Multigate device

Source: Wikipedia, the free encyclopedia.
(Redirected from
Multi-gate
)
A dual-gate MOSFET and schematic symbol

A multigate device, multi-gate MOSFET or multi-gate field-effect transistor (MuGFET) refers to a

FinFET (fin field-effect transistor) and the GAAFET
(gate-all-around field-effect transistor), which are non-planar transistors, or 3D transistors.

Multi-gate

silicon-on-insulator-based technologies, and high-κ
/metal gate materials.

Dual-gate MOSFETs are commonly used in very high frequency (VHF) mixers and in sensitive VHF front-end amplifiers. They are available from manufacturers such as Motorola, NXP Semiconductors, and Hitachi.[3][4][5]

Types

Several multigate models

Dozens of multigate transistor variants may be found in the literature. In general, these variants may be differentiated and classified in terms of architecture (planar vs. non-planar design) and the number of channels/gates (2, 3, or 4).

Planar double-gate MOSFET (DGMOS)

A planar double-gate MOSFET (DGMOS) employs conventional planar (layer-by-layer) manufacturing processes to create double-gate MOSFET (metal–oxide–semiconductor field-effect transistor) devices, avoiding more stringent lithography requirements associated with non-planar, vertical transistor structures. In planar double-gate transistors the drain–source channel is sandwiched between two independently fabricated gate/gate-oxide stacks. The primary challenge in fabricating such structures is achieving satisfactory self-alignment between the upper and lower gates.[6]

FlexFET

FlexFET is a planar, independently double-gated transistor with a

damascene metal top gate MOSFET and an implanted JFET bottom gate that are self-aligned in a gate trench. This device is highly scalable due to its sub-lithographic channel length; non-implanted ultra-shallow source and drain extensions; non-epi raised source and drain regions; and gate-last flow. FlexFET is a true double-gate transistor in that (1) both the top and bottom gates provide transistor operation, and (2) the operation of the gates is coupled such that the top gate operation affects the bottom gate operation and vice versa.[7]
FlexFET was developed and is manufactured by American Semiconductor, Inc.

FinFET

FinFET
device
An SOI FinFET MOSFET
The NVIDIA GTX 1070 from 2016, which uses a 16 nm FinFET-based Pascal chip manufactured by TSMC

FinFET (fin field-effect transistor) is a type of non-planar transistor, or "3D" transistor (not to be confused with 3D microchips).[8] The FinFET is a variation on traditional MOSFETs distinguished by the presence of a thin silicon "fin" inversion channel on top of the substrate, allowing the gate to make two points of contact: the left and right sides of the fin. The thickness of the fin (measured in the direction from source to drain) determines the effective channel length of the device. The wrap-around gate structure provides a better electrical control over the channel and thus helps in reducing the leakage current and overcoming other short-channel effects
.

The first FinFET transistor type was called a "Depleted Lean-channel Transistor" or "DELTA" transistor, which was first

P-channel FinFETs.[12] They coined the term "FinFET" (fin field-effect transistor) in a December 2000 paper.[13]

In current usage the term FinFET has a less precise definition. Among

Freescale describe their double-gate development efforts as FinFET[14] development, whereas Intel avoids using the term when describing their closely related tri-gate architecture.[15] In the technical literature, FinFET is used somewhat generically to describe any fin-based, multigate transistor architecture regardless of number of gates. It is common for a single FinFET transistor to contain several fins, arranged side by side and all covered by the same gate, that act electrically as one, to increase drive strength and performance.[16]
The gate may also cover the entirety of the fin(s).

A 25 nm transistor operating on just 0.7 

gate delay of just 0.39 picosecond
(ps) for the N-type transistor and 0.88 ps for the P-type.

In 2004,

nanoelectronic device, based on FinFET technology.[17][18] In 2011, Rice University researchers Masoud Rostami and Kartik Mohanram demonstrated that FINFETs can have two electrically independent gates, which gives circuit designers more flexibility to design with efficient, low-power gates.[19]

In 2012, Intel started using FinFETs for its future commercial devices. Leaks suggest that Intel's FinFET has an unusual shape of a triangle rather than rectangle, and it is speculated that this might be either because a triangle has a higher structural strength and can be more reliably manufactured or because a triangular prism has a higher area-to-volume ratio than a rectangular prism, thus increasing switching performance.[20]

In September 2012, GlobalFoundries announced plans to offer a 14-nanometer process technology featuring FinFET three-dimensional transistors in 2014.[21] The next month, the rival company TSMC announced start early or "risk" production of 16 nm FinFETs in November 2013.[22]

In March 2014,

processes:[23]

AMD released GPUs using their Polaris chip architecture and made on 14 nm FinFET in June 2016.[24] The company has tried to produce a design to provide a "generational jump in power efficiency" while also offering stable frame rates for graphics, gaming, virtual reality, and multimedia applications.[25]

In March 2017, Samsung and eSilicon announced the tapeout for production of a 14 nm FinFET ASIC in a 2.5D package.[26][27]

Tri-gate transistor

A tri-gate transistor, also known as a triple-gate transistor, is a type of MOSFET with a gate on three of its sides.[28] A triple-gate transistor was first demonstrated in 1987, by a Toshiba research team including K. Hieda, Fumio Horiguchi and H. Watanabe. They realized that the fully depleted (FD) body of a narrow bulk Si-based transistor helped improve switching due to a lessened body-bias effect.[29][30] In 1992, a triple-gate MOSFET was demonstrated by IBM researcher Hon-Sum Wong.[31]

Intel announced this technology in September 2002.[32] Intel announced "triple-gate transistors" which maximize "transistor switching performance and decreases power-wasting leakage". A year later, in September 2003, AMD announced that it was working on similar technology at the International Conference on Solid State Devices and Materials.[33][34] No further announcements of this technology were made until Intel's announcement in May 2011, although it was stated at IDF 2011, that they demonstrated a working SRAM chip based on this technology at IDF 2009.[35]

On April 23, 2012, Intel released a new line of CPUs, termed

Atom chips for low-powered devices.[38]

Tri-gate fabrication was used by

leakage and consume far less power than previous transistors. This allows up to 37% higher speed or a power consumption at under 50% of the previous type of transistors used by Intel.[40][41]

Intel explains: "The additional control enables as much transistor current flowing as possible when the transistor is in the 'on' state (for performance), and as close to zero as possible when it is in the 'off' state (to minimize power), and enables the transistor to switch very quickly between the two states (again, for performance)."[42] Intel has stated that all products after Sandy Bridge will be based upon this design.

The term tri-gate is sometimes used generically to denote any multigate FET with three effective gates or channels.[43]

Gate-all-around FET (GAAFET)

Gate-all-around FETs (GAAFETs) are the successor to FinFETs, as they can work at sizes below 7 nm. They were used by IBM to demonstrate 5 nm process technology.

GAAFET, also known as a surrounding-gate transistor (SGT),[44][45] is similar in concept to a FinFET except that the gate material surrounds the channel region on all sides. Depending on design, gate-all-around FETs can have two or four effective gates. Gate-all-around FETs have been successfully characterized both theoretically and experimentally.[46][47] They have also been successfully etched onto InGaAs nanowires, which have a higher electron mobility than silicon.[48]

A gate-all-around (GAA) MOSFET was first demonstrated in 1988, by a

gate-all-around (GAA) FinFET technology.[52][18] GAAFET transistors may make use of high-k/metal gate materials. GAAFETs with up to 7 nanosheets have been demonstrated which allow for improved performance and/or reduced device footprint. The widths of the nanosheets in GAAFETs is controllable which more easily allows for the adjustment of device characteristics.[53]

As of 2020, Samsung and Intel have announced plans to mass produce GAAFET transistors (specifically MBCFET transistors) while TSMC has announced that they will continue to use FinFETs in their 3 nm node,[54] despite TSMC developing GAAFET transistors.[55]

Multi-bridge channel (MBC) FET

A multi-bridge channel FET (MBCFET) is similar to a GAAFET except for the use of nanosheets instead of nanowires.[56] MBCFET is a word mark (trademark) registered in the U.S. to Samsung Electronics.[57] Samsung plans on mass producing MBCFET transistors at the 3 nm node for its foundry customers.[58] Intel is also developing RibbonFET, a variation of MBCFET "nanoribbon" transistors.[59][60] Unlike FinFETs, both the width and the number of the sheets can be varied to adjust drive strength or the amount of current the transistor can drive at a given voltage. The sheets often vary from 8 to 50 nanometers in width. The width of the nanosheets is known as Weff, or effective width.[61][62]

Industry need

Planar transistors have been the core of integrated circuits for several decades, during which the size of the individual transistors has steadily decreased. As the size decreases, planar transistors increasingly suffer from the undesirable short-channel effect, especially "off-state" leakage current, which increases the idle power required by the device.[63]

In a multigate device, the channel is surrounded by several gates on multiple surfaces. Thus it provides better electrical control over the channel, allowing more effective suppression of "off-state" leakage current. Multiple gates also allow enhanced current in the "on" state, also known as drive current. Multigate transistors also provide a better analog performance due to a higher intrinsic gain and lower channel length modulation.[64] These advantages translate to lower power consumption and enhanced device performance. Nonplanar devices are also more compact than conventional planar transistors, enabling higher transistor density which translates to smaller overall microelectronics.

Integration challenges

The primary challenges to integrating nonplanar multigate devices into conventional semiconductor manufacturing processes include:

  • Fabrication of a thin silicon "fin" tens of nanometers wide
  • Fabrication of matched gates on multiple sides of the fin

Compact modeling

Different FinFET structures, which can be modeled by BSIM-CMG

BSIMCMG106.0.0,[65] officially released on March 1, 2012 by UC Berkeley BSIM Group, is the first standard model for FinFETs. BSIM-CMG is implemented in Verilog-A. Physical surface-potential-based formulations are derived for both intrinsic and extrinsic models with finite body doping. The surface potentials at the source and drain ends are solved analytically with poly-depletion and quantum mechanical effects. The effect of finite body doping is captured through a perturbation approach. The analytic surface potential solution agrees closely with the 2-D device simulation results. If the channel doping concentration is low enough to be neglected, computational efficiency can be further improved by a setting a specific flag (COREMOD = 1).

All of the important multi-gate (MG) transistor behavior is captured by this model. Volume inversion is included in the solution of Poisson's equation, hence the subsequent I–V formulation automatically captures the volume-inversion effect. Analysis of electrostatic potential in the body of MG MOSFETs provided a model equation for short-channel effects (SCE). The extra electrostatic control from the end gates (top/bottom gates) (triple or quadruple-gate) is also captured in the short-channel model.

See also

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External links