Chemical Vapor Deposition of Cuprous Halide Semiconductors and Polymer Dielectrics for Applications in Optoelectronics and Flexible Microelectronics
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Chang, Christina Marie
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CitationChang, Christina Marie. 2020. Chemical Vapor Deposition of Cuprous Halide Semiconductors and Polymer Dielectrics for Applications in Optoelectronics and Flexible Microelectronics. Doctoral dissertation, Harvard University, Graduate School of Arts & Sciences.
AbstractThis dissertation presents the development of new chemical vapor deposition (CVD) processes, with an emphasis on imparting desired properties to thin film layers for next-generation devices. To this end, two research areas are described: CVD of metal halide semiconductors for optoelectronic devices, and CVD of dielectrics for 3-D microelectronic devices.
P-type semiconducting metal halide (MX) thin films are promising for use in optical coatings, imaging devices and optoelectronic devices like photovoltaics, but existing methods typically yield MX films of too poor quality (purity, continuity, and smoothness) to be used in these devices. CVD is one of the main techniques used in industry to fabricate device-quality films of other materials, because of its molecular-level control of the fabrication process. However, research efforts in the development of a CVD process to deposit continuous metal halide thin films have met several reactivity challenges. The few known metal halide CVD and ALD processes have been confined almost entirely to metal fluorides, and have typically required ancillary metal halides as the halide source. A more general route to metal halide vapor deposition, such as one using the hydrogen halides (HX) as the halide source, would be of considerable interest. Some researchers have succeeded in producing discontinuous ``islands'' of metal halides (e.g., CuCl, CuI) using HX as a precursor, but continuous thin films of metal chlorides, bromides, and iodides have remained elusive.
In response to this challenge, we have developed two vapor deposition methods that produce continuous CuX thin films. Chapter 2 of this dissertation discusses the vapor conversion of thin films of copper sulfides and oxides to CuX by exposure to HX gas. Chapter 3 of this dissertation discusses CVD of CuBr thin films by reaction between HBr gas and vinyltrimethylsilane(hexafluoro-acetylacetonato)copper(I). Our methods not only provide the desired device-quality films, but also expand the possibilities of metal halide CVD more generally. To the best of our knowledge, our method constitutes the first continuous, non-fluoride metal halide thin films deposited by CVD using the hydrogen halide as the vapor source. Our method provides a reaction pathway that may offer a more general route to CVD of metal halide thin films.
Finally, Chapter 4 of this dissertation describes work toward developing a CVD process to deposit a hybrid organic/inorganic dielectric material that is flexible, robust at elevated temperature, and highly tunable. This work is motivated by the emerging field of flexible electronics, which requires flexible dielectric materials. Polymers are widely used, but cannot withstand the extreme conditions required by some applications. Organic/inorganic hybrid dielectrics have the potential to provide both flexibility and stability to extreme conditions. However, the few existing hybrid dielectrics suffer from drawbacks such as limited tunability of the thickness or chemistry of the organic component. To begin to meet these challenges, a new hybrid dielectric is proposed, and several known vapor deposition processes for ceramics and polymers are implemented and assessed. Principally, we study the atomic layer deposition of alumina and aluminum silicate ceramic thin films, and the molecular layer deposition of parylene and polyimide thin films. These dielectric thin films are deposited on planar and wire substrates and characterized mechanically, thermally, compositionally, and electrically. Our results point toward promising next directions for research on hybrid dielectric thin films for flexible electronic devices.
Citable link to this pagehttps://nrs.harvard.edu/URN-3:HUL.INSTREPOS:37365136
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