Patent ID: 7026693

Claim:
An insulating film comprising: n (n being an integer larger than 2) layers of barrier layer each consisting of a material having a bandgap larger than a first bandgap and having a relative permittivity smaller than a first relative permittivity; and (n−1) layers each consisting of a material having a bandgap smaller than the first bandgap and having a relative permittivity larger than the first relative permittivity, each of the barrier layers and each of the well layers being stacked by turns, discrete energy levels being formed in each of the well layers by a quantum effect, each of the barrier layers having a thickness not smaller than 2.5 angstroms, and the following condition being satisfied; 2.5>( d 1 /∈ 1 + d 2 /∈ 2 + . . . + dn/∈n ) where dm (m=1, 2, . . . n) is the thickness of the m-th layer of the barrier layers and ∈m (m=1, 2, . . . n ) is the relative permittivity of m-th layer of the barriers layers.