Patent ID: 7208802

Claim:
An insulating film comprising: a first barrier layer consisting of a material having a first bandgap and a first relative permittivity; a well layer provided on the first barrier layer, consisting of a material having a second bandgap smaller than the first bandgap and having a second relative permittivity larger than first relative permittivity, discrete energy levels being formed in the well layer by a quantum effect; and a second barrier layer provided on the well layer, consisting of a material having a third bandgap larger than the second bandgap and having a third relative permittivity smaller than second relative permittivity, each of the first and second barrier layers having a thickness not smaller than 2.5 angstroms, and the following condition being satisfied: 2.5>( d 1/ε1+ d 2/ε2) where d 1 (angstrom) is the thickness of the first barrier layer, ε 1 is the relative permittivity of the first barrier layer, d 2 (angstrom) is the thickness of the second barrier layer and ε 2 is the third permittivity of the second barrier layer, wherein the first bandgap is a bandgap of SiO 2 .