Investigation of thermal damage in continuous wave laser-induced nanowelding

Abstract

Continuous wave (CW) laser-induced nanowelding holds great promise in micro-and nano-devices. However, because of the lengthy irradiation duration, the heat effect from CW laser irradiation may harm the manufactured devices. The simulation results show that an increase in irradiation duration will slightly improve the welding temperature but greatly expand the heat-affected area when the irradiation time exceeds 100 ms. Experimental results confirm that Cu nanowires irradiated for 20 ms are slightly oxidized. As the irradiation period is increased to 10,000 ms, the oxygen concentration in Cu nanowires significantly increases, and the color of Cu nanowires becomes first black, then green. The electrical property of the oxidized Cu-Au nanojunction shifts from ohmic contact to Schottky contact. Furthermore, the large heat-affected area will weaken the adhesion between the Au pad and the substrate due to the large difference in thermal expansion coefficient between the metal film and the insulating layer. Consequently, CW laser-induced thermal damage not only impairs the electrical properties of nanostructures but also their reliability.