Fracture properties of atomic layer deposited aluminum oxide free-standing membranes

Abstract

The fracture strength of Al2O3 membranes deposited by atomic layer deposition at 110, 150, 200, and 300 °C was investigated. The fracture strength was found to be in the range of 2.25–3.00 GPa using Weibull statistics and nearly constant as a function of deposition temperature. This strength is superior to common microelectromechanical systems materials such as diamondlike carbon, SiO2, or SiC. As-deposited membranes sustained high cycling pressure loads >10 bar/s without fracture. Films featured, however, significant reduction in the resistance to failure after annealing (800 °C) or high humidity (95%, 60 °C) treatments.

Elastic and fracture properties of free-standing amorphous ALD Al2O3thin films measured with bulge test

“…The mechanical properties of the Al2O3 membranes that we measured are comparable to what has been previously measured [Ylivaara 2014], [Berdova 2014], [Berdova 2015], [Wang 2012]. The elastic modulus of our 48.1-nm thick film is low, but there is a noticeable increase in the elastic modulus for the thinner film.…”

“…(8) and the material parameters obtained for our 14.8-nm thick film, we reach an expected mean fracture strength of 4.1 GPa. This value is higher thanBerdova et al [2015] obtained and not much different from the fracture strength of our 14.8-nm film because of the very high Weibull modulus measured for our films. Weibull moduli that we have measured for both 48.1-nm and 14.8-nm thick films (49 and 55) are much higher than whatBerdova et al [2015] measured for their films (15).…”

“…The difference between the residual stress values for our 14.8-nm and 48.1-nm thick films is within the error margins and there appears to be no thickness dependence on the residual stress, which is in accordance to previous studies. [Ylivaara 2014] The mean fracture strength for the 48.1-nm thick membranes were lower than reported previously by Berdova et al [2015] The pressure tolerance and the increase of the fracture strength for the thinner membranes are noticeable. The 14.8-nm thick membranes withstood similar pressures as the 48.1-nm thick membranes when the pressure ramp rate was 100 mbar/s leading to the very high fracture strength values.…”

“…Bulge test [Beams 1959] [Vlassak 1992] [Sharpe 2004] [Berdova 2014] [Berdova 2015] is a suitable method to measure thin film elastic properties such as elastic modulus, residual stress and fracture strength. In a bulge test, a free-standing membrane that is fixed from the edges is loaded from one side by a fluid.…”

“…Ylivaara et al reported [Ylivaara 2014] a thorough investigation on the elastic properties of ALD Al2O3 measuring elastic modulus, hardness and residual stress for a wide range of film thicknesses and growth temperatures, but they did not report fracture properties. We have previously studied [Berdova 2014] [Berdova 2015] the elastic modulus, residual stress and fracture strength of ALD Al2O3 measured by the bulge test and the shaft-loading technique, but have not studied scale nor strain-rate dependency of the elastic and fracture properties. We have now measured the elastic and fracture properties of freestanding ALD Al2O3 thin films with the bulge test and observed strain-rate dependent properties.…”