Chemical vapor deposition of functional and conformal polymer thin films for the formation and modification of nanostructures

Abstract

Autonomous mini- and microscale devices require the miniaturization of component devices such as on board integrated circuits (ICs) and electrochemical power sources. A paradigm shift to micro/nanostructured 3D geometries can enable high device performance within a small areal footprint. Fabrication of such devices requires processes to form structures in a material of interest and subsequently modify the structure with additional functional materials. This thesis explores the chemical vapor deposition (CVD) of polymer thin films to enable both the formation and modification of nanostructures. The CVD method allows for simultaneous polymer synthesis and thin film formation. The broad range of applications studied in this thesis all benefit from the single-step, in-situ control of the final polymer functionality and thin film properties enabled by the CVD of polymers. The first portion of this thesis studies the formation of nanostructures for ICs via the directed self-assembly (DSA) of block copolymers (BCPs). Initiated CVD (iCVD) is used to form cross-linked poly(divinyl benzene) (pDVB) films that control the orientation of self-assembled BCPs. The cross-linking mechanism of pDVB is first ascertained to form durable films. In-situ chemical modification of iCVD pDVB is then used to tune the final orientation of the selfassembled BCP film. A conformal iCVD pDVB film is then integrated into existing DSA processes to yield a nano-template that could be used to fabricate nanostructured ICs. The second portion of this thesis studies the modification of nanostructures by active and supporting materials used in electrochemical power systems. The iCVD process is used to develop conformal, solid polymer electrolytes, a supporting material for solid state lithium ion batteries. Out of several multi-vinyl cyclic chemistries, poly(tetravinyltetramethylcyclotetrasiloxane) (pV4D4) films displayed the highest ionic conductivity (10-⁷ S cm-¹) and high conformality. Active materials for supercapacitors were developed using the oxidative chemical vapor deposition (oCVD) of conductive polymers. The oCVD process was used to control the crystallographic texture of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films. Edge-on texture maximized the pseudocapacitive charge storage of this material. Conformal PEDOT thin films on micro-structured current collectors enabled higher energy densities in a high power, asymmetric supercapacitor.