Niobium-Containing DLC Coatings on Various Substrates for Strain Gauges

Maria Grein,Andreas Dietzel,Ralf Bandorf,Günter Bräuer,Jessica Gerstenberg,Chresten Von Der Heide

doi:10.3390/coatings9070417

Abstract

Niobium-containing diamond-like carbon films (a-C:H:Nb) were deposited in a hybrid plasma-enhanced chemical vapor deposition (PECVD) and direct-current magnetron sputtering (DCMS) process, using a niobium target in an argon/acetylene atmosphere on industrial polyimide foil, spin-coated polyimide foil, and alumina substrates. While the coating on the industrial foil tends to crack, the thin films on the spin-coated polyimide and the ceramic substrates showed good adhesion, as well as a smooth and dense topography. Investigations of the electrical properties revealed their suitability as biocompatible sensor materials in strain gauges, with a gauge factor of up to 3.2 and a temperature coefficient of the electrical resistance (TCR) of −200 ppm/K.

Highlights

The deposition of thin films on flexible polymer foils is of growing interest, especially for microelectronic systems
Materials and Methods a-C:H:Nb films were deposited by a combined plasma-enhanced chemical vapor deposition (PECVD)/physical vapor deposition (PVD) process using a 3” Torus cathode with balanced magnetron from Kurt J
In our earlier work we found, that elevated gauge factors on the industrial polyimide foil are only occurring at certain Nb contents of between 50 and 70 at %

Summary

Introduction

The deposition of thin films on flexible polymer foils is of growing interest, especially for microelectronic systems. In the field of biomedical applications, sensor systems on polyimide have been successfully investigated for 25 years [1,2,3] This investigation is concerned with the coating of a nanocomposite of niobium and carbon (a-C:H:Nb) on a polyimide foil as a base for biocompatible strain gauges with the objective of high sensitivity and low temperature dependence. A hybrid process of sputtering and PECVD was used, in which a niobium target was sputtered in an Ar + C2 H2 atmosphere to produce an amorphous hydrogenated carbon layer (a-C:H) with enclosed Nbx Cy particles. This type of “metal-doped” material is often referred to as a-C:H:Me or Me-DLC in the literature. Our earlier investigations of a-C:H:Nb stated its great potential for strain sensors with a gauge factor of 35.5 and an TCR near zero [10]

Methods

Results

Conclusion