Staggered Vertical Comb Drive Fabrication via Self-Aligned Etching
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Solution Overview
Problem
Existing methods for fabricating staggered vertical comb drive (SVCD) actuators face challenges with stringent alignment requirements, leading to impaired actuator performance and reliability due to electrical breakdown and mechanical interference, and previous solutions either limit rotation angle or are sensitive to dust particles or oxide layer drift.
Innovation Solution
A method involving a silicon-on-isolator wafer with a two-layer mask to etch and vertically shorten comb fingers, allowing for self-aligned fabrication with relaxed alignment tolerances, enabling greater control over finger alignment and actuation range without electrical shorting or oxide layer issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If separate wafers are etched and bonded to form stator and rotor comb assemblies, then the fabrication process can be performed using standard semiconductor processes, but the alignment between the two wafers is imprecise (approximately 3 microns) which impairs actuator performance and reliability
Solution Approach 1:
The patent merges the fabrication of stator and rotor comb assemblies into a single wafer, eliminating the need for separate wafer bonding and alignment processes. Both comb structures are formed simultaneously in the same device layer through a unified etching process, ensuring precise alignment while maintaining compatibility with standard semiconductor fabrication processes
Solution Approach 2:
The patent introduces vertical dimensionality by forming one comb structure extending from the front surface and another comb structure extending from the back surface of the same wafer. This three-dimensional arrangement allows both combs to be self-aligned through the wafer thickness, achieving precise alignment without requiring complex lateral alignment procedures
2Manufacturing precision
If self-aligned manufacturing is used with both rotor and stator fabricated from the same device layer, then alignment precision is improved, but the technique is sensitive to dust particles and oxide layer drift
Solution Approach 1:
The patent segments the two comb structures into separate front and back surface formations, with each comb etched independently through its respective surface. This segmentation allows the use of separate masking and etching processes for each comb, reducing sensitivity to dust particles that might affect a single monolithic structure, while maintaining precise alignment through the wafer's geometric constraints
3Reliability
If rotor and stator are aligned laterally to approximately one micron or better, then actuator performance is improved, but the alignment process becomes considerably more complex
Solution Approach 1:
The patent implements self-alignment where the wafer itself serves as the alignment reference for both comb structures. The front and back surface combs automatically align through the wafer's inherent geometric constraints and thickness, eliminating the need for complex external alignment procedures while achieving sub-micron alignment precision and improving actuator reliability
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 approach provides precise lateral and vertical alignment of rotor and stator fingers, enhancing the actuation range and reliability of SVCD devices while maintaining low operating voltages and reducing sensitivity to environmental factors.
Implementation Method 1
When a voltage is applied between them, the movable comb (rotor) is drawn toward the stationary comb (stator) until the teeth of the stator and rotor overlap and the electrostatic field energy is minimized
Implementation Method 2
a) providing a wafer comprising a device layer, b) etching the device layer to form therein two comb structures comprising a first set of fingers interdigited with a second set of fingers
Data Source
AI summary
The invention relates to a method of fabrication of staggered vertical comb drive actuators with relaxed lateral alignment tolerances. A device layer of a wafer is first etched from a front side using a self-aligned two-layer mask to define interdigited fingers of both moving and stationary combs. A second etch step is used for vertically thinning one of the two sets of fingers by selectively removing their top portions. The front side of the wafer is then bonded to a carrier wafer. The wafer is then selectively etched from the back side of the device layer so as to remove lower portions of the second set of fingers, thereby forming interdigited moving and stationary combs having vertically offset fingers.