Patent Publication Number: US-2009220822-A1

Title: Ferroelectric recording medium and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims priority from Korean Patent Application No. 10-2008-0019303, filed on Feb. 29, 2008 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a recording medium and a method of manufacturing the same, and more particularly, to a ferroelectric recording medium onto which high density data can be recorded and a method of manufacturing the same. 
     2. Description of the Related Art 
     With the rapid development of data storage apparatuses such as conventional hard discs and optical discs, information storage apparatuses having a recording density of 1 Gbit/inch 2  or more have been developed, and the rapid development of digital techniques demand for a further increase in the capacity of information storage apparatuses. However, the recording density of conventional information storage apparatuses is limited due to super paramagnetic limitations of hard discs or diffraction limitations of a laser of an optical disc. 
     Recently, studies have been conducted with regard to a ferroelectric recording medium on which data is recorded by using an electric field instead of a magnetic field. In an electric field recording method, after forming electric domains polarized in a first direction and a second direction which is opposite to the first direction are formed on a surface of a ferroelectric recording medium using an electric field, the electric domains polarized in the first and second directions respectively correspond to data ‘0’ and ‘1’. A reproduction process is performed using an electric field sensor in which resistance changes according to polarization directions of the electric domains. In an electric field recording and reproducing method, a high recording density of 1 Tb/in 2  or more can be obtained. 
     The electric field recording and reproducing method can use a driving mechanism of a hard disc drive used in the conventional magnetic recording method and can also greatly increase the recording density. Thus, there is a need to develop a ferroelectric recording medium and a method of manufacturing the same. 
     SUMMARY OF THE INVENTION 
     The present invention provides a ferroelectric recording medium that allows high density recording and reproducing data, and a method of manufacturing the same. 
     According to an aspect of the present invention, there is provided a method of manufacturing a ferroelectric recording medium, the method comprising: forming an electrode layer of a conductive material on a substrate; forming an intermediate layer of a dielectric material on the electrode layer; forming a source material layer on the intermediate layer; and forming a ferroelectric layer from the source material layer by performing an annealing process. 
     The method may further comprise forming a capping layer on the source material layer to prevent volatilization of the source material layer. 
     The ferroelectric layer may be formed of a material selected from the group consisting of PbTiO 3 , Pb(Zr, Ti)O 3 , LiNbO 2 , LiTaO 3 , BiFeO 3 , and PVDF. 
     The intermediate layer may be formed of a material selected from the group consisting of ZrO 2 , TiO 2 , MgO 2 , SrTiO 3 , Al 2 O 3 , HfO 2 , Nb oxide, SiO 2 , and ZnO 2 . 
     The source material layer may be the same material layer as the ferroelectric layer. 
     The source material layer may comprise a plurality of material layers that form the ferroelectric layer by a reaction occurring between the material layers, and the material layers may comprise first and second material layers that are alternately stacked at least two times. 
     The annealing process for forming the ferroelectric layer may be performed at a temperature of 500° C. or below. 
     The forming of the electrode layer may comprise forming the conductive material layer on the substrate by depositing a conductive material and annealing the substrate on which the conductive material layer is formed at a temperature of 500° C. or below. 
     Prior to annealing the substrate on which the conductive material layer is formed, the forming of the electrode layer may further comprise forming a deformation prevention layer on a surface of the substrate opposite to the surface on which the conductive material layer is formed to prevent the substrate from being deformed during the annealing process. 
     The forming of the intermediate layer may comprise depositing a seed material, which is a dielectric material, on the substrate and forming the dielectric material layer by oxidizing the seed material by performing an annealing process in a gas atmosphere that contains oxygen. 
     According to another aspect of the present invention, there is provided a method of manufacturing a ferroelectric recording medium, the method comprising: forming an electrode layer on a substrate by depositing and annealing a conductive material layer on the substrate; forming an intermediate layer on the electrode layer, in which the intermediate layer is formed of one material selected from the group consisting of ZrO 2 , TiO 2 , MgO 2 , SrTiO 3 , Al 2 O 3 , HfO 2 , Nb oxide, SiO 2 , and ZnO 2 ; depositing at least one source material layer on the intermediate layer to form a ferroelectric layer formed of one material selected from the group consisting of PbTiO 3 , Pb(Zr, Ti)O 3 , LiNbO 2 , LiTaO 3 , BiFeO 3 , and PVDF; and forming the ferroelectric layer from the source material layer by performing an annealing process at a temperature of 500° C. or below in an Ar—O 2  mixture gas atmosphere which contains 5% oxygen. 
     According to an aspect of the present invention, there is provided a ferroelectric recording medium including a substrate; an electrode layer disposed on the substrate; a ferroelectric layer; and an intermediate layer between the electrode layer and the ferroelectric layer, wherein the intermediate layer induces the crystal orientation direction of the ferroelectric layer in a predetermined dominant orientation direction. 
     The ferroelectric recording medium may further comprise a deformation prevention layer disposed on a surface of the substrate opposite to the surface on which the electrode layer is disposed in order to prevent the substrate from being deformed. 
     The ferroelectric recording medium may further comprise: an adhesive layer disposed between the substrate and the electrode layer; and a deformation prevention layer disposed on a surface of the substrate opposite to the surface on which the electrode layer is formed in order to prevent the substrate from being deformed, wherein the deformation prevention layer may have a multi-layer structure formed of the same material used to form the electrode layer and the adhesive layer. 
     The ferroelectric layer may be formed of one material selected from the group consisting of PbTiO 3 , Pb(Zr, Ti)O 3 , LiNbO 2 , LiTaO 3 , BiFeO 3 , and PVDF. 
     The intermediate layer may be formed of one material selected from the group consisting of ZrO 2 , TiO 2 , MgO 2 , SrTiO 3 , Al 2 O 3 , HfO 2 , Nb oxide, SiO 2 , and ZnO 2 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIGS. 1A through 1C  are cross-sectional views for explaining a method of forming an electrode layer according to an exemplary embodiment of the present invention; 
         FIG. 1D  is a cross-sectional view for explaining a method of forming an intermediate layer according to an exemplary embodiment of the present invention; 
         FIGS. 1E through 1G  are cross-sectional views for explaining a method of forming a ferroelectric layer according to an exemplary embodiment of the present invention; 
         FIG. 1H  is a cross-sectional view of a ferroelectric recording medium manufactured by using the processes described with reference to  FIGS. 1A through 1G  according to an exemplary embodiment of the present invention; 
         FIG. 2A  is a graph showing X-ray scan data with respect to a sample; 
         FIG. 2B  is a graph showing synchrotron scan data with respect to the sample; 
         FIG. 2C  is a magnified portion of A of  FIG. 2B ; 
         FIG. 2D  is a graph showing X-ray scan data of a thin film of the sample; 
         FIG. 2E  is a schematic drawing for explaining a method of testing a ferroelectric characteristic of the sample; and 
         FIG. 3  is a perspective view of an electric field recording and reproducing apparatus having a driving mechanism of a hard disc drive. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION 
     The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as being limited to the exemplary embodiments set forth herein; rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those of ordinary skill in the art. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. Like reference numerals in the drawings denote like elements, and thus their description will be omitted. 
       FIGS. 1A through 1C  are cross-sectional views for explaining a method of forming an electrode layer  20  according to an exemplary embodiment of the present invention. Referring to  FIG. 1A , a conductive material such as Pt, Ir, Ru, Al, Au, RuO 2 , SrRuO 3 , or IrO 3  is deposited on a substrate. The deposition process may be performed by sputtering, thermal evaporation, chemical vapor deposition (CVD), metal organic chemical vapor deposition (MOCVD), atomic layer deposition (ALD), or pulsed laser deposition (PLD). A thickness of the electrode layer  20  may be 0.5 to 100 nm. The substrate  10  may be various types of substrates, for example, a glass substrate, a silicon substrate, or a polymer substrate. 
     Referring to  FIG. 1B , the process of forming the electrode layer  20  may include a process of depositing an adhesion layer  21  on the substrate  10  and a process of forming the electrode layer  20  by depositing a conductive material on the adhesion layer  21 . The adhesion layer  21  may be formed by depositing, for example, Ti, Zr, TiO 2 , ZrO 2 , Hf, HfO 2  to a thickness of 0.5 to 100 nm on the substrate  10  by using a sputtering method, a thermal evaporation method, a chemical vapor deposition (CVD) method, a metal organic chemical vapor deposition (MOCVD) method, an atomic layer deposition (ALD) method, or a pulsed laser deposition (PLD) method. 
     Referring to  FIG. 1C , the forming of the electrode layer  20  may include an annealing process of the substrate  10  on which the conductive material is deposited by the process described with reference to  FIG. 1A  or the substrate  10  on which the conductive material and the adhesion layer  21  are deposited by the processes described with reference to  FIGS. 1A and 1B . The annealing process may be performed at a temperature in a range from room temperature to 500° C. under an atmosphere of a gas mixture of Ar—O 2 . For example, the annealing process may include a step of annealing at a temperature of 400° C. for 2 minutes. The annealing facilitates the formation of crystalline of the electrode layer  20 . As a result of annealing, the electrode layer  20  has a very smooth surface. Also, stress that is applied to the substrate  10  during the deposition process may be mitigated due to the annealing. 
     Prior to performing the annealing process, the process of forming the electrode layer  20  may further include a process of forming a deformation prevention layer  23  on a surface of the substrate  10  opposite to the surface on which the electrode layer  20  is formed as indicated by a dotted line in  FIG. 1A . The deformation prevention layer  23  prevents the substrate  10  from bending during the annealing process described above, and thus, increases electrical contact between the electrode layer  20  and the substrate  10 . The deformation prevention layer  23  may be formed of the same material used to form the electrode layer  20 . As depicted in  FIG. 1B , if the electrode layer  20  is formed on the adhesion layer  21 , a deformation prevention layer  26  may be a multi-layer structure in which the deformation prevention layer  26  is formed of the same materials used to form the adhesion layer  21  and the electrode layer  20 . The deformation prevention layer  23  may be formed on the substrate  10  by depositing the same material used to form the electrode layer  20  by using a sputtering method, a thermal evaporation method, a chemical vapor deposition (CVD) method, a metal organic chemical vapor deposition (MOCVD) method, or an atomic layer deposition (ALD) method. Also, the deformation prevention layer  26  may be formed by sequentially depositing the same materials used to form the adhesion layer  21  and the electrode layer  20  by using a sputtering method, a thermal evaporation method, a chemical vapor deposition (CVD) method, a metal organic chemical vapor deposition (MOCVD) method, an atomic layer deposition (ALD) method, or a pulsed laser deposition (PLD) method. 
       FIG. 1D  is a cross-sectional view for explaining a method of forming an intermediate layer  30  according to an exemplary embodiment of the present invention. Referring to  FIG. 1D , the process of forming the intermediate layer  30  includes a process of forming a dielectric material layer formed of, for example, ZrO 2 , TiO 2 , MgO 2 , SrTiO 3 , Al 2 O 3 , HfO 2 , Nb oxide, SiO 2 , or ZnO 2  on the electrode layer  20 . The intermediate layer  30  may be formed by oxidizing a seed material by using annealing under a gas atmosphere containing oxygen after depositing the seed material, for example, Zr, Ti, Mg, Sr, Al, Hf, Nb, Si, or Zn on the electrode layer  20  by using a sputtering method, a thermal evaporation method, a chemical vapor deposition (CVD) method, a metal organic chemical vapor deposition (MOCVD) method, an atomic layer deposition (ALD) method, or a pulsed laser deposition (PLD) method. The annealing may be performed at a temperature of 500° C. or below. For example, the annealing process may include a step of annealing at a temperature of 400° C. for 1 minute. The intermediate layer  30  may also be formed by depositing a dielectric material, for example, ZrO 2 , TiO 2 , MgO 2 , SrTiO 3 , Al 2 O 3 , HfO 2 , Nb oxide, SiO 2 , or ZnO 2  directly on the electrode layer  20  by using a sputtering method, a thermal evaporation method, a chemical vapor deposition (CVD) method, a metal organic chemical vapor deposition (MOCVD) method, an atomic layer deposition (ALD) method, or a pulsed laser deposition (PLD) method. Also, the intermediate layer  30  may be formed by depositing a seed material, for example, Zr, Ti, Mg, Sr, Al, Hf, Nb, Si, or Zn on the electrode layer  20  at the same time as oxidizing the material by using a reactive deposition process. The annealing process described above may be performed after performing the direct deposition or the reactive deposition. The intermediate layer  30  may be formed to a thickness of 0.5 to 10 nm, and preferably, to a thickness of 1 to 4 nm. The material used to form the intermediate layer  30  has a very smooth surface. In a subsequent process for forming a ferroelectric layer, the intermediate layer  30  maintains high crystallinity in a crystallization process of the ferroelectric layer by inducing the ferroelectric layer to have a predetermined dominant orientation direction. Also, the intermediate layer  30  makes the surface of the ferroelectric layer smooth. 
     Next, a process of forming the ferroelectric layer is performed.  FIGS. 1E through 1G  are cross-sectional views for explaining a method of forming a ferroelectric layer according to an exemplary embodiment of the present invention. Referring to  FIG. 1E , the process of forming the ferroelectric layer includes a process of depositing a source material layer  40  on the intermediate layer  30  and a process of annealing the source material layer  40  to form the ferroelectric layer. The ferroelectric layer may be a material layer such as PbTiO 3 , Pb(Zr, Ti)O 3 , LiNbO 2 , LiTaO 3 , BiFeO 3 , or PVDF. 
     Referring to  FIG. 1F , the source material layer  40  may be formed by depositing a plurality of material layers  41  and  42  that form a material layer of PbTiO 3 , Pb(Zr, Ti)O 3 , LiNbO 2 , LiTaO 3 , BiFeO 3 , or PVDF by reacting each other, on the intermediate layer  30  by using, for example, a sputtering method, a thermal evaporation method, a chemical vapor deposition (CVD) method, a metal organic chemical vapor deposition (MOCVD) method, an atomic layer deposition (ALD) method, or a pulsed laser deposition (PLD) method. The material layers  41  and  42  may be alternately deposited at least two times. The material layers  41  and  42  are formed in an appropriate ratio in consideration of a stoichiometric composition and required ferroelectric characteristics of the ferroelectric layer. A capping layer  43  may further be formed on the material layers  41  and  42  in order to prevent or compensate for the source material loss due to volatilization when the material layers  41  and  42  react with each other in an annealing process which will be described later. The capping layer  43  may be one material layer of the material layers  41  and  42 . 
     Referring to  FIG. 1G , the source material layer  40  may be formed by depositing a material, for example, PbTiO 3 , Pb(Zr, Ti)O 3 , LiNbO 2 , LiTaO 3 , BiFeO 3 , or PVDF on the intermediate layer  30  by using a sputtering method, a thermal evaporation method, a chemical vapor deposition (CVD) method, a metal organic chemical vapor deposition (MOCVD) method, an atomic layer deposition (ALD) method, or a pulsed laser deposition (PLD) method. At this point also, a capping layer  43  may further be formed on the source material layer  40  in order to prevent or compensate for source material loss due to volatilization of the source material layer  40  in an annealing process which will be described later, and the capping layer  43  may be one material layer of the material layers  41  and  42  described above. Also, a starting layer  44  may further be formed between the intermediate layer  30  and the source material layer  40 . The starting layer  44  may be one material layer of the material layers  41  and  42 . 
     The annealing process may be performed at a temperature in a range from room temperature to 500° C. For example, the annealing process may include a step of annealing at a temperature 400 to 500° C. for 4 minutes. By performing the annealing process, the material layers  41  and  42  react with each other to form a ferroelectric layer on the intermediate layer  30 , and the ferroelectric layer crystallizes in a predetermined orientation direction. If a ferroelectric material is directly used as a source material, the source material crystallizes in a predetermined orientation direction due to the annealing. 
     As a result of performing the above processes, a ferroelectric recording medium is manufactured as depicted in  FIG. 1H . Conventional thin film manufacturing processes are performed at a high temperature of 500° C. or above, and produce a thin film having a very rough surface. According to the method of manufacturing a ferroelectric layer  50  using deposition and annealing at a temperature of 500° C. or below, the ferroelectric layer  50  is formed through a reaction and crystallization process from a solid state source material. Thus, the ferroelectric layer  50  having a minute and predetermined dominant orientation direction, and a high crystallinity can be obtained. Also, since the stoichiometric composition of the ferroelectric layer  50  can be readily controlled, a ferroelectric layer  50  having high ferroelectric characteristic can be obtained, thereby increasing recording density. Also, the ferroelectric layer  50  having a surface roughness of approximately 1 nm or less, that is, a very smooth surface, and a thickness of 20 nm or less can be manufactured. 
     As an example, a ferroelectric recording medium  500  is manufactured as a rotatable disc type, and thus, may be applied to an electric field recording/reproducing apparatus that employs a driving mechanism of a hard disc drive.  FIG. 3  is a perspective view of an electric field recording and reproducing apparatus having a driving mechanism of a hard disc drive. An electric field recording/reproducing head  100  is mounted on a suspension arm  200  provided on an end portion of a swing arm  300 . The swing arm  300  is rotated by a voice coil motor  400 . When the ferroelectric recording medium  500  is rotated, the electric field recording/reproducing head  100  rises from a surface of the ferroelectric recording medium  500  due to an air bearing effect. The electric field recording and reproducing apparatus of  FIG. 3  has a driving system identical to that of a conventional hard drive disc (HDD), and a magnetic recording medium in the conventional HDD is replaced by the ferroelectric recording medium  500 , and thus, a magnetic recording and reproducing head is replaced by the electric field recording/reproducing head  100 . If a driving mechanism of a HDD is employed, generally, the electric field recording and reproducing head  100  performs a recording/reproducing operation of information in a state in which the electric field recording/reproducing head  100  is raised from the surface of the ferroelectric recording medium  500  due to the air bearing effect. If the surface roughness of the ferroelectric layer  50  is large, an air bearing surface of the electric field recording/reproducing head  100  collides with the ferroelectric layer  50  in a recording/reproducing operation, and thus, the air bearing surface of the electric field recording/reproducing head  100  and the surface of the ferroelectric layer  50  may be damaged. The ferroelectric layer  50  manufactured according to the method described above has a very smooth surface, that is, has a surface roughness of approximately 1 nm or less, and thus, collision between the air bearing surface of the electric field recording/reproducing head  100  and the ferroelectric layer  50  may be prevented. And, since the ferroelectric layer  50  manufactured according to the method described above has a very smooth surface, even though there is no protective layer and/or no lubricant such as diamond like carbon (DLC) for protecting the surface of the ferroelectric layer  50 , the electric field recording/reproducing head  100  can be raised from the surface of the ferroelectric layer  50  due to the air bearing effect. 
     The method of manufacturing a ferroelectric recording medium according the exemplary embodiment will be described below. A glass substrate may be employed as the substrate  10 . The glass substrate is inexpensive, and thus, if a ferroelectric recording medium is manufactured using the glass substrate, price competitiveness may be ensured. 
     Formation of an adhesive layer: After placing a Zr-target in a sputtering chamber, the adhesion layer  21  is formed to a thickness of approximately 8 nm on the substrate  10  by depositing Zr using a sputtering process. The sputtering process may be performed under predetermined conditions of, for example, a room temperature, an Ar gas atmosphere with 4 mTorr, and an RF power of 50 W. 
     Formation of an electrode layer: A Pt target is placed in the sputtering chamber. For example, the electrode layer  20  is formed to a thickness of approximately 25 nm by depositing Pt on the adhesion layer  21  using a sputtering process under predetermined conditions of, for example, an Ar atmosphere of 4 mTorr and an RF power of 50 W. 
     Formation of a deformation prevention layer: The deformation prevention layer  23  is formed on the substrate  10  by sequentially depositing Zr to a thickness of approximately 20 nm and Pt to a thickness of approximately 150 nm using a sputtering process. The sputtering process may be performed under predetermined conditions of, for example, a room temperature, an Ar gas atmosphere with 4 mTorr, and an RF power of 50 W. 
     Annealing: An Ar—O 2  mixture gas atmosphere which contains 5% oxygen is formed in an annealing chamber. The annealing chamber may be set at a pressure of 40 mTorr. The annealing chamber is preheated to approximately 300° C. prior to placing the substrate  10  in the annealing chamber. After placing the substrate  10  in the annealing chamber, the annealing chamber is maintained at a temperature of approximately 300° C. for approximately 2 minutes. The temperature of the annealing chamber is slowly increased to approximately 400° C. in order to prevent the substrate  10  from being applied by thermal stress that causes bending of the substrate  10 . After maintaining the annealing chamber at the temperature of approximately 400° C. for approximately 2 minutes, the substrate  10  is taken out from the annealing chamber. In this process, oxygen is diffused into the adhesion layer  21  through the Pt-electrode layer  20  and oxidizes Zr into ZrO 2 . 
     Cooling: The resultant product is cooled for approximately 30 minutes in a vacuum state. 
     Formation of an intermediate layer: Zr is deposited to a thickness of 2.6 nm on the electrode layer  20  using a sputtering process. The sputtering process may be performed under predetermined conditions of, for example, a room temperature, an Ar gas atmosphere with 4 mTorr, and an RF power of 50 W. Afterwards, an Ar—O 2  mixture gas atmosphere which contains 5% oxygen is formed in an annealing chamber. The annealing chamber may be set at a pressure of 40 mTorr. The annealing chamber may be preheated to a temperature of approximately 300° C. prior to placing the substrate  10  in the annealing chamber. The annealing chamber is maintained at the temperature of approximately 300° C. for approximately 2 minutes. The temperature of the annealing chamber is slowly increased to approximately 400° C. in order to prevent the substrate  10  from being applied by thermal stress that causes bending of the substrate  10 . After maintaining the annealing chamber at the temperature of approximately 400° C. for approximately 1 minute, the substrate  10  is taken out of the annealing chamber. As a result of annealing, Zr is oxidized into ZrO 2  by oxygen on the Ar—O 2  mixture gas. ZrO 2  may be directly deposited on the electrode layer  20  from a ZrO 2  target, or ZrO 2  may be deposited on the electrode layer  20  by using a reactive sputtering using a Zr target. In this case, the annealing process may also be performed with respect to the resultant product. 
     Cooling: The resultant product is cooled for approximately 30 minutes in a vacuum state. 
     Formation of a ferroelectric layer: A PbO-material layer and a TiO 2 -material layer are used as the source material layer  40  for forming a PbTiO 3 -ferroelectric layer. In consideration of the stoichiometric composition of the PbTiO 3 -ferroelectric layer, the thickness of the PbO-material layer must be 1.26 times of that of the TiO 2 -material layer. However, the PbTiO 3 -ferroelectric layer is a material that allows a large deviation from the stoichiometric composition, and thus, the composition ratio of the PbO-material layer may be controlled slightly over or under the stoichiometric composition. Four layers of the PbO-material layer having a thickness of 1.8 nm and the TiO 2 -material layer having a thickness of 1.5 nm are deposited using a sputtering process at room temperature and a pressure of 10 mTorr under an Ar—O 2  mixture gas which contains 5% oxygen. In the present exemplary embodiment, the PbO-material layer is a starting layer; however, the TiO 2 -material layer may be employed as the starting layer. A PbO-material layer as the capping layer  43  is deposited to a thickness of 1 nm on the source material layer  40  in order to prevent loss of Pb having volatility. Of course, PbTiO 3  may be directly deposited on the intermediate layer  30 , and also, in this case, the PbO-material layer as the capping layer  43  may be deposited to a thickness of 1 nm on the PbTiO 3  layer. When the deposition of the source material  40  is completed, an annealing process for forming a ferroelectric layer is performed. An Ar—O 2  mixture gas atmosphere which contains 5% oxygen is formed in an annealing chamber. The pressure of the annealing chamber is controlled at 40 mTorr. Prior to placing the substrate  10  in the annealing chamber, the annealing chamber is preheated to a temperature of approximately 300° C. After placing the substrate  10  in the annealing chamber, the annealing chamber is maintained at the temperature of 300° C. for 2 minutes. The temperature of the annealing chamber is slowly increased to approximately 480° C. in order to prevent the substrate  10  from being subjected to thermal stress that causes bending of the substrate  10 . After maintaining the annealing chamber at the temperature of approximately 480° C. for approximately 2 minutes, the temperature of the annealing chamber is reduced to 430° C. and is maintained for 1 minute at this temperature, and then, is reduced to 400° C. and is maintained for 1 minute at this temperature. The annealing chamber is cooled at a pressure of 40 mTorr under an Ar—O 2  mixture gas atmosphere which contains 5% oxygen. Afterwards, the substrate  10  is taken out from the annealing chamber. Thus, a PbTiO 3 -ferroelectric layer having a thickness of 14 nm is formed on the intermediate layer  30 . 
     The ferroelectric recording medium manufactured according to the exemplary embodiment of the present invention described above is referred to as sample  1 .  FIG. 2A  is a graph showing X-ray scan data with respect to sample  1 . In  FIG. 2A , a peak of the PbTiO 3 -ferroelectric layer is not seen because the PbTiO 3 -ferroelectric layer is too thin to generate a sufficient signal. In  FIG. 2A , it is seen that a Pt-electrode layer is almost completely oriented in a (111) direction.  FIG. 2B  is a graph showing synchrotron scan data with respect to sample  1 , and  FIG. 2C  is a magnified portion of A of  FIG. 2B . The data of  FIGS. 2B and 2C  are obtained in an 8 degree offset state in order to prevent resonance of the Pt-electrode layer. Referring to  FIG. 2C , (a) indicates a ZrO 2 -intermediate layer having a tetragonal structure oriented in the (111) direction, (b) indicates a PbTiO 3 -ferroelectric layer oriented in a (101) direction and (c) indicates a PbTiO 3 -ferroelectric layer oriented in a (110) direction.  FIG. 2D  is a graph showing X-ray scan data of a thin film of sample  1 . The peak of the PbTiO 3 -ferroelectric layer can be clearly seen in  FIG. 2D . Thus, the formation of the PbTiO 3 -ferroelectric layer having a dominant orientation direction of (110) is confirmed since the (110) direction and the (101) direction belong to the same family.  FIG. 2E  is a schematic drawing for explaining a method of testing a ferroelectric characteristic of sample  1 . +5 V and −5 V are sequentially applied to rectangular regions having side lengths of 4 μm, 3.4 μm, 2.8 μm, 2.2 μm, 1.6 μm, and 1.0 μm, respectively, on a surface of the ferroelectric of sample  1 . Afterwards, polarization directions were investigated using a piezoelectric force microscope (PFM). It is observed that sample  1  was clearly switched due to the application of +5 V. The surface roughness of the sample  1  was measured using an atomic force microscope (ATM), and the result showed that a smooth surface having a root mean square (RMS) value of approximately 0.38 and a peak-to-peak value of approximately 4.9 nm was obtained. 
     Sample  2  was formed using the same process for forming sample  1  except that a ZrO 2 -intermediate layer was not used in sample  2 . The surface roughness of sample  2  was measured, and the result showed that sample  2  had a very rough surface having an RMS value of approximately 1 nm and a peak-to-peak value of approximately 56 nm. Also, the ferroelectric characteristic of sample  2  was investigated by applying voltages of ±5V, and showed an insufficient switching characteristic, that is, an insufficient ferroelectric characteristic. 
     Sample  3  was formed using the same process for forming sample  1  except that 2×(a PbO layer with a thickness of 3.6 nm and a TiO2 layer with a thickness of 3.0 nm) were used as a source material layer. The surface roughness of sample  3  was measured, and the result showed that sample  3  had a very smooth surface having an RMS value of approximately 0.47 nm and a peak-to-peak value of approximately 4.9 nm. Also, the ferroelectric characteristic of sample  3  was investigated by applying voltages of ±5V, and the result showed that sample  3  had a very clean switching characteristic. 
     Sample  4  was formed using the same process for forming sample  1  except that a ZrO 2 -intermediate layer having a thickness of 1.6 nm was used. The ferroelectric characteristic of sample  4  was investigated by applying voltages of ±5 V, and the result showed that sample  4  had a very clean switching characteristic. 
     Sample  5  was formed using the same process for forming sample  3  except that a ZrO 2 -intermediate layer having a thickness of 1.0 nm was used as a source material layer. The surface roughness of sample  5  was measured, and the result showed that sample  5  had a very smooth surface having an RMS value of approximately 0.54 nm and a peak-to-peak value of approximately 5.9 nm. Also, the ferroelectric characteristic of sample  2  was investigated by applying voltages of ±5 V, and the result showed that sample  5  had a very clean switching characteristic. 
     Sample  6  was formed using the same process for forming sample  1  except that 2×(a TiO2 layer with a thickness of 3.0 nm and a PbO layer with a thickness of 4.1 nm) were used as a source material layer and the TiO 2  layer was used as a starting layer instead of the PbO layer. The surface roughness of sample  6  was measured, and the result showed that sample  6  had a very smooth surface having an RMS value of approximately 0.35 nm and a peak-to-peak value of approximately 2.8 nm. Also, the ferroelectric characteristic of the sample  6  was investigated by applying voltages of ±5 V, and the result showed that the sample  6  had a very clean switching characteristic. 
     In the exemplary embodiment of the present invention, a method of manufacturing a PbTiO 3 -ferroelectric layer using a ZrO 2 -intermediate layer has been described. However, the method described above can also be applied to manufacture the PbTiO 3 -ferroelectric layer using an intermediate layer of, for example, TiO 2 , MgO 2 , SrTiO 3 , Al 2 O 3 , HfO 2 , Nb oxide, SiO 2 , or ZnO 2 , and also, can be applied to manufacture other ferroelectric layers of, for example, Pb(Zr, Ti)O 3 , LiNbO 2 , LiTaO 3 , BiFeO 3 , or PVDF. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.