Synthesis and Characterization of Piezoelectric and Piezoelectric-Multiferroic Composite Thin Films for MEMS Applications

Abstract

The lead-zirconate-titanate (PZT) solid solutions system is currently the workhorse of piezoelectric-based microelectromechanical systems (MEMS) research. Among bulk material it is known to be one of the strongest piezoelectric, with extremely high piezoelectric coefficients and electromechanical coupling factor. Reproducing these properties in thin film form, however, require precise control of composition and texture. in this thesis, method to grow textured or epitaxial PZT thin film are investigated. The aim is to develop maximize crystallinity and minimize resistivity through precursor modification and thermal treatments. Lead zirconate titanates (PZTs and PLZTs) are being used in bulk as well as in thin film forms for various applications like transducers, actuators and FERAMs for civil and military applications. The piezoelectric and electro mechanical property of these materials are excellent inspite of their toxic behavior and have always attracted the researchers for its maximum exploitation. The bulk PZTs are extensively used for under water and ultrasound applications. The commercial uses of these compounds are in inkjet printers, precise cutting machines and many other vibrators. The thin films of these materials can be used for making vibration sensors, MEMS (Micro Electro Mechanical Systems) switches etc. The preparation and characterization of ferroelectric/piezoelectric in bulk and thin film forms of PZT with suitable substituent‟s are presented in this thesis. After a brief introduction to ferroelectric/piezoelectric materials and their studies done in the past the thesis starts with defining the objectives and scope of the present work. Since our aim was to make thin films of PZT on platinized silicon substrates, it was important to look at their lattice parameters for minimum lattice mismatch. In this research the platinized silicon substrate of 1500 Å platinum thickness substrates have been used for thin films study. Further platinum <111> has a lattice constant ~ 3.92 Å. Thus a PZT system which can be more suitable near MPB of PbZrO3 – PbTiO3 will be none other than the PZT with a molar Zr/Ti ratio of 52/48 whose lattice constant is also ~ 4 Å. These literature results were primary basis for the present research. Thus this particular Zr/Ti ratio of 52/48 was chosen for further study. Furthermore a high value of remnant polarization has been observed for the PZT (52/48) bulk ceramics. Hence for making a thin film of the same composition based devices like (FERAM, MEMS based vibration sensors etc.), it would be interesting to deposit thin films of PZT on suitable substrates. A systematic study had been planned to investigate the structural, morphological and electrical properties of these ceramics in bulk and thin films. Chemical solution deposition (CSD) and physical vapor deposition (PVD) technique were also used to optimize orientation in PZT thin films. A comprehensive investigation of lead chemistry as well as pyrolysis and annealing conditions was performed to determine the processing-structure-property relationships in PZT films. in concert, sputtering methods were also developed for comparison of thin films PZT properties from PZT and CSD method. It is expected that these films will offer enhanced piezoelectric actuation due to their high degree of orientation, relatively small amount of high-angle grain boundaries and their superior ferroelectric characteristics. Additionally, the flexibility of substrate open doors to many exiting materials integration possibilities for MEMS devices including energy harvesting applications and flexible sensor.