Capacitive Micromechanical Sensor Structure for High Sensitivity
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Solution Overview
Problem
Existing micromechanical accelerometers face challenges in achieving high sensitivity and linearity while minimizing sticking issues and pull-in effects, especially with small finger side gaps, which complicates manufacturing and testing.
Innovation Solution
A capacitive micromechanical sensor structure that combines the advantages of closing gap and linear combs by varying the finger overlap length and fingertip gap, allowing for tunable sensitivity and linearity, and incorporating stopper bumps to prevent sticking and pull-in effects, enabling higher measurement voltage and robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If closing gap combs are used to increase sensitivity, then larger signals are produced, but the signal becomes very nonlinear and sticking issues occur with small finger side gaps
Solution Approach 1:
The sensor structure is divided into two independent comb structures: a linear comb for primary sensitivity and a closing gap comb for signal enhancement. Each comb operates independently with its own fingers and support structure, allowing the linear comb to maintain reliability while the closing gap comb provides additional sensitivity without causing sticking issues
Solution Approach 2:
The patent combines both linear comb and closing gap comb structures into a single sensor device, merging their advantages. The linear comb provides linearity and reliability, while the closing gap comb contributes to higher sensitivity. The two combs are electrically connected in parallel to combine their output signals
2Reliability
If linear combs are used to minimize sticking and maintain linearity, then reliability is improved, but sensitivity is reduced with the same displacement
Solution Approach 1:
The patent merges linear comb and closing gap comb structures to simultaneously achieve high sensitivity and reliability. The linear comb maintains sticking resistance and linearity, while the closing gap comb enhances sensitivity. Together they provide both desired characteristics that neither could achieve alone
Solution Approach 2:
The patent optimizes geometric parameters including finger width, gap sizes, and number of fingers in both comb structures. By carefully selecting these parameters, the closing gap comb achieves high sensitivity without excessive electrical forces that would cause sticking, while the linear comb maintains its reliability advantages
3Measurement precision
If small finger side gaps are used in closing gap combs to increase sensitivity, then larger signals are produced, but manufacturing complexity increases and reliability issues arise
Solution Approach 1:
The sensor is segmented into two comb structures with different gap requirements. The closing gap comb uses small gaps only between opposing fingers for sensitivity, while the linear comb uses larger gaps for ease of manufacture. This segmentation allows small gaps to be used only where necessary for sensitivity without compromising manufacturing
Solution Approach 2:
The patent carefully selects the finger side gap dimension to be sufficiently large (e.g., ≥2 micrometers) to avoid manufacturing difficulties and reliability issues, while the fingertip gap is optimized for sensitivity. This parameter optimization balances manufacturing ease with performance requirements
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 proposed structure increases sensitivity by 20-50% compared to pure linear combs, reduces the risk of sticking, and allows for higher measurement voltage, enhancing the robustness and reliability of the sensor, while optimizing damping and noise performance.
Implementation Method 1
capacitive micromechanical sensor structure...comb fingers move in measurement mode closer to each other eventually causing the gap between the fingers to close...capacitance behavior of the comb fingers can be approximately modeled by a parallel plate capacitor
Implementation Method 2
a rotor structure movably anchored by means of spring structures to the substrate
Implementation Method 3
incorporating stopper bumps to prevent sticking and pull-in effects
Data Source
Figure 1
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AI summary
The invention relates to a capacitive micromechanical sensor structure comprising a stator structure (1) rigidly anchored to a substrate (2) and a rotor structure (3) movably anchored by means of spring structures (4; 4a, 4b) to the substrate (2). The stator structure (1) has a plurality of stator finger support beams (5) and the rotor structure (3) has a plurality of rotor finger support beams (7). Stator fingers (10) along the stator finger support beam (5) of the stator structure (9) extend into rotor gaps (14) along the rotor finger support beam (7) of the rotor structure (12), and rotor fingers (13) along the rotor finger support beam (7) of the rotor structure (12) extend into stator gaps (11) along the stator finger support beam (5) of the stator structure (9).