Touch Sensor Shielding Against Film Stack Deflection
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Solution Overview
Problem
Proximity sensor devices experience performance degradation due to changes in background capacitance caused by the deflection of the film stack when exposed to input forces, such as touch events, which affects the accuracy of touch sensing.
Innovation Solution
Incorporating an electrically conductive shield with an areal extent equal to or greater than the sensor electrodes, coupled with a compressible layer between the film stack and the housing, to mitigate changes in background capacitance by maintaining a consistent distance between the shield and the routing traces and sensor electrodes during deflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the film stack is made flexible to allow deflection during touch events, then the device can respond to input forces, but the conductive routing traces become displaced causing changes in background capacitance and image distortion
Solution Approach 1:
A compressible layer is introduced as an intermediary element between the film stack and the housing. This layer allows the film stack to deflect in response to touch forces while maintaining a consistent gap between the routing traces and the housing, thereby preventing direct contact and capacitance changes that would cause image distortion.
Solution Approach 2:
The device structure is segmented into distinct functional layers: the film stack containing routing traces, the compressible layer as a buffer, and the housing as a fixed reference. This segmentation allows each component to perform its specific function independently - the film stack responds to touch while the compressible layer maintains structural relationships.
2Device complexity
If the conductive routing traces are positioned close to the housing to minimize space, then the device structure is compact, but any deflection of the film stack causes significant changes in the distance between traces and housing, degrading performance
Solution Approach 1:
The compressible layer is positioned in advance between the film stack and the housing to cushion and absorb the effects of film stack deflection. This pre-positioned buffer ensures that even when the film stack deflects during touch events, the routing traces maintain a stable relationship with the housing, preventing performance degradation.
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
This configuration enhances the resistance of the sensor device to performance degradation by maintaining consistent capacitance measurements despite film stack deflection, thereby improving touch sensing accuracy and reliability.
Implementation Method 1
The compressible layer is configured to allow the display film stack to deflect towards a bottom of the housing
Implementation Method 2
The resulting change in distance between the conductive routing traces and the housing causes a change in the background capacitance, which produces a distortion in an image of measured response from the sensor device
Data Source
AI summary
Disclosed herein include an input device, processing system and methods for touch sensing. Implementations advantageously are resistive to diminished performance when a film stack of an input device is bent in response to an input (touch) event. In one implementation, an input device is provided that includes a housing, a plurality of sensor electrodes disposed in a pattern on a substrate, a plurality of routing traces coupled to the sensor electrodes, an electrically conductive shield and a compressible layer. The electrically conductive shield has an areal extent approximately equal or greater than an areal extent of the pattern of sensor electrodes. The electrically conductive shield and the substrate are part of a display film stack disposed in the housing. The compressible layer is disposed between the display film stack and housing. The compressible layer is configured to allow the display film stack to deflect towards a bottom of the housing.