Implementation and Optimization of SPS Sintering for a printed Piezoelectric Energy Harvester MEMS

Energy harvester MEMS based on screen-printed thick films (1 to 100 µm) leads to better energy densities than the thin layers and overcomes the assembly difficulties of bulk ceramics. Previous work showed the feasibility of a... [ view full abstract ]

Energy harvester MEMS based on screen-printed thick films (1 to 100 µm) leads to better energy densities than the thin layers and overcomes the assembly difficulties of bulk ceramics. Previous work showed the feasibility of a printed energy harvester constituted of Au/PZT/Au/Stainless Steel (SS) multilayer structure [1]. The co-sintering of such multilayer structure faces several issues including the presence of sintering aids affecting the electromechanical properties, the volatility of PbO and the presence of metals that significantly limit the temperature window for densification. However highly densified PZT is mandatory to ensure performant electromechanical properties [2]. In order to avoid the use of sintering additives, which decrease the firing temperature but can modify the microstructure, we aim a two-fold strategy based on Spark Plasma Sintering. The objective is to improve PZT densification without any sintering aids, while reducing the sintering temperature to a suitable one for the Au/PZT/Au/SS multilayer assembly in one step. The ceramics are processed using a Dr Sinter 515 SPS machine. Sintering optimization of the PZT powder (Pz26 from Ferroperm) is first investigated under vacuum, with an axial pressure of 50MPa and a heating rate of 100°C/min. Four sintering temperatures (800, 850°C, 875°C, and 900°C) are selected. Results show high densifications of around 98%, even for temperature as low as 850°C. The electromechanical properties are close to those of commercial pellets. This has allowed us to carry out the first attempts of SPS sintering on a simple printed multilayer Au/PZT/Au/SS structure by using a modified graphite set-up. Further characterizations are under progress.

[1]     Egon Fernandes et al, “Design, Fabrication, and Testing of a Low Frequency MEMS Piezoelectromagnetic Energy Harvester”. Smart Materials and Structures, IOP Publishing, 2018.

[2]    F. Kenso et al, “PZT Consolidation by Spark Plasma Sintering”, in 21^st Congress of mechanical engineering, Natal, Brazil, 2011.