Advancements in polymer films expand resistive touchscreen use

Touchscreens are the primary input interface for industrial controls and a variety of other growing markets and applications. Touch input technologies—whether resistive, capacitive, infrared (IR), or surface acoustic wave (SAW)—simplify accurate and efficient user input. The differences between the technologies are in how touch input is detected and in the manufacturing cost.

By Bruce DeVisser February 1, 2007

Touchscreens are the primary input interface for industrial controls and a variety of other growing markets and applications. Touch input technologies—whether resistive, capacitive, infrared (IR), or surface acoustic wave (SAW)—simplify accurate and efficient user input. The differences between the technologies are in how touch input is detected and in the manufacturing cost.

Resistive touch panels are by far the most common type used today. They accept input from virtually any means (gloved or bare finger, stylus, credit card edge, etc.). They are easy to integrate into equipment designs and are the most cost effective. Despite widespread use, resistive panels have a drawback in rugged environments: a glass support panel, which contains the mating conductive surface that works with the PET (pixel extraction table) file to make a complete circuit. The glass can be strengthened by increasing the thickness or applying a chemical treatment, but it is still breakable. However, recent developments in plastics technology have led to an unbreakable film-film-plastic structure.

Another weakness of the resistive panel is the hard, ceramic ITO (indium tin oxide) conductive layer applied to the pliable, plastic (polyethylene terephthalate) film used to detect touch input. This layer requires a high-vacuum deposition process that is expensive and environmentally unfriendly, and the ITO performance degrades with repeated touch impact.

The solution has been to develop a flexible, transparent touch conductor to provide a more durable touch surface, be cost efficient, and ecologically sound. Such features would increase useful life and open up new, rugged applications for touch panel use.

Developing such a touch panel has not been easy, but a recently available organic, conductive polymer film is flexible and durable enough to extend touch panel life by five times (see illustration). The manufacturing process is also improved: Instead of being sputtered on, a very thin layer of the liquid polymer solution, combined with a water-based solvent, is roll-coated onto the touch panel’s PET film. The technique is economical and environmentally friendly, and creates a uniform surface resistance within the range of ITO coatings.

The thin-film coating increases the polymer’s transparency to more than 90% (about 1% less than ITO), but also increases resistivity. Modifying the polymer’s chemical structure using a molecular-orientation technology reduces resistance to 600 to 800 Ohms/square, similar to ITO.

These improvements have produced thin, unbreakable conductive polymer panels that are scratch resistant, sealable, and resistant to harsh chemicals and input abuse. These characteristics allow resistive touch panels to be used in more rugged applications, such as complex and portable flow controls, POS devices, and handheld industrial terminals used in field testing. Improvements have poised the panels to expand into more rugged environments, the mobile industrial device market, and more stringent manufacturing environments at little or no cost increase.

Author Information

Bruce DeVisser, product marketing manager, input devices, Fujitsu Components America Inc., Sunnyvale, CA; bdevisser@fcai.fujitsu.com .