CNT reinforced Materials

A new research topic deals with incorporation of nanotubes into metal or ceramic matrices to form composite structures to enhance special properties of matrix materials for microelectronic, microacoustic or microelectromechanical systems (MEMS). Therefore, carbon nanotubes (CNTs) can be especially considered as excellent candidates to enhance electrical, mechanical or thermal properties of different ceramic or metallic thin film materials whereas the advanced properties of composite films strongly depend on type and quality as well as the incorporation principle of CNTs.

At this stage, and regarding to our other research on power loaded metallization thin films, we are interested in copper-matrix multiwall CNT (MWCNT) composite layers. However, adhesion behavior of the matrix material on the outer graphene sheet of the CNTs predominantly determines the properties of composite films. In the case of copper-based films an important fabrication problem exists because of the low interaction strength of copper with carbon. Therefore, we develop a preparation technique to enhance copper adhesion on CNTs for efficient fabrication of copper matrix-CNTs composites. A very thin Ta-based adhesion layer was deposited on chemical vapor deposited CNTs by using a plasma enhanced atomic layer deposition (PEALD) technique. This work is done together with our cooperation partner of the University of Technology Dresden. The PEALD process is carried in a hot wall reactor by using TBTDET and hydrogen processing gas. Various pre-treatment steps of the nanotubes are investigated for enhancing the adhesion and quality of the ALD layers. Investigations by using scanning (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX) as well as other analytical methods show that a suitable wetting of thin Ta(N,C,O) layers on the MWCNTs surface can be obtained that should suggest an enhanced copper plating or metal organic CVD process on CNTs.

Fig. 1: Deposition experiments to deposit copper onto MWCNTs without an adhesion layer using MOCVD (deposition: C. Täschner/IFW).

Fig. 2: a) SEM picture of the Ta(N,C,O)-coated MWCNTs (Fe-filled), b) EDX analysis at marked position in a).

Fig. 3: Electroplated copper grains on a Si-wafer substrate with incorporated Ta(N,C,O)-coated MWCNTs.
Fig. 3: Electroplated copper grains on a Si-wafer substrate with incorporated Ta(N,C,O)-coated MWCNTs.