Article Analysis



Article Analysis

Article: Nanoparticle Selective Laser Processing for a Flexible Display Fabrication

In this article, the author introduces an integrative step for a novel nanomaterial based laser processing scheme to demonstrate two basic flexible display components: organic light emitting diode (OLED) and organic field effect transistor (OFET) on the polymer substrate using the same platform. (Ko et. al 2010)

Manufacture of electric circuits on polymer substrates is broadly referred to as flexible electronics and has gained significant interest as a pathway to low-cost or large-area electronics. Although conventional vacuum deposition and photolithographic patterning methods are well developed for inorganic microelectronics, they are not appropriate for this application. Flexible polymer substrates are chemically incompatible with resists, etchants, and developers used in conventional integrated circuit (IC) processing. In practice, the usual IC fabrication processes involve multiple steps and high processing temperatures and produce toxic waste, all of which add to their cost. Furthermore, the increasing size of electronic devices such as displays poses great difficulty in adapting standard microfabrication techniques, including lithographic patterning.

We recently demonstrated fabrication of the basic building blocks for complex flexible electronics, organic field effect transistors (OFETs). The process consists of first depositing metal nanoparticles using inkjet printing, subsequent laser processing of the nanoparticles, and then using inkjet printing to deposit a semiconducting polymer. The gold nanoparticles (1-3nm diameter) encapsulated by a hexanethiol self-assembled monolayer in organic solvent were synthesized using a two-phase reduction method. The semiconducting polymer used in this research is a new, modified polythiophene containing electron-withdrawing alkyl carboxylate substituents. It exhibits high charge mobility as well as air stability, which is one of the key characteristics necessary for producing cost-effective electronics.

All-printed electronics is the key technology to ultra-low-cost electronics such as radiofrequency identification devices and large-area displays. As a critical step in this direction, airstable OFETs were fabricated using inkjet printing and lowtemperature selective laser sintering. OFET electrodes having great resolution and highly electrically conductive gold lines were fabricated in ambient pressure and at room temperature without using any lithographic process. To overcome the shortcomings of conventional organic semiconducting polymers and maintain the great advantage of the inkjet direct writing process, carboxylate-functionalized polythiophene with increased air stability was used as the semiconducting material for OFETs fabricated by a laser sintering process. The OFET performance can be enhanced by further shrinking of the channel dimension and by applying other metal nanoparticles and semiconducting polymers. This maskless and direct writing process can contribute to the development of inexpensive and large-area macro-electronics. Furthermore, the local material deposition of the inkjetting process could minimize material waste. Local thermal control of the laser sintering process could confine the heat-affected zone and help avoid thermal damage to the substrate.

The performance of the OFET by selective laser sintering of metal NPs was compared with a standard FET sample fabricated by a lithography technique to verify the device performance. The gold electrode was patterned by a lift-off technique using directional gold deposition on a p+ silicon wafer with 115 nm SiO2 dielectric ...