MEMS Travel Stop Roughness to Reduce Stiction
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Solution Overview
Problem
Microelectromechanical systems (MEMS) devices face stiction issues due to electrostatic and Van der Waals forces, which can cause parts to adhere and become unusable, and traditional methods to mitigate this, such as increasing spring constants or distance, compromise device sensitivity.
Innovation Solution
Increasing surface roughness of travel stop regions in MEMS devices by depositing a polysilicon layer using gaseous hydrochloric acid and subsequent etching to reduce the contact surface area, thereby decreasing stiction forces without affecting sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the distance between MEMS device parts is increased to reduce stiction forces, then stiction is reduced, but device sensitivity decreases
Solution Approach 1:
The patent applies local quality by modifying only the surface properties of specific contact regions (travel stop regions) rather than changing the entire device structure. By increasing surface roughness locally at the travel stop regions where contact occurs, the patent reduces stiction forces without requiring increased distances between all device parts, thereby maintaining sensitivity in non-contact regions.
2Object-affected harmful factors
If spring constants are increased to compensate for stiction forces, then stiction effects are reduced, but device sensitivity decreases
Solution Approach 1:
The patent changes the surface roughness parameter of the travel stop regions to reduce stiction forces. By modifying the surface topology (increasing roughness), the effective contact area is reduced, which decreases stiction forces without requiring changes to spring constants or device geometry, thereby preserving device sensitivity.
3Object-affected harmful factors
If surface roughness is increased to reduce stiction forces, then stiction is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent modifies the surface roughness parameter during the existing polysilicon deposition process by adjusting deposition conditions (such as using gaseous HCl and controlling deposition rate). This approach integrates the surface roughness modification into the standard fabrication process, avoiding the need for separate complex manufacturing steps while achieving reduced stiction forces.
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 approach effectively reduces stiction forces between MEMS device components, maintaining sensitivity by allowing lower spring constants and smaller part distances, thus improving device performance and enabling smaller device sizes.
Implementation Method 1
depositing a polysilicon layer on the insulating layer by reacting a silicon-containing gas, gaseous hydrochloric acid, and hydrogen
Implementation Method 2
etching the polysilicon layer using gaseous hydrochloric acid and hydrogen
Data Source
AI summary
A mechanism for reducing stiction in a MEMS device by decreasing surface area between two surfaces, such as a travel stop and travel stop region, that can come into close contact is provided. Reduction in contact surface area is achieved by increasing surface roughness of the travel stop region. This is achieved by depositing a polysilicon layer over a dielectric layer using gaseous hydrochloric acid as one of the reactants. A subsequent etch back is performed to further increase the roughness. The deposition of polysilicon and subsequent etch back may be repeated one or more times in order to obtain the desired roughness. A final polysilicon layer may then be deposited to achieve a desired thickness. This final polysilicon layer is patterned to form the travel stop regions. The rougher surface decreases the surface area available for contact and, in turn, decreases the area through which stiction can be imparted.