Low-temperature strength tests and SEM imaging of hydroxide catalysis bonds in silicon

Abstract\nSilicon is under consideration as a substrate material for the test masses and suspension elements of gravitational wave detectors of improved sensitivity. Hydroxide catalysis bonding is a candidate technique for jointing silicon elements with the potential for both high strength and low mechanical loss. A future detector with quasi-monolithic silicon final stages may operate at cryogenic temperatures. Here we present the first studies of the strength of siliconsilicon bonds at 77 K (liquid nitrogen temperature) and show characteristic strengths of ~ 44 MPa are achieved. When comparing cryogenic to room temperature results no significant difference is apparent in the strength. We also show that a minimum thickness of oxide layer of 50 nm is desirable to achieve reliably strong bonds. Bonds averaging 47 nm in thickness are achieved for oxide thicknesses greater than 50 nm.