Stress reduction in ultra-small thin film Al2O3 diaphragms by atomic layer deposition

In this paper we present a concept of reducing the residual stress in atomic-layer-deposited Al2O3 diaphragms by compensating the tensile intrinsic stress with a compressive thermal stress. This is facilitated by using single-crystal quartz substrates which exhibit a high coefficient of thermal expansion. We studied the stress in diaphragms fabricated at different deposition temperatures and showed that there is a transition from tensile to compressive residual stress with increasing deposition temperature. An optimal temperature for stress-free films was proposed and diaphragms with a compressive residual stress as small as −10 MPa were fabricated.