Paul Moses

The wafer flexure technique for the determination of the transverse piezoelectric coefficient (d31) of PZT thin films

Abstract This paper describes a simple and inexpensive method for evaluating the transverse piezoelectric coefficient ( d 31 ) of piezoelectric thin films. The technique is based upon the flexure of a coated substrate which imparts an ac two-dimensional stress to the piezoelectric film. The surface charge generated via the mechanical loading is converted to a voltage by an active integrator. Plate theory and elastic stress analyses are used to calculate the principal stresses applied to the film. The d 31 coefficient can then be determined from knowledge of the electric charge produced and the calculated mechanical stress. For 52/48 sol-gel lead zirconate titanate (PZT) thin films, the d 31 coefficient was found to range from − 5 to − 59 pC/N and is dependent on poling field.

Charge release of lanthanum-doped lead zirconate titanate stannate antiferroelectric thin films

The charge release speed and backward phase switching time of lanthanum-doped lead zirconate titanate stannate antiferroelectric thin films were investigated by directly measuring the switching current upon removal of the applied electric field. The backward switching time is about 6 ns. The maximum switching current density can reach 9400 A/cm2, and more than half of the stored charge can be released in 10 ns. These results show that the obtained antiferroelectric thin films are very promising for decoupling capacitor applications in high speed multichip modules.

A bimorph based dilatometer for field induced strain measurement in soft and thin free standing polymer films

A bimorph based dilatometer has been developed which enables one to characterize the electric field induced strain response in the out-of-plane direction in thin and soft free standing polymer film samples conveniently over a relatively wide frequency range (1 Hz to 1 kHz). The test results demonstrate that the newly developed dilatometer is capable of detecting displacement down to sub-angstrom range. The agreement between the test results from the bimorph dilatometer, the results from a laser dilatometer, and the model analysis indicates that the device can indeed be used reliably for these measurement with high sensitivity.

Converse electrostriction in polymers and composites

Abstract The evaluation of electrostrictive properties of low permittivity dielectrics requires extremely sensitive instrumentation. In the present work, a modified compressometer capable of resolving fractional changes in capacitance of the order of 10 −6 is used. In the compressometric method, a high sensitivity capacitance bridge, GenRad 1615, is coupled with two lock-in amplifiers to detect attofarad (10 −18 F) level capacitance changes caused by in-phase cyclic uniaxial stresses on the samples. In studying low-permittivity polymers, we have obtained extensive electrostriction data, which along with widely accepted data on ferroelectric materials and soft polymers, verify the linear relationship between electrostriction coefficient ( Q ) and the ratio of elastic compliance and dielectric permittivity (s/ ϵ 0 ϵ r ). This leads to an effective way to predict the electrostriction coefficient in dielectric materials.

Piezoelectric accelerometers for ultrahigh temperature application

High temperature sensors are of major importance to aerospace and energy related industries. In this letter, a high temperature monolithic compression-mode piezoelectric accelerometer was fabricated using YCa4O(BO3)3 (YCOB) single crystals. The performance of the sensor was tested as function of temperature up to 1000 °C and over a frequency range of 100–600 Hz. The accelerometer prototype was found to possess sensitivity of 2.4±0.4 pC/g, across the measured temperature and frequency range, indicating a low temperature coefficient. Furthermore, the sensor exhibited good stability over an extended dwell time at 900 °C, demonstrating that YCOB piezoelectric accelerometers are promising candidates for high temperature sensing applications.

Transversely reinforced 1-3 and 1-3-0 piezoelectric composites

Abstract Piezoelectric PZT-polymer 1-3 and 1-3-0 composites were transversely reinforced with glass fibers to increase the hydrostatic piezoelectric coefficients for possible use in hydrophone applications. Modeling of these composites theoretically showed that the dhgh figure of merit is a function of the volume fractions of PZT rods, glass fibers, and polymer porosity, and of the Poissons ratio and compliance of the polymer matrix. Experimental results showed significant enhancements of the dhgh figure of merit with the addition of glass fibers. Comparisons of the theoretical predictions and the experimental results were made.

Pb(Zr,Ti)O3 [PZT] fibers–fabrication and properties

Abstract Abstract Fine scale lead zirconate titanate (PZT) and niobium substituted PZT (Nb-PZT) piezoelectric fibers were fabricated from sol-gel processed viscous “sol” using the “spinning” methodology developed for the continuous production of glass fibers. Subsequent drying and firing at above 750°C gave pure perovskite PZT and Nb-PZT fibers of 30 μm in average diameter. Further densification and grain growth were evident for fibers fired at 1250°C. Experimental methods for the determination of dielectric and polarization properties were developed to overcome inherent electric field difficulty relevant to fine scale fibers. The dielectric constant and polarization hysteresis values of the fibers were comparable with that of bulk ceramics. Preliminary single fiber mechanical pull tests indicated that the tensile strength of 30 μm diameter PZT fibers were similar to that of bulk ceramics, being in the ange of 35–55 MPa.

Electrostriction measurements on low permittivity dielectric materials

Abstract To measure the electrostrictive effects in low permittivity materials, extremely sensitive instrumentation is required. A modified compressometer for resolving fractional changes in capacitance on the order of 10−6 is used in this work, along with a modified single beam interferometer capable of sub-angstrom resolution in displacement. For the compressometric method, a high sensitivity capacitance bridge, GenRad 1615, is coupled with two lock-in amplifiers to detect attofarad (10−18F) level capacitance changes caused by in-phase cyclic uniaxial stresses on samples. The interferometer is a Michelson –Morley type instrument modified to detect changes in interference fringe intensity for very small changes in path length. The measurements confirmed by both techniques are used to establish a set of reliable and accurate data of electrostriction coefficients for low permittivity materials. Using these recent data, along with widely accepted data on ferroelectric materials and soft polymers, the linear relationship between electrostriction coefficient (Q) and the ratio of elastic compliance over dielectric permittivity (s/e0er) is obtained. This leads to an effective way to predict the electrostriction coefficient in dielectric materials.

A dynamic compressometer for converse electrostriction measurements

A simple dynamic instrument for measuring very small stress dependence of capacitance is presented in this article. We describe the design and development of a dynamic compressometer for converse electrostrictive measurements on low dielectric constant materials. This redesigned system is capable of resolving a change in capacitance of 10−17 F or smaller. The most important feature is the dynamic stressing system incorporated to improve the accuracy and the reproducibility of the measurements. Furthermore, the uniaxiality and uniformity of the applied stress are found to be critical to the measurements. Therefore, a uniaxial stress delivery scheme using ball bearings is employed in the measurements to improve the accuracy of the experimental results. The converse electrostrictive coefficients obtained from this instrument agree reasonably well with those measured directly by a single-beam interferometer.

Electrostrictive Strain in Low-Permittivity Dielectrics

A single-beam interferometer capable of resolving displacements on the order of 10−4 Å was used to examine the field-induced displacement in several low-permittivity dielectric materials. The experimental principle and procedures of the single-beam interferometer are described in this article. The importance and the accuracy of the Maxwell stress and the thermal stress corrections are also discussed. We present in this article the field-induced strains and the apparent electrostrictive coefficients of several common dielectric materials, including Al2O3, BeO, MgO, AlN ceramics, and SiO2 glass. Under application of an electric field, these common ceramic materials become thicker in the field direction, while glasses and glass-ceramics get thinner. The magnitude of the displacements varies between 10−2 to 10−3 Å under 1 MV/m electric field. By comparison, the field-induced displacements in these common electronic materials are approximately 3 to 5 orders of magnitude smaller than those observed in relaxor materials, such as PMN and PVDF, and soft polymers.