Estudo de junções túnel magnéticas com barreiras isolantes piezoelétricas de AlN
Autor(a) principal: | |
---|---|
Data de Publicação: | 2015 |
Tipo de documento: | Tese |
Idioma: | por |
Título da fonte: | Manancial - Repositório Digital da UFSM |
Texto Completo: | http://repositorio.ufsm.br/handle/1/3929 |
Resumo: | We analyze the possibility of using aluminum nitride (AlN) as a piezoelectric tunnel barrier in magnetic or non-magnetic tunnel junctions. Samples in the form of monolayers, bilayers, multilayers and tunnel junctions were produced by magnetron sputtering from an aluminum metal target. The insulating AlN barrier was grown in a reactive atmosphere of argon and nitrogen. Through the monolayers and bilayers we investigated the growth conditions of AlN onto different substrates, buffer, and cap layers. Using x-ray diffraction and transmission electronic microscopy it was possible to verify the excellent degree of texturing of AlN films with the direction <002> perpendicular the substrate plane. The multilayer showed that the use of AlN as a piezoelectric tunnel barrier is feasible, since the crystallographic structure remains when the thickness of the AlN is drastically reduced to a thickness so that quantum tunneling is possible. We also held magnetization measurements and tunnel magnetoresistance in magnetic tunnel junctions. It is important that the coercive fields of the electrodes are different, so that from the application of an external field can be obtained a situation where the magnetization of the electrodes point in opposite directions. The average thickness of the tunnel barrier in multilayers and tunnel junctions were obtained by x-ray diffraction and transmission electron microscopy. The nonlinear IxV curves of tunnel junctions were measured at room temperature and at lower temperatures, and showed a linear behavior at low voltages, and a nonlinear behavior for higher voltages. Measurements of tunnel magnetoresistance showed spin dependent tunneling. Simulations using the Simmons model for symmetric barrier allowed us to obtain the effective area of tunneling, effective thickness of the barrier, and the height of the barrier. Effective area values are some orders of magnitude smaller than the actual area of the junctions, and transmission electron microscopy pictures show that the tunnel transport occurs at some hot spots. In the measurements of the IxV curves we observe a minimum thickness of 6nm for the insulating barrier to be piezoelectric, as the polarization effect was detected. The curves have a shift to negative bias, both in magnetic and non-magnetic tunnel junctions. Using the results of the simulation we verified the exponential pattern of resistance, normalized by the effective area of tunneling, depending on the thickness of the insulator. For effective barrier thickness above 1nm, the barrier height increases with insulator thickness, as expected. For barrier thickness between 0;8 and 1nm, there is a decline in barrier height. We have not found recorded in the literature this type of behavior for normal insulating systems or for piezoelectric materials. |
id |
UFSM_6a919b307c855caaf36cedc821aaff4e |
---|---|
oai_identifier_str |
oai:repositorio.ufsm.br:1/3929 |
network_acronym_str |
UFSM |
network_name_str |
Manancial - Repositório Digital da UFSM |
repository_id_str |
|
spelling |
Estudo de junções túnel magnéticas com barreiras isolantes piezoelétricas de AlNStudy of magnetic tunnel junctions with insulating barriers piezoelectric of AlNTunelamentoJunções túnel magnéticasPiezoelétricosMagnetorresistência túnelTunnellingMagnectic tunnel junctionsPiezoelectricTunneling MagnetoresistanceCNPQ::CIENCIAS EXATAS E DA TERRA::FISICAWe analyze the possibility of using aluminum nitride (AlN) as a piezoelectric tunnel barrier in magnetic or non-magnetic tunnel junctions. Samples in the form of monolayers, bilayers, multilayers and tunnel junctions were produced by magnetron sputtering from an aluminum metal target. The insulating AlN barrier was grown in a reactive atmosphere of argon and nitrogen. Through the monolayers and bilayers we investigated the growth conditions of AlN onto different substrates, buffer, and cap layers. Using x-ray diffraction and transmission electronic microscopy it was possible to verify the excellent degree of texturing of AlN films with the direction <002> perpendicular the substrate plane. The multilayer showed that the use of AlN as a piezoelectric tunnel barrier is feasible, since the crystallographic structure remains when the thickness of the AlN is drastically reduced to a thickness so that quantum tunneling is possible. We also held magnetization measurements and tunnel magnetoresistance in magnetic tunnel junctions. It is important that the coercive fields of the electrodes are different, so that from the application of an external field can be obtained a situation where the magnetization of the electrodes point in opposite directions. The average thickness of the tunnel barrier in multilayers and tunnel junctions were obtained by x-ray diffraction and transmission electron microscopy. The nonlinear IxV curves of tunnel junctions were measured at room temperature and at lower temperatures, and showed a linear behavior at low voltages, and a nonlinear behavior for higher voltages. Measurements of tunnel magnetoresistance showed spin dependent tunneling. Simulations using the Simmons model for symmetric barrier allowed us to obtain the effective area of tunneling, effective thickness of the barrier, and the height of the barrier. Effective area values are some orders of magnitude smaller than the actual area of the junctions, and transmission electron microscopy pictures show that the tunnel transport occurs at some hot spots. In the measurements of the IxV curves we observe a minimum thickness of 6nm for the insulating barrier to be piezoelectric, as the polarization effect was detected. The curves have a shift to negative bias, both in magnetic and non-magnetic tunnel junctions. Using the results of the simulation we verified the exponential pattern of resistance, normalized by the effective area of tunneling, depending on the thickness of the insulator. For effective barrier thickness above 1nm, the barrier height increases with insulator thickness, as expected. For barrier thickness between 0;8 and 1nm, there is a decline in barrier height. We have not found recorded in the literature this type of behavior for normal insulating systems or for piezoelectric materials.Conselho Nacional de Desenvolvimento Científico e TecnológicoNesta tese analizamos a possibilidade do uso de nitreto de alumínio (AlN) como barreira túnel piezoelétrica em junções túnel magnéticas ou não magnéticas. Amostras na forma de monocamadas, bicamadas, multicamadas e junções túnel foram produzidas pela técnica de "magnetron sputtering"a partir de um alvo metálico de alumínio. A barreira isolante de AlN foi crescida em uma atmosfera reativa de argônio e nitrogênio. Através das monocamadas e das bicamadas investigamos as condições de crescimento do AlN sobre diferentes substratos, e camadas "buffer"e camadas "cap". Utilizando difração de raio-x e microscopia eletrônica de transmissão foi possível verificar o excelente grau de texturização dos filmes de AlN com a direção <002> perpendicular ao plano do substrato. As multicamadas mostraram que a utilização do AlN como barreira túnel piezoelétrica é viável, pois a estrutura cristalográfica se mantém quando a espessura do AlN é drasticamente reduzida até uma espessura que ocorra o fenômeno de tunelamento quântico. Também foram realizadas medidas de magnetização e de magnetorresistência túnel em junções túnel magnéticas. Nestas, é importante que os campos coercivos dos eletrodos sejam diferentes, para que a partir da aplicação de um campo externo seja possível obter uma situação onde os momentos magnéticos dos eletrodos apontem em sentidos contrários. A espessura média da barreira túnel nas multicamadas e junções túnel foram obtidas através de difração de raio-x e de microscopia eletrônica de transmissão. As curvas IxV não lineares das junções túnel foram medidas a temperatura ambiente e a baixa temperatura, e apresentaram um comportamento linear a baixas tensões e uma relação não linear para tensões mais elevadas. Para a realização de simulações foi utilizado modelo de Simmons para barreira simétrica. Os parâmetros obtidos através deste modelo são, a área efetiva de tunelamento Se f , a espessura efetiva da barreria te f e a altura da barreira f0. Através da observação dos resultados da área efetiva que são algumas ordens de grandeza menores que a área real da junção, e das imagens de microscopia eletrônica de transmissão podemos afirmar que o transporte túnel se dá por "hot spots". Nas medidas das curvas IxV observamos uma espessura mínima de 6nm para a barreira isolante piezoelétrica onde o efeito de polarização foi detectado. As curvas sofrem um deslocamento para tensões negativas, isto ocorre tanto nas junções túnel magnéticas como nas não magnéticas. Utilizando os resultados dos ajustes foi possível verificar o caráter exponencial da resistência, normalizada pela área efetiva de tunelamento, em função da espessura do isolante. Para espessura efetiva da barreira, a partir de 1nm, a altura da barreira aumenta com a espessura do isolante. Resultado este esperado, mostrando uma tendência do crescimento da altura da barreia com a espessura. Para espessura de barreia entre 0;8 e 1nm, há presença de um declínio na altura da barreira. Não encontramos registro na literatura deste tipo de comportamento para sistemas isolantes normais nem para materiais piezoelétricos. Medidas de magnetorresistência túnel nas junções mostraram que o tunelamento é dependente de spin.Universidade Federal de Santa MariaBRFísicaUFSMPrograma de Pós-Graduação em FísicaDorneles, Lucio Strazzaboscohttp://lattes.cnpq.br/7244173039310066Fichtner, Paulo Fernando Papaleohttp://lattes.cnpq.br/3107128880946249Radtke, Cláudiohttp://lattes.cnpq.br/4839018758765203Denardin, Juliano Casagrandehttp://lattes.cnpq.br/5425237044575885Zimmer, Fábio Mallmannhttp://lattes.cnpq.br/6328420212181284Della Pace, Rafael Domingues2015-06-022015-06-022015-01-20info:eu-repo/semantics/publishedVersioninfo:eu-repo/semantics/doctoralThesisapplication/pdfapplication/pdfPace, Rafael Domingues Della. Study of magnetic tunnel junctions with insulating barriers piezoelectric of AlN. 2015. 149 f. Tese (Doutorado em Física) - Universidade Federal de Santa Maria, Santa Maria, 2015.http://repositorio.ufsm.br/handle/1/3929porinfo:eu-repo/semantics/openAccessreponame:Manancial - Repositório Digital da UFSMinstname:Universidade Federal de Santa Maria (UFSM)instacron:UFSM2022-01-06T12:40:35Zoai:repositorio.ufsm.br:1/3929Biblioteca Digital de Teses e Dissertaçõeshttps://repositorio.ufsm.br/ONGhttps://repositorio.ufsm.br/oai/requestatendimento.sib@ufsm.br||tedebc@gmail.comopendoar:2022-01-06T12:40:35Manancial - Repositório Digital da UFSM - Universidade Federal de Santa Maria (UFSM)false |
dc.title.none.fl_str_mv |
Estudo de junções túnel magnéticas com barreiras isolantes piezoelétricas de AlN Study of magnetic tunnel junctions with insulating barriers piezoelectric of AlN |
title |
Estudo de junções túnel magnéticas com barreiras isolantes piezoelétricas de AlN |
spellingShingle |
Estudo de junções túnel magnéticas com barreiras isolantes piezoelétricas de AlN Della Pace, Rafael Domingues Tunelamento Junções túnel magnéticas Piezoelétricos Magnetorresistência túnel Tunnelling Magnectic tunnel junctions Piezoelectric Tunneling Magnetoresistance CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA |
title_short |
Estudo de junções túnel magnéticas com barreiras isolantes piezoelétricas de AlN |
title_full |
Estudo de junções túnel magnéticas com barreiras isolantes piezoelétricas de AlN |
title_fullStr |
Estudo de junções túnel magnéticas com barreiras isolantes piezoelétricas de AlN |
title_full_unstemmed |
Estudo de junções túnel magnéticas com barreiras isolantes piezoelétricas de AlN |
title_sort |
Estudo de junções túnel magnéticas com barreiras isolantes piezoelétricas de AlN |
author |
Della Pace, Rafael Domingues |
author_facet |
Della Pace, Rafael Domingues |
author_role |
author |
dc.contributor.none.fl_str_mv |
Dorneles, Lucio Strazzabosco http://lattes.cnpq.br/7244173039310066 Fichtner, Paulo Fernando Papaleo http://lattes.cnpq.br/3107128880946249 Radtke, Cláudio http://lattes.cnpq.br/4839018758765203 Denardin, Juliano Casagrande http://lattes.cnpq.br/5425237044575885 Zimmer, Fábio Mallmann http://lattes.cnpq.br/6328420212181284 |
dc.contributor.author.fl_str_mv |
Della Pace, Rafael Domingues |
dc.subject.por.fl_str_mv |
Tunelamento Junções túnel magnéticas Piezoelétricos Magnetorresistência túnel Tunnelling Magnectic tunnel junctions Piezoelectric Tunneling Magnetoresistance CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA |
topic |
Tunelamento Junções túnel magnéticas Piezoelétricos Magnetorresistência túnel Tunnelling Magnectic tunnel junctions Piezoelectric Tunneling Magnetoresistance CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA |
description |
We analyze the possibility of using aluminum nitride (AlN) as a piezoelectric tunnel barrier in magnetic or non-magnetic tunnel junctions. Samples in the form of monolayers, bilayers, multilayers and tunnel junctions were produced by magnetron sputtering from an aluminum metal target. The insulating AlN barrier was grown in a reactive atmosphere of argon and nitrogen. Through the monolayers and bilayers we investigated the growth conditions of AlN onto different substrates, buffer, and cap layers. Using x-ray diffraction and transmission electronic microscopy it was possible to verify the excellent degree of texturing of AlN films with the direction <002> perpendicular the substrate plane. The multilayer showed that the use of AlN as a piezoelectric tunnel barrier is feasible, since the crystallographic structure remains when the thickness of the AlN is drastically reduced to a thickness so that quantum tunneling is possible. We also held magnetization measurements and tunnel magnetoresistance in magnetic tunnel junctions. It is important that the coercive fields of the electrodes are different, so that from the application of an external field can be obtained a situation where the magnetization of the electrodes point in opposite directions. The average thickness of the tunnel barrier in multilayers and tunnel junctions were obtained by x-ray diffraction and transmission electron microscopy. The nonlinear IxV curves of tunnel junctions were measured at room temperature and at lower temperatures, and showed a linear behavior at low voltages, and a nonlinear behavior for higher voltages. Measurements of tunnel magnetoresistance showed spin dependent tunneling. Simulations using the Simmons model for symmetric barrier allowed us to obtain the effective area of tunneling, effective thickness of the barrier, and the height of the barrier. Effective area values are some orders of magnitude smaller than the actual area of the junctions, and transmission electron microscopy pictures show that the tunnel transport occurs at some hot spots. In the measurements of the IxV curves we observe a minimum thickness of 6nm for the insulating barrier to be piezoelectric, as the polarization effect was detected. The curves have a shift to negative bias, both in magnetic and non-magnetic tunnel junctions. Using the results of the simulation we verified the exponential pattern of resistance, normalized by the effective area of tunneling, depending on the thickness of the insulator. For effective barrier thickness above 1nm, the barrier height increases with insulator thickness, as expected. For barrier thickness between 0;8 and 1nm, there is a decline in barrier height. We have not found recorded in the literature this type of behavior for normal insulating systems or for piezoelectric materials. |
publishDate |
2015 |
dc.date.none.fl_str_mv |
2015-06-02 2015-06-02 2015-01-20 |
dc.type.status.fl_str_mv |
info:eu-repo/semantics/publishedVersion |
dc.type.driver.fl_str_mv |
info:eu-repo/semantics/doctoralThesis |
format |
doctoralThesis |
status_str |
publishedVersion |
dc.identifier.uri.fl_str_mv |
Pace, Rafael Domingues Della. Study of magnetic tunnel junctions with insulating barriers piezoelectric of AlN. 2015. 149 f. Tese (Doutorado em Física) - Universidade Federal de Santa Maria, Santa Maria, 2015. http://repositorio.ufsm.br/handle/1/3929 |
identifier_str_mv |
Pace, Rafael Domingues Della. Study of magnetic tunnel junctions with insulating barriers piezoelectric of AlN. 2015. 149 f. Tese (Doutorado em Física) - Universidade Federal de Santa Maria, Santa Maria, 2015. |
url |
http://repositorio.ufsm.br/handle/1/3929 |
dc.language.iso.fl_str_mv |
por |
language |
por |
dc.rights.driver.fl_str_mv |
info:eu-repo/semantics/openAccess |
eu_rights_str_mv |
openAccess |
dc.format.none.fl_str_mv |
application/pdf application/pdf |
dc.publisher.none.fl_str_mv |
Universidade Federal de Santa Maria BR Física UFSM Programa de Pós-Graduação em Física |
publisher.none.fl_str_mv |
Universidade Federal de Santa Maria BR Física UFSM Programa de Pós-Graduação em Física |
dc.source.none.fl_str_mv |
reponame:Manancial - Repositório Digital da UFSM instname:Universidade Federal de Santa Maria (UFSM) instacron:UFSM |
instname_str |
Universidade Federal de Santa Maria (UFSM) |
instacron_str |
UFSM |
institution |
UFSM |
reponame_str |
Manancial - Repositório Digital da UFSM |
collection |
Manancial - Repositório Digital da UFSM |
repository.name.fl_str_mv |
Manancial - Repositório Digital da UFSM - Universidade Federal de Santa Maria (UFSM) |
repository.mail.fl_str_mv |
atendimento.sib@ufsm.br||tedebc@gmail.com |
_version_ |
1805922056086224896 |