Long-Stroke MEMS Actuator Geometry to Prevent Pull-In
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Solution Overview
Problem
Existing MEMS actuators face limitations in stroke length due to the pull-in phenomenon, where the rotor region becomes unstable and translates uncontrollably along the X-axis, restricting the maximum voltage that can be applied.
Innovation Solution
The proposed MEMS actuator design incorporates a unique geometry with multiple stator regions and front protruding parts, allowing for a longer stroke without increasing the size, by balancing forces and torques and minimizing the superimposition area between the shuttle and stator regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the voltage between stator region and rotor region is increased to increase stroke, then the stroke length increases, but the pull-in phenomenon occurs causing instability
Solution Approach 1:
The stator region is divided into multiple stator regions (first, second, third stator regions) arranged along the Y-axis, and the rotor region is divided into multiple rotor regions (first, second rotor regions). This segmentation allows the electrostatic force to be distributed across multiple interfaces, enabling longer stroke accumulation without concentrating excessive electrostatic force at a single interface that would trigger pull-in instability.
Solution Approach 2:
The patent introduces a third dimension (Y-axis) for arranging multiple stator and rotor regions, in addition to the traditional X-axis stroke direction. By stacking actuation cells along the Y-axis and using bending beams that are compliant along Y but rigid along X, the design achieves long stroke in X-direction through dimensional separation, preventing pull-in while maintaining stability.
2Force
If the overlapping area between stator and rotor regions is increased to enhance electrostatic force, then the actuation force increases, but the pull-in phenomenon is more likely to occur
Solution Approach 1:
The total overlapping area is segmented into multiple smaller overlapping interfaces between corresponding stator and rotor regions. Each interface generates moderate electrostatic force, and the forces accumulate along the Y-axis to produce the required total actuation force, preventing any single interface from experiencing excessive force that would cause pull-in.
Solution Approach 2:
The bending beams are designed with specific local properties: rigid along the X-axis to prevent lateral displacement and pull-in, but compliant along the Y-axis to allow vertical movement for stroke accumulation. This local quality differentiation enables force generation without triggering instability.
3Length of moving object
If the number of stator and rotor regions is increased to achieve longer stroke, then the stroke length increases, but the device complexity increases
Solution Approach 1:
Multiple stator regions and rotor regions are merged into integrated structures where corresponding regions are mechanically coupled through bending beams. The first and second rotor regions are merged with the bridge region to form a unified movable structure, reducing the number of independent components while achieving long stroke through coordinated movement of integrated units.
Solution Approach 2:
The bending beams serve multiple functions: they provide mechanical coupling between stator and rotor regions, enable compliance along Y-axis for stroke accumulation, maintain rigidity along X-axis to prevent pull-in, and transmit electrostatic forces from multiple interfaces to the rotor regions. This multi-functionality reduces the need for additional specialized components.
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 effectively increases the stroke length of the MEMS actuator while maintaining stability and avoiding the pull-in phenomenon, even at higher voltages, thus enhancing the actuator's performance and reliability.
Implementation Method 1
the rotor region 3 is subject to an elastic return force along Y (represented by the elastic constant k travel indicated in Figure 2), which is due to the stiffness, along the Y axis, of the bending beams 11
Implementation Method 2
by applying a voltage between the stator region 2 and the rotor region 3, an electrostatic force is generated along the Y axis, which tends to translate the rotor region 3 along the Y axis towards the stator region 2
Implementation Method 3
the rotor region 3 is subject to an electrostatic force along the X axis, which induces a decrease in stiffness along the X axis as the voltage between the rotor region 2 and the stator region 3 increases
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
MEMS actuator (20) including: a substrate (21); a first and a second semiconductive layer (31,32); a frame (27) including transverse regions (62) formed by the second semiconductive layer (32), elongated parallel to a first direction (X) and offset along a second direction (Y), the frame (27) being movable parallel to the second direction (Y). The MEMS actuator (20) includes, for each transverse region (62): corresponding front rotor regions (65), which are fixed to the transverse region (62) and are suspended above the substrate (21); a first and a second stator region (70,72), which are formed by the first semiconductive layer (31) in such a way that, when the frame (27) is in rest position, the transverse region (62) is laterally offset with respect to the first and the second stator regions (70,72) and a first front rotor region (65') partially faces the first stator region (70), and in such a way that, during a translation of the frame (27) along the second direction (Y), the first and/or a second front rotor region (65', 65") at least partially face the second stator region (72), when the transverse region (62) begins to superimpose on the first stator region (70).