A review on microholes formation in glass-based substrates by electrochemical discharge drilling for MEMS applications

Continuous demands to develop advanced radio-frequency transmission at higher frequencies have initiated glass-based materials as a substrate in radio-frequency micro-electro-mechanical-systems (MEMS) applications. Due to its superior electrical insulation characteristics, glass has lower substrate losses than silicon when an electrical signal is transmitted at higher frequencies. The optical transparent nature of glass substrate makes it an attractive choice for microfluidics and Bio-MEMS applications. Despite having superior properties, glass usage has remained limited mainly due to the lack of suitable micromachining processes. Due to its hard and brittle nature, creating microfeatures by conventional methods has been a challenge. To date, laser ablation and plasma etching have been employed to create micro-size through-holes in glass substrate; however, both have severe process limitations. Electrochemical discharge drilling (ECDD) is an emerging method that possesses similar capabilities as existing technologies at a low cost. Therefore, this manuscript is presented to describe the ECDD process's potential and their hybrid methods in the direction of fabricating micro-holes for MEMS applications. This manuscript includes the fundamental aspects of the ECDD process and a detailed description of components used to develop its various configurations. ECDD-based hybrid methods have also been presented along with their mechanisms and capabilities. The existing challenges and the possible research potentials have been derived based on previously reported capabilities to establish the correlation between the ECDD process and MEMS devices.