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Piezoelectric materials have excellent energy conversion efficiency between mechanical and electrical domains and have been used in a variety of electromechanical devices. These technologies include new piezoelectric thin-film materials, innovative thin-film processes, and new evaluation methods with the goal of advancing the piezo-MEMS applications. Evolving around the development of piezo-MEMS are interdisciplinary and intertwined technologies, including materials science, surface and thin-film processes, measurement and device technologies, etc. This APL Special Topic "Piezoelectric thin films for MEMS" features recent advances in piezoelectric thin films and related technologies aimed for MEMS applications. [Extracted from the article]

Ultrathin aluminum nitride (AlN) films are of great interest for integration into nanoelectromechanical systems for actuation and sensing. Given the direct relationship between crystallographic texture and piezoelectric (PZE) response, x-ray diffraction has become an important metrology step. However, signals from layers deposited below the PZE AlN thin film may skew the crystallographic analysis and give misleading results. In this work, the authors compare the use of a Ti or AlN seed layer on the crystallographic quality of PZE AlN. The authors also analyze the influence of several AlN seed layer thicknesses on the rocking curve FWHM of PZE AlN and demonstrate a larger effect of the AlN seed layer on the θ-2θ AlN <0002> crystallographic peak for increasing AlN seed layer thickness. [ABSTRACT FROM AUTHOR]

A five-layer stack of lead zirconate titanate ( PZT) thin films with Pt electrodes was fabricated for potential applications in nanoactuator systems. The 1 μm thick PZT films were deposited by a sol-gel technique, the platinum electrodes by sputtering. The PZT films were crack-free, in spite of the use of silicon as a substrate, suggesting an increased toughness of the metal-ceramic composite. For piezoelectric characterization, the intermediate electrodes were liberated by successive etching of the PZT and Pt layers, obtaining a functional three- layer stack. A total thickness change of 5.2 nm was achieved with 10 V, measured by double beam laser interferometry. The small signal response was obtained as 0.49 nm/V. Finite element simulations were made to account for the thickness change in the substrate due to the transverse piezoelectric effect. The average response corresponds to an average d33,f of 120 pm/V. The multiple annealed buried layers show clearly a better performance with up to 175 pm/V. It is concluded that the electrode interfaces in the interior exhibit higher qualities, as supported by transmission electron microscopy, and that the multiple anneals were beneficial for PZT thin film quality. [ABSTRACT FROM AUTHOR]

High-Q, bulk acoustic wave composite resonators based on a symmetric layer sequence of SiO2-A1N-SiO2 sandwiched between electrodes have been developed. Acoustic isolation was achieved by means of deep silicon etching to obtain membrane type thin film bulk acoustic wave resonators (TFBARs). Three different device versions were investigated. The SiO2 film thicknesses were varied (0 nm, 70 nm, 310 nm, and 770 nm) while the piezoelectric A1N film had a constant thickness of 1.2 μm. The sputter-deposited A1N film grown on the amorphous, sputter-deposited SiO2 layer exhibited a d331 of 4.0 pm/V. Experimental results of quality factors (Q) and coupling coefficients (kt²) are in agreement with finite element calculations. A Q of 2000 is observed for the first harmonic of the 310 nm oxide devices. The most intense resonance of the 770 nm oxide device is the third harmonic reaching Q factors of 1450. The temperature drift reveals the impact of the SiO2 layers, which is more pronounced on the first harmonic, reducing the TCF to 4 ppm/K for the 3rd harmonic of the 310 nm oxide devices. [ABSTRACT FROM AUTHOR]

Piezoelectric materials play a crucial role in a large number of devices and applications modern society would not like to miss. Mobile phones and ultrasonic imaging are just the most prominent ones. Since two decades, miniaturization of mechanical devices in silicon technology is a major research direction in engineering known under name of MEMS, which stands for micro-electro-mechanical systems. Piezoelectricity fits very well into this concept and was expected right from the beginning to play its role in MEMS. The breakthrough was made with RF filters in mobile phones working on the principle of standing thickness waves in AlN films. What counts here is acoustic quality and stability. The force champion among piezoelectric thin film materials, Pb(Zr,Ti)O3 gave more problems in processing, and requires more patience to meet requirements and needs for a mass applications. It seems, however, that the breakthrough is imminent. This article attempts to give an overview of the field, highlighting recent achievements, introduce operation principles, and describe some applications. [ABSTRACT FROM AUTHOR]

A highly sensitive piezoelectric ultrasonic micro-sensor with a grooved multilayer membrane was developed by a Si-based MEMS technique. The groove was located at one-quarter of the distance away from the edge of the membrane and opened into piezoelectric layer. The piezoelectric layer Pb(Zr,Ti)O3 (PZT) was 2.2 μm thick and was prepared by a sol-gel method. The prepared PZT film was pure perovskite and showed a highly (100) textured structure. The sensitivity of the fabricated piezo- electric ultrasonic sensor without the groove structure was 100 μV/Pa. In comparison, the sensitivity of the ultrasonic sensor with the groove structure was about 500 μV/Pa, which is 5 times that without the groove structure. The diaphragm having grooves showed a corrugate-like structure that was formed by residual stress. The high sensitivity of the membrane with the grooved diaphragm is considered to relate to the corrugate-like structure. [ABSTRACT FROM AUTHOR]

We present a new measurement method to characterize piezoelectric thin films utilizing a four-point bending setup. In combination with a single- or a double- beam laser interferometer, this setup allows the determination of the effective transverse and longitudinal piezoelectric coefficients e31,f and d33,f, respectively. Additionally, the dielectric coefficient and the large signal electrical poIarization are measured to add further important characteristics of the film. These data are essential for piezoelectric thin film process specification and the design and qualification of microelectromechanical systems devices. [ABSTRACT FROM AUTHOR]

Growth and properties of sputter in situ sputter deposited Pb(Z,Ti)O3 (PZT) thin films have been studied on (111)-textured Pt electrodes as a function of seed layers of the type (TiO2)x(PbO)y. The PZT process was run with a limited lead excess resulting in pyrochlore nucleation on bare Pt electrodes. When the electrode was covered with a dense seed layer, perovskite was obtained everywhere. Ti rich seed layers yielded (111)-textured PZT even for very thin seed layers. Pb rich seed layers nucleated as PbTiO3{100} and gave rise to (100)-textured PZT. In an intermediate zone, the major perovskite orientations (100), (110) and (111) have been found together with pyrochlore for a small seed layer thickness. In this zone, the seed layer nucleates in islands leaving bare Pt spots. The intermediate region is a transition region between (111) seeds and (100) seeds. The latter exhibit diverging critical sizes at a given critical flux ratio, leading to large nuclei and bare Pt. [Copyright &y& Elsevier]