Many applications of ultrasound for sensing, actuation and imaging require miniaturized and low power transducers and transducer arrays integrated with electronic systems. Piezoelectric micromachined ultrasound transducers (PMUTs), diaphragm-like thin film flexural transducers typically formed on silicon substrates, are a potential solution for integrated transducer arrays. This paper presents an overview of the current development status of PMUTs and a discussion of their suitability for miniaturized and integrated devices. The thin film piezoelectric materials required to functionalize these devices are discussed, followed by the microfabrication techniques used to create PMUT elements and the constraints the fabrication imposes on device design. Approaches for electrical interconnection and integration with on-chip electronics are discussed. Electrical and acoustic measurements from fabricated PMUT arrays with up to 320 diaphragm elements are presented. The PMUTs are shown to be broadband devices with an operating frequency which is tunable by tailoring the lateral dimensions of the flexural membrane or the thicknesses of the constituent layers. Finally, the outlook for future development of PMUT technology and the potential applications made feasible by integrated PMUT devices are discussed.

The role of long-range strain interactions on domain wall dynamics is explored through macroscopic and local measurements of nonlinear behavior in mechanically clamped and released polycrystalline lead zirconate-titanate (PZT) films. Released films show a dramatic change in the global dielectric nonlinearity and its frequency dependence as a function of mechanical clamping. Furthermore, we observe a transition from strong clustering of the nonlinear response for the clamped case to almost uniform nonlinearity for the released film. This behavior is ascribed to increased mobility of domain walls. These results suggest the dominant role of collective strain interactions mediated by the local and global mechanical boundary conditions on the domain wall dynamics. The work presented in this Letter demonstrates that measurements on clamped films may considerably underestimate the piezoelectric coefficients and coupling constants of released structures used in microelectromechanical systems, energy harvesting systems, and microrobots. Strain in epitaxial oxide films has become a universally recognized method for tuning materials properties [1][2][3], enabling novel couplings between magnetic, lattice, and strain behaviors [4][5][6], stabilizing new phases [7] or domain morphologies [8]. Systematic studies of a material's response to strain enable exploration of the fundamental mechanisms responsible for, e.g., the ferroelectric instability [9][10][11][12].While strain effects on intrinsic properties [9,12] and domain morphologies [13,14] are readily amenable to theoretical and experimental studies, their role on local and emergent properties [15] in disordered materials, including polycrystalline ferroelectric films and relaxors, remains virtually unexplored [16,17], Indeed, many of these materials exhibit unique physical properties including giant electromechanical coupling coefficients, broad dispersions of dielectric permittivity, etc. [18][19][20][21]. These phenomena are often associated with the presence of nanoscale textures of domains or nanoscale phase separation [22][23][24]. In all these materials, the dominant order parameter is either strain (ferroelastics) or is strongly coupled to strain (relaxors, morphotropic systems), suggesting the significant role of frustrated or random strain interactions [25][26][27]. Correspondingly, tuning mechanical boundary conditions can significantly affect emergent behaviors in disordered ferroics and provide insight into corresponding coupling mechanisms.Here, we aim to explore domain wall dynamics as reflected in ferroelectric nonlinearities in model PbZr 0:52 Ti 0:48 O 3 thin films. In polycrystalline lead zirconate-titanate (PZT) ceramics, domain wall motion may contribute more than 50% of the dielectric and piezoelectric properties at room temperature [23,28]. However, in thin films these extrinsic contributions to the piezoelectric response can be severely limited by several factors, including substrate clamping [29]. Recent spatially resolved studies of piezoelectri...