Development and Evaluation of Copper Based Transparent Heat Reflectors Obtained by Magnetron Sputtering

Within the next few years climate change is likely to become a major concern for mankind. In addition, the current electronic components shortage crisis has led to an urgent need for alternative solutions in the main industry sectors (the raw materials, manufacturing, and construction industries). The current trends of research are focused on developing smart materials with functional properties, using abundant raw materials. The energy saving efforts are sustained in the glazing industries by several approaches based on dielectric-metal-dielectric multilayer structures. The use of silver to achieve a high reflectivity in near-infrared spectral range has been proposed and is already adopted as a commercially available solution. This work is focused on developing a transparent heat reflector (THR) with prefigured optical properties, using copper as a reflective layer, a material that is more abundant and cheaper than silver. The conductive copper layers obtained by the High Power Impulse Magnetron Sputtering (HiPIMS) method were interposed between two silicon nitride layers deposited by the Radio-Frequency Magnetron Sputtering (RFMS) technique. The structural, optical, and elemental composition of monolayers was investigated, qualifying each individual material for use in the multilayer structure. The time stability of films deposited on microscope glass substrates was also investigated, as an important criterion for the selection of monolayers. The obtained results revealed that the SiN_x/Cu/SiN_x with the Cu layer deposited by using a negative substrate bias of -100 V showed the most stable behavior over time. Optical modeling was performed to design a THR multilayer structure, which was successfully obtained experimentally. A maximum optical transparency as high as 75% in the visible range and a reflectivity of ~ 85% in near infrared spectral interval was confirmed for the experimentally obtained multilayer structures.