A MIS capacitor is a capacitor formed from a layer of

metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...

, a layer of insulating material and a layer of

semiconductor A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...

material. It gets its name from the initials of the metal-insulator-semiconductor (MIS) structure. As with the MOS

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 ...

structure, for historical reasons, this layer is also often referred to as a MOS capacitor, but this specifically refers to an oxide insulator material. The maximum capacitance, ''C''_MIS(max) is calculated analogously to the plate capacitor: :

C_\mathrm=\varepsilon_0\varepsilon_r \cdot

where : *''ε_r'' is the insulator's

relative permittivity 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 insulat ...

*''ε₀'' is the

permittivity In electromagnetism, the absolute permittivity, often simply called permittivity and denoted by the Greek letter ''ε'' ( epsilon), is a measure of the electric polarizability of a dielectric. A material with high permittivity polarizes more in ...

of the

vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often dis ...

*''A'' is the area *''d'' is the insulator thickness The production method depends on materials used (it is even possible that polymers can be used as both the insulator or the semiconductor layers). We will consider an example of an inorganic MOS capacitor based on

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 ...

and

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 ...

. On the semiconductor substrate, a thin layer of oxide (silicon dioxide) is applied (by, for example,

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 ...

, or

chemical vapour deposition Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films. In typical CVD, the wafer (substra ...

) and then

coated A coating is a covering that is applied to the surface of an object, usually referred to as the substrate. The purpose of applying the coating may be decorative, functional, or both. Coatings may be applied as liquids, gases or solids e.g. Powder ...

with a metal. This structure and thus a capacitor of this type is present in every MIS field-effect transistor, such as

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 ...

s. For the steady reduction of the size of structures in microelectronics, the ever thinner insulation layers are required (to keep the same capacitance for smaller area). However when the oxide thickness falls below ~ 5 nm there arise parasitic leakages due to the tunneling effect. From this reason, the use of so-called high-κ dielectrics as the insulator material is being investigated. In the MOSFET R&D, the MIS capacitors are extensively used as a relatively simple testing bench, e.g. to examine fabrication process and properties of the novel insulator materials, to measure leakage currents and charge-to-breakdown, to get the trap density value, to verify different models for carrier transport. Furthermore the capacitors are often included in tutorial courses, particularly to discuss their charge states (inversion, depletion, accumulation) which also occur in the more complex transistor systems.

References

{{Reflist Capacitors