Degradation of Pt/PLZT/Pt capacitors caused by hydrogen in interlayer dielectrics

Abstract

A correlation between ferroelectric properties of the PLZT capacitors and amount of H₂ and H₂O gasses desorbed from interlayer dielectrics were investigated quantitatively. H₂ and H₂O gasses desorbed from interlayer dioxides were analyzed using thermal desorption spectroscopy. Polarization charges and its aging characteristics of memory array capacitors with area of 2 μm squares did not depend on amount of desorbed H₂ explicitly, but strongly on H₂O desorption. It is considered that silanol and hydroxyalkyl groups worked as hydrogen donor with catalytic activities of Pt top electrodes. As a result, hydrogen atoms should work as a major degradation agent for the imprint phenomena of memory array capacitors. Precise control of hydroxyl groups contained in the interlayer dielectrics and passivation films resulted in very small retention degradation caused by imprint phenomena, and realized high reliability and high density FRAM technologies.     

Imaging the dynamic behaviour of individual retinal chromophores confined inside carbon nanotubes

Retinal is the molecule found in photoreceptor cells that undergoes a change in shape when it absorbs light. Specifically, the cis/trans isomerization of a carbon-carbon double bond in this chromophore sets in motion the chain of biochemical processes responsible for vision. Here, we obtain atomically resolved images of individual structural isomers of the retinal chromophore attached to C60 molecules and study their dynamic behaviour inside a confined space--that is, inside single-walled carbon nanotubes--using high-resolution transmission electron microscopy (HR-TEM). Sequential HR-TEM images with sub-second time resolution directly reveal the isomerization between the cis and all-trans forms of retinal, as well as conformational changes and volume-conserving effects. This work opens up the possibility of investigating in vitro the biological activities of these photoresponsive molecules on an individual basis, and the molecular imaging technique described here is a general one that can be applied to a wide range of systems.     

Plumbing carbon nanotubes

Since their discovery, the possibility of connecting carbon nanotubes together like water pipes has been an intriguing prospect for these hollow nanostructures. The serial joining of carbon nanotubes in a controlled manner offers a promising approach for the bottom-up engineering of nanotube structures--from simply increasing their aspect ratio to making integrated carbon nanotube devices. To date, however, there have been few reports of the joining of two different carbon nanotubes. Here we demonstrate that a Joule heating process, and associated electro-migration effects, can be used to connect two carbon nanotubes that have the same (or similar) diameters. More generally, with the assistance of a tungsten metal particle, this technique can be used to seamlessly join any two carbon nanotubes--regardless of their diameters--to form new nanotube structures.