Editing Non-volatile memory (section)

== Electrically addressed ==
{{Main|Non-volatile random-access memory}}

Electrically addressed semiconductor non-volatile memories can be categorized according to their write mechanism. 

=== Read-only and read-mostly devices ===
[[Mask ROM]]s are factory programmable only and typically used for large-volume products which are not required to be updated after the memory device is manufactured. 

[[Programmable read-only memory]] (PROM) can be altered once after the memory device is manufactured using a [[PROM programmer]]. Programming is often done before the device is installed in its target system, typically an [[embedded system]]. The programming is permanent, and further changes require the replacement of the device. Data is stored by physically altering (burning) storage sites in the device.

An [[EPROM]] is an erasable ROM that can be changed more than once. However, writing new data to an EPROM requires a special programmer circuit. EPROMs have a quartz window that allows them to be erased with ultraviolet light, but the whole device is cleared at one time. A [[one-time programmable]] (OTP) device may be implemented using an EPROM chip without the quartz window; this is less costly to manufacture. An electrically erasable programmable read-only memory [[EEPROM]] uses voltage to erase memory. These erasable memory devices require a significant amount of time to erase data and write new data; they are not usually configured to be programmed by the processor of the target system. Data is stored using [[floating-gate transistor]]s, which require special operating voltages to trap or release electric charge on an insulated control gate to store information.

=== Flash memory ===
{{Main|Flash memory}}

[[Flash memory]] is a solid-state chip that maintains stored data without any external power source. It is a close relative to the EEPROM; it differs in that erase operations must be done on a block basis, and its capacity is substantially larger than that of an EEPROM. Flash memory devices use two different technologies—NOR and NAND—to map data. NOR flash provides high-speed random access, reading and writing data in specific memory locations; it can retrieve as little as a single byte. NAND flash reads and writes sequentially at high speed, handling data in blocks. However, it is slower on reading when compared to NOR. NAND flash reads faster than it writes, quickly transferring whole pages of data. Less expensive than NOR flash at high densities, NAND technology offers higher capacity for the same-size silicon.<ref name="Flash1">{{cite magazine |author=Russell Kay |magazine=ComputerWorld |url=http://www.computerworld.com/s/article/349425/Flash_Memory |title=Flash memory |archive-url=https://web.archive.org/web/20100610065251/http://www.computerworld.com/s/article/349425/Flash_Memory |archive-date=10 June 2010 |date=7 June 2010}}</ref>

=== Ferroelectric RAM (F-RAM) ===
{{Main|Ferroelectric RAM}}

'''Ferroelectric RAM''' ('''FeRAM''', '''F-RAM''' or '''FRAM''') is a form of [[random-access memory]] similar in construction to [[DRAM]], both use a capacitor and transistor but instead of using a simple [[dielectric]] layer the capacitor, an F-RAM cell contains a thin ferroelectric film of lead zirconate titanate {{chem2|[Pb(Zr,Ti)O3]}}, commonly referred to as PZT. The Zr/Ti atoms in the PZT change polarity in an electric field, thereby producing a binary switch. Due to the PZT crystal maintaining polarity, F-RAM retains its data memory when power is shut off or interrupted.

Due to this crystal structure and how it is influenced, F-RAM offers distinct properties from other nonvolatile memory options, including extremely high, although not infinite, endurance (exceeding 10<sup>16</sup> read/write cycles for 3.3&nbsp;V devices), ultra-low power consumption (since F-RAM does not require a charge pump like other non-volatile memories), single-cycle write speeds, and gamma radiation tolerance.<ref>{{citation |url=http://www.ramtron.com/about-us/what-is-f-ram.aspx |title=F-RAM Memory Technology |publisher=Ramtron.com |access-date=30 January 2012 |url-status=live |archive-url=https://web.archive.org/web/20120127063617/http://ramtron.com/about-us/what-is-f-ram.aspx |archive-date=27 January 2012}}</ref>

=== Magnetoresistive RAM (MRAM) ===
{{Main|Magnetoresistive random-access memory}}

Magnetoresistive RAM stores data in magnetic storage elements called [[magnetic tunnel junctions]] (MTJs). The first generation of MRAM, such as [[Everspin Technologies]]' 4&nbsp;Mbit, utilized field-induced writing. The second generation is developed mainly through two approaches: [[Thermal-assisted switching]] (TAS)<ref name="white paper">The Emergence of Practical MRAM {{cite web |url=http://www.crocus-technology.com/pdf/BH%20GSA%20Article.pdf |title=Crocus Technology &#124; Magnetic Sensors &#124; TMR Sensors |access-date=2009-07-20 |url-status=dead |archive-url=https://web.archive.org/web/20110427022729/http://www.crocus-technology.com/pdf/BH%20GSA%20Article.pdf |archive-date=27 April 2011}}</ref> which is being developed by [[Crocus Technology]], and [[Spin-transfer torque]] (STT) which [[Crocus Technology|Crocus]], [[Hynix]], [[IBM]], and several other companies are developing.<ref>{{cite web|url=http://www.eetimes.com/news/latest/showArticle.jhtml?articleID=218000269|archive-url=https://web.archive.org/web/20120119111746/http://www.eetimes.com/news/latest/showArticle.jhtml?articleID=218000269|archive-date=19 January 2012|url-status=dead|title=Latest News|website=EE{{!}}Times}}</ref>

=== Phase-change Memory (PCM) ===
{{Main|Phase-change memory}}

Phase-change memory stores data in [[chalcogenide glass]], which can reversibly change the phase between the amorphous and the [[Crystalline|crystalline state]], accomplished by heating and cooling the glass.  The [[crystalline]] state has low resistance, and the amorphous phase has high resistance, which allows currents to be switched ON and OFF to represent digital 1 and 0 states.<ref>{{Cite journal|last1=Hudgens|first1=S.|last2=Johnson|first2=B.|date=November 2004|title=Overview of Phase-Change Chalcogenide Nonvolatile Memory Technology|url=https://www.cambridge.org/core/journals/mrs-bulletin/article/abs/overview-of-phasechange-chalcogenide-nonvolatile-memory-technology/91060FF69176FEC7222376C1E3FA1FC3|journal=MRS Bulletin|language=en|volume=29|issue=11|pages=829–832|doi=10.1557/mrs2004.236|s2cid=137902404 |issn=1938-1425|url-access=subscription}}</ref><ref>{{Cite book|last1=Pirovano|first1=A.|last2=Lacaita|first2=A.L.|last3=Benvenuti|first3=A.|last4=Pellizzer|first4=F.|last5=Hudgens|first5=S.|last6=Bez|first6=R.|title=IEEE International Electron Devices Meeting 2003 |chapter=Scaling analysis of phase-change memory technology |date=December 2003|chapter-url=https://ieeexplore.ieee.org/document/1269376|pages=29.6.1–29.6.4|doi=10.1109/IEDM.2003.1269376|isbn=0-7803-7872-5 |s2cid=1130884 }}</ref>

===FeFET memory===
[[FeFET memory]] uses a transistor with [[ferroelectric]] material to permanently retain state.

===RRAM memory===
{{Main|Resistive random-access memory}}

RRAM (ReRAM) works by changing the resistance across a dielectric solid-state material often referred to as a memristor. ReRAM involves generating defects in a thin oxide layer, known as oxygen vacancies (oxide bond locations where the oxygen has been removed), which can subsequently charge and drift under an electric field. The motion of oxygen ions and vacancies in the oxide would be analogous to the motion of electrons and holes in a semiconductor.

Although ReRAM was initially seen as a replacement technology for flash memory, the cost and performance benefits of ReRAM have not been enough for companies to proceed with the replacement. Apparently, a broad range of materials can be used for ReRAM. However, the discovery <ref>Lee, H. Y.; Chen, P. S.; Wu, T. Y.; Chen, Y. S.; Wang, C. C.; Tzeng, P. J.; Lin, C. H.; Chen, F.; Lien, C. H.; Tsai, M. J. (2008). Low power and high speed bipolar switching with a thin reactive Ti buffer layer in robust Hf{{not a typo}}O2-based RRAM. 2008 IE</ref> that the popular high-κ gate dielectric HfO<sub>2</sub> can be used as a low-voltage ReRAM has encouraged researchers to investigate more possibilities.