Display Uses Polymeric Semiconductor for Pixel Driving

The lower cost of producing a polymer-based active-matrix display is an enormous advantage, Philips Research says. This comes from the need for fewer production steps and less stringent cleanliness in the cleanrooms. It is also possible, at least in principle, to print the switches onto plastic foil in a reel-to-reel process to form a matrix of switches that can be very large.

An active-matrix, polymer-dispersed liquid crystal display was selected to demonstrate the functioning of the new polymer electronics based on an active matrix (Figure). This type of low-power display is a high-contrast reflective unit. Unlike most currently used LCDs, this display does not depend on any polarization phenomena, so it can be used to make a flexible display.

In a polymer-dispersed LCD, the light may be scattered by non-aligned molecules in the domains of the liquid crystal. Alternatively, the liquid crystal domains may be transparent because the molecules are aligned by an electric field. However, the relationship between the applied voltage and the resulting image contrast in this type of display does not permit multiplexing, thus preventing the use of a passive-matrix driving system.

Transistors consisting only of polymers on flexible substrates have already been demonstrated by the same research group, which intends to incorporate all-polymer thin-film transistors in its next prototype flexible display. The use of polymer electronics - instead of conventional silicon-based technology - to address active-matrix displays could bring high-volume, flexible display systems much closer to reality. .

Palladium Oxide Can Mark Memory Damage

Various materials are being investigated as replacements for the traditional dielectric materials employed for memory storage in DRAM and NVDRAM (non-volatile DRAM) capacitors. They include high-permittivity and ferroelectric perovskites, such as barium strontium titanate and strontium bismuth titanate.

The electrode materials used in these capacitors must be able to withstand the high-temperature oxidizing conditions required for the perovskite deposition, so researchers have investigated noble metals and their conducting oxides as barriers. The reducing environments required for processing the devices can remove oxygen from the perovskite layer, which results in the layer having an unacceptably high leakage.

As detailed in the July issue of Platinum Metals Review, researchers at IBM's Watson Research Center (Yorktown Heights, N.Y.) have found that an additional decomposable palladium oxide lower electrode could act as a marker for observing any damage to the perovskite due to the reducing environment. They monitored oxygen loss from films of palladium oxide with and without a perovskite overlayer in situ during heating in an inert atmosphere. Oxygen could cross the perovskite layer in either direction, while the palladium could lose or gain oxygen and form an alloy with the underlying platinum layer. The platinum layer reduced the temperature at which oxygen left the palladium oxide. The workers concluded that the palladium oxide layer could act as both a monitor and as an oxygen source for the perovskite. .