[Interview] What Does Future Hold for Printable Electronics?

Mar 16, 2009 16:12 Hideo Ampo, Editorial Staff

Printable electronics, which uses printing technologies to manufacture electronic devices, is commanding attention. It enables to form micro patterns on flexible substrates by screen printing and inkjet printing, possibly realizing simpler and lower temperature manufacturing processes, shortening production periods and reducing costs.

We interviewed Kaneki Yoshida about the trend in the application of printable electronics, the technological issues and the challenges the industry has to address. He is a guest researcher at the Photonics Research Institute, the National Institute of Advanced Industrial Science and Technology (AIST), who was formerly involved in the development of printing and material processing technologies for many years at Toppan Printing Co Ltd and Adeka Corp. (Interviewer: Hideo Ampo, editorial staff).

Q: What kind of fields is the printable electronics applicable to?

Yoshida: It is applicable to paper-like displays, paper keyboards, lamps, solar cells, smart cards and other devices using organic wiring, organic transistors and sensors. In the future, they are expected to be introduced into the ubiquitous market, which covers healthcare, environment monitoring, security systems, wearable five-sense sensors and so forth.

Inverters, memories, RFIDs (IC tags), antennas, solar cell modules and printed boards incorporating TFTs were exhibited at Printable Electronics 2009 as well as nano tech 2009 (2009 International Nanotechnology Exhibition & Conference), which took place in February.

When printing technologies are employed to manufacture electronics parts, high precision is required. Though they can not have a precision equivalent to that of a photolithography method, increasing number of companies are planning to use them by finding a right material for a right device.

Q: Are there any technological issues?

Yoshida: We need materials and devices that contribute to both high precision and high properties (conductive property, responsiveness, etc).

In respect to materials, it is important to develop an ink appropriate for printing processes. A material is processed into an ink so that it can be used for printing, and functional particles are required to be evenly scattered in the solvent and the binder resin. Then, after printing process, the solvent and the resin should be volatilized, leaving only the functional particles. However, it is difficult to make such an ink.

For example, there is pentacene, a typical organic semiconductor material. It is a low molecular compound made up of five benzene rings. Its conductivity is generated by the shift of π electrons that exist in double-bonded benzene rings. The thin film is normally formed by a vacuum deposition method, and it is difficult to make an ink from insoluble pentacene for printing.

On the other hand, if substituent introduction is carried out by molecular designing, pentacene will be soluble and an ink can be made from pentacene, but the electrical characteristics will be deteriorated due to the interference by the substituent.

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