Impact of Cu Film Microstructure on Resistivity of CFRP Surface AITranslate

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Basic Information:

DOI：10.13373/j.cnki.cjrm.XY25030009

Chinese Library Classification Number:TF831

Citation Information:

Carbon fiber reinforced plastics （CFRP），characterized by high specific strength，fatigue resistance，and a low coefficient of thermal expansion，have found widespread applications in fields such as aerospace. However，with a resistivity ranging from approximately 1.3×10^-5 to 1.9×10^-5 Ω·m，CFRP exhibits poor conductivity when used as antenna reflectors and waveguides. Furthermore，due to its anisotropic properties，surface metallization is required to enhance microwave transmission efficiency. To achieve metallization of CFRP surface，Cu film with Ti interlayer was deposited on CFRP surface using direct current pulsed magnetron sputtering technology in this paper. The thickness of Ti interlayer was approximately 50 nm，and the thickness of Cu film was approximately 1.2 μm. During the preparation of this thin film，sputtering power and deposition pressure were varied to optimize the relationship between resistivity and deposition parameters. To investigate the microstructural changes in Cu film，various analytical techniques such as scanning electron microscopy （SEM），dual beam focused ion beam （FIB） microscope，X-ray diffraction （XRD），four-point probe resistivity tester，stylus profilometer，and transmission electron microscopy （TEM） were employed to analyze the film microstructures. Additionally，given the temperature resistance characteristics of CFRP，close attention was paid to the changes in deposition temperature during the film deposition process. The results showed that as the sputtering power was increased from 300 to 700 W，the enhanced sputtering yield increased the bombardment effect of particles on the film surface，which in turn boosted the mobility of atoms on the film surface. This promoted the preferential growth of the film along the （111） crystal plane. Consequently，the average grain diameter in the film increased from approximately 35 to 47 nm，and the texture coefficient value of the （111） plane rose from 1.99 to 2.63. Additionally，a twinned structure gradually formed，and the resistivity decreased from 4.36×10^-8 to 3.77×10^-8 Ω·m. However，when the sputtering power continued to be increased，the grain size in the film began to decrease，resulting in a subsequent increase in resistivity to approximately 3.98×10^-8 Ω·m. When the sputtering power was set at 700 W，cross-sectional images revealed the abundant presence of layered columnar crystals，which were entirely perpendicular to the surface. The cross-sections of these columnar crystals measured between tens of nanometers and one or two hundred nanometers. Other grains，observable with distinct background colors，exhibited relatively irregular shapes and extended obliquely towards the surface. TEM analysis of the layered columnar crystals showed that they possessed a twinned crystal structure，with the growth direction of the twinned grains perpendicular to the film surface. This occurred because during the film deposition process，when particles incident on the film surface carried appropriate energy，sufficient compressive stress formed in the sub-surface layer. This compressive stress promoted the transformation of grains into twins and contributed to the formation of a dense film structure，thereby reducing the resistivity of the Cu film. The shift in the diffraction angle of Cu film's （111） plane during XRD testing further confirmed the presence of compressive stress within the film. Surface morphology tests indicated that，when the sputtering power was 700 W，grain growth in the sub-surface layer was particularly pronounced. When the sputtering power was maintained at 700 W and the deposition pressure was increased from 0.20 to 0.60 Pa，collisions between ions became more frequent. Consequently，the number of charged ions began to decrease，and the energy transferred by charged particles to the film surface started to diminish. This led to a reduction in the compressive stress within the film. The average grain diameter decreased slightly，from 47 to 41 nm. Simultaneously，the twinned crystal structure ceased to appear. As a result，the resistivity of the film increased from 3.77×10^-8 to 5.17×10^-8 Ω·m. When the deposition pressure exceeded 0.40 Pa，as observed in XRD patterns，there was no shift in the diffraction angle position of Cu film's （111） plane，indicating that the stress state within the film remained unchanged during the deposition process. At a deposition pressure of 0.80 Pa，due to a further weakening of ion collisions with the film，the deposited atoms exhibited island-like growth on the film surface，resulting in a zigzag pattern. The gaps between these islands provided space for grain growth，leading to a slight increase in grain diameter. Simultaneously，the resistivity of the film decreased slightly to 4.84×10^-8 Ω·m. During the magnetron sputtering deposition of Cu films，increasing the bias voltage could enhance ion beam bombardment，generating compressive stress that densifies the film and might even lead to the formation of twin crystal structures. However，excessively high bias voltage resulted in a gradual rise in the deposition temperature. Continuously applying a high negative bias voltage during film deposition on CFRP surfaces could elevate the temperature，causing components such as resin in CFRP to 'vaporize' and escape，thereby contaminating the metallic film. This study provided technical support for the low-temperature deposition of dense Cu films.