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Atomic Layer Deposition of Al2O3 Dielectrics for Low-Temperature TFT Process

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Resumo:Thin-film-transistor (TFT) technology has been prominent in the modern era, being devices particularly suitable for large-area applications such as displays and flexible electronics. When thinking about applications demanding low cost and/or mechanical flexibility, there is a need for a process that can deliver quality films in substrates which require a low thermal budget. In this work, Atomic Layer Deposition (ALD) is studied as a process for low-temperature depositions of Al2O3 dielectric layers to be used in a well-established oxide TFT process. The first part of this work focused on establishing and optimizing a 150 ºC ALD process for Al2O3, through adjustment of precursor exposure and purge times, which was done by studying both the optical and electrical properties of the dielectrics and comparing these to ones grown at 200 ºC. Optical results showed good quality film growth, uniform film thickness throughout 3” substrates, and a constant growth-per-cycle for a given process. The optimized 150 ºC Al2O3 layers had a dielectric constant of 8.4±0.6 and a breakdown field of 4.0±2.1 MV/cm, which are comparable to state-of-the-art Al2O3 films fabricated at 200 °C or higher temperatures. The second part of this work was the implementation of the 50 nm thick optimized ALD dielectric as a gate insulator in top-gate and bottom-gate oxide TFTs based on indium-gallium zinc oxide (IGZO) semiconductor. The bottom-gate transistors show hysteresis in the transfer curves, unlike the top-gate transistors, associated to charge trapping at the Al2O3/IGZO interface arising from the damage of the IGZO sputtering process. The bottom-gate and top-gate transistors have average saturation mobility of 6.3 cm2/Vs and 1.3 cm2/Vs, respectively, and a SS of approximately 0.1 V/dec and 0.2 V/dec. While future engineering of the dielectric/semiconductor stack can further improve device performance and stability, the results obtained already demonstrate that 150 °C Al2O3 layers by ALD are very good candidates for flexible oxide TFTs on temperature-sensitive substrates.
Autores principais:Carioca, Ricardo Filipe Moreira Bárbora Fidalgo
Assunto:ALD Al2O3 low temperature IGZO TFT
Ano:2021
País:Portugal
Tipo de documento:dissertação de mestrado
Tipo de acesso:acesso aberto
Instituição associada:Universidade Nova de Lisboa
Idioma:inglês
Origem:Repositório Institucional da UNL

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