Gate oxide

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The gate oxide is the dielectric layer that separates the gate terminal of a MOSFET (metal-oxide-semiconductor field-effect transistor) from the underlying source and drain terminals as well as the conductive channel that connects source and drain when the transistor is turned on. Gate oxide is formed by thermal oxidation of the silicon of the channel to form a thin (5 - 200 nm) insulating layer of silicon dioxide. The insulating silicon dioxide layer is formed through a process of self-limiting oxidation, which is described by the Deal-Grove model. A conductive gate material is subsequently deposited over the gate oxide to form the transistor. The gate oxide serves as the dielectric layer so that the gate can sustain as high as 1 to 5 MV/cm transverse electric field in order to strongly modulate the conductance of the channel.

Dielectric electrically poorly conducting or non-conducting, non-metallic substance of which charge carriers are generally not free to move

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 they do in an electrical conductor but only slightly shift from their average equilibrium positions causing dielectric polarization. Because of dielectric polarization, positive charges are displaced in the direction of the field and negative charges shift in the direction opposite to the field. This creates an internal electric field that reduces the overall field within the dielectric itself. If a dielectric is composed of weakly bonded molecules, those molecules not only become polarized, but also reorient so that their symmetry axes align to the field.

Metal gate

A metal gate, in the context of a lateral metal-oxide-semiconductor (MOS) stack, is just that—the gate material is made from a metal.

MOSFET Transistor used for amplifying or switching electronic signals.

The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET), also known as the metal–oxide–silicon transistor (MOS transistor, or MOS), is a type of field-effect transistor that is fabricated by the controlled oxidation of a semiconductor, typically silicon. It has a covered gate, whose voltage determines the conductivity of the device. This ability to change conductivity with the amount of applied voltage can be used for amplifying or switching electronic signals. The MOSFET was invented by Egyptian engineer Mohamed M. Atalla and Korean engineer Dawon Kahng at Bell Labs in November 1959. It is the basic building block of modern electronics, and the most widely manufactured device in history, with an estimated total of 13 sextillion (1.3 × 1022) MOSFETs manufactured between 1960 and 2018.

Above the gate oxide is a thin electrode layer made of a conductor which can be aluminium, a highly doped silicon, a refractory metal such as tungsten, a silicide (TiSi, MoSi, TaSi or WSi) or a sandwich of these layers. This gate electrode is often called "gate metal" or "gate conductor". The geometrical width of the gate conductor electrode (the direction transverse to current flow) is called the physical gate width. The physical gate width may be slightly different from the electrical channel width used to model the transistor as fringing electric fields can exert an influence on conductors that are not immediately below the gate.

Electrical conductor object or material which permits the flow of electricity

In physics and electrical engineering, a conductor is an object or type of material that allows the flow of charge in one or more directions. Materials made of metal are common electrical conductors. Electrical current is generated by the flow of negatively charged electrons, positively charged holes, and positive or negative ions in some cases.

Aluminium Chemical element with atomic number 13

Aluminium is a chemical element with the symbol Al and atomic number 13. It is a silvery-white, soft, non-magnetic and ductile metal in the boron group. By mass, aluminium makes up about 8% of the Earth's crust; it is the third most abundant element after oxygen and silicon and the most abundant metal in the crust, though it is less common in the mantle below. The chief ore of aluminium is bauxite. Aluminium metal is highly reactive, such that native specimens are rare and limited to extreme reducing environments. Instead, it is found combined in over 270 different minerals.

Silicon Chemical element with atomic number 14

Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard and brittle crystalline solid with a blue-grey metallic lustre; and it is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic table: carbon is above it; and germanium, tin, and lead are below it. It is relatively unreactive. Because of its high chemical affinity for oxygen, it was not until 1823 that Jöns Jakob Berzelius was first able to prepare it and characterize it in pure form. Its melting and boiling points of 1414 °C and 3265 °C respectively are the second-highest among all the metalloids and nonmetals, being only surpassed by boron. Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure element in the Earth's crust. It is most widely distributed in dusts, sands, planetoids, and planets as various forms of silicon dioxide (silica) or silicates. More than 90% of the Earth's crust is composed of silicate minerals, making silicon the second most abundant element in the Earth's crust after oxygen.

The electrical properties of the gate oxide are critical to the formation of the conductive channel region below the gate. In NMOS-type devices, the zone beneath the gate oxide is a thin n-type inversion layer on the surface of the p-type semiconductor substrate. It is induced by the oxide electric field from the applied gate voltage VG. This is known as the inversion channel. It is the conduction channel that allows the electrons to flow from the source to the drain. [1]

Voltage difference in the electric potential between two points in space

Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential between two points. The difference in electric potential between two points in a static electric field is defined as the work needed per unit of charge to move a test charge between the two points. In the International System of Units, the derived unit for voltage is named volt. In SI units, work per unit charge is expressed as joules per coulomb, where 1 volt = 1 joule per 1 coulomb. The official SI definition for volt uses power and current, where 1 volt = 1 watt per 1 ampere. This definition is equivalent to the more commonly used 'joules per coulomb'. Voltage or electric potential difference is denoted symbolically by V, but more often simply as V, for instance in the context of Ohm's or Kirchhoff's circuit laws.

Electron subatomic particle with negative electric charge

The electron is a subatomic particle, symbol
e
or
β
, whose electric charge is negative one elementary charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no known components or substructure. The electron has a mass that is approximately 1/1836 that of the proton. Quantum mechanical properties of the electron include an intrinsic angular momentum (spin) of a half-integer value, expressed in units of the reduced Planck constant, ħ. Being fermions, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of both particles and waves: they can collide with other particles and can be diffracted like light. The wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a longer de Broglie wavelength for a given energy.

Overstressing the gate oxide layer, a common failure mode of MOS devices, may lead to gate rupture or to stress induced leakage current.

Stress induced leakage current is an increase in the gate leakage current of a MOSFET, used in semiconductor physics. SILC occurs due to defects created in the gate oxide during electrical stressing. SILC is perhaps the largest factor inhibiting device miniaturization. Increased leakage is a common failure mode of electronic devices.

History

The first MOSFET (metal-oxide-semiconductor field-effect transistor, or MOS transistor) was invented by Egyptian engineer Mohamed Atalla and Korean engineer Dawon Kahng at Bell Labs in 1959. [2] In 1960, Atalla and Kahng fabricated the first MOSFET with a gate oxide thickness of 100 nm, along with a gate length of 20 µm. [3] In 1987, Bijan Davari led an IBM research team that demonstrated the first MOSFET with a 10 nm gate oxide thickness, using tungsten-gate technology. [4]

Dawon Kahng South Korean engineer

Dawon Kahng was a Korean-American electrical engineer and inventor, known for his work in solid-state electronics. He is best known for inventing the MOSFET, also known as the MOS transistor, with Mohamed Atalla in 1959. Atalla and Kahng developed both the PMOS and NMOS processes for MOSFET semiconductor device fabrication. The MOSFET is the most widely used type of transistor, and the basic element in most modern electronic equipment.

Bell Labs Research and scientific development company

Nokia Bell Labs is an industrial research and scientific development company owned by Finnish company Nokia. With headquarters located in Murray Hill, New Jersey, the company operates several laboratories in the United States and around the world. Bell Labs has its origins in the complex past of the Bell System.

Semiconductor device fabrication manufacturing process used to create integrated circuits

Semiconductor device fabrication is the process used to manufacture semiconductor devices, typically the metal-oxide-semiconductor (MOS) devices used in the integrated circuit (IC) chips 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 made of pure semiconducting material. Silicon is almost always used, but various compound semiconductors are used for specialized applications.

Related Research Articles

CMOS Technology for constructing integrated circuits

Complementary metal–oxide–semiconductor (CMOS), also known as complementary-symmetry metal–oxide–semiconductor (COS-MOS), is a type of MOSFET fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSFETs for logic functions. CMOS technology is used for constructing integrated circuits (ICs), including microprocessors, microcontrollers, memory chips, and other digital logic circuits. CMOS technology is also used for analog circuits such as image sensors, data converters, RF circuits, and highly integrated transceivers for many types of communication.

Thin-film transistor field-effect transistor device

A thin-film transistor (TFT) is a special type of MOSFET made by depositing thin films of an active semiconductor layer as well as the dielectric layer and metallic contacts over a supporting substrate. A common substrate is glass, because the primary application of TFTs is in liquid-crystal displays (LCDs). This differs from the conventional bulk MOSFET transistor, where the semiconductor material typically is the substrate, such as a silicon wafer.

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 performance. SOI-based devices differ from conventional silicon-built devices in that the silicon junction is above an electrical insulator, typically silicon dioxide or sapphire. The choice of insulator depends largely on intended application, with sapphire being used for high-performance radio frequency (RF) and radiation-sensitive applications, and silicon dioxide for diminished short-channel effects in other microelectronics devices. The insulating layer and topmost silicon layer also vary widely with application.

Organic field-effect transistor

An organic field-effect transistor (OFET) is a field-effect transistor using an organic semiconductor in its channel. OFETs can be prepared either by vacuum evaporation of small molecules, by solution-casting of polymers or small molecules, or by mechanical transfer of a peeled single-crystalline organic layer onto a substrate. These devices have been developed to realize low-cost, large-area electronic products and biodegradable electronics. OFETs have been fabricated with various device geometries. The most commonly used device geometry is bottom gate with top drain and source electrodes, because this geometry is similar to the thin-film silicon transistor (TFT) using thermally grown SiO2 as gate dielectric. Organic polymers, such as poly(methyl-methacrylate) (PMMA), can also be used as dielectric.

In electronics, a self-aligned gate is a transistor manufacturing feature whereby a refractory gate electrode region of a MOSFET is used as a mask for the doping of the source and drain regions. This technique ensures that the gate will slightly overlap the edges of the source and drain.

Multigate device type of MOS field-effect transistor with more than one gate

A multigate device, multi-gate MOSFET or multi-gate field-effect transistor (MuGFET) refers to a MOSFET that incorporates more than one gate into a single device. The multiple gates may be controlled by a single gate electrode, wherein the multiple gate surfaces act electrically as a single gate, or by independent gate electrodes. A multigate device employing independent gate electrodes is sometimes called a multiple-independent-gate field-effect transistor (MIGFET). The most widely used multi-gate devices are the FinFET and the GAAFET, which are non-planar transistors, or 3D transistors.

Nanocircuits are electrical circuits operating on the nanometer scale. This is well into the quantum realm, where quantum mechanical effects become very important. One nanometer is equal to 10−9 meters or a row of 10 hydrogen atoms. With such progressively smaller circuits, more can be fitted on a computer chip. This allows faster and more complex functions using less power. Nanocircuits are composed of three different fundamental components. These are transistors, interconnections, and architecture, all fabricated on the nanometer scale.

PMOS logic p-type MOSFETs to implement logic gates

P-type metal-oxide-semiconductor logic uses p-channel metal-oxide-semiconductor field effect transistors (MOSFETs) to implement logic gates and other digital circuits. PMOS transistors operate by creating an inversion layer in an n-type transistor body. This inversion layer, called the p-channel, can conduct holes between p-type "source" and "drain" terminals.

A transistor is a semiconductor device with at least three terminals for connection to an electric circuit. The vacuum-tube triode, also called a (thermionic) valve, was the transistor's precursor, introduced in 1907. The principle of a field-effect transistor was proposed by Julius Edgar Lilienfeld in 1925.

In semiconductor fabrication, the International Technology Roadmap for Semiconductors (ITRS) defines the 10 nanometer (10 nm) node as the MOSFET technology node following the 14 nm node. "10 nm class" denotes chips made using process technologies between 10 and 20 nanometers.

In field effect transistors (FETs), depletion mode and enhancement mode are two major transistor types, corresponding to whether the transistor is in an ON state or an OFF state at zero gate–source voltage.

Polysilicon depletion effect is the phenomenon in which unwanted variation of threshold voltage of the MOSFET devices using polysilicon as gate material is observed, leading to unpredicted behavior of the electronic circuit. Polycrystalline silicon, also called polysilicon, is a material consisting of small silicon crystals. It differs from single-crystal silicon, used for electronics and solar cells, and from amorphous silicon, used for thin film devices and solar cells.

Mohamed M. Atalla mechanical engineer

Mohamed Mohamed Atalla was an Egyptian-American engineer, physical chemist, cryptographer, inventor and entrepreneur. His pioneering work in semiconductor technology laid the foundations for modern electronics. Most importantly, his invention of the MOSFET in 1959, along with his earlier surface passivation and thermal oxidation processes, revolutionized the electronics industry. He is also known as the founder of the data security company Atalla Corporation, founded in 1972, which introduced the first hardware security module and was a pioneer in online security. He received the Stuart Ballantine Medal and was inducted into the National Inventors Hall of Fame for his important contributions to semiconductor technology as well as data security.

Field-effect transistor transistor that uses an electric field to control the electrical behaviour of the device. FETs are also known as unipolar transistors since they involve single-carrier-type operation

The field-effect transistor (FET) is an electronic device which uses an electric field to control the flow of current. FETs are devices with three terminals: source, gate, and drain. FETs control the flow of current by the application of a voltage to the gate, which in turn alters the conductivity between the drain and source.

The metal–nitride–oxide–semiconductor or metal–nitride–oxide–silicon (MNOS) transistor is a type of MOSFET in which the oxide layer is replaced by a double layer of nitride and oxide. It is an alternative and supplement to the existing standard MOS technology, wherein the insulation employed is a nitride-oxide layer. It is used in non-volatile computer memory.

Bijan Davari is an Iranian-American engineer. He is an IBM Fellow and Vice President at IBM Thomas J Watson Research Center, Yorktown Hts, NY. His pioneering work in the miniaturization of semiconductor devices changed the world of computing. His research led to the first generation of voltage-scaled deep-submicron CMOS with sufficient performance to totally replace bipolar technology in IBM mainframes and enable new high-performance UNIX servers. He is credited with leading IBM into the use of copper and silicon on insulator before its rivals. He is a member of the U.S. National Academy of Engineers and is known for his seminal contributions to the field of CMOS technology. He is an IEEE Fellow, recipient of the J J Ebers Award in 2005 and IEEE Andrew S. Grove Award in 2010. At the present time, he leads the Next Generation Systems Area of research.

References

  1. Fundamentals of Solid-State Electronics, Chih-Tang Sah. World Scientific, first published 1991, reprinted 1992, 1993 (pbk), 1994, 1995, 2001, 2002, 2006, ISBN   981-02-0637-2. -- ISBN   981-02-0638-0 (pbk).
  2. "1960 - Metal Oxide Semiconductor (MOS) Transistor Demonstrated". The Silicon Engine. Computer History Museum . Retrieved 25 September 2019.
  3. Sze, Simon M. (2002). Semiconductor Devices: Physics and Technology (PDF) (2nd ed.). Wiley. p. 4. ISBN   0-471-33372-7.
  4. Davari, Bijan; Ting, Chung-Yu; Ahn, Kie Y.; Basavaiah, S.; Hu, Chao-Kun; Taur, Yuan; Wordeman, Matthew R.; Aboelfotoh, O. (1987). "Submicron Tungsten Gate MOSFET with 10 nm Gate Oxide". 1987 Symposium on VLSI Technology. Digest of Technical Papers: 61–62.