External magnetic field guiding in HiPIMS to control sp³ fraction of tetrahedral amorphous carbon films

Abstract

Amorphous carbon films have many applications that require control over their sp3 fraction to customise the electrical, optical and mechanical properties. Examples of these applications include coatings for machine parts, biomedical and microelectromechanical devices. In this work, we demonstrate the use of a magnetic field with a high-power impulse magnetron sputtering (HiPIMS) source as a simple, new approach to give control over the sp3 fraction. We provide evidence that this strategy enhances the deposition rate by focusing the flux, giving films with high tetrahedral bonding at the centre of the deposition field and lower sp3 fractions further from the centre. Resistive switching appears in films with intermediate sp3 fractions. The production of thin amorphous carbon films with selected properties without the need for electrical bias opens up applications where insulating substrates are required. For example, deposition of sp3 rich films on polymers for wear resistant coatings as well as fabrication of resistive switching devices for neuromorphic technologies that require tuning of the sp3 fraction on insulating substrates are now possible.

Noble gas control of diamond-like content and compressive stress in carbon films by arc-mixed mode high power impulse magnetron sputtering

“…The arc generation does not need a separate triggering operation but instead arises from the runaway increase in current. The characteristics of arcs generated in the mixed-mode are similar to those observed in cathodic arcs, including retrograde motion driven by the magnetic field and fractal-like branching of the arc spots generating carbon ions with an average energy of at least 20 eV [11,[17][18][19]. These arcs contribute to the enhanced ionization of deposited carbon atoms and subsequently pave the way for the high sp 3 fraction in the films by application of substrate bias, replicating the "energy window" effect wherein the sp 3 hybridization is maximum for a bias voltage of 100 V, approximately [2,10,20].…”

“…This technology, however, cannot be applied in commercial ta-C deposition because of the low deposition rate associated with the process and low sp 3 content of the resulting coatings compared to other technologies such as filtered cathodic arc [7]. Following the advent of high-power impulse magnetron sputtering (HiPIMS), amorphous carbon coatings with a wide range of sp 3 fractions [3,4,[8][9][10][11], a smooth surface topography [3,12] and improved coating-substrate adhesion with excellent wear resistance at high radii of curvature [4,13] have been produced and commercial applications of diamond-like carbon (DLC) coatings have widened. However, increasing the deposition rate of carbon films with high sp 3 contents remains a key challenge in the field [14,15].…”

Modeling of high power impulse magnetron sputtering discharges with graphite target

“…There are several options how to exploit this situation by attempting to reduce the backattraction of these late-formed ions: using ultra-short and ultrahigh current peaks; applying a reversed-polarity peak after these HiPIMS peaks, so called bipolar HiPIMS [88,89]; and/or tailoring the magnetic geometry (in particular the degree of magnetic unbalance) in order to minimize any back-attracting electric fields between the IR and the substrate during the offtime. An example of utilization of this is demonstrated in the work of Akhavan et al [33] which apply an external magnetic field during the end of the pulse where the ionization probability is the highest, enabling more efficient transport of the carbon ions to the substrate.…”

“…It has been observed experimentally that the film mass density varies linearly with the sp 3 content [5,37,38]. The film mass density has been reported to be in the range 2.2-3.15 g cm −3 for HiPIMSdeposited films [15,17,33] compared to roughly 2.0 g cm −3 for dcMS deposited films, 3.1 g cm −3 for rf magnetron sputter deposited films on biased substrate [38], up to 3.2 g cm −3 for films deposited by filtered cathodic arc [34,39], and up to 3.5 g cm −3 for PLD films [40,41]. It should be noted that the filtered cathodic arc has very high ionized flux fraction >96% [42].…”

Achieving ultra‐low friction of a‐C:H film grown on 9Cr18Mo steel for industrial application via programmable high power pulse magnetron sputtering

“…Ganesan et al obtained ta‐C films with an sp 3 content of 80%, which were produced by HIPIMS operating in a mixed sputtering/arc mode 26 . Akhavan et al demonstrated that the use of a magnetic field with an HIPIMS source is a simple and new approach to give control over the sp 3 fraction 27 . Huang et al deemed that increasing fraction of sp 2 is favorable for enhanced tribological properties of the graphite‐like carbon films deposited by HIPIMS 28 …”