Use of a piezo-electric microarrayer for site-specific, high throughput contact angle measurements

Quality control of surfaces at sub-mm resolution is necessary for many active devices, like biosensors, when moving from development to mass-production. Low cost and high throughput site-specific surface measurements on surfaces with topography are difficult or simply impossible using many conventional techniques. As a route towards fast, in-line quality control, we demonstrate top-view contact angle measurements using a non-contact microarrayer. The method was explored and validated by comparing obtained contact angles to a commercial goniometer tool. Using similar liquid volumes and environmental conditions in both tools, excellent correlation was achieved. The influence of experimental conditions appeared to have a great effect on the accuracy of this approach. Changing relative humidity induced contact angle changes proportionally with exposure time. Droplet evaporation only affected the accuracy if the droplet diameter decreased before image analysis. Droplet volume impacts the accuracy below 10 nL; below this threshold, increasing optical resolution by switching to a higher-magnification lens leads to improved accuracy. High spatial resolution measurement was performed on silicon substrates to reveal vapor-phase siloxane formation patterns. Large area and site-specific measurements in mmsized features were performed to demonstrate the potential for high throughput contact angle measurement on both flat and more complex substrates. Considering non-contact microarrayers are used in high throughput production environments already, this approach of doing contact angle measurements can be added as a quick quality control.