Ferroelectric ceramics were born in the early 1940s with the discovery of the phenomenon of ferroelectricity as the source of the unusually high dielectric constant in ceramic barium titanate capacitors. Since that time, they have been the heart and soul of several multibillion dollar industries, ranging from high-dielectric-constant capacitors to later developments in piezoelectric transducers, positive temperature coefficient devices, and electrooptic light valves. Materials based on two compositional systems, barium titanate and lead zirconate titanate, have dominated the field throughout their history. The more recent developments in the field of ferroelectric ceramics, such as medical ultrasonic composites, high-displacement piezoelectric actuators (Moonies, RAINBOWS), photostrictors, and thin and thick films for piezoelectric and integrated-circuit applications have served to keep the industry young amidst its growing maturity. Various ceramic formulations, their form (bulk, films), fabrication, function (properties), and future are described in relation to their ferroelectric nature and specific areas of application.

/pdf/ferroelectric-ceramics-history-and-technology-40j9enkrwl.pdf

Ferroelectric ceramics : History and technology

This paper provides a detailed overview of developments in transducer materials technology relating to their current and future applications in micro-scale devices. Recent advances in piezoelectric, magnetostrictive and shape-memory alloy systems are discussed and emerging transducer materials such as magnetic nanoparticles, expandable micro-spheres and conductive polymers are introduced. Materials properties, transducer mechanisms and end applications are described and the potential for integration of the materials with ancillary systems components is viewed as an essential consideration. The review concludes with a short discussion of structural polymers that are extending the range of micro-fabrication techniques available to designers and production engineers beyond the limitations of silicon fabrication technology.

/pdf/new-materials-for-micro-scale-sensors-and-actuators-an-21qnaonn0l.pdf

New materials for micro-scale sensors and actuators An engineering review

Piezoelectric microelectromechanical systems (MEMS) offer the opportunity for high-sensitivity sensors and large displacement, low-voltage actuators. In particular, recent advances in the deposition of perovskite thin films point to a generation of MEMS devices capable of large displacements at complementary metal oxide semiconductor-compatible voltage levels. Moreover, if the devices are mounted in mechanically noisy environments, they also can be used for energy harvesting. Key to all of these applications is the ability to obtain high piezoelectric coefficients and retain these coefficients throughout the microfabrication process. This article will review the impact of composition, orientation, and microstructure on the piezoelectric properties of perovskite thin films such as PbZr1−xTixO3 (PZT). Superior piezoelectric coefficients (e31, f of −18 C/m2) are achieved in {001}-oriented PbZr0.52Ti0.48O3 films with improved compositional homogeneity on Si substrates. The advent of such high piezoelectric responses in films opens up a wide variety of possible applications. A few examples of these, including low-voltage radio frequency MEMS switches and resonators, actuators for millimeter-scale robotics, droplet ejectors, energy scavengers for unattended sensors, and medical imaging transducers, will be discussed.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/AC28E0B7FC52ADDE14E1F58F59416494/S0883769400003614a.pdf/div-class-title-piezoelectric-thin-films-for-sensors-actuators-and-energy-harvesting-div.pdf

Piezoelectric Thin Films for Sensors, Actuators, and Energy Harvesting

Piezoelectric films for high frequency ultrasonic transducers in biomedical applications

This paper discusses the development of a 64-element 35-MHz composite ultrasonic array. This array was designed primarily for ocular imaging applications, and features 2-2 composite elements mechanically diced out of a fine-grain high-density Navy Type VI ceramic. Array elements were spaced at a 50-micron pitch, interconnected via a custom flexible circuit and matched to the 50-ohm system electronics via a 75-ohm transmission line coaxial cable. Elevation focusing was achieved using a cylindrically shaped epoxy lens. One functional 64-element array was fabricated and tested. Bandwidths averaging 55%, 23-dB insertion loss, and crosstalk less than -24 dB were measured. An image of a tungsten wire target phantom was acquired using a synthetic aperture reconstruction algorithm. The results from this imaging test demonstrate resolution exceeding 50 /spl mu/m axially and 100 /spl mu/m laterally.

Development of a 35-MHz piezo-composite ultrasound array for medical imaging

An ultrasonic transducer comprises a stack having a first face, an opposed second face and a longitudinal axis extending therebetween. The stack comprises a plurality of layers, each layer having a top surface and an opposed bottom surface, wherein the plurality of layers of the stack comprises a piezoelectric layer and a dielectric layer. The dielectric layer is connected to the piezoelectric layer and defines an opening extending a second predetermined length in a direction substantially parallel to the axis of the stack. A plurality of first kerf slots are defined therein the stack, each first kerf slot extending a predetermined depth therein the stack and a first predetermined length in a direction substantially parallel to the axis. The first predetermined length of each first kerf slot is at least as long as the second predetermined length of the opening defined by the dielectric layer and is shorter than the longitudinal distance between the first face and the opposed second face of the stack in a lengthwise direction substantially parallel to the axis.

Arrayed ultrasonic transducer

A sol gel composite process has been used to produce lead zirconate titanate coatings in the thickness range of 3 to 100 pm on aluminum substrates. The complex permittivity (E&), elastic stiffness (cg), and the piezoelec- tric constant (h33) of the coating and the complex elastic stiffness (cz) of the substrate have been determined us- ing impedance measurements and a commercially available software program (Piezoelectric Resonance Analysis Pro- gram PRAP 2.0, TASI Technical Software, Kingston, On- tario, Canada). The complex components of the material parameters account for the losses within the film and the substrate. Sol gel composite films on aluminum have a di- electric constant of 220 with an imaginary component of 1% and an electromechanical coupling coefficient of up to 0.24 with an imaginary component of 3%. These films are applied to the fabrication of high frequency transducers suitable for ultrasound biomicroscopy (UBM). By combin- ing the sol gel composite material with existing transducer fabrication techniques, single-element focusing transducers have been produced that operate in the frequency range of 70 to 160 MHz. Devices have -6-dB bandwidths up to 52% and minimum insertion losses ranging from -47 to -58 dB. Real-time images of phantom materials and ex vivo biolog- ical samples are shown.

Single Element High Frequency (<50 MHz) PZT Sol Gel Composite Ultrasound

A sol gel composite process has been used to produce lead zirconate titanate coatings in the thickness range of 3 to 100 /spl mu/m on aluminum substrates. The complex permittivity (/spl epsi//sub 33//sup S/), elastic stiffness (c/sub 33//sup D/), and the piezoelectric constant (h/sub 33/) of the coating and the complex elastic stiffness (c/sub 33//sup D/) of the substrate have been determined using impedance measurements and a commercially available software program [Piezoelectric Resonance Analysis Program PRAP 2.0, TASI Technical Software, Kingston, Ontario, Canada]. The complex components of the material parameters account for the losses within the film and the substrate. Sol gel composite films on aluminum have a dielectric constant of 220 with an imaginary component of 1% and an electromechanical coupling coefficient of up to 0.24 with an imaginary component of 3%. These films are applied to the fabrication of a high frequency transducers suitable for ultrasound biomicroscopy (UBM). By combining the sol gel composite material with existing transducer fabrication techniques, single-element focusing transducers have been produced that operate in the frequency range of 70 to 160 MHz. Devices have -6-dB bandwidths up to 52% and minimum insertion losses ranging from -47 to -58 dB. Real-time images of phantom materials and ex vivo biological samples are shown.

Single element high frequency (<50 MHz) PZT sol gel composite ultrasound transducers

New thick film ceramic processing techniques and microelectromechanical systems require material characterization of a piezoelectric film supported by a substrate. An analytical solution of the one-dimensional wave equation for multiple layered systems driven in the thickness mode is presented. The impedance across the piezoelectric layer is derived and expressed in terms of the material properties of the two materials. This includes the open-circuit elastic stiffness c33D, the clamped permittivity e33S and the h33 piezoelectric constant of the piezoelectric layer and the elastic stiffness csD of the substrate. The properties are expressed as complex variables in order to account for the losses within the materials. The material parameters of the solution are extracted from experimental results using a modified Levenberg–Marquardt technique. The capabilities of this nondestructive technique are demonstrated using experimental and simulated impedance spectra of lead zirconium titanate sol gel composite coa...

Thickness mode material constants of a supported piezoelectric film

Piezoelectric ceramics have been patterned by means of laser micromachining to create ultrasonic arrays resonating in the frequency range of 35-45 MHz. The Lumonics PM-844 excimer laser with a KrF gas mixture (248 nm) has been used to micromachine trenches with a width to depth aspect ratio of up to 1:5. By using a projection etch approach, the large aperture of the excimer laser is used to simultaneously ablate the features of a complex geometrical pattern. Pre-poled ceramic structures >20 /spl mu/m wide and >35 /spl mu/m thick have been cut and validated with SEM images. The dielectric, piezoelectric and acoustic properties have been evaluated using an impedance analyser and pulse-echo techniques.

Marc Lukacs

Papers

Arrayed ultrasonic transducer

Single Element High Frequency (<50 MHz) PZT Sol Gel Composite Ultrasound

Single element high frequency (<50 MHz) PZT sol gel composite ultrasound transducers

Thickness mode material constants of a supported piezoelectric film

Laser micromachined high frequency ultrasonic arrays