Advantages of PZT thick film for MEMS sensors

For all MEMS devices a high coupling between the mechanical and electrical domain is desired. Figures of merit describing the coupling are important for comparing different piezoelectric materials. The existing figures of merit are discussed and a new figure of merit is introduced for a fair comparison of piezoelectric thin and thick films based MEMS devices, as cantilevers, beams, bridges and membranes. Simple analytical modeling is used to define the new figure of merit. The relevant figure of merits is compared for the piezoelectric material of interest for MEMS applications: ZnO, AlN, PZT thin film and PZT thick film. It is shown that MEMS sensors with the PZT thick film TF2100 from InSensor A/S have potential for significant higher voltage sensitivities compared to PZT thin film base MEMS sensors when the total thickness of the MEMS cantilever, beam, bridge or membrane is high. Improved figure of merit is reached in the piezoelectric PZT thick film, TF2100CIP, by using cold isostatic pressure in the PZT preparation process. The porosity of TF2100 is decreased 38%, hence, allowing an increase of charge sensitivity for MEMS sensors of 59%.