Knowledge of the mechanical properties and fatigue behavior of thin films is important for the design and reliability of microfabricated devices. This study uses the bulge test to measure the residual stress, Young's modulus, and fracture strength of aluminum nitride (AlN) thin films with different microstructures prepared by sputtering, metalorganic vapor phase epitaxy

The atomic layer deposition (ALD) of AlN from AlCl 3 was investigated using a thermal process with NH 3 and a plasma-enhanced (PE)ALD process with Ar/NH 3 plasma. The growth was limited in the thermal process by the low reactivity of NH 3 , and impractically long pulses were required to reach saturation. Despite the plasma activation, the growth per cycle in the PEALD process was lower than that in the thermal process (0.4 Å vs 0.7 Å). However, the plasma process resulted in a lower concentration of impurities in the films compared to the thermal process. Both the thermal and plasma processes yielded crystalline films; however, the degree of crystallinity was higher in the plasma process. The films had a preferential orientation of the hexagonal AlN [002] direction normal to the silicon (100) wafer surface. With the plasma process, film stress control was possible and tensile, compressive, or zero stress films were obtained by simply adjusting the plasma time.

We have measured mechanical and fracture properties of amorphous Al2O3 thin films deposited by atomic layer deposition with bulge test technique using a free-standing thin film membrane. Elastic modulus was determined to be 115 GPa for a 50-nm thick film and 170 GPa for a 15-nm thick film. Residual stress was 142 MPa in the 50-nm film while it was 116 MPa in the 15-nm film. XRR density was 3.11 g/cm 3 for the 50-nm film and 3.28 g/cm 3 for the 15-nm film. Fracture strength of the 15-nm film was 4.21 GPa while the 50-nm film had only 1.72 GPa at a 100 hPa/s pressure ramp rate. Fracture strength was observed to be positively strain-rate dependent. The effective volume of a circular film in bulge test was determined from a FEM model enabling comparison of fracture strength data between different techniques.

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.

Superomniphobic surfaces that repel liquids of extremely low surface tension rely on carefully fabricated doubly re-entrant topographies, typically made by silicon deep reactive ion etching technology. However, previously published processes have depended on critically timed etching steps, which are difficult to downscale. We present a scalable process that eliminates the critically timed etching steps. It is based on the use of silicon-on-insulator wafers and a silicon oxide foot of the micropillar, which makes the isotropic silicon release step noncritical. The process allows easy downscaling of pillars from 20 μm to 10 μm and 5 μm. The downscaling increases the stability of the Cassie state. Based on the process, we are able to create superomniphobic surfaces that sustain perfluorohexane (FC-72), which has the lowest surface tension of the known liquids at room temperature (γ lv = 11.91 mN/m at 20 • C), in the Cassie state at droplet diameters down to 200 micrometers. These are the smallest perfluorohexane droplets repelled to date.