Investigations on the passivation of thin film flow sensors on flexible substrates

To ensure an enhanced life-time of micromachined devices, passivation layers are commonly applied to protect functionalized components against environmental stress. For flow sensitive elements on a flexible polyimide foil the use of reactively sputter-deposited aluminium oxide is investigated. Due to a high defect density located at the interface between the passivation layer and the organic substrate, the adhesion of the pure aluminium oxide thin films on the organic substrate was found to be poor when applying a combination of mechanical and thermal treatment as an accelerated ageing procedure. A bi-layer consisting of aluminium nitride and aluminium oxide is proposed to enhance. the low adhesion capability being strongly disadvantageous for any technical application.