breaking. Here, the sensor material technology of choice is
CNT (Carbon Nano Tubes) which is another transparent
conductive material that only recently achieved a
transparency level at the required conductivity sufficient
for touch sensors. The CNT material could be coated
on either PET-film or other birefringence free films,
depending on the optical requirements of the end product.
The limitation of this approach is that it can only be used
in conjunction with curved plastic lenses and not with
When glass is thinned down to a thickness 0.25mm or less
it can be bent to a certain degree without breaking. This
property is utilized when laminating glass sensors at this
thickness onto curved glass lenses, however this process
is in trial phases and has only been proven to work on a
sample level. Due to the tension forced upon the glass
during the lamination process, it is difficult to use liquid
glue: The glass will always try to revert back to its natural
flat shape and would have to be kept in its bent shape
during the lamination process until the glue is cured.
Also, due to gravity, the liquid glue would not spread
evenly on a bent surface. Therefore, OCA film would
be the adhesive of choice for this process. It would be
laminated on the flat glass first and then into or onto the
curved lens. Even with flat glass, the yield of the dry OCA
process is lower than that of liquid glue. For curved lenses,
lamination yields are expected to be even lower due to the
tendency of the bent glass to revert back to its flat shape.
The greater the level of curvature, the lower that yield
would be. Long term reliability of such a solution still has
to be proven as the delaminating force will remain in the
glass even after completion of the lamination process.
Continued on page 16