In the
semiconductor industry
The semiconductor industry is the aggregate of companies engaged in the design and fabrication of semiconductors and semiconductor devices, such as transistors and integrated circuits. Its roots can be traced to the invention of the transistor ...
, the term high-κ dielectric refers to a material with a high
dielectric constant
The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insul ...
(κ,
kappa
Kappa (; uppercase Κ, lowercase κ or cursive ; , ''káppa'') is the tenth letter of the Greek alphabet, representing the voiceless velar plosive sound in Ancient and Modern Greek. In the system of Greek numerals, has a value of 20. It was d ...
), as compared to
silicon dioxide
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundan ...
. High-κ dielectrics are used in
semiconductor manufacturing
Semiconductor device fabrication is the process used to manufacture semiconductor devices, typically integrated circuits (ICs) such as microprocessors, microcontrollers, and memories (such as Random-access memory, RAM and flash memory). It is a ...
processes where they are usually used to replace a silicon dioxide
gate dielectric or another dielectric layer of a device. The implementation of high-κ gate dielectrics is one of several strategies developed to allow further miniaturization of microelectronic components, colloquially referred to as extending
Moore's Law
Moore's law is the observation that the Transistor count, number of transistors in an integrated circuit (IC) doubles about every two years. Moore's law is an observation and Forecasting, projection of a historical trend. Rather than a law of ...
.
Sometimes these materials are called "high-k" (pronounced "high kay"), instead of "high-κ" (high kappa).
Need for high-κ materials
Silicon dioxide
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundan ...
() has been used as a
gate oxide
The gate oxide is the dielectric layer that separates the metal gate, 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 ...
material for decades. As
metal–oxide–semiconductor field-effect transistor
upright=1.3, Two power MOSFETs in amperes">A in the ''on'' state, dissipating up to about 100 watt">W and controlling a load of over 2000 W. A matchstick is pictured for scale.
In electronics, the metal–oxide–semiconductor field- ...
s (MOSFETs) have decreased in size, the thickness of the silicon dioxide gate dielectric has steadily decreased to increase the
gate capacitance (per unit area) and thereby drive current (per device width), raising device performance. As the thickness scales below 2
nm, leakage currents due to
tunneling increase drastically, leading to high power consumption and reduced device reliability. Replacing the silicon dioxide gate dielectric with a high-κ material allows decreasing gate thickness thus increasing gate capacitance without the associated leakage effects.
First principles

The gate oxide in a
MOSFET
upright=1.3, Two power MOSFETs in amperes">A in the ''on'' state, dissipating up to about 100 watt">W and controlling a load of over 2000 W. A matchstick is pictured for scale.
In electronics, the metal–oxide–semiconductor field- ...
can be modeled as a parallel plate capacitor. Ignoring quantum mechanical and depletion effects from the
Si substrate and gate, the
capacitance
Capacitance is the ability of an object to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized are two closely related ...
of this parallel plate
capacitor
In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...
is given by
:
where
* is the capacitor area
* is the
relative dielectric constant of the material (3.9 for
silicon dioxide
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundan ...
)
* is the
permittivity of free space
Vacuum permittivity, commonly denoted (pronounced "epsilon nought" or "epsilon zero"), is the value of the absolute dielectric permittivity of classical vacuum. It may also be referred to as the permittivity of free space, the electric const ...
* is the thickness of the capacitor oxide insulator
Since leakage limitation constrains further reduction of , an alternative method to increase gate capacitance is to alter κ by replacing silicon dioxide with a high-κ material. In such a scenario, a thicker gate oxide layer might be used which can reduce the
leakage current flowing through the structure as well as improving the gate dielectric
reliability.
Gate capacitance impact on drive current
The drain current for a
MOSFET
upright=1.3, Two power MOSFETs in amperes">A in the ''on'' state, dissipating up to about 100 watt">W and controlling a load of over 2000 W. A matchstick is pictured for scale.
In electronics, the metal–oxide–semiconductor field- ...
can be written (using the gradual channel approximation) as
:
where
* is the width of the transistor channel
* is the channel length
* is the channel carrier mobility (assumed constant here)
* is the capacitance density associated with the gate dielectric when the underlying channel is in the inverted state
* is the voltage applied to the transistor gate
* is the
threshold voltage
The threshold voltage, commonly abbreviated as Vth or VGS(th), of a field-effect transistor (FET) is the minimum gate-to-source voltage (VGS) that is needed to create a conducting path between the source and drain terminals. It is an important s ...
The term is limited in range due to reliability and room temperature operation constraints, since a too large would create an undesirable, high electric field across the oxide. Furthermore, cannot easily be reduced below about 200 mV, because leakage currents due to increased oxide leakage (that is, assuming high-κ dielectrics are not available) and
subthreshold conduction raise stand-by power consumption to unacceptable levels. (See the industry roadmap, which limits threshold to 200 mV, and Roy ''et al.''
[
]). Thus, according to this simplified list of factors, an increased requires a reduction in the channel length or an increase in the gate dielectric capacitance.
Materials and considerations
Replacing the silicon dioxide gate dielectric with another material adds complexity to the manufacturing process. Silicon dioxide can be formed by
oxidizing
Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...
the underlying silicon, ensuring a uniform, conformal oxide and high interface quality. As a consequence, development efforts have focused on finding a material with a requisitely high dielectric constant that can be easily integrated into a manufacturing process. Other key considerations include
band alignment to
silicon
Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...
(which may alter leakage current), film morphology, thermal stability, maintenance of a high
mobility of charge carriers in the channel and minimization of electrical defects in the film/interface. Materials which have received considerable attention are
hafnium silicate,
zirconium silicate,
hafnium dioxide and
zirconium dioxide, typically deposited using
atomic layer deposition
Atomic layer deposition (ALD) is a thin-film deposition technique based on the sequential use of a gas-phase chemical process; it is a subclass of chemical vapour deposition. The majority of ALD reactions use two chemicals called wiktionary:precu ...
.
It is expected that defect states in the high-κ dielectric can influence its electrical properties. Defect states can be measured for example by using zero-bias thermally stimulated current, zero-temperature-gradient zero-bias thermally stimulated
current spectroscopy, or
inelastic electron tunneling spectroscopy (IETS).
Use in industry
Industry has employed
oxynitride gate dielectrics since the 1990s, wherein a conventionally formed silicon oxide dielectric is infused with a small amount of nitrogen. The nitride content subtly raises the dielectric constant and is thought to offer other advantages, such as resistance against dopant diffusion through the gate dielectric.
In 2000,
Gurtej Singh Sandhu and Trung T. Doan of
Micron Technology
Micron Technology, Inc. is an American producer of computer memory and computer data storage including dynamic random-access memory, flash memory, and solid-state drives (SSDs). It is headquartered in Boise, Idaho. Micron's consumer produc ...
initiated the development of
atomic layer deposition
Atomic layer deposition (ALD) is a thin-film deposition technique based on the sequential use of a gas-phase chemical process; it is a subclass of chemical vapour deposition. The majority of ALD reactions use two chemicals called wiktionary:precu ...
high-κ
films
A film, also known as a movie or motion picture, is a work of Visual arts, visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, emotions, or atmosphere through the use of moving images that are gen ...
for
DRAM
Dram, DRAM, or drams may refer to:
Technology and engineering
* Dram (unit), a unit of mass and volume, and an informal name for a small amount of liquor, especially whisky or whiskey
* Dynamic random-access memory, a type of electronic semicondu ...
memory devices. This helped drive cost-effective implementation of
semiconductor memory
Semiconductor memory is a digital electronic semiconductor device used for digital data storage, such as computer memory. It typically refers to devices in which data is stored within metal–oxide–semiconductor (MOS) memory cells on a si ...
, starting with
90-nm node
In general, a node is a localized swelling (a "knot") or a point of intersection (a vertex).
Node may refer to:
In mathematics
* Vertex (graph theory), a vertex in a mathematical graph
*Vertex (geometry), a point where two or more curves, lines ...
DRAM.
In early 2007,
Intel
Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California, and Delaware General Corporation Law, incorporated in Delaware. Intel designs, manufactures, and sells computer compo ...
announced the deployment of
hafnium
Hafnium is a chemical element; it has symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in many zirconium minerals. Its existence was predicted by Dm ...
-based high-κ dielectrics in conjunction with a metallic gate for components built on
45 nanometer technologies, and has shipped it in the 2007 processor series codenamed
Penryn. At the same time,
IBM
International Business Machines Corporation (using the trademark IBM), nicknamed Big Blue, is an American Multinational corporation, multinational technology company headquartered in Armonk, New York, and present in over 175 countries. It is ...
announced plans to transition to high-κ materials, also hafnium-based, for some products in 2008. While not identified, the most likely dielectric used in such applications are some form of nitrided hafnium silicates (). and are susceptible to crystallization during dopant activation annealing.
NEC
is a Japanese multinational information technology and electronics corporation, headquartered at the NEC Supertower in Minato, Tokyo, Japan. It provides IT and network solutions, including cloud computing, artificial intelligence (AI), Inte ...
Electronics has also announced the use of a dielectric in their 55 nm ''UltimateLowPower'' technology.
However, even is susceptible to trap-related leakage currents, which tend to increase with stress over device lifetime. This leakage effect becomes more severe as hafnium concentration increases. There is no guarantee, however, that hafnium will serve as a de facto basis for future high-κ dielectrics. The 2006
ITRS roadmap predicted the implementation of high-κ materials to be commonplace in the industry by 2010.
See also
*
Low-κ dielectric
*
Silicon–germanium
*
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 perf ...
References
Further reading
Review articleby Wilk ''et al.'' in the
Journal of Applied Physics
*Houssa, M. (Ed.) (2003) ''High-k Dielectrics'' Institute of Physics
CRC Press Online*Huff, H.R., Gilmer, D.C. (Ed.) (2005) ''High Dielectric Constant Materials : VLSI MOSFET applications'' Springer
*Demkov, A.A, Navrotsky, A., (Ed.) (2005) ''Materials Fundamentals of Gate Dielectrics'' Springer
*"High dielectric constant gate oxides for metal oxide Si transistors"
Robertson, J. (''Rep. Prog. Phys.'' 69 327-396 2006) ''Institute Physics Publishing'' High dielectric constant gate oxides]
*Media coverage of March, 2007 Intel/IBM announcement
BBC NEWS, Technology, Chips push through nano-barrier*Gusev, E. P. (Ed.) (2006) "Defects in High-k Gate Dielectric Stacks: Nano-Electronic Semiconductor Devices", Springer
{{DEFAULTSORT:High-k dielectric
High-κ dielectrics,
Electronic engineering
Transistors
Semiconductor fabrication materials
MOSFETs