ITO Sheet Resistance: What is it and why Does it Matter?

Diamond Coatings offer ITO coatings in an extensive range of thicknesses and sheet resistances. The question is, what is ITO sheet resistance and why does it matter? Here’s everything you need to know…

What is Sheet Resistance?

Expressed not in ohms (Ω) like a material’s resistivity but in ohms per square (ohms/sq. or Ω/sq.), sheet resistance is defined as the measurement of thin, nominally uniform (thickness) films’ resistance. Commonly used to characterise the uniformity (a factor of importance in terms of quality assurance) of a semi-conductive or conductive coating/material, it:

• Can be measured either indirectly by use of non-contact eddy current system testing devices or directly via four terminal/probe sensing.
• Does not vary under film contact scaling (unlike resistivity), which basically means that the actual resistance of a sheet/film with a sheet resistance of, for example, 30 Ω/sq. is, irrespective of the sheet’s size, 30 Ω.

The latter allows sheet resistance to be used to compare devices’ electrical properties even if their sizes differ significantly.

So, why does ITO Sheet Resistance Matter?

Highly conductive and optically clear, ITO coatings are vacuum deposited onto diverse glass, and plastic substrates (i.e. polycarbonate, PEN/PET films, acrylic) for a multitude of commercial, industrial and R&D applications like, for instance:

• Touch screens/panels
• Thin film photovoltaics
• Solar cells
• Smart windows
• Shielding (EMI, RFI, ESD)
• Polymer-based electronics
• Plasma displays
• Liquid crystal displays
• Heater windows
• Glass doors (i.e. supermarket freezers)
• Flat-panel displays
• Electroluminescent lamps
• Architectural windows (conversation of energy)
• Antistatic coatings and more

These applications obviously all require different conductivity levels and the greater the sheet resistance of an ITO coating is, the lower its conductivity will be (and vice versa) – which is, of course, why ITO sheet resistance matters.

The sheet resistance of ITO coatings varies with the coatings’ thickness – the greater the thickness, the lower the resulting sheet resistance – we therefore produce these coatings in varying thicknesses to cater for diverse applications’ different conductivity requirements,

What About Transparency?

Different thickness/resistances do have an impact on the transmission in the visible, but this effect is generally inconsequential. It should, however, be noted that within the range of near-infra red wavelengths, increasing thickness can result in a significant drop in transmission rates.

More Information

To learn more about ITO coatings, sheet resistance options to meet your project’s specific requirements and more, please do not hesitate to contact our helpful technical team today.