Memory cell (computing)

Layout for the silicon implementation of a six transistor SRAM memory cell.
Square array of DRAM memory cells being read
32x32 core memory plane storing 1024bits of data.
Intel 1103, a 1970 metal-oxide-semiconductor (MOS) dynamic random-access memory (DRAM) chip.
Die of the MT4C1024 (1994) integrating one-mebibit of DRAM memory cells.
SRAM memory cell depicting Inverter Loop as gates
A flash memory cell

Fundamental building block of computer memory.

- Memory cell (computing)

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Static random-access memory

Type of random-access memory (RAM) that uses latching circuitry (flip-flop) to store each bit.

A static RAM chip from a Nintendo Entertainment System clone (2K × 8 bits)
SRAM cells on the die of a STM32F103VGT6 microcontroller as seen by a scanning electron microscope. Manufactured by STMicroelectronics using a 180 nanometre process.
Comparison image of 180 nanometre SRAM cells on a STM32F103VGT6 microcontroller as seen by an optical microscope
A six-transistor CMOS SRAM cell
Four transistor SRAM provides advantages in density at the cost of manufacturing complexity. The resistors must have small dimensions and large values.

In 1965, Arnold Farber and Eugene Schlig, working for IBM, created a hard-wired memory cell, using a transistor gate and tunnel diode latch.

Random-access memory

Form of computer memory that can be read and changed in any order, typically used to store working data and machine code.

Example of writable volatile random-access memory: Synchronous Dynamic RAM modules, primarily used as main memory in personal computers, workstations, and servers.
8GB DDR3 RAM stick with a white heatsink
These IBM tabulating machines from the mid-1930s used mechanical counters to store information
1-megabit (Mbit) chip, one of the last models developed by VEB Carl Zeiss Jena in 1989
A SO-DIMM stick of laptop RAM, roughly half the size of desktop RAM.

In today's technology, random-access memory takes the form of integrated circuit (IC) chips with MOS (metal-oxide-semiconductor) memory cells.

EPROM

Type of programmable read-only memory (PROM) chip that retains its data when its power supply is switched off.

An EPROM: the Texas Instruments TMS27C040, a CMOS chip with 4 megabits of storage and 8-bit output (shown here in a 600-mil ceramic dual-in-line package). The TMS27C040 operates at 5 volts, but must be programmed at 13 volts.
An Intel 1702A EPROM, one of the earliest EPROM types (1971), 256 by 8 bit. The small quartz window admits UV light for erasure.
A cross-section of a floating-gate transistor
Atmel AT27C010 - an OTP EPROM
A 32 KB (256 Kbit) EPROM
This 8749 Microcontroller stores its program in internal EPROM
NEC 02716, 16 KBit EPROM

Development of the EPROM memory cell started with investigation of faulty integrated circuits where the gate connections of transistors had broken.

Flash memory

Electronic non-volatile computer memory storage medium that can be electrically erased and reprogrammed.

A disassembled USB flash drive. The chip on the left is flash memory. The controller is on the right.
A flash memory cell
NOR flash memory wiring and structure on silicon
Programming a NOR memory cell (setting it to logical 0), via hot-electron injection
Erasing a NOR memory cell (setting it to logical 1), via quantum tunneling
NAND flash memory wiring and structure on silicon
3D NAND continues scaling beyond 2D.
Minimum bit cost of 3D NAND from non-vertical sidewall. The top opening widens with more layers, counteracting the increase in bit density.
NOR flash by Intel
Serial Flash: Silicon Storage Tech SST25VF080B
An Intel mSATA SSD

They proposed that it could be used as floating-gate memory cells for storing a form of programmable read-only memory (PROM) that is both non-volatile and re-programmable.

Floating-gate MOSFET

Type of metal–oxide–semiconductor field-effect transistor (MOSFET) where the gate is electrically isolated, creating a floating node in direct current, and a number of secondary gates or inputs are deposited above the floating gate (FG) and are electrically isolated from it.

A cross-section of a floating-gate transistor

The FGMOS is commonly used as a floating-gate memory cell, the digital storage element in EPROM, EEPROM and flash memory technologies.

Computer memory

Device or system that is used to store information for immediate use in a computer or related computer hardware and digital electronic devices.

Modern DDR4 SDRAM module, usually found in desktop computers.
Detail of the back of a section of ENIAC, showing vacuum tubes.
8GB microSDHC card on top of 8bytes of magnetic-core memory (1core is 1bit).
Various memory modules containing different types of DRAM (from top to bottom): DDR SDRAM, SDRAM, EDO DRAM, and FPM DRAM

Modern memory is implemented as semiconductor memory, where data is stored within memory cells built from MOS transistors and other components on an integrated circuit.

Dynamic random-access memory

A die photograph of the Micron Technology MT4C1024 DRAM integrated circuit (1994). It has a capacity of 1 megabit equivalent of 2^{20}bits or 128 kB.
Motherboard of the NeXTcube computer, 1990, with 64 MiB main memory DRAM (top left) and 256 KiB of VRAM (lower edge, right of middle).
A schematic drawing depicting the cross-section of the original one-transistor, one-capacitor NMOS DRAM cell. It was patented in 1968.
The principles of operation for reading a simple 4 \times4 DRAM array
Basic structure of a DRAM cell array
Writing to a DRAM cell
Self-aligned storage node locations simplify the fabrication process in modern DRAM.
A pair of 32 MB EDO DRAM modules
The die of a Samsung DDR-SDRAM 64MBit package
A 512 MBit Qimonda GDDR3 SDRAM package
Inside a Samsung GDDR3 256MBit package
1 Mbit high speed CMOS pseudo static RAM, made by Toshiba

Dynamic random-access memory (dynamic RAM or DRAM) is a type of random-access semiconductor memory that stores each bit of data in a memory cell, usually consisting of a tiny capacitor and a transistor, both typically based on metal-oxide-semiconductor (MOS) technology.

Semiconductor memory

Digital electronic semiconductor device used for digital data storage, such as computer memory.

RAM chips for computers usually come on removable memory modules like these. Additional memory can be added to the computer by plugging in additional modules.

It typically refers to MOS memory, where data is stored within metal–oxide–semiconductor (MOS) memory cells on a silicon integrated circuit memory chip.

Non-volatile memory

Type of computer memory that can retain stored information even after power is removed.

Modern DDR4 SDRAM module, usually found in desktop computers.

Non-volatile memory typically refers to storage in semiconductor memory chips, which store data in floating-gate memory cells consisting of floating-gate MOSFETs (metal–oxide–semiconductor field-effect transistors), including flash memory storage such as NAND flash and solid-state drives (SSD).

Dawon Kahng

Korean-American electrical engineer and inventor, known for his work in solid-state electronics.

The MOSFET was invented by Kahng along with his colleague Mohamed Atalla at Bell Labs in 1959.

Kahng and Sze proposed that FGMOS could be used as floating-gate memory cells for non-volatile memory (NVM) and reprogrammable read-only memory (ROM), which became the basis for EPROM (erasable programmable ROM), EEPROM (electrically erasable programmable ROM) and flash memory technologies.