Patent attributes
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>(d1/ε1+d2/ε2) is satisfied where d1 and d2 (angstrom) are the thicknesses of the first and second barrier layers, respectively, ε1 is the first relative permittivity, and ε2 is the third permittivity.
