NiMnGa nanostructures produced by electron beam lithography and argon ion etching
|Daniel Auernhammer 1, Mario Schmitt 3, Makoto Ohtsuka 2, Manfred Kohl 3|
1. Universität Karlsruhe, Karlsruhe 76128, Germany
NiMnGa nanostructures open up an unforeseen variety of opportunities for the development of novel nanomachines, which may be controlled by local heating and a magnetic field. Nanoindentation experiments on conventional shape memory alloys have already demonstrated the scalability of the shape memory effect to nanometer-sized depths. The purpose of this study is to explore the technologies of electron beam lithography and Ar ion-etching for fabrication of NiMnGa structures with critical dimensions in the sub-micrometer range.
One micron thick films of Ni2MnGa are deposited on a PVA substrate by RF magnetron sputtering at 200 W. The sputtering target of nominal composition Ni52Mn24Ga24 is fabricated by hot pressing. During sputtering the substrate temperature is kept at 50 °C. An Argon gas flow is maintained at 230 mm3s-1. After release from the substrate the films are heat-treated at 800 °C for 36 ks.
Electron beam lithography is used to generate a primary pattern in a PMMA resist layer, which has been deposited on the Ni2MnGa thin film. Its thickness is adjusted in the range of 1-3 µm by varying the spin-coating parameters. During the subsequent ion-etching process the resist is used as a protective layer for the functional structures. Therefore, the minimum resist thickness is given by the ablation rates of resist and thin film. The anisotropic behavior of the ion-etching process enables aspect ratios larger than 1, and thus, lateral structures with sub-micrometer dimensions. The process steps of lithography, pattern transfer and electrical contacting are performed on an auxiliary substrate with an adhesive bonding layer in-between, which is removed finally to obtain freely movable structures.
Presentation: Oral at E-MRS Fall Meeting 2007, Symposium E, by Daniel Auernhammer
See On-line Journal of E-MRS Fall Meeting 2007
Submitted: 2007-05-14 16:03 Revised: 2009-06-07 00:44