Dencho Spassov

All articles published by MDPI are made immediately available worldwide under an open access license. No special permission is required to reuse all or part of the article published by MDPI, including figures and tables. For articles published under an open access Creative Common CC BY license, any part of the article may be reused without permission provided that the original article is clearly cited. For more information, please refer to https://www.mdpi.com/openaccess.

1. Introduction Flash memory is an electronic, non-volatile information storage device that can be electrically erased and reprogrammed. Ideally, the information stored in such a device should be preserved for long when the power is switched off. Flash memories are the primary means to realize low-cost and high-density data storage needed for all major end-user gadgets (smartphones, PCs, USBs, medical devices, electronic games, etc.).