Method for producing transparent conductive coatings for emi protection using HiPIMS
A method for forming a coating on a substrate formed from zinc sulfide (ZnS) is provided. A ZnS film is grown on the substrate with a radio frequency sputtering process and metal dopants are sputtered on the substrate with a high-power impulse magnetron sputtering process. The metal dopants can be molybdenum or tungsten and simultaneously sputtered while growing the ZnS film. The sputtering ionizes the coating where the coating has a sheet resistance that is less than 50 ohm/square and the metal dopants form n-type dopants in the ZnS film. The metal dopants can be formed at a concentration that varies with a thickness of the ZnS film. At a first thickness, the concentration is at a first concentration and at a second thickness greater than the first thickness, the concentration is at a second concentration less than the first concentration.
1 . A method for forming a coating on a substrate, the method comprising:
growing a zinc sulfide (ZnS) film on a surface of the substrate with a radio frequency (RF) sputtering process; and
sputtering metal dopants on the substrate at concentrations between 1×10 16 cm −3 and 1×10 20 cm −3 with a high-power impulse magnetron sputtering (HiPIMS) process, wherein:
the metal dopants are ionized and one of molybdenum or tungsten;
the metal dopants are simultaneously sputtered with a RF sputtering process while growing the ZnS film, wherein:
the RF sputtering process and HiPIMS process are simultaneously performed such that the ZnS film is grown on the substrate during the RF sputtering process; and
the HiPIMS process is performed such that the ionized metals dopants are interspersed in the ZnS film as the ZnS film is grown on the substrate;
the sputtering the metal dopants ionizes the coating on the substrate such that the coating has a sheet resistance that is less than 50 ohm/square and the metal dopants form n-type dopants in the ZnS film; and
the concentrations at which the metal dopants are sputtered varies with a thickness of the ZnS film such that at a first ZnS film thickness, there is a first concentration and at a second ZnS film thickness that is greater than the first ZnS film thickness, there is a second concentration that is less than the first concentration where the second ZnS film thickness is separate from the first ZnS film thickness, wherein:
the ZnS film is formed in a stepwise fashion to achieve the first and second film thicknesses with corresponding gradient concentrations of the metal dopants distributed throughout the coating; and
the greater thickness of the second ZnS film dilutes the metal dopants throughout the coating thereby allowing for a lower concentration of the metal dopants.
2 . The method of claim 1 , wherein the first concentration of metals of the metal dopants is in a range between 1×10 18 cm −3 and 1×10 20 cm −3 when the first ZnS film thickness is less than 1 micron.
3 . The method of claim 1 , wherein the second concentration of metals of the metal dopants is in a range between 1×10 16 cm −3 and 1×10 18 cm −3 when the second ZnS film thickness is greater than 1 micron.
4 . The method of claim 1 , wherein the coating is a transparent coating and is configured to allow detection of infrared signatures through the coating and the substrate.
5 . The method of claim 4 , wherein the coating and the substrate form a window for a vehicle having a detector that allows for the detection of optical signals and thermal signatures through the window and into an interior of the vehicle.
6 . The method of claim 1 , further comprising adding a p-type conductive coating on the coating of the substrate.
7 . The method of claim 6 , wherein the p-type conductive coating is barium copper sulfur fluoride.