Touch Sensor Developments
August 6, 2013, Emerging Display Technologies Conference, San Jose, CA-A panel moderated by Paul Semenza from NPD DisplaySearch looked at the developing technologies for touch sensors. The panel included Ola Wassvik from FlatFrog, Kelly Ingham from Cima Nanotech, Jim Tassone from Unipixel Displays, and Bob Senior form Canatu.
Wassvik started with large area touch using optical sensors. The industry is moving from a display plus information to consumer applications. their technology uses planar scatter detection in a manner similar to a CT scan to detect disturbances on the surface of the glass. This technology is high accuracy and redundancy and replaces complex sensors with simple electronics and DSP algorithms. The biggest issue is to detect all touches. They can detect pressure with 10-bit resolution for most soft materials like skin, gloves, etc. and can detect pressure to a lower resolution on harder, deformable materials. Current costs for the sensor array is about $3 per inch of the periphery of the display.
Ingham expressed the concept of smart materials. Self assembly of metals into a mesh can be transferred to other substrates. The resulting material is fairly low resistance, under 50 ohms, and has a high transparency. These materials can be used for heating, shielding, and are compatible with all touch stacks. Patterning the mesh creates a random network with low resistivity for faster responses. The materials are relatively low cost due to their low materials requirements in grams per square meter density.
Tassone talked about performance engineered films that can enable cost reductions compared to ITO. The materials are applied on both sides of a substrate in one pass and can do all layers including the bezel frame. Their materials are low resistance, offer good optical transmission and are capable of 6 +/-1 micron line widths. The additive process is extendable to roll-to-roll processing.
Another technology is their coating for hardening surfaces. It can be used as a cover glass replacement and can also be used in stacks and cover stacks. It has a hardness of 6-8 and is also available in a roll-to-roll flow.
Senior presented flexible and formed displays for fashion items like the coming smart watches. Current designs are bulky due to their displays and the underlying electronics. For fashionable devices, you need curved and flexible displays. The barriers are that flexible OLED is still rigid due to the encapsulation, and the ITO conductors are brittle and hazy. Their alternative is a direct, dry print, gas-based application process. The resulting connectors are high contrast, low tint, low haze carbon nano-buds that are a combination of carbon nanotubes and fullerenes. This conductor material will enable other display form factors.
Integrating sensors with existing glass or new covers, challenges of surface chemistry?
Senior is using polycarbonate with a diamond coat. For apps like in-car navigation, the touch panels are resistive, so they can be made of plastic. The industry needs to advance and see the cost benefits to grow.
Tassone noted that they are investigating the surface chemistries and energies. It is always possible to laminate materials in a roll-to-roll process between substrates.
Ingham noted that their process uses a transfer technology, so they can direct coat to polycarbonate or transfer to large surfaces in polycarbonate or PET for better rigidity.
Wassvik stated that any waveguide material works. Polycarbonate or PMA is actually preferred over glass due to better indices of refraction. The pressure sensing sees changes in the ridges, so even a stylus deforms a little at the microscopic level.
