Toward tinier transistors
Jul 03, 2013 by Laura Mgrdichian
That leak was the result of a too-small "band offset." This means that the TiO2 conduction bands were not adequately separated from the Si and Ge bands, allowing electrons to leak from the Si or Ge to the TiO2. A large band offset is essential when the layers are so thin, helping to keep electrons from moving between them. One research group (led by Christophe Detavernier at Ghent University in Belgium) has found a good solution: adding a thin intermediate "interlayer" to their heterojunctions before depositing the TiO2 layer. The interlayer has a more reasonable band offset. The NSLS study has used this development as a jumping-off point.
"This way, you get the best of both: the good band offset from the interlayer and the high dielectric constant of titanium oxide," said NSLS scientist Abdul Rumaiz, the study's lead author. "However, with the scaling of devices to smaller sizes, the interlayer thickness needs to be less than one nanometer. Thus it is very crucial to understand the band offsets at such reduced dimensions."
Rumaiz and colleagues from the National Institute of Standards and Technology (NIST), Ghent University, Quaid-i-Azam University (Pakistan), and the University of Delaware studied how interlayer thickness affected band offsets. Using x-rays at beamline X24A, which is run by NIST, they investigated germanium-based transistor structures containing TiO2 and a hafnium oxide (HfO2) interlayer. This work and future studies will be important in determining how thin the layers can be
while still yielding a highly performing transistor.
The team created six samples with different interlayer thicknesses, from 0.4 nanometers (nm) to 3 nm, and a fixed TiO2 thickness of 2 nm. They studied the structure with hard x-ray photoelectron spectroscopy, or HAXPES, a technique that
measures the electrons a material emits when exposed to a beam of high-energy (hard) x-rays. These measurements can tell scientists about the bulk electronic properties of a material and also reveal information about the interfaces between materials.
Read more at:
Toward tinier transistors
