Editing Dielectric (section)

==Applications==

===Capacitors===
{{Main|Capacitor}}
[[Image:Capacitor schematic with dielectric.svg|thumb|upright|Charge separation in a parallel-plate capacitor causes an internal electric field. A dielectric (orange) reduces the field and increases the capacitance.]]

Commercially manufactured capacitors typically use a [[solid]] dielectric material with high [[permittivity]] as the intervening medium between the stored positive and negative charges. This material is often referred to in technical contexts as the ''capacitor dielectric''.<ref>Müssig, Hans-Joachim. ''Semiconductor capacitor with praseodymium oxide as dielectric'', {{US Patent|7113388}} published 2003-11-06, issued 2004-10-18, assigned to IHP GmbH- Innovations for High Performance Microelectronics/Institute Fur Innovative Mikroelektronik</ref>

The most obvious advantage to using such a dielectric material is that it prevents the conducting plates, on which the charges are stored, from coming into direct electrical contact. More significantly, however, a high permittivity allows a greater stored charge at a given voltage. This can be seen by treating the case of a linear dielectric with permittivity ''ε'' and thickness ''d'' between two conducting plates with uniform charge density ''σ<sub>ε</sub>''. In this case the charge density is given by

<math display="block">\sigma_{\varepsilon}=\varepsilon\frac{V}{d}</math>

and the [[capacitance]] per unit area by

<math display="block">c=\frac{\sigma_{\varepsilon}}{V}=\frac{\varepsilon}{d}</math>

From this, it can easily be seen that a larger ''ε'' leads to greater charge stored and thus greater capacitance.

Dielectric materials used for capacitors are also chosen such that they are resistant to [[ionisation]]. This allows the capacitor to operate at higher voltages before the insulating dielectric ionises and begins to allow undesirable current.

===Dielectric resonator===
{{Main|Dielectric resonator}}

A ''dielectric resonator oscillator'' (DRO) is an electronic component that exhibits [[resonance]] of the polarisation response for a narrow range of frequencies, generally in the microwave band. It consists of a "puck" of ceramic that has a large dielectric constant and a low [[dissipation factor]]. Such resonators are often used to provide a frequency reference in an oscillator circuit. An unshielded dielectric resonator can be used as a [[Dielectric Resonator Antenna|dielectric resonator antenna]] (DRA).

===BST thin films===
From 2002 to 2004, the United States [[Army Research Laboratory]] (ARL) conducted research on thin film technology. Barium strontium titanate (BST), a ferroelectric thin film, was studied for the fabrication of radio frequency and microwave components, such as voltage-controlled oscillators, tunable filters and phase shifters.<ref name=Cole>{{cite journal|title=Novel tunable acceptor doped BST thin films for high quality tunable microwave devices|journal=Revista Mexicana de Fisica|volume=50|bibcode=2004RMxF...50..232C|last1=Cole|first1=M. W.|last2=Geyer|first2=R. G.|year=2004|issue=3|page=232}}</ref>

The research was part of an effort to provide the Army with highly-tunable, microwave-compatible materials for broadband electric-field tunable devices, which operate consistently in extreme temperatures.<ref>{{cite book|url=https://books.google.com/books?id=XzZLtRlUPNoC&q=tunable+microwave+devices+army+research+laboratory&pg=PA57|title=Developments in Dielectric Materials and Electronic Devices: Proceedings of the 106th Annual Meeting of The American Ceramic Society, Indianapolis, Indiana, USA 2004|last1=Nair|first1=K. M.|last2=Guo|first2=Ruyan|last3=Bhalla|first3=Amar S.|last4=Hirano|first4=S.-I.|last5=Suvorov|first5=D.|date=2012-04-11|publisher=John Wiley & Sons|isbn=9781118408193|language=en}}</ref> This work improved tunability of bulk barium strontium titanate, which is a thin film enabler for electronics components.<ref>{{cite book|url=https://books.google.com/books?id=gt_4CiNliKEC&q=tunable+microwave+devices+army+research+laboratory&pg=PA229|title=Ceramic Materials and Multilayer Electronic Devices|last1=Nair|first1=K. M.|last2=Bhalla|first2=Amar S.|last3=Hirano|first3=S.-I.|last4=Suvorov|first4=D.|last5=Schwartz|first5=Robert W.|last6=Zhu|first6=Wei|date=2012-04-11|publisher=John Wiley & Sons|isbn=9781118406762|language=en}}</ref>

In a 2004 research paper, U.S. ARL researchers explored how small concentrations of acceptor dopants can dramatically modify the properties of ferroelectric materials such as BST.<ref>{{cite journal|last1=Cole|first1=M. W.|last2=Hubbard|first2=C.|last3=Ngo|first3=E.|last4=Ervin|first4=M.|last5=Wood|first5=M.|last6=Geyer|first6=R. G.|date=July 2002|title=Structure–property relationships in pure and acceptor-doped Ba1−xSrxTiO3 thin films for tunable microwave device applications|journal=Journal of Applied Physics|language=en|volume=92|issue=1|pages=475–483|doi=10.1063/1.1484231|issn=0021-8979|bibcode=2002JAP....92..475C}}</ref>

Researchers "doped" BST thin films with magnesium, analyzing the "structure, microstructure, surface morphology and film/substrate compositional quality" of the result. The Mg doped BST films showed "improved dielectric properties, low leakage current, and good tunability", meriting potential for use in microwave tunable devices.<ref name=Cole/>