DEGREE PROJECT, IN NANOTECHNOLOGY , SECOND LEVEL STOCKHOLM, SWEDEN 2014 High Temperature Memories in SiC Technology MATTIAS EKSTRÖM KTH ROYAL INSTITUTE OF TECHNOLOGY SCHOOL OF INFORMATION AND COMMUNICATION TECHNOLOGY IT261X 2014 High Temperature Memories in SiC Technology Mattias Ekström 900502-4972 [email protected] Nanotechnology High Temperature Memories in SiC Technology Page 1 of 179 IT261X 2014 High Temperature Memories in SiC Technology Mattias Ekström 900502-4972 [email protected] Nanotechnology Abstract This thesis is part of the Working On Venus (WOV) project. The aim of the project is to design electronics in silicon carbide (SiC) that can withstand the extreme surface environment of Venus. This thesis investigates some possible computer memory technologies that could survive on the surface of Venus. A memory must be able to function at 460 °C and after a total radiation dose of at least 200 Gy (SiC). This thesis is a literature survey. The thesis covers several Random-Access Memory (RAM) technologies: Static RAM (SRAM), Dynamic RAM (DRAM), Ferroelectric RAM (FeRAM), Magnetic RAM (MRAM), Resistive RAM (RRAM) and Phase Change Memory (PCM). The Electrical Erasable Programmable Read-Only Memory, Flash memory and SONOS are also covered. Focus lies on device- and material-physics of the memory cells, and their extreme environment behaviour. This thesis concludes with a discussion on technology options. The technologies are compared for their suitability for extreme environment. The thesis gives a recommendation for which memory technologies should be investigated. The final recommendation is to investigate SRAM, SONOS, FeRAM and RRAM technologies for high temperature applications. Sammanfattning Denna uppsats är en del av projektet Working On Venus (WOV). Projektets mål är att designa elektronik i kiselkarbid (SiC) som tål Venus extrema ytmiljö. Denna uppsats undersöker några möjliga datorminnestekniker som kan överleva på Venus yta. Ett minne måste kunna fungera vid 460 °C och efter en total strålningsdos på minst 200 Gy (SiC). Denna uppsats är en litteraturstudie. Uppsatsen täcker flera olika typer av RAM-minnes teknologier (eng. Random-Access Memory): Statiskt RAM-minne (SRAM), Dynamiskt RAM-minne (DRAM), Ferroelektriskt RAM-minne (FeRAM), Magnetiskt RAM-minne (MRAM), Resistivt RAM-minne (RRAM) och fasändringsminnen (PCM). EEPROM (eng. Electrical Erasable Programmable Read-Only Memory), Flash-minnen och SONOS täcks också. Fokus ligger på minnescellernas komponent- och materialfysik, samt deras extremmiljösbeteende. Denna uppsats avslutas med en diskussion om teknikmöjligheter. Teknikerna jämförs för hur passande de är för extrema miljöer. Uppsatsen ger en rekommendation för vilka minnestekniker som bör undersökas. Den slutliga rekommendationen är att undersöka SRAM, SONOS, FeRAM och RRAM teknologier för högtemperatursanvändning. Page 2 of 179 IT261X 2014 High Temperature Memories in SiC Technology Mattias Ekström 900502-4972 [email protected] Nanotechnology Table of Contents Units............................................................................................................................................5 Chapter 1 – Introduction.............................................................................................................7 1.1 – Venus and extreme environment electronics.................................................................7 1.2 – Properties of silicon carbide........................................................................................11 1.3 – Extreme environment memory technology.................................................................15 Chapter 2 – Memory technology theory...................................................................................17 2.1 – Thermodynamics of memory technologies.................................................................17 2.2 – Current and charge leakage mechanisms....................................................................21 2.3 – Physics of ferroelectrics..............................................................................................27 2.4 – Physics of magnetics and spintronics..........................................................................34 2.5 – Physics of resistive switching......................................................................................44 2.6 – Physics of chalcogenide glassy semiconductors.........................................................48 Chapter 3 – High temperature memories in SiC technology....................................................52 3.1 – Memory hierarchy.......................................................................................................52 3.2 – Static RAM (SRAM)...................................................................................................55 3.2.1 – SRAM cell and basic operations..........................................................................55 3.2.2 – SRAM high temperature behaviour.....................................................................57 3.2.2 – SRAM radiation effects.......................................................................................59 3.2.3 – SRAM summary..................................................................................................62 3.3 – Dynamic RAM (DRAM).............................................................................................63 3.3.1 – DRAM cell and basic operations.........................................................................63 3.3.2 – DRAM high temperature behaviour....................................................................65 3.3.4 – DRAM summary.................................................................................................66 3.4 – Electrical Erasable Programmable ROM (EEPROM) and Flash................................66 3.4.1 – EEPROM and Flash cell and basic operations....................................................66 3.4.2 – EEPROM and Flash high temperature behaviour...............................................72 3.4.3 – EEPROM and Flash radiation effects..................................................................76 3.4.4 – EEPROM and Flash summary.............................................................................78 3.5 – Ferroelectric RAM (FeRAM)......................................................................................81 3.5.1 – FeRAM devices and basic operations..................................................................81 3.5.2 – FeRAM high temperature behaviour...................................................................91 3.5.3 – FeRAM radiation effects.....................................................................................98 3.5.4 – FeRAM summary................................................................................................99 3.6 – Magnetic RAM (MRAM).........................................................................................101 3.6.1 – MRAM devices and basic operations................................................................101 3.6.2 – MRAM high temperature behaviour.................................................................107 3.6.3 – MRAM radiation effects....................................................................................110 3.6.4 – MRAM summary...............................................................................................111 3.7 – Resistive RAM (RRAM)...........................................................................................112 3.7.1 – RRAM devices and basic operations.................................................................112 3.7.2 – RRAM high temperature behaviour..................................................................114 Page 3 of 179 IT261X 2014 High Temperature Memories in SiC Technology Mattias Ekström 900502-4972 [email protected] Nanotechnology 3.7.3 – RRAM radiation effects.....................................................................................122 3.7.5 – RRAM summary................................................................................................123 3.8 – Phase Change Memory (PCM)..................................................................................125 3.8.1 – PCM devices and basic operations....................................................................125 3.8.2 – PCM high temperature behaviour......................................................................126 3.8.4 – PCM summary...................................................................................................127 Chapter 4 – Sustainability and environment impact...............................................................128 4.1 – Introduction to the issues of sustainability................................................................128 4.2 – Primary source: Mining.............................................................................................129 4.3 – Secondary source: Recycling....................................................................................131 4.4 – Sustainability and environment impact summary.....................................................133 Chapter 5 – Discussion...........................................................................................................134 Chapter 6 – Summary and future work...................................................................................140 6.1 – Summary...................................................................................................................140