(4ea) Zeolite Films and Membranes for Computer Microprocessors and Biofuel Production
Zeolite thin films and membranes have been widely investigated over the last 15 years, mainly as separation membranes and membrane reactors. Their uniform microporosity and the ability to fine-tune their chemical composition and physical architecture lead to important macroscopic properties that can be exploited in a growing number of applications. The diversity in their use is demonstrated in this work through the exploration of zeolites as low-dielectric constant (low-k) films for computer microprocessors and catalytic membrane reactors for the production of biofuels.
Next-generation microprocessors require smaller feature sizes, but the slow development of new low-k films with better material properties is reducing progress toward improved computing performance. Pure-silica-zeolites (PSZ) are a strong candidate for replacement low-k materials because their intrinsic porosity and crystallinity gives them a low k value and strong mechanical properties. However, several other characteristics, including hydrophobicity, wet-etch chemical resistance, and pore size distribution, were not previously evaluated or optimized for low-k applications. Successful device integration of a viable new low-k alternative requires that all of these properties meet minimum specifications.
PSZ films were carefully engineered through different synthesis and modification techniques to obtain the desired aforementioned properties. PSZ MFI and MEL frameworks were functionalized with fluoroorganic groups through a direct synthesis method. The resulting hydrophobic films reduced moisture adsorption, which mitigated significant increases in the k value after exposure to ambient conditions. Wet-etch chemical resistance was imparted to PSZ films by annealing them in hydrophobic silanes. By silylating the films before cross-linking of the silica matrix occurred, a high carbon content was incorporated throughout the bulk of the films, thus making them water- and wet-etch chemical-resistant. The mesopore diameter and pore size distribution was controlled and narrowed through the addition of tetraethylorthosilicate to the spin-on zeolite nanoparticle suspension. After calcination and silylation, the induced changes in porosity and carbon content dramatically improved the mechanical properties and wet-etch chemical resistance. The results obtained during this process also indicate that zeolite can be crystallized ?on-wafer? under ambient pressures. As a result of the methods developed in this work, PSZ low-k films are a leading low-k candidate and considerably outperform other alternative materials.
Studies are currently being performed to develop catalytic coatings of exfoliated and pillared zeolites for the production of hydrocarbons from biomass. These materials are derivatives of a certain class of layered materials that consist of microporous, zeolitic layers. They can, in principle, be pillared by inserting silica or other oxide pillars in the spaces between the layers (often called the gallery). They can also be exfoliated to yield single zeolitic layers of nanometer thickness. The pillared zeolites contain tunable mesoporosity in the gallery, while the single exfoliated layers allow for external surface catalysis at sites with catalytic activity similar to that of zeolite pores.