Angular Vertical Comb Actuator for MEMS Mirror Tilt Control
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Solution Overview
Problem
Conventional MEMS devices face challenges in achieving high tilt angles and low actuation voltages, particularly in the switching axis, due to pull-in instability and complex electrode configurations, and require precise sub-micron alignment of comb fingers for vertical comb drives.
Innovation Solution
The use of an angular vertical comb drive with interleaving rotor and stator combs at an acute angle, processed in the same layer to reduce alignment complexity, and a hybrid actuator combining angular vertical comb drive for tilt and parallel plate electro-static actuator for roll, allowing for self-alignment and reduced voltage requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If parallel plate electro-static electrodes are used for both tilt and roll movements, then the device can achieve biaxial control, but the actuation voltage is high and the angular range is limited due to pull-in instability
Solution Approach 1:
The device segments the actuation mechanism into two distinct types: parallel plate electrodes for roll control and vertical comb drives for tilt control. This segmentation allows each actuator type to operate in its optimal performance range, with the comb drive avoiding pull-in instability in the tilt axis while the parallel plate provides roll control.
Solution Approach 2:
The patent transitions from two-dimensional parallel plate electrodes to three-dimensional vertical comb structures for the tilt actuator. The comb fingers extend vertically along the tilt axis, creating an electrostatic field that generates torque without the pull-in instability limitation of parallel plates, enabling larger angular ranges.
2Reliability
If conventional vertical comb drives are used for tilt control, then the actuation voltage is reduced and tilt angle is improved, but sub-micron comb finger alignment accuracy is required
Solution Approach 1:
The patent performs preliminary alignment actions during the fabrication process by establishing precise reference structures and alignment marks before comb finger formation. The stator comb is fabricated first as a reference, and the rotor comb is then aligned to it using self-alignment techniques and photolithographic registration marks, ensuring sub-micron accuracy is achieved through process design rather than post-fabrication adjustment.
Solution Approach 2:
The device employs self-aligning features where the comb fingers are designed to automatically position themselves relative to each other during assembly. The stator and rotor combs include alignment protrusions and recesses that guide precise positioning, and the electrostatic field distribution naturally favors the aligned configuration, providing self-correcting alignment during operation.
3Power
If staggered vertical comb drive with multi-layer fabrication is used, then the actuator power is increased, but the device processing complexity is considerably increased and device yield is negatively affected
Solution Approach 1:
The patent merges the stator and rotor comb fabrication into a single-layer process where both comb structures are formed in the same silicon layer. The comb fingers are patterned and etched simultaneously, eliminating the need for separate wafer fabrication and assembly steps. This consolidation maintains the high actuator power of vertical comb drives while dramatically simplifying the fabrication process and improving device yield.
Solution Approach 2:
The single silicon layer serves multiple functions: it forms both the stator comb structure and the rotor comb structure, provides mechanical support for both components, and contains all alignment features. This multi-functional design eliminates the need for separate layers and assembly operations, reducing process complexity while maintaining actuator performance.
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 configuration enables a larger tilt angle and lower actuation voltage while simplifying the fabrication process and improving yield by eliminating the need for post-fabrication alignment and reducing the complexity of electrode configurations.
Implementation Method 1
When a voltage is applied between them, a torque is developed from the electrostatic field causing the movable comb to rotate about supporting hinges toward the stationary comb
Implementation Method 2
the electrostatic torque is balanced by the restoring mechanical torque of the hinge springs
Data Source
AI summary
A vertical comb electro-static actuator for rotating a micro-electro-mechanical micro-mirror device about a tilt axis or rotation. The rotor comb fingers of the comb drive extend from a sub-frame of the micro-mirror, which includes a prestressed layer for bending the rotor comb fingers at an angle to the substrate and mirrored platform, enabling the platform, the hinges, the rotor comb fingers and the stator comb fingers to be formed in the same layer, i.e. the same etching step.