Ruzhong Zuo

Experimental determination of sintering stresses and sintering viscosities

A loading dilatometer assisted by two high-resolution lasers was applied for the accurate measurement of radial and axial strains during uniaxial load assisted sintering. An improved hot forging technique was employed for the first time for the experimental determination of sintering stress and sintering viscosity by hot forging samples under various loads which were pre-sintered to different densities. The technique of discontinuous hot forging was discussed in detail and the effect of the developing anisotropy and different grain growth were analysed. The sintering stress and uniaxial viscosity were both obtained as functions of density ranging from 65 to 96% and compared with theoretical models. Alumina powder with a grain size of about 150 nm was used in this study.

Influence of silver migration on dielectric properties and reliability of relaxor based MLCCs

In order to study the micro-mechanism of silver migration which influences the reliability of relaxor based multilayer ceramic capacitors (MLCCs), micro-silver-doped PMN-PZN based relaxor ferroelectric ceramics were investigated for their microstructural and dielectric properties. SEM observations showed that the microstructure near the interface of MLCCs was greatly changed by the action of the inner silver/palladium electrode. The results indicate that silver migration causes grain growth, changes dielectric properties and decreases insulation resistance. Defect chemistry principles were used to explain the micro-mechanism of action of the silver dopant.

Viscous Poisson's coefficient determined by discontinuous hot forging

A high-resolution laser-assisted loading dilatometer was applied for the precise measurement of radial and axial strain rates under different uniaxial loads, using alumina as a model material. As a continuous application of an external load can lead to an anisotropic microstructure, a discontinuous hot forging technique was utilized to determine the viscous Poissons coefficient. In these studies, samples were presintered to different densities and only then were hot-forging tests performed. The result provides an isotropic viscous Poissons coefficient, which increases smoothly between 0.21 and 0.42 within the accessible density range. Combined with the uniaxial viscosity measured before using the same technique, the hydrostatic sintering stress, bulk viscosity, and shear viscosity as a function of density are now available for solid-state sintering. A comparison of the experimentally obtained results with several theoretical models is included.

Laser-assisted high-resolution loading dilatometer and applications

A new hot forging apparatus has been sucessfully developed and applied for the experimental determination of continuum mechanical sintering parameters and theoretical modeling of thin-film sintering. A precise automatic loading system and high-resolution laser measurement system enable accurate measurement of radial and axial strains of cylindrical specimens under constant or intermittent uniaxial loads of 0-5000 N during high-temperature densification. Preliminary experimental results are demonstrated and the key features of technological significance in the design introduced in detail.

Interfacial development and microstructural imperfection of multilayer ceramic chips with Ag/Pd electrodes

Abstract The interfacial microstructure between Ag/Pd electrodes and PMN–PZN–PT relaxor ferroelectric ceramics in cofired multilayer ceramic devices was investigated by transmission electron microscopy and scanning electron microscopy. Disadvantageous interfacial defects, such as delaminations, warping, gas holes and exaggerated grain growth, were identified. In addition to the preparation process, the composition of the inner electrode paste and the sintering densification compatibility between the layers played important roles in the interfacial development. The relationship of the interfacial microstructure to the reliability of the device is discussed.

Modified cofiring behaviors between PMN-PNN-PZT piezoelectric ceramics and PZT-doped 70Ag–30Pd alloy metallization

Abstract The cofiring behaviors between PMN-PNN-PZT piezoelectric ceramics and 70Ag–30Pd electrode paste were investigated in view of sintering densification behavior, thermal expansion coefficients (TEC) and interfacial physical integrity. The results showed that mismatched cofiring characteristics have greatly affected the reliability of multilayer piezoelectric ceramic devices. The application of a PZT additive to 70Ag–30Pd electrode technology has markedly improved the above-mentioned cofiring mismatch. Favorable cofiring behavior was obtained, including a reduced differential shrinkage and TEC and modified interfacial microstructure.

Interfacial reaction of Ag/Pd metals with Pb-based relaxor ferroelectrics including additives

Abstract In order to effectively control the interfacial reactions during co-firing a multilayer ceramic device (MLCD), different effects of silver/palladium on Pb-based relaxor ferroelectric ceramics were investigated by means of a series of powder X-ray diffraction (XRD) spectra and chemical reaction thermodynamics. It is found that the reaction kinetics of palladium and Pb-based relaxor ceramics lies in the activity of palladium and the structural stability of relaxor ferroelectric ceramics. In this respect, silver can decrease the activity of palladium so that a less serious interfacial problem exists in a MLCD with 30Pd/70Ag electrodes. Moreover, BaTiO 3 and SrTiO 3 ceramic additives were found to effectively suppress Pd-PNN reactions because of increasing the structural stability of PNN. It is pointed out that the addition of BaTiO 3 or SrTiO 3 ceramic powders into the dielectric layers and particularly into the inner electrode pastes may play dual roles, including modifying the densification mismatch and preventing the interfacial reactions between the electrodes and the dielectric layers.

Preparation and properties of PLZT thick films on silicon

Abstract Lead-lanthanum-zirconate-titanate (PLZT) thick films were prepared on Pt/Ti/SiO 2 /Si substrates with PZT/PT seeding layer by the screen-printing method. Phase characterization and crystal orientation of the PLZT thick films were investigated by X-ray diffraction analysis (XRD). The ferroelectric hysteresis loop, high-frequency dielectric constant, dielectric loss and piezoelectric constant of the PLZT thick films were measured. The remnant polarization of the silicon-based PLZT thick films was about 32 μC cm −2 , the coercive field was about 20 kV cm −1 and the piezoelectric constant d 33 was about 630 pC N −1 . In the frequency range from 1 to 300 MHz, the dielectric constant was about 3000 and the dielectric loss was less than 0.03, respectively. The PLZT thick films with excellent ferroelectric, high frequency and force–electric coupling properties should be suitable for the ferroelectrics–silicon integrated system, and be a good candidate material for the third-generation (3G) mobile communication and the force–electric coupling microelectromechanical system (MEMS) device applications.

Sintering characteristics and dielectric properties of silver-doped PMN-PZN-PT relaxor ferroelectric ceramics

The effects of silver doping on PMN-PZN-PT relaxor ferroelectric ceramics were investigated in order to demonstrate the roles of the inner electrodes in the cofiring of MLCCs, because silver could diffuse from an electrode layer into a dielectric layer. Even if the addition of silver promoted the sintering of ceramics, the insulation resistance and the dielectric properties were changed to a certain extent so that they had a great influence on the reliability of MLCCs. Defect chemistry principles were used to analyze the mechanism of action of silver doping. The relationship of silver migration and microstructural formation was also discussed

TEM and EDS investigation of heterogeneous interfaces in cofired multilayer ceramic capacitors

Abstract The interfacial microstructure and cofiring migration between Ag–Pd electrode and Pb-based relaxor ferroelectric ceramics were directly investigated via transmission electron microscope and energy dispersive X-ray spectroscopy (EDS). Different silver migration abilities of 70Ag–30Pd and 90Ag–10Pd electrodes were confirmed by EDS microanalysis. This difference is generally considered to be responsible for different effects of inside electrode on the reliability of multilayer cofired devices. Further, Pb diffusion and new phase formation near the interface were detected, incorporating interfacial microstructural observation. A good consistency of direct experimental evidence to the following theoretic analyses was well combined in this paper.