Semiconductor memory

The semiconductor memory is a data memory composed of a semiconductor.

In and on a semiconductor crystal microelectronic memory structures can be realized, so that a memory chip (see also the coordinates). The chips used to complete integrated circuits or further processed uncapped.

The data is stored in the form of binary electronic switching states in the integrated circuits. Predecessors were the magnetic core memory working, who were replaced only in the early 1970s by the semiconductor memories. More recent developments aim to combine the magnetic storage principle microelectronically to high-density, non-volatile memories ( MRAM).

Memory cell


A memory cell is the smallest unit of a physical realization of the memory of logic states. The term, depending on the context, either to realize the smallest possible unit, the 1-bit storage element, or the implementation of the minimum addressable, that is, at an access les or writable, unit, a so-called word or data word of n bits is (n> 1).

Personal computer nowadays work with a word length (also called " word size " called ) of 32 or 64 bits. Previously, for example, in the first pocket calculators ( or a nibble nibble) were memory cells 4 bits in size. The first PCs, however, had 8 -bit wide memory cells. Still 8 bits are used: For simple controls ( see microcontroller ).

In earlier computers and word widths of 6 or 7 bits were in use, since one could perform an alpha-numeric processing with 64 or 128 storable characters. This memory had not yet been implemented as semiconductor memories. The Hollerith punch card had a word length of 12 bits.

The memory cells are divided into volatile and non-volatile memory cells. In non-volatile memory cells, the information on time is maintained even if the power supply is interrupted. For volatile memory cells, the information is lost in such a case.


The 1-bit storage element can be realized by means of fewer transistors and capacitors. At analog memory cells, the memory device of said elementary capacitor and digital memory cells are a ( 1-T DRAM ) or a plurality of transistors is required, such as in a static RAM, or in the back -coupled transistors, the so-called flip-flop.

Random access

Memory cells arranged in a matrix 2R × 2C. Via word lines and bit lines, the memory cells can be addressed and written or read. To this end, a row and a column decoder necessary. This allows direct access to any storage cells ( random access). Therefore, this arrangement is referred to as random access memory ( RAM).

Sequential access

Here, the addressing of commands, similar to hard drives. The types Compact Flash ( CF) and PCMCIA for example, use the tried and tested with disks ATA / ATAPI command set.

This addressing mode requires less pads on the chip, thus their production is cheaper.

See also: Memory card, sequential access

Semiconductor memory types

  • Table memory Volatile memory (RAM) SRAM Asynchronous SRAM   Low -Power SRAM
  • Burst SRAM   Pipelined Burst SRAM
  • Asynchronous DRAM standardized   FPM DRAM
  • BM- DRAM
  • Standardized SDRAM   SDR SDRAM
  • Embedded DRAM
  • Customized DRAM
  • Cache DRAM ( CDRAM )
  • Enhanced DRAM ( ESDRAM )
  • Virtual Channel DRAM ( VC DRAM)
  • Reduced Latency DRAM ( RLDRAM )
  • DRAM having low power   Mobile RAM
  • Pseudo - Satic RAM ( PSRAM )
  • Cellular RAM
  • Synclink DRAM ( SLDRAM )
  • Direct Rambus DRAM ( DRDRAM )
  • Sophisticated material ROM   MROM12
  • Programmable Read - Only Memory (PROM )   One Time Programmable ROM ( OTP)
  • Erasable Programmable ROM (EPROM )   Ultra - Violet Erasable PROM ( UV EPROM)
  • Electrically Erasable PROM ( EEPROM)
  • NAND Single Level Cell (SLC )   Standard NAND
  • Assisted AND gate (AG - AND)
  • Standard NAND
  • Twin Flash ( NROM )
  • Single Level Cell (SLC )   Standard NOR
  • Strata Flash
  • Mirror bit ( NROM )
  • Ferroelectric RAM (FRAM, FeRAM )
  • Magnetoresistive random access memory ( MRAM)
  • Phase Change Memory (PCM )
  • Phase -change RAM ( PCRAM )
  • Chalcogenide RAM (C- RAM)
  • Ovonic Unified Memory ( OUM )
  • Programmable Metallization Cell (PMC )
  • Organic RAM ( ORAM )
  • Conductive Bridge RAM ( CBRAM )
  • Nanotube RAM ( NRAM )
  • Racetrack memory (English Racetrack memory)
  • Memristor

Turnover figures

An overview of the different types of memory, the following table ( the sales figures indicated refer to the year 2005 and are the electronic Scout 2006 taken; SRAM is not included in processors SRAMs. ):

Manufacturer (selection)