EPROM

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An EPROM (rarely EROM), 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 (such as from a mercury-vapor lamp). 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.

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 is 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.

Integrated circuit electronic circuit manufactured by lithography; set of electronic circuits on one small flat piece (or "chip") of semiconductor material, normally silicon

An integrated circuit or monolithic integrated circuit is a set of electronic circuits on one small flat piece of semiconductor material that is normally silicon. The integration of large numbers of tiny MOS transistors into a small chip results in circuits that are orders of magnitude smaller, faster, and less expensive than those constructed of discrete electronic components. The IC's mass production capability, reliability, and building-block approach to circuit design has ensured the rapid adoption of standardized ICs in place of designs using discrete transistors. ICs are now used in virtually all electronic equipment and have revolutionized the world of electronics. Computers, mobile phones, and other digital home appliances are now inextricable parts of the structure of modern societies, made possible by the small size and low cost of ICs.

Ultraviolet Electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays

Ultraviolet (UV) designates a band of the electromagnetic spectrum with wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays. UV radiation is present in sunlight, and contributes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights. Although long-wavelength ultraviolet is not considered an ionizing radiation because its photons lack the energy to ionize atoms, it can cause chemical reactions and causes many substances to glow or fluoresce. Consequently, the chemical and biological effects of UV are greater than simple heating effects, and many practical applications of UV radiation derive from its interactions with organic molecules.

Contents

Operation

An Intel 1702A EPROM, one of the earliest EPROM types (1971), 256 by 8 bit. The small quartz window admits UV light for erasure. Eprom.jpg
An Intel 1702A EPROM, one of the earliest EPROM types (1971), 256 by 8 bit. The small quartz window admits UV light for erasure.

Development of the EPROM memory cell started with investigation of faulty integrated circuits where the gate connections of transistors had broken. Stored charge on these isolated gates changed their properties.

Memory cell (computing) part of computer memory

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.

Following the invention of the MOSFET (metal-oxide-semiconductor field-effect transistor) by Mohamed Atalla and Dawon Kahng at Bell Labs, presented in 1960, Frank Wanlass studied MOSFET structures in the early 1960s. In 1963, he noted the movement of charge through oxide onto a gate. While he did not pursue it, this idea would later become the basis for EPROM technology. [1]

MOSFET Transistor used for amplifying or switching electronic signals.

The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET), also known as the metal–oxide–silicon transistor (MOS transistor, or MOS), is a type of field-effect transistor that is fabricated by the controlled oxidation of a semiconductor, typically silicon. It has an insulated gate, whose voltage determines the conductivity of the device. This ability to change conductivity with the amount of applied voltage can be used for amplifying or switching electronic signals. The MOSFET is the basic building block of modern electronics. Since its invention by Mohamed Atalla and Dawon Kahng at Bell Labs in November 1959, the MOSFET has become the most widely manufactured device in history, with an estimated total of 13 sextillion (1.3 × 1022) MOS transistors manufactured between 1960 and 2018.

Mohamed Atalla mechanical engineer

Mohamed Atalla was an Egyptian-American engineer, physical chemist, cryptographer, inventor, and entrepreneur. His pioneering work in semiconductor technology laid the foundations for modern electronics. Most importantly, his invention of the MOSFET in 1959, along with his earlier surface passivation and thermal oxidation processes, revolutionized the electronics industry. He is also known as the founder of the data security company Atalla Corporation, which he founded after he invented the first hardware security module (HSM) in 1972. He received the Stuart Ballantine Medal and was inducted into the National Inventors Hall of Fame for his important contributions to semiconductor technology as well as data security.

Dawon Kahng South Korean engineer

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.

In 1967, Dawon Kahng and Simon Sze at Bell Labs proposed that the floating gate of a MOSFET could be used for the cell of a reprogrammable ROM (read-only memory). [2] Building on this concept, Dov Frohman of Intel invented EPROM in 1971, [2] and was awarded U.S. Patent 3,660,819 in 1972. Frohman designed the Intel 1702, a 2048-bit EPROM, which was announced by Intel in 1971. [2]

Dr. Simon Min Sze is a Chinese-American electrical engineer.

Read-only memory non-volatile memory used in computers and other electronic devices; class of storage medium used in computers and other electronic devices

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, sometimes known as firmware. Software applications for programmable devices can be distributed as plug-in cartridges containing read-only memory.

Dov Frohman Israeli electrical engineer

Dov Frohman is an Israeli electrical engineer and business executive. A former vice president of Intel Corporation, he is the inventor of the erasable programmable read only memory (EPROM) and the founder and first general manager of Intel Israel. He is also the author of Leadership the Hard Way.

Each storage location of an EPROM consists of a single field-effect transistor. Each field-effect transistor consists of a channel in the semiconductor body of the device. Source and drain contacts are made to regions at the end of the channel. An insulating layer of oxide is grown over the channel, then a conductive (silicon or aluminum) gate electrode is deposited, and a further thick layer of oxide is deposited over the gate electrode. The floating-gate electrode has no connections to other parts of the integrated circuit and is completely insulated by the surrounding layers of oxide. A control gate electrode is deposited and further oxide covers it. [3]

Field-effect transistor transistor that uses an electric field to control the electrical behaviour of the device. FETs are also known as unipolar transistors since they involve single-carrier-type operation

The field-effect transistor (FET) is an electronic device which uses an electric field to control the flow of current. FETs are devices with three terminals: source, gate, and drain. FETs control the flow of current by the application of a voltage to the gate, which in turn alters the conductivity between the drain and source.

To retrieve data from the EPROM, the address represented by the values at the address pins of the EPROM is decoded and used to connect one word (usually an 8-bit byte) of storage to the output buffer amplifiers. Each bit of the word is a 1 or 0, depending on the storage transistor being switched on or off, conducting or non-conducting.

A cross-section of a floating-gate transistor Floating gate transistor.png
A cross-section of a floating-gate transistor

The switching state of the field-effect transistor is controlled by the voltage on the control gate of the transistor. Presence of a voltage on this gate creates a conductive channel in the transistor, switching it on. In effect, the stored charge on the floating gate allows the threshold voltage of the transistor to be programmed.

Storing data in the memory requires selecting a given address and applying a higher voltage to the transistors. This creates an avalanche discharge of electrons, which have enough energy to pass through the insulating oxide layer and accumulate on the gate electrode. When the high voltage is removed, the electrons are trapped on the electrode. [4] Because of the high insulation value of the silicon oxide surrounding the gate, the stored charge cannot readily leak away and the data can be retained for decades.

The programming process is not electrically reversible. To erase the data stored in the array of transistors, ultraviolet light is directed onto the die. Photons of the UV light cause ionization within the silicon oxide, which allow the stored charge on the floating gate to dissipate. Since the whole memory array is exposed, all the memory is erased at the same time. The process takes several minutes for UV lamps of convenient sizes; sunlight would erase a chip in weeks, and indoor fluorescent lighting over several years. [5] Generally, the EPROMs must be removed from equipment to be erased, since it is not usually practical to build in a UV lamp to erase parts in-circuit. The Electrically Erasable Programmable Read-Only Memory (EEPROM) was developed to provide an electrical erase function and has now mostly displaced ultraviolet-erased parts.

Details

Atmel AT27C010 - an OTP EPROM Dr. Neuhaus, Smarty 28.8 TI - Atmel AT27C010-9401.jpg
Atmel AT27C010 - an OTP EPROM

As the quartz window is expensive to make, OTP (one-time programmable) chips were introduced; here, the die is mounted in an opaque package so it cannot be erased after programming – this also eliminates the need to test the erase function, further reducing cost. OTP versions of both EPROMs and EPROM-based microcontrollers are manufactured. However, OTP EPROM (whether separate or part of a larger chip) is being increasingly replaced by EEPROM for small sizes, where the cell cost isn't too important, and flash for larger sizes.

A programmed EPROM retains its data for a minimum of ten to twenty years, [6] with many still retaining data after 35 or more years, and can be read an unlimited number of times without affecting the lifetime. The erasing window must be kept covered with an opaque label to prevent accidental erasure by the UV found in sunlight or camera flashes. Old PC BIOS chips were often EPROMs, and the erasing window was often covered with an adhesive label containing the BIOS publisher's name, the BIOS revision, and a copyright notice. Often this label was foil-backed to ensure its opacity to UV.

Erasure of the EPROM begins to occur with wavelengths shorter than 400 nm. Exposure time for sunlight of one week or three years for room fluorescent lighting may cause erasure. The recommended erasure procedure is exposure to UV light at 253.7 nm of at least 15 Ws/cm2, usually achieved in 20 to 30 minutes with the lamp at a distance of about 2.5 cm. [7]

Erasure can also be accomplished with X-rays:

Erasure, however, has to be accomplished by non-electrical methods, since the gate electrode is not accessible electrically. Shining ultraviolet light on any part of an unpackaged device causes a photocurrent to flow from the floating gate back to the silicon substrate, thereby discharging the gate to its initial, uncharged condition (photoelectric effect). This method of erasure allows complete testing and correction of a complex memory array before the package is finally sealed. Once the package is sealed, information can still be erased by exposing it to X radiation in excess of 5*104 rads, [lower-alpha 1] a dose which is easily attained with commercial X-ray generators. [8]

In other words, to erase your EPROM, you would first have to X-ray it and then put it in an oven at about 600 degrees Celsius (to anneal semiconductor alterations caused by the X-rays). The effects of this process on the reliability of the part would have required extensive testing so they decided on the window instead. [9]

EPROMs had a limited but large number of erase cycles; the silicon dioxide around the gates would accumulate damage from each cycle, making the chip unreliable after several thousand cycles. EPROM programming is slow compared to other forms of memory. Because higher-density parts have little exposed oxide between the layers of interconnects and gate, ultraviolet erasing becomes less practical for very large memories. Even dust inside the package can prevent some cells from being erased. [10]

Application

For large volumes of parts (thousands of pieces or more), mask-programmed ROMs are the lowest cost devices to produce. However, these require many weeks lead time to make, since the artwork for an IC mask layer must be altered to store data on the ROMs. Initially, it was thought that the EPROM would be too expensive for mass production use and that it would be confined to development only. It was soon found that small-volume production was economical with EPROM parts, particularly when the advantage of rapid upgrades of firmware was considered.

Some microcontrollers, from before the era of EEPROMs and flash memory, use an on-chip EPROM to store their program. Such microcontrollers include some versions of the Intel 8048, the Freescale 68HC11, and the "C" versions of the PIC microcontroller. Like EPROM chips, such microcontrollers came in windowed (expensive) versions that were used for debugging and program development. The same chip came in (somewhat cheaper) opaque OTP packages for production. Leaving the die of such a chip exposed to light can also change behavior in unexpected ways when moving from a windowed part used for development to a non-windowed part for production.

EPROM generations, sizes and types

The first generation 1702 devices were fabricated with the p-MOS technology. They were powered with VCC = VBB = +5 V and VDD = VGG = -9 V in Read mode, and with VDD = VGG = -47 V in Programming mode [11] [12] .

The second generation 2704/2708 devices switched to n-MOS technology and to three-rail VCC = +5 V, VBB = -5 V, VDD = +12 V power supply with VPP = 12 V and a +25 V pulse in Programming mode.

The n-MOS technology evolution introduced single-rail VCC = +5 V power supply and single VPP = +12 V programming voltage without pulse in the third generation. The unneeded VBB and VDD pins were reused for additional address bits allowing larger capacities (2716/2732) in the same 24-pin package, and even larger capacities with larger packages. Later the decreased cost of the CMOS technology allowed same devices to be fabricated using it, adding the letter "C" to the device numbers (27xx(x) are n-MOS and 27Cxx(x) are CMOS).

While parts of the same size from different manufacturers are compatible in read mode, different manufacturers added different and sometimes multiple programming modes leading to subtle differences in the programming process. This prompted larger capacity devices to introduce a "signature mode", allowing the manufacturer and device to be identified by the EPROM programmer. It was implemented by forcing +12 V on pin A9 and reading out two bytes of data. However, as this was not universal, programmer software also would allow manual setting of the manufacturer and device type of the chip to ensure proper programming. [13]

EPROM TypeYearSize — bits Size — bytes Length (hex)Last address (hex)Technology
1702, 1702A19712 Kbit 256100FFPMOS
270419754 Kbit5122001FFNMOS
270819758 Kbit1 KB 4003FFNMOS
2716, 27C16, TMS2716, 2516197716 Kbit2 KB8007FFNMOS/CMOS
2732, 27C32, 2532197932 Kbit4 KB1000FFFNMOS/CMOS
2764, 27C64, 256464 Kbit8 KB20001FFFNMOS/CMOS
27128, 27C128128 Kbit16 KB40003FFFNMOS/CMOS
27256, 27C256256 Kbit32 KB80007FFFNMOS/CMOS
27512, 27C512512 Kbit64 KB10000FFFFNMOS/CMOS
27C010, 27C1001 Mbit 128 KB200001FFFFCMOS
27C0202 Mbit256 KB400003FFFFCMOS
27C040, 27C400, 27C40014 Mbit512 KB800007FFFFCMOS
27C0808 Mbit1 MB 100000FFFFFCMOS
27C16016 Mbit2 MB2000001FFFFFCMOS
27C320, 27C32232 Mbit4 MB4000003FFFFFCMOS

See also

Notes

  1. 500 J/kg

Related Research Articles

Computer memory physical device used to store information for immediate use in a digital electronic device

In computing, memory refers to the computer hardware integrated circuits that store information for immediate use in a computer; it is 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.

Microcontroller small computer on a single integrated circuit

A microcontroller is a small computer on a single integrated circuit. In modern terminology, it is similar to, but less sophisticated than, a system on a chip (SoC); an SoC may include a microcontroller as one of its components. A microcontroller contains one or more CPUs along with memory and programmable input/output peripherals. Program memory in the form of ferroelectric RAM, NOR flash or OTP ROM is also often included on chip, as well as a small amount of RAM. Microcontrollers are designed for embedded applications, in contrast to the microprocessors used in personal computers or other general purpose applications consisting of various discrete chips.

CMOS Technology for constructing integrated circuits

Complementary metal–oxide–semiconductor (CMOS), also known as complementary-symmetry metal–oxide–semiconductor (COS-MOS), is a type of MOSFET fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSFETs for logic functions. CMOS technology is used for constructing integrated circuits (ICs), including microprocessors, microcontrollers, memory chips, and other digital logic circuits. CMOS technology is also used for analog circuits such as image sensors, data converters, RF circuits, and highly integrated transceivers for many types of communication.

Flash memory Electronic non-volatile computer storage device

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.

EEPROM nonvolatile memory comprising arrays of floating-gate transistors used in computers, microcontrollers &c. to store relatively small amounts of data but allowing individual bytes to be erased/reprogrammed in-circuit through special programming signals

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.

Programmable logic device reprogrammable computer hardware technology

A programmable logic device (PLD) is an electronic component used to build reconfigurable digital circuits. Unlike integrated circuits (IC) which consist of logic gates and have a fixed function, a PLD has an undefined function at the time of manufacture. Before the PLD can be used in a circuit it must be programmed (reconfigured) by using a specialized program.

Non-volatile random-access memory (NVRAM) is random-access memory that is non-volatile. 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.

PIC microcontrollers

PIC is a family of microcontrollers made by Microchip Technology, derived from the PIC1650 originally developed by General Instrument's Microelectronics Division. The name PIC initially referred to Peripheral Interface Controller, and is currently expanded as Programmable Intelligent Computer. The first parts of the family were available in 1976; by 2013 the company had shipped more than twelve billion individual parts, used in a wide variety of embedded systems.

Mask ROM (MROM) is a type of read-only memory (ROM) whose contents are programmed by the integrated circuit manufacturer. The terminology mask comes from integrated circuit fabrication, where regions of the chip are masked off during the process of photolithography.

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.

Programmer (hardware) device that configures programmable non-volatile integrated circuits

A programmer (hardware), device programmer, chip programmer, device burner, or PROM writer is a piece of electronic equipment that arrange written software to configure programmable non-volatile integrated circuits, called programmable devices. The target devices include; PROM, EPROM, EEPROM, Flash memory, eMMC, MRAM, FeRAM, NVRAM, PLD, PLA, PAL, GAL, CPLD, FPGA, and MCU. These are terminologies in the field of computer hardware.

Semiconductor memory is a digital electronic data storage device, implemented with semiconductor devices. It is often used as computer memory, implemented with metal-oxide-semiconductor (MOS) memory cells on an integrated circuit (IC) chip. There are many different types of implementations using various technologies.

The floating-gate MOSFET (FGMOS) 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. The technology differs from the more conventional floating-gate MOSFET 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:

  1. Fewer process steps are required to form a charge storage node
  2. Smaller process geometries can be used
  3. Multiple bits can be stored on a single flash memory cell.
  4. Improved reliability
  5. Higher yield since the charge trap is less susceptible to point defects in the tunnel oxide layer

SONOS, short for "silicon–oxide–nitride–oxide–silicon", more precisely, "polycrystalline silicon"—"silicon dioxide"—"silicon nitride"—"siicon dioxide"—"silicon", is a cross sectional structure of MOSFET, realized by P.C.Y. Chen 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.

Single-board microcontroller

A single-board microcontroller is a microcontroller built onto a single printed circuit board. This board provides all of the circuitry necessary for a useful control task: a microprocessor, I/O circuits, a clock generator, RAM, stored program memory and any necessary support ICs. The intention is that the board is immediately useful to an application developer, without requiring them to spend time and effort to develop controller hardware.

The following outline is provided as an overview of and topical guide to electronics:

References

  1. "People". The Silicon Engine. Computer History Museum . Retrieved 17 August 2019.
  2. 1 2 3 "1971: Reusable semiconductor ROM introduced". Computer History Museum . Retrieved 19 June 2019.
  3. Sah 1991, p. 639.
  4. Oklobdzija, Vojin G. (2008). Digital Design and Fabrication. CRC Press. pp. 5–17. ISBN   0-8493-8602-0.
  5. Ayers, John E (2004), Digital integrated circuits: analysis and design, CRC Press, p. 591, ISBN   0-8493-1951-X .
  6. Horowitz, Paul; Hill, Winfield (1989), The Art of Electronics (2nd ed.), Cambridge: Cambridge University Press, p. 817, ISBN   0-521-37095-7 .
  7. "M27C512 Datasheet" (PDF). Archived (PDF) from the original on 2018-09-06. Retrieved 2018-10-07.
  8. Frohman, Dov (May 10, 1971), Electronics Magazine (article).
  9. Margolin, J (May 8, 2009). "EPROM"..
  10. Sah 1991, p. 640.
  11. Intel 1702A 2K (256 x 8) UV Erasable PROM
  12. AMD Am1702A 256-Word by 8-Bit Programmable Read Only Memory
  13. U.S. International Trade Commission, ed. (October 1998). Certain EPROM, EEPROM, Flash Memory and Flash Microcontroller Semiconductor Devices and Products Containing Same, Inv. 337-TA-395. Diane Publishing. pp. 51–72. ISBN   1-4289-5721-9. The details of SEEQ's Silicon Signature method of a device programmer reading an EPROM's ID.

Bibliography