tyle=" margin-top: 60pt; margin-bottom: 0pt; margin-left: 0pt; margin-right: 0pt;
text-align: center; text-indent: 0pt; line-height: 52pt;">Dielectric Materials

Chapter 10 of Solymar

Introduction

Dielectrics are insulators

No distinction between semiconductors and dielectrics in terms of
band structure
Dielectrics have larger band gap (>3 eV)

Macroscopic Approach

Under an electric field, there is no charge carriers moving from one
end to the other end no conduction
Charges respond to electric field - displacement
Dielectric displacement

Electric field E
Dielectric constant e = e</span><span style=" font-family: 'Times New Roman', 'Arial';
font-size: 24pt; font-weight: normal; font-style: normal; text-decoration: none;
">_r</span><span style=" font-family: 'Symbol', 'Arial'; font-size: 24pt;
font-weight: normal; font-style: normal; text-decoration: none;">_e</span><span
style=" font-family: 'Times New Roman', 'Arial'; font-size: 24pt; font-weight: normal;
font-style: normal; text-decoration: none;"><sub>o


Permittivity of free space
e</sub></span><span
style=" font-family: 'Times New Roman', 'Arial'; font-size: 20pt; font-weight: normal;
font-style: normal; text-decoration: none;"><sub>o

Relative dielectric constant
e</sub></span><span
style=" font-family: 'Times New Roman', 'Arial'; font-size: 20pt; font-weight: normal;
font-style: normal; text-decoration: none;"><sub>r

Capacitor

A capacitor consists of two conductive plates, separated by an insulator
(Fig. 10.1)

Charge accumulates on the plates with voltage

If the insulator is vacuum, the surface charge density on one of the
plates is


If a dielectric is inserted between plates, surface charge density
increases


The increase in surface charge density


Dielectric susceptibility

Microscopic Approach

How atoms react to an external electric field

The centers of positive and negative charges coincide with no electric
field
With an electric field, there is a shift in negative charge center
(electrons are easily moved with respect to nucleus)
If the separation between centers is d and
the total charge is q, the atom has an induced dipole moment m = q</span><span style=" font-family: 'Symbol', 'Arial'; font-size: 28pt;
font-weight: normal; font-style: normal; text-decoration: none;">d

Surface Charge Density