A ferroelectric field-effect transistor (Fe FET) is a type of
field-effect transistor
The field-effect transistor (FET) is a type of transistor that uses an electric field to control the flow of current in a semiconductor. FETs (JFETs or MOSFETs) are devices with three terminals: ''source'', ''gate'', and ''drain''. FETs contro ...
that includes a
ferroelectric
Ferroelectricity is a characteristic of certain materials that have a spontaneous electric polarization that can be reversed by the application of an external electric field. All ferroelectrics are also piezoelectric and pyroelectric, with the add ...
material sandwiched between the gate electrode and source-drain conduction region of the device (the
channel
Channel, channels, channeling, etc., may refer to:
Geography
* Channel (geography), in physical geography, a landform consisting of the outline (banks) of the path of a narrow body of water.
Australia
* Channel Country, region of outback Austral ...
). Permanent electrical field polarisation in the ferroelectric causes this type of device to retain the transistor's state (on or off) in the absence of any electrical bias.
FeFET based devices are used in FeFET memory - a type of single transistor
non-volatile memory
Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data.
Non-volatile memory typic ...
.
Description
In 1955,
Ian Munro Ross
Ian Munro Ross FREng (15 August 1927 – 10 March 2013) was an early pioneer in transistors, and for 12 years President of Bell Labs.
Ross was born in Southport, England, and in 1948 received his bachelor's degree in electrical engineering from ...
filed a patent for a
FeFET
A ferroelectric field-effect transistor (Fe FET) is a type of field-effect transistor that includes a ferroelectric material sandwiched between the gate electrode and source-drain conduction region of the device (the channel). Permanent electric ...
or MFSFET. Its structure was like that of a modern inversion channel MOSFET, but ferroelectric material was used as a dielectric/insulator instead of oxide. Use of a ferroelectric (
triglycine sulfate
Triglycine sulfate (TGS) is a chemical compound with a formula (NH2CH2COOH)3·H2SO4. The empirical formula of TGS does not represent the molecular structure, which contains protonated glycine moieties and sulfate ions. TGS with protons replaced by ...
) in a solid state memory was proposed by Moll and Tarui in 1963 using a
thin film transistor
A thin-film transistor (TFT) is a special type of field-effect transistor (FET) where the transistor is thin relative to the plane of the device. TFTs are grown on a supporting (but non-conducting) substrate. A common substrate is glass, becaus ...
. Further research occurred in the 1960s, but the retention characteristics of the thin film based devices was unsatisfactory. Early
field effect transistor
The field-effect transistor (FET) is a type of transistor that uses an electric field to control the flow of current in a semiconductor. FETs (JFETs or MOSFETs) are devices with three terminals: ''source'', ''gate'', and ''drain''. FETs control ...
based devices used
bismuth titanate
Bismuth titanate or bismuth titanium oxide is a solid inorganic compound of bismuth, titanium and oxygen with the chemical formula of Bi12TiO20,
Bi 4Ti3O12 or Bi2Ti2O7.
Synthesis
Bismuth titanate ceramics can be produced by heating a mixture of ...
(Bi
4Ti
3O
12) ferroelectric, or Pb
1−xLn
xTiO
3 (
PLT) and related mixed zirconate/titanates (
PLZT
Lead zirconate titanate is an inorganic compound with the chemical formula (0≤''x''≤1), commonly abbreviated as PZT. Also called lead zirconium titanate, it is a ceramic perovskite material that shows a marked piezoelectric effect, meaning ...
). In the late 1980
Ferroelectric RAM
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 one of a growing number of alternative non-vol ...
was developed, using a ferroelectric thin film as capacitor, connected to an addressing FET.
FeFET based memory devices are read using voltages below the coercive voltage for the ferroelectric.
Issues involved in realising a practical FeFET memory device include (as of 2006) : choice of a high permitivity, highly insulating layer between ferroelectric and gate; issues with high remanent polarisation of ferroelectrics; limited retention time (c. a few days, cf required 10 years).
[
Provided the ferroelectric layer can be scaled accordingly FeFET based memory devices are expected to scale (shrink) as well as MOSFET devices; however a limit of ~20 nm laterally ''may'' exist (the superparaelectric limit, aka ferroelectric limit). Other challenges to feature shrinks include : reduced film thickness causing additional (undesired) polarisation effects; charge injection; and leakage currents.][
]
Research and development
In 2017 FeFET based non-volatile memory
Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data.
Non-volatile memory typic ...
was reported as having been built at 22nm node using FDSOI CMOS (fully depleted silicon on insulator
In semiconductor manufacturing, silicon on insulator (SOI) technology is fabrication of silicon semiconductor devices in a layered silicon–insulator–silicon substrate, to reduce parasitic capacitance within the device, thereby improving perfo ...
) with hafnium dioxide
Hafnium(IV) oxide is the inorganic compound with the formula . Also known as hafnium dioxide or hafnia, this colourless solid is one of the most common and stable compounds of hafnium. It is an electrical insulator with a band gap of 5.3~5.7 eV. H ...
(HfO2) as the ferroelectric- the smallest FeFET cell size reported was 0.025 μm2, the devices were built as 32Mbit arrays, using set/reset pulses of ~10ns duration at 4.2V - the devices showed endurance of 105 cycles and data retention up to 300C.[
the startup 'Ferroelectrc Memory Company' is attempting to develop FeFET memory into a commercial device, based on Hafnium dioxide. The company's technology is claimed to scale to modern ]process node
Semiconductor device fabrication is the process used to manufacture semiconductor devices, typically integrated circuit (IC) chips such as modern computer processors, microcontrollers, and memory chips such as NAND flash and DRAM that are pres ...
sizes, and to integrate with contemporary production processes, i.e. HKMG, and is easily integrable in to conventional CMOS processes, requiring only two additional masks.
See also
*Ferroelectric RAM
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 one of a growing number of alternative non-vol ...
- RAM that uses a ferrolectric material in the capacitor of a conventional DRAM structure
References
*
Further reading
*{{citation, title = Multifunctional Oxide Heterostructures , chapter = FeFET and ferroelectric random access memories , first = Hiroshi , last = Ishiwara , doi = 10.1093/acprof:oso/9780199584123.003.0012 , year = 2012, pages = 340–363 , isbn = 978-0-19-958412-3
Non-volatile memory
Field-effect transistors
Ferroelectric materials