MEMS Sensor Cavities with Sequential Pressure Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge lies in manufacturing micromechanical components with two sensor cavities that require different internal pressures, where the existing methods face issues with gas diffusion and anti-stiction coating degradation, leading to potential failure of rotation rate sensors due to pressure changes and adhesion problems.
Innovation Solution
A method involving sequential opening and closing of access holes in MEMS and cap wafers to set defined pressures in each sensor cavity, using gas exchange and anti-stick layer application post-bonding to prevent gas diffusion and maintain anti-stiction properties, allowing for flexible processing and efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard bonding processes (glass frit bonding or eutectic bonding) are carried out at elevated temperatures higher than 400°C, then hermetic sealing of the chip is achieved, but ASC molecules evaporate from the silicon surfaces and increase the cavity internal pressure
Solution Approach 1:
The anti-stiction coating is applied after wafer bonding rather than before, reversing the conventional sequence. This preliminary action (in terms of process timing) ensures the ASC is deposited on clean surfaces at low temperature, preventing evaporation during bonding while maintaining anti-stiction functionality
Solution Approach 2:
The conventional process sequence is inverted: instead of applying ASC before bonding and risking evaporation, the patent applies ASC after bonding. This inversion resolves the contradiction by eliminating the temperature exposure that causes ASC degradation while preserving both hermetic sealing and anti-stiction properties
2Productivity
If a completely flat cap wafer is used for small cavity volumes, then integration density is improved, but particle density of ASC molecules in the gaseous phase increases, worsening anti-stick properties
Solution Approach 1:
By applying the anti-stiction coating after bonding when the cavity is already sealed, the process prevents ASC molecules from evaporating into the small cavity volume. The preliminary sealing action creates a controlled environment that preserves coating integrity despite high integration density
Solution Approach 2:
The hermetically sealed cavity creates an inert, controlled environment that prevents ASC molecule evaporation and degradation. This inert atmosphere maintains the anti-stiction properties even in small cavity volumes with high integration density
3Adaptability or versatility
If access holes are opened and closed sequentially for different pressure cavities, then manufacturing flexibility is improved, but process complexity increases
Solution Approach 1:
The chip is divided into separate cavity regions with independent access holes, allowing each cavity to be processed independently. This segmentation enables sequential opening and closing of access holes for different pressure requirements, providing manufacturing flexibility through modular cavity management
Solution Approach 2:
Temporary access holes serve as intermediaries that allow pressure adjustment and gas evacuation during manufacturing. These intermediary structures enable flexible pressure control in each cavity while being removed or sealed in the final product, adding functionality during manufacturing without compromising the final device
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 ensures stable internal pressures in both sensor cavities, preventing gas diffusion and maintaining anti-stiction properties, thereby enhancing the reliability and efficiency of micromechanical components, particularly in consumer and automotive electronics.
Implementation Method 1
a getter is chemically activated via a temperature step and effectuates a greatly reduced internal pressure in the cavity of the rotation rate sensor
Implementation Method 2
The ASC is typically applied prior to the wafer bonding, and forms a Teflon-like monolayer on the silicon surfaces. The undesirable adhesion forces between movable structures and mechanical stops may be greatly reduced in this way
Implementation Method 3
a so-called laser reseal, in which a surrounding area around an access hole, close to the surface, is locally melted by localized heat input with the aid of a laser
Data Source
AI summary
A method for manufacturing a micromechanical component, including: providing a MEMS wafer and a cap wafer; forming micromechanical structures in the MEMS wafer for at least two sensors; hermetically sealing the MEMS wafer with the cap wafer; forming a first access hole in a first cavity of a first sensor; introducing a defined first pressure into the cavity of the first sensor via the first access hole; closing the first access hole; forming a second access hole in a second cavity of a second sensor; introducing a defined second pressure into the cavity of the second sensor via the second access hole; and closing the second access hole.