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Encyclopedia > Phase change memory
This article contains information about scheduled or expected future computer chips.
It may contain preliminary or speculative information, and may not reflect the final specification of the product.
Computer memory types
Volatile
Non-Volatile

Phase-change memory (also known as PCM, PRAM, Ovonic Unified Memory and Chalcogenide RAM [C-RAM]) is a type of non-volatile computer memory. PRAM uses the unique behavior of chalcogenide glass, which can be "switched" between two states, crystalline and amorphous, with the application of heat. PRAM is one of a number of new memory technologies that are attempting to compete in the non-volatile role with the almost universal Flash memory, which has a number of practical problems these replacements hope to address. Image File history File links Current_event_marker. ... The terms storage (U.K.) or memory (U.S.) refer to the parts of a digital computer that retain physical state (data) for some interval of time, possibly even after electrical power to the computer is turned off. ... Volatile memory refers to computer memory that must be powered to maintain its data. ... Dynamic random access memory (DRAM) is a type of random access memory that stores each bit of data in a separate capacitor within an integrated circuit. ... A high-speed DRAM chip developed by Ramtron International Corporation, Colorado Springs, CO. It allows overlap of a read at the trailing end of a write operation to obtain its speed. ... Static random access memory (SRAM) is a type of semiconductor memory. ... 1T-SRAM is MoSyss implementation of embedded-DRAM on a conventional digital-logic (standard-cell) ASIC process. ... Z-RAM, short for zero capacitor DRAM is a new type of computer memory in development by Innovative Silicon Inc. ... TTRAM, short for Twin Transistor RAM is new type of computer memory in development by Renesas. ... Non-volatile memory, or non-volatile storage, is computer memory that can retain the stored information even when not powered. ... Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and other electronic devices. ... D23128C PROM on the board of ZX Spectrum A programmable read-only memory (PROM) or field programmable read-only memory (FPROM) is a form of digital memory where the setting of each byte is locked by a fuse or antifuse. ... Read-only memory (ROM) is used as a storage medium in computers. ... EPROM. The small quartz window admits UV light during erasure. ... An EEPROM (also called an E2PROM)[] or Electronically Erasable Programmable Read-Only Memory, is a non-volatile storage chip used in computers and other devices to store small amounts of volatile (configuration) data. ... A USB flash drive. ... Ferroelectric RAM (FRAM or FeRAM) is a type of non-volatile computer memory, similar to EEPROM but based on electric field orientation and with near-unlimited number (exceeding 1010 for 5V devices and even more for 3. ... Magnetoresistive Random Access Memory (MRAM) is a non-volatile computer memory (NVRAM) technology, which has been in development since the 1990s. ... Wikipedia does not have an article with this exact name. ... RRAM or Resistive Random Access Memory is a new non-volatile memory type begin developed by Sharp, Samsung, Fujitsu, Spansion, Macronix, Winbond and other companies. ... Nano-RAM, is a proprietary computer memory technology from the company Nantero. ... Non-Volatile Random Access Memory (NVRAM) is a type of computer memory chip which does not lose its information when power is turned off. ... A Chalcogenide glass is a glass containing a chalcogenide element (sulphur, selenium or tellurium) as a substantial constituent. ... Quartz crystal Synthetic bismuth hopper crystal Insulin crystals Gallium, a metal that easily forms large single crystals A huge monocrystal of potassium dihydrogen phosphate grown from solution by Saint-Gobain for the megajoule laser of CEA. In chemistry and mineralogy, a crystal is a solid in which the constituent atoms... An amorphous solid is a solid in which there is no long-range order of the positions of the atoms. ... A USB flash drive. ...

Contents

Background

The properties of chalcogenide glasses were first explored as a potential memory technology by Stanford Ovshinsky of Energy Conversion Devices in the 1960s. In the September 1970 issue of Electronics, Gordon Moore—co-founder of Intel—published an article on the technology. However, material quality and power consumption issues prevented commercialization of the technology. More recently, interest and research have resumed as flash and DRAM memory technologies are expected to encounter scaling difficulties as chip lithography shrinks. This article needs to be cleaned up to conform to a higher standard of quality. ... Electronics, an American trade journal published until 1995, was best known for publishing the April 19, 1965 article by Intel co-founder Gordon Moore in which he outlined what came to be known as Moores Law. ... Gordon Earle Moore (b. ... Intel Corporation (NASDAQ: INTC, SEHK: 4335), founded in 1968 as Integrated Electronics Corporation, is an American multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... Dynamic random access memory (DRAM) is a type of random access memory that stores each bit of data in a separate capacitor within an integrated circuit. ... Lithography stone and mirror-image print of a map of Munich. ...


The crystalline and amorphous states of chalcogenide glass have dramatically different electrical resistivity values, and this forms the basis by which data are stored. The amorphic, high resistance state is used to represent a binary 0, and the crystalline, low resistance state represents a 1. Chalcogenide is the same material utilized in re-writable optical media (such as CD-RW and DVD-RW). In those instances, the material's optical properties are manipulated, rather than its electrical resistivity, as chalcogenide's refractive index also changes with the state of the material. Electrical resistivity (also known as specific electrical resistance) is a measure of how strongly a material opposes the flow of electric current. ... The binary numeral system, or base-2 number system, is a numeral system that represents numeric values using two symbols, usually 0 and 1. ... Compact Disc ReWritable (CD-RW) is a rewritable optical disc format. ... The title given to this article is incorrect due to technical limitations. ... The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ...


Although PRAM has not yet reached the commercialization stage for consumer electronic devices, nearly all prototype devices make use of a chalcogenide alloy of germanium, antimony and tellurium (GeSbTe) called GST. It is heated to a high temperature (over 600°C), at which point the chalcogenide becomes a liquid. Once cooled, it is frozen into an amorphic glass-like state and its electrical resistance is high. By heating the chalcogenide to a temperature above its crystallization point, but below the melting point, it will transform into a crystalline state with a much lower resistance. This phase transition process can be completed in as quickly as five nanoseconds, according to a January 2006 Samsung Electronics patent application concerning the technology. This is comparable to conventional memory devices, for instance, modern DRAM cells have a switching time on the order of two nanoseconds. A chalcogenide is a binary compound consisting of a chalcogen and a more electropositive element. ... General Name, Symbol, Number germanium, Ge, 32 Chemical series metalloids Group, Period, Block 14, 4, p Appearance grayish white Atomic mass 72. ... General Name, Symbol, Number antimony, Sb, 51 Chemical series metalloids Group, Period, Block 15, 5, p Appearance silvery lustrous grey Standard atomic weight 121. ... General Name, Symbol, Number tellurium, Te, 52 Chemical series metalloids Group, Period, Block 16, 5, p Appearance silvery lustrous gray Standard atomic weight 127. ... GeSbTe, or Germanium-Antimony-Tellurium, is a phase change material from the group of chalcogenide glasses, used in rewritable optical discs and phase-change memory applications. ... A liquid will usually assume the shape of its container A liquid is one of the main states of matter. ... Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ... Frost crystallization on a shrub. ... The melting point of a crystalline solid is the temperature at which it changes state from solid to liquid. ... Dram can mean several things: For the imperial unit of volume see dram (unit), commonly used to describe a measure of Scotch whisky For the imperial unit of weight or mass see avoirdupois and apothecaries system (of mass) For the Armenian monetary unit see dram (currency) DRAM is a type...


PRAM vs. flash

It is the switching time that makes PRAM, and other replacements for flash memory, most interesting. Flash memory works by trapping electrons within the gate of a MOS transistor, which has been constructed with a special gate "stack" designed to trap charges (either on a floating gate or in insulator "traps"). The presence of a charge within the gate shifts the transistor's threshold voltage, and represents a logic 1. In order to change the state of the cell, from 1 to 0 for instance, this charge has to be removed. This is accomplished by applying a relatively large voltage across the cell, which effectively "sucks" the electrons out of the insulating layer. This burst of voltage is provided by a charge pump which takes some time to build up power. General write times for common Flash devices are on the order of one ms (for a block of data), about 100 000 times the typical 10 ns read time (for a byte). Thus PRAM can offer much higher performance in applications where writing quickly is important. Another difference, and potentially more interesting, is that each burst of voltage across the flash cell degrades it slightly, so most flash devices are only rated for something on the order of 10 000 to 100 000 writes per sector, and many flash controllers perform wear levelling to spread writes across many physical sectors. This makes them unsuitable for hard drive replacements in desktop computers[citation needed] and accounts for the shortened life-expectancy of many popular flash-based portable music devices.[citation needed] PRAM appears to have no such limit. Combined with their high speed, thousands of times quicker than conventional hard drives, this makes them particularly interesting in roles that are currently performance-limited by memory access speed. A USB flash drive. ... e- redirects here. ... The metal-oxide-semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is by far the most common field-effect transistor in both digital and analog circuits. ... Charge Trap Flash (Often abbreviated to CTF) is a new technology to fabricate a NAND flash device invented by Samsung Electronics in 2006. ... Depletion Region of an NMOS The threshold voltage of a MOSFET is usually defined as the gate voltage where a depletion region forms in the substrate (body) of the transistor. ... A charge pump is an electronic circuit that uses capacitors as energy storage elements to create either a higher or lower voltage power source. ... Wear levelling (also written -levelling) is a technique for prolonging the service life of some kinds of eraseable computer storage media, e. ... Typical hard drives of the mid-1990s. ...


Because they are not based on maintaining a floating charge in the cells, PRAM may be better for archival storage than Flash.


PRAM can be constructed in a number of different ways, but there are two notable methods. In one method, diodes are used as selection elements instead of transistors. This cuts down on cost since a diode is smaller and cheaper than a transistor. Taking this one degree further, Macronix pioneered cross-point PRAM, which is composed simply of a self-aligned chalcogenide cell sandwiched between the address lines (that is, with no transistor or diode selection element). In this manner, the chalcogenide itself serves as the rectifying element so the low-resistance crystalline state is never used. Instead, the cell is manipulated between distinct amorphic states. This type of cell is very low cost since it only requires two masking steps. Types of diodes closeup, showing germanium crystal In electronics, a diode is a component that restricts the direction of movement of charge carriers. ... Assorted discrete transistors A transistor is a semiconductor device, commonly used as an amplifier. ...


2000 and later

In August of 2004, Nanochip licensed PRAM technology for use in MEMS (micro-electric-mechanical-systems) probe storage devices. These devices are not solid state. Instead, a very small platter coated in chalcogenide is dragged beneath many (thousands or even millions) of electrical probes which can read and write the chalcogenide. Hewlett-Packard's micro-mover technology can accurately position the platter to 3 nanometers so densities of more than 1 terabit per square inch will be possible if the technology can be perfected. The basic idea is to reduce the amount of wiring needed on-chip; instead of wiring every cell, the cells are placed closer together and read by current passing through the MEMS probes, acting like wires. A mite next to a gear set produced using MEMS. Courtesy Sandia National Laboratories, SUMMiTTM Technologies, www. ... A terabit 1 terabit = 1012 bits = 1,000,000,000,000 bits (one trillion, long scale: one billion) The terabit is closely related to the tebibit, which is equal to 240 bits. ...


In September 2006, Samsung announced a prototype 512 Mb device using diode switches[1]. The announcement was something of a surprise, and it was especially notable for its fairly high density. The prototype features a cell size of only 46.7 nm, which is even better than commercial Flash devices currently available. Although Flash devices of even higher capacities were already available (8 GB was just coming to market for instance) other Flash competitors are generally much lower density. The only production MRAM and FeRAM devices are only 4 Mb, for example. The high density of this prototype PRAM device suggests that it could be a real Flash competitor, and not limited to niche roles as these other devices have been. This is especially true in the case of NOR Flash, which allows per-bit addressing (the more common NAND flash can only be accessed in "banks" of many bytes at a time), which has generally lagged NAND densities and appears to be about the same density as this PRAM device. Samsung Group is one of the largest South Korean business groupings. ... Magnetoresistive Random Access Memory (MRAM) is a non-volatile computer memory (NVRAM) technology, which has been in development since the 1990s. ... Ferroelectric capacitor is a capacitor used in digital electronics as a component of computer memory. ... ...


Samsung's announcement was followed by one from Intel and STMicroelectronics, who demonstrated their own PCM devices at the 2006 Intel Developer Forum in October[2]. They showed a 128 Mb part that had very recently started fabbing at STMicroelectronics's line in Italy. Intel stated that the devices were strictly proof-of-concept, but they expect to start sampling within months, and have widespread commercial production within a few years. Intel is already the leading NOR Flash producer, and appears to be aiming their PCM at the same market as Samsung. Intel Corporation (NASDAQ: INTC, SEHK: 4335), founded in 1968 as Integrated Electronics Corporation, is an American multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... STMicroelectronics is an international leading supplier of semiconductors. ... Intel Developer Forum (IDF), is a twice yearly gathering of technologists to discuss Intel products and products based around Intel products. ...


PCM is also a promising technology in the military and aerospace industries where radiation effects make the use of standard non-volatile memories such as Flash impractical. PCM memory devices have been introduced by BAE Systems, referred to as C-RAM, claiming excellent radiation tolerance (rad-hard) and latchup immunity. Additionally, BAE claims a write cycle endurance of 108, which will allow it to be a contender for replacing PROMs and EEPROMs in space systems. BAE Systems plc is the worlds fourth largest defence contractor,[3] the largest in Europe and a commercial aerospace manufacturer. ... Microelectronics designed for environments with high levels of ionizing radiation have special design challenges. ... A latchup is the inadvertent creation of a low-impedance path between the power supply rails as a result of triggering a parasitic device, which then opens and acts as a short circuit, leading to ceasement of proper function of the part and perhaps even its destruction with the overcurrent. ... This article or section does not cite any references or sources. ... An EEPROM (also called an E2PROM)[] or Electronically Erasable Programmable Read-Only Memory, is a non-volatile storage chip used in computers and other devices to store small amounts of volatile (configuration) data. ...


Timeline

  • September 1966: Stanford Ovshinsky files first patent on phase change technology
  • June 1969: US Patent 3,448,302 licensed to Ovshinsky claims first reliable operation of phase change memory
  • September 1970: Gordon Moore publishes research in Electronics Magazine
  • June 1999: Ovonyx joint venture is formed to commercialize PRAM technology
  • November 1999: Lockheed Martin works with Ovonyx on PRAM for space applications
  • February 2000: Intel invests in Ovonyx, licenses technology
  • December 2000: ST Microelectronics licenses PRAM technology from Ovonyx
  • March 2002: Macronix files a patent application for transistor-less PRAM
  • July 2003: Samsung begins work on PRAM technology
  • 2003 through 2005: PRAM-related patent applications filed by Toshiba, Hitachi, Macronix, Renesas, Elpida, Sony, Matsushita, Mitsubishi, Infineon and more
  • August 2004: Nanochip licenses PRAM technology from Ovonyx for use in MEMS probe storage
  • August 2004: Samsung announces successful 64Mbit PRAM array
  • February 2005: Elpida licenses PRAM technology from Ovonyx
  • September 2005: Samsung announces successful 256Mbit PRAM array, touts 400µA programming current
  • October 2005: Intel increases investment in Ovonyx
  • December 2005; Hitachi and Renesas announce 1.5volt PRAM with 100µA programming current
  • December 2005: Samsung licenses PRAM technology from Ovonyx
  • July 2006: BAE Systems (formerly Lockheed Martin) introduces a Radiation Hardened C-RAM 512Kx8 chip
  • September 2006: Samsung announces 512Mbit PRAM device
  • October 2006: Intel and STMicroelectronics show a 128Mbit PRAM chip
  • December 2006: IBM Research Labs demonstrate a prototype 3 by 20 nanometers[3]
  • January 2007: Qimonda licenses PRAM technology from Ovonyx
  • April 2007: Intel's chief technology officer Justin Rattner is set to give the first public demonstration of the company's PRAM (phase-change RAM) technology [1]

// Qimonda AG, the new memory company carved out of Infineon Technologies AG on May 1, 2006, is the 2nd largest DRAM company worldwide (according to the industry research firm Gartner Dataquest), a leader in 300mm manufacturing, and one of the top suppliers of DRAM products for the PC and Server...

References

  1. ^ SAMSUNG Introduces the Next Generation of Nonvolatile Memory - PRAM
  2. ^ Intel Previews Potential Replacement for Flash
  3. ^ Phase Change to Replace Flash?

External links

  • Ovonyx, Inc.
  • Energy Conversion Devices, Inc.
  • Hitachi/Renesas Low-Power PRAM
  • Hewlett-Packard Probe Storage
  • Nanochip
  • Samsung 512Mbit PRAM prototype
  • BAE C-RAM Radiation-Hardened NVM press release
  • BAE C-RAM Radiation-Hardened NVM data sheet

 
 

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