Complementary metal oxide semiconductor (CMOS) is one of several semiconductor fabrication technologies and currently the most popular partly because it conserves power by putting p and n type transistors back to back. This is also possible with nanosilicon ink-based TFTCs and ones made using organic semiconducting films.
Achieving both p and n type with polymer films based on printing inks is a relatively recent development. The combination of the two for chip cards, tickets and tags generally means faster, power-efficient digital circuits that are resistant to electronic noise. They can operate over a wide range of supply voltages although CMOS circuits are susceptible to damage by static electricity so care is required when handling them.
Recent developments come from researchers at Polyera and BASF Future Business GmbH who have invented a novel n-type organic polymer semiconductor with high mobilities (greater than 0.5) and robust processability.
Together with existing polymer semiconductors, the new material was used to print complementary metal-oxide semiconductor (CMOS) circuits, the type that make up today's silicon logic.
A paper was published last month that described how the new material called ActivInkTM N2200 showed electron mobility - the speed with which an electron traverses the semiconductor and a key determinant of how quickly a transistor can switch between 0.45 and 0.85 centimeter squared per volt second.
The paper described in the journal "Nature"
"a highly soluble ( 60 g l-1) and printable n-channel polymer exhibiting unprecedented OTFT characteristics (electron mobilities up to 0.45-0.85 cm2 V-1 s-1) under ambient conditions in combination with Au contacts and various polymeric dielectrics. Several top-gate OTFTs on plastic substrates were fabricated with the semiconductor-dielectric layers deposited by spin-coating as well as by gravure, flexographic and inkjet printing, demonstrating great processing versatility. Finally, all-printed polymeric complementary inverters (with gain 25-65) have been demonstrated."
Several p-channel semiconductors exist, but "polymeric n-channel semiconductors - practical ones - were unknown until our work," says Antonio Facchetti, Polyera's chief technology officer and an adjunct chemistry professor at Northwestern University. "If you want to enable high-performance CMOS electronics, you need both p-channel and n-channel semiconductors."
The companies hope the new development will reach mobilities of 1 or higher and believe it should be possible to optimize these materials for use in industrial printing processes within the next two to three years.