MEMS Electric Field Sensor with Resonant Torsional Shutter
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Solution Overview
Problem
Existing MEMS electric field sensors using torsional shutters face challenges in manufacturing complexity, limited torsional angle, and inefficient bidirectional electric field sensing due to the need for bottom electrode-driven torsional shutter mechanisms.
Innovation Solution
A MEMS electric field sensor is developed using a comb drive actuator with a torsional shutter that is resonantly torsionally driven without a bottom electrode, simplifying the manufacturing process and enabling bidirectional sensing by utilizing differential sensing with two sensing electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a bottom electrode is used to drive the torsional shutter, then the shutter can be driven, but the manufacturing process becomes complicated requiring wafer alignment and anode bonding
Solution Approach 1:
The invention removes the bottom electrode from the device structure entirely. Instead of using a bottom electrode to drive the torsional shutter, the patent employs a top electrode configuration where the driving electrode is positioned above the shutter. This extraction of the problematic bottom electrode eliminates the need for complex wafer alignment and anode bonding processes, directly resolving the manufacturing complexity issue while maintaining the essential driving function.
Solution Approach 2:
The invention inverts the traditional electrode configuration by placing the driving electrode on top of the shutter rather than at the bottom. This inversion changes the driving mechanism from bottom-up actuation to top-down actuation, eliminating the need for bottom electrode integration and its associated complex manufacturing steps while achieving the same torsional shutter driving effect.
2Adaptability or versatility
If a bottom electrode is present, then the shutter can be driven, but the torsional angle is limited and bidirectional sensing is restricted
Solution Approach 1:
By removing the bottom electrode that constrained the shutter's motion, the invention enables the shutter to rotate freely in both clockwise and counter-clockwise directions. The top electrode configuration provides driving force without physically blocking the shutter's path, thereby achieving unlimited torsional angle and bidirectional sensing capability that was previously restricted by the bottom electrode structure.
3Reliability
If a shutter designed for lateral and vertical motions is used, then multiple resonance modes are achieved, but the structure is inappropriate for torsional resonant driving
Solution Approach 1:
The invention modifies the shutter structure to have specific local characteristics optimized for torsional motion. The shutter is designed with a central pivot point and distributed mass configuration that creates a moment of inertia optimized for rotational acceleration. This local structural optimization ensures efficient torsional resonant driving while maintaining simplicity, rather than using a complex multi-mode structure designed for lateral and vertical motions.
4Productivity
If wafer alignment and anode bonding are performed, then the bottom electrode can be integrated, but manufacturing time and cost increase
Solution Approach 1:
By eliminating the bottom electrode from the design, the invention removes the need for wafer alignment and anode bonding processes. These complex steps are replaced with a simpler top electrode fabrication approach that can be integrated using standard semiconductor manufacturing techniques, significantly improving manufacturing efficiency and reducing production time and cost.
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 solution reduces manufacturing costs and enhances productivity by simplifying the manufacturing process, allows for efficient resonant torsional motion of the shutter, and enables bidirectional electric field sensing without limitations on the torsional angle.
Implementation Method 1
a comb drive actuator on the device layer, the comb drive actuator including a sensing electrode and a torsional shutter configured to be resonant torsionally driven
Implementation Method 2
a field mill electric field sensor configured to sense a change in electric charges induced in a sensing electrode according to a motion of a grounded shutter
Data Source
AI summary
A micro-electromechanical system (MEMS) electric field sensor using a resonant torsional shutter and a method of manufacturing the MEMS electric field sensor are described. A method of manufacturing a micro-electromechanical system (MEMS) electric field sensor according an embodiment includes: forming a metal layer on a wafer having a handle layer, a buried oxide layer arranged on the handle layer, and a device layer arranged on the buried oxide layer; patterning the metal layer to form a plurality of electrical pads thereon, forming a comb drive actuator on the device layer, the comb drive actuator including a sensing electrode and a torsional shutter configured to be resonant torsionally driven; forming a driving space of the torsional shutter in the handle layer; and etching and releasing the buried oxide layer.