Influence of edge Laser-Induced Periodic Surface Structures (LIPSS) on the electrical properties of fs laser-machined ITO microcircuits

Abstract

Scalable and cost-effective methods for processing transparent electrodes at the microscale are transversal for advancing in electrochemistry, optoelectronics, microfluidics, and energy harvesting. In these fields, the precise fabrication of micrometric circuits plays a critical role in determining device performance and integration with added-value substrates. In this context, Laser Subtractive Manufacturing stands out among microfabrication techniques for its adaptability to diverse materials and complex configurations, as well as its straightforward scalability and affordability nature. However, a challenge in micromachining metals and metal oxides is the inherent formation of LIPSS, which can significantly impair electrical conductivity, particularly when circuit dimensions fall within the micrometer range. Herein, we investigate the micromachining of TCOs using ultrashort pulse laser systems applied to ITO thin films. We analyze the formation of LIPSS at the edges of the micromachined regions associated with the Gaussian distribution of the energy within the laser spot and their impact on the electrical properties depending on the circuit characteristics. Thus, we evaluate the influence of LIPSS orientation and periodicity by fabricating various circuit patterns using femtosecond lasers at green (515 nm) and ultraviolet (343 nm) wavelengths. A correlation between electrical resistivity measurements and structural analysis reveals distinct effects of nanostructure formation depending on the laser source. For green wavelength, the regions where LIPSS are oriented perpendicular to the ITO track exhibit higher resistance, by a factor just above two, compared to those where LIPSS are parallel. Additionally, UV laser processing results in a pronounced reduction of ITO thickness at the boundary between the LIPSS region and the substrate.