Estudo do comportamento de transistores FinFETs com subposição de porta aplicados como sensores
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2020-10-09
Autores
Fonseca, William da Silva
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Universidade Estadual Paulista (Unesp)
Resumo
Com a miniaturização dos transistores e com a crescente necessidade de se obter dispositivos mais eficientes, as tecnologias fabricadas em lâminas de silício sobre isolante (SOI) vem se destacando devido aos inúmeros benefícios relacionados ao menor consumo de energia, maiores velocidades de processamento e menores efeitos de canal curto (SCE). Para nós tecnológicos abaixo de 32 nm, mesmo a tecnologia planar SOI começa a sofrer com os efeitos de canal curto e uma das soluções encontradas foi o uso dos transistores de múltiplas portas. Além disso, conhecendo a grande vantagem do transistor SOI FinFET em ambientes sujeitos à radiação de prótons, neste trabalho realizou-se o estudo comparativo entre o transistor SOI FinFET autoalinhado e o transistor SOI FinFET com subposição de porta (underlapped SOI FinFET) afim de se obter resultados que possam qualificar o dispositivo quando aplicado ao sensoriamento de cargas. Inicialmente foi avaliado o impacto da radiação nos parâmetros elétricos do transistor underlapped SOI FinFET através do estudo comparativo entre este transistor e o transistor SOI FinFET autoalinhado. Posteriormente a mesma análise foi realizada considerando ambos os transistores aplicados no sensoriamento da radiação de prótons. Ao longo deste estudo foi avaliado o impacto da variação do comprimento da região de underlap, do tipo de material e da espessura do óxido espaçador nas características elétricas dos transistores FinFETs. A ausência do eletrodo de porta sobre parte do canal causou o aumento da resistência série que, por sua vez, resultou em uma degradação da corrente do estado ligado do dispositivo. Melhores resultados nas características elétricas do dispositivo, como o aumento da corrente de dreno e da transcondutância dos transistores com subposição de porta foram observadas quando utilizados materiais de altas constantes dielétricas (k) e maiores espessuras desta região devido a melhor distribuição do campo elétrico na região de óxido espaçador, o que propicia a redução da resistência série e o retorno da melhoria da performance. Focando no sensoriamento da radiação, observou-se grandes sensitividades considerando duas formas distintas de sensoriamento: i) ao se incrementar o comprimento do underlap e aumentar a permissividade do material desta região para sensores baseados nas comparações entre transistores que apresentam e não apresentam oxido espaçador nesta região. ii) reduzindo-se a permissividade e espessura do óxido espaçador na região de underlap quando utilizamos um único transistor, comparando suas características antes e depois do acumulo de cargas causado pela radiação. Neste segundo caso, atingiu-se uma sensitividade de até 190% quando utilizamos dispositivos com óxido espaçador de SiO2 com baixa espessuras (ex: 2 nm). O alto grau de sensitividade obtido pelo transistor underlapped FinFET se manteve mesmo variando-se a temperatura entre -40ºC e 150ºC (faixa de uso militar), demonstrando que o dispositivo possui características suficientemente fortes para ser utilizado em diversas aplicações de sensoriamento que envolvam o sensoriamento de cargas.
With the miniaturization of the transistors and the growing need to obtain more efficient devices, the technologies manufactured in silicon on insulator wafers (SOI) have stood out due to the countless benefits related to lower energy consumption, higher processing speeds and lesser short channel effects (SCE). For technological nodes below 32 nm, even the planar SOI technology begins to suffer from the short channel effects and one of the solutions found was the use of multiple gates transistors. Furthermore, knowing the great advantage of the SOI FinFET transistor in environments subject to proton radiation, in this work a comparative study was carried out between the self-aligned SOI FinFET transistor and the underlapped SOI FinFET in order to obtain results that can qualify the device when applied to charge sensing. Initially, the impact of radiation on the electrical parameters of the underlapped SOI FinFET transistor was evaluated through a comparative study between this transistor and the self-aligned SOI FinFET transistor. Subsequently, the same analysis was performed considering both transistors applied in the proton radiation sensing. Throughout this study, the impact of varying the underlap region length, the type of material and the thickness of the spacer oxide on the electrical characteristics of the FinFET transistors was evaluated. The absence of the gate electrode over part of the channel caused an increase in the series resistance, which, in turn, resulted in an ON state current degradation of the device. Better results in the electrical device characteristics, such as the drain current increasing and the transconductance of the transistors with gate underlap were observed when using materials with high dielectric constants (k) and greater thicknesses in this region due to the better electric field distribution in the spacer oxide region, which provides a reduction in series resistance and a return to improved performance. Focusing on radiation sensing, great sensitivities were observed considering two different forms of sensing: i) by increasing the underlap length and increasing the material permittivity in this region for sensors based on the comparisons between transistors that present and do not present spacer oxide in this region. ii) reducing the spacer oxide permissiveness and thickness in the underlap region when using a single transistor, comparing its characteristics before and after the charges accumulation caused by radiation. In this second case, a sensitivity up to 190% was achieved when using devices with SiO2 spacer oxide with low thicknesses (e.g. 2 nm). The high degree of sensitivity obtained by the underlapped FinFET transistor was kept even when the temperature varied between -40ºC and 150ºC (military use range), demonstrating that the device has sufficiently strong characteristics to be used in several sensing applications that involve charges sensing.
With the miniaturization of the transistors and the growing need to obtain more efficient devices, the technologies manufactured in silicon on insulator wafers (SOI) have stood out due to the countless benefits related to lower energy consumption, higher processing speeds and lesser short channel effects (SCE). For technological nodes below 32 nm, even the planar SOI technology begins to suffer from the short channel effects and one of the solutions found was the use of multiple gates transistors. Furthermore, knowing the great advantage of the SOI FinFET transistor in environments subject to proton radiation, in this work a comparative study was carried out between the self-aligned SOI FinFET transistor and the underlapped SOI FinFET in order to obtain results that can qualify the device when applied to charge sensing. Initially, the impact of radiation on the electrical parameters of the underlapped SOI FinFET transistor was evaluated through a comparative study between this transistor and the self-aligned SOI FinFET transistor. Subsequently, the same analysis was performed considering both transistors applied in the proton radiation sensing. Throughout this study, the impact of varying the underlap region length, the type of material and the thickness of the spacer oxide on the electrical characteristics of the FinFET transistors was evaluated. The absence of the gate electrode over part of the channel caused an increase in the series resistance, which, in turn, resulted in an ON state current degradation of the device. Better results in the electrical device characteristics, such as the drain current increasing and the transconductance of the transistors with gate underlap were observed when using materials with high dielectric constants (k) and greater thicknesses in this region due to the better electric field distribution in the spacer oxide region, which provides a reduction in series resistance and a return to improved performance. Focusing on radiation sensing, great sensitivities were observed considering two different forms of sensing: i) by increasing the underlap length and increasing the material permittivity in this region for sensors based on the comparisons between transistors that present and do not present spacer oxide in this region. ii) reducing the spacer oxide permissiveness and thickness in the underlap region when using a single transistor, comparing its characteristics before and after the charges accumulation caused by radiation. In this second case, a sensitivity up to 190% was achieved when using devices with SiO2 spacer oxide with low thicknesses (e.g. 2 nm). The high degree of sensitivity obtained by the underlapped FinFET transistor was kept even when the temperature varied between -40ºC and 150ºC (military use range), demonstrating that the device has sufficiently strong characteristics to be used in several sensing applications that involve charges sensing.
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Palavras-chave
Radiação ionizante, Radiação Dosimetria, Semicondutores dopados, Tecnologia de silício sobre isolante, Transistores