The gate oxide is the
dielectric
In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the mate ...
layer that separates the
gate
A gate or gateway is a point of entry to or from a space enclosed by walls. The word derived from old Norse "gat" meaning road or path; But other terms include ''yett and port''. The concept originally referred to the gap or hole in the wall ...
terminal of a
MOSFET
The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which d ...
(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
In microfabrication, thermal oxidation is a way to produce a thin layer of oxide (usually silicon dioxide) on the surface of a wafer. The technique forces an oxidizing agent to diffuse into the wafer at high temperature and react with it. The rat ...
of the silicon of the channel to form a thin (5 - 200 nm) insulating layer of
silicon dioxide
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
. The insulating silicon dioxide layer is formed through a process of self-limiting oxidation, which is described by the
Deal–Grove model
The Deal–Grove model mathematically describes the growth of an oxide layer on the surface of a material. In particular, it is used to predict and interpret thermal oxidation of silicon in semiconductor device fabrication. The model was first pu ...
. A conductive gate material is subsequently deposited over the gate oxide to form the transistor. The gate oxide serves as the
dielectric
In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the mate ...
layer so that the gate can sustain as high as 1 to 5 MV/cm transverse
electric field
An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...
in order to strongly modulate the
conductance of the channel.
Above the gate oxide is a thin electrode layer made of a
conductor which can be
aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
, a highly doped
silicon
Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...
, a
refractory metal
Refractory metals are a class of metals that are extraordinarily resistant to heat and wear. The expression is mostly used in the context of materials science, metallurgy and engineering. The definition of which elements belong to this group diff ...
such as
tungsten
Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isolat ...
, a
silicide
A silicide is a type of chemical compound that combines silicon and a (usually) more electropositive element.
Silicon is more electropositive than carbon. Silicides are structurally closer to borides than to carbides.
Similar to borides and carb ...
(
TiSi,
MoSi2,
TaSi
Tasi (Greek: Τάσι) is an old neighbourhood in the city of Patras. It is located close to the castle in the modern upper city. During the Frankish rule, it contained a square named Tasso. During the Ottoman rule, the area around the square ...
or
WSi2) 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.
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
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
V
G. This is known as the inversion channel. It is the conduction channel that allows the
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no kn ...
s to flow from the source to the drain.
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 (SILC) is an increase in the gate leakage current of a MOSFET, used in semiconductor physics. It occurs due to defects created in the gate oxide during electrical stressing. SILC is perhaps the largest factor inhib ...
.
During manufacturing by
reactive-ion-etching the gate oxide may damaged by
antenna effect
The antenna effect, more formally plasma induced gate oxide damage, is an effect that can potentially cause yield and reliability problems during the manufacture of MOS integrated circuits. Factories (''fabs'') normally supply antenna rules, wh ...
.
History
The first
MOSFET
The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which d ...
(metal-oxide-semiconductor field-effect transistor, or MOS transistor) was invented by Egyptian engineer
Mohamed Atalla and Korean engineer
Dawon Kahng
Dawon Kahng ( ko, 강대원; May 4, 1931 – May 13, 1992) was a Korean-American electrical engineer and inventor, known for his work in solid-state electronics. He is best known for inventing the MOSFET (metal–oxide–semiconductor field-effe ...
at
Bell Labs
Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984),
then AT&T Bell Laboratories (1984–1996)
and Bell Labs Innovations (1996–2007),
is an American industrial research and scientific development company owned by mult ...
in 1959.
In 1960, Atalla and Kahng
fabricated the first MOSFET with a gate oxide thickness of
100 nm, along with a
gate
A gate or gateway is a point of entry to or from a space enclosed by walls. The word derived from old Norse "gat" meaning road or path; But other terms include ''yett and port''. The concept originally referred to the gap or hole in the wall ...
length of
20µm.
In 1987,
Bijan Davari
Bijan Davari (born September 16, 1954) 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 ...
led an
IBM research team that demonstrated the first MOSFET with a
10 nm gate oxide thickness, using
tungsten
Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isolat ...
-gate technology.
[{{cite journal , last1=Davari , first1=Bijan , author1-link=Bijan Davari , last2=Ting , first2=Chung-Yu , last3=Ahn , first3=Kie Y. , last4=Basavaiah , first4=S. , last5=Hu , first5=Chao-Kun , last6=Taur , first6=Yuan , last7=Wordeman , first7=Matthew R. , last8=Aboelfotoh , first8=O. , title=Submicron Tungsten Gate MOSFET with 10 nm Gate Oxide , journal=1987 Symposium on VLSI Technology. Digest of Technical Papers , date=1987 , pages=61–62 , url=https://ieeexplore.ieee.org/document/4480422]
References
MOSFETs
Semiconductor devices
Semiconductor fabrication materials
Semiconductor structures
Arab inventions
Egyptian inventions
South Korean inventions