EPFL and Fraunhofer in general worked on sputtering platforms of differing complexity for wafer sizes of 150 mm (EPFL) and 200 mm (ISiT) built-up by Oerlikon in the beginning of the project. Although both institutions pursued different processing routes, EPFL as well as ISIT achieved remarkable ferroelectric, piezoelectric and dielectric properties for their optimised in-situ sputtered PZT thin films.
EPFL investigated the influence of lead and non-lead based seeding layers for an improved nucleation and growth of subsequently sputter-deposited PZT films. Providing a suitable seeding, EPFL achieved highly textured, (100) oriented PZT thin films on 6” substrates with a deposition rate of 42.5 nm/min.
ISiT's work focused on the development of an in-situ PZT sputtering process for 200 mm substrates and the integration of this process in a MEMS compatible production line as existent at Fraunhofer ISiT. The process and its integration was optimized taking into account factors like the pre-processing of substrates (cleaning, de-gas, soft-etch), different variants of substrates and also cost of manufacture in general. Therefore the PZT was directly sputtered on evaporated electrodes without use of an extra seed layer deposition process.
In conclusion, the work of both institutions yielded in in-situ sputter-deposited PZT thin films of remarkable ferroelectric, piezoelectric and dielectric properties. The targeted piezoelectric values of d33,f > 100 pm/V and |e31,f| > 14 C/m² were achieved and exceeded on both 150 mm and 200 mm substrates. Some innovative processes have been developed for direct sputtering of PZT without need of an additional post-annealing treatment as well as for suitable seeding layers. In case of the 200 mm process the notable piezoelectric properties were achieved even without a supplemental seeding layer process.
Published December 11, 2012
The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2010-2013) under grant agreement n° 229196