NiMnGa nanostructures produced by electron beam lithography and argon ion etching

Daniel Auernhammer 1Mario Schmitt 3Makoto Ohtsuka 2Manfred Kohl 3

1. Universität Karlsruhe, Karlsruhe 76128, Germany
2. Tohoku University, Sendai, Japan
3. Forschungszentrum Karlsruhe, IMT, Postfach 3640, Karlsruhe 76021, Germany

Abstract

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.

 

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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