MEMS Accelerometer Oxide Layer for Reduced Electrostatic Charge
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Solution Overview
Problem
MEMS devices, such as accelerometers, face performance degradation due to electrostatic charges formed between components with different materials, which increases cavity volume when trying to mitigate these charges.
Innovation Solution
A method involving multiple mask formations and etching processes on a substrate to form an oxide layer, selectively removing it around bumpstop features, and fusion bonding a silicon wafer to reduce electrostatic charges without increasing cavity volume.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the distance between the proof mass and UCAV oxide layer is increased to eliminate contact and reduce electrostatic charges, then electrostatic charge is reduced, but cavity volume increases which adversely impacts accelerometer performance
Solution Approach 1:
The patent applies local quality by differentiating the treatment of the oxide layer in different regions: the oxide layer is retained on the UCAV to prevent electrostatic charge accumulation, while selective etching removes oxide from specific areas to prevent stiction. This localized differentiation allows the system to simultaneously address electrostatic charge and stiction issues without increasing cavity volume.
Solution Approach 2:
The patent extracts the harmful oxide layer from specific regions where it causes stiction problems, while preserving it in regions where it prevents electrostatic charge. The selective etching process removes oxide material from the proof mass surface in contact areas, while maintaining the oxide layer on the UCAV, thereby separating the harmful effects from the beneficial effects of the oxide layer.
2Object-generated harmful factors
If multiple mask formations and selective etching processes are implemented to selectively remove oxide layer, then stiction is prevented and electrostatic charge is reduced, but manufacturing process complexity increases
Solution Approach 1:
The patent segments the oxide layer removal process into multiple stages using different masks: a first mask for initial pattern definition, a second mask for selective oxide removal, and a third mask for final precision etching. This segmentation allows complex selective removal patterns to be achieved through simpler, sequential steps rather than attempting to create the entire pattern in a single complex etching step.
Solution Approach 2:
The patent performs preliminary actions by forming multiple masks and performing selective etching steps before the final device assembly. The oxide layer is selectively removed in advance from specific regions, and the proof mass is pre-formed with the correct surface characteristics, preventing stiction issues before they can manifest during device operation or assembly.
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
The method effectively reduces electrostatic charges and prevents stiction between wafers while maintaining performance by retaining the oxide layer on bumpstop features, thus minimizing cavity volume.
Implementation Method 1
forming an oxide layer on the first surface of the substrate
Implementation Method 2
fusion bonding a silicon wafer to a third portion of the first surface of the substrate that is covered by the oxide layer
Implementation Method 3
electrostatic charges may form from contact between two components with different materials
Data Source
AI summary
A method includes forming a first mask on a first portion of a first surface of a substrate, forming a second mask on the first mask and further forming the second mask on a second portion of the first surface of the substrate, and etching an exposed portion of the first surface of the substrate and removing the second mask. According to some embodiments, an exposed portion of the first surface of the substrate is etched and the first mask is removed. An oxide layer is formed on the first surface of the substrate. A third mask is formed on the oxide layer except for a portion of the oxide layer corresponding to bumpstop features. The portion of the oxide layer corresponding to the bumpstop features is removed. An exposed portion of the first surface of the substrate is etched and the third mask is removed.