MEMS Capacitive Force Sensor Piston-Tube Electrode Configuration
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Solution Overview
Problem
Conventional touch-sensitive screens, particularly capacitive ones, are limited in detecting force applied by users as they are only responsive to capacitive objects and have restricted dynamic range, while piezoresistive screens suffer from low sensitivity and temperature sensitivity issues.
Innovation Solution
A MEMS capacitive force sensor using a piston-tube electrode configuration that detects a wide range of forces with high sensitivity, incorporating mechanical stoppers to withstand excessive forces and provide 3-dimensional information through capacitive read-out circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If parallel plate capacitor configuration is used to increase sensitivity, then sensitivity is improved, but the dynamic range is limited because the plate stroke is restricted to one third of the initial gap
Solution Approach 1:
The patent transitions from a 2D parallel plate capacitor to a 3D piston-tube capacitor configuration. The piston can move axially within the tube, utilizing the third dimension (depth) to achieve large stroke while maintaining small gap for high sensitivity. This dimensional change allows simultaneous achievement of both sensitivity and dynamic range.
Solution Approach 2:
The piston is nested inside the tube, with the piston moving within the confined space of the tube. This nested configuration allows the piston to achieve large axial displacement (stroke) while maintaining a small radial gap between the piston surface and tube inner surface, thereby achieving both large dynamic range and high sensitivity.
2Adaptability or versatility
If piezoresistive touch screens are used to detect force, then force detection capability is provided, but sensitivity is low when forces are limited to small range
Solution Approach 1:
The patent replaces the piezoresistive mechanical sensing mechanism with an electrostatic capacitive sensing mechanism. The piston-tube capacitor detects force through changes in capacitance caused by piston displacement, providing higher sensitivity compared to piezoresistive effects, especially for small force ranges.
3Measurement precision
If small gap between capacitor plates is used to increase sensitivity, then sensitivity is improved, but the range of force applied is limited
Solution Approach 1:
The patent utilizes the axial dimension (depth) for stroke while maintaining small radial gap. The piston moves axially within the tube, allowing large displacement for wide force range while keeping the radial gap small for high sensitivity capacitance detection.
Solution Approach 2:
The nested piston-tube configuration allows the piston to traverse a large axial distance within the tube while maintaining a small radial clearance. This enables the capacitor to achieve both small gap (for sensitivity) and large stroke (for force range) simultaneously.
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 MEMS capacitive force sensor enables detection of forces from pN to mN with high sensitivity and a large stroke, providing accurate 3D information and withstanding forces beyond its range without damage, enhancing user experience by linear capacitance changes with applied force.
Implementation Method 1
any small displacements of the rotor corresponding to an applied mechanical force/pressure induce measurable changes in the capacitance of the structure which can be detected by the sensing readout circuit
Data Source
AI summary
A touch-sensitive interface module that is able to provide 3-dimensional information about a touch by a user is disclosed. The touch-sensitive interface can detect the x-y position and the amount of the force applied on the interface. It comprises of a flexible display panel, an array of MEMS capacitive force sensors, each of which is electrically addressable and/or a circuit board of electrical connections. The force sensors comprise of a piston-tube electrode configuration that allows for easy to detect capacitive changes even when a small force is applied.