Buried Conduit for Independent Pressure Control in Micromechanical Sensors
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Solution Overview
Problem
Manufacturing micromechanical sensor combinations, such as rotation rate and acceleration sensors, is challenging due to the need for different pressure environments within a single chip, as existing methods require complex processes to achieve and maintain distinct pressures in separate cavities.
Innovation Solution
A buried conduit is created beneath the cap wafer to establish a fluid connection between the encapsulated volume and the environment, allowing for the hermetic closure of the acceleration sensor cavity at a desired low pressure and subsequent adjustment of the rotation rate sensor cavity to a low pressure through a venting process, while maintaining compatibility with existing manufacturing processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cap wafer is used to encapsulate multiple sensor cavities, then hermetic sealing is achieved, but independent pressure control of each cavity becomes difficult
Solution Approach 1:
The cap wafer is segmented into different sealing regions (first sealing region and second sealing region) that can be independently sealed. The first sealing region seals the acceleration sensor cavity hermetically, while the second sealing region remains open to allow pressure adjustment in the rotation rate sensor cavity through the buried conduit. This segmentation enables independent pressure control while maintaining hermetic sealing where needed.
Solution Approach 2:
A buried conduit is introduced as an intermediary element beneath the cap wafer to provide fluid connection between the rotation rate sensor cavity and the environment. This conduit allows pressure adjustment in the rotation rate sensor cavity without compromising the hermetic seal of the acceleration sensor cavity. The conduit acts as a mediator that enables pressure control while maintaining the integrity of the sealed cavity.
2Reliability
If different pressures are required in sensor cavities, then sensor performance is optimized, but manufacturing process complexity increases
Solution Approach 1:
The buried conduit is created and positioned beneath the cap wafer during the manufacturing process before final sealing. This preliminary action allows the rotation rate sensor cavity to be pressure-adjusted through the conduit after the cap wafer is attached, while the acceleration sensor cavity is already hermetically sealed. The preliminary placement of the conduit simplifies the overall manufacturing process by enabling post-assembly pressure control.
Solution Approach 2:
Different regions of the cap wafer are given different sealing qualities: the first sealing region provides hermetic sealing for the acceleration sensor cavity, while the second sealing region is designed to be non-hermetic or selectively sealable to allow pressure adjustment in the rotation rate sensor cavity through the buried conduit. This local differentiation of sealing quality enables independent pressure control while maintaining manufacturing simplicity.
3Reliability
If a getter is used to achieve low pressure in rotation rate sensor, then pressure control is achieved, but the process requires additional manufacturing steps
Solution Approach 1:
The pressure control function is extracted from the cavity interior (where a getter would be placed) and moved to the exterior through the buried conduit. Instead of incorporating a getter inside the rotation rate sensor cavity, the buried conduit provides a direct fluid connection to the environment, allowing pressure adjustment without requiring additional getter materials or activation steps. This extraction simplifies the manufacturing process by eliminating the need for getter incorporation and activation.
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 method enables the economical and robust manufacturing of sensor combinations by allowing for the independent pressure control of cavities within a single chip, enhancing the operational efficiency and reliability of both rotation rate and acceleration sensors.
Implementation Method 1
a buried conduit is provided beneath an edge region of the cap in such a way that said conduit forms a fluid connection between the encapsulated volume and the environment
Data Source
AI summary
A method for manufacturing a micromechanical structure, and a micromechanical structure. The micromechanical structure encompasses a first micromechanical functional layer, made of a first material, that comprises a buried conduit having a first end and a second end; a micromechanical sensor structure having a cap in a second micromechanical functional layer that is disposed above the first micromechanical functional layer; an edge region in the second micromechanical functional layer, such that the edge region surrounds the sensor structure and defines an inner side containing the sensor structure and an outer side facing away from the sensor structure; such that the first end is located on the outer side and the second end on the inner side.