Selective Tungsten Coating for MEMS Sensor Charge Control
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Solution Overview
Problem
Capacitive microelectromechanical systems (MEMS) sensors face issues with surface charge buildup on silicon surfaces, leading to offset signals and reduced performance, as silicon readily forms native oxides prone to charge accumulation.
Innovation Solution
The use of a conductive coating, such as tungsten, selectively applied to non-contacting surfaces of MEMS sensors after release from the substrate, encapsulating the structures and preventing surface charge accumulation while avoiding dielectric layers, thereby enhancing sensor performance and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If silicon surfaces are used in capacitive MEMS sensors, then the sensor structure is simple and manufacturable, but surface charge buildup occurs leading to offset signals and reduced performance
Solution Approach 1:
A conductive coating layer is introduced as an intermediary between the silicon surface and the environment. This coating mediates the interaction by providing a controlled conductive surface that prevents charge buildup while maintaining the underlying silicon structure's manufacturability. The coating acts as a buffer that eliminates the harmful electrostatic effects without requiring changes to the core silicon fabrication process.
Solution Approach 2:
The sensor structure transitions from pure silicon to a composite structure with a conductive coating layer. This composite material combines the manufacturing advantages of silicon with the electrostatic properties of conductive materials, achieving both ease of manufacture and reliability by leveraging the complementary strengths of different materials.
2Reliability
If a conductive coating is applied to silicon surfaces, then surface charge buildup is reduced and sensor performance improves, but the manufacturing process becomes more complex
Solution Approach 1:
The conductive coating is applied in advance during the fabrication process, before the sensor is released and deployed. This preliminary action ensures that the protective coating is already in place to prevent charge buildup from the moment the sensor begins operation, eliminating the need for post-fabrication treatments or complex operational conditioning procedures.
Solution Approach 2:
The conductive coating serves as an intermediary layer that simplifies the overall system by providing a straightforward solution to the charge buildup problem. Rather than requiring complex circuitry or operational adjustments to compensate for offset signals, the coating provides a passive, structural solution that maintains performance stability throughout the sensor's operational life.
3Ease of manufacture
If conventional coating methods are used before releasing silicon structures, then coating application is straightforward, but the coating cannot selectively encapsulate only the desired surfaces
Solution Approach 1:
The silicon structures are released from the substrate before the conductive coating is applied. This preliminary release action exposes only the specific surfaces that require coating, allowing the subsequent coating process to selectively deposit material only on the intended capacitor plates and movable structures, achieving both simplicity and precision.
Solution Approach 2:
The conventional sequence is inverted: instead of coating first then releasing, the process releases first then coats. This inversion allows the coating to be applied only to exposed surfaces, achieving selective encapsulation with a straightforward coating process. The inversion of the process sequence resolves the contradiction between simplicity and precision.
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 conductive coating effectively reduces or eliminates surface charge, improving the accuracy of capacitance measurements and increasing the sensitivity of MEMS sensors like inertial sensors by preventing unwanted charge buildup and maintaining electrical connections.
Implementation Method 1
forming a layer of conductive material on the exterior surface of the first capacitor plate subsequent to releasing the capacitor plate from the substrate
Data Source
AI summary
A capacitive microelectromechanical systems (MEMS) sensor is provided, having conductive coatings on opposing surfaces of capacitive structures. The capacitive structures may be formed of silicon, and the conductive coating is formed of tungsten in some embodiments. The structure is formed in some embodiments by first releasing the silicon structures and then selectively coating them in the conductive material. In some embodiments, the coating may result in encapsulating the capacitive structures.