| abstract |
An insulating film includes a first barrier layer, a well layer provided on the first barrier layer, a second barrier layer provided on the well layer. The first barrier layer consists of a material having a first bandgap and a first relative permittivity. The well layer consists of a material having a second bandgap smaller than the first bandgap and having a second relative permittivity larger than first relative permittivity. The second barrier layer consists of a material having a third bandgap larger than the second bandgap and having a third relative perminivity smaller than second relative permittivity. Each of the first and second barrier layers has a thickness not smaller than 2.5 angstroms, and 2.5>(d 1/ε1 +d 2/ε2 ) is satisfied where d 1 and d 2 (angstrom) are the thicknesses of the first and second barrier layers, respectively, ε 1 is the first relative permittivity, and ε 2 is the third permittivity. |