Ferroelectric RAM
Encyclopedia
Ferroelectric RAM is a random-access memory
similar in construction to DRAM
but uses a ferroelectric layer instead of a dielectric
layer to achieve non-volatility. FeRAM is one of a growing number of alternative non-volatile memory
technologies that offer the same functionality as Flash memory
. FeRAM advantages over Flash include: lower power usage, faster write performance and a much greater maximum number (exceeding 1016 for 3.3 V devices) of write-erase cycles. Disadvantages of FeRAM are much lower storage densities
than Flash devices, storage capacity limitations, and higher cost.
in his master's thesis, Ferroelectrics for Digital Information Storage and Switching, published in 1952.
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. Much of the current FeRAM technology was developed by Ramtron, a fabless semiconductor company
. One major licensee is Fujitsu
, who operate what is probably the largest semiconductor foundry production line with FeRAM capability. 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. Since at least 2001 Texas Instruments
has collaborated with Ramtron to develop FeRAM test chips in a modified 130 nm process. 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
).
consists of a grid of small capacitor
s and their associated wiring and signaling transistor
s. 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. 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 in general 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 must 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).
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. 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. 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. 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".
In terms of operation, 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 electron
s out of the metal on the "down" side. 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.
In general, the operation of FeRAM is similar to ferrite core memory, one of the primary forms of computer memory in the 1960s. In comparison, FeRAM requires far less power to flip the state of the polarity, and does so much faster.
The lower limit to this scaling process is an important point of comparison. In general, the technology that scales to the smallest cell size will end up being the least expensive per bit. In terms of construction, FeRAM and DRAM are similar, and can in general 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 as to whether 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.
An additional limitation on size is that materials tend to stop being ferroelectric when they are too small. (This effect is related to the ferroelectric's "depolarization field".) There is ongoing research on addressing the problem of stabilizing ferroelectric materials; one approach, for example, uses molecular adsorbates.
To date, the commercial FeRAM devices have been produced at 350 nm and 130 nm. Early models required two FeRAM cells per bit, leading to very low densities, but this limitation has since been removed.
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 works by pushing electrons across a high-quality insulating barrier where they get "stuck" on one terminal of a transistor
. This process requires high voltages, which are built up in a charge pump
over time. 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 the difference might be slight, but for devices with more balanced read and write the difference could be expected to be much higher.
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. However, 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" current, a process that FeRAM does not need. Flash memories commonly need a millisecond or more to complete a write, whereas current FeRAMs may complete a write in less than 150 ns.
The theoretical performance of FeRAM is not entirely clear. Existing 350 nm devices have read times on the order of 50-60 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, so FeRAM performance appears to be comparable given the same fabrication technology.
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. In 2005, Ramtron reported significant sales of its FeRAM products in a variety of sectors including (but not limited to) electricity meter
s, automotive (e.g. black boxes
, smart air bags
), business machines (e.g. printers, RAID
disk controllers), instrumentation, medical equipment, industrial microcontroller
s, and radio frequency identification
tags. The other emerging NVRAMs, such as MRAM, may seek to enter similar niche markets in competition with FeRAM.
Texas Instruments
proved it to be possible to embed FeRAM cells using two additional masking steps during conventional CMOS semiconductor manufacture. Flash typically requires nine masks. This makes it possible for example, the integration of FeRAM on microcontrollers, where a simplified process would reduce costs. However, the materials used to make FeRAMs are not commonly used in CMOS integrated circuit manufacturing. Both the PZT ferroelectric layer and the noble metals used for electrodes raise CMOS process compatibility and contamination issues. Texas Instruments
have incorporated an amount of FRAM memory into its MSP430 microcontrollers in its new FRAM series.
IC Chips
Random-access memory
Random access memory is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order with a worst case performance of constant time. Strictly speaking, modern types of DRAM are therefore not random access, as data is read in...
similar in construction to DRAM
Dynamic random access memory
Dynamic random-access memory is a type of random-access memory that stores each bit of data in a separate capacitor within an integrated circuit. The capacitor can be either charged or discharged; these two states are taken to represent the two values of a bit, conventionally called 0 and 1...
but uses a ferroelectric layer instead of a dielectric
Dielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
layer to achieve non-volatility. FeRAM is one of a growing number of alternative non-volatile memory
Non-volatile memory
Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, in the most basic sense, is computer memory that can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory, flash memory, ferroelectric RAM, most types of magnetic computer...
technologies that offer the same functionality as Flash memory
Flash memory
Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...
. FeRAM advantages over Flash include: lower power usage, faster write performance and a much greater maximum number (exceeding 1016 for 3.3 V devices) of write-erase cycles. Disadvantages of FeRAM are much lower storage densities
Computer storage density
Memory 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 volume of a computer storage medium. Generally, higher density is more desirable, for it allows greater volumes of data to be stored in the same...
than Flash devices, storage capacity limitations, and higher cost.
History
Ferroelectric RAM was proposed by MIT graduate student Dudley Allen BuckDudley Allen Buck
Dr. Dudley Allen Buck was an electrical engineer and inventor of components for high-speed computing devices in the 1950s. He is best known for invention of the cryotron, a superconductive computer component that is operated in liquid helium at a temperature near absolute 0...
in his master's thesis, Ferroelectrics for Digital Information Storage and Switching, published in 1952.
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. Much of the current FeRAM technology was developed by Ramtron, a fabless semiconductor company
Fabless semiconductor company
A fabless semiconductor company specializes in the design and sale of hardware devices and semiconductor chips while outsourcing the fabrication or "fab" of the devices to a specialized manufacturer called a semiconductor foundry...
. One major licensee is Fujitsu
Fujitsu
is a Japanese multinational information technology equipment and services company headquartered in Tokyo, Japan. It is the world's third-largest IT services provider measured by revenues....
, who operate what is probably the largest semiconductor foundry production line with FeRAM capability. 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. Since at least 2001 Texas Instruments
Texas Instruments
Texas Instruments Inc. , widely known as TI, is an American company based in Dallas, Texas, United States, which develops and commercializes semiconductor and computer technology...
has collaborated with Ramtron to develop FeRAM test chips in a modified 130 nm process. 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
Samsung
The Samsung Group is a South Korean multinational conglomerate corporation headquartered in Samsung Town, Seoul, South Korea...
, Matsushita, Oki
Oki Electric Industry
, commonly referred to as OKI, OKI Electric or the OKI Group, is a Japanese company manufacturing and selling info-telecom and printer products. Headquartered in Tokyo, Japan, OKI operates in over 120 countries around the world....
, Toshiba
Toshiba
is a multinational electronics and electrical equipment corporation headquartered in Tokyo, Japan. It is a diversified manufacturer and marketer of electrical products, spanning information & communications equipment and systems, Internet-based solutions and services, electronic components and...
, Infineon, Hynix
Hynix
Hynix Semiconductor Inc. chips and flash memory chips. Founded in 1983, Hynix is the world's second-largest memory chipmaker, the largest being Samsung Electronics. Formerly known as Hyundai Electronics, the company has manufacturing sites in Korea, the U.S., China and Taiwan...
, Symetrix
Symetrix
Symetrix is a manufacturer of professional audio signal processing products based in Mountlake Terrace, Washington, USA.The company was founded in Seattle, WA in 1976 by Dane Butcher who was at that time working as a recording engineer. Symetrix currently specializes in audio DSP hardware and...
, Cambridge University
University of Cambridge
The University of Cambridge is a public research university located in Cambridge, United Kingdom. It is the second-oldest university in both the United Kingdom and the English-speaking world , and the seventh-oldest globally...
, University of Toronto
University of Toronto
The University of Toronto is a public research university in Toronto, Ontario, Canada, situated on the grounds that surround Queen's Park. It was founded by royal charter in 1827 as King's College, the first institution of higher learning in Upper Canada...
, and the Interuniversity Microelectronics Centre (IMEC, Belgium
Belgium
Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...
).
Description
Conventional DRAMDram
Dram or DRAM may refer to:As a unit of measure:* Dram , an imperial unit of mass and volume* Armenian dram, a monetary unit* Dirham, a unit of currency in several Arab nationsOther uses:...
consists of a grid of small capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
s and their associated wiring and signaling transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
s. 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
Semiconductor fabrication
Semiconductor device fabrication is the process used to create the integrated circuits that are present in everyday electrical and electronic devices. It is a multiple-step sequence of photolithographic and chemical processing steps during which electronic circuits are gradually created on a wafer...
process being used to make it. 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 in general 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 must 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
Dynamic random access memory
Dynamic random-access memory is a type of random-access memory that stores each bit of data in a separate capacitor within an integrated circuit. The capacitor can be either charged or discharged; these two states are taken to represent the two values of a bit, conventionally called 0 and 1...
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
Lead zirconate titanate
Lead zirconate titanate , also called PZT, is a ceramic perovskite material that shows a marked piezoelectric effect. PZT-based compounds are composed of the chemical elements lead and zirconium and the chemical compound titanate which are combined under extremely high temperatures. A filter is...
(PZT).
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
Hysteresis
Hysteresis is the dependence of a system not just on its current environment but also on its past. This dependence arises because the system can be in more than one internal state. To predict its future evolution, either its internal state or its history must be known. If a given input alternately...
loop, which is very similar in shape to the hysteresis loop of ferromagnetic materials. The dielectric constant
Dielectric constant
The relative permittivity of a material under given conditions reflects the extent to which it concentrates electrostatic lines of flux. In technical terms, it is the ratio of the amount of electrical energy stored in a material by an applied voltage, relative to that stored in a vacuum...
of a ferroelectric is typically much higher than that of a linear dielectric because of the effects of semi-permanent electric dipoles
Dipole
In physics, there are several kinds of dipoles:*An electric dipole is a separation of positive and negative charges. The simplest example of this is a pair of electric charges of equal magnitude but opposite sign, separated by some distance. A permanent electric dipole is called an electret.*A...
formed in the crystal structure
Crystal structure
In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
of the ferroelectric material. 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. 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".
In terms of operation, 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 electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s out of the metal on the "down" side. 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.
In general, the operation of FeRAM is similar to ferrite core memory, one of the primary forms of computer memory in the 1960s. In comparison, FeRAM requires far less power to flip the state of the polarity, and does so much faster.
Density
The main determinant of a memory system's cost is the density of the components used to make it up. Smaller components, and fewer 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. In general, the technology that scales to the smallest cell size will end up being the least expensive per bit. In terms of construction, FeRAM and DRAM are similar, and can in general 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 as to whether 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.
An additional limitation on size is that materials tend to stop being ferroelectric when they are too small. (This effect is related to the ferroelectric's "depolarization field".) There is ongoing research on addressing the problem of stabilizing ferroelectric materials; one approach, for example, uses molecular adsorbates.
To date, the commercial FeRAM devices have been produced at 350 nm and 130 nm. 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) 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 works by pushing electrons across a high-quality insulating barrier where they get "stuck" on one terminal of a transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
. This process requires high voltages, which are built up in a charge pump
Charge pump
A charge pump is a kind of DC to DC converter that uses capacitors as energy storage elements to create either a higher or lower voltage power source. Charge pump circuits are capable of high efficiencies, sometimes as high as 90–95% while being electrically simple circuits.Charge pumps use some...
over time. 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 the difference might be slight, but for devices with more balanced read and write the difference could be expected to be much higher.
Performance
DRAM performance is limited by the rate at which the charge stored in the cells can be drained (for reading) or stored (for writing). In general, 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. However, 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" current, a process that FeRAM does not need. Flash memories commonly need a millisecond or more to complete a write, whereas current FeRAMs may complete a write in less than 150 ns.
The theoretical performance of FeRAM is not entirely clear. Existing 350 nm devices have read times on the order of 50-60 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, so FeRAM performance appears to be comparable given the same fabrication technology.
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 $18.6 billion (according to IC Insights). The 2005 annual sales of Ramtron, perhaps the largest FeRAM vendor, were reported to be US $32.7 million. 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 semiconductor linewidths of 30 nm at Samsung (2007) while FeRAMs are produced in linewidths of 350 nm at Fujitsu and 130 nm at Texas Instruments (2007). Flash memory cells can store multiple bits per cell (currently 3 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. As a consequence, the areal bit densities of flash memory are much higher than those of FeRAM, and thus the cost per bit of flash memory is orders of magnitude lower than that of FeRAM.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. In 2005, Ramtron reported significant sales of its FeRAM products in a variety of sectors including (but not limited to) electricity meter
Electricity meter
An electricity meter or energy meter is a device that measures the amount of electric energy consumed by a residence, business, or an electrically powered device....
s, automotive (e.g. black boxes
Event Data Recorder
An event data recorder or EDR is a device installed in some automobiles to record information related to vehicle crashes or accidents. In modern diesel trucks, EDRs are triggered by electronically sensed problems in the engine , or a sudden change in wheel speed. One or more of these conditions...
, smart air bags
Airbag
An Airbag is a vehicle safety device. It is an occupant restraint consisting of a flexible envelope designed to inflate rapidly during an automobile collision, to prevent occupants from striking interior objects such as the steering wheel or a window...
), business machines (e.g. printers, RAID
RAID
RAID is a storage technology that combines multiple disk drive components into a logical unit...
disk controllers), instrumentation, medical equipment, industrial microcontroller
Microcontroller
A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM...
s, and radio frequency identification
Radio Frequency Identification
Radio-frequency identification is a technology that uses radio waves to transfer data from an electronic tag, called RFID tag or label, attached to an object, through a reader for the purpose of identifying and tracking the object. Some RFID tags can be read from several meters away and beyond the...
tags. The other emerging NVRAMs, such as MRAM, may seek to enter similar niche markets in competition with FeRAM.
Texas Instruments
Texas Instruments
Texas Instruments Inc. , widely known as TI, is an American company based in Dallas, Texas, United States, which develops and commercializes semiconductor and computer technology...
proved it to be possible to embed FeRAM cells using two additional masking steps during conventional CMOS semiconductor manufacture. Flash typically requires nine masks. This makes it possible for example, the integration of FeRAM on microcontrollers, where a simplified process would reduce costs. However, the materials used to make FeRAMs are not commonly used in CMOS integrated circuit manufacturing. Both the PZT ferroelectric layer and the noble metals used for electrodes raise CMOS process compatibility and contamination issues. Texas Instruments
Texas Instruments
Texas Instruments Inc. , widely known as TI, is an American company based in Dallas, Texas, United States, which develops and commercializes semiconductor and computer technology...
have incorporated an amount of FRAM memory into its MSP430 microcontrollers in its new FRAM series.
See also
- MRAMMRAMMagnetoresistive Random-Access Memory is a non-volatile computer memory technology that has been under development since the 1990s. Continued increases in density of existing memory technologies – notably flash RAM and DRAM – kept it in a niche role in the market, but its proponents...
- nvSRAMNvSRAMnvSRAM 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, or Battery Backed Static Random Access Memory. However, BBSRAMs are slow and suffer from ROHS compliance issues...
- Phase-change memoryPhase-change memoryPhase-change memory is a type of non-volatile computer memory. PRAMs exploit the unique behavior of chalcogenide glass. Heat produced by the passage of an electric current switches this material between two states, crystalline and amorphous...
- Programmable metallization cellProgrammable metallization cellThe programmable metallization cell, or PMC, is a new form of non-volatile computer memory being developed at Arizona State University and its spinoff, Axon Technologies....
- MemristorMemristorMemristor is a passive two-terminal electrical component envisioned by Leon Chua as a fundamental non-linear circuit element relating charge and magnetic flux linkage...
- Racetrack memoryRacetrack memoryRacetrack memory is an experimental non-volatile memory device under development at IBM's Almaden Research Center by a team led by Stuart Parkin. In early 2008, a 3-bit version was successfully demonstrated...
- Flash memoryFlash memoryFlash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...
- Ferroelectricity
- lead zirconate titanateLead zirconate titanateLead zirconate titanate , also called PZT, is a ceramic perovskite material that shows a marked piezoelectric effect. PZT-based compounds are composed of the chemical elements lead and zirconium and the chemical compound titanate which are combined under extremely high temperatures. A filter is...
- Black boxBlack Box (transportation)The term black box is a placeholder name used casually to refer to a collection of several different recording devices used in transportation: the flight recorders in aircraft, the event recorder in railway locomotives, the event data recorder in automobiles, message case in ships, and other...
External links
- FRAM(FeRAM) Application Community Sponsored by Ramtron[Language: Chinese]
- FRAM overview by Fujitsu
- FeRAM Tutorial by the Department of Electrical and Computer Engineering at the University of Toronto
IC Chips