Ultrathin polymer insulators key to low-power soft electronics

Researchers at the Korea Advanced Institute of Science and Technology (KAIST) have developed a high-performance ultrathin polymeric insulator for field-effect transistors (FETs). The researchers used vaporised monomers to form polymeric films grown conformally on various surfaces including plastics to produce a versatile insulator that meets a wide range of requirements for next-generation electronic devices.

Along with three electrodes (gate, source and drain), FETs consist of an insulating layer and a semiconductor channel layer. The insulator in FETs plays an important role in controlling the conductance of the semiconductor channel and thus current flow within the translators. For reliable and low-power operation of FETs, electrically robust, ultrathin insulators are essential.

Conventionally, such insulators are made of inorganic materials (eg, oxides and nitrides) built on a hard surface such as silicon or glass due to their excellent insulating performance and reliability. However, these insulators were difficult to implement into soft electronics due to their rigidity and high process temperature. In recent years, many researchers have studied polymers as promising insulating materials that are compatible with soft unconventional substrates and emerging semiconductor materials. The traditional technique employed in developing a polymer insulator, however, had the limitations of low surface coverage at ultralow thickness, hindering FETs adopting polymeric insulators from operating at low voltage.

A KAIST research team led by Professor Sung Gap Im of the Chemical and Biomolecular Engineering Department and Professor Seunghyup Yoo and Professor Byung Jin Cho of the Electrical Engineering Department developed an insulating layer of organic polymers - pV3D3 - that can be greatly scaled down, without losing its ideal insulating properties, to a thickness of less than 10 nm using the all-dry vapour-phase technique called the initiated chemical vapour deposition (iCVD). Their research results were published online in Nature Materials.

The iCVD process allows gaseous monomers and initiators to react with each other in a low vacuum condition and, as a result, conformal polymeric films with excellent insulating properties are deposited on a substrate. Unlike the traditional technique, the surface-growing character of iCVD can overcome the problems associated with surface tension and produce uniform and pure ultrathin polymeric films over a large area with virtually no surface or substrate limitations. Furthermore, most iCVD polymers are created at room temperature, which lessens the strain exerted on and damage done to the substrates.

With the pV3D3 insulator, the research team built low-power, high-performance FETs based on various semiconductor materials such as organics, graphene and oxides, demonstrating the pV3D3 insulator’s wide range of material compatibility. They also manufactured a stick-on, removable electronic component using conventional packaging tape as a substrate. The team successfully developed a transistor array on a large-scale flexible substrate with the pV3D3 insulator, in collaboration with Professor Yong-Young Noh from Dongguk University in Korea.

Professor Im said, “The down-scalability and wide range of compatibility observed with iCVD-grown pV3D3 are unprecedented for polymeric insulators. Our iCVD pV3D3 polymeric films showed an insulating performance comparable to that of inorganic insulating layers, even when their thickness was scaled down to sub-10 nm. We expect our development will greatly benefit flexible or soft electronics, which will play a key role in the success of emerging electronic devices such as wearable computers.”