Piezoelectric thin films formed by MOD on cantilever beams for micro sensors and actuators

Abstract

Novel piezoelectric cantilever beams for micro sensors and actuators based on PZT thin films have been batch fabricated by surface micromachining. Lead zirconate titanate (PZT) thin film is formed by metalorganic deposition (MOD) on Pt/Ti/SiO 2 /Si (1 0 0) substrates and Pt/Ti/LTO/Si 3 N 4 cantilever beams and then annealed at 700°C in air. The PZT thin film is 0.5 lm thick and has dielectric permittivity of 1698, remanent polarization of 13.66 lC/cm 2 , and coercive field of 44.5 kV/cm. The influence of deposition temperatures on PZT thin film stress has been investigated. When continuously controlling the deposition temperatures, the stress of the thin film is reduced from 0.313 · 10 8 to 0.269 · 10 8 N/m, that is 16.4% decrease. With the total 120 designed devices on 4-inch wafers, the number of functional devices is increased from 82 to 97, that is 12.47%. IntroductionPZT thin films have been intensively investigated since they offered promising piezoelectric and ferroelectric properties that can be applied to microelectronic, optoelectronic, and micromechanical devices [1,2]. Recently the PZT thin film has attracted more attention to its applications to microelectromechanical systems (MEMS) due to its desirable properties such as spontaneous polarization, high piezoelectric constant, and pyroelectricity [3][4][5]. There are several methods to deposit PZT thin films such as sol-gel process which was employed to fabricate ultrasonic micromotors [6], hydrothermally synthesized PZT films which were deposited on metal to form bimorph cantilever [7], screen printing PZT for dynamic micropumps [8], sputtering [9], laser ablation [10], electron beam deposition [11], ion beam deposition [12], metalorganic chemical vapor deposition (MOCVD) [13,14], and metalorganic decomposition (MOD) [15]. Here MOD is defined as a metalorganic deposition method to spin-coat a PZT solution on substrates, then to cure and anneal the PZT thin films by heating the substrates. The precursors of MOD PZT are metalorganic materials different from that of sol-gel. The precursors of MOD PZT are less harmful compared to that of sol-gel PZT. Among all the techniques, the MOD method appear to be most promising in the area of MEMS because it offers the advantages of simplified apparatus, excellent film uniformity, good composition control, high film density, high deposition rate, excellent step coverage, and amenability to large scale processing. However, currently very few reports are available on MOD PZT films for MEMS applications. At present cracking of the MOD PZT film is the most serious problem to delay the applications of MOD PZT thin films to micro devices. In contrast, the unique aspects of this research are the following: (1) Novel MOD procedures to fabricate MOD PZT thin films on Pt/Ti/SiO 2 /Si (1 0 0) substrates and Pt/Ti/LTO/Si 3 N 4 cantilever beams, (2) Measurement of curvature change to characterize the stress of PZT thin films, and (3) Demonstration of functional piezoelectric cantilever beams based on MOD PZT thin films to veri...

Enhanced electrical properties of PZT thick films prepared by sol–gel technique through step-by-step crystallization process

“…For example, Chen et al [6] illustrated a crack alleviation (on Pt buffer layer) process by employing a lower gel concentration of 0.2 M and a lower heating rate. Cui et al [7] and Lu et al [8] presented an approach for reducing film stress to lessen the occurrence of film cracking. Xie et al [4] introduced seed layer to improve the interfaces between the film and electrode.…”

A Novel Miniature Optical Switch With Double Vertical Micromirrors Driven by Piezoelectric Cantilever

“…In particular, piezoelectric cantilever structures have attracted more and more concern and been extensively studied in silicon-based microsystems as basic actuation structure [5,6]. Many micro devices actuated by piezoelectric cantilevers have been demonstrated such as scanning micromirrors, microphones, accelerometers and so on.…”

Elastic–plastic modeling of heat-treated bimorph micro-cantilevers

“…However, in spite an elastic-plastic model was used to analyze layered solids with rough surfaces in ref (Peng and Bhushan 2003), previous studies generally did not consider the plastic characteristics of bimorph cantilevers. In micro-cantilevers manufacturing process, a gap is formed by etching sacrificial layers in surface micro-machining (Cui et al 2004) or by back-etching substrates in bulk micro-machining . This gap is maintained between the beam and the hot plate in the heat treatment process.…”