Abstract
Compared to present devices based on bulk piezoelectric elements or other working principles, new piezoelectric microsystems (piezo-MEMS) may feature improved functionality and reliability, increased complexity, reduced energy consumption, smaller volume and lower cost. However, before industrial production of piezo-MEMS can be realised, the performance and reliability of the resulting devices have to be verified. A process resulting in high and even device performance, as well as long lifetime, across a wafer and from wafer to wafer must be chosen. Thin films of PZT (Pb(Zr,Ti)O3), being one of the most utilized piezoelectric materials, can be deposited by several methods, such as sputtering, metal organic chemical vapour deposition (MOCVD), pulsed laser deposition (PLD) and chemical solution deposition (CSD). When fabricating a piezo-MEMS device based on basic structures such as cantilevers, diaphragms and bridges, the transversal piezoelectric coefficient, e31,f, is the most important performance parameter. In this context it is interesting to note that thin films of PZT deposited by CSD display much higher e31,f values than films made by other methods. It is therefore important to be able to produce piezo-MEMS on an industrial scale by CSD of PZT. The goals of the authors have been to make validated procedures for integration of state-of-the-art CSD PZT thin films into MEMS on an industrial scale. The resulting qualified production routes have formed the basis for a new foundry service offering piezo-MEMS with record high e31,f on a semi-industrial scale1. Test wafers with more than 500 model elements of the three categories ranging in size from 50 to 1500 µm have been prepared. A review will be given on the preparation of the test wafers and some results from testing and characterisation. Some thoughts concerning scale-up of CSD will be given.
