Switchable Capacitor With Reference Top Plate for RF MEMS Stiction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional RF MEMS switches face issues with high pull-down voltage leading to solid dielectric breakdown and excessive charging, causing the flexible electrode to stick in the closed position, which affects the switch's ability to return to the deactivated state.
Innovation Solution
A switchable capacitor design featuring a solid dielectric, a pair of electrodes, and a top plate connected to a reference potential, with apertures in the top plate to shield charges and a discharge path to prevent residual charges from affecting the activation voltage, allowing the flexible electrode to return to its original position when the switch is deactivated.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pull-down voltage on the second, flexible electrode is increased for high power applications, then the switch can remain deactivated at higher RF signal levels, but the electric field strength in the solid dielectric increases causing dielectric breakdown or excessive charging leading to stiction
Solution Approach 1:
A top plate is introduced as an intermediary component between the second flexible electrode and the solid dielectric. This top plate is connected to a reference potential and provides a discharge path for charges, acting as a mediator that protects the solid dielectric from excessive electric field strength while maintaining the necessary pull-down voltage on the flexible electrode for reliable switching operation
Solution Approach 2:
The top plate is provided with apertures that create local variations in the structure. These apertures allow the flexible electrode to contact the solid dielectric at specific locations while the top plate shields other areas, creating localized charge discharge paths and preventing excessive charging in critical regions of the solid dielectric
2Strength
If the solid dielectric is charged excessively due to high pull-down voltage, then the flexible electrode sticks in the closed position, but the switch cannot return to the deactivated state
Solution Approach 1:
The top plate serves as a charge reservoir and discharge path intermediary. When the flexible electrode contacts the solid dielectric, charges are transferred to the top plate rather than accumulating in the solid dielectric. The top plate connected to reference potential provides a controlled discharge path, preventing excessive charging that would cause stiction and ensuring the switch can return to the deactivated state
Solution Approach 2:
The top plate temporarily stores (discards) charges during the activated state when the flexible electrode contacts the solid dielectric, and then releases (recovers) them through the discharge path to the reference potential when the switch returns to the deactivated state, maintaining switch reversibility
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 design reduces the voltage across the dielectric, minimizing the risk of dielectric breakdown and stiction, ensuring reliable switching between activated and deactivated states while maintaining high capacitance when closed.
Implementation Method 1
The switch includes a switchable voltage source coupled between the top and bottom electrode for producing a switchable electrostatic force between the first electrode and to second electrodes
Implementation Method 2
the second, flexible one of the electrodes being suspended over the solid dielectric when the switchable capacitor is in an de-activated state
Data Source
Figure 1
Figure 2A~2B
Figure 2C
AI summary
A switchable capacitor having: a dielectric; a pair of electrodes, a first one of the electrodes having the dielectric thereon and a second, flexible one of the electrodes being suspended over the dielectric when the switchable capacitor is in an de-activated state; and top plate disposed between the dielectric and the second, flexible electrode and connected to a reference potential. When the switchable capacitor is electrostatically driven to an activated state, the second one of the electrodes contacts the top plate and when the switchable capacitor is returned to the de-activated state, charge on the top plate is discharged to the reference potential.