Ferroelectric capacitor and method for fabricating the same

Abstract

In a ferroelectric capacitor comprising: a lower electrode; a ferroelectric film formed on the lower electrode; and an upper electrode formed on the ferroelectric film, the coercive voltage of the ferroelectric film is 1.5 V or less and the polarization switching time of the ferroelectric film is 200 ns or less.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C are sectional views showing a method for fabricating a ferroelectric capacitor according to a first embodiment of the present invention in the order of its fabrication process steps.

FIGS. 2A and 2B are sectional views showing the method for fabricating a ferroelectric capacitor according to the first embodiment of the present invention in the order of its fabrication process steps.

FIG. 3 is a graph showing the amount of polarization obtained by the ferroelectric capacitor according to the first embodiment of the present invention and the ferroelectric capacitor according to the conventional example.

FIG. 4A is a graph showing the relation between the coercive voltage (V) of a ferroelectric film and the percentage (%) of polarization reversal obtained by the ferroelectric capacitor according to the first embodiment of the present invention. FIG. 4B is a graph showing the relation between the ratio between Ta and Nb that are the B-site metal elements and the coercive voltage obtained by the ferroelectric capacitor with SBTN used for a ferroelectric film according to the first embodiment of the present invention.

FIGS. 5A to 5C are sectional views showing a fabrication method of a ferroelectric capacitor made of SBTN according to a second embodiment of the present invention in the order of its fabrication process steps.

FIGS. 6A and 6B are sectional views showing the fabrication method of a ferroelectric capacitor made of SBTN according to the second embodiment of the present invention in the order of its fabrication process steps.

FIGS. 7A to 7C are sectional views showing a fabrication method of a ferroelectric capacitor made of PZT according to the second embodiment of the present invention in the order of its fabrication process steps.

FIGS. 8A and 8B are sectional views showing the fabrication method of a ferroelectric capacitor made of PZT according to the second embodiment of the present invention in the order of its fabrication process steps.

FIGS. 9A to 9C are sectional views showing a fabrication method of a ferroelectric capacitor made of BLT((Bi,La)₄Ti₃O₁₂) according to the second embodiment of the present invention in the order of its fabrication process steps.

FIGS. 10A and 10B are sectional views showing the fabrication method of a ferroelectric capacitor made of BLT according to the second embodiment of the present invention in the order of its fabrication process steps.

Claims

1. A ferroelectric capacitor comprising: a lower electrode; a ferroelectric film formed on the lower electrode; and an upper electrode formed on the ferroelectric film, wherein the coercive voltage of the ferroelectric film is 1.5 V or less, and the polarization switching time of the ferroelectric film is 200 ns or less.

2. The capacitor of claim 1, wherein the ferroelectric film has a bismuth layer perovskite structure made by alternately stacking a bismuth oxide layer and a perovskite layer,the ferroelectric film has a general formula represented by (Bi2O2)2+(Am−1BmO3m+1)2−

3. The capacitor of claim 1, wherein the coercive voltage of the ferroelectric film is 1.0 V or less, and the polarization switching time of the ferroelectric film is 100 ns or less.

4. The capacitor of claim 3, wherein the ferroelectric film has a bismuth layer perovskite structure made by alternately stacking a bismuth oxide layer and a perovskite layer,the ferroelectric film has a general formula represented by (Bi2O2)2+(Am−1BmO3m+1)2−

5. The capacitor of claim 1, wherein the coercive voltage of the ferroelectric film is 0.6 V or less, and the polarization switching time of the ferroelectric film is 20 ns or less.

6. The capacitor of claim 5, wherein the ferroelectric film has a bismuth layer perovskite structure made by alternately stacking a bismuth oxide layer and a perovskite layer,the ferroelectric film has a general formula represented by (Bi2O2)2+(Am−1BmO3m+1)2−

7. The capacitor of claim 1, wherein the ferroelectric film has a composition in which the amount of shift from the stoichiometric composition is within 10%.

8. The capacitor of claim 7, wherein the stoichiometric composition is SrBi2(Ta1−bNbb)2O9, andthe composition of the ferroelectric film is SrxBiy(Ta1−bNbb)2O5+x+3y/2 (0.9≦x≦1, 2≦y≦2.2, 0.5<b≦1).

9. A method for fabricating a ferroelectric capacitor comprising: a lower electrode; a ferroelectric film formed on the lower electrode; and an upper electrode formed on the ferroelectric film, wherein the ferroelectric film is formed by an MOCVD method which employs at least one metal organic material of which main component is one of elements constituting the ferroelectric film, andthe coercive voltage of the ferroelectric film is 1.5 V or less, and the polarization switching time of the ferroelectric film is 200 ns or less.

10. The method of claim 9, wherein the lower electrode is formed by an MOCVD method which employs at least one metal organic material of which main component is noble metal, andthe upper electrode is formed by an MOCVD method which employs at least one metal organic material of which main component is noble metal.