Flash Memories

A Flash memory is a Non Volatile Memory (NVM) whose "unit cells" are fabricated in CMOS technology and programmed and erased electrically. In 1971, Frohman-Bentchkowsky developed a folating polysilicon gate tran­ sistor [1, 2], in which hot electrons were injected in the floating gate and removed by either Ultra-Violet (UV) internal photoemission or by Fowler­ Nordheim tunneling. This is the "unit cell" of EPROM (Electrically Pro­ grammable Read Only Memory), which, consisting of a single transistor, can be very densely integrated. EPROM memories are electrically programmed and erased by UV exposure for 20-30 mins. In the late 1970s, there have been many efforts to develop an electrically erasable EPROM, which resulted in EEPROMs (Electrically Erasable Programmable ROMs). EEPROMs use hot electron tunneling for program and Fowler-Nordheim tunneling for erase. The EEPROM cell consists of two transistors and a tunnel oxide, thus it is two or three times the size of an EPROM. Successively, the combination of hot carrier programming and tunnel erase was rediscovered to achieve a single transistor EEPROM, called Flash EEPROM. The first cell based on this concept has been presented in 1979 [3]; the first commercial product, a 256K memory chip, has been presented by Toshiba in 1984 [4]. The market did not take off until this technology was proven to be reliable and manufacturable [5].

Most of the current applications of electronics require non-volatile memories, which can keep stored information when the power supply is switched off. Flash memories (in which a single cell can be electrically programmed and a large number of cells are usually electrically erased at the same time) are the most versatile non-volatile memories. They are widely used to store the basic input-output system (BIOS) of personal computers, the software and personal data of cellular phones, identification codes in smart cards and many other applications. Flash memories allow software updates, change of passwords and codes, and reconfiguration of the system in the field. They can be designed and optimized to create large-size memories which can successfully substitute hard disks for specific applications, having lower power consumption and weight, shorter access times, and far better robustness. This book is devoted entirely to flash memories and has been designed to provide comprehensive information on basic memory cell structures, device physics and technology, simulation circuit architecture, system issues, testing and reliability. It also provides data on advanced subjects related to multi-level storage cells, embedded memories and system applications of flash memories.

Front Matter....Pages i-xi Flash Memories: An Overview....Pages 1-35 The Industry Standard Flash Memory Cell....Pages 37-90 Binary and Multilevel Flash Cells....Pages 91-152 Physical Aspects of Cell Operation and Reliability....Pages 153-239 Memory Architecture and Related Issues....Pages 241-360 Multilevel Flash Memories....Pages 361-397 Flash Memory Reliability....Pages 399-441 Flash Memory Testing....Pages 443-479 Flash Memories: Market, Marketing and Economic Challenges....Pages 481-526 Back Matter....Pages 527-540 "This book is devoted entirely to flash memories and has been designed to provide comprehensive information on basic memory cell structures, device physics and technology, simulation circuit architecture, system issues, testing and reliability. It also provides data on advanced subjects related on multi-level storage cells, embedded memories and system applications of flash memories."--BOOK JACKET