Estudo e fabricação de MOSFETs robustos à radiação para aplicações espaciais de circuitos integrados
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Dissertação
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2011
Autores
Cirne, K. H.
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Gimenez, S. P.
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CIRNE, K. H. Estudo e fabricação de MOSFETs robustos à radiação para aplicações espaciais de circuitos integrados. 2011. 229 f. Dissertação (Mestrado em Engenharia Elétrica) - Centro Universitário da FEI, São Bernardo do Campo, 2011 Disponível em: . Acesso em: 14 jun. 2011.
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Transistor de efeito de campo de metal-óxido semicondutor,Radiação
Resumo
Atualmente circuitos integrados comerciais robustos a radiacao tem alto valor comercial, por causa da alta tecnologia envolvida (processo de manufatura e leiautes especiais), baixo volume de producao, acordos comerciais, etc. Assim, agencias do ramo aeroespacial, principalmente as norte-americanas, tem incentivado empresas e pesquisadores a desenvolverem dispositivos semicondutores e circuitos integrados que utilizam processos de fabricacao CMOS convencionais, para baratear os custos de
fabricacao e que atendam as exigencias de robustez a radiacao, para aplicacao em eletronica embarcada espacial. E importante enfatizar que essas expectativas tambem fazem parte dos objetivos do programa espacial brasileiro, pois atualmente os circuitos integrados imunes a radiacao sao importados, o que gera um custo adicional muito significativo, principalmente na fabricacao de equipamentos especiais, como satelites, avioes, etc. A forma pelo qual o leiaute dos transistores e concebido nos circuitos integrados pode produzir diferentes comportamentos quando submetidos a radiacao. Assim, foi realizado um estudo para verificar os efeitos da radiacao em transistores de
geometria retangular convencional (RGT), de porta em anel circular (CGT), wave MOSFET (formato de "S") e Overlapping Circular-Gate Transistor (O-CGT), concebidos com o processo de fabricacao CMOS convencional (Bulk) de 0,5 Êm da AMI (On Semiconductor), via MOSIS EDUCATIONAL PROGRAM (MEP) e transistores de potencia (transistores planares conectados em paralelo), concebidos com o processo convencional CMOS de fabricacao AMS 0,35 Êm, cedidos pelo Centro a Tecnologia da
Informacao Renato Archer (CTI). Este trabalho visa caracterizar eletricamente tais dispositivos emicondutores, antes e apos o processo de radiacao, nas condicoes de polarizado e nao polarizado para a irradiacao por raios-X e na condicao de polarizado para a irradiacao por feixe de protons. Assim, espera-se identificar qual e a estrutura de leiaute mais adequada para ser utilizada nas aplicacoes aeroespaciais. MOSFETs de Potencia, projetados pelo prof. Dr. Jader Alves de Lima Filho, foram utilizados em dois ensaios. A partir dos resultados, observou-se que os MOSFETs de potencia com geometria retangular convencional, apresentaram variacao de 3 a 4 decadas em sua corrente de fuga em estado desligado (IOFF), um aumento de 3 a 5 decadas na corrente de fuga do substrato no estado
ligado (IBULK) e aumento de 25 % a 50 % em sua inclinacao de sub-limiar (S). Em contrapartida, os O-CGTs, praticamente nao apresentaram variacao na corrente de fuga no estado desligado e de substrato no estado ligado, alem de apresentarem variacao maxima de 10 % em sua inclinacao de sub-limiar. Dessa forma, o O-CGT se mostrou como o dispositivo mais indicado para aplicacoes aeroespaciais. Outros MOSFETs concebidos com o processo de fabricacao CMOS convencional (Bulk) de 0,5 Êm da AMI (On Semiconductor) foram expostos ate 60 Mrad de radiacao por raios-X, enquanto eram polarizados com tensao constante de dreno e porta e ate 3,2 Grad de radiacao por protons, onde foram extraidas curvas IDSxVGS durante e apos da exposicao a radiacao. Durante a irradiacao por raios-X, observou-se que o MOSFET de geometria convencional apresentou aumento de 210 mV na tensao de limiar e variacao de 57,40 % na inclinacao de sub-limiar. Em contrapartida, O-CGT apresentou diminuicao de 90 mV na tensao de limiar e variacao de 5,44 % na inclinacao de sub-limiar. Assim, o O-CGT e a estrutura mais robusta a radiacao, em comparacao ao MOSFET de geometria convencional. O
MOSFET de geometria convencional que foi exposto a radiacao por protons apresentou variacao máxima de 540 mV na tensao de limiar, variacao de ate 6 decadas na corrente de estado desligado e variacao maxima de 219 mV/dec na inclinacao de sub-limiar. Por outro lado, o O-CGT apresentou variacao de 400 mV na tensao de limiar, variacao maxima de 4 decadas na corrente de estado desligado e variacao maxima de 51 mV/dec na inclinacao de sub-limiar. Embora todos os MOSFETs tenham sofrido reducao na mobilidade dos portadores, os de geometria circular mostraram ser mais obustos por nao terem a regiao do bico de passaro.
Nowadays radiation hardened commercial integrated circuits have a high commercial value, because of the high technological value which is applied (manufacturing process, special layout), low production, commercial agreements, etc. The aerospace agencies, mainly the North-American, are encouraging companies and researchers to develop semiconductor devices and integrated circuits, which are manufactured with standard CMOS fabrication processes, in order to cheapen the manufacture costs and meet the radiation hardness requirements, for embedded electronics space applications. Those expectations also have an important role in the objectives for the Brazilian aerospace program, because the hard-rad circuits are imported, which generates a significant additional cost, mainly for special equipment, such as satellites, airplanes, etc. The manner by which the integrated circuits layout is designed can affect its behavior when they are exposed to radiation. A study was performed to attest the radiation effects in Rectangular Gate Transistors (RGT), Circular Gate Transistors (CGT), Wave MOSFETs ("S" shaped) and Overlapping Circular-Gate Transistors (O-CGT), designed with the standard manufacturing CMOS process (Bulk) of 0.5 Êm from AMI (On Semiconductor), via MOSIS EDUCATIONAL PROGRAM (MEP) and power transistors (planar transistor in parallel), designed with the standard CMOS fabrication process of 0.35 Êm from AMS, prototyped in Centro de Tecnologia da formacao Renato Archer (CTI). The objective of this work is to electrically characterize those conductor devices, before and after the irradiation process, for the conditions of biased and unbiased for the X-ray radiation and for the condition of biased devices for the protons beam radiation. After those experiments, it is expected to attest which most appropriate layout for aerospace applications is. Power MOSFETs prototyped by Prof. Dr. Jader Alves de Lima Filho were used in two experiments. In the experimental results, it was observed that the rectangular gate power MOSFETs presented a variation of 3 to 4 orders of magnitude in the off-state current (IOFF), an increase of 3 to 5 orders of magnitude in the bulk's current (IBULK) and an increase of 25 % to 50 % in the subthreshold slope (S). In counterpart, the O-CGTs practically did not present a significant variation in the off-state and bulk's current and presented a maximum variation of 10 % in the subthreshold slope. Based in these results, it is possible to conclude that the O-CGT is more suitable for aerospace applications. The MOSFETs which were manufactured with the standard CMOS fabrication process of 0.5 Êm form AMI (On Semiconductor) were exposed to X-ray radiation doses up to 60 Mrad, while their gate and drain's contacts were biased with constant voltage values and to Proton Beam radiation doses up to 3.2 Grad, while IDSxVGS curves were measured during the radiation exposure. During the X-ray radiation, was observed that the rectangular gate MOSFET presented an increase of 210 mV in its threshold voltage and a variation of 57.4 % in its subthreshold slope. In counterpart, the O-CGT presented a reduction of 90 mV in its threshold voltage and a variation of 5.4 % in its subthreshold slope. Therefore, it can be concluded that the O-CGT is the most radiation hardened structure, compared to the Rectangular Gate MOSFET. The rectangular gate MOSFET that were exposed to the Proton Beam radiation presented a maximum variation of 540 mV in its threshold voltage, 6 orders of magnitude in the off-state current and 219 mV/dec in its subthresold slope. On th
Nowadays radiation hardened commercial integrated circuits have a high commercial value, because of the high technological value which is applied (manufacturing process, special layout), low production, commercial agreements, etc. The aerospace agencies, mainly the North-American, are encouraging companies and researchers to develop semiconductor devices and integrated circuits, which are manufactured with standard CMOS fabrication processes, in order to cheapen the manufacture costs and meet the radiation hardness requirements, for embedded electronics space applications. Those expectations also have an important role in the objectives for the Brazilian aerospace program, because the hard-rad circuits are imported, which generates a significant additional cost, mainly for special equipment, such as satellites, airplanes, etc. The manner by which the integrated circuits layout is designed can affect its behavior when they are exposed to radiation. A study was performed to attest the radiation effects in Rectangular Gate Transistors (RGT), Circular Gate Transistors (CGT), Wave MOSFETs ("S" shaped) and Overlapping Circular-Gate Transistors (O-CGT), designed with the standard manufacturing CMOS process (Bulk) of 0.5 Êm from AMI (On Semiconductor), via MOSIS EDUCATIONAL PROGRAM (MEP) and power transistors (planar transistor in parallel), designed with the standard CMOS fabrication process of 0.35 Êm from AMS, prototyped in Centro de Tecnologia da formacao Renato Archer (CTI). The objective of this work is to electrically characterize those conductor devices, before and after the irradiation process, for the conditions of biased and unbiased for the X-ray radiation and for the condition of biased devices for the protons beam radiation. After those experiments, it is expected to attest which most appropriate layout for aerospace applications is. Power MOSFETs prototyped by Prof. Dr. Jader Alves de Lima Filho were used in two experiments. In the experimental results, it was observed that the rectangular gate power MOSFETs presented a variation of 3 to 4 orders of magnitude in the off-state current (IOFF), an increase of 3 to 5 orders of magnitude in the bulk's current (IBULK) and an increase of 25 % to 50 % in the subthreshold slope (S). In counterpart, the O-CGTs practically did not present a significant variation in the off-state and bulk's current and presented a maximum variation of 10 % in the subthreshold slope. Based in these results, it is possible to conclude that the O-CGT is more suitable for aerospace applications. The MOSFETs which were manufactured with the standard CMOS fabrication process of 0.5 Êm form AMI (On Semiconductor) were exposed to X-ray radiation doses up to 60 Mrad, while their gate and drain's contacts were biased with constant voltage values and to Proton Beam radiation doses up to 3.2 Grad, while IDSxVGS curves were measured during the radiation exposure. During the X-ray radiation, was observed that the rectangular gate MOSFET presented an increase of 210 mV in its threshold voltage and a variation of 57.4 % in its subthreshold slope. In counterpart, the O-CGT presented a reduction of 90 mV in its threshold voltage and a variation of 5.4 % in its subthreshold slope. Therefore, it can be concluded that the O-CGT is the most radiation hardened structure, compared to the Rectangular Gate MOSFET. The rectangular gate MOSFET that were exposed to the Proton Beam radiation presented a maximum variation of 540 mV in its threshold voltage, 6 orders of magnitude in the off-state current and 219 mV/dec in its subthresold slope. On th