Patterned thick films are used in the manufacture of integrated circuits and sensors for applications ranging from camera sensors, to medical implants, to computer networks. Currently, most thick films are produced by a screen printing process, which involves deposition of pastes containing fine metal particles which are then heated to high temperatures to bond the particles so that the conductivity is increased to an acceptable level. The need for high processing temperature limits the choices of substrates upon which the films can be deposited, and often requires expensive and rigid glass or ceramic substrates. This award supports research towards advancing a new method for depositing thick films that can dramatically reduce processing temperatures and would allow deposition on lower-cost and flexible substrates, while also allowing novel material structures that have the potential to produce films with superior properties. Such patterned films that exhibit improved properties would have applications in many devices including high power electronics and solar cells, and other applications that could advance US competitiveness in manufacturing. The multidisciplinary approach which involves a combination of computer simulations and experiments will enable the education of graduate students, and the outreach activities will integrate this research with a proven program that enables high school teachers to effectively teach engineering to encourage and prepare their students to enter engineering and science careers.
The laser ablation of microparticle aerosol process is a relatively new process for depositing patterned, micro-scale thick films with nanostructured features. Nanoparticles are produced from commonly available and inexpensive powders via an aerosol ablation and then impacted at high velocities onto a substrate. High production rates allow direct writing of inorganic (metallic, semiconductor, or ceramic) thick films without a mask at room temperature onto polymeric, metallic, or ceramic substrates. The grain size and porosity in the films can be controlled through the ablation and deposition parameters. The current process, however, is limited to producing polycrystalline or amorphous films with a maximum as-deposited relative density of about 70 percent. A combination of predictive molecular dynamics computer simulations and experimental studies of the nanoparticle impaction and film growth processes are planned to develop an understanding of how processing parameters influence deposition efficiency, the film morphology, and film structure on a nano- to-micro scale. Computer simulations will be used to systematically study the influence of particle size, impaction energy, substrate temperature, material composition and crystallinity, defect orientation and concentration, and particle/substrate misorientation on the resulting films. In combination with the computer simulations, the experimental apparatus will be modified to allow experiments to be conducted under conditions in which the simulations can be validated. The experimental data will be used to modify the computer simulations as needed so that accurate predictions of the resulting film microstructures can be made. It is expected that by studying the factors that control deposition and film growth will lead to a much larger range of microstructures and densities than is currently possible, including single crystal patterned films with relative densities approaching 100 percent.
