|Computer memory types|
|Early stage NVRAM|
EEPROM (also E2PROM) stands for electrically erasable programmable read-only memory and is a type of non-volatile memory used in computers, integrated in microcontrollers for smart cards and remote keyless systems, and other electronic devices to store relatively small amounts of data but 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 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 microcontrollers include both: flash memory for the firmware, and a small EEPROM for parameters and history.
As of 2019, flash memory costs much less than byte-programmable EEPROM and had become the dominant memory type wherever a system required 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 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 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-oxide-nitride-oxide-semiconductor) technology,which used Renesas Electronics' flash memory integrated in single-chip microcontrollers.
In 1972, a type of electrically re-programmable non-volatile memory was invented by Fujio Masuoka at Toshiba, who is also known as the inventor of flash memory .Most of the major semiconductor manufactures, such as Toshiba, Sanyo (later, ON Semiconductor), IBM, Intel, NEC (later, Renesas Electronics), Philips (later, NXP Semiconductors), Siemens (later, Infineon Technologies), Honeywell (later, Atmel), Texas Instruments, studied, invented, and manufactured some electrically re-programmable non-volatile devices until 1977.
The theoretical basis of these devices is Avalanche hot-carrier injection. 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's semiconductor operations unit, later NEC Electronics, currently Renesas Electronics, applied the trademark 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 layer between the floating-gate and the wafer. Hughes went on to produce this new EEPROM devices.But this patent cited NEC's EEPROM® invention.
In May 1977, some important research result was disclosed by Fairchild and Siemens. They used SONOS (polysilicon-oxynitride-nitride-oxide-silicon) 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. –22V VPP bias voltage supply for byte erase, except for 5V read operations. :5-86 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 E2PROMs. In 1984, Perlogos left Seeq Technology to found Atmel, then Seeq Technology was acquired by Atmel.In 1978, they developed a 16K (2K word × 8) bit Intel 2816 device with a thin silicon dioxide 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 20
As is described in former section, old EEPROMs are based on Avalanche breakdown-based hot-carrier injection with high reverse breakdown voltage. But FLOTOX's theoretical basis is Fowler–Nordheim tunneling hot-carrier injection through a thin silicon dioxide layer between the floating-gate and the wafer. In other words, it uses a tunnel junction.
Theoretical basis of the physical phenomenon itself is the same as today's flash memory. 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's 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.
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 has 1 transistor per bit to erase a region of the memory. 245, PDF:2:
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.
EEPROM devices use a serial or parallel interface for data input/output.
The common serial interfaces are SPI, I²C, Microwire, UNI/O, and 1-Wire. 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:
Other operations supported by some EEPROM devices are:
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.
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.
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.
Flash memory 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 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.
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 via hot carrier injection onto the floating gate. Erase is via an ultraviolet 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.
|Type||Inject electrons onto gate|
(mostly interpreted as Bit=0)
|Duration||Remove electrons from gate|
(mostly interpreted as Bit=1)
|EEPROM||field electron emission||0,1 ... 5 ms, bytewise||field electron emission||0,1 ... 5 ms, blockwise|
|NOR Flash memory||hot carrier injection||0,01 ... 1 ms||field electron emission||0,01 ... 1 ms, blockwise|
|EPROM||hot carrier injection||3 ... 50 ms, bytewise||UV light||5 ... 30 minutes, whole chip|
The Stanford Graduate Students in Electrical Engineering (GSEE) has annually hosted a dance (i.e. prom) called EEPROMsince 2012.
In computing, memory refers to a device that is used to store information for immediate use in a computer or related computer hardware device. It typically refers to semiconductor memory, specifically metal–oxide–semiconductor (MOS) memory, where data is stored within MOS memory cells on a silicon integrated circuit chip. The term "memory" is often synonymous with the term "primary storage". Computer memory operates at a high speed, for example random-access memory (RAM), as a distinction from storage that provides slow-to-access information but offers higher capacities. If needed, contents of the computer memory can be transferred to secondary storage; a very common way of doing this is through a memory management technique called "virtual memory". An archaic synonym for memory is store.
A programmable read-only memory (PROM) is a form of digital memory where the setting of each bit is locked by a fuse or antifuse. It is one type of ROM. The data in them are permanent and cannot be changed. PROMs are used in digital electronic devices to store permanent data, usually low level programs such as firmware or microcode. The key difference from a standard ROM is that the data is written into a ROM during manufacture, while with a PROM the data is programmed into them after manufacture. Thus, ROMs tend to be used only for large production runs with well-verified data, while PROMs are used to allow companies to test on a subset of the devices in an order before burning data into all of them.
Flash memory is an electronic (solid-state) non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory are named after the NAND and NOR logic gates. The individual flash memory cells, consisting of floating-gate MOSFETs, exhibit internal characteristics similar to those of the corresponding gates.
An EPROM, or erasable programmable read-only memory, is a type of programmable read-only memory (PROM) chip that retains its data when its power supply is switched off. Computer memory that can retrieve stored data after a power supply has been turned off and back on is called non-volatile. It is an array of floating-gate transistors individually programmed by an electronic device that supplies higher voltages than those normally used in digital circuits. Once programmed, an EPROM can be erased by exposing it to strong ultraviolet light source. EPROMs are easily recognizable by the transparent fused quartz window in the top of the package, through which the silicon chip is visible, and which permits exposure to ultraviolet light during erasing.
Non-volatile random-access memory (NVRAM) is random-access memory that retains data without applied power. This is in contrast to dynamic random-access memory (DRAM) and static random-access memory (SRAM), which both maintain data only for as long as power is applied, or such forms of memory as magnetic tape, which cannot be randomly accessed but which retains data indefinitely without electric power.
Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retrieve stored information even after having been power cycled. In contrast, volatile memory needs constant power in order to retain data. Examples of non-volatile memory include flash memory, read-only memory (ROM), ferroelectric RAM, most types of magnetic computer storage devices, optical discs, and early computer storage methods such as paper tape and punched cards.
Semiconductor memory is a digital electronic semiconductor device used for digital data storage, such as computer memory. It typically refers to MOS memory, where data is stored within metal–oxide–semiconductor (MOS) memory cells on a silicon integrated circuit memory chip. There are numerous different types using different semiconductor technologies. The two main types of random-access memory (RAM) are static RAM (SRAM), which uses several transistors per memory cell, and Dynamic random-access memory (DRAM), which uses a single transistor and MOS capacitor per cell. Non-volatile memory uses floating-gate memory cells, which consist of a single transistor per cell.
A fin field-effect transistor (FinFET) is a multigate device, a MOSFET built on a substrate where the gate is placed on two, three, or four sides of the channel or wrapped around the channel, forming a double gate structure. These devices have been given the generic name "finfets" because the source/drain region forms fins on the silicon surface. The FinFET devices have significantly faster switching times and higher current density than planar CMOS technology.
The floating-gate MOSFET (FGMOS), also known as a floating-gate transistor, is a type of MOSFET where the gate is electrically isolated, creating a floating node in DC, and a number of secondary gates or inputs are deposited above the floating gate (FG) and are electrically isolated from it. These inputs are only capacitively connected to the FG. Since the FG is completely surrounded by highly resistive material, the charge contained in it remains unchanged for long periods of time. Usually Fowler-Nordheim tunneling and hot-carrier injection mechanisms are used to modify the amount of charge stored in the FG.
Charge trap flash (CTF) is a semiconductor memory technology used in creating non-volatile NOR and NAND flash memory. It is a type of floating-gate MOSFET memory technology, but differs from the conventional floating-gate technology in that it uses a silicon nitride film to store electrons rather than the doped polycrystalline silicon typical of a floating-gate structure. This approach allows memory manufacturers to reduce manufacturing costs five ways:
SONOS, short for "silicon–oxide–nitride–oxide–silicon", more precisely, "polycrystalline silicon"—"silicon dioxide"—"silicon nitride"—"silicon dioxide"—"silicon", is a cross sectional structure of MOSFET (metal-oxide-semiconductor field-effect transistor), realized by P.C.Y. Chen of Fairchild Camera and Instrument in 1977. This structure is often used for non-volatile memories, such as EEPROM and flash memories. It is sometimes used for TFT LCD displays. It is one of CTF (charge trap flash) variants. It is distinguished from traditional non-volatile memory structures by the use of silicon nitride (Si3N4 or Si9N10) instead of "polysilicon-based FG (floating-gate)" for the charge storage material. A further variant is "SHINOS" ("silicon"—"hi-k"—"nitride"—"oxide"—"silicon"), which is substituted top oxide layer with high-κ material. Another advanced variant is "MONOS" ("metal–oxide–nitride–oxide–silicon"). Companies offering SONOS-based products include Cypress Semiconductor, Macronix, Toshiba, United Microelectronics Corporation and Floadia.
The programmable metallization cell, or PMC, is a non-volatile computer memory developed at Arizona State University. PMC, a technology developed to replace the widely used flash memory, providing a combination of longer lifetimes, lower power, and better memory density. Infineon Technologies, who licensed the technology in 2004, refers to it as conductive-bridging RAM, or CBRAM. CBRAM became a registered trademark of Adesto Technologies in 2011. NEC has a variant called "Nanobridge" and Sony calls their version "electrolytic memory".
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 flash and NAND flash types in the 1980s. He also invented the first gate-all-around (GAA) MOSFET (GAAFET) transistor, an early non-planar 3D transistor, in 1988.
Read-only memory (ROM) is a type of non-volatile memory used in computers and other electronic devices. Data stored in ROM cannot be electronically modified after the manufacture of the memory device. Read-only memory is useful for storing software that is rarely changed during the life of the system, also known as firmware. Software applications for programmable devices can be distributed as plug-in cartridges containing read-only memory.
Dawon Kahng was a Korean-American electrical engineer and inventor, known for his work in solid-state electronics. He is best known for inventing the MOSFET, also known as the MOS transistor, with Mohamed Atalla in 1959. Atalla and Kahng developed both the PMOS and NMOS processes for MOSFET semiconductor device fabrication. The MOSFET is the most widely used type of transistor, and the basic element in most modern electronic equipment.
The memory cell is the fundamental building block of computer memory. The memory cell is an electronic circuit that stores one bit of binary information and it must be set to store a logic 1 and reset to store a logic 0. Its value is maintained/stored until it is changed by the set/reset process. The value in the memory cell can be accessed by reading it.
The metal–nitride–oxide–semiconductor or metal–nitride–oxide–silicon (MNOS) transistor is a type of MOSFET in which the oxide layer is replaced by a double layer of nitride and oxide. It is an alternative and supplement to the existing standard MOS technology, wherein the insulation employed is a nitride-oxide layer. It is used in non-volatile computer memory.
Tsu-Jae King Liu is an American academic and engineer who serves as the Dean and Roy W. Carlson Professor of Engineering at the UC Berkeley College of Engineering.
George Perlegos is a Greek-American computer scientist and engineer, best known for pioneering the use of EEPROM and founding Atmel.
Read-mostly memory (RMM) is a type of memory that can be read fast, but written to only slowly.
The Intel 2816 uses the FLOTOX structure, which has been discussed in detail in the literaturel. Basically, it uses an oxide of less than 200A thick between the floating polysilicon gate and the N+ region as shown in Figure 1.