Ferroelectric thin film device and method of producing the same

A ferroelectric thin film device comprises: a Si substrate; a TiN thin film epitaxially grown on the Si substrate in which Ti is partially substituted by Al; a metal thin film epitaxially grown on the TiN thin film; and a ferroelectric thin film grown and oriented on the metal thin film and composed of an oxide having a perovskite structure. The amount of Al substituted at Ti sites in the TiN thin film is about 1 to 30% in terms of Al atoms, and the oxygen content of the TiN thin film is about 5% or less in terms of oxygen atoms.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a ferroelectric thin film device having a
 Si substrate, and more specifically, relates to a ferroelectric thin film
 device comprising a highly-oriented ferroelectric thin film provided on a
 Si substrate, and suitable for use as capacitors for DRAM and
 ferroelectric RAM (Fe RAM), as well as for application to a pyroelectric
 element, a micro-actuator, a thin film capacitor, a small piezoelectric
 element, and the like. The present invention also relates to a production
 method for the ferroelectric thin film device.
 2. Description of the Related Art
 In recent years, studies have actively been conducted on formation of thin
 films of Pb type and non-Pb type perovskite compounds such as BaTiO.sub.3
 (abbreviated to "BTO" hereinafter), SrTiO.sub.3 (abbreviated to "STO"
 hereinafter), (Ba, Sr)TiO.sub.3 (abbreviated to "BSTO" hereinafter),
 PbTiO.sub.3, (Pb, La)TiO.sub.3 (abbreviated to "PLT" hereinafter), PZT,
 PLZT, Pb(Mg, Nb)O.sub.3 (abbreviated to "PMN" hereinafter), and the like.
 Particularly, when a Pb type perovskite compound having high residual
 polarization, such as PZT, PLZT, or the like can be epitaxially grown,
 spontaneous polarization can be arranged in one direction, thereby
 obtaining higher polarization values and switching characteristics.
 Therefore, under present conditions, application to a high-density
 recording medium is significantly increased, and there is thus a strong
 demand for developing a technique for epitaxially growing a Pb type
 perovskite compound.
 However, in application in which spontaneous polarization is arranged in
 one direction, e.g., in the direction of the film thickness, a structure
 in which a ferroelectric thin film is held between conductive layers
 (electrode layers) on a Si substrate, i.e., a metal-ferroelectric
 material-metal (MFM) structure, is required. A triaxially-oriented
 ferroelectric oxide thin film having good crystallinity is difficult to
 obtain from the following reasons:
 (1) When a metal thin film of Ag, Au or the like is formed as a conductor
 on a Si substrate, mutual diffusion occurs between the metal thin film and
 the Si substrate as a base during growth of the ferroelectric oxide thin
 film.
 (2) A method using a Pt thin film as a metal thin film can be considered.
 Although Pt can be epitaxially grown on an oxide single crystal substrate
 such as MgO, SrTiO.sub.3, or the like, direct epitaxial growth of Pt on a
 Si substrate cannot be realized at present.
 (3) A method using an oxide such as (La, Sr)CoO.sub.3 (abbreviated to
 "LSCO" hereinafter) for a conductive thin film can be considered. In this
 case, it is necessary to insert other layers between the Si substrate and
 the LSCO layer, for example, as in PLZT/LSCO/BiTO/YSZ/Si, thereby causing
 difficulties in improving epitaxy of the ferroelectric layer as the
 uppermost layer. Here, BiTO represents Bi.sub.4 Ti.sub.3 O.sub.12, and YSZ
 represents ZrO.sub.2 to which Y (yttrium) is added.
 (4) There is also a method comprising forming a TiN thin film by ion beam
 deposition, forming SrRuO.sub.3 (abbreviated to "SRO" hereinafter) as a
 buffer layer on the Pt thin film formed on the TiN thin film, and the
 epitaxially growing a (Ba, Sr)TiO.sub.3 (BSTO) thin film thereon. This
 method has problems in that a multilayer structure of BSTO/SRO/Pt/TAN/Si
 causes a significant increase in cost, and deterioration in crystallinity
 with lamination of the thin films. In addition, SRO is considered to
 impart ferroelectricity to BSTO by applying a stress stain to BSTO, but
 there is now no success of growth of a Pb type perovskite compound.
 For the forgoing reasons, there is a need for a ferroelectric thin film
 device comprising a ferroelectric thin film of a perovskite oxide, which
 is highly oriented and formed in a simple film structure on a Si substrate
 without requiring a complicated multilayer structure, and a method of
 producing a ferroelectric thin film device, which is capable of
 efficiently producing the ferroelectric thin film device.
 SUMMARY OF THE INVENTION
 The present invention is directed to a ferroelectric thin film device and a
 method of producing a ferroelectric thin film device that satisfied this
 need. The ferroelectric thin film device comprises: a Si substrate; a TiN
 thin film epitaxially grown on the Si substrate in which the Ti is
 partially substituted by Al; a metal thin film epitaxially grown on the
 TiN thin film; and a ferroelectric thin film grown and oriented on the
 metal thin film and composed of an oxide having a perovskite structure.
 The amount of Al substituted at Ti sites in the TiN thin film is about 1
 to 30% in terms of Al atoms, and the oxygen content of the TiN thin film
 is about 5% or less in terms of oxygen atoms.
 The method of producing a ferroelectric thin film device comprises the
 steps of: epitaxially growing, on a Si substrate, a TiN thin film in which
 the Ti is partially substituted by Al; epitaxially growing a metal thin
 film on the TiN thin film; and orienting and growing a ferroelectric thin
 film of an oxide having a perovskite structure on the metal thin film. The
 amount of Al substituted at the Ti sites in the TiN thin film is in the
 range of about 1 to 30% in terms of Al atoms, and the oxygen content of
 the TiN thin film is about 5% or less in terms of oxygen atoms.
 According to the present invention, it is possible to obtain the element
 having a structure in which the ferroelectric thin film is oriented and
 grown on the Si substrate without requiring a complicated multilayer
 structure.
 Namely, although a complicated multilayer structure is conventionally
 required for orienting and growing a perovskite type oxide ferroelectric
 thin film on the Si substrate, the construction of the present invention
 enables epitaxial growth of the perovskite type oxide ferroelectric thin
 film on the Si substrate by using only two buffer layers including the TiN
 thin film and the metal thin film.
 Particularly, the present invention enables growth of a Pb perovskite type
 oxide ferroelectric thin film having a high degree of orientation (at
 least monoaxial orientation).
 In addition, when a Pt thin film is formed as the metal thin film, the Pt
 thin film also functions as an oxidation barrier layer for the TiN thin
 film, and exhibits a catalytic ability in the process for forming the
 ferroelectric thin film, thereby obtaining the ferroelectric thin film
 having excellent crystallinity.
 Furthermore, when the ferroelectric thin film is epitaxially grown, all
 thin films are epitaxial films, and thus mutual diffusion does not occur
 at the interfaces between the respective thin films, thereby obtaining the
 ferroelectric thin film device which is thermally stable.
 Furthermore, the present invention permits epitaxial grown of the
 perovskite type oxide ferroelectric thin film on the Si substrate by using
 only two buffer layers including the TiN thin film and the metal thin
 film, thereby decreasing the process time and production cost.
 As a result, it is possible to easily realize epitaxial growth of a
 perovskite type oxide ferroelectric material, particularly a Pb type
 perovskite compound, on the single crystal Si substrate, which is
 conventionally very difficult, and thus provide a ferroelectric thin film
 device which can be applied to capacitors for DRAM and FeRAM, a
 pyroelectric element, a micro-actuator, a thin film capacitor, a small
 piezoelectric element, and the like.
 For the purpose of illustrating the invention, there is shown in the
 drawings several forms which are presently preferred, it being understood,
 however, that the invention is not limited to the precise arrangements and
 instrumentalities shown.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
 Embodiments of the ferroelectric thin film device of the present invention
 and the production method therefor will be described below with reference
 to examples.
 As shown in FIG. 1, a ferroelectric thin film device 50 of the present
 invention comprises a Si substrate 51, a TiN thin film 52 epitaxially
 grown on the Si substrate 51, a metal thin film 53 epitaxially grown on
 the TiN thin film 52 and a ferroelectric thin film 54 epitaxially grown on
 the metal thin film 53 and composed of an oxide having a perovskite
 structure. In the TiN thin film 52, the Ti is partially substituted by Al,
 and the amount of Al substituted at the Ti sites in the TiN thin film 52
 is about 1 to 30% in terms of Al atoms, and the oxygen content of the TiN
 thin film is about 5% or less in terms of oxygen atoms. The ferroelectric
 thin film device 50 may further comprises a metal film 55 on the
 ferroelectric thin film 54 so that the ferroelectric thin film device 50
 has a suitable structure in accordance with its application.
 In the above construction, the ferroelectric oxide thin film 54 oriented
 and grown on the Si substrate 51 and having perovskite structure can be
 formed with only two buffer layers including the TiN thin film 52 and the
 metal thin film 53, without requiring a complicated multilayer structure.
 It is thus possible to obtain the ferroelectric thin film device which can
 be applied to capacitors of DRAM and FeRAM, as well as a pyroelectric
 element, a micro-actuator, a thin film capacitor, a small piezoelectric
 element, and the like.
 In the ferroelectric thin film device 50 of the present invention, the TiN
 thin film 52 and the metal thin film 53 are epitaxially grown on the Si
 substrate 51. This makes it possible for the ferroelectric thin film 54
 which is formed on the TiN thin film 52 and the metal thin film 53 to grow
 with high orientation, thereby obtaining good electric properties.
 In the present invention, the reason why the amount of Al substituted at
 the Ti sites in the TiN thin film 52 is in the range of about 1 to 30% is
 that with an amount of Al substituted of less than about 1%, sufficient
 oxidation resistance cannot be obtained, and with an amount of Al
 substituted of over about 30%, conductivity of TiN significantly
 deteriorates.
 When the oxygen content of TiN exceeds about 5% by weight, oxidation
 resistance deteriorates and satisfactory epitaxial growth is inhibited.
 Therefore, the oxygen content of TiN is preferably about 5% or less, more
 preferably about 1% or less.
 The metal thin film 53 preferably comprises at lease one selected from the
 group consisting of Au, Pt, Pd, Rh, Ir and Ru, at a content of 50% or
 more. In order to orient and grow the ferroelectric thin film 54,
 generally, the ferroelectric thin film 54 must be grown in an atmosphere
 of 600.degree. C. or more. It is thus preferable to use, as the metal thin
 film, a material containing a noble metal such as Au, Pt, Pd, Rh, Ir and
 Ru, or an alloy composed of at least two metals. Particularly, the metal
 content is preferably not less than about 50%. In the case where Pt is
 used for the metal thin film 53, the Pt thin film has a lattice constant
 suitable for epitaxial growth on the TiN thin film 52, functions as an
 oxidation barrier layer for TiN, and has a lattice constant suitable for
 epitaxial growth of the ferroelectric thin film 54, and Pt has a catalytic
 function, thereby obtaining the ferroelectric thin film 54 having
 excellent crystallinity.
 It is preferable that the ferroelectric thin film 54 comprises a Pb type
 perovskite oxide thin film. This is because the Pb type perovskite oxide
 thin film has excellent properties and is suitable to be highly oriented
 (at least monoaxially oriented). The Pb type perovskite oxide preferably
 comprises Pb or Pb and at least La as a component element at A site
 represented by ABO.sub.3, and at least one element of Ti, Zr, Mg and Nb as
 a component element of B site. This is because a material composition
 having properties including a high residual polarization value as an index
 of ferroelectricity and a small electric field (anti-electric field)
 required for reversing polarization can be obtained.
 The TiN thin film 52 preferably has a thickness in the range of about 100
 to 1000 nm, the metal thin film 53 preferably has a thickness in the range
 of about 10 to 200 nm, and the ferroelectric thin film 54 preferable has a
 thickness in the range of about 50 to 3000 nm. The reason why the
 aforementioned thickness of the TiN thin film 52 is preferable is that
 with a thickness of less than about 100 nm, the stress of the TiN is not
 sufficiently transmitted to the ferroelectric thin film 54, while with a
 thickness of over about 1000 nm, film deposition requires much time and is
 thus unpractical.
 Why the aforementioned thickness of the metal thin film 53 is preferable is
 that with a thickness of less than about 10 nm, the effect as a protective
 film for TiN deteriorates and a continuous film is difficult to form,
 while with a thickness of over about 200 nm, the stress of the TiN thin
 film is not sufficiently transmitted to the ferroelectric thin film.
 Further, if the thickness of the ferroelectric thin film 54 is less than
 about 50 nm, the ferroelectric thin film 54 does not show the
 ferroelectric properties in the same degree as the bulk ferroelectric
 material does. If the thickness of the ferroelectric thin film 54 is
 greater than about 3000 nm, the stress of the TiN thin film 52 is not
 sufficiently transmitted to the ferroelectric thin film 54.
 In the present invention, the ratio of the thickness of the metal thin film
 53 to the thickness of the TiN thin film 52 is preferably about 0.5 or
 less, and the ratio of the thickness of the ferroelectric thin film 54 to
 the thickness of the TiN thin film 52 is preferably about 3 or less. The
 reason for this is that when the ratio of the thickness of the metal thin
 film 53 to the thickness of the TiN thin film 52 exceeds about 0.5, the
 stress of TiN is not sufficiently transmitted to the ferroelectric thin
 film 54, and similarly, when the ratio of the thickness of the
 ferroelectric thin film 54 to the thickness of the TiN thin film 52
 exceeds about 3, the stress of the TiN thin film 52 is not sufficiently
 transmitted to the ferroelectric thin film 54.
 In the case where the metal thin film 53 is made of Pt, the ratio of the
 thickness of the Pt thin film to the thickness of the TiN thin film is
 preferably about 0.4 or less. This is because, with a thickness ratio of
 over 0.4, the stress of the TiN thin film is not sufficiently transmitted
 to the ferroelectric thin film.
 The ferroelectric thin film 54 is preferably formed by epitaxial growth. In
 the case, all thin films comprise epitaxial films, and substantially no
 mutual diffusion occurs at the interfaces between the respective thin
 films, thereby obtaining a ferroelectric thin film device which is
 thermally stable.
 The TiN thin film 52 is preferably formed by a pulsed laser deposition
 method (PLD method), or an ion beam sputtering method. When the TiN thin
 film 52 is formed by the pulsed laser deposition method or ion beam
 sputtering method, the TiN thin film 52 can easily epitaxially be grown on
 the Si substrate 51 within a short time, thereby making the present
 invention more practical. In the case, it is preferable that the TiN thin
 film 52 is formed by the pulsed laser deposition method (PLD method) under
 a pressure of 10.sup.-6 Torr or less, or the ion beam sputtering method
 under a pressure of 10.sup.-3 Torr or less.
 The Pt thin film is preferably formed by a sputtering method. The use of
 the sputtering method for forming the Pt thin film enables easy epitaxial
 growth of the Pt thin film on the TiN thin film 52, as well as secure
 formation of the ferroelectric thin film on the Pt thin film, thereby
 obtaining a ferroelectric thin film device having desired properties. In
 this case, the Pt thin film is preferably formed by the sputtering method
 in an Ar gas atmosphere containing 0.01% by volume or less of oxygen.
 The ferroelectric thin film 54 is preferably formed by a chemical vapor
 deposition method. When the ferroelectric thin film is formed by the
 chemical vapor deposition method, the ferroelectric thin film 54 can
 easily be epitaxially grown in a large area on the metal thin film,
 thereby making the present invention more practical.
 EXAMPLES
 A TiN thin film, a Pt thin film, and a Pb type perovskite ferroelectric
 oxide thin film were formed in this order on a Si single crystal
 substrate, from which the natural oxide film was removed, by the method of
 each of examples and a comparative example, which will be described below,
 to produce a ferroelectric thin film device comprising an oriented
 ferroelectric thin film.
 Then, an Au upper electrode having a diameter of 0.5 mm was formed on the
 Pb type perovskite ferroelectric oxide thin film by the vapor deposition
 method using a mask, and the electric characteristics of the ferroelectric
 thin film device were evaluated.
 Example 1
 Si (100) having a thickness of 50.8 mm was used as a silicon substrate.
 However, in the present invention, the Si substrate is not limited to Si
 (100), and Si (111) and Si (110) can also be used. Any one of these Si
 substrates can be used as long as the miss-cut angle is 5% or less.
 The Si (100) substrate was ultrasonically cleaned in an organic solvent
 such as acetone, ethanol, or the like, and then dipped in a 10% HF
 solution to remove the oxide film from the surface of the Si substrate.
 Then, a TiN thin film in which the Ti sites were partially substituted by
 Al (abbreviated to "the TAN thin film" thereinafter) was epitaxially grown
 to a thickness of about 500 nm by a pulsed laser deposition (PLD)
 apparatus in a vacuum under conditions including a substrate temperature
 of 550 to 650.degree. C., a laser cycle frequency of 5 to 10 Hz and a
 laser energy density of 4.5 J/cm.sup.2 (KrF). As a result of measurement
 of the oxygen content of the thus-obtained TAN [(Ti.sub.0.9 Al.sub.0.1)N]
 thin film by Auger electron spectroscopy (AES), the oxygen content was 1%
 or less in terms of oxygen atoms.
 In Example 1, the TAN thin film was deposited by using such a PLD apparatus
 as shown in FIG. 2. The PLD apparatus comprises a vacuum container 1
 provided with a gas inlet tube 3 for introducing an atmospheric gas into
 the container, and an exhaust port 8 for exhausting the inner atmospheric
 gas, and a target 4 and a substrate heater 5 for heating the substrate,
 both of which are provided in the vacuum container 1, so that an excimer
 laser beam 10 passing through a laser condensing lens 2 is introduced into
 the vacuum container 1 through a synthetic quartz window 9.
 As the target for forming the TAN thin film, a TAN sintered compact
 represented by the composition formula (Ti.sub.0.9 Al.sub.0.1)N was used.
 Besides the PLD method, the TAN thin film can also be formed by an electron
 beam deposition method, a rf sputtering method, a DC sputtering method, an
 ion beam sputtering method, an ECR sputtering method, a MBE method, or the
 like. Furthermore, an ion beam or a laser beam can be used for assisting
 the formation of the TAN thin film in order to improve crystallinity.
 The Pt thin film was epitaxially grown to a thickness of 100 nm on the TAN
 thin film by a rf magnetron sputtering apparatus under conditions
 including a total pressure of 2 mTorr (oxygen partial pressure 0.2 mTorr)
 and a substrate temperature of 600.degree. C.
 Besides the rf magnetron sputtering method, the Pt thin film can be formed
 by an electron beam deposition method, a rf sputtering method, a DC
 sputtering method, an ion beam sputtering method, an ECR sputtering
 method, or the like.
 Then, a Pb(Zr.sub.0.52 Ti.sub.0.48)O.sub.3 (abbreviated to "PZT"
 hereinafter) thin film was epitaxially grown to a thickness of 400 to 600
 nm on the Pt thin film by a MOCVD apparatus under conditions including a
 total pressure of 10 Torr (oxygen partial pressure 5 Torr) and a substrate
 temperature of 700.degree. C. As precursors of Pb, Zr and Ti,
 Pb(DPM).sub.2, Zr(O-t-C.sub.4 H.sub.9).sub.4, and Ti(O-i-C.sub.3
 H.sub.7).sub.4 were respectively used.
 In Example 1, the PZT thin film was formed by such a MOCVD apparatus as
 shown in FIG. 3. The MOCVD apparatus comprises a vacuum container 21 which
 can be evacuated by a vacuum pump 26, a gas blowout nozzle 22 for
 supplying gases from a gas mixer 25 into the vacuum container 21, and a
 substrate heater 23 for heating a substrate 24. The MOCVD apparatus also
 comprises a solid vaporizer 31 for vaporizing Pb(DPM).sub.2 (solid) as a
 precursor of Pb, a liquid vaporizer 32 for vaporizing Zr(O-t-C.sub.4
 H.sub.9).sub.4 (liquid) as a precursor of Zr, and a liquid vaporizer 33
 for vaporizing Ti(O-i-C.sub.3 H.sub.7).sub.4 (liquid) as a precursor of Ti
 so that the thin film raw material gases of Pb, Zr and Ti generated in the
 solid vaporizer 31 and the liquid vaporizers 32 and 33 are sent to the
 vacuum container 21 by Ar gas (carrier gas), and 30, respectively, and
 O.sub.2 gas is supplied to the vacuum container 21 through a mass flow
 controller 27.
 Table 1 shows detailed conditions for forming the PZT thin film.
 TABLE 1
 Vaporization Flaw rate of Vaporizer
 temperature carrier gas pressure
 Items (.degree. C.) (SCCM) (Torr)
 Pb raw material 135 200 (Ar) 10
 Zr raw material 35 50 (Ar) 10
 Ti raw material 50 50 (Ar) 50
 Oxygen gas -- 500 (Ar) --
 Comparative Example 1
 A TAN thin film (Ti.sub.0.9 Al.sub.0.1 N: TAN) was epitaxially grown to a
 thickness of about 150 nm on a Si (100) substrate by the same PLD method
 as Example 1 under conditions in which the pressure was about 10.sup.-5
 Torr higher than Example 1, the substrate temperature was 550 to
 650.degree. C., the laser cycle frequency was 5 Hz, and the laser energy
 density was 4.5 J/cm.sup.2 (KrF). As a result of measurement of the oxygen
 content of the thus-obtained TAN thin film by the same Auger electron
 spectroscopy as Example 1, the oxygen content was about 10% in terms of
 oxygen atoms.
 Then, the Pt thin film was epitaxially grown to a thickness of 100 nm on
 the TAN thin film by the same rf magnetron sputtering apparatus as Example
 1 under conditions including a total pressure of 2 mTorr (oxygen partial
 pressure 0.2 mTorr) and a substrate temperature of 600.degree. C.
 Then, a Pb(Zr.sub.0.52 Ti.sub.0.48)O.sub.3 (abbreviated to "PZT"
 hereinafter) thin film was epitaxially grown to a thickness of 500 to 600
 nm on the Pt thin film by the same MOCVD method as Example 1 under
 conditions including a total pressure of 10 Torr (oxygen partial pressure
 5 Torr) and a substrate temperature of 600.degree. C.
 Comparison between Example 1 and Comparative Example 1
 FIG. 4 shows a XRD pattern of the PZT/Pt/TAN thin films formed on the Si
 substrate in Example 1. FIG. 5 shows the results of pole figure analysis
 for examining orientation in the film plane of the same sample. This
 analysis was carried out for TAN (220), and peaks of four-fold symmetry
 were obtained. This indicates that the TAN thin film is epitaxially grown
 on the Si substrate.
 FIG. 6 shows the results of pole figure analysis for Pt (200) of the same
 sample, and FIG. 7 shows the results of pole figure analysis for PZT
 (220).
 FIGS. 6 and 7 show that Pt peaks of four-fold symmetry and PZT peaks of
 four-fold symmetry are obtained. This also indicates that the Pt thin film
 and the PZT thin film are also epitaxially grown.
 FIG. 8 shows the results of scanning for examining the orientation of the
 entire multilayer structure comprising PZT/Pt/TAN/Si thin films.
 The results indicate that each of the TAN thin film, the Pt thin film and
 the PZT thin film is epitaxially grown.
 On the other hand, FIG. 9 shows a XRD pattern of the PZT thin film obtained
 in Comparative Example 1. FIG. 9 reveals that the PZT thin film is a
 perovskite structure thin film, but shows no tendency to orient in a
 specified axis, and thus it is not epitaxially grown.
 FIG. 10 shows a P-E hysteresis loop drawn by using the PZT thin film
 epitaxially grown by the method of Example 1.
 Table 2 shows the results of evaluation of electric properties of each of
 the PZT thin film devices obtained in Example 1 and Comparative Example 1.
 TABLE 2
 Relative
 tan .delta. * dielectric
 Sample (%) constant * Remarks
 PZT thin film 2.1 370 Thickness:
 of Example 1 500 nm
 PZT thin film 4.3 510 Thickness:
 of Comparative 500 nm
 Example 1
 * tan .delta. and the relative dielectric constant were measured at 1 kHz
 and 0.1 V.
 Table 2 indicates that the PZT thin film device of Example 1 has good
 electric properties.
 Example 2
 A TAN thin film (Ti.sub.0.7 Al.sub.0.3 N) was epitaxially grown to a
 thickness of 300 nm on a Si substrate by the same PLD method as Example 1.
 A Pt thin film was epitaxially grown to a thickness of 100 nm on the TAN
 thin film by the rf sputtering method, and then a PLT (Pb.sub.0.9
 La.sub.0.1 TiO.sub.3) was epitaxially grown to a thickness of about 600 to
 800 nm by the PLD method under conditions including a pressure of 5 Torr
 (O.sup.2 atmosphere), a substrate temperature of 500.degree. C., a laser
 cycle frequency of 5 Hz, and a laser energy density of 4.5 J/cm.sup.2
 (KrF).
 In Example 2, as a target for obtaining the PLT thin film, a ceramic
 sintered target represented by the composition formula Pb.sub.0.9
 La.sub.0.1 TiO.sub.3 was used.
 FIG. 11 shows a XRD pattern of the thus-obtained epitaxial PLT thin film.
 FIG. 10 indicates that the use of the method of producing a ferroelectric
 thin film device of the present invention permits epitaxial growth of the
 PLT thin film on the Si substrate.
 Example 3
 A TAN thin film (Ti.sub.0.99 Al.sub.0.01 N) was epitaxially grown to a
 thickness of 150 nm on a Si substrate by the same PLD method as Example 1.
 A Pt thin film was epitaxially grown to a thickness of 50 nm on the TAN
 thin film by the rf sputtering method, and then a BSTO (Ba.sub.0.7
 Sr.sub.0.3 TiO.sub.3) was epitaxially grown to a thickness of about 50 nm
 by the PLD method under conditions including a pressure of 10.sup.-4 Torr,
 a substrate temperature of 600.degree. C., a laser cycle frequency of 5
 Hz, and a laser energy density of 4.5 J/cm.sup.2 (KrF). As a target for
 obtaining the BSTO thin film, a ceramic sintered target represented by the
 composition formula Ba.sub.0.7 Sr.sub.0.3 TiO.sub.3 was used.
 FIG. 12 shows a XRD pattern of the thus-obtained epitaxial BSTO thin film.
 FIG. 13 shows a P-E hysteresis loop drawn by using the epitaxial BSTO thin
 film. These results indicate that the use of the method of producing a
 ferroelectric thin film device of the present invention also permits
 epitaxial growth of the BSTO thin film on the Si substrate.
 Example 4
 FIG. 14A schematically shows, in part, a memory device 60 in which the
 ferroelectric thin film device shown in FIG. 1 is used as a capacitor. As
 shown in FIG. 14A, The memory device 60 comprises a Si substrate 61, an
 field effect transistor (FET) 62 and a capacitor 63. The FET 62 includes a
 source 64 and a drain 65 formed in the Si substrate 61, and a gate 67
 formed on the Si substrate 61 via a SiO.sub.2 film 66. The gate 67 is used
 as a word line. The source 64 is connected to a data line.
 The capacitor 63 comprises a TiN thin film 70, a Pt thin film 71 on the TiN
 thin film 70, a PZT thin film 72 on the Pt thin film 71 and upper
 electrode 73 on the PZT thin film 72. The TiN thin film 70 is formed on
 the Si substrate 61 so as to electrically contact with the drain 65 and
 acts as a lower electrode of the capacitor 63.
 The memory device 60 may be operated as either a dynamic random access
 memory (DRAM) or a non-volatile memory (FeRAM) in accordance with a
 driving method and an operation voltage. Equivalent circuits as a DRAM and
 a FeRAM are shown in FIGS. 14B and 14C, respectively. In either operation,
 since the PZT thin film 72 having a excellent properties is formed on the
 Si substrate 61, it is possible to realize a memory device having a
 excellent device characteristics.
 While preferred embodiments of the invention have been disclosed, various
 modes of carrying out the principles disclosed herein are contemplated as
 being within the scope of the following claims. Therefore, it is
 understood that the scope of the invention is not to be limited except as
 otherwise set forth in the claims.