Each touch sensor features 2 sets of electrodes: the Transmitting ones (also known as Tx, or the driving electrodes, or simply X electrodes) and the Receiving ones (also known as Rx, or the sensing electrodes or simply Y electrodes).
Electrodes are usually made of Indium Tin Oxide, also known as ITO. However, during the last years, ITO alternatives have gained momentum and this trend is expected to continue in the years to come.
The most popular ITO alternative is Metal Mesh. Carbon nanotubes, PEDOT, copper mesh and silver nanowires are promising technologies that have emerged recently and
show potential in replacing ITO too.
When selecting electrode material, there are 3 major things to consider:
1) Resistance of the material: ITO has a resistance of about 100 ohms/square, while metal mesh has 10-30 ohms/ square.
2) Optical transmission of the material: Non index-matched ΙΤΟ has a 90-95% light transmittance rate, while silver nanowires more than 94%.
3) Design of the sensor itself: If it’s a large or a bent sensor, then ITO might not be preferred. These two design trends are those that have paved the way for ITO
alternatives.
ITO has high sheet resistance.The sheet resistance affects the charge time of the sensor and it’s proportional to its size. That’s why ITO is not favored in large touch sensors.
Bent touch sensors require the electrodes to be bent too (not just the cover glass). That’s where another drawback of ITO is evident: ITO breaks easily when bent, while its alternatives, e.g. metal mesh can be bent to a radius of up to 4mm without breaking.
You can learn more about common electrode patterns and examples of the most common stackup configurations here.
