Publicação
Non-volatile memory devices based on ferroelectric oxide thin films
| Resumo: | Information storage is a paramount challenge in the current century driven by the need to scale down memory cells and lower their operating voltages while ensuring high-speed and non-volatile characteristics. Over the last century, ferroelectric materials have emerged as promising candidates for the development of non-volatile memories where two electrical switching states can be written and retained for a long time. The use of conventional ferroelectrics (perovskite oxides) for memory applications has been intensively studied for decades. However, they are not CMOS compatible and are limited by the high growth temperature. Recently, the discovery of ferroelectricity in binary oxides, such as zirconium oxide, ZrO2, or hafnium oxide, HfO2, added new advantages and functionalities in ferroelectrics-based memory devices. This thesis explores the potential of using ferroelectric HfO2- and ZrO2-based materials for non volatile memory applications. In the first stage, it was investigated the impact of annealing temperature on the ferroelectric properties of (HfxZr1-x)O2 films x = 0, 0.3 and 0.5 in a Pt/(HfxZr1-x)O2/W capacitor structure. It was found that an annealing at 680 ºC is the optimal choice for improving ferroelectric properties in terms of thermal budget resulting in a remanent polarization ( ) of 9.2 µC/cm2 for the (Hf0.3Zr0.7)O2 composition. Moreover, the device showed a stable performance up to 1.8x106 cycles. In a second research study, a La0.7Sr0.3MnO3 (LSMO)/HfO2/W stack was grown on a Nb:SrTiO3 substrate. The 3 nm-thick epitaxially grown HfO2 layer was found to crystallize in the polar rhombohedral phase. Although no evidence of ferroelectric properties was found, a bipolar interfacial resistive switching behaviour was reported in the fabricated device. It is suggested that this RS behaviour is explained by phase transitions at the LSMO/HfO2 interface caused by a reversible migration of oxygen vacancies. The device showed a memory window of almost 10 and a non-volatility retention of at least 100 seconds. |
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| Autores principais: | Silva, Nuno Manuel Estrócio e |
| Assunto: | Ferroelectricity Non-centrosymmetric phases Non-volatile memory Thin film Fases não-centrossimétricas Ferroeletricidade Filme fino Memória não volátil Engenharia e Tecnologia::Nanotecnologia |
| Ano: | 2023 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso restrito |
| Instituição associada: | Universidade do Minho |
| Idioma: | inglês |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | Information storage is a paramount challenge in the current century driven by the need to scale down memory cells and lower their operating voltages while ensuring high-speed and non-volatile characteristics. Over the last century, ferroelectric materials have emerged as promising candidates for the development of non-volatile memories where two electrical switching states can be written and retained for a long time. The use of conventional ferroelectrics (perovskite oxides) for memory applications has been intensively studied for decades. However, they are not CMOS compatible and are limited by the high growth temperature. Recently, the discovery of ferroelectricity in binary oxides, such as zirconium oxide, ZrO2, or hafnium oxide, HfO2, added new advantages and functionalities in ferroelectrics-based memory devices. This thesis explores the potential of using ferroelectric HfO2- and ZrO2-based materials for non volatile memory applications. In the first stage, it was investigated the impact of annealing temperature on the ferroelectric properties of (HfxZr1-x)O2 films x = 0, 0.3 and 0.5 in a Pt/(HfxZr1-x)O2/W capacitor structure. It was found that an annealing at 680 ºC is the optimal choice for improving ferroelectric properties in terms of thermal budget resulting in a remanent polarization ( ) of 9.2 µC/cm2 for the (Hf0.3Zr0.7)O2 composition. Moreover, the device showed a stable performance up to 1.8x106 cycles. In a second research study, a La0.7Sr0.3MnO3 (LSMO)/HfO2/W stack was grown on a Nb:SrTiO3 substrate. The 3 nm-thick epitaxially grown HfO2 layer was found to crystallize in the polar rhombohedral phase. Although no evidence of ferroelectric properties was found, a bipolar interfacial resistive switching behaviour was reported in the fabricated device. It is suggested that this RS behaviour is explained by phase transitions at the LSMO/HfO2 interface caused by a reversible migration of oxygen vacancies. The device showed a memory window of almost 10 and a non-volatility retention of at least 100 seconds. |
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