- This article is about an information storage medium. For other uses, see Fram (disambiguation).
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Ferroelectric RAM (FeRAM or FRAM[1]) is a low-density random access memory. DDR SDRAM ( double data rate synchronous dynamic random access memory) is a class of memory Integrated circuit used in Computers It achieves nearly twice Static random access memory (SRAM is a type of Semiconductor memory where the word static indicates that unlike ''dynamic'' RAM (DRAM, it does not Z-RAM, short for " zero capacitor RAM " is a new type of Computer memory in development by Innovative Silicon Inc Twin Transistor RAM ( TTRAM) is a new type of Computer memory in development by Renesas The Williams tube or the Williams-Kilburn tube (after inventors Freddie Williams and Tom Kilburn) developed about 1946 or 1947 Genesis in radar The basic concept of the delay line originated with World War II Radar research as a system to reduce clutter from reflections from the ground Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, is Computer memory that can retain the stored information A programmable read-only memory ( PROM) or field programmable read-only memory ( FPROM) is a form of digital memory where the setting of each bit is EEPROM (also written E2PROM and pronounced e-e-prom or simply e-squared which stands for E lectrically E rasable P rogrammable An EPROM, or E rasable P rogrammable '''''R'''ead-'''O'''nly '''M'''emory'', is a type of memory chip that retains its EEPROM (also written E2PROM and pronounced e-e-prom or simply e-squared which stands for E lectrically E rasable P rogrammable Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed Magnetoresistive Random Access Memory ( MRAM) is a non-volatile computer memory ( NVRAM) technology which has been under development since The programmable metallization cell, or PMC, is a new form of non-volatile Computer memory being developed at Arizona State University and Phase-change memory (also known as PCM, PRAM, PCRAM, Ovonic Unified Memory, Chalcogenide RAM and C-RAM) is a type This article is about the music device manufacturer For the computer memory system see SONOS. Resistive random-access memory ( RRAM) is a new Non-volatile memory type being developed by Fujitsu, Sharp, Samsung, Micron IBM Racetrack Memory is an experimental Non-volatile memory device under development at IBM 's Almaden Research Center by a team led by Stuart Nano-RAM is a proprietary Computer memory technology from the company Nantero. Drum memory is a magnetic Data storage device and was an early form of Computer memory widely used in the 1950s and into the 1960s invented by Gustav Tauschek Magnetic core memory, or ferrite-core memory, is an early form of Random access Computer memory. Prehistory twistor memory Bubble memory is largely the brainchild of a single person Andrew Bobeck. Twistor is a form of Computer memory, similar to Core memory, formed by wrapping or closing Magnetic tape around a current-carrying wire Computer storage density is a measure of the quantity of information Bits that can be stored on a given length of track, area of Surface, or in a given It is similar in construction to DRAM but uses a ferroelectric layer to achieve non-volatility. Ferroelectricity is a physical property of a material whereby it exhibits a spontaneous electric polarization, the direction of which can be switched between equivalent
FeRAM is with nvSRAM, MRAM, PCM and PMC one of several alternative non-volatile memory technologies that aim at replacing Flash memory. nvSRAM is a type of non-volatile computer memory. It is similar in operation to SRAMs The current market for non volatile memory is dominated by BBSRAMs Magnetoresistive Random Access Memory ( MRAM) is a non-volatile computer memory ( NVRAM) technology which has been under development since Phase-change memory (also known as PCM, PRAM, PCRAM, Ovonic Unified Memory, Chalcogenide RAM and C-RAM) is a type The programmable metallization cell, or PMC, is a new form of non-volatile Computer memory being developed at Arizona State University and Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, is Computer memory that can retain the stored information Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed The market for non-volatile memory is largely dominated by high-density Flash memory but FeRAM offers a number of advantages, notably lower power usage, faster write speed and a much greater maximum number (exceeding 1016 for 3. 3 V devices) of write-erase cycles.
Neither FeRAM nor MRAM even come close to offering the high storage density nor the low cost per storage bit of Flash, currently 256 gigabytes in laptop solid-state drives (SSDs), while nvSRAM, PCM (also called PRAM) and PMC memory density is significantly higher than FeRAM and MRAM. Phase-change memory (also known as PCM, PRAM, PCRAM, Ovonic Unified Memory, Chalcogenide RAM and C-RAM) is a type
FeRAM is competitive in niche applications where only tiny amounts of data need to be stored while its operating characteristics give it an advantage over Flash. Compared to its more modern competitors MRAM and PCM, FeRAM volume production at Fujitsu began in 1999. is a Japanese company specializing in Semiconductors Computers ( Supercomputers Personal computers, servers, Telecommunications FeRAMs at 1 megabit density were available in high volume in 2006 from both Fujitsu and Ramtron. } Ramtron International Corporation ( located in Colorado Springs CO, is the main supplier of F-RAM chips and integrated semiconductor products Simtek Corporation [1] introduced the first first 256K monolithic nvSRAM in 1994, currently 4 megabit nvSRAM chips are available. Limited volume production of a 4 megabit MRAM began at Freescale Semiconductor in July 2006. Freescale Semiconductor Inc is an American Semiconductor manufacturer Intel Corporation and STMicroelectronics began shipping prototype samples of 128 megabit PCM memory in February 2008 [2]. STMicroelectronics (,)is an franco-italian Electronics and Semiconductor manufacturer headquartered in in Geneva, Switzerland. The first chip containing high-density and low-cost PMC memory was announced by ASU's Center for Applied Nanoionics in October 2007 to become available in 18 months[3].
Development of FeRAM began in the late 1980s. Work was done in 1991 at NASA's Jet Propulsion Laboratory on improving methods of read out, including a novel method of non-destructive readout using pulses of UV radiation. [2]
Much of the current FeRAM technology was developed by Ramtron a fabless semiconductor company. A fabless semiconductor company specializes in the design and sale of Hardware devices implemented on Semiconductor One major licensee is Fujitsu, who operate what is probably the largest semiconductor foundry production line with FeRAM capability. In the Microelectronics industry a semiconductor fabrication plant (commonly called a fab) is a factory where devices such as Integrated circuits are manufactured Since 1999 they have been using this line to produce standalone FeRAMs, as well as specialized chips (e. g. chips for smart cards) with embedded FeRAMs within. Fujitsu produces devices for Ramtron. Several other companies are known to be active in developing FeRAM. For example, since at least 2001 Texas Instruments has collaborated with Ramtron to develop FeRAM test chips in a modified 130 nm process. Texas Instruments ( better known in the electronics industry (and popularly as TI, is an American company based in Dallas, Texas, USA In the fall of 2005 Ramtron reported that they were evaluating prototype samples of an 8 megabit FeRAM manufactured using Texas Instruments' FeRAM process. Fujitsu and Seiko-Epson were in 2005 collaborating in the development of a 180 nm FeRAM process. FeRAM research projects have also been reported at Samsung, Matsushita, Oki, Toshiba, Infineon, Hynix, Symetrix, Cambridge University, University of Toronto and the Interuniversity Microelectronics Centre (IMEC, Belgium). The Samsung Group ( Korean:, Samsung Guerup) is South Korea 's largest company or Chaebol and the world's largest conglomerate ( is a Japanese electronics company founded (as Meikosha Ltd in January 1881 by Kibataro Oki ( is a multinational conglomerate manufacturing company headquartered in Tokyo, Japan. Infineon Technologies AG () was founded in April 1999 when the Semiconductor operations of parent company Siemens AG, were spun off to form a separate Hynix Semiconductor Inc of South Korea is a memory Semiconductor supplier of Dynamic random access memory ('DRAM' chips and Flash memory Symetrix is an Audio electronics manufacturer based in Mountlake Terrace WA, USA The University of Cambridge (often Cambridge University) located in Cambridge, England, is the second-oldest university in the This article is about the University of Toronto's St George Campus IMEC ( Interuniversity Microelectronics Centre) is a micro- and Nanoelectronics research center located in Leuven, Belgium with affiliated The Kingdom of Belgium is a Country in northwest Europe. It is a founding member of the European Union and hosts its headquarters as well as those
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Description
Conventional DRAM consists of a grid of small capacitors and their associated wiring and signaling transistors. A capacitor is a passive electrical component that can store Energy in the Electric field between a pair of conductors In Electronics, a transistor is a Semiconductor device commonly used to amplify or switch electronic signals Each storage element, a cell, consists of one capacitor and one transistor, a so-called "1T-1C" device. DRAM cells scale directly with the size of the semiconductor fabrication process being used to make it. Semiconductor device fabrication is the process used to create chips the Integrated circuits that are present in everyday Electrical and electronic For instance, on the 90 nm process used by most memory providers to make DDR2 DRAM, the cell size is 0. 22 μm², which includes the capacitor, transistor, wiring, and some amount of "blank space" between the various parts – it appears 35% utilization is typical, leaving 65% of the space wasted.
Data in a DRAM is stored as the presence or lack of an electrical charge in the capacitor, with the lack of charge generally representing "0". Writing is accomplished by activating the associated control transistor, draining the cell to write a "0", or sending current into it from a supply line if the new value should be "1". Reading is similar in nature; the transistor is again activated, draining the charge to a sense amplifier. If a pulse of charge is noticed in the amplifier the cell held a charge and thus reads "1", the lack of such a pulse indicates a "0". Note that this process is destructive, once the cell has been read, if it did hold a "1" it must be re-charged to that value again. Since a cell loses its charge after some time due to leak currents, it needs to be actively refreshed at intervals.
The 1T-1C storage cell design in an FeRAM is similar in construction to the storage cell in widely used DRAM in that both cell types include one capacitor and one access transistor. In a DRAM cell capacitor a linear dielectric is used whereas in an FeRAM cell capacitor the dielectric structure includes ferroelectric material, typically lead zirconate titanate (PZT). Ferroelectricity is a physical property of a material whereby it exhibits a spontaneous electric polarization, the direction of which can be switched between equivalent Lead zirconate titanate ( 0 x Ceramic Perovskite material that shows a marked piezoelectric effect.
As shown in the figure, a ferroelectric material has a nonlinear relationship between the applied electric field and the apparent stored charge. Specifically, the ferroelectric characteristic has the form of a hysteresis loop, which is very similar in shape to the hysteresis loop of ferromagnetic materials. A system with hysteresis can be summarised as a system that may be in any number of states independent of the inputs to the system Ferromagnetism is the basic mechanism by which certain materials (such as Iron) form Permanent magnets and/or exhibit strong interactions with Magnets it The dielectric constant of a ferroelectric is typically much higher than that of a linear dielectric because of the effects of semi-permanent electric dipoles formed in the crystal structure of the ferroelectric material. Measurement The relative static permittivity εr can be measured for static Electric fields as follows first the Capacitance of a test In physics there are two kinds of dipoles ( Hellènic: di(s- = two- and pòla = pivot hinge An electric dipole is a In Mineralogy and Crystallography, a crystal structure is a unique arrangement of Atoms in a Crystal. When an external electric field is applied across a dielectric, the dipoles tend to align themselves with the field direction, produced by small shifts in the positions of atoms and shifts in the distributions of electronic charge in the crystal structure. After the charge is removed, the dipoles retain their polarization state. Typically binary "0"s and "1"s are stored as one of two possible electric polarizations in each data storage cell. For example, in the figure a "1" is encoded using the negative remnant polarization "-Pr", and a "0" is encoded using the positive remnant polarization "+Pr".
Operationally FeRAM is similar to DRAM. Writing is accomplished by applying a field across the ferroelectric layer by charging the plates on either side of it, forcing the atoms inside into the "up" or "down" orientation (depending on the polarity of the charge), thereby storing a "1" or "0". Reading, however, is somewhat different than in DRAM. The transistor forces the cell into a particular state, say "0". If the cell already held a "0", nothing will happen in the output lines. If the cell held a "1", the re-orientation of the atoms in the film will cause a brief pulse of current in the output as they push electrons out of the metal on the "down" side. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J The presence of this pulse means the cell held a "1". Since this process overwrites the cell, reading FeRAM is a destructive process, and requires the cell to be re-written if it was changed.
Generally the operation of FeRAM is similar to ferrite core memory, one of the primary forms of computer memory in the 1960s. Magnetic core memory, or ferrite-core memory, is an early form of Random access Computer memory. In comparison, FeRAM requires far less power to flip the state of the polarity, and does so much faster. The requirement for a write cycle for each read cycle, together with the high but not infinite write cycle limit, poses a potential problem for some special applications.
Comparison with other systems
Density
The main determinant of a memory system's cost is the density of the components used to make it up. Smaller components, and less of them, means that more cells can be packed onto a single chip, which in turn means more can be produced at once from a single silicon wafer. This improves yield, which is directly related to cost.
The lower limit to this scaling process is an important point of comparison, generally the technology that scales to the smallest cell size will end up being the least expensive per bit. FeRAM and DRAM are constructionally similar, and can generally be built on similar lines at similar sizes. In both cases the lower limit seems to be defined by the amount of charge needed to trigger the sense amplifiers. For DRAM this appears to be a problem at around 55 nm, at which point the charge stored in the capacitor is too small to be detected. It is not clear if FeRAM can scale to the same size, as the charge density of the PZT layer may not be the same as the metal plates in a normal capacitor.
That said, to date the only commercial FeRAM devices appear to have been produced on many-generations-old fabs, at 350 nm. Experimental processes at 180 nm and 130 nm are ongoing. Early models required two FeRAM cells per bit, leading to very low densities, but this limitation has since been removed.
Power consumption
The key advantage to FeRAM over DRAM is what happens between the read and write cycles. In DRAM, the charge deposited on the metal plates leaks across the insulating layer and the control transistor, and disappears. In order for a DRAM to store data for anything other than a microscopic time, every cell must be periodically read and then re-written, a process known as refresh. Each cell must be refreshed many times every second (~65 ms[3]) and this requires a continuous supply of power.
In contrast, FeRAM only requires power when actually reading or writing a cell. The vast majority of power used in DRAM is used for refresh, so it seems reasonable to suggest that the benchmark quoted by TTR-MRAM researchers is useful here too, indicating power usage about 99% lower than DRAM.
Another non-volatile memory type is Flash RAM, and like FeRAM it does not require a refresh process. Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed Flash works by pushing electrons across a high-quality insulating barrier where they get "stuck" on one terminal of a transistor. In Electronics, a transistor is a Semiconductor device commonly used to amplify or switch electronic signals This process requires high voltages, which are built up in a charge pump over time. A charge pump is an Electronic circuit that uses Capacitors as energy storage elements to create either a higher or lower Voltage power source This means that FeRAM could be expected to be lower power than Flash, at least for writing, as the write power in FeRAM is only marginally higher than reading. For a "mostly-read" device like the iPod nano the difference might be slight, but for devices with more balanced read and write, like a digital camera, the difference could be expected to be much higher. The iPod Nano (marketed lowercase as iPod nano) is a Portable media player designed and marketed by Apple Inc. Many compact digital still cameras can record Sound and moving Video as well as still Photograph.
Speed
DRAM speed is limited by the speed at which the current stored in the cells can be drained (for reading) or stored (for writing). Generally this ends up being defined by the capability of the control transistors, the capacitance of the lines carrying power to the cells, and the heat that power generates.
FeRAM is based on the physical movement of atoms in response to an external field, which happens to be extremely fast, settling in about 1 ns. In theory, this means that FeRAM could be much faster than DRAM. However, since power has to flow into the cell for reading and writing, the electrical and switching delays would likely be similar to DRAM overall. It does seem reasonable to suggest that FeRAM would require less charge than DRAM, because DRAMs need to hold the charge, whereas FeRAM would have been written to before the charge would have drained. That said, there is a delay in writing because the charge has to flow through the control transistor, which limits current somewhat.
In comparison to Flash the advantages are much more obvious. Whereas the read operation is likely to be similar in performance, the charge pump used for writing requires a considerable time to "build up" power, a process that FeRAM does not need. Flash memories commonly need about 1 ms to write a bit, whereas even current FeRAMs are at least 100 times that speed.
The theoretical performance of FeRAM is not entirely clear. Existing 350 nm devices have read times on the order of 50 to 60 ns. Although slow compared to modern DRAMs, which can be found with times on the order of 2 ns, common 350 nm DRAMs operated with a read time of about 35 ns,[4] so FeRAM performance appears to be comparable given the same fab.
Overall
FeRAM remains a relatively small part of the overall semiconductor market. In 2005 worldwide semiconductor sales were US $235 billion (according to the Gartner Group), with the flash memory market accounting for US $18. Gartner, Inc ( is an information technology research and advisory firm headquartered in Stamford, Connecticut. 6 billion (according to IC Insights). The 2005 annual sales of Ramtron, perhaps the largest FeRAM vendor, were reported to be US $32. 7 million. Flash memory is currently the overwhelmingly dominant NVRAM technology, and this situation seems likely to continue for at least the rest of the decade. The much larger sales of flash memory compared to the alternative NVRAMs support a much larger research and development effort. Flash memory is produced using the latest semiconductor linewidths (e. g. 70 nm at Samsung in 2006) whereas production FeRAMs are produced in linewidths that are several generations older (e. g. 350 nm at Fujitsu in 2006). Flash memory cells can store multiple bits per cell (currently 2 in the highest density NAND flash devices), and the number of bits per flash cell is projected to increase to 4 or even to 8 as a result of innovations in flash cell design. The areal bit densities of flash memory are consequently much higher than FeRAM, and thus the cost per bit of flash memory is orders of magnitude cheaper than FeRAM.
FeRAM must find niche markets where its advantages over flash (e. g. faster write speed and greater write-erase endurance) offset its higher cost and much smaller storage density. The density of FeRAM arrays might be increased by improvements in FeRAM foundry process technology and cell structures, such as the development of vertical capacitor structures (in the same way as DRAM) to reduce the area of the cell footprint. However, reducing the cell size may cause the data signal to become to too weak to be detectable. Both the existing and new markets for FeRAM need to be exploited to support increased levels of research and development spending. In its 2005 annual meeting Ramtron reported significant sales of its FeRAM products in a variety of sectors including (but not limited to) electronic metering, automotive (e. g. black boxes, smart air bags), business machines (e. An Event Data Recorder or EDR is a device installed in some Automobiles and Trucks to record information related to vehicle crashes or accidents An airbag is part of a vehicle's safety restraint system a flexible envelope designed for rapid inflation in an automobile Collision, to prevent vehicle occupants g. printers, RAID disk controllers), instrumentation, medical equipment, industrial microcontrollers, and radio frequency identification tags. RAID — which stands for Redundant Array of Inexpensive Disks,or alternatively Redundant Array of Independent Disks (a less specific name and thus now the A microcontroller (also MCU or µC is a functional Computer system-on-a- chip. Radio-frequency identification ( RFID) is an automatic identification method relying on storing and remotely retrieving data using devices called RFID tags or Ramtron's product mix might not be representative of the overall FeRAM market; however, its sales numbers give a useful indication of the wide variety of possible applications of FeRAM. The other emerging NVRAMs, such as MRAM, may seek to enter similar niche markets in competition with FeRAM. According to Gartner, the flash memory market grew at an annual rate of 20% in 2005. Judging from Ramtron's released sales numbers, in 2005 the FeRAM market was probably growing at least as fast as the flash memory market and probably faster. The company is projecting annual sales growth in the range of from 30 to 35% in 2006 and 2007 across its diversified FeRAM product line.
It is possible to make FeRAM cells using two additional masking steps during conventional CMOS semiconductor manufacture, leading to the possibility of full integration of FeRAM into other chips. Flash typically requires nine masks. This makes FeRAM particularly attractive as an embedded non-volatile memory on microcontrollers, where the simpler process can reduce costs. However, the materials used to make FeRAMs are not commonly used elsewhere in integrated circuit manufacturing. Both the PZT ferroelectric layer and the noble metals used for electrodes raise process compatibility and contamination issues.
References
- ^ FRAM is used by Ramtron and its licencees to refer to FeRAM technology developed by Ramtron. FeRAM is the accepted generic acronym for ferroelectric random-access memory.
- ^ Optically Addressed Ferroelectric Memory with Non-Destructive Read-Out
- ^ TN-47-16: Designing for High-Density DDR2 Memory
- ^ IEEE Xplore - Login
See also
- MRAM
- nvSRAM
- Phase-change memory
- Programmable metallization cell
- Memristor
- Racetrack memory
- Flash memory
- Stabilizing ferroelectric materials
- Ferroelectricity
- lead zirconate titanate
- Black box (disambiguation)#transportation
External links
- FRAM overview by Fujitsu
- FeRAM Tutorial by the Department of Electrical and Computer Engineering at the University of Toronto
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