Jun 3, 2009
I-V study details flexible organic memory device
Scientists in Korea have fabricated and investigated non-volatile flexible organic bistable devices (OBDs) that feature ZnO semiconductor nanoparticles embedded in a poly(methyl methacrylate) polymer single layer on PET polymer substrates for use in flexible electronics. Recently, OBDs have emerged as excellent candidates for next-generation organic memory devices and designs consisting of a single layer offer advantages of low cost and simple fabrication.
To make the non-volatile OBDs, the researchers embedded nanocrystals in a polymer layer above an ITO film on top of a PET substrate. The design was produced using a KIST roll-to-roll coater known as Vic-Mama.
Transmission electron microscopy (TEM) images revealed that ZnO nanoparticles were formed inside the PMMA polymer layer. Current-voltage (I-V) measurements on the Al/ZnO nanoparticles embedded in an insulating PMMA polymer layer/ITO/PET assembly at 300 K showed a non-volatile electrical bistability with a flat-band voltage shift due to the existence of the ZnO nanoparticles, indicative of trapping, storing and emission of charges in the electronic states of the ZnO nanoparticles.
The I-V response of hybrid PMMA:ZnO nanoparticles was evaluated by considering three fundamental carrier injection processes – a thermionic emission (TE) conduction model, a space–charge-limited-current (SCLC) conduction model and a Fowler–Nordheim (FN) tunnelling model. The carrier transport mechanism of the bistable behaviour for the fabricated organic bistable device (OBD) structures is described on the basis of the I-V results by analyzing the effect of space charge.
By considering the effect of space charge in the hybrid PMMA–ZnO nanoparticle device, it was revealed that the I-V characteristics are controlled by the SCLC in the low current region and by Ohm's law in the high current region through intermediate trapped charge-limit current. These results indicate that the nanocrystal-based OBDs, which are constructed using a flexible sheet and are easy to fabricate, hold promise for potential applications in next-generation flexible non-volatile flash memory devices.
About the author
Dong-Ick Son is a PhD student researcher at the Korea Institute of Science and Technology (KIST) and a PhD student in the Department of Information Display Engineering, Division of Electronics and Computer Engineering at Hanyang University. Dong-Hee Park is a research scientist in the Materials Science and Technology Research Division at KIST. Sung-Hwan Cho is a graduate student in the Division of Electronics and Computer Engineering at Hanyang University. Won-Tae Kim is a graduate student in the Division of Electronics and Computer Engineering at Hanyang University. Tae-Whan Kim is a professor of the Division of Electronics and Computer Engineering at Hanyang University. Won-Kook Choi, who is a team leader, is a principal research scientist in the Materials Science and Technology Research Division at KIST.