Electronics Production | April 08, 2011

Peratech's QTC Clear for force sensitive touch screens

Peratech, the innovators in touch technology, have developed a see through version of their Quantum Tunnelling Composite (QTC) material called QTC Clear.
This force sensing material can be used to create a whole new class of Force Sensitive touch screens that can completely replace current Resistive touch screen technologies or enhance Capacitive ones to create superior solutions with more features such as 3D input.

“Both Resistive and Capacitive touch screen technologies have their drawbacks,” explained Philip Taysom, Peratech’s Joint CEO. “Resistive is not very accurate and can’t do multi-touch so it is becoming less popular than Capacitive, but the latter uses a lot of power constraining it to smaller screen sizes. Our new, QTC Clear touch screen design offers the best of both technologies without their drawbacks. It can be made in any size and provides multi-touch, high sensitivity with great accuracy, ultra low power consumption and additional intuitive features with the third dimension of pressure to more easily manipulate and control information on the screen.”

The QTC Clear layer is only 6-8 microns thick with a transparency that is very similar to the existing touch screen technologies. This is sandwiched between two layers of ITO (Indium Tin Oxide), which is in turn sandwiched between two hard sheets, typically glass.

It is so sensitive that it can detect deflections of only a few microns so that the top surface can be rigid and robust, e.g. glass, unlike current Resistive designs that have to be soft enough to deform easily making them susceptible to damage. QTC’s unique properties means that virtually no current flows unless a force is applied. This overcomes the drawbacks of Capacitive designs that constantly draw current and create design challenges to overcome EMI issues.

Paul O’Donovan, Principal Analyst at Gartner’s semiconductor division, commented, “This is a very interesting new technology that could revolutionise the whole touch screen industry from automotive to computers.”

Background information on Capacitive and Resistive touch screens

Current Resistive touch screens designs use a sandwich of a soft top layer and a hard bottom layer with small spacer bumps to keep them apart. When the soft top layer is pressed it deforms and contact is made between two thin films of conductive material (ITO) on the inside of the two structural layers.

The drawbacks are that the top layer has to be soft enough to deform easily when pressed which makes it vulnerable to damage by scratching etc. and it cannot be used to provide the increasing important multi-touch functionality. No current flows unless pressure is applied, there are no EMI issues and they can be made any size. They can be used with gloves and in any humidity conditions.

Capacitive touch screens have become more popular as they overcome the drawbacks of Resistive because they have a robust, hard top surface and provide multi-touch. However, the design uses a lot of current to provide the touch detection which is a constraint on screen size and potential interference issues that require careful design to overcome, making large Capacitive screen solutions expensive. Also gloves and high humidity prevent them from working.
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