Simultaneous enhancement of electromagnetic interference shielding and infrared transmittance based on SnO₂ thin films

Mn-doped SnO₂ thin films were fabricated to enhance two conflicting properties of the electromagnetic interference (EMI) shielding effectiveness and the infrared (IR) wavelength ranges. As a magnetic element, manganese (Mn) was doped into the SnO₂ thin films at an over-doping level of 300 mM to increase its magnetic permeability. As the molar content of Mn increases, the preferred growth plane of the SnO₂ thin films changes from (200) to (115) planes. Although all SnO₂ thin films showed diamagnetic properties due to the strong diamagnetism of the substrate and SnO₂, the magnetic susceptibility of the Mn-doped SnO₂ films slightly decreased with increasing the Mn content from 0 to 60 mM, while it increased again with the doping content above it. As the Mn doping content increased from 0 to 150 mM, the sheet resistance of SnO₂ films continuously increased from 98 to 128 Ω/sq. As the Mn content increases from 30 to 120 mM, the IR transmittance at 4 μm increases from 37 to 47%, while the EMI shielding effectiveness at 10 GHz increases from 8.7 to 9.0 dB. The abnormal result of increased shielding effectiveness despite increased sheet resistance was due to increased magnetic permeability due to the addition of Mn. As the Mn content exceeds 150 mM, Mn-related metal clusters are formed inside the thin film, reducing the magnetic susceptibility and EMI shielding.