Adhesion performance and tribological properties of atomic layer deposited aluminum oxide films

The atomic layer deposited (ALD) thin films typically used for microelectromechanical system (MEMS) devices need to have sufficient adhesion to the substrate in order to be functional in the application. It is also important to understand the tribological performance of the coatings in order to take into account the friction and wear related issues in MEMS device design. In this study we have applied the micro-scratch test to evaluate the adhesion performance of aluminum oxide (Al2O3) films on Si by using a diamond tip with the radius of 20 µm. For the friction and wear studies of Al2O3 film the tribological tests, such as pin-on-disc was applied. The Al2O3 films were deposited on Si wafers in the deposition temperatures that varied from 110 to 300 °C. The coating adhesion was studied for coating thicknesses in the range 20 to 300 nm. For the tribological tests the friction and wear performance of Al2O3 films was studied against Si, Al2O3, steel bulk materials and diamond-like carbon (DLC) coatings. The Al2O3 coating with 300 nm thickness (300 °C) was also deposited on stainless steel (AISI 440B) pins for tribological tests. of 300 °C. According to micro-scratch testing the adhesion of the 300 nm thick Al2O3 films was good on Si, since the coating delamination was observed only when the Si wafer was cracking. The friction force and penetration depth measured during scratching also showed the sudden breakage of the substrate material. The friction coefficient of Al2O3 film measured against steel and bulk Al2O3 was high which caused the delamination of the coating. When the Al2O3 film was sliding against the DLC coating, the friction was remaining low and the coating performance was excellent.