FERROELECTRIC DEVICE AND METHOD FOR FABRICATING THE SAME

1 . A ferroelectric device comprising:

a MOS transistor formed in a substrate;

a polycrystalline electrode formed on or above the substrate; and

a polycrystalline ferroelectric film formed on the polycrystalline electrode, the polycrystalline ferroelectric film being made up of a large number of bismuth titanate crystals having a layered perovskite structure,

wherein a (104) plane in the bismuth titanate crystals is oriented substantially in parallel to an interface of the polycrystalline electrode and the polycrystalline ferroelectric film.

2 . The ferroelectric device of claim 1 , further comprising an insulation film formed on or above the substrate so as to have a concave portion,

wherein the polycrystalline electrode is formed so as to cover inner walls of the concave portion.

3 . The ferroelectric device of claim 1 , wherein the bismuth titanate crystals occupy 70% or more of an area of the polycrystalline ferroelectric film, and

the (104) plane in the bismuth titanate crystals is tilted from the interface by an angle in the range from −15° or more to +15° or less.

4 . The ferroelectric device of claim 1 , wherein the polycrystalline electrode is formed of platinum or strontium ruthenium oxide, and

a (111) plane in the polycrystalline electrode is oriented substantially in parallel to the interface.

5 . The ferroelectric device of claim 1 , wherein the polycrystalline ferroelectric film contains a rare earth element.

6 . A method for fabricating a ferroelectric device, the method comprising the steps of:

a) forming a polycrystalline electrode on or above a substrate in which a MOS transistor is formed;

b) performing metal organic chemical vapor deposition to form an amorphous film of bismuth titanate on the polycrystalline electrode; and

c) performing annealing at a temperature in a predetermined range to make the amorphous film be a polycrystalline ferroelectric film made up of a large number of bismuth titanate having a layered perovskite structure,

wherein the step c) includes a sub-step of increasing a temperature of the amorphous film to a lower limit of the predetermined temperature range at a temperature increase rate at which crystal nuclei are not grown, and

a (104) plane in the bismuth titanate crystals is oriented substantially in parallel to an interface of the polycrystalline electrode and the polycrystalline ferroelectric film.

7 . The method of claim 6 , further comprising, before the step a), a step d) forming on or above the substrate an insulation film having a concave portion,

wherein in the step a), the polycrystalline electrode is formed so as to cover inner walls of the concave portion.

8 . The method of claim 6 , wherein in the step c),

the temperature increase rate is 10° C./sec or more on an average, and

the predetermined temperature range is 680° C. or more and 780° C. or less.

9 . The method of claim 6 , wherein in the step b),

a bismuth composition in the amorphous film is 3.8 or more and 4.1 or less where a titanium composition is standardized with 3.

10 . The method of claim 6 , wherein in the step b),

the amorphous film contains a rare earth element, and

a composition of a sum of bismuth and the rare earth element in the amorphous film is 3.8 or more and 4.1 or less where a titanium composition is standardized with 3.

11 . The method of claim 6 , wherein the step a) includes a sub-step of performing sputtering or metal organic chemical vapor deposition to form the polycrystalline electrode of platinum or strontium ruthenium oxide.