MEMS Vibration System Transducer Plate Geometry Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for producing piezoelectric micromachined ultrasonic transducers result in channels with wide and flat undercuts, which can lead to structural disadvantages and limitations in precision and geometry.
Innovation Solution
A method involving the creation of a peripheral channel on a silicon substrate, followed by epitaxial growth of a polysilicon layer and the use of a second etch stop layer to control isotropic silicon etching, allowing for precise definition and geometry of the transducer plate, and enabling the production of multiple channels with improved protection against undesired etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a channel is produced completely through the carrier substrate by trenching until the polysilicon layer is reached, then the channel provides structural support and defines the transducer element position, but the channel develops a wide and flat undercut that compromises manufacturing precision
Solution Approach 1:
A first trench mask is applied to define the first channel geometry before etching, establishing precise boundaries that prevent unwanted undercut formation during the trenching process
Solution Approach 2:
A first etch stop layer is deposited at the bottom of the first channel to act as an intermediary barrier, preventing the etching process from creating excessive undercut while still allowing the channel to provide structural support
2Productivity
If multiple second channels are produced close to one another to increase productivity, then the production efficiency improves, but the channels may become unintentionally connected due to lack of protection
Solution Approach 1:
A second etch stop layer is deposited on the outer walls of the second channels to act as a protective intermediary barrier during isotropic silicon etching, preventing adjacent channels from connecting while allowing multiple channels to be produced in close proximity
Solution Approach 2:
The second etch stop layer is selectively deposited only on the outer walls of the second channels, providing localized protection where it is most needed to prevent channel connection, while leaving other areas unaffected
3Ease of manufacture
If the isotropic silicon etching step is performed without additional protection, then the etching process is simple and fast, but the outer walls of the channels are subject to undesired etching that compromises geometry
Solution Approach 1:
The second etch stop layer serves as a protective intermediary coating on the outer walls of the second channels, allowing the isotropic etching step to proceed while preventing undesired etching of the channel walls, thus maintaining both process simplicity and geometric 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
This approach allows for the production of micro-electromechanical vibration systems with precise transducer plate dimensions and geometries, reducing stress peaks and enabling the creation of diverse channel geometries without unintended connections, thus overcoming the structural limitations of previous methods.
Implementation Method 1
a first polysilicon layer grows on the passivation layer and/or the first surface of the carrier substrate. In particular, the first polysilicon layer grows epitaxially on the passivation layer and/or the first surface of the carrier substrate
Implementation Method 2
in a subsequent isotropic silicon etching step, the second channel is enlarged, in particular until the passivation layer is reached
Data Source
AI summary
A method for producing a micro-electromechanical vibration system. A carrier substrate is provided. A peripheral first channel extending from a first surface of the carrier substrate at least partially through the carrier substrate, is produced. A passivation layer is applied to the first surface, and the peripheral first channel is at least partially filled with the passivation layer. A first polysilicon layer grows on the passivation layer and/or the first surface of the carrier substrate. A transducer element of the micro-electromechanical vibration system is arranged on a second surface of the first polysilicon layer. A second channel is produced completely through the carrier substrate in the direction of the transducer element. The second channel extends as far as the passivation layer, so that the vibratable transducer plate of the micro-electromechanical vibration system is produced adjacently to the second channel using the first polysilicon layer.