrificial layer structure, where the second sacrificial layer is patterned to determine the cavity shape and then removed through an insulating layer opening, allowing for selective etching to form the cavity, enabling precise control of cavity diameter and independent determination of membrane thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the thickness of the sacrificial layer is increased to increase the cavity height and transmission sound pressure, then the transmission sound pressure is improved, but the thickness of the vibration membrane must be increased accordingly, reducing design flexibility
Solution Approach 1:
The sacrificial layer is divided into two separate layers: a first sacrificial layer that determines the cavity height and a second sacrificial layer that determines the cavity diameter. This segmentation allows independent control of cavity dimensions without requiring the vibration membrane to cover the entire combined height, thus resolving the trade-off between transmission sound pressure and design flexibility.
2Power
If the height of the cavity is increased to increase the vibration membrane displacement and transmission sound pressure, then the transmission sound pressure is improved, but the thickness of the membrane support portion must be sufficiently secured, requiring increased membrane thickness
Solution Approach 1:
By segmenting the sacrificial layer into two functional layers, the cavity height is determined by the first sacrificial layer while the cavity diameter is determined by the second sacrificial layer. This allows the vibration membrane thickness to be optimized for covering only the second sacrificial layer's diameter, rather than the combined height, enabling precise thickness control while maintaining high cavity height for sound pressure.
3Manufacturing precision
If the thickness of the sacrificial layer is increased to control transducer characteristics, then the cavity height is improved, but the trade-off relationship with membrane thickness makes it difficult to reduce membrane thickness
Solution Approach 1:
The sacrificial layer is segmented into two independent layers with distinct functions: the first sacrificial layer controls cavity height through its thickness, while the second sacrificial layer controls cavity diameter through its lateral dimensions. This segmentation breaks the direct trade-off relationship, allowing the vibration membrane thickness to be determined by the second layer's diameter rather than the first layer's height, thereby simplifying the design relationship and enabling independent optimization of both parameters.
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 increased design freedom by accurately controlling the cavity diameter and height while reducing the membrane thickness, enhancing the transducer's performance and reliability.
Implementation Method 1
a second sacrificial layer removing step of removing the second sacrificial layer by etching through an opening formed in the insulating layer
Data Source
AI summary
In a method for producing a capacitive micromachined ultrasonic transducer having a cell of a structure having a first electrode and a vibration membrane containing a second electrode provided with a cavity interposed between the first electrode and the second electrode, a first sacrificial layer is formed on the first electrode. A second sacrificial layer is formed on a portion corresponding to a part of a cavity is formed on the first sacrificial layer, and then an insulating layer configuring a part of the vibration membrane is formed on the second sacrificial layer. The second sacrificial layer is removed by etching through an opening formed in the insulating layer, and then a part of the first sacrificial layer is removed.