High Quality Ferroelectric Memory with Tb/In2 Density Realized by Nanotechnology (2008.6.15)
Ajoint research between POSTECH (Pohang University of Science and Technology) and Max Planck Institute of Microstructure Physics, Halle, has produced an advanced technology applicable to the development of the permanent memory, FeRAM, which can save 176 billion bits per square inch (published in Nature Nanotechnology, vol. 3, page 402).
FeRAM has attracted many researchers’ interest because of its excellent characters such as nonvolatility, fast read and write, and high reliability. However, limitation in realizing large scale integration of ferroelectrics on a single chip has hindered the wide applications of FeRAM. In order to achieve the density of terabit per square inch, the size of ferroelectrics must be less than 25nm. It is well known that ferroelectric properties could be vanished if the size of ferroelectrics reduces down to nano scales: the size effect. Therefore, it is necessary to not only develop a novel method to fabricate nano-sized ferroelectrics, but also to investigate the intrinsic size effects of ferroelectrics in order for the widespread use of the computers containing memories with ultra high density, no booting, and no refresh process to be advanced. In this sense, the development of 65nm sized metal (Pt) – ferroelectric (PZT) – metal (Pt) nanocapacitors is a valuable work for the potential applications of FeRAM.
Metal-ferroelectric-metal nanocapacitors were fabricated by stencil method using ultra-thin anodic alumina mask with honeycomb arrayed 65nm sized pores.
Firstly, an aluminum plate was electrochemically oxidized. In this process, the 65nm sized pores were self-ordered. When the aluminum is shaped with a punch beforehand, the pores arrange themselves in a completely regular pattern. The anodic alumina mask was then transferred to platinum coated magnesium oxide substrate. By taking advantage of excellent thermal stability of anodic alumina, ferroelectric materials as well as electrode materials could be deposited into the extremely tiny pores at a high temperature. During the entire process, there was no thermal treatment nor use of chemicals or physical damages, resulting in high quality nanocapacitors. By removing the mask after deposition of platinum top electrode material, 176 billion bits per square inch of Pt-PZT-Pt nanocapacitors were obtained. In principle, other materials could be used as well for the ferroelectrics and electrodes as fatigue free capacitors.
The success of this project is due to the fruitful Korea- Germany cooperation. The project was supported by the Korea Research Foundation, the ‘Brain Korea 21 Program’, the Volkswagen Foundation, and the German Research Foundation.
Professor Sunggi Baik
Department of Materials Science and Engineering