Characterisation of thin film piezoelectric materials by differential interferometric techniques

摘要

Piezoelectric thin films are considered emergent materials for integration within Micro Systems Technology (MST) or MEMS devices. The development of suitable measurement facilities to characterise the materials functional properties is complicated by the fact that the film is often attached to a substrate which acts to clamp the film thus affecting the system performance. This paper describes a new differential interferometer system based on common path Jamin optics and measurement lock-in techniques that is able to analyse the displacements of the thin film to 1/10's of pm resolution. The film/substrate acts as a natural bending element and this effect means that the displacement measurements must be carefully controlled to minimise any substrate bending. The system designed at NPL is able to measure the degree of substrate bend so that an 'effective' piezoelectric coefficient may be calculated. Results will be shown for ceramic monolithic materials, quartz single crystal material and sol-gel derived thin and thick films of PZT on Si substrates.