MIS capacitor

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MIS structure (metal / SiO 2 / p-Si) in a vertical MIS capacitor

The MIS capacitor is a special capacitor in electrical engineering , which is constructed in the form of the name -giving metal-insulator-semiconductor structure . As with the MOS field effect transistor , this layer structure is often referred to as a MOS capacitor for historical reasons. An oxide is specifically required as the insulator material ( dielectric ).

The maximum capacitance C MIS (max) is calculated analogously to the plate capacitor.

With:

  • ε r … relative (material- specific ) permittivity of the insulator
  • ε 0 … permittivity of the vacuum
  • A … area
  • d … thickness of the insulator

Production takes place in different ways depending on the material system ( polymers are also conceivable as insulators). A MOS capacitor based on silicon and silicon dioxide will serve as an example at this point . A thin layer of oxide (silicon dioxide) is applied to the semiconductor substrate ( substrate ) (e.g. thermal oxidation or TEOS - CVD ) and then vaporized with a metal .

The structure and thus the capacitor occurs in every MIS field effect transistor. The following situation arises for the constant downsizing of structures in microelectronics . From the formula above it follows that the capacitance increases as the insulating layers become thinner. However, this insulating layer, which is important for all MIS components, should not be less than 10 nm thick. Below this, tunnel currents through the insulator material increase with decreasing layer thickness . These leakage currents degrade, among other things, the electrical properties of MIS capacitors and MIS field effect transistors.

The continuous scaling of the components in microelectronics led to the fact that in the commercially available integrated circuits of the 2000s, the silicon dioxide insulation layer was only 1–2 nm and losses due to tunnel currents were too high. For this reason, some leading manufacturers switched to so-called high-k materials as insulator materials in the mid and late 2000s .

literature

  • Simon Min Sze, Kwok Kwok Ng: Physics of semiconductor devices . 3. Edition. John Wiley and Sons, 2006, ISBN 0-471-14323-5 , Chapter: Metal-Insulator-Semiconductor Capacitors , pp. 197-243 .