Observing and measuring strain in nanostructures and devices with transmission electron microscopy
- PDF / 821,424 Bytes
- 9 Pages / 585 x 783 pts Page_size
- 65 Downloads / 192 Views
Introduction Strain is a key parameter for understanding many physical phenomena at the nanoscale. The mechanical and electronic properties of a material are directly related to the strain in the material, and the response of a material to an applied strain is fundamental to the engineering of mechanical or electronic properties. Strain fields in materials have always been one of the main contrast mechanisms in a transmission electron microscope (TEM), generating contrast by altering the diffracting conditions around a defect, for example. In recent years, TEM methods have been used and developed specifically to study strain fields, either to measure strain directly or to apply strains and observe the evolution of materials in situ. This article will review the current state of the art in this field. The first part will concentrate on the measurement of strain from imaging and diffraction, and the second on the quantitative measurement of strain during in situ experiments. The concept of elastic strain engineering for electronic properties came originally from the field of microelectronics, and naturally many of the examples will be taken from this area. By straining silicon, the mobility of carriers can be increased significantly. Engineering strain in the active region of transistors has been, and continues to be, essential in helping the industry upgrade performance year after year. Different
methods have been employed to inject strain into the channel region of devices, including recessed sources and drains of alloys of silicon and stress liners.1 The complex geometry of devices also leads to non-uniform strain distributions. It is therefore important to be able to measure the strain at a very local level and ideally to be able to map the strain over the whole device. It is also important to understand that the physical phenomena of interest, such as stress, piezoresistivity, and piezoelectricity, are all related by tensor relations, which means that there is a complex interplay between the components in the different directions of the crystal.2 Stress, for example, does not depend uniquely on the strain in one particular direction: σ ij = c ijkl ε kl ,
(1)
where σij are the stress components, cijkl are the constants of elasticity, and εkl are the different strain components. To determine stress from strain, it is therefore necessary to measure all the strain components. Naturally, the most significant contribution for the σxx stress component is εxx, but not uniquely so. The same goes for mobility and the piezoelectric effect; even mobility is affected by shear components.
Martin J. Hÿtch, CEMES-CNRS, Toulouse; [email protected] Andrew M. Minor, University of California, Berkeley; [email protected] DOI: 10.1557/mrs.2014.4
138
MRS BULLETIN • VOLUME 39 • FEBRUARY 2014 • www.mrs.org/bulletin
© 2014 Materials Research Society
OBSERVING AND MEASURING STRAIN IN NANOSTRUCTURES AND DEVICES WITH TRANSMISSION ELECTRON MICROSCOPY
A distinction needs to be made between strain, which has a mechanical sense in Equati
Data Loading...
