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Adhesion Enhancement Between Top Electrodes and Piezoelectric Films for MEMS Process
Keywords: MEMS process, metal elecreode adhesion, PZT thin film
During the recent years, MEMS (Micro electro mechanical system) process has been applied for making electrical and mechanical devices using ferroelectric materials, such as bulk acoustic resonators (FBAR) based on piezoelectric materials film or inkjet printer heads for next generation printers. Cantilevers used as micro switches or membranes for particle detection. One of ferroelectric materials, PZT is supposed as most powerful candidates for MEMS application devices due to high mechanical performance in piezoelectric characteristics. The bulk micromachining and surface micromachining processes are used to make the 3-dimensional structure type devices. These MEMS processes were done by stacking structure type, which have top and bottom electrode. There are adhesion troubles between oxide thin films and metal electrode films because of the different stress levels and different lattice parameters from various thin film materials. But, the bottom electrode adhesion from substrate films have been studied for a long times. Therefore, Ir, Ti and Ta films were adopted to improve the adhesion and enhance the electrical properties between bottom metal electrode films and the substrate. Otherwise, the top electrode adhesion, although it is very critical problems during the MEMS processing, is to be considered not so important part of those micromachining processes. Hereby, we explore the study of improving top electrode adhesion for the MEMS processing. While top platinum electrode was deposited on PZT thin films the oxygen was included in Ar inert gas. The oxygen pressures were changed by MFC from 0.1sccm to 10sccm and 20nm Ta, Ti thin films deposited on PZT thin films to improve the adhesion between top electrode and PZT films. The measurements of the physical properties of the thin films were using X.R.D and S.E.M. The ferroelectric properties were evaluated using the TF 2000 from Aixacct. And KEITHLEY 6430 voltage source was utilized for getting leakage current characteristics.
Chang Young Koo , Senior Researcher
Sangnok-gu, Ansan-si, Gyeonggi-do 425-791,

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