Laser alteration of the mechanical properties of photostructurable glass-ceramic

Abstract

Photostructurable glass-ceramics (PSGCs) present an attractive alternative to silicon as substrates for microfabrication. Moving a laser beam with a focal volume a few microns across and a few tens of microns high through a transparent PSGC induces a cascade of reactions that results in selective crystallization in the laser-exposed regions. The process offers excellent 3-D shaping control. Crystal formation alters many material properties, including opacity, index of refraction, etch rates, density, stiffness, and strength. Presented here are the results of bulk mechanical measurements of the mass density and the velocity of sound in several phases of Foturan, a commercially available PSGC. The measurements are nondestructive and easily repeatable at many stages of processing. From the velocity and the mass density, we calculated the elastic modulus for each Foturan phase. The measured samples included native, amorphous Foturan; exposed Foturan that was not thermally treated; and exposed, thermally treated Foturan. Results show that Foturan becomes somewhat stiffer with higher crystal content; the elastic modulus of Foturan rises from about 78 GPa in the original amorphous glass state to about 88 GPa in a crystal-rich, exposed, baked state. The speed of sound in Foturan rises from about 5.8 km/s to 6.1 km/s.