Ferroelectric RAM

thumb|FeRAM by Ramtron

thumb|FRAM ferroelectric capacitor

Ferroelectric RAM (FeRAM, F-RAM or FRAM) is a random-access memory similar in construction to DRAM but using a ferroelectric layer instead of a dielectric layer to achieve non-volatility. FeRAM is an alternative non-volatile random-access memory technology that offers the same functionality as flash memory. An FeRAM chip contains a thin film of ferroelectric material, often lead zirconate titanate, commonly referred to as PZT. The atoms in the PZT layer change polarity in an electric field, thereby producing a power-efficient binary switch. However, the most important aspect of the PZT is that it is not affected by power disruption or magnetic interference, making FeRAM a reliable nonvolatile memory.

FeRAM's advantages over Flash include: lower power usage, faster write speeds and a much greater maximum read/write endurance (about 1010 to 1015 cycles). The primary disadvantages of FeRAM are much lower storage densities than flash devices, storage capacity limitations and higher cost. Like DRAM, FeRAM's read process is destructive, necessitating a write-after-read architecture.

In 1955, Bell Telephone Laboratories was experimenting with ferroelectric-crystal memories. Following the introduction of metal–oxide–semiconductor (MOS) dynamic random-access memory (DRAM) chips in the early 1970s, development of FeRAM began in the late 1980s. Work was done in 1991 at NASA's Jet Propulsion Laboratory (JPL) on improving methods of read out, including a novel method of non-destructive readout using pulses of UV radiation.

FeRAM was commercialized in the mid-1990s. In 1994, video game company Sega used FeRAM chips to store saved games in Sonic the Hedgehog 3, which shipped several million game cartridges that year. In 1996, Samsung Electronics introduced a 4Mb FeRAM chip fabricated using NMOS logic. In 1998, Hyundai Electronics (now SK Hynix) also commercialized FeRAM technology. The earliest known commercial product to use FeRAM is Sony's PlayStation 2 Memory Card (8MB), released in 2000. The Memory Card's microcontroller (MCU) manufactured by Toshiba contained 32kb (4 kB) embedded FeRAM fabricated using a 500 nm complementary MOS (CMOS) process. In 2010 Ramtron switched to Texas Instruments and IBM.

In 2024–2025 ferroelectric RAM research was driven by HfO₂-based materials for CMOS compatibility, scalability to <10 nm, and integration into advanced nodes (22–28 nm). Cycle counts exceeded 10¹², with reduced power requirements.

Prototypes offered 9–16 Mb arrays with 10¹² endurance and 5–7 ns read/write.

Vendors

Ramtron is a fabless semiconductor company. One major licensee is Fujitsu, which operates one of the largest semiconductor foundry production lines with FeRAM capability. In 2012 Ramtron was acquired by Cypress Semiconductor.

FeRAM research projects were reported at Samsung, Matsushita, Oki, Toshiba, Infineon, Hynix, Symetrix, Cambridge University, University of Toronto, and the Interuniversity Microelectronics Centre (IMEC, Belgium).

Description

thumb|300px|right|Structure of a FeRAM cell

Conventional DRAM consists of a grid of small capacitors and their associated wiring and signaling transistors. Each storage element, a cell, consists of one capacitor and one transistor, a so-called "1T-1C" device.

The 1T-1C storage cell design in a FeRAM is similar in construction to the storage cell in 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 a FeRAM cell capacitor the dielectric structure includes ferroelectric material, typically lead zirconate titanate (PZT). 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. 2021 2027 Global And Regional Ferroelectric Ram Industry Status And Prospects Professional Market – Market Reports World.

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" Introduction to DRAM (Dynamic Random-Access Memory) - Technical Articles. Reading operation is also similar to DRAM Ferroelectric RAM: FRAM Technology Operation » Electronics Notes. 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.

In general, the operation of FeRAM is similar to ferrite core memory, one of the primary forms of computer memory in the 1960s Computer Memory Technology: From Ferrite Rings to FRAM. However, compared to core memory, FeRAM requires far less power to flip the state of the polarity and does so much faster.

Features and properties

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.

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.

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. 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 very short 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 (typically times per second) and this requires a continuous supply of power. In contrast, FeRAM only requires power when actually reading or writing a cell FRAM Can Lower Power and Increase Performance in MCU-Based Systems.

Another non-volatile memory type is flash, and like FeRAM it does not require a refresh process. F-RAM devices are immune to the strong magnetic fields and do not show any failures under the maximum available magnetic field strengths (3,700 gauss for horizontal insertion and 2,000 gauss for vertical insertion) FRAM - Smart IC Memory from Texas Instruments. In addition, the F-RAM devices allow rewriting with a different data pattern after exposure to the magnetic fields. 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.

On the other hand, FeRAM has its own reliability issues, including imprint and fatigue. Imprint is the preferential polarization state from previous writes to that state, and fatigue is the increase of minimum writing voltage due to loss of polarization after extensive cycling. so FeRAM speed appears to be comparable given the same fabrication technology.

Additional metrics

{| class="wikitable"

! Ferroelectric RAM

! Magnetoresistive random-access memory

! nvSRAM

! Technique

| The basic storage element is a ferroelectric capacitor. The capacitor can be polarized up or down by applying an electric field

| Similar to ferroelectric RAM, but the atoms align themselves in the direction of an external magnetic force. This effect is used to store data

| Has non-volatile elements along with high speed SRAM

! Data retention

| 10–160 yrs || 20 yrs || 20 yrs

! Endurance

|1010 to 1015|| 108 || Unlimited

! Speed (best)

| 55 ns

| 35 ns

| 15–45 ns

Applications

Datalogger in portable/implantable medical devices, as FeRAM consumes less energy compared to other non-volatile memories such as EEPROM
Feram's energy-efficient and reliable data retention, makes them an ideal choice for IoT devices such as wearable electronics, sensors, and actuators [https://www.lenovo.com/us/en/glossary/what-is-fram/?orgRef=https%253A%252F%252Fwww.google.com%252F].
FeRAM is used in wearables, smart meters, and medical monitors [https://www.lenovo.com/us/en/glossary/what-is-fram/?orgRef=https%253A%252F%252Fwww.google.com%252F].
FRAM holds significant promise in the automotive industry, with one of its main benefits being its rapid write capability Infineon Welcomes New Devices to Fleet of Automotive Ferroelectric RAM - News.
They are often integrated into RFID tags to provide fast writes, low power consumption, and high endurance, enabling secure and frequent data updates for applications such as supply chain tracking, access control, and smart cards Reasons to Choose FeRAM-embedded RFIDs｜RAMXEED.

Market

FeRAM remains a relatively small part of the overall semiconductor market Ramtron. 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) Introduction to FRAM (Ferroelectric RAM) including Its History. Flash memory cells can store multiple bits per cell (currently 4 in the highest density NAND flash devices), and the number of bits per flash cell is projected to increase to 8 as a result of innovations in flash cell design A Guide to NAND Flash Memory: Comparing SLC, MLC, TLC, and QLC. 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. automotive (e.g. black boxes, smart air bags), business machines (e.g. printers, RAID disk controllers), instrumentation, medical equipment, industrial microcontrollers, 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 possible for example, the integration of FeRAM onto 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 has incorporated an amount of FRAM memory into its MSP430 microcontrollers in its new FRAM series.

Capacity timeline

As of 2021 different vendors were selling chips with no more than 16Mb of memory in storage size (density).

References

External links

FRAM(FeRAM) [Cypress
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
FRAM operation and technology tutorial

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