Estudo do efeito NBTI em transistores MOS sem junções
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Dissertação
Data
2018
Autores
Graziano Júnior, N.
Orientador
Doria, R. T.
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Citação
GRAZIANO JÚNIOR, N. Estudo do efeito NBTI em transistores MOS sem junções. 2018. 126 f. Dissertação (Mestrado em Engenharia Elétrica) - Centro Universitário FEI, São Bernardo do Campo, 2018 Disponível em: . Acesso em: 17 ago. 2018.
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Transistores,Degradação por efeito NBTI,Tecnologia SOI
Resumo
No presente trabalho, a degradação por efeito NBTI (Negative Bias Temperature Instability) foi analisada em transistores MOS sem junções (JNTs) com canal tipo P. O efeito NBTI incide sobre a confiabilidade dos dispositivos, especialmente para comprimentos de canal nanométricos. Este efeito está associado à degradação do dielétrico de porta dos dispositivos ao longo do tempo devido à presença de armadilhas de interface, sendo responsável por uma
degradação da corrente (ID) e tensão de limiar (VTH) dos dispositivos. Os transistores JNTs são dopados com o mesmo tipo de dopante no canal, fonte e dreno, fato este que redunda em vantagens como o menor efeito de canal curto e beneficia o maior escalamento em relação a outras estruturas1 . Os dispositivos JNTs possuem a maior parte da carga fluindo pelo interior do canal, além de apresentarem menor campo elétrico na região de canal. Portanto, observa-se que tais dispositivos estão menos sujeitos as armadilhas de interface. Assim, ao longo deste trabalho, objetivou-se verificar se estas características fazem com que transistores produzidos nessa tecnologia sejam menos suscetíveis à degradação por efeito NBTI. Para tal, foram simulados dispositivos JNTs com concentração de dopantes de 5x1018 cm-3 e 1x1019 cm-3 e diferentes comprimentos de canal entre 20 nm e 100 nm. Para fins comparativos, usamos transistores FinFET (FD-SOI) como referência, pois já possuem uma grande gama de estudos. Todos os dispositivos foram submetidos a duas tensões de dreno diferentes, -0,05 V e -0,9 V. A princípio, as simulações tiveram por objetivo a obtenção dos valores da tensão de limiar para cada dispositivo estudado. Depois, com os valores das tensões de limiar calculados, foi obtida a degradação da tensão de limiar dos dispositivos devido ao NBTI. A análise descrita acima foi repetida em dispositivos JNTs experimentais e o comportamento destes foi comparado com os
simulados. Pôde-se concluir que a degradação por efeito NBTI em transistores JNT é inferior à obtida em transistores modo inversão de dimensões similares. Em dispositivo JNTs com concentração de dopantes de 1x1019 cm-3
a variação média da tensão de limiar foi de 0,04 V, enquanto que FinFETs apresentaram uma degradação da ordem de 0,06 V. Observou-se, outrossim, que a degradação por efeito NBTI em dispositivos JNTs é inversamente proporcional ao comprimento de canal, à concentração de dopantes e à tensão de dreno.
In this work, the Negative Bias Temperature Instability (NBTI) degradation was evaluated for p-type channel MOS junctionless nanowire transistors (JNTs). The NBTI effect focuses on the reliability of the devices, especially for nanometric channel lengths. This effect is associated to the degradation of the gate dielectric of the devices along the time due to the presence of interface traps and is responsible for the degradation of the drain current and threshold voltage of the transistors. The JNTs are doped with the same type of dopant, for the channel, source and drain, which results in advantages such as the smaller short-channel effect, allowing for a greater miniaturization in relation to other structures1 . JNTs present most of the charge, flowing through the interior of the channel instead of the interfaces, besides presenting a lower electric field in the channel region. Therefore, it is less susceptible to interface traps. So that, this work aimed to verify if these features make transistors produced in this technology less susceptible to NBTI degradation. For that, JNTs with channel doping concetrations of 5x1018 cm-3 , 1x1019 cm-3 with differnet channel lengths from 20 nm up to 100 nm were simulated. For comparative purposes, we have used FinFET transistors as reference, since these devices already have a wide range of studies available in literature. All the devices were subjected to two different drain voltages, -0.05 V and -0.9 V. Initially, the simulations had the objective of obtaining the threshold voltage values for each device. Then, with the values of the threshold voltages calculated, the degradation of the threshold voltage due to the NBTI was extracted. The same analysis was repeated for experimental devices and their behavior were compared to the simulated one. It was possible to conclude that the degradation by NBTI effect in JNT transistors is inferior to that obtained in inversion mode transistors of similar dimensions. In JNTs with channel doping concentration of 1x1019 cm-3 the mean degradation due to the NBTI was in the order of 0.04 V whereas FinFETs presented a mean threshold voltage variation of about 0.06 V. It was also observed that the degradation by NBTI effect in JNTs devices is inversely proportional to the channel length and directly proportional to the channel doping concentration and the drain voltage.
In this work, the Negative Bias Temperature Instability (NBTI) degradation was evaluated for p-type channel MOS junctionless nanowire transistors (JNTs). The NBTI effect focuses on the reliability of the devices, especially for nanometric channel lengths. This effect is associated to the degradation of the gate dielectric of the devices along the time due to the presence of interface traps and is responsible for the degradation of the drain current and threshold voltage of the transistors. The JNTs are doped with the same type of dopant, for the channel, source and drain, which results in advantages such as the smaller short-channel effect, allowing for a greater miniaturization in relation to other structures1 . JNTs present most of the charge, flowing through the interior of the channel instead of the interfaces, besides presenting a lower electric field in the channel region. Therefore, it is less susceptible to interface traps. So that, this work aimed to verify if these features make transistors produced in this technology less susceptible to NBTI degradation. For that, JNTs with channel doping concetrations of 5x1018 cm-3 , 1x1019 cm-3 with differnet channel lengths from 20 nm up to 100 nm were simulated. For comparative purposes, we have used FinFET transistors as reference, since these devices already have a wide range of studies available in literature. All the devices were subjected to two different drain voltages, -0.05 V and -0.9 V. Initially, the simulations had the objective of obtaining the threshold voltage values for each device. Then, with the values of the threshold voltages calculated, the degradation of the threshold voltage due to the NBTI was extracted. The same analysis was repeated for experimental devices and their behavior were compared to the simulated one. It was possible to conclude that the degradation by NBTI effect in JNT transistors is inferior to that obtained in inversion mode transistors of similar dimensions. In JNTs with channel doping concentration of 1x1019 cm-3 the mean degradation due to the NBTI was in the order of 0.04 V whereas FinFETs presented a mean threshold voltage variation of about 0.06 V. It was also observed that the degradation by NBTI effect in JNTs devices is inversely proportional to the channel length and directly proportional to the channel doping concentration and the drain voltage.