[How to] 5 Electrode Materials for Capacitive Touch Sensors

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Electrode behavior heavily depends on the material they are made off.

To know if emerging materials can potentially be used as electrodes in touch sensors, we must first describe the properties we would want such a material to have.

Desired properties differ depending on one’s point of view. Engineers tend to focus more on physical properties and performance, while managers focus more on the cost-effectiveness of the proposed material. 

How to choose the ideal electrode material for your touch sensor?

Engineers are mostly concerned about three main performance categories:
electrical, optical and mechanical.

a. Electrical properties
Electrical performance boils down to the resistivity and capacitance of the electrodes. The capacitance is affected, among other parametres, by the shape and size of the electrodes.

To compare resistivities, the industry uses the term sheet resistance. Sheet resistance needs to be as low as possible. This allows for faster response times, and use in large screens.

b. Optical properties
Optical performance is crucial when a screen is housed underneath the touch sensor. Great optical performance is crucial as it allows the user to have an unobstructed
view of the screen. Focus lies on two properties here, transmittance and haze.

c. Mechanical properties
The device’s design dictates the mechanical properties the electrodes should have. For example, if a device is bent or flexible, then electrodes should also be able to bend or flex. The main property engineers take into account when it comes to mechanical properties is that of brittleness. Brittleness expresses how much energy can a material absorb prior to fracture. Common measures of brittleness include the strain-stress graph and the material’s bending radius.

The materials we examine:

ITO

Maturity: Very high
Sheet resistance: Moderate
Flexibility: Very limited
Optical performance: Very high
Applications: Most of flat touch sensors under 22”

Metal Mesh

Maturity: Medium
Sheet resistance: Low
Flexibility: Moderate
Optical performance: Moderate-High
Applications: Large flat (up to 65”),curved, bent touch sensors

Silver Nanowires (AgNW)

Maturity: High
Sheet resistance: Low
Flexibility: High
Optical performance: High
Applications: Flat (up to 15”), bend, flexible touch sensors

Carbon Nanotubes (CNT)
Maturity: High
Sheet resistance: Moderate
Flexibility: High
Optical performance: Moderate
Applications: Wearables, flexible, stretchable touch sensors

PEDOT:PSS
Maturity: High
Sheet resistance: Moderate
Flexibility: High
Optical performance: Moderate
Applications: Flexible, stretchable touch sensor

You can learn more about the processing, the cost along with technical details such as the sheet resistance and the transmittance of each material in our electrode materials guide.

 You can get it HERE for free.