MEMS Inertial Sensor Trenches for Low Parasitic Capacitance
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Solution Overview
Problem
Inertial sensors suffer from reduced sensitivity due to parasitic capacitances arising from the substrate underneath sense capacitors, leading to noise interference that masks the signals generated by the sense capacitors, particularly in MEMS gyroscopes and accelerometers.
Innovation Solution
Forming localized regions of thick dielectric material inside trenches in the substrate under sense capacitors, filled partially or completely with dielectric materials like silicon oxide, to increase vertical separation and reduce parasitic capacitance, utilizing lateral oxidation to expedite dielectric growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the substrate is placed close to the sense capacitor, then the device structure is simple and manufacturing is easier, but parasitic capacitance increases causing noise interference
Solution Approach 1:
The patent introduces trenches that extend vertically into the substrate, transforming a two-dimensional proximity problem into a three-dimensional solution. By creating deep vertical trenches beneath the sense capacitor and filling them with dielectric material, the design increases the vertical separation distance between the capacitor and substrate, thereby reducing parasitic capacitance while maintaining a compact lateral footprint.
Solution Approach 2:
The patent introduces a dielectric material as an intermediary substance filled within the trenches. This dielectric layer acts as a mediator between the sense capacitor and the substrate, providing electrical isolation and reducing parasitic capacitance coupling while allowing the physical structure to remain compact.
2Object-affected harmful factors
If the vertical separation between sense capacitor and substrate is increased, then parasitic capacitance is reduced, but device structure becomes more complex
Solution Approach 1:
The patent segments the substrate structure by introducing localized trenches only in specific regions beneath the sense capacitor, rather than uniformly increasing separation across the entire device. This segmented approach reduces parasitic capacitance where needed while maintaining structural simplicity in other areas.
Solution Approach 2:
The patent applies the thick dielectric isolation structure locally only beneath the sense capacitor where parasitic capacitance is most problematic, rather than uniformly throughout the entire device. This localized quality change reduces parasitic capacitance at the critical interface while minimizing overall device complexity.
3Productivity
If lateral oxidation is used to form dielectric material, then dielectric growth is accelerated, but manufacturing process becomes more complex
Solution Approach 1:
The patent replaces conventional thermal oxidation processes with lateral oxidation, which proceeds faster and more efficiently. This substitution of the oxidation mechanism accelerates dielectric material formation while the trench geometry naturally guides the lateral growth direction, simplifying process control despite the advanced oxidation method.
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
Reduces noise at the detection circuit, enhancing the sensitivity of MEMS inertial sensors to detect acceleration and angular rates by minimizing parasitic capacitance, while maintaining cost-effectiveness through efficient manufacturing processes.
Implementation Method 1
parasitic capacitances arising from the substrate underneath sense capacitors
Implementation Method 2
Fabrication of these trenches may involve lateral oxidation, whereby columns of semiconductor material are oxidized
Data Source
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AI summary
Microelectromechanical system (MEMS) inertial sensors exhibiting reduced parasitic capacitance are described. The reduction in the parasitic capacitance may be achieved by forming localized regions of thick dielectric material. These localized regions may be formed inside trenches. Formation of trenches enables an increase in the vertical separation between a sense capacitor and the substrate, thereby reducing the parasitic capacitance in this region. The stationary electrode of the sense capacitor may be placed between the proof mass and the trench. The trench may be filled with a dielectric material. Part of the trench may be filled with air, in some circumstances, thereby further reducing the parasitic capacitance. These MEMS inertial sensors may serve, among other types of inertial sensors, as accelerometers and/or gyroscopes. Fabrication of these trenches may involve lateral oxidation, whereby columns of semiconductor material are oxidized.