Flash memories are, by far, the most important type of non-volatile memory in use today. They are employed widely in mobile, embedded, and mass-storage applications, and the growth in this sector continues at a staggering pace. Moreover, since flash memories do not suffer from the mechanical limitations of magnetic disk drives, solid-state drives have the potential to upstage the magnetic recording industry in the foreseeable future. The research goal of this dissertation is the discovery of new coding theory methods that supports efficient design of flash memories. Flash memory is comprised of blocks of cells, wherein each cell can take on q>̲ 2 levels. While increasing the cell level is easy, reducing its level can be accomplished only by erasing an entire block. Such block erasures are not only time-consuming, but also degrade the memory lifetime. Our main contribution in this research is the design of rewriting codes that maximize the number of times that information can be written prior to incurring a block erasure. Examples of such coding schemes are flash/floating codes and buffer codes, introduced by Jiang and Bruck et al. in 2007, and WOM-codes that were presented by Rivest and Shamir almost three decades ago. The overall goal in these codes is to maximize the amount of information written to a fixed number of cells in a fixed number of writes. Furthermore, the design of error-correcting codes in flash memories is extensively studied. It is shown how to modify WOM-codes to support an error-correction capability. Motivated by the asymmetry of the error behavior of flash memories and the work by Cassuto et al., a coding scheme to correct asymmetric errors is presented. An extensive empirical database of errors was used to develop a comprehensive understanding of the error behavior as well as to design specific error-correcting codes for flash memories. This research on flash memories is expanded to other directions. Wear leveling techniques are widely used in flash memories in order to reduce and balance block erasures. It is shown that coding schemes to be used in these techniques can significantly reduce the number block erasures incurred during data movement. Also, the design of parallel cell programming algorithms is studied for the specific constraints and behavior of flash cells.

Mohammed Rajab proposes different technologies like the error correction coding (ECC), sources coding and offset calibration that aim to improve the reliability of the NAND flash memory with low implementation costs for industrial application. The author examines different ECC schemes based on concatenated codes like generalized concatenated codes (GCC) which are applicable for NAND flash memories by using the hard and soft input decoding. Furthermore, different data compression schemes are examined in order to reduce the write amplification effect and also to improve the error correct capability of the ECC by combining both schemes.

NAND flash memory has become a widely used data storage technology. It uses rectangular arrays, or blocks of floating-gate transistors (commonly referred to as cells) to store information. The flash memory cells gradually wear out with repeated writing and erasing, referred to as program/erase (P/E) cycling, but the damage caused by P/E cycling is dependent on the programmed cell level. For example, in SLC flash memory, each cell has two different states, erased and programmed, represented by 1 and 0, respectively. Storing 1 in a cell causes less damage, or wear, than storing 0. More generally, in multilevel flash memories, the cell wear is an increasing function of the programmed cell level. The main research goal of this dissertation is to design new coding techniques that can extend the lifetime of flahs [flash] memories. The damage caused by programming the cell is usually modeled as a cost, and increasing the lifetime of flash memories can be converted to the problem of encoding information for use on channels with a cost constraint. This type of code is often referred to as a shaping code. Therefore in this dissertation we study rate-constrained shaping codes for noiseless costly channels. We systematically investigate the fundamental performance limits of fixed-to-variable length shaping codes from a rate and distribution perspective for a memoryless channel. Then, we study a recently proposed rate-1 direct shaping code and study its error propagation property. In addition, we consider shaping codes for finite-state noiseless costly channels. One observation from the above analysis is that an optimal shaping code for a memoryless channel generates a codeword sequence that approximates an i.i.d. process, and an optimal shaping code for a finite-state channel generates a codeword sequence that approximates a stationary Markov process. In this dissertation, we study the connection between shaping codes and distribution matching codes that map a sequence of i.i.d. source symbols into an output sequence that approximates an i.i.d. or a stationary Markov process. In the flash memory device, the bit error count (BEC) behavior varies significantly among pages. Therefore we propose a bad page detector, which predicts whether a page will become a "bad" page in the near future based on its current and previous BEC information. Two machine learning algorithms, based upon time-dependent neural network and long-short term memory architectures, are used to design the detector.

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].

Nowadays it is hard to find an electronic device which does not use codes: for example, we listen to music via heavily encoded audio CD's and we watch movies via encoded DVD's. There is at least one area where the use of encoding/decoding is not so developed, yet: Flash non-volatile memories. Flash memory high-density, low power, cost effectiveness, and scalable design make it an ideal choice to fuel the explosion of multimedia products, like USB keys, MP3 players, digital cameras and solid-state disk. In ECC for Non-Volatile Memories the authors expose the basics of coding theory needed to understand the application to memories, as well as the relevant design topics, with reference to both NOR and NAND Flash architectures. A collection of software routines is also included for better understanding. The authors form a research group (now at Qimonda) which is the typical example of a fruitful collaboration between mathematicians and engineers.

Flash memories and memory systems are key resources for the development of electronic products implementing converging technologies or exploiting solid-state memory disks. This book illustrates state-of-the-art technologies and research studies on Flash memories. Topics in modeling, design, programming, and materials for memories are covered along with real application examples.

Digital photography, MP3, digital video, etc. make extensive use of NAND-based Flash cards as storage media. To realize how much NAND Flash memories pervade every aspect of our life, just imagine how our recent habits would change if the NAND memories suddenly disappeared. To take a picture it would be necessary to find a film (as well as a traditional camera...), disks or even magnetic tapes would be used to record a video or to listen a song, and a cellular phone would return to be a simple mean of communication rather than a multimedia console. The development of NAND Flash memories will not be set down on the mere evolution of personal entertainment systems since a new killer application can trigger a further success: the replacement of Hard Disk Drives (HDDs) with Solid State Drives (SSDs). SSD is made up by a microcontroller and several NANDs. As NAND is the technology driver for IC circuits, Flash designers and technologists have to deal with a lot of challenges. Therefore, SSD (system) developers must understand Flash technology in order to exploit its benefits and countermeasure its weaknesses. Inside NAND Flash Memories is a comprehensive guide of the NAND world: from circuits design (analog and digital) to Flash reliability (including radiation effects), from testing issues to high-performance (DDR) interface, from error correction codes to NAND applications like Flash cards and SSDs.