Novel gate dielectric materials: perfection is not enough

October 16, 2007

For the first time theoretical modeling has provided a glimpse into how promising dielectric materials are able to trap charges, something which may affect the performance of advanced electronic devices. This is revealed in a paper published on the 12th October in Physical Review Letters by researchers at the London Centre for Nanotechnology and SEMATECH, a company in Austin, Texas.

Through the constant quest for miniaturization, transistors and all their components continue to decrease in size. A similar reduction has resulted in the thickness of a component material known as the gate dielectric - typically a thin layer of silicon dioxide, which has now been in use for decades. Unfortunately, as the thickness of the gate dielectric decreases, silicon dioxide begins to leak current, leading to unwieldy power consumption and reduced reliability. Scientists hope that this material can be replaced with others, known as high-dielectric constant (or high-k) dielectrics, which mitigate the leakage effects at these tiny scales.

Metal oxides with high-k have attracted tremendous interest due to their application as novel materials in the latest generation of devices. The impetus for their practical introduction would be further helped if their ability to capture and trap charges and subsequent impact on instability of device performance was better understood. It has long been believed that these charge-trapping properties originate from structural imperfections in materials themselves. However, as is theoretically demonstrated in this publication, even if the structure of the high k dielectric material is perfect, the charges (either electrons or the absence of electrons - known as holes) may experience 'self trapping'. They do so by forming polarons - a polarizing interaction of an electron or hole with the perfect surrounding lattice. Professor Alexander Shluger of the London Centre for Nanotechnology and the Department of Physics & Astronomy at UCL says: "This creates an energy well which traps the charge, just like a deformation of a thin rubber film traps a billiard ball."

The resulting prediction is that at low temperatures electrons and holes in these materials can move by hopping between trapping sites rather than propagating more conventionally as a wave. This can have important practical implications for the materials' electrical properties. In summary, this new understanding of the polaron formation properties of the transition metal oxides may open the way to suppressing undesirable characteristics in these materials.
-end-
Notes to editors:

Contact details:

For more information, please contact Dave Weston at the London Centre for Nanotechnology on tel: +44 (0)20 7679 7678, mobile: +44 (0) 7733 307 596, out of hours +44 (0)7917 271 364, e-mail: d.weston@ucl.ac.uk

Images:

The following hi-res image is available by contacting the Press Office on the contact details above. On the left is an Illustration of the displacement of hafnium atoms (white) in the structure of hafnium oxide to accommodate the presence of the self-trapped hole in the oxygen atom (red).

On the right is the quantum mechanics view of the probability of finding a hole near certain atoms (larger blue structures represent higher probability).

Funding

The work at the London Centre for Nanotechnology and UCL Department of Physics & Astronomy was funded by the EPSRC. Access to computer time on the HPCx facility was awarded to the Materials Chemistry Consortium with funding from the EPSRC.

Article

The article "Theoretical Prediction of Intrinsic Self-Trapping of Electrons and Holes in Monoclinic HfO2", authored by D. Muñoz Ramo, A. L. Shluger, J. L. Gavartin, and G. Bersuker was published in Physical Review Letters volume 99 issue 15, page 155504, on the 12 October 2007

About the London Centre for Nanotechnology

The London Centre for Nanotechnology is a joint enterprise between University College London and Imperial College London. In bringing together world-class infrastructure and leading nanotechnology research activities, the Centre aims to attain the critical mass to compete with the best facilities abroad. Furthermore by acting as a bridge between the biomedical, physical, chemical and engineering sciences the Centre will cross the 'chip-to-cell interface' - an essential step if the UK is to remain internationally competitive in biotechnology.
Website: www.london-nano.com

About UCL

Founded in 1826, UCL was the first English university established after Oxford and Cambridge, the first to admit students regardless of race, class, religion or gender, and the first to provide systematic teaching of law, architecture and medicine. In the government's most recent Research Assessment Exercise, 59 UCL departments achieved top ratings of 5* and 5, indicating research quality of international excellence.

UCL is the fourth-ranked UK university in the 2006 league table of the top 500 world universities produced by the Shanghai Jiao Tong University. UCL alumni include Mahatma Gandhi (Laws 1889, Indian political and spiritual leader); Jonathan Dimbleby (Philosophy 1969, writer and television presenter); Junichiro Koizumi (Economics 1969, Prime Minister of Japan); Lord Woolf (Laws 1954, Lord Chief Justice of England & Wales); Alexander Graham Bell (Phonetics 1860s, inventor of the telephone), and members of the band Coldplay.
Website: www.ucl.ac.uk

About SEMATECH:

For 20 years, SEMATECH® (www.sematech.org) has set global direction, enabled flexible collaboration, and bridged strategic R&D to manufacturing. Today, we continue accelerating the next technology revolution with our nanoelectronics and emerging technology partners.

University College London

Related Nanotechnology Articles from Brightsurf:

Hiring antibodies as nanotechnology builders
Researchers at the University of Rome Tor Vergata recruit antibodies as molecular builders to assemble nanoscale structures made of synthetic DNA.

Nanotechnology delivers hepatitis B vaccine
X-ray imaging shows that nanostructured silica acts as a protective vehicle to deliver intact antigen to the intestine so that it can trigger an immune response.

Want in on nanotechnology? Capitalize on collaborative environments
Patent law experts demonstrate that private-public partnerships lead to promising innovation output measured in patents.

Nanotechnology makes it possible for mice to see in infrared
Mice with vision enhanced by nanotechnology were able to see infrared light as well as visible light, reports a study published Feb.

Healing kidneys with nanotechnology
In new research appearing in the journal Nature Biomedical Engineering, Hao Yan and his colleagues at the University of Wisconsin-Madison and in China describe a new method for treating and preventing Acute Kidney Injury.

A treasure trove for nanotechnology experts
A team from EPFL and NCCR Marvel has identified more than 1,000 materials with a particularly interesting 2-D structure.

Nanotechnology could redefine oral surgery
A trip to the dentist or orthodontist usually instills a sense of dread in most patients, and that's before the exam even begins.

MEDLINE indexes Pharmaceutical Nanotechnology
Pharmaceutical Nanotechnology, an important journal published by Benthm Science, is accepted to be included in MEDLINE.

Nanotechnology and nanopore sequencing
DNA is the hereditary material in our cells and contains the instructions for them to live, behave, grow, and develop.

Nanotechnology: Lighting up ultrathin films
Based on a study of the optical properties of novel ultrathin semiconductors, researchers of Ludwig-Maximilians-Universitaet in Munich have developed a method for rapid and efficient characterization of these materials.

Read More: Nanotechnology News and Nanotechnology Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.