Ionic Conductive Ink for Stretchable Touch Sensors
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Solution Overview
Problem
Existing touch sensor technologies face challenges in maintaining sensitivity and accuracy under deformation, particularly with multi-touch functionality, due to limitations in electrode patterning and the use of dielectric layers which can lead to unwanted capacitance changes when stretched or bent.
Innovation Solution
The development of an inkjet printable ionic conductive ink comprising a hydrophilic polymer, ionic salt, and surfactant, which forms a thin layer of ionic conductive gel for use in a coplanar electrode layout, eliminating the need for a middle dielectric layer and enhancing sensitivity by suppressing deformation-induced capacitance changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dielectric layer is used to separate x and y direction electrodes in stretchable touch sensors, then the electrodes are electrically isolated, but the dielectric layer thickness reduces under stretching and bending leading to unwanted capacitance increment
Solution Approach 1:
The patent removes the middle dielectric layer entirely from the sensor structure. Instead of using a dielectric layer to separate x and y electrodes, the invention employs a coplanar electrode layout where both electrode sets are formed on the same plane of the elastomeric substrate, eliminating the source of deformation-induced capacitance errors
Solution Approach 2:
The patent transitions from a three-layer structure (x-electrodes/dielectric/y-electrodes) to a two-dimensional coplanar arrangement where both x and y electrodes exist on the same plane. This dimensional reorganization allows electrical isolation through spatial separation rather than requiring a dielectric barrier, thus maintaining reliability while avoiding the capacitance stability issue
2Reliability
If conventional electronic conductors are used in flexible touch sensors, then electrical conductivity is achieved, but optical transmittance and mechanical flexibility properties must be compromised due to trade-offs
Solution Approach 1:
The patent changes the fundamental conduction mechanism from electronic to ionic. By using ionic conductive ink containing lithium ions that move through the elastomeric substrate, the system achieves electrical conductivity without the material constraints of metallic conductors, thereby maintaining optical transparency and mechanical flexibility simultaneously
Solution Approach 2:
The patent substitutes electronic conduction with ionic conduction. Instead of using electron-based metallic conductors that compromise optical and mechanical properties, the invention employs ion-based conduction through the elastomeric substrate itself, replacing the mechanical conductor with a chemical/ionic conduction mechanism that preserves the substrate's desirable properties
3Ease of manufacture
If inkjet printing is used to pattern ionic conductive ink, then flexible electrode patterning is achieved, but the ink formulation must be optimized for printability while maintaining ionic conductivity
Solution Approach 1:
The patent creates a composite ionic conductive ink formulation combining lithium salts (for ionic conductivity), hydrophilic polymers (for structure and printability), and surfactants (for inkjet printing performance). This composite material simultaneously achieves printability and ionic conductivity, resolving the contradiction between ease of manufacture and reliability
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 solution results in a touch sensor panel with improved sensitivity (up to 60.5% capacitance change) and signal-to-noise ratio, maintaining stability and accuracy under various deformations, including stretching and bending, while being flexible and suitable for curved surfaces.
Implementation Method 1
ionic conductors act as dielectrics at visible light wavelengths... utilizing ionic conductors as electrodes remains suitable for applications such as soft actuators, electroluminescent (EL) devices, strain sensors, and capacitive touch sensors, where only small current is needed
Implementation Method 2
Although an ion's mobility may be thousand of times lower than that of an electron, utilizing ionic conductors as electrodes remains suitable for applications such as soft actuators, electroluminescent (EL) devices, strain sensors, and capacitive touch sensors
Implementation Method 3
The present approach harnesses drop-on-demand (DOD) inkjet printing technology... An inkjet printable ionic conductive ink may be prepared using a hydrophilic polymer, an ionic salt, binary mixture solvent, and a surfactant
Implementation Method 4
A general p-cap touch sensor may consist of individual conductive electrodes arranged separately in perpendicular directions (along x and y axes in different planes), and capacitors are formed at each intersection... the capacitor's mutual capacitance (Cm) gets reduced
Implementation Method 5
An object, which is grounded but conductive (e.g. a human finger), approaching the electrodes tends to disturb fringing electric field and weaken charge coupling between x and y electrodes
Data Source
AI summary
An inkjet printable ionic conductive ink for producing a touch sensor device is provided. The inkjet printable ionic conductive ink includes a hydrophilic polymer and an ionic salt, a mixture of solvents in which the hydrophilic polymer and the ionic salt are dissolved therein to form a solution, and a surfactant to render the solution inkjet printable. A method of producing the inkjet printable ionic conductive ink is also provided. The method includes dissolving a hydrophilic polymer and an ionic salt in a mixture of solvents to form a solution, and mixing the solution with a surfactant to render the solution inkjet printable. A touch sensor panel comprising the ionic conductive ink and a method of producing the touch sensor panel are also provided.