Yung-Cheng Lee

Three-Dimensional Ni/TiO2 Nanowire Network for High Areal Capacity Lithium Ion Microbattery Applications

The areal capacity of nanowire-based microbatteries can be potentially increased by increasing the length of nanowires. However, agglomeration of high aspect ratio nanowire arrays could greatly degrade the performance of nanowires for lithium ion (Li-ion) battery applications. In this work, a three-dimensional (3-D) Ni/TiO(2) nanowire network was successfully fabricated using a 3-D porous anodic alumina (PAA) template-assisted electrodeposition of Ni followed by TiO(2) coating using atomic layer deposition. Compared to the straight Ni/TiO(2) nanowire arrays fabricated using conventional PAA templates, the 3-D Ni/TiO(2) nanowire network shows higher areal discharging capacity. The areal capacity increases proportionally with the length of nanowires. With a stable Ni/TiO(2) nanowire network structure, 100% capacity is retained after 600 cycles. This work paves the way to build reliable 3-D nanostructured electrodes for high areal capacity microbatteries.

Al2O3 and TiO2 Atomic Layer Deposition on Copper for Water Corrosion Resistance

Al(2)O(3) and TiO(2) atomic layer deposition (ALD) were employed to develop an ultrathin barrier film on copper to prevent water corrosion. The strategy was to utilize Al(2)O(3) ALD as a pinhole-free barrier and to protect the Al(2)O(3) ALD using TiO(2) ALD. An initial set of experiments was performed at 177 °C to establish that Al(2)O(3) ALD could nucleate on copper and produce a high-quality Al(2)O(3) film. In situ quartz crystal microbalance (QCM) measurements verified that Al(2)O(3) ALD nucleated and grew efficiently on copper-plated quartz crystals at 177 °C using trimethylaluminum (TMA) and water as the reactants. An electroplating technique also established that the Al(2)O(3) ALD films had a low defect density. A second set of experiments was performed for ALD at 120 °C to study the ability of ALD films to prevent copper corrosion. These experiments revealed that an Al(2)O(3) ALD film alone was insufficient to prevent copper corrosion because of the dissolution of the Al(2)O(3) film in water. Subsequently, TiO(2) ALD was explored on copper at 120 °C using TiCl(4) and water as the reactants. The resulting TiO(2) films also did not prevent the water corrosion of copper. Fortunately, Al(2)O(3) films with a TiO(2) capping layer were much more resilient to dissolution in water and prevented the water corrosion of copper. Optical microscopy images revealed that TiO(2) capping layers as thin as 200 Å on Al(2)O(3) adhesion layers could prevent copper corrosion in water at 90 °C for ~80 days. In contrast, the copper corroded almost immediately in water at 90 °C for Al(2)O(3) and ZnO films by themselves on copper. Ellipsometer measurements revealed that Al(2)O(3) films with a thickness of ~200 Å and ZnO films with a thickness of ~250 Å dissolved in water at 90 °C in ~10 days. In contrast, the ellipsometer measurements confirmed that the TiO(2) capping layers with thicknesses of ~200 Å on the Al(2)O(3) adhesion layers protected the copper for ~80 days in water at 90 °C. The TiO(2) ALD coatings were also hydrophilic and facilitated H(2)O wetting to copper wire mesh substrates.

Particle Dynamics and Particle Heat and Mass Transfer in Thermal Plasmas. Part II. Particle Heat and Mass Transfer in Thermal Plasmas

This paper is concerned with a review of heat and mass transfer between thermal plasmas and particulate matter. In this situation various effects which are not present in ordinary heat and mass transfer have to be considered, including unsteady conditions, modified convective heat transfer due to strongly varying plasma properties, radiation, internal conduction, particle shape, vaporization and evaporation, noncontinuum conditions, and particle charging. The results indicate that (i) convective heat transfer coefficients have to be modified due to strongly varying plasma properties; (ii) vaporization, defined as a mass transfer process corresponding to particle surface temperatures below the boiling point, describes a different particle heating history than that of the evaporation process which, however, is not a critical control mechanism for interphase mass transfer of particles injected into thermal plasmas; (iii) particle heat transfer under noncontinuum conditions is governed by individual contributions from the species in the plasma (electrons, ions, neutral species) and by particle charging effects.

Solder self-assembly for three-dimensional microelectromechanical systems

Abstract A solder technology has been developed that utilizes molten solder surface tension forces to self-assemble MEMS 3-D structures. Using solder, a single batch reflow process can be used to accomplish hundreds or thousands of precision assemblies, and the cost per assembly can be reduced considerably. A model, based on surface energy minimization of molten liquids, has been developed for predicting assembly motion. The modeling, combined with experimental studies, have demonstrated ±2° assembly angle control is possible when the MEMS structures are assembled by solder alone. To improve the self-assembly angle precision, a self-locking mechanism can be added, which reduces the assembly angle variation down to ±0.3°.

Particle dynamics and particle heat and mass transfer in thermal plasmas. Part I. The motion of a single particle without thermal effects

A particle injected into a thermal plasma will experience a number of effects which are not present in an ordinary gas. In this paper effects exerted on the motion of a particle will be reviewed and analyzed in the context of thermal plasma processing of materials. The primary purpose of this paper is an assessment of the relative importance of various effects on particle motion.Computer experiments are described, simulating motion of a spherical particle in a laminar, confined plasma jet or in a turbulent, free plasma jet. Particle sizes range from 5 to 50 µm, and as sample materials alumina and tungsten are considered.The results indicate that (i) the correction term required for the viscous drag coefficient due to strongly varying properties is the most important factor; (ii) non-continuum effects are important for particle sizes <10 µm at atmospheric pressure and these effects will be enhanced for smaller particles and/or reduced pressures; (iii) the Basset history term is negligible, unless relatively large and light particles are considered over long processing distances; (iv) thermophoresis is not crucial for the injection of particles into thermal plasmas; (v) turbulent dispersion becomes important for particle <10 µm in diameter.

Design and modeling of RF MEMS tunable capacitors using electro-thermal actuators

A series mounted MEMS tunable capacitor in a CPW line is reported. An electro-thermal actuator has been used for driving the top plate of the parallel plate capacitor. The MEMS structure is bonded on an alumina substrate using flip-chip technology so that the silicon on the backside of the MEMS can be removed to reduce the RF losses. The lumped-element model of the capacitor up to 40 GHz has been developed based on Y-parameters, which are derived from measured S-parameters. The measured Q-factor is 256 at 1 GHz for a 0.102 pF capacitor and C/sub max//C/sub min/ ratio of the capacitor is about 2:1.

The mechanical robustness of atomic-layer- and molecular-layer-deposited coatings on polymer substrates

films was determined to be KIC= 1.89 0.10 and 0.17 0.02 MPa m 0.5 , respectively. From measurements of the saturated crack density, the critical interfacial shear stress was estimated to be c = 39.5 8.3 and 66.6 6.1 MPa, respectively. The toughness of nanometer-scale alumina was comparable to that of alumina thin films grown using other techniques, whereas alucone was quite brittle. The use of alucone as a spacer layer between alumina films was not found to increase the critical strain at fracture for the composite films. This performance is attributed to the low toughness of alucone. The experimental results were supported by companion simulations using fracture mechanics formalism for multilayer films. To aid future development, the modeling method was used to study the increase in the toughness and elastic modulus of the spacer layer required to render improved critical strain at fracture. These results may be applied to a broad variety of multilayer material systems composed of ceramic and spacer layers to yield robust coatings for use in chemical barrier and other applications.

Design of solder joints for self-aligned optoelectronic assemblies

Self-aligning soldering is the critical technology for precision optoelectronic assembly. The pre-assembly solder joint design can improve the final alignment accuracy. In this paper, a public domain software Surface Evolver is modified as a modeling tool for the design of solder joints for self-aligned assemblies. Furthermore, for convenient and efficient design, the results from the numerical model are nondimensionalized and regressed as a polynomial regression model, which describes the relationships between the surface tension forces and the solder joint design parameters explicitly. The regression model is established based on 1100 data points calculated for solder joints with circular pads. We apply this model tool to several design case studies, including the joint array design for self-alignment and the solder assembly of a FLC/VLSI spatial light modulator. It is demonstrated that the model developed here is a very powerful and convenient tool to aid in the design of solder joints for various applications. >

Soldering technology for optoelectronic packaging

Soldering technology for optoelectronic packaging is reviewed by studying modules in four categories: solder assembly with no precision self-alignments, and self-aligned solder assembly with no, one or two mechanical stops. There have been at least 60 papers and 8 U.S. patents published between 1990 and 1995. In addition to die-attachments, soldering technology has been successfully demonstrated for precision alignments. However, some packaging issues may hamper the progress of its manufacturing insertion for wide applications. Four of the issues to be discussed are solder materials, fluxless reflow, design, and reliability. More studies on these issues are needed to support the advancement of optoelectronic packaging for low-cost, high-performance and high-reliability modules.

The realization and design considerations of a flip-chip integrated MEMS tunable capacitor

Abstract Microelectromechanical systems (MEMS)-based radio frequency (RF) components are being developed for various microwave and millimeter-wave applications. Using standard foundry processes, it is possible to create very complex MEMS devices. However, most RF MEMS need to be fabricated using GaAs, ceramics, high resistivity silicon or other RF-compatible materials. Such fabrication techniques are not commonly used by the mainstream silicon-based MEMS manufacturing infrastructure. As a result, the complexities of these MEMS devices are very limited. What is needed is a way to utilize the existing cost effective foundry processes, but not sacrifice RF performance. Utilizing a flip-chip transfer process, a complex, foundry fabricated, MEMS tunable capacitor has been demonstrated that yields high quality RF performance ( Q ∼100 at 10 GHz, 1050 at 1 GHz). The transfer process is described, and its performance (control, success rate, etc.) is presented. Several major design considerations for implementing the tunable capacitor using flip-chip technology are presented, including warpage, actuator design, and structural rigidity. Using the transfer process and design considerations, there is an opportunity to integrate complex MEMS onto any RF compatible substrate without the silicon semiconductor effects. Thus, it is possible to manufacture complex MEMS cost-effectively for a new generation of RF MEMS with superior functionality.