Single Layer Capacitive Touch Force Sensor Design

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Solution Overview

Problem

Existing force sensors require significant pressure for accurate detection, leading to degraded user experience, and three-dimensional touch detection is challenging due to the need for a two-layer structure, which increases thickness, counter to the trend of thin electronic devices.

Innovation Solution

A single layer capacitive touch force sensor using a plurality of receiving electrodes, first drive electrodes, and second drive electrodes, where the receiving electrodes are arranged to generate different capacitances with each type of drive electrode, allowing for touch and force detection using the same receiving electrode, with a polymer material layer between substrates to change capacitance with force application.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a two-layer structure is used for three-dimensional touch detection, then both position detection and force detection can be achieved, but the thickness of the sensor increases

Engineering Contradiction:

Improvethree-dimensional touch detection capabilityVSAvoidsensor thickness

Core Design Contradiction:

Adaptability or versatilityVSLength of stationary object

Solution Approach 1:

The patent merges position detection and force detection functions into a single layer structure. The receiving electrode interacts with different drive electrode groups to simultaneously obtain position information (from capacitive coupling with drive electrodes in the same layer) and force information (from capacitive coupling with drive electrodes in the opposite layer), eliminating the need for stacked two-layer structures while maintaining three-dimensional touch detection capability

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The receiving electrode serves multiple functions: it detects both touch position (through capacitive coupling with first drive electrode group) and applied force (through capacitive coupling with second drive electrode group). This multi-functional design allows a single layer sensor to perform what traditionally required two separate layers, reducing overall sensor thickness

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Measurement precision

If a resistive force sensor is used for force detection, then force can be detected by measuring voltage or current, but significant pressure is required and the resistance variation with pressure is not linear, degrading user experience

Engineering Contradiction:

Improveforce detection accuracyVSAvoiduser experience

Core Design Contradiction:

Measurement precisionVSEase of operation

Solution Approach 1:

The patent replaces the resistive sensing mechanism (mechanical deformation-based) with a capacitive sensing mechanism (electrical field-based). The capacitive sensor detects force through changes in capacitance between the receiving electrode and drive electrodes, which occurs with minimal applied pressure and provides a more linear response, thereby improving both measurement precision and ease of operation

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the detection parameter from resistance (in resistive sensors) to capacitance (in capacitive sensors). Capacitance changes more linearly with applied force and requires significantly less pressure to produce detectable changes, resulting in improved measurement precision and better user experience without requiring significant pressing force

Inventive Principle:

Principle #35Parameter changes

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

Enables both touch and force detection with improved user experience and reduced thickness by identifying capacitance variations through voltage or charging/discharging time changes, allowing for precise detection without the need for multiple layers.

Implementation Method 1

Each of the plurality of receiving electrodes is overlapped with one of the plurality of first drive electrodes... each first drive electrode is configured to generate a first capacitance with a corresponding receiving electrode

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

The polymer material layer is arranged between the first substrate and the second substrate, and configured to have a dielectric constant variation while receiving a force to change the first capacitance

Methodology Applied

Scientific EffectDielectric constant variation: Dielectric Permittivity

Data Source

PatentUS11726599B2Single layer capacitive touch force sensor

Publication Date: 2023.08.15 PIXART IMAGING INC

AI summary

There is provided a touch force sensor including a first drive electrode, a second drive electrode and a receiving electrode. The first drive electrode is used to form a first capacitance with the receiving electrode. The second drive electrode is used to form a second capacitance with the receiving electrode. The receiving electrode shields the first drive electrode such that when a conductor approaches the receiving electrode, only the second capacitance is changed but the first capacitance is not changed. The first capacitance is changed only when the conductor gives a force upon the receiving electrode.