Abstract:
A thin film capacitor including a first electrode structural body, a second electrode structural body and a dielectric thin film provided between the first and second electrode structural bodies and containing a bismuth layer structured compound. The surface of the first electrode structural body in contact with the dielectric thin film is oriented in the [001] direction. As a result, the dielectric thin film is naturally oriented so that its c axis is substantially perpendicular to the electrode structural bodies. When a voltage is applied between the first and second electrode structural bodies, since the direction of the electric field substantially coincides with the c axis of the bismuth layer structured compound, the bismuth layer structured compound can be prevented from exhibiting the ferroelectric property and made to sufficiently exhibit the paraelectric property. Further, a bismuth oxide layer (Bi 2 O 2 ) 2+  functions as an insulating layer, thereby improves the insulation property of the dielectric thin film while makes the thin film much thinner.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a thin film capacitor and a method for fabricating the same and, particularly, to a thin film capacitor and a method for fabricating a thin film capacitor suitable for use as a decoupling capacitor for an LSI having a high operating frequency. 
   DESCRIPTION OF THE PRIOR ART 
   Recently, the operating frequency of LSIs (Large Scale Integrated circuits), typically CPUs (Central Processing Units), has become higher and higher. In the LSI having a high operating frequency, power supply noise is very likely to be generated, and once power supply noise occurs, a voltage drop occurs due to parasitic resistance and parasitic inductance of the power supply wiring, causing the LSI to operate erroneously. 
   In order to prevent such a voltage drop caused by power supply noise, a decoupling capacitor is generally connected between the terminals of the LSI power supply. In the case where ea decoupling capacitor is connected between the terminals of the LSI power supply, the impedance of the power supply wiring decreases to effectively prevent voltage drop caused by power supply noise. 
   The impedance required of the power supply wiring is proportional to the operating voltage of the LSI and inversely proportional to the integration density of the LSI, the switching current of the LSI and the operating frequency of the LSI. Therefore, incurrent LSIs, which have high integration density, low operating voltage and high operating frequency, the impedance required of the power supply wiring is extremely low. In order to achieve such low impedance of the power supply wiring, it is necessary to increase the capacitance of the decoupling capacitor and considerably lower the inductance of the wiring connecting the terminals of the LSI power supply and the decoupling capacitor. 
   As a decoupling capacitor having a large capacitance, an electrolytic capacitor or a multilayer ceramic capacitor is generally employed. However, since the size of an electrolytic capacitor or multilayer ceramic capacitor is relatively large, it is difficult to integrate it with an LSI. Therefore, the electrolytic capacitor or multilayer ceramic capacitor has to be mounted on a substrate independently of the LSI and, as a result, the length of wiring for connecting the terminals of the LSI power supply and the decoupling capacitor is inevitably long. Accordingly, in the case where an electrolytic capacitor or a multilayer ceramic capacitor is employed as a decoupling capacitor, it is difficult to lower the inductance of the wiring. 
   In order to shorten the wiring for connecting the terminals of the LSI power supply and the decoupling capacitor, use of a thin film capacitor having a smaller size than that of an electrolytic capacitor or a multilayer ceramic capacitor is suitable. An example of a thin film capacitor having a large capacitor is disclosed in Japanese Patent Application Laid Open No. 2001-15382. 
   However, since PZT, PLZT, (Ba, Sr) TiO 3  (BST), Ta 2 O 5  or the like is employed as a dielectric material in the thin film capacitor disclosed in the above identified Japanese Patent Application Laid Open No. 2001-15382, the temperature characteristic thereof is poor. For example, since the dielectric constant of BST has a temperature dependency of −1000 to −4000 ppm/° C., in the case where BST is employed as a dielectric material, the capacitance of the thin film capacitor at 80° C. varies between −6% and −24% in comparison with that at 20° C. Therefore, use of a thin film capacitor employing BST as a dielectric material is not suitable for use as a decoupling capacitor for a high operating frequency LSI whose ambient temperature frequently reaches 80° C. or higher owing to heat generated by electric power consumption. 
   Furthermore, the dielectric constant of a dielectric thin film formed of any one of the above mentioned materials decreases as the thickness thereof decreases and the capacitance thereof greatly decreases when an electric field of 100 kV/cm, for example, is applied thereto. Therefore, in the case where any one of the above mentioned materials is used as a dielectric material for a thin film capacitor, it is difficult to simultaneously make the thin film capacitor small and the capacitance thereof great. Moreover, since the surface roughness of a dielectric thin film formed of any one of the above mentioned materials is high, its insulation performance tends to be lowered when formed thin. 
   It might be thought possible to overcome these problems by using a bismuth layer structured compound as a dielectric material for a thin film capacitor. The bismuth layer structured compound is discussed by Tadashi Takenaka in “Study on the particle orientation of bismuth layer structured ferroelectric ceramics and their application to piezoelectric or pyroelectric materials” Engineering Doctoral Thesis at the University of Kyoto (1984), Chapter 3, pages 23 to 36. The bismuth layer structured compound has an anisotropic crystal structure and behaves as a ferroelectric material. However, the bismuth layer structured compound exhibits only weak property as a ferroelectric material and behaves like as a paraelectric material along a certain axis of orientation. 
   Although the bismuth layer structured compound must have the property of a ferroelectric material when it is utilized to form a capacitor of a ferroelectric material memory, this property of the bismuth layer structured compound is undesirable when the bismuth layer structured compound is utilized as a dielectric material for a thin film capacitor since it causes variation in dielectric constant. Therefore, when a bismuth layer structured compound is used as a dielectric material for a thin film capacitor, it is necessary to suppress its ferroelectric property and use it under an environment where its paraelectric property can be fully exhibited. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide a thin film capacitor using a bismuth layer structured compound so that its ferroelectric property is suppressed and its paraelectric property is fully exhibited, and a method for fabricating the thin film capacitor. 
   A thin film capacitor according to the present invention comprises a first electrode structural body, a second electrode structural body and a dielectric thin film provided between the first electrode structural body and the second electrode structural body and containing a bismuth layer structured compound, and the surface of the first electrode structural body in contact with the dielectric thin film is oriented in the [001] direction. The [001] direction as termed herein means the [001] direction of a cubic crystal, a tetragonal crystal, a monoclinic crystal or an orthorhombic crystal. 
   Further, a method for fabricating a thin film capacitor according to the present invention comprises a first step of preparing a first electrode structural body whose surface is oriented in the [001] orientation, a second step of forming a dielectric thin film containing a bismuth layer structured compound on the surface of the first electrode structural body and a third step of forming a second electrode structural body on the dielectric thin film. 
   According to the present invention, since the surface of the first electrode structural body in contact with the dielectric thin film is oriented in the [ 001 ] direction, it is possible to improve the degree of orientation of the bismuth layer structured compound contained in the dielectric thin film in the [001] direction, namely, in the c axis direction. In other words, the c axis of the bismuth layer structured compound can be oriented so as to be perpendicular to the first electrode structural body and the second electrode structural body. 
   Therefore, when a voltage is applied between the first electrode structural body and the second electrode structural body, since the direction of the electric field substantially coincides with the c axis of the bismuth layer structured compound, the ferroelectric property of the bismuth layer structured compound can be suppressed and the paraelectric property thereof can be fully exhibited. Further, since a bismuth oxide layer (Bi 2 O) 2+  functions as an insulating layer, the insulation property of the dielectric thin film can be improved, whereby the dielectric thin film can be made much thinner. Since it is therefore possible to simultaneously make a thin film capacitor small and the capacitance thereof great, the thin film capacitor is suitable for use as a decoupling capacitor, in particular, a decoupling capacitor for an LSI having a high operating frequency. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic cross-sectional view showing a basic structure of a thin film capacitor according to the present invention. 
       FIG. 2  is a drawing schematically showing the structure of a thin film capacitor according to the present invention. 
       FIG. 3  is a schematic cross-sectional view showing one example of the arrangement of thin film capacitors according to the present invention in the case where the thin film capacitors are used as decoupling capacitors. 
       FIG. 4  is a schematic cross-sectional view showing the structure of a thin film capacitor according to a preferred embodiment of the present invention. 
       FIG. 5  is a schematic cross-sectional view showing the structure of a thin film capacitor according to another preferred embodiment of the present invention. 
   

   The above and other objects and features of the present invention will become apparent from the following description and the corresponding drawings. 
   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Prior to describing a preferred embodiment of the present invention, the basic structure of a thin film capacitor according to the present invention will be described. 
   As shown in  FIG. 1 , a thin film capacitor  10  having the basic structure of the present invention includes a lower electrode structural body  2 , an upper electrode structural body  4  and a dielectric thin film  6  formed between the lower electrode structural body  2  and the upper electrode structural body  4 . The thin film capacitor  10  having such a structure is manufactured by forming the dielectric thin film  6  on the lower electrode structural body  2  and further forming the upper electrode structural body  4  on the dielectric thin film  6 . As described later in detail, the thin film capacitor according to the present invention is suitable for use as a decoupling capacitor, in particular, a decoupling capacitor for an LSI having a high operating frequency, since it is possible to simultaneously make the thin film capacitor small and the capacitance thereof great, and the temperature characteristic thereof is excellent. 
   The lower electrode structural body  2  includes at least a lower electrode thin film serving as one of the electrodes of the thin film capacitor  10  and the surface  2   a thereof on the side of the dielectric thin film  6  is oriented in the [001] direction. However, it is not absolutely necessary for the entire surface  2   a of the lower electrode structural body  2  to be oriented in the [001] direction and it is sufficient for a portion of the surface  2   a  of the lower electrode structural body  2  in contact with the dielectric thin film  6  to be substantially oriented in the [001] direction. The lower electrode structural body  2  may have a single layer structure including only a lower electrode thin film or may have a multilayered structure including the lower electrode thin film and other layers. 
   The upper electrode structural body  4  includes at least an upper electrode thin film serving as the other electrode of the thin film capacitor  10 . The upper electrode structural body  4  may have a single layer structure including only an upper electrode thin film or may have a multilayered structure including the upper electrode thin film and other layers. 
   The dielectric thin film  6  comprises a dielectric material containing a bismuth layer structured compound. The bismuth layer structured compound is represented by the compositional formula: (Bi 2 O 2 ) 2+  (A m−1 B m O 3m+1 ) 2−  or Bi 2 A m−1 B m O 3m+3 , where the symbol m is a natural number, the symbol A is at least one element selected from a group consisting of sodium (Na), potassium (K), lead (Pb), barium (Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B is at least one element selected from a group consisting of iron (Fe), cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobitim (Nb), tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten (W). In the case where the symbol A and/or B includes two or more elements, the ratio of the elements can be arbitrarily determined. 
   As shown in  FIG. 2 , the bismuth layer structured compound has a layered stricture formed by alternately laminating perovskite layers  16  each including perovskite lattices  16   a  made of (m−1) ABO 3  and (Bi 2 O 2 ) 2+  layers  18 . The number of laminates each consisting of the perovskite layer  16  and the (Bi 2 O 2 ) 2+  layer  18  is not particularly limited and it is sufficient for the bismuth layer structured compound to include at least one pair of (Bi 2 O 2 ) 2+  layers  18  and one perovskite layer  16  sandwiched therebetween. 
   In the thin film capacitor according to the present invention, the degree of orientation of the bismuth layer structured compound contained in the dielectric thin film  6  in the [001] direction, namely, the degree of c axis orientation of the bismuth layer structured compound is improved. That is to say, the c axis of the bismuth layer structured compound is oriented so as to be substantially perpendicular to the lower electrode structural body  2  and the upper electrode structural body  6 . In other words, the c axis of the bismuth layer structured compound substantially coincides with the direction of an electric field to be generated by applying a voltage between the lower electrode structural body  2  and the upper electrode structural body  6 . 
   In the present invention, it is most preferable for the degree of c axis orientation to be 100% but it is not absolutely necessary for the degree of c axis orientation of the bismuth layer structured compound to be 100%. It is preferable for the degree of c axis orientation of the bismuth layer structured compound to be equal to or more than 80% and it is more preferable for the degree of c axis orientation of the bismuth layer structured compound to be equal to or more than 90%. Further, it is much more preferable for the degree of c axis orientation of the bismuth layer structured compound to be equal to or more than 95%. 
   The degree F of the c axis orientation of the bismuth layer structured compound is defined by the following formula, where P 0  is defined as X-ray diffraction intensity of polycrystal whose orientation is completely random in the c axis direction and P is defined as X-ray diffraction intensity of the actual bismuth layer structured compound in the c axis direction.
 
 F =( P−P   0 )/(1 −P   0 )×100  (Formula 1)
 
   Each of P and P 0  in the Formula 1 is defined by a ratio of the sum ΣI(001) of reflection intensities I(001) from the surface of [001] and the sum ΣI(hk 1 ) of reflection intensities I(hk 1 ) from the surface of [hk 1 ]. In Formula 1, the X-ray diffraction intensity P of the bismuth layer structured compound which is completely oriented in the c axis direction is normalized to be 1. From the Formula 1, F is equal to 0% if the bismuth layer structured compound is completely oriented in random directions (P=P 0 ) and F is equal to 100% if the bismuth layer structured compound is completely oriented in the c axis direction (P=1). 
   The c axis of the bismuth layer structured compound means the direction obtained by connecting the pair of (Bi 2 O 2 ) 2+  layers  18 , namely, the [001] direction. The dielectric characteristic of the dielectric thin film  6  can be exhibited up to the maximum thereof by orienting the bismuth layer structured compound in the c axis direction in this manner. Specifically, even if the thickness of the dielectric thin film  6  is equal to or thinner than 100 nm, a thin film capacitor having a relatively high dielectric constant and low loss (tan δ) can be obtained. Further, a thin film capacitor having an excellent leak characteristic, an improved breakdown voltage, an excellent temperature coefficient of the dielectric constant and an excellent surface smoothness can be obtained. If tan δ decreases, the loss value Q(1/tan δ) of the thin film capacitor increases. 
   In the compositional formula, the symbol m is not particularly limited insofar as it is a natural number but the symbol m is preferably an even number. If the symbol m is an even number, the dielectric thin film  6  has a mirror plane of symmetry perpendicular to the c axis, so that spontaneous polarization components in the c axis direction cancel each other on opposite sides of the mirror plane of symmetry, whereby the dielectric thin film  6  has no polarization axis in the c axis direction. As a result, it is possible to maintain the paraelectric property of the dielectric thin film  6 , to improve the temperature coefficient of the dielectric constant and to lower loss (tan δ). If the symbol m is large, the dielectric constant of the dielectric thin film  6  tends to increase. 
   In the present invention, the bismuth layer structured compound contained in the dielectric thin film is preferably represented by the chemical formula: Ca x Sr (1−x) Bi 4 Ti 4 O 15 , where x is equal to or larger than 0 and equal to or smaller than 1. If the bismuth layer structured compound having such a composition is used, the symbol m is equal to 4 and the dielectric constant of the dielectric thin film  6  is therefore relatively high and the temperature characteristic thereof is further improved. 
   Part of the elements represented by the symbols A or B are preferably replaced with at least one element Re (yttrium (Y) or a rare-earth element) selected from a group consisting of scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu). The preferable amount of replacement by the element Re depends upon the value of the symbol m. For example, in the case where the symbol m is equal to 3, in the compositional formula: Bi 2 A (2−x) Re x B 3 O 12 , x is preferably equal to or larger than 0.4 and equal to or smaller than 1.8 and more preferably equal to or larger than 1.0 and equal to or smaller than 1.4. If the amount of replacement by the element Re is determined within this range, the Curie temperature (phase transition temperature from ferroelectric to paraelectric) of the dielectric thin film  6  can be controlled preferably to be equal to or higher than −100° C. and equal to or lower than 100° C. and more preferably to be equal to or higher than −50° C. and equal to or lower than 50° C. If the Curie point is equal to or higher than −100° C. and equal to or lower than 100° C., the dielectric constant of the dielectric thin film  6  increases. The Curie temperature can be measured by DSC (differential scanning calorimetry) or the like. If the Curie point becomes to be lower than room temperature (25° C.), tan δ further decreases and as a result, the loss value Q further increases. 
   Furthermore, in the case where the symbol m is equal to 4, in the compositional formula: Bi 2 A (3−x) Re x B 4 O 15 , x is preferably equal to or larger than 0.01 and equal to or smaller than 2.0 and more preferably equal to or larger than 0.1 and equal to or smaller than 1.0. 
   Although the dielectric thin film  6  has an excellent leak characteristic even if it does not contain the element Re, it is possible to further improve the leak characteristic by replacing part of the elements represented by the symbols A or B with the element Re. 
   For example, in the dielectric thin film  6  containing no element Re, the leak current measured at the electric filed strength of 50 kV/cm can be controlled preferably to be equal to or lower than 1×10 −7  A/cm 2  and more preferably to be equal to or lower than 5×10 −8 A/cm 2  and the short circuit ratio can be controlled preferably to be equal to or lower than 10% and more preferably to be equal to or lower than 5%. 
   To the contrary, in the dielectric thin film  6  containing the element Re, the leak current measured under the same condition can be controlled preferably to be equal to or lower than 5×10 −8 A/cm 2  and more preferably to be equal to or lower than 1×10 −8 A/cm 2  and the short circuit ratio can be controlled preferably to be equal to or lower than 5% and more preferably to be equal to or lower than 3%. 
   In the present invention, the dielectric thin film  6  can be formed on the surface  2   a  of the lower electrode structural body  2  using various thin film forming processes such as a vacuum deposition process, a sputtering process, a pulsed laser deposition process (PLD), a MOCVD (Metal Organic Chemical Vapor Deposition) process, a chemical solution deposition process (CSD process) or the like Particularly, in the case where the dielectric thin film  6  has to be formed at a low temperature, a plasma CVD process, a photo-CVD process, a laser CVD) process, a photo-CSD process, a laser CSD process or the like is preferably used for forming the dielectric thin film  6 . 
   In the present invention, since the surface  2   a  of the lower electrode structural body  2  is oriented in the [001] direction, even if the dielectric thin film  6  containing the bismuth layer structured compound is formed on the surface  2   a  of the lower electrode structural body  2  by any of the foregoing methods, the bismuth layer structured compound is naturally oriented in the most thermodynamically stable direction and, therefore, the bismuth layer structured compound is naturally oriented so that the c axis thereof is substantially perpendicular to the lower electrode structural body  2  and the upper electrode structural body  4 . 
   Since the thin film capacitor  10  having the above described structure has various excellent characteristics, it is possible to simultaneously make the thin film capacitor small and the capacitance thereof great by forming the dielectric thin film  6  thin, e.g., so that the thickness thereof is equal to 1 to 100 nm. Therefore, for example, in the case where the thin film capacitor  10  is utilized as a decoupling capacitor for an LSI, the thin film capacitor  10  can be disposed between an LSI  12  and a printed circuit board  14  as shown in FIG.  3  and the inductance of the wiring connecting the terminal of the power supply of the LSI  12  and the decoupling capacitor can be markedly lowered. Moreover, since the thus constituted thin film capacitor  10  has an excellent temperature characteristic, even if the temperature of the thin film capacitor  10  considerably increases owing to heating caused by electric power consumption by the LSI  12 , change in the capacitance of the thin film capacitor  10  can be kept very small. 
   Next, explanation will be made regarding a thin film capacitor according to a preferred embodiment of the present invention and a method for fabricating the thin film capacitor. 
   As shown in  FIG. 4 , the thin film capacitor  20  according to this embodiment includes a lower electrode structural body  22 , an upper electrode structural body  24  and a dielectric thin film  26  provided between the lower electrode structural body  22  and the upper electrode structural body  24 . 
   The lower electrode structural body  22  includes a support substrate  30  whose surface  30   a  is oriented in the [001] direction, a buffer layer  32  formed on the surface  30   a  of the lower electrode structural body  22  and a lower electrode thin film  34  formed on the surface  32   a  of the buffer layer  32 . The surface  34   a  of the lower electrode thin film  34  is in contact with the dielectric thin film  26 . 
   The support substrate  30  serves to ensure the mechanical strength of the entire thin film capacitor  20  and also serves as a base for orienting the surface  32   a  of the buffer layer  32  in the [001] direction. The material for forming the support substrate is not particularly limited insofar as the surface  30   a  thereof is oriented in the [001] direction, and the support substrate can be formed of silicon (Si) single crystal, SiGe single crystal, Ga As single crystal, InP single crystal, SrTiO 3  single crystal, MgO single crystal, LaAlO 3  single crystal, ZrO 2  single crystal, MgAl 2 O 4  single crystal, NdGaO 3  single crystal, NdAlO 3  single crystal, LaGaO 3  single crystal or the like. Among these, silicon (Si) single crystal is most preferable because of low cost. The thickness of the support substrate  30  is not particularly limited insofar as the mechanical strength of the entire thin film capacitor  20  can be ensured and may be determined to be about 10 to 1000 μm, for example. 
   The buffer layer  32  serves as a barrier layer for preventing the support substrate  30  and the lower electrode thin film  34  from reacting with each other and also serves as a base for orienting the surface  34   a  of the lower electrode thin film  34  in the [001] direction. The material for forming the buffer layer  32  is not particularly limited insofar as the surface  32   a  of the buffer layer  32  can be influenced by the orientation of the surface  30   a  of the support substrate  30  so as to be oriented in the [001] direction. For example, the buffer layer  32  can be formed of ZrO 2  or ReO 2 , ReO 2 —ZrO 2 , where Re is yttrium (Y) or a rare earth element, MgO, MgAl 2 O 4 , γ-Al 2 O 3 , SrTiO 3 , LaAlO 3  or the like. It is preferable to select from among these materials a material which has a small lattice mismatch with the support substrate  30  and whose thermal expansion coefficient lies between that of the support substrate  30  and that of the dielectric thin film  26 . The buffer layer  32  may have a single layer structure or a multilayer structure. The thickness of the buffer layer  32  is not particularly limited insofar as it can serve as a barrier layer and may be determined to be about 10 to 1000 nm, for example. 
   The lower electrode thin film  34  serves as one of electrodes of the thin film capacitor  20  and also serves as a base for orienting the c axis of the bismuth layer structured compound constituting the dielectric thin film  26  so as to be substantially parallel with the electric field. In order to achieve the latter function, the surface  34   a  of the lower electrode thin film  34  has to be oriented in the [001] direction. The material for forming the lower electrode thin film  34  is not particularly limited insofar as it is conductive and can be influenced by the orientation of the surface  32   a  of the buffer layer  32  so that the surface  34   a  of the lower electrode thin film  34  is oriented in the [001] direction. For example, the lower electrode thin film  34  can be formed of a metal such as platinum (Pt), ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir), gold (Au), silver (Ag), copper (Cu), nickel (Ni) or the like, alloy containing at least one of these metal as a principal component, conductive oxide having a perovskite structure such as SrRuO 3 , CaRuO 3 , SrVO 3 , SrCrO 3 , SrCoO 3 , LaNiO 3 , Nb doped SrTiO 3 , or the like, a mixture of these, a superconductor having a superconductive layered bismuth structure such as Bi 2 Sr 2 CuO 6 , or the like. It is preferable to select from among these materials a material having a small lattice mismatch with the buffer layer  32 . 
   Therefore, it is necessary to select a material having a small lattice mismatch with the support substrate  30  and the lower electrode thin film  34  as a material for forming the buffer layer  32 . For example, in the case where silicon (Si) single crystal is employed as a material for forming the support substrate  30  and platinum (Pt) is employed as a material for forming the lower electrode thin film  34 , it is preferable to employ, as a material for forming the buffer layer  32 , ZrO 2 , ReO 2  or ReO 2 —ZrO 2 , where Re is yttrium (Y) or a rare earth element, MgO, MgAl 2 O 4  or the like that has a small lattice mismatch with silicon (Si) single crystal and platinum (Pt). 
   The thickness of the lower electrode thin film  34  is not particularly limited insofar as the lower electrode thin film  34  can serve as one of electrodes of the thin film capacitor  20  and may be determined to be about 10 to 1,000 nm, for example. 
   The upper electrode thin film  24  serves as the other electrode of the thin film capacitor  20 . The material for forming the upper electrode thin film  24  is not particularly limited insofar as it is conductive and the upper electrode thin film  24  can be formed of the same materials as those for forming the lower electrode thin film  34 . Further, since it is unnecessary to consider the lattice matching characteristic of the upper electrode thin film  24  and the like and the upper electrode thin film  24  can be formed at a room temperature, a base metal such as iron (Fe), nickel (Ni) or the like, or an alloy such as WSi, MoSi or the like can be used for forming the upper electrode thin film  24 . The thickness of the upper electrode thin film  24  is not particularly limited insofar as the upper electrode thin film  24  can serve as the other electrode of the thin film capacitor  20  and may be determined to be about 10 to 10,000 nm, for example. 
   Similarly to the dielectric thin film  6  of the thin film capacitor  10  shown in  FIG. 1 , the dielectric thin film  26  is formed of a dielectric material including a bismuth layer structured compound. The thickness of the dielectric thin film  26  is not particularly limited and depends upon the symbol m in the above mentioned compositional formula and the number of the laminates each consisting of the perovskite layer  16  and the (Ri 2 O 2 ) 2+  layer  18 . As described above, the symbol m is preferably an even number. For example, in the case where the symbol m is equal to 4, since the lattice constant in the c axis direction of the bismuth layer structured compound is about 4 nm wherein each lattice includes two perovskite layers  16  and two (Bi 2 O 2 ) 2+  layers  18 , if the number of lattices is equal to 50, the thickness of the dielectric thin film  26  is equal to about 200 nm. 
   The thin film capacitor  20  having the above described structure can be made by sequentially layering the buffer layer  32 , the lower electrode thin film  34 , the dielectric thin film  26  and the upper electrode thin film  24  on the support substrate  30  whose surface  30   a  is oriented in the [001] direction in this order. 
   A support substrate  30  whose surface  30   a  is oriented in the [001] direction is first prepared and a buffer layer  32  is formed on the surface  30   a  of the support substrate  30  using an epitaxial growth process. The method for forming the buffer layer  32  is not particularly limited insofar as the buffer layer  32  can be epitaxially grown and the buffer layer  32  can be formed using various thin film preparing processes such as a vacuum deposition process, a sputtering process, a pulsed laser deposition process (PLD), a chemical vapor deposition process (CVD), a chemical solution deposition process (CSD process) or the like. The surface  32   a  of the buffer layer  32  epitaxially grown in this manner is oriented in the [001] direction similarly to the surface  30   a  of the support substrate  30 . 
   Then, a lower electrode thin film  34  is epitaxially grown on the surface  32   a  of the buffer layer  32 . The method for forming the lower electrode thin film  34  is not particularly limited insofar as the lower electrode thin film  34  can be epitaxially grown. As a result, the surface  34   a  of the lower electrode thin film  34  epitaxially grown in this manner is oriented in the [001] direction similarly to the surface  32   a  of the buffer layer  32 . 
   A dielectric thin film  26  containing a bismuth layer structured compound is then formed on the surface  34   a  of the lower electrode thin film  34 . Similarly to the above described dielectric thin film  6 , the dielectric thin film  26  can be formed using various thin film preparing processes such as a vacuum deposition process, a sputtering process, a pulsed laser deposition process (PLD), a MOCVD (Metal Organic Chemical Vapor Deposition) process, a chemical solution deposition process (CSD process) or the like. 
   For example, if Ca(C 11 H 19 O 2 ) 2 (C 8 H 23 N 5 ) 2 , Bi(CH 3 ) 3  and Ti(O-i-C 3 H 7 ) 4  are used as constituent gases and a bismuth layer structured compound is deposited on the surface  34   a  of the lower electrode thin film  34  by the MOCVD process, a thin film having a composition represented by the chemical formula: CaBi 4 Ti 4 O 15  (a CBTi thin film obtained by replacing the symbol m by 4, the symbol A 3  by (Ca+Bi 2 ), and the symbol B 4  by Ti 4  in the compositional formula: Bi 2 A m−1 B m O 3m+3 ) is formed as a dielectric thin film  26 . On the other hand, if Sr(C 11 H 19 O 2 ) 2 (C 8 H 23 N 5 ) 2 , Bi(CH 3 ) 3  and Ti(O-i-C 3 H 7 ) 4  are used as constituent gases and a bismuth layer structured compound is deposited on the surface  34   a  of the lower electrode thin film  34  by the MOCVD process, a thin film having a composition represented by the chemical formula: Sr Bi 4 Ti 4 O 15  (a SBTi thin film obtained by replacing the symbol m by 4, the symbol A 3  by (Sr+Bi 2 ), and the symbol B 4  by Ti 4  in the compositional formula: Bi 2 A m−1 B m O 3m+3 ) is formed as a dielectric thin film  26 . 
   When the dielectric thin film  26  containing the bismuth layer structured compound is formed on the surface  34   a  of the lower electrode thin film  34  oriented in the [001] direction as described above, the bismuth layer structured compound is naturally oriented in the most thermodynamically stable direction and, therefore, the bismuth layer structured compound is naturally oriented so that the c axis thereof is substantially perpendicular to the lower electrode thin film  34 . 
   Then, an upper electrode thin film  24  is formed on the dielectric thin film  26 . The method for forming the upper electrode thin film  24  is not particularly limited and the upper electrode thin film  24  can be formed using the same methods as those for forming the lower electrode thin film  34 . It is preferable to form the upper electrode thin film  24  using a sputtering process from the viewpoint of the thin film forming rate. 
   The foregoing completes the fabrication of the thin film capacitor according to this embodiment. 
   As described above, in this embodiment, the buffer layer  32  and the lower electrode thin film  34  are epitaxially grown on the surface  30   a  of the support substrate  30  oriented in the [001] direction and the dielectric thin film  26  containing the layer bismuth compound is then formed on the surface  34   a  of the lower electrode thin film  34 . Therefore, the bismuth layer structured compound can be oriented so that the c axis thereof is substantially perpendicular to the lower electrode thin film  34  and the upper electrode thin film  24 . As a result, when a voltage is applied between the lower electrode thin film  34  and the upper electrode thin film  24 , the dielectric thin film  26  exhibits the property of a paraelectric material. Accordingly, it is possible to fabricate a thin film capacitor  20  having a small size, a large capacitance and an excellent temperature characteristic by an extremely simple process. As described above, the thin film capacitor having such characteristics can be preferably utilized as a decoupling capacitor, in particular, a decoupling capacitor for an LSI having a high operating frequency. 
   Next, explanation will be made regarding a thin film capacitor according to another preferred embodiment of the present invention and a method for fabricating the same. 
   As shown in  FIG. 5 , the thin film capacitor  40  includes a plurality of the dielectric thin films  26  used for constituting the thin film capacitor  20  shown in  FIG. 4 , and first electrode thin films  41  and a second electrode thin films  42  are alternately disposed between neighboring dielectric thin films  26 . The first electrode thin films  41  are short-circuited and so are the second electrode thin films  42 , whereby the thin film capacitor  40  can be made to have a larger capacitance than that of the thin film capacitor  20  shown in FIG.  4 . 
   As the material for forming the first electrode thin films  41  and the second electrode thin films  42  of the thin film capacitor  40 , it is necessary to employ a material which has conductivity and can be influenced by the orientation of the surface  26   a  of the dielectric electrode thin film  26  serving as a base so that each of the surfaces  24   a  thereof can be oriented in the [001] direction Illustrative examples of these materials include the same materials as those for forming the lower electrode thin film  34 , namely, metals such as platinum (Pt), ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir), gold (Au), silver (Ag), copper (Cu), nickel (Ni) or the like, alloys containing at least one of these metals as a principal component, conductive oxides having a perovskite structure such as SrRuO 3 , CaRuO 3 , SrVO 3 , SrCrO 3 , SrCoO 3 , LaNiO 3 , Nb doped SrTiO 3  or the like, mixtures of these, superconductors having a superconductive layered bismuth structure such as Bi 2 Sr 2 CuO 6  and the like. It is preferable to select from among these materials a material having a very small lattice mismatch with the dielectric thin film  26 . 
   However, the material for forming the uppermost electrode thin film (the first electrode thin film  41  in  FIG. 5 ) is not particularly limited insofar as it has conductivity and the uppermost electrode thin film can be formed of the same materials as those for forming the upper electrode thin film  24  of the thin film capacitor  20 . Namely, the uppermost electrode thin film can be formed of a base metal such as iron (Fe), nickel (Ni) or the like or an alloy such as WSi, MoSi or the like. 
   The thin film capacitor  40  having the above described structure can be fabricated by forming a buffer layer  32  on the support substrate  30  whose surface  30   a  is oriented in the [001] direction and alternately forming a first electrode thin film  41  or a second electrode thin film  42  and a dielectric thin film  26 . 
   As in the case of the lower electrode thin film  34 , an epitaxial growth process is used for forming the first electrode thin film  41  and the second electrode thin film  42 . As a result, the surface  41   a  of the first electrode thin film  41  and the surface  42   a  of the second electrode thin film  42  are oriented in the [001] direction in accordance with the orientation of the surface  32   a  of the buffer layer  32  or the surface  26   a  of the dielectric thin film  26 . Therefore, the bismuth layer structured compound contained in the dielectric thin film  26  can be naturally oriented so that the c axis thereof is substantially perpendicular to the first electrode thin film  41  or the second electrode thin film  42 . 
   It is unnecessary to use an epitaxial growth process for forming the uppermost electrode thin film. 
   The present invention has thus been shown and described with reference to specific embodiments. However, it should be noted that the present invention is in no way limited to the details of the described arrangements but changes and modifications may be made without departing from the scope of the appended claims. 
   For example, in the embodiment shown in  FIG. 4 , although the lower electrode thin film  34  and the dielectric thin film  26  are in contact with each other, another dielectric thin film whose surface on the side of the dielectric thin film  26  is oriented in the [001] direction may be interposed between the lower electrode thin film  34  and the dielectric thin film  26 . Similarly, in the embodiment shown in  FIG. 5 , another dielectric thin film whose surface on the side of the dielectric thin film  26  is oriented in the [001] direction may be interposed between the first electrode thin film  41  and/or the second electrode thin film  42  and the dielectric thin film  26 . However, since the capacitance of the thin film capacitor decreases when a dielectric thin film having a low dielectric constant is interposed between the electrode thin film and the dielectric thin film, as in the above described embodiments, it is preferable for each of the electrode thin films and the dielectric thin film to be directly in contact with each other. 
   Further, in the above described embodiments, although the buffer layer  32  is interposed between the support substrate  30  and the electrode thin film (the lower electrode thin film  34  or the first electrode thin film  41 ), the buffer layer  32  may be omitted in the case where the material for forming the support substrate  30  and the material for forming the electrode thin film do not react with each other even if they are in contact and where the lattice constants thereof are sufficiently close to each other.