Flexible semiconductors are essential for future portable electronics technologies, but they are difficult to integrate into complex architectures. Now, in a recently published study Advanced Electronic MaterialsResearchers in Japan have developed a simple way to make high-quality soft semiconductors for advanced electrical circuits.

Modern integrated circuit technology is based on basic elements known as complementary metal oxide semiconductor (CMOS) circuits. Silicon is the semiconductor component of most modern CMOS technologies. However, since future CMOS circuits (for example) need to be molded to the shape of the body or integrated into clothing, many studies have focused on the development of soft, flexible polymer-based semiconductors.

In order to integrate such semiconductors, especially n-type electron-permeable semiconductors, into CMOS circuits, several technical difficulties have to be overcome. For example, the preparation of high-quality layer-by-layer structures important to the functionality of CMOS devices is often rather slow and difficult. Solving these problems is a challenge that researchers at the Nara Institute of Science and Technology (NAIST) are trying to solve.

“Ideally, polymer films can be deposited on liquid substrates to facilitate transfer to any other substrate,” said lead author Manish Pandey. “Our strategy offers better control over the morphology of the final semiconductor film, which is critical for electrical properties, compared to conventional solution processing.”

This work is based on one-way transfer of a floating film. Using a liquid substrate that does not dissolve the polymer, the polymer dissolved in the solvent can be added dropwise to the substrate to form a one-dimensional floating polymer film. When the solvent evaporates, the polymer molecules are oriented perpendicular to the direction of the length of the film. This molecular morphology optimizes the electrical properties of the polymer film. As soon as the film cures, it can be easily transferred to another substrate, for example, for layer-by-layer application.

“We have prepared an n-channel transistor that exhibits almost no threshold voltage, which is important for maintaining energy efficiency,” says senior author Masakazu Nakamura. “Using our approach, the preparation and integration of n-channel and p-channel transistors into a single device based on flexible semiconductors should be simple.”

In this study, it was possible to obtain polymer-based one-dimensional semiconductor films in an inexpensive and easily reproducible manner. The polymer film bonding methodology developed by NAIST researchers will be useful for the development of flexible electronics and will help replace silicon in the latest CMOS technology.