Method for manufacturing ferroelectric capacitor

Abstract

A ferroelectric capacitor and a method for manufacturing the same includes a lower electrode, a dielectric layer, and an upper electrode layer, which are sequentially stacked, wherein the dielectric layer has a multi-layer structure including a plurality of sequentially stacked ferroelectric films, and wherein two adjacent ferroelectric films have either different compositions or different composition ratios. Use of a ferroelectric capacitor according to an embodiment of the present invention, it is possible to hold stable polarization states of ferroelectric domains for a long retention time, and thus data written in the ferroelectric capacitor a long time ago can be accurately written, thereby improving the reliability of a ferroelectric random access memory (FRAM).

1 - 25 . (canceled)  
   
   
       26 . A method for manufacturing a ferroelectric capacitor in which a lower electrode, a dielectric layer, and an upper electrode layer are sequentially stacked, comprising: 
 forming a first ferroelectric film on the lower electrode; and    forming a second ferroelectric film on the first ferroelectric film, wherein the second ferroelectric film has a different composition or a different composition ratio from the composition or composition ratio of the first ferroelectric film, to form the dielectric layer.    
   
   
       27 . The method as claimed in  claim 26 , wherein the first ferroelectric film is formed to a thickness of 3 nm-50 nm and the second ferroelectric film is formed to a thickness of 30 nm-150 nm.  
   
   
       28 . The method as claimed in  claim 26 , further comprising: 
 forming a third ferroelectric film on the second ferroelectric film, wherein the third ferroelectric film has a different composition or a different composition ratio from the composition or composition ratio of the second ferroelectric film.    
   
   
       29 . The method as claimed in  claim 28 , wherein the third ferroelectric film is formed to a thickness of 3 nm-50 nm.  
   
   
       30 . The method as claimed in  claim 26 , wherein each of the ferroelectric films is formed at a temperature of 300-450° C.  
   
   
       31 . The method as claimed in  claim 28 , further comprising: 
 annealing at a temperature that is higher than the temperature for the formations of the first through third ferroelectric films after forming the ferroelectric films.    
   
   
       32 . The method as claimed in  claim 31 , wherein the annealing temperature is 450-650° C.  
   
   
       33 . The method as claimed in  claim 26 , wherein the first and the second ferroelectric films are formed using different formation processes to have the same composition but different composition ratios.  
   
   
       34 . The method as claimed in  claim 26 , wherein the first and the second ferroelectric films are formed using the same formation process to have different compositions.  
   
   
       35 . The method as claimed in  claim 33 , wherein the first and the second ferroelectric films are formed of a material selected from the group consisting of a PZT film, a PLZT film, and a BSO-PZT film.  
   
   
       36 . The method as claimed in  claim 34 , wherein the first and the second ferroelectric films are formed of a material selected from the group consisting of a PZT film, a PLZT film, and a BSO-PZT film.  
   
   
       37 . The method as claimed in  claim 35 , wherein the first and the second ferroelectric films are formed using either a chemical solution deposition (CSD), a metal organic chemical vapor deposition (MOCVD), or a combination of the two deposition processes.  
   
   
       38 . The method as claimed in  claim 36 , wherein the first and the second ferroelectric films are formed using either a chemical solution deposition (CSD), a metal organic chemical vapor deposition (MOCVD), or a combination of the two deposition processes.  
   
   
       39 . The method as claimed in  claim 28 , wherein the second and the third ferroelectric films are formed using different formation processes to have the same composition but different composition ratios.  
   
   
       40 . The method as claimed in  claim 28 , wherein the second and the third ferroelectric films are formed using the same formation process to have different compositions.  
   
   
       41 . The method as claimed in  claim 28 , wherein the first and the second ferroelectric films are formed using different formation processes to have the same composition but different composition ratios, and 
 wherein the second and the third ferroelectric films are formed using the same formation process to have different compositions.    
   
   
       42 . The method as claimed in  claim 39 , wherein the second and the third ferroelectric films are formed of a material selected from the group consisting of a PZT film, a PLZT film, and a BSO-PZT film.  
   
   
       43 . The method as claimed in  claim 40 , wherein the second and the third ferroelectric films are formed of a material selected from the group consisting of a PZT film, a PLZT film, and a BSO-PZT film.  
   
   
       44 . The method as claimed in  claim 42 , wherein the second and the third ferroelectric films are formed using either a chemical solution deposition (CSD), a metal organic chemical vapor deposition (MOCVD), or a combination of the two deposition processes.  
   
   
       45 . The method as claimed in  claim 43 , wherein the second and the third ferroelectric films are formed using either a chemical solution deposition (CSD), a metal organic chemical vapor deposition (MOCVD), or a combination of the two deposition processes.  
   
   
       46 . The method as claimed in  claim 26 , further comprising: 
 forming an interlayer between the lower electrode and the dielectric layer to facilitate the formation of the first ferroelectric film.    
   
   
       47 . The method as claimed in  claim 28 , further comprising: 
 forming an interlayer between the upper electrode and the dielectric layer to facilitate the formation of the third ferroelectric film.    
   
   
       48 . The method as claimed in  claim 26 , wherein at least one ferroelectric film is a BSO-PZT film.