Semiconductor memory

This article covers the basics. For the commercially available designs see memory module

A semiconductor memory is a data memory that consists of a semiconductor .

Microelectronic memory structures are implemented in and on a semiconductor crystal so that a memory chip (see also Die ) is created. The chips are completed to form integrated circuits or processed further without caps.

The data are stored in the integrated circuits in the form of binary electronic switching states . Its predecessors were the magnetically operating core memories , which were not replaced by semiconductor memories until the early 1970s. More recent developments aim to combine the magnetic storage principle microelectronically into high-density, non-volatile memories ( MRAM ).

Storage cell

Various semiconductor memories

description

A memory cell is the physical realization of the smallest unit of a memory of logical states. The term depending on the context, either the realization of the smallest unit, the 1- bit - storage element , or the realization of the smallest addressable , that is in an access readable or writable, unit, a so-called word or data word consisting of n bits exists (n> 1).

Nowadays, personal computers work with a word length (also called “word width”) of 32 or 64 bits. In the past, for example in the first pocket calculators , memory cells were 4 bits (a half-byte or nibble ) in size. The first PCs, on the other hand, had 8-bit wide memory cells. For simple controls (see: Microcontroller ) 8 bits are still used today.

Word widths of 6 or 7 bits were also used in earlier computers , since alphanumeric processing could be carried out with 64 or 128 storable characters . However, these memories were not yet 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. The information is permanently retained in non-volatile memory cells, even if the power supply is interrupted. In the case of volatile memory cells, the information is lost in such a case.

realization

The 1-bit memory element can be implemented using fewer transistors and capacitors . In the case of analog memory cells, the elementary memory component is the capacitor, and in the case of digital memory cells, one (1-T DRAM ) or more transistors are required, e.g. B. with static RAM or with feedback transistors, the so - called flip - flops .

Random access

Memory cells are arranged in a 2 ^R × 2 ^C matrix. The memory cells are addressed and written to or read out via word lines and bit lines. A row and a column decoder are required for this. This enables direct access to any memory cells ( random access ). Therefore this arrangement is called Random Access Memory (RAM).

Sequential access

Addressing takes place here using commands, similar to hard drives . The CompactFlash (CF) and PCMCIA designs use e.g. B. the tried and tested ATA / ATAPI command set for hard disks .

This type of addressing requires fewer contact areas on the chip, making it cheaper to manufacture.

See also: memory card , sequential access

Semiconductor memory types

Family tree of semiconductor memory

Table storage Volatile memory ( RAM ) SRAM Asynchronous SRAM Low power SRAM Synchronous SRAM Burst SRAM Pipelined burst SRAM E.g. SRAM QDR-SRAM DRAM Asynchronous DRAM Standardized FPM DRAM BM-DRAM EDO DRAM Not standardized WRAM VRAM Synchronous DRAM ( SDRAM ) Standardized SDRAM SDR-SDRAM DDR SDRAM QDR-SDRAM ( DDR2-SDRAM ) ODR-SDRAM ( DDR3-SDRAM ) GDDR-SDRAM Non-standardized SDRAM embedded DRAM customized DRAM cache DRAM ( CDRAM ) enhanced DRAM ( ESDRAM ) virtual channel DRAM ( VC DRAM ) reduced latency DRAM ( RLDRAM ) Low performance DRAM mobile RAM COSMO RAM pseudo-static RAM ( PSRAM ) cellular RAM Protocol based DRAM synclink DRAM ( SLDRAM ) direct Rambus DRAM ( DRDRAM ) XDR DRAM Non-volatile memory Mature material ROME MROM 1 2 Programmable Read-Only Memory (PROM) One Time Programmable ROM (OTP) Erasable Programmable ROM ( EPROM ) ultra-violet erasable PROM (UV- EPROM ) electrically erasable PROM ( EEPROM ) Flash NAND Single Level Cell (SLC) Standard NAND Assisted Gate AND (AG-AND) Multi-Level Cell (MLC) Standard NAND Multibit Twin Flash (NROM) NOR Single Level Cell (SLC) Standard NOR Multi-Level Cell (MLC) Strata Flash Multibit Mirror Bit (NROM) Innovative material Ferroelectric RAM (FRAM, FeRAM) Magnetoresistive RAM (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

1 A PLE corresponds to an MROM and vice versa 2 Microcontrollers with MROM are still produced in large numbers (as of the end of 2008).

Meaning of the most important abbreviations

abbreviation	meaning
R.A.M.	Random Access Memory
ROME	Read-only memory
SRAM	Static RAM
DRAM	Dynamic RAM
PRAM	Phase-change RAM
MRAM	Magnetoresistive RAM
M ...	Mask programmed
P…	Programmable
EP ...	Erasable and programmable
EEP ...	Electrically erasable and programmable
SD	Synchronous Dynamic (RAM)
GDR	Double data rate (RAM)
QDR	Quad Data Rate (RAM)
ODR	Octo Data Rate (RAM)
GDDR	Graphics DDR (RAM)
RDRAM	Rambus DRAM
E.g. SRAM	Zero Bus turnaround SRAM

	in production
	production stopped
	in development

Sales figures

The following table gives an overview of the different memory types (the sales figures given relate to the year 2005 and are taken from the Elektronik Scout 2006; SRAM does not stand for SRAMs contained in processors.):

Sales figures for semiconductor memory components in 2005 (source: Elektronik Scout 2006)

Storage technology			sales
Volatile memory (RAM)
Static RAM ( SRAM )			$ 2 billion
Dynamic RAM ( DRAM )			$ 27 billion
Non-volatile memory
Mature material	Read Only Memory ( ROM )		$ 2 billion
	Flash	NAND	$ 8 billion
		NOR	$ 9 billion
Innovative material			$ 0.01 billion
Total sales			$ 48 billion

Manufacturer (selection)

• Acer
• Adata
• Corsair
• Crucial
• Cypress Semiconductor
• Elpida Memory ( joint venture between NEC and Hitachi )
• Hewlett-Packard
• Hitachi
• Hynix Semiconductor (formerly Hyundai Electronics)
• IBM
• Infineon
• Kingston Technology
• Micron Technology
• Mitsubishi
• NXP Semiconductors (formerly Philips )
• OCZ Technology
• Samsung Electronics
• Sony
• Toshiba
• Transcend

See also

• Soft error

Web links

• Jürgen Plate: Introduction to data processing systems - 7th storage unit (main memory) . FH Munich.
• Interactive CMOS 6T SRAM CELL

Individual evidence

1. ↑ Advances in MRAM technology ( Memento of the original from April 13, 2016 in the Internet Archive ) Info: The  archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . itse-wissen.de. Retrieved September 30, 2010.