EEPROM (also called E
2PROM) stands for electrically erasable programmable read-only memory and is a type of
non-volatile memory used in computers, usually integrated in
microcontrollers such as
smart cards 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, now 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 electronic 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 the NOR and NAND logic gates. Both use ...
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 included both (flash memory for the
firmware 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.
History
In the early 1970s, some studies,
inventions, and development for electrically re-programmable
non-volatile memories were performed by various companies and organizations.
In 1971, the earliest research report was presented at ''the 3rd Conference on
Solid State Devices,
Tokyo
Tokyo (; ja, 東京, , ), officially the Tokyo Metropolis ( ja, 東京都, label=none, ), is the capital and largest city of Japan. Formerly known as Edo, its metropolitan area () is the most populous in the world, with an estimated 37.46 ...
'' in Japan by Yasuo Tarui, Yutaka Hayashi, and Kiyoko Nagai at ''
Electrotechnical Laboratory''; a Japanese national research institute.
They
fabricated an EEPROM device in 1972, and continued this study for more than 10 years.
These papers have been repeatedly cited by later papers and patents.
[
]
One of their research studies includes ''MONOS'' (
metal
A metal (from ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, e ...
-
oxide-
nitride-oxide-
semiconductor
A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way ...
) technology,
which used
Renesas Electronics
is a Japanese semiconductor manufacturer headquartered in Tokyo, Japan, initially incorporated in 2002 as Renesas Technology, the consolidated entity of the semiconductor units of Hitachi and Mitsubishi excluding their dynamic random-access ...
'
flash memory
Flash memory is an electronic 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 the NOR and NAND logic gates. Both use ...
integrated in single-chip
microcontrollers.
[
]
In 1972, a type of electrically re-programmable non-volatile memory was invented by
Fujio Masuoka
is a Japanese engineer, who has worked for Toshiba and Tohoku University, and is currently chief technical officer (CTO) of Unisantis Electronics. He is best known as the inventor of flash memory, including the development of both the NOR fla ...
at Toshiba, who is also known as the inventor of ''
flash memory
Flash memory is an electronic 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 the NOR and NAND logic gates. Both use ...
''.
[
]
Most of the major semiconductor manufactures, such as
Toshiba,
Sanyo (later,
ON Semiconductor),
IBM,
Intel
Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the developers of the x86 ser ...
,
NEC
is a Japanese multinational information technology and electronics corporation, headquartered in Minato, Tokyo. The company was known as the Nippon Electric Company, Limited, before rebranding in 1983 as NEC. It provides IT and network soluti ...
(later,
Renesas Electronics
is a Japanese semiconductor manufacturer headquartered in Tokyo, Japan, initially incorporated in 2002 as Renesas Technology, the consolidated entity of the semiconductor units of Hitachi and Mitsubishi excluding their dynamic random-access ...
),
[
]
Philips
Koninklijke Philips N.V. (), commonly shortened to Philips, is a Dutch multinational conglomerate corporation that was founded in Eindhoven in 1891. Since 1997, it has been mostly headquartered in Amsterdam, though the Benelux headquarters is ...
(later,
NXP Semiconductors),
Siemens (later,
Infineon Technologies
Infineon Technologies AG is a German semiconductor manufacturer founded in 1999, when the semiconductor operations of the former parent company Siemens AG were spun off. Infineon has about 50,280 employees and is one of the ten largest semico ...
),
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 technologies, performance ma ...
(later,
Atmel),
Texas Instruments
Texas Instruments Incorporated (TI) is an American technology company headquartered in Dallas, Texas, that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globa ...
,
studied, invented, and manufactured some electrically re-programmable non-volatile devices until 1977.
The theoretical basis of these devices is
''Avalanche'' hot-carrier injection
Hot carrier injection (HCI) is a phenomenon in solid-state electronic devices where an electron or a “ hole” gains sufficient kinetic energy to overcome a potential barrier necessary to break an interface state. The term "hot" refers to th ...
. But 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.
[
]
In 1975,
NEC
is a Japanese multinational information technology and electronics corporation, headquartered in Minato, Tokyo. The company was known as the Nippon Electric Company, Limited, before rebranding in 1983 as NEC. It provides IT and network soluti ...
's
semiconductor
A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way ...
operations unit, later NEC Electronics, currently
Renesas Electronics
is a Japanese semiconductor manufacturer headquartered in Tokyo, Japan, initially incorporated in 2002 as Renesas Technology, the consolidated entity of the semiconductor units of Hitachi and Mitsubishi excluding their dynamic random-access ...
, applied the
trademark
A trademark (also written trade mark or trade-mark) is a type of intellectual property consisting of a recognizable sign, design, or expression that identifies products or services from a particular source and distinguishes them from ot ...
name ''EEPROM®'' to Japan Patent Office.
In 1978, this trademark right is granted and registered as No.1,342,184 in Japan, and still survives as of March 2018.
In February 1977, Eliyahou Harari at
Hughes Aircraft Company invented a new EEPROM technology using
''Fowler-Nordheim tunnelling'' through a thin
silicon dioxide
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
layer between the
floating-gate and the
wafer.
Hughes went on to produce this new EEPROM devices.
But this patent
cited IBM's contribution of EEPROM technology and NEC's EEPROM® invention.
In May 1977, some important research result was disclosed by
Fairchild and
Siemens. 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 produce ...
-
oxynitride-
nitride-
oxide-
silicon
Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...
) structure with thickness of silicon dioxide less than 30
Å, and ''SIMOS'' (stacked-gate
injection MOS
MOS or Mos may refer to:
Technology
* MOSFET (metal–oxide–semiconductor field-effect transistor), also known as the MOS transistor
* Mathematical Optimization Society
* Model output statistics, a weather-forecasting technique
* MOS (fil ...
) structure, respectively, for using
''Fowler-Nordheim tunnelling'' hot-carrier injection
Hot carrier injection (HCI) is a phenomenon in solid-state electronic devices where an electron or a “ hole” gains sufficient kinetic energy to overcome a potential barrier necessary to break an interface state. The term "hot" refers to th ...
.
Around 1976 to 1978, Intel's team, including
George Perlegos, made some inventions to improve this tunneling E
2PROM 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 , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
layer, which was less than 200
Å.
In 1980. this structure was publicly introduced as ''FLOTOX'';
floating gate tunnel oxide.
The ''FLOTOX'' structure improved reliability of erase/write cycles per byte up to 10,000 times.
But this device required additional 2022V V
PP bias voltage supply for byte erase, except for 5V read operations.
In 1981, Perlegos and 2 other members left Intel to form
Seeq Technology,
which used on-device
charge pumps to supply the high voltages necessary for programming E
2PROMs.
In 1984, Perlogos left Seeq Technology to found
Atmel, then Seeq Technology was acquired by Atmel.
Theoretical basis of FLOTOX structure
As is described in former section, old EEPROMs are based on
avalanche breakdown-based
hot-carrier injection
Hot carrier injection (HCI) is a phenomenon in solid-state electronic devices where an electron or a “ hole” gains sufficient kinetic energy to overcome a potential barrier necessary to break an interface state. The term "hot" refers to th ...
with high
reverse breakdown voltage. But ''FLOTOX'' theoretical basis is
Fowler–Nordheim tunneling
Field electron emission, also known as field emission (FE) and electron field emission, is emission of electrons induced by an electrostatic field. The most common context is field emission from a solid surface into a vacuum. However, field emi ...
hot-carrier injection
Hot carrier injection (HCI) is a phenomenon in solid-state electronic devices where an electron or a “ hole” gains sufficient kinetic energy to overcome a potential barrier necessary to break an interface state. The term "hot" refers to th ...
through a thin
silicon dioxide
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
layer between the
floating gate and the wafer. In other words, it uses a
tunnel junction
In electronics/spintronics, 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 ...
.
[
]
Theoretical basis of the physical phenomenon itself is the same as today's
flash memory
Flash memory is an electronic 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 the NOR and NAND logic gates. Both use ...
. 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, a detailed academical explanation of FLOTOX device structure can be found in various materials.
Today's EEPROM structure
Nowadays, EEPROM is used for embedded
microcontrollers 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 electronic 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 the NOR and NAND logic gates. Both use ...
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 card, SIM card, 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, ), alternatively known as I2C or IIC, is a synchronous, multi-controller/multi-target (master/slave), packet switched, single-ended, serial communication bus invented in 1982 by Philips Semiconductors. It is wid ...
,
Microwire,
UNI/O, and
1-Wire
1-Wire is a device communications bus system designed by Dallas Semiconductor Corp. that provides low-speed (16.3 kbit/s) data, signaling, and power over a single conductor.
1-Wire is similar in concept to I²C, but with lower data rates and ...
. These use from 1 to 4 device pins and allow devices to use packages with 8 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
microcontrollers 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 sensor Mechanical temperature sensors
* Thermometer
* Therm
Electrical temperature sensors
* Thermistor- Thermistors are thermally sensitive resistors whose prime function is to exhibit a large, predictable and precise change in electrical resistance wh ...
s, 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 cartridge
A ROM cartridge, usually referred to in context simply as a cartridge, cart, or card, is a replaceable part designed to be connected to a consumer electronics device such as a home computer, video game console or, to a lesser extent, electron ...
s 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 electronic 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 the NOR and NAND logic gates. Both use ...
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, while flash memory erase circuits are shared by large blocks of cells (often 512×8).
Newer non-volatile memory technologies such as
FeRAM
Ferroelectric RAM (FeRAM, F-RAM or FRAM) is a random-access memory similar in construction to DRAM but using a ferroelectric layer instead of a dielectric layer to achieve non-volatility. FeRAM is one of a growing number of alternative non-vol ...
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 and EEPROM lies in the way that the memory programs and erases. EEPROM can be programmed and erased electrically using
field electron emission (more commonly known in the industry as "Fowler–Nordheim tunneling").
EPROMs can't be erased electrically and are programmed by
hot-carrier injection
Hot carrier injection (HCI) is a phenomenon in solid-state electronic devices where an electron or a “ hole” gains sufficient kinetic energy to overcome a potential barrier necessary to break an interface state. The term "hot" refers to th ...
onto the floating gate. Erase is by an
ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
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
Hot carrier injection (HCI) is a phenomenon in solid-state electronic devices where an electron or a “ hole” gains sufficient kinetic energy to overcome a potential barrier necessary to break an interface state. The term "hot" refers to th ...
and erase is through
Fowler–Nordheim tunneling
Field electron emission, also known as field emission (FE) and electron field emission, is emission of electrons induced by an electrostatic field. The most common context is field emission from a solid surface into a vacuum. However, field emi ...
.
See also
*
Avalanche breakdown
*
DataFlash
*
EPROM
*
*
Flash memory
Flash memory is an electronic 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 the NOR and NAND logic gates. Both use ...
*
Floating-gate MOSFET
*
Intel HEX – file format
*
Programmer (hardware)
*
Quantum tunnelling
*
SREC – file format
*
Tunnel junction
In electronics/spintronics, 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 ...
*
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