The Limitations of ITO on Plastic Films

By Ken Klapproth - April 22, 2019

While many innovations, such as penicillin, semiconductors, or nuclear fission, result from scientific or academic research, the evolution of innovative products is also often driven by market conditions. Right now, we are seeing a similar shift in the transparent conductive film (TCF) market; it is responding to evolutionary market pressures because the need for flexible films is testing the capabilities of existing solutions. Indium tin oxide (ITO), the longstanding incumbent in the TCF market, can no longer meet the market’s needs—so what now?

First Thing’s First: What Are TCFs?

There are many available transparent materials and there are many materials that are electrically conductive, but very few available materials are both.

This means that manufacturers’ options are often limited when it comes to applications that demand transparent conductive materials. This can apply to a wide range of commercial applications, including, but not limited to:

  • Information displays
  • Capacitive touch sensors
  • Solar photovoltaic modules
  • EMI shielding windows
  • HMIs
  • Transparent heaters

Indium Tin Oxide is one material which satisfies both properties. Its excellent optoelectronic performance has allowed it to dominate the TCF materials market for the past four decades, particularly on rigid glass substrates.

However, when applied to plastic substrates, the drawbacks of ITO outweigh its benefits, and manufacturers are beginning to look for other options.

The Limitations of ITO

ITO has been the winner in the TCF market for years, but the demand for ITO is changing. Many product designs are moving towards thin, flexible and 3D-shaped form factors, and ITO just can’t keep up. Limitations of the material include:

Composition

Compositionally, ITO is a ceramic, making it brittle and susceptible to cracking when flexed. This represents a huge limitation as product designs rely more and more on flexibility.

Glass vs. Plastic

ITO does have excellent optoelectronic properties, but these are contingent upon the temperatures that can be safely reached during the vapor deposition process. The higher temperatures possible on rigid glass substrates contributing to those optoelectronic properties are not achievable on plastic films due to the temperature limitations of the plastic substrates.

Circuit Patterning on Flexible Plastic

Finally, circuit patterning of ITO on flexible plastic films is expensive due to handling damage which increases in probability as the circuit area increases. There are two common methods of patterning for ITO:

  • Photolithographic etching. The process steps include applying the etch mask, developing, etching, capturing/treating the etch waste streams, stripping off the etch mask, then finally cleaning the circuit. This amounts to quite a few steps with materially significant costs both in terms of dollar value and manufacturing process time.
  • Laser ablation. For this process, a laser is used to vaporize unwanted material. Care must be taken not to damage the underlying substrate. The material properties of glass make it more durable for laser ablation while flexible films are more susceptible to damage. The risk of damage from laser ablation also increases with the amount of material that is being removed.

As an example, projects that require circuit areas representing only 15% of the total area will require ablating 85% of the area. That means a significant amount of time on the laser, increasing the chance for damage to a substrate of plastic. These costs can add up. Conservative estimates put the cost of laser ablation at triple the cost of the ITO film alone. As product designs are moving towards thinner and larger area substrates, the challenges, costs, and risks of chemical or laser patterning are further compounded.

The Future of the TCF Market

The market for TCF materials is forecasted to exceed $5 billion by 2022 (Source: MarketWatch). By that date, more than half of the market is expected to be comprised of TCFs on flexible plastic films versus glass.

The market is not going to stop advancing, and product designers are not going to stop striving for thinner, more flexible and adaptable products just because ITO can’t achieve these standards. In answer to the limitations of ITO, there is now a wide market of ITO alternatives which are designed for use on flexible plastic films. Want to learn more about the types of alternatives that are available?

Download your free guide, The State of ITO Alternatives, to learn about the materials that are available, as well as their advantages and disadvantages. Get your guide now.

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