Integrated Force Sensor in Display Stack Using Meandering Trace
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Solution Overview
Problem
Conventional force input sensors in electronic displays increase device thickness and weight, require specific materials, and are often affected by temperature changes, making them inefficient for accurate force input detection.
Innovation Solution
Integrating a strain-sensitive electrical trace into the display stack, which measures electrical properties like inductance, resistance, or capacitance to correlate input forces, reducing the need for additional sensors and materials, and minimizing thickness and weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional force input sensor is positioned between the display stack and the protective cover, then force input detection is enabled, but the device thickness and weight increase
Solution Approach 1:
The force input sensor is merged with the display stack by integrating the sensor trace directly into one of the display layers (such as the transparent conductive oxide layer, electrode layer, or encapsulation layer). This consolidation eliminates the need for a separate sensor layer, thereby maintaining force detection capability while reducing overall device thickness.
Solution Approach 2:
Existing display stack layers are designed to serve dual functions: their primary function (such as electrical conduction, encapsulation, or light emission) and a secondary function as the force sensing element. For example, the transparent conductive oxide layer simultaneously provides electrical conductivity and serves as the substrate for the sensor trace pattern, enabling force detection without adding separate components.
2Measurement precision
If a conventional force input sensor is positioned between the display stack and the protective cover, then force input detection is enabled, but the device weight increases
Solution Approach 1:
The sensor functionality is combined with existing display layers rather than adding a separate sensor component. The sensor trace is formed using materials and processes already present in the display manufacturing stack, such as patterned conductive layers or encapsulation materials, thereby avoiding additional weight from separate sensor assemblies.
Solution Approach 2:
The sensor trace is created by patterning existing materials in the display stack that already have the necessary mechanical and electrical properties. Instead of introducing new sensor materials, the invention uses copies of existing layer structures (such as repeating the conductive material pattern) to create the sensing element, minimizing material additions and associated weight.
3Measurement precision
If conventional force input sensors are used, then force detection is achieved, but specific materials with specific properties are required
Solution Approach 1:
The invention uses materials that already serve multiple functions within the display stack. For example, the transparent conductive oxide layer provides both electrical conduction for pixel operation and serves as the base layer for the force sensor trace. This eliminates the need for specialized sensor materials and allows use of standard display manufacturing materials.
Solution Approach 2:
The invention changes the functional parameters of existing materials rather than requiring new materials. By adjusting the pattern geometry, trace width, or material thickness of existing layers, the force sensing capability is achieved using the same material composition already present in the display, thereby simplifying manufacturing and material selection.
4Measurement precision
If conventional force input sensors are used, then force detection is achieved, but temperature changes significantly affect sensor performance
Solution Approach 1:
The display stack's existing structural layers provide thermal stability to the sensor trace. Since the sensor is integrated into layers designed to maintain structural integrity across temperature ranges (such as encapsulation layers and substrate materials), the sensor benefits from the thermal management properties of the surrounding display structure without requiring separate temperature compensation mechanisms.
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 allows for accurate force input detection within the display stack, reducing thickness and weight while minimizing material and temperature-related issues, enhancing user interaction and device performance.
Implementation Method 1
The electrical trace is configured to couple to a force input sensor that, in turn, is configured to measure one or more electrical properties of the electrical trace that correspond to physical deformations of that trace
Data Source
AI summary
A force input sensor can include a strain-sensitive region disposed as a meandering electrical trace onto a structural or functional layer of a display stack. In particular, the meandering electrical trace can include one or more diversions from a linear path, each diversion configured to increase the length of the electrical trace. A diversion can form a loop to increase the inductance of the meandering electrical trace; the inductance of the meandering electrical trace can be correlated to length of the inductive trace which, in turn, can be correlated to strain experienced by the structural or functional layer.