How Does Flash Memory Retain Data
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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].
The Industrial Electronics Handbook - Five Volume Set
Industrial electronics systems govern so many different functions that vary in complexity-from the operation of relatively simple applications, such as electric motors, to that of more complicated machines and systems, including robots and entire fabrication processes. The Industrial Electronics Handbook, Second Edition combines traditional and new
Resistive RAM and Peripheral Circuitry
This book is written as an introductory textbook on Resistive Random Access Memory (ReRAM). ReRAM is a prominent emerging memory among other competing Non-Volatile Memories (NVM) seeking to replace flash memory. This book is based on the author's peer-reviewed research conducted at the Chair of Computer Architecture, FAU, Germany. Referring to his research and the most relevant research from the literature, the author presents the developments in this field concisely. The purpose is to clarify basic concepts and introduce the reader to ReRAM with an emphasis on circuit design. Hence, this book is written for university students considering a career in the semiconductor industry. Since the author's research was conducted in collaboration with a silicon foundry, hardware engineers will find this book practical and industry-relevant. Researchers in the field of In-Memory Computing will also benefit from this book since the NVM array is the basic substrate for such computing paradigms. This three-part book condenses the research and development of the last decade into eight chapters. In Part I, a good foundation is laid for understanding the individual device structure, its electrical characteristics, and modeling methodology. The different array configurations in which these memory devices are fabricated are also discussed. In Part II, the peripheral circuits -the CMOS circuits around the ReRAM array are discussed. They include sense amplifiers, programming circuits, and row/column access circuits. Recent developments such as the possibility to perform certain computing tasks in the ReRAM array are discussed in Part III.