UDC 621.317

Measurement of the optical coefficients of nanometer metal films at a frequency of 10 GHz

 

V. G. Andreev ¹, V. A. Vdovin ², S. M. Pronin ¹, I. A. Khorin ³

¹ Faculty of Physics, M.V. Lomonosov Moscow State University, Leninskie Gory, 1-2, Moscow 119991, Russia
² Kotelnikov Institute of Radioengineering and Electronics of Russian Academy of Sciences, Mokhovaya,11-7, Moscow 125009, Russia

³ Physical-Technological Institute of Russian Academy of Sciences,  Nakhimovskiy prospect 36-1, Moscow 117218, Russia

 

The paper is received on November 16, 2017

 

Abstract. The optical coefficients of ultrathin (1-30 nm) films of copper, gold and platinum on silicon and quartz substrates at a frequency of 10 GHz are studied. The films are produced by magnetron sputtering. Measurements of the reflection and transmission coefficients were carried out in the waveguide using a matched termination. As an additional, a resonator method with a tunable reflecting mirror is proposed. The reflection coefficients of the films obtained by both methods agree with one another within the error of measurement. Theoretical calculations were performed using a semiempirical model that takes into account the dependence of the film conductivity on the thickness. It was showed that the conductivity of the films is almost an order of magnitude lower than in the bulk metal. The measured reflection coefficient of platinum films is very small, and only for thicknesses exceeding 15 nm it begins to grow. A detailed analysis of the morphology of the surface of the produced films was carried out using electron microscopy methods. It is shown that copper films with a thickness of up to 4 nm oxidize very rapidly in air, as a result of which a stable oxide layer with a complex structure is formed. However, starting from a thickness of 4 nm, the films exhibit metallic properties, and their structure becomes fairly homogeneous. Platinum films on the Si (100) substrate grow in a two-dimensional manner. Grains become conical with increasing the thickness of the film. At a thickness of 5 nm, a grain structure with clear intergranular gaps is already observed. A further increase in the thickness of the film leads to an increase in the grains, but the voids between them become wider, which reduces the conductivity of the films.

Key words: optical coefficients, waveguide measurements, ultrathin films of metals, morphological structure.

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For citation:

V. G. Andreev, V. A. Vdovin, S. M. Pronin, I. A. Khorin. Measurement of the optical coefficients of nanometer metal films at a frequency of 10 GHz. Zhurnal Radioelektroniki - Journal of Radio Electronics, 2017, No. 11. Available at http://jre.cplire.ru/jre/nov17/17/text.pdf. (In Russian)