Synthesis of Next Generation Dielectric Materials through Rational Exploration of Chemical Space

The search for new dielectric materials has grown exponentially as more emphasis has been placed on the fabrication of new devices such as photovoltaics, transistors and capacitors. This dissertation focuses on the exploration of chemical space through rational design as a means of identifying such potential dielectric materials for capacitors, though these materials can be potentially used for any applications mentioned. Chapter 3. Dielectric materials that can operate at elevated temperatures are desired as space could be a limiting factor for the large capacitor banks that are envisioned. Polyimides are demonstrated to have thermal and dielectric stability up to 125-150 oC. It was found that as the conjugation length of the dianhydride monomer or the number of ether linkages in the diamine monomer was increased so was the dielectric constant. The polyimide based on the longest conjugated dianhydride and ether diamine achieved the highest reported dielectric constant, 7.8, but at a cost of low Tg. Copolymerization is undertaken to improve the thermal properties and further tested for breakdown strength. Chapter 4. The incorporation of silicon into a polymer theoretically increases the dielectric constant due to the increase of polarizability of silicon versus carbon. However, the synthesis of polysilanes is problematic, as large amounts of salt impurities are formed. Attempts to wash out the impurity from the polymer proved futile as the polysilane films were still very conductive. The synthesis of polysilanes guided our other attempts to create new dielectric materials by enlightening us on the need for high purity of polymers. Chapter 5. A series of organotin polymers were synthesized and from this poly(organotin esters) were identified as the most promising candidate as a dielectric. Theoretically and experimentally it was found that the structure of the polymers were quite complex due to coordination of oxygen and tin. The dielectric constant of a series of aliphatic poly(dimethyltin esters) were evaluated and exhibited dielectric constants between 5.3-8.7. Further analysis of the role of aromaticity and chirality within the polymer backbone was also performed. Also blending a homopolymer that had protruding methyl groups aided in the reduction of crystal size, improving the quality of films. Chapter 6. Other metals are incorporated into the polymer backbone due to their lower electronegativity versus oxygen. It was shown that these polymers could have a dielectric constant ranging from 3.3 to approximately 8. The role of bound water on dielectric properties was also explored to start to build a fundamental understanding.