Publications

Sandia National Laboratories is developing a new technology to fabricate three-dimensional metallic components directly from CAD solid models. This process, called Laser Engineered Net Shaping (LENS{trademark}), exhibits enormous potential to revolutionize the way in which metal parts, such as complex prototypes, tooling, and small lot production parts, are produced. To perform the process, metal powder is injected into a molten pool created by a focused, high powered laser beam. Simultaneously, the substrate on which the deposition is occurring is scanned under the beam/powder interaction zone to fabricate the desired cross-sectional geometry. Consecutive layers are sequentially deposited, thereby producing a three-dimensional metal component.

The need for advanced (electronic) ceramic components with smaller size, greater functionality, and enhanced reliability requires the ability to integrate electronic ceramics in complex 3-D architectures. For rapid prototyping and small-lot manufacturing, traditional tape casting and screen printing approaches are poorly suited. To address this need, the authors are developing a direct-write approach for fabricating highly integrated, multilayer components using a micropen to deposit slurries in precise patterns. With this technique, components can be constructed layer by layer, simplifying fabrication. It can also be used to produce structures combining several materials in a single layer. The parts are either cofired or sequentially fired, after each layer is deposited. Since differential shrinkage can lead to defects in these multilayer structures, they are characterizing the sintering behavior of individual layers. This technique has been used to fabricate devices such integrated RC filters, multilayer voltage transformers, and other passive components. The direct-write approach provides the ability to fabricate multifunctional, multimaterial integrated ceramic components (MMICCs) in an agile and rapid way.

Thin-film decoupling capacitors based on ferroelectric (Pb,La)(Zr,Ti)O3 films are being developed for use in advanced packaging applications. The increased integration that can be achieved by replacing surface-mount capacitors should lead to decreased package volume and improved high-speed performance. For this application, chemical solution deposition is an appropriate fabrication technique since it is a low-cost, high-throughput process. The use of relatively thick Pt electrodes (approximately 1 μm) to minimize series resistance and inductance is a unique aspect to fabricating these devices. In addition, the important electrical properties are discussed, with particular emphasis on lifetime measurements, which suggest that resistance degradation will not be a severe limitation on device performance. Finally, some of the work being done to develop methods of integrating these thin-film capacitors with ICs and MCMs is presented.

Epitaxial SrRuO{sub 3} thin films were deposited by RF sputtering on SrTiO{sub 3} or MgO substrates for use as underlying electrodes. On these conductive substrates, epitaxial Pb(Zr{sub 0.35}Ti{sub 0.65})O{sub 3} (PZT) and PbTiO{sub 3} (PT) thin films were, deposited by metalorganic chemical vapor deposition (MOCVD). X-ray diffraction (XRD), RBS channeling (RBS), transmission electron microscopy (TEM) and optical waveguiding were used to characterize phase, microstructure, defect structure, refractive index, and film thickness of the deposited films. The PZT and PT films were epitaxial and c-axis oriented. 90{degree} domains, interfacial misfit dislocations and dislocations and threading dislocations were the primary structural defects, and the films showed a 70% RBS channeling reduction. Hysteresis and dielectric measurements of epitaxial PZT ferroelectric capacitor structures formed using evaporated Ag or ITO glass top electrode showed: a remanent polarization of 46.2 mC/cm{sup 2}, a coercive field of 54.9 KV/cm, a dielectric constant of 410, a bipolar resistivity of {approximately}5.8 {times} 10{sup 9} {Omega}-cm at a field of 275 KV/cm, and a breakdown strength of >400 KV/cm.

The photocurrent response, photo-induced changes in hysteresis behavior, and electrooptic (birefringence) effects of sol-gel derived PZT film have been characterized as part of an effort to evaluate ferroelectric films for image storage and processing applications.

Although the feasibility of using PZT and PLZT films for optical data processing applications, such as optical storage disks, image comparators, and spatial light modulators, has clearly been established, most of the critical parameters related to the storage and readout processes still need to be evaluated. Optical readout techniques capable of nondestructively determining the value of polarization are based either on the quadratic electrooptic effect or on a photocurrent response. In reflection, large electrooptic retardations (>60{degrees}) have now been achieved with thin PZT films ({approx equal} 0.5 {mu}m) under conditions that optimize interference effects. These results are quite attractive for device applications. Model calculations, based on the equations of reflection ellipsometry, have been used to develop a framework for understanding those results. The magnitude of the photocurrent response has also been used to determine the polarization state. However, the photocurrent always has the same sign, regardless of the sign of the polarization, which suggests the presence of a strong bias field due to at least one of the interfaces. In addition, the accumulation of space charge after a succession of measurements suppresses the photocurrent transient, which severely limits the utility of a photocurrent based readout. 7 refs., 9 figs.