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EEPROM or E2PROM (electrically erasable programmable read-only memory) is a type of
non-volatile memory Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data. Non-volatile memory typ ...
. It is used in computers, usually integrated in
microcontrollers A microcontroller (MC, uC, or μC) or microcontroller unit (MCU) is a small computer on a single integrated circuit. A microcontroller contains one or more CPUs (processor cores) along with memory and programmable input/output peripherals. Pro ...
such as
smart card A smart card (SC), chip card, or integrated circuit card (ICC or IC card), is a card used to control access to a resource. It is typically a plastic credit card-sized card with an Embedded system, embedded integrated circuit (IC) chip. Many smart ...
s and remote keyless systems, or as a separate chip device, to store relatively small amounts of data by allowing individual bytes to be erased and reprogrammed. EEPROMs are organized as arrays of floating-gate transistors. EEPROMs can be programmed and erased in-circuit, by applying special programming signals. Originally, EEPROMs were limited to single-byte operations, which made them slower, but modern EEPROMs allow multi-byte page operations. An EEPROM has a limited life for erasing and reprogramming, reaching a million operations in modern EEPROMs. In an EEPROM that is frequently reprogrammed, the life of the EEPROM is an important design consideration.
Flash memory Flash memory is an Integrated circuit, electronic Non-volatile memory, non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash, are named for t ...
is a type of EEPROM designed for high speed and high density, at the expense of large erase blocks (typically 512 bytes or larger) and limited number of write cycles (often 10,000). There is no clear boundary dividing the two, but the term "EEPROM" is generally used to describe non-volatile memory with small erase blocks (as small as one byte) and a long lifetime (typically 1,000,000 cycles). Many past
microcontrollers A microcontroller (MC, uC, or μC) or microcontroller unit (MCU) is a small computer on a single integrated circuit. A microcontroller contains one or more CPUs (processor cores) along with memory and programmable input/output peripherals. Pro ...
included both (flash memory for the
firmware In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and the development of both computer hardware, h ...
and a small EEPROM for parameters), though the trend with modern microcontrollers is to emulate EEPROM using flash. As of 2020, flash memory costs much less than byte-programmable EEPROM and is the dominant memory type wherever a system requires a significant amount of non-volatile solid-state storage. EEPROMs, however, are still used on applications that only require small amounts of storage, like in
serial presence detect In computing, serial presence detect (SPD) is a standardized way to automatically access information about a memory module. Earlier 72-pin SIMMs included five pins that provided five bits of ''parallel presence detect'' (PPD) data, but the 168- ...
.


History


Early attempts

In the early 1970s, some studies,
inventions An invention is a unique or novel device, method, composition, idea, or process. An invention may be an improvement upon a machine, product, or process for increasing efficiency or lowering cost. It may also be an entirely new concept. If an ...
, and development for electrically re-programmable non-volatile memories were performed by various companies and organizations. In 1971, early research was presented at ''the 3rd Conference on Solid State Devices,
Tokyo Tokyo, officially the Tokyo Metropolis, is the capital of Japan, capital and List of cities in Japan, most populous city in Japan. With a population of over 14 million in the city proper in 2023, it is List of largest cities, one of the most ...
'' in Japan by Yasuo Tarui, Yutaka Hayashi, and Kiyoko Nagai at '' Electrotechnical Laboratory''; a Japanese national research institute. They fabricated an electrically re-programmable non-volatile memory in 1972, and continued this study for more than 10 years. However this early memory depended on capacitors to work, which modern EEPROM lacks. In 1972 IBM patented an electrically re-programmable non-volatile memory invention. Later that year, an avalanche injection type MOS was patented by Fujio Masuoka, the inventor of
flash memory Flash memory is an Integrated circuit, electronic Non-volatile memory, non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash, are named for t ...
, at Toshiba and IBM patented another later that year. In 1974,
NEC is a Japanese multinational information technology and electronics corporation, headquartered at the NEC Supertower in Minato, Tokyo, Japan. It provides IT and network solutions, including cloud computing, artificial intelligence (AI), Inte ...
patented a electrically erasable carrier injection device. The next year, NEC applied for the trademark "EEPROM®" with the Japan Patent Office. The trademark was granted in 1978. The theoretical basis of these devices is
avalanche An avalanche is a rapid flow of snow down a Grade (slope), slope, such as a hill or mountain. Avalanches can be triggered spontaneously, by factors such as increased precipitation or snowpack weakening, or by external means such as humans, othe ...
hot-carrier injection. In general, programmable memories, including EPROM, of early 1970s had reliability and endurance problems such as the data retention periods and the number of erase/write cycles. Most of the major semiconductor manufactures, such as
Toshiba is a Japanese multinational electronics company headquartered in Minato, Tokyo. Its diversified products and services include power, industrial and social infrastructure systems, elevators and escalators, electronic components, semiconductors ...
,
Sanyo is a former Japanese electronics manufacturer founded in 1947 by Toshio Iue, the brother-in-law of Kōnosuke Matsushita, the founder of Matsushita Electric Industrial, now known as Panasonic. Iue left Matsushita Electric to start his own bu ...
(later,
ON Semiconductor ON Semiconductor Corporation (stylized and doing business as onsemi) is an American semiconductor supplier company, based in Scottsdale, Arizona. Products include power and signal management, logic, discrete, and custom devices for automotive, c ...
),
IBM International Business Machines Corporation (using the trademark IBM), nicknamed Big Blue, is an American Multinational corporation, multinational technology company headquartered in Armonk, New York, and present in over 175 countries. It is ...
,
Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California, and Delaware General Corporation Law, incorporated in Delaware. Intel designs, manufactures, and sells computer compo ...
,
NEC is a Japanese multinational information technology and electronics corporation, headquartered at the NEC Supertower in Minato, Tokyo, Japan. It provides IT and network solutions, including cloud computing, artificial intelligence (AI), Inte ...
(later, Renesas Electronics),
Philips Koninklijke Philips N.V. (), simply branded Philips, is a Dutch multinational health technology company that was founded in Eindhoven in 1891. Since 1997, its world headquarters have been situated in Amsterdam, though the Benelux headquarter ...
(later,
NXP Semiconductors NXP Semiconductors N.V. is a Dutch semiconductor manufacturing and design company with headquarters in Eindhoven, Netherlands. It is the third largest European semiconductor company by market capitalization as of 2024. The company employs approx ...
),
Siemens Siemens AG ( ) is a German multinational technology conglomerate. It is focused on industrial automation, building automation, rail transport and health technology. Siemens is the largest engineering company in Europe, and holds the positi ...
(later,
Infineon Technologies Infineon Semiconductor solutions is the largest microcontroller manufacturer in the world, as well as Germany's largest semiconductor manufacturer. It is also the leading automotive semiconductor manufacturer globally. Infineon had roughly 58,0 ...
),
Honeywell Honeywell International Inc. is an American publicly traded, multinational conglomerate corporation headquartered in Charlotte, North Carolina. It primarily operates in four areas of business: aerospace, building automation, industrial automa ...
(later, Atmel),
Texas Instruments Texas Instruments Incorporated (TI) is an American multinational semiconductor company headquartered in Dallas, Texas. It is one of the top 10 semiconductor companies worldwide based on sales volume. The company's focus is on developing analog ...
, studied, invented, and manufactured some electrically re-programmable non-volatile devices until 1977.


Modern EEPROM

The first EEPROM that used Fowler-Nordheim tunnelling to erase data was invented by Bernward and patented by
Siemens Siemens AG ( ) is a German multinational technology conglomerate. It is focused on industrial automation, building automation, rail transport and health technology. Siemens is the largest engineering company in Europe, and holds the positi ...
in 1974. In February 1977, Israeli-American Eliyahou Harari at
Hughes Aircraft Company The Hughes Aircraft Company was a major American aerospace and defense contractor founded on February 14, 1934 by Howard Hughes in Glendale, California, as a division of the Hughes Tool Company. The company produced the Hughes H-4 Hercules air ...
patented in the US a modern EEPROM technology, based on Fowler-Nordheim tunnelling through a thin
silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundan ...
layer between the
floating-gate The floating-gate MOSFET (FGMOS), also known as a floating-gate MOS transistor or floating-gate transistor, is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) where the gate is electrically isolated, creating a floating no ...
and the wafer. Hughes went on to produce this new EEPROM devices. In May 1977, some important research result was disclosed by
Fairchild Fairchild may refer to: Organizations * Fairchild Aerial Surveys, operated in cooperation with a subsidiary of Fairey Aviation Company * Fairchild Camera and Instrument * List of Sherman Fairchild companies, "Fairchild" companies * Fairchild ...
and
Siemens Siemens AG ( ) is a German multinational technology conglomerate. It is focused on industrial automation, building automation, rail transport and health technology. Siemens is the largest engineering company in Europe, and holds the positi ...
. They used ''SONOS'' (
polysilicon Polycrystalline silicon, or multicrystalline silicon, also called polysilicon, poly-Si, or mc-Si, is a high purity, polycrystalline form of silicon, used as a raw material by the solar photovoltaic and electronics industry. Polysilicon is produ ...
- oxynitride-
nitride In chemistry, a nitride is a chemical compound of nitrogen. Nitrides can be inorganic or organic, ionic or covalent. The nitride anion, N3−, is very elusive but compounds of nitride are numerous, although rarely naturally occurring. Some nitr ...
-
oxide An oxide () is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of −2) of oxygen, an O2− ion with oxygen in the oxidation st ...
-
silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...
) structure with thickness of silicon dioxide less than 30 Å, and ''SIMOS'' (stacked-gate injection MOS) structure, respectively, for using ''Fowler-Nordheim tunnelling'' hot-carrier injection. Around 1976 to 1978, Intel's team, including George Perlegos, made some inventions to improve this tunneling E2PROM technology. In 1978, they developed a 16K (2K word × 8) bit ''Intel 2816'' chip with a thin
silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundan ...
layer, which was less than 200 Å. In 1980, this structure was publicly introduced as ''FLOTOX''; floating gate
tunnel A tunnel is an underground or undersea passageway. It is dug through surrounding soil, earth or rock, or laid under water, and is usually completely enclosed except for the two portals common at each end, though there may be access and ve ...
oxide An oxide () is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of −2) of oxygen, an O2− ion with oxygen in the oxidation st ...
. The ''FLOTOX'' structure improved reliability of erase/write cycles per byte up to 10,000 times. But this device required additional 2022V VPP bias voltage supply for byte erase, except for 5V read operations. In 1981, Perlegos and 2 other members left Intel to form
Seeq Technology Seeq may refer to: * Seeq Technology, a semiconductor company founded in 1981 and sold to LSI Corporation in 1999 * SEEQ Card, an electronic smartcard ticketing system used on the Translink (Queensland) network * A race in the fictional universe ...
, which used on-device charge pumps to supply the high voltages necessary for programming E2PROMs. In 1984, Perlogos left Seeq Technology to found Atmel, then Seeq Technology was acquired by Atmel. Electrically alterable read-only memory (EAROM) is a type of EEPROM that can be modified one or a few bits at a time. Writing is a very slow process and again needs higher voltage (usually around 12 V) than is used for read access. EAROMs are intended for applications that require infrequent and only partial rewriting.


Theoretical basis of FLOTOX structure

As is described in former section, old EEPROMs are based on avalanche breakdown-based hot-carrier injection with high reverse breakdown voltage. But ''FLOTOX'' theoretical basis is Fowler–Nordheim tunneling hot-carrier injection through a thin
silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundan ...
layer between the floating gate and the wafer. In other words, it uses a
tunnel junction In electronics, a tunnel junction is a barrier, such as a thin insulating layer or electric potential, between two electrically conducting materials. Electrons (or quasiparticles) pass through the barrier by the process of quantum tunnelling. Clas ...
. Theoretical basis of the physical phenomenon itself is the same as today's
flash memory Flash memory is an Integrated circuit, electronic Non-volatile memory, non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash, are named for t ...
. But each FLOTOX structure is in conjunction with another read-control transistor because the floating gate itself is just programming and erasing one data bit. Intel's FLOTOX device structure improved EEPROM reliability, in other words, the endurance of the write and erase cycles, and the data retention period. A material of study for single-event effect about FLOTOX is available. Today, an academic explanation of the FLOTOX device structure can be found in several sources.


Today's EEPROM structure

Nowadays, EEPROM is used for embedded
microcontrollers A microcontroller (MC, uC, or μC) or microcontroller unit (MCU) is a small computer on a single integrated circuit. A microcontroller contains one or more CPUs (processor cores) along with memory and programmable input/output peripherals. Pro ...
as well as standard EEPROM products. EEPROM still requires a 2-transistor structure per bit to erase a dedicated byte in the memory, while
flash memory Flash memory is an Integrated circuit, electronic Non-volatile memory, non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash, are named for t ...
has 1 transistor per bit to erase a region of the memory.


Security protections

Because EEPROM technology is used for some security gadgets, such as credit cards, SIM cards, key-less entry, etc., some devices have security protection mechanisms, such as copy-protection.


Electrical interface

EEPROM devices use a serial or parallel interface for data input/output.


Serial bus devices

The common serial interfaces are SPI,
I²C I2C (Inter-Integrated Circuit; pronounced as "" or ""), alternatively known as I2C and IIC, is a synchronous, multi-master/multi-slave, single-ended, serial communication bus invented in 1980 by Philips Semiconductors (now NXP Semiconduct ...
, Microwire, UNI/O, and 1-Wire. These use from one to four device pins and allow devices to use packages with eight pins or less. A typical EEPROM serial protocol consists of three phases: OP-code phase, address phase and data phase. The OP-code is usually the first 8 bits input to the serial input pin of the EEPROM device (or with most I²C devices, is implicit); followed by 8 to 24 bits of addressing, depending on the depth of the device, then the read or write data. Each EEPROM device typically has its own set of OP-code instructions mapped to different functions. Common operations on SPI EEPROM devices are: * Write enable (WRENAL) * Write disable (WRDI) * Read status register (RDSR) * Write status register (WRSR) * Read data (READ) * Write data (WRITE) Other operations supported by some EEPROM devices are: * Program * Sector erase * Chip erase commands


Parallel bus devices

Parallel EEPROM devices typically have an 8-bit data bus and an address bus wide enough to cover the complete memory. Most devices have chip select and write protect pins. Some
microcontroller A microcontroller (MC, uC, or μC) or microcontroller unit (MCU) is a small computer on a single integrated circuit. A microcontroller contains one or more CPUs (processor cores) along with memory and programmable input/output peripherals. Pro ...
s also have integrated parallel EEPROM. Operation of a parallel EEPROM is simple and fast when compared to serial EEPROM, but these devices are larger due to the higher pin count (28 pins or more) and have been decreasing in popularity in favor of serial EEPROM or flash.


Other devices

EEPROM memory is used to enable features in other types of products that are not strictly memory products. Products such as real-time clocks, digital potentiometers, digital temperature sensors, among others, may have small amounts of EEPROM to store calibration information or other data that needs to be available in the event of power loss. It was also used on video game cartridges to save game progress and configurations, before the usage of external and internal flash memories.


Failure modes

There are two limitations of stored information: endurance and data retention. During rewrites, the gate oxide in the floating-gate transistors gradually accumulates trapped electrons. The electric field of the trapped electrons adds to the electrons in the floating gate, lowering the window between threshold voltages for zeros vs ones. After sufficient number of rewrite cycles, the difference becomes too small to be recognizable, the cell is stuck in programmed state, and endurance failure occurs. The manufacturers usually specify the maximum number of rewrites being 1 million or more. During storage, the electrons injected into the floating gate may drift through the insulator, especially at increased temperature, and cause charge loss, reverting the cell into erased state. The manufacturers usually guarantee data retention of 10 years or more.System Integration - From Transistor Design to Large Scale Integrated Circuits


Related types

Flash memory Flash memory is an Integrated circuit, electronic Non-volatile memory, non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash, are named for t ...
is a later form of EEPROM. In the industry, there is a convention to reserve the term EEPROM to byte-wise erasable memories compared to block-wise erasable flash memories. EEPROM occupies more die area than flash memory for the same capacity, because each cell usually needs a read, a write, and an erase
transistor A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...
, while flash memory erase circuits are shared by large blocks of cells (often 512×8). Newer non-volatile memory technologies such as FeRAM and MRAM are slowly replacing EEPROMs in some applications, but are expected to remain a small fraction of the EEPROM market for the foreseeable future.


Comparison with EPROM and EEPROM/flash

The difference between
EPROM An EPROM (rarely EROM), or erasable programmable read-only memory, is a type of programmable read-only memory (PROM) integrated circuit, chip that retains its data when its power supply is switched off. Computer memory that can retrieve stored d ...
and EEPROM lies in the way that the memory programs and erases. EEPROM can be programmed and erased electrically using
field electron emission Field electron emission, also known as field-induced electron emission, field emission (FE) and electron field emission, is the emission of electrons from a material placed in an electrostatic field. The most common context is field emission from ...
(more commonly known in the industry as "Fowler–Nordheim tunneling"). EPROMs can't be erased electrically and are programmed by hot-carrier injection onto the floating gate. Erase is by an
ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...
light source, although in practice many EPROMs are encapsulated in plastic that is opaque to UV light, making them "one-time programmable". Most NOR flash memory is a hybrid style—programming is through hot-carrier injection and erase is through Fowler–Nordheim tunneling.


See also

* Avalanche breakdown * DataFlash *
EPROM An EPROM (rarely EROM), or erasable programmable read-only memory, is a type of programmable read-only memory (PROM) integrated circuit, chip that retains its data when its power supply is switched off. Computer memory that can retrieve stored d ...
* *
Flash memory Flash memory is an Integrated circuit, electronic Non-volatile memory, non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash, are named for t ...
* Floating-gate MOSFET * Intel HEX – file format *
Programmer (hardware) In the context of Installation (computer programs), installing firmware onto a device, a programmer, device programmer, chip programmer, Programmable read-only memory#Programming, device burner, or PROM writer is a device that writes, a.k.a ...
*
Quantum tunnelling In physics, quantum tunnelling, barrier penetration, or simply tunnelling is a quantum mechanical phenomenon in which an object such as an electron or atom passes through a potential energy barrier that, according to classical mechanics, shoul ...
* SREC – file format *
Tunnel junction In electronics, a tunnel junction is a barrier, such as a thin insulating layer or electric potential, between two electrically conducting materials. Electrons (or quasiparticles) pass through the barrier by the process of quantum tunnelling. Clas ...
* Read-mostly memory (RMM)


References


External links


Gutmann (2001) papaer: "Data Remanence in Semiconductor Devices" USENIX
{{DEFAULTSORT:Eeprom American inventions Japanese inventions Non-volatile memory Computer memory