Paper Electronics
December 1,2011, Printed Electronics USA 2011, Santa Clara, CA—Philip Cooper from the DeLaRue Group described the need for a full systems level analysis when looking at novel electronics. Many of the assumptions about electronic systems fall by the wayside when nontraditional materials are used.
One of the big challenges is to develop sources of power for the electronics that are compatible with a flexible substrate like paper. The company has a lot of experience in printing high security documents like banknotes and stamps. Now, the world is looking for the next level in these documents to detect and prevent counterfeiting.
For a while, holograms have been technology of choice to secure documents. These images enable forensics, detailed inspection through specialized, dedicated readers or detectors, and provide the consumer with the validation information. The growing use of holograms in higher-value product tags and labels are becoming one of the criteria for consumers’ acceptance of a genuine product.
Printed electronics could enhance document security through the printed displays using LEDs and animation through some dedicated reader. The main issues for this approach is creating an environment that supports an ease of developments while addressing cost and power. The options for power are printed batteries, photovoltaic, and batteries attached to the document.
The problems with all of these are the form factor- the thickness and area, and the expected lifetime, which must be between 2 and 10 years. Printed batteries must have very high efficiency as well as high energy density. For paper electronics with embedded power systems, processing must be compatible with in-line printing in order to manage production flows and to keep costs within a reasonable range.
In other areas, energy harvesting is an alternative. One possible energy source is the mobile phone, with energy scavenging taking some of the energy from the RF signals. One challenge is that output power that is available is distance related. This energy can be used to power printable semiconductors which are capable of operating a low-power display. The basic technology involves rectifying the RF through Schottky diodes that are printed on an inorganic substrate. The diode and its accompanying interconnects must have very low RC in an area of less than 100 x 100 µ squared.
These technologies need to be moved into some form of manufacturing equipment that permits a roll to roll manufacturing process which would reduce costs by an order of magnitude. These developments would enable consumers to scan high security documents by passing their cell phone near it and seeing if the document lights up. In this way, you remove the requirement for dedicated reading equipment.
