Mechanical properties of helically perforated thin films
- PDF / 206,377 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 77 Downloads / 248 Views
The mechanical behavior of a helically perforated thin film structure was simulated by finite element analysis. The validity of the results was confirmed by comparison to a nanoindentation measurement performed on a nickel helically perforated thin film sample. It was found that variation of the helical pitch angle from 35° to 70° resulted in a change of 1.5 times in the elastic modulus. Since the fabrication process used to create the actual samples allows for variation of the pitch angle, this result may enable the tailoring of materials for use in micro- and nanoscale devices.
I. INTRODUCTION
As the field of micro- and nanoscaled devices matures, a larger variety of materials are being used at everdiminishing scales, with a resultant need to better understand and control the properties of these materials. Additionally, significant efforts have been made to develop techniques allowing for the prediction, modeling, and measurement of fundamental mechanical properties such as hardness and elastic modulus at the nanoscale, as these properties change dramatically as dimensions are reduced.1–3 One fabrication method that offers control over the mechanical properties of a material is the creation of a nanostructured thin film by glancing angle deposition (GLAD).4,5 This process differs from ordinary physical vapor deposition in that the incoming flux forms an extreme angle (greater than 80°) with the substrate normal. This results in the growth of very porous thin films consisting of distinct columnar structures (with crosssectional dimensions typically around 100 nm). The specific morphology of these columns can be controlled by rotating the substrate (both in-plane and out-of-plane) in specific patterns during the deposition. Rotation algorithms exist to create shapes such as helices, square spirals, slanted and vertical posts, and zig-zag structures. It has also been shown that this process can be used to create helical SiO2 features that deform in a spring-like manner when compressed; the specific stiffness was determined by the pitch angle of the helices and could be changed by adjusting the deposition parameters.6 Overall, it was found that the stiffness could be reduced by 3
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0160 J. Mater. Res., Vol. 21, No. 5, May 2006
orders of magnitude, allowing the mechanical behavior of SiO2 thin films to be tuned over a wide range. The GLAD technique produces thin films which are uniform over large (4-in. Si wafer) areas, promising potential for application to microelectromechanical systems (MEMS) and other fabrication processes. However, because the films consist of individual columns, they lack structural integrity and are easily damaged. For this reason, a templating procedure has been developed allowing for the creation of solid thin films with helical pores.7 In this process, a porous GLAD film master is filled with another material, and the original film is etched away. This structure’s geometry is tunable due to the
Data Loading...
