INPLANE INTERDIGITATED (IPID) ELECTRODES FOR THIN-FILM APPLICATIONS

Microstructured substrates featuring interdigitated electrodes with a large length to width ratio allow the evaluation of thin films with ve ry high sheet resistivity even in environments with large electromagne tic interference. However thin phthalocyanine (Pc) films, vacuum evapo rated on substrates with conventional interdigitated (ID) electrodes d eposited on top of a planar surface, develop cracks at the edges of th e contact stripes. For samples with a film thickness of 200 monolayers (ML) corresponding to 80 nm this causes a resistance two orders of ma gnitude higher than that expected for the chosen length to width ratio . A new microstructured Si-substrate with in-plane interdigitated (IPI D) electrodes has been designed to achieve minimum height differences on the surface. This substrate features interdigitated electrodes with a length to width ratio of 52,000: 1 and additionally an integrated h eating element and a temperature sensitive resistor. Thin Pc-films wit h various thicknesses between 50 ML (= 20 nm) and 500 ML (= 200 nm) ex hibit sheet resistivities as were expected for the chosen length to wi dth ratio. These sensing elements were successfully employed in the de tection of NO(x) emissions in cars and their stability and sensitivity have been proved over several months in polluted air.