MEMS Substrate Recesses for Charging Reduction
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Solution Overview
Problem
Dielectric charging in electrostatic RF-MEMS devices leads to shifts and deformations in actuation characteristics, causing reliability issues and premature failure due to trapped charges in the dielectric interposer and substrate, which existing solutions fail to adequately address.
Innovation Solution
The introduction of recesses in the substrate surface area, created by etching away part of the substrate, reduces electrostatic stress and increases the gap between the substrate and moveable electrode, thereby minimizing substrate charging and enhancing the reliability and lifetime of MEMS devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a continuous substrate is used to support the MEMS device, then mechanical strength and structural stability are improved, but substrate charging increases due to electrostatic stress, reducing device reliability
Solution Approach 1:
The substrate is segmented by introducing recesses that divide the continuous substrate into separate regions. These recesses create physical discontinuities in the substrate surface, reducing the area exposed to electrostatic stress and thereby minimizing charge accumulation while maintaining structural support through the remaining substrate regions.
Solution Approach 2:
The substrate is modified locally by creating recesses in specific areas where charge accumulation occurs. The recesses are strategically positioned to reduce electrostatic stress in critical regions while preserving the overall structural integrity of the substrate. This local modification allows the substrate to maintain mechanical strength while reducing parasitic charging in specific locations.
2Volume of moving object
If the gap between the substrate and moveable electrode is reduced to improve device compactness, then device size is reduced, but electrostatic stress on the substrate increases, leading to more severe substrate charging
Solution Approach 1:
The solution addresses the electrostatic stress problem by introducing a vertical dimension modification through recesses in the substrate. Instead of only reducing the horizontal gap distance, the recesses create a localized vertical relief that increases the effective gap distance in specific regions, thereby reducing electrostatic stress without compromising overall device compactness.
3Reliability
If recesses are introduced in the substrate to reduce electrostatic stress and substrate charging, then device reliability is improved, but manufacturing complexity increases due to additional etching steps
Solution Approach 1:
The recess formation process is merged with existing substrate preparation steps in the manufacturing flow. By integrating the recess etching into the standard fabrication sequence and using the same etching equipment and materials, the additional process complexity is minimized while achieving the reliability improvement through reduced substrate charging.
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 recesses effectively reduce substrate charging, as evidenced by extended device lifetime and stable capacitance-voltage (C-V) profiles, preventing the device from getting stuck in actuated positions and improving overall reliability.
Implementation Method 1
the presence of the recess is believed to lower the charging because of a reduced electrostatic stress, e.g. it increases the travelling distance of parasitic current between the first and second conductors via the substrate
Data Source
AI summary
An electrostatically actuatable micro electromechanical device is provided with enhanced reliability and lifetime. The electrostatically actuatable micro electromechanical device comprises: a substrate, a first conductor fixed to the top layer of the substrate, forming a fixed electrode, a second conductor fixed to the top layer of the substrate, and a substrate area. The second conductor is electrically isolated from the first conductor and comprises a moveable portion, suspended at a predetermined distance above the first conductor, the moveable portion forming a moveable electrode which approaches the fixed electrode upon applying an actuation voltage between the first and second conductors. The selected substrate surface area is defined as the orthogonal projection of the moveable portion on the substrate between the first and second conductors. In the substrate surface area at least one recess is provided in at least the top layer of the substrate.