Abstract
The adhesion strength between thin films has a significant effect on performance of micro-devices. It is introduced that the effects of three pre-treatment methods: acid, pulse reverse current and anodic current, on the adhesion performance of electrodeposited Ni films on Ni substrate. The adhesion strength, surface and fracture morphology of the Ni films were investigated. The dense oxide films on the Ni substrate were removed effectively by using the anodic dissolution current method in the acidic chloride solutions. Meanwhile, the Ni films treated with specific treatment conditions produced different roughness, which was responsible for the improved adhesion strength. The adhesion strength of the Ni films increased up to 629.8 MPa when substrates were treated with anodic current density of 30 mA/cm2 for 10 min, which is nearly two times higher than that of films treated by 5 vol % HCl for 10 min. The results indicate that the anodic current treatment method effectively improves the adhesion strength of Ni films.
Highlights
With the rapid development of micro-electro-mechanical systems (MEMS) technology, a large number of materials including silicon, metal and polymers are widely used in MEMS field
The results indicate that an average shear adhesion strength of approximately 400 MPa is achieved for the Ni laminated films treated by pulse reverse (PR) method, which is higher than that of the Ni laminated films treated by hydrochloric acid
The results indicate that the dense oxides on the top of the metal Ni substrate can be removed effectively by anodic dissolution current in the nickel chloride solution
Summary
With the rapid development of micro-electro-mechanical systems (MEMS) technology, a large number of materials including silicon, metal and polymers are widely used in MEMS field. Electrochemistry as a general method is used to fabricate metal films, nanowires, honeycomb-like structures and microstructures with high aspect ratio [16,17,18,19] This method could improve the adhesion strength of the film structure to some extent, but it is rarely studied in field of MEMS devices. The metal Ni materials are frequently applied in the MEMS field, the systematic study of the adhesion strength between Ni/Ni films is lacking It limits the process of microstructure devices based on metal Ni. In our previous work, it has been demonstrated that a hydrochloric acid and pulse reverse (PR) current treatments method could well improve the adhesion strength between Ni laminated films [20]. The anodic current treatment method significantly improves adhesion strength, because it removes the oxygen between interfaces and increases the surface roughness
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