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...

The crystallization kinetics of mullite formation in a diphasic precursor consisting of a silicone resin filled with commercial c-alumina nanoparticles (15 nm mean particle size, specific surface area of 100 m 2 /g), heated in air from 12501 to 13501C, was studied by X-ray diffraction. Transitional c-alumina and amorphous silica from the pyrolysis of the preceramic polymer exhibited a remarkable reactivity, as demonstrated by a very low incubation time (from 500 s at 12501C to 20 s at 13501C), a high mullite yield (about 80 vol%, after 100 s at 13501C), and a low activation energy for nucleation (677760 kJ/mol). The activation energy values found were lower than those reported previously for other diphasic systems, including sol-gel precursors. Besides the high specific surface of nanosized c-alumina particles, the low energy barrier could be attributed to the highly reactive silica deriving from the oxidation of Si-CH 3 bonds in the silicone and to the homogeneous dispersion of the nanosized filler inside the preceramic polymer. Furthermore, the possibility of applying plastic shaping processing methods to the mixture of a preceramic polymer and nanosized filler makes this approach particularly valuable, in comparison, for instance, with sol-gel based alternatives.

Piezoelectric thin films are of increasing interest in low-voltage micro electromechanical systems for sensing, actuation, and energy harvesting. They also serve as model systems to study fundamental behavior in piezoelectrics. Next-generation technologies such as ultrasound pill cameras, flexible ultrasound arrays, and energy harvesting systems for unattended wireless sensors will all benefit from improvements in the piezoelectric properties of the films. This paper describes tailoring the composition, microstructure, orientation of thin films, and substrate choice to optimize the response. It is shown that increases in the grain size of lead-based perovskite films from 75 to 300 nm results in 40 and 20% increases in the permittivity and piezoelectric coefficients, respectively. This is accompanied by an increase in the nonlinearity in the response. Band excitation piezoresponse force microscopy was used to interrogate the nonlinearity locally. It was found that chemical solution-derived PbZr(0.52)Ti(0.48)O(3) thin films show clusters of larger nonlinear response embedded in a more weakly nonlinear matrix. The scale of the clusters significantly exceeds that of the grain size, suggesting that collective motion of many domain walls contributes to the observed Rayleigh behavior in these films. Finally, it is shown that it is possible to increase the energy-harvesting figure of merit through appropriate materials choice, strong imprint, and composite connectivity patterns.

The proposed CMOS ultrasound transceiver chip will enable the development of portable high resolution, high-frequency ultrasonic imaging systems. The transceiver chip is designed for close-coupled MEMS transducer arrays which operate with a 3.3-V power supply. In addition, a transmit digital beamforming system architecture is supported in this work. A prototype chip containing 16 receive and transmit channels with preamplifiers, time-gain compensation amplifiers, a multiplexed analog-to-digital converter with 3 kB of on-chip SRAM, and 50-MHz resolution time delayed excitation pulse generators has been fabricated. By utilizing a shared A/D converter architecture, the number of A/D converter and SRAM is cut down to one, unlike typical digital beamforming systems which need 16 A/D converters for 16 receive channels. The chip was fabricated in a 0.35-mum standard CMOS process. The chip size is 10 mm(2), and its average power consumption in receive mode is approximately 270 mW with a 3.3-V power supply. The transceiver chip specifications and designs are described, as well as measured results of each transceiver component and initial pulse-echo experimental results are presented.

An approach for probing dynamic phenomena during hysteresis loop measurements in piezoresponse force microscopy (PFM) is developed. Dynamic PFM (D-PFM) necessitates development of 5-dimensional (5D) data acquisition protocols and associated methods for analysis and visualization of multidimensional data. Using a combination of multivariate statistical analysis and phenomenological fitting, we explore dynamic behavior during polarization switching in model ferroelectric films with dense ferroelastic domain structures and in ferroelectric capacitors. In polydomain films, multivariate analysis of the switching data suggests that ferroelectric and ferroelastic components can be decoupled and time dynamics can be explored. In capacitors, a strong correlation between polarization dynamics and microstructure is observed. The future potential of D-PFM for probing time-dependent hysteretic phenomena in ferroelectrics and ionic systems is discussed.

A chemical solution deposition procedure was developed for lead nickel niobate-lead zirconate titanate (0.3)Pb(Ni0.33Nb0.67)O3–(0.7)Pb(Zr0.45Ti0.55O3) ferroelectric thin films. On tailoring the heat-treatment conditions and excess lead content, the average grain diameters could be varied from 110 to 270 nm. Dielectric permittivities ranging from 1350 to 1520 and a transverse piezoelectric coefficient e31,f as high as −9.7 C/m2 were observed for films of about 0.25 μm in thickness. The permittivity and piezoelectric response increased for samples with larger grain size. Higher thermal budgets also imposed higher levels of in-plane tensile stress on the perovskite layer; the imposed stress reduced the remanent polarization for the samples. Nonetheless, samples processed at higher temperatures showed larger average grain diameters and higher extrinsic contributions to the properties.

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