Abstract:
Performance of an electronic device is highly improved by epitaxially growing a perovskite-type oxide thin film on an inorganic amorphous layer or an organic solid layer in a desired direction; and furthermore, a high performance electronic device is provided by incorporating the electronic device into an integrated circuit, wherein oxide thin layers are formed on the inorganic amorphous layer or the organic solid layer, and the perovskite-type oxide thin film is grown epitaxially on the oxide layer, the oxide thin layers being able to be at least one of strontium oxide, magnesium oxide, cerium oxide, zirconium oxide, yttrium stabilized zirconium oxide, and strontium titanate; and as the perovskite-type oxide thin film, the perovskite-type oxide thin film being a piezoelectric or ferroelectric material, for example, is used.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a divisional patent application of U.S. Ser. No. 10/108,180 filed Mar. 27, 2002, claiming priority to JPSN 2001-093924 filed Mar. 28, 2001, JPSN 2002-076695 filed Mar. 19, 2002 and JPSN 2002-085812 filed Mar. 26, 2002, all of which are hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an electronic device, especially, a ferroelectric device, a surface acoustic device, and a piezoelectric device, based on a perovskite-type oxide thin film grown epitaxially on an oxide thin layer on an inorganic amorphous layer or an organic solid layer, and an electronic apparatus comprising the electronic device.  
         [0004]     2. Description of the Related Art  
         [0005]     Conventionally, when a perovskite-type oxide thin film is grown epitaxially, a single crystal substrate or a crystallized buffer layer is chosen by considering lattice matching with a perovskite-type oxide to be grown epitaxially. For example, for a surface acoustic device using a perovskite-type oxide thin film, as described in Japanese Unexamined Patent Application, First Publication No. Hei 2000-278084, good properties have been obtained by growing a potassium niobate (described as “KNbO 3 ” hereafter) thin film having a high electromechanical coupling factor (described as “k 2 ” hereafter) on a single crystal substrate of strontium titanate (described as “SrTiO 3 ” hereafter) with (110) orientation epitaxially. Also, as described in Japanese Unexamined Patent Application, First Publication No. Hei 9-100125, an example is presented of obtaining a KNbO 3  film with (110) orientation on an amorphous substrate.  
         [0006]     On the other hand, for a piezoelectric device such as a ferroelectric memory device or an actuator, as described in Japanese Unexamined Patent Application, First Publication No. Hei 8-330540 or Japanese Applied Physics Lett., 70, 1378-1380 (1997), attempts have been made to fabricate a device by using a thin film grown epitaxially or grown with an orientation on a crystal substrate in order to improve their properties.  
         [0007]     Generally, a polarization direction is determined by a material, so that an epitaxial film with a controlled polarization direction is preferable in order to control device characteristics. Also, an epitaxial film is advantageous for reducing the effects of grain boundaries on the device characteristics. Furthermore, an ultra-thin film will be required for a ferroelectric memory element or a ferroelectric memory device having a ferroelectric memory cell array, which is an assembly of ferroelectric memory elements. From this viewpoint, an epitaxial film is also advantageous in order to reduce leakage current or to improve a square-loop characteristic. A mere oriented film is inferior to an epitaxial film in these points. In an oriented film, packing density is lower than that in an epitaxial film, in-plane orientation is not as uniform, and crystallization is not as fully controlled. Consequently, in recent years, an epitaxial film of a perovskite-type oxide is receiving serious attention for fabricating devices.  
         [0008]     Conventional technologies for growing perovskite-type oxide thin films epitaxially have problems described below.  
         [0009]     First, as described above, when a perovskite-type oxide thin film is grown epitaxially, a single crystal substrate or a crystallized buffer layer having a lattice matching with a perovskite-type oxide must be used.  
         [0010]     Even though oxide ceramics such as SrTiO 3  are normally used as a single crystal substrate, the cost of oxide ceramic substrates is generally high, and fabrication of large substrates of 3 inches or more in diameter is difficult depending on the types. On the other hand, as described in Japanese Unexamined Patent Application, First Publication No. Hei 8-330540, examples are shown of epitaxially growing a perovskite-type oxide thin film via a buffer layer crystallized on a silicon substrate, which is inexpensive and suitable for large diameters. However, when a capacity increase or a miniaturization is attempted by integrating a ferroelectric memory device or surface acoustic device on a semiconductor device, usually, these must be formed on a silicon oxide amorphous interlayer insulating film of the semiconductor device; therefore, a technology to grow a perovskite-type oxide thin film epitaxially on an amorphous layer is required.  
         [0011]     Even though a technology to grow a perovskite-type oxide thin film epitaxially on a silicon substrate is highly valuable in terms of cost and other factors, the technology alone cannot accomplish the desired integration with semiconductor devices. Also, when a piezoelectric device such as an actuator is fabricated, a perovskite-type oxide thin film must be formed on a thermally oxidized film of a silicon oxide as well, so that a technology to form a perovskite-type oxide thin film on a silicon substrate alone is not sufficient. There are examples of forming perovskite-type oxide thin films on a crystallized film of platinum or the like formed on an amorphous silicon oxide film; however, even though oriented films can be obtained in such cases, epitaxial films cannot be obtained.  
         [0012]     As described above, an epitaxial film is superior to an oriented film for device performance. Therefore, if a perovskite-type oxide thin film could be formed on an amorphous layer, integration with a semiconductor device would become possible and not only could a high performance device be built, but a perovskite-type oxide thin film could be grown epitaxially on any substrate regardless of whether or not the substrate is crystal, thereby expanding the application range enormously. That is, any substrate could be used as long as it can withstand a temperature for forming a perovskite-type oxide thin film.  
         [0013]     As described in Japanese Unexamined Patent Application, First Publication No. 9-100125, there is an example of forming KNbO 3  on an amorphous substrate; however, what is obtained is an oriented film, and obtaining an epitaxial film is still difficult. It is difficult, furthermore, to grow a crystal in a desired orientation direction.  
       SUMMARY OF THE INVENTION  
       [0014]     Objects of the present invention are: to solve the problems described above; to provide an electronic device having a perovskite-type oxide thin film grown epitaxially in a desired direction on an inorganic amorphous layer or an organic solid layer; and additionally, to provide an electric apparatus comprising the electronic device.  
         [0015]     The present invention provides an electronic device having an inorganic amorphous layer or an organic solid layer; an oxide thin layer formed on the inorganic amorphous layer or the organic solid layer; and a perovskite-type oxide thin film grown epitaxially on the oxide thin layer.  
         [0016]     With the configuration described above, by using any substrate having an inorganic amorphous layer or an organic solid layer, an electronic device can be provided having a perovskite-type oxide thin film grown epitaxially on the layer in a desired direction. Furthermore, a high performance electronic device can be provided by incorporating the electronic device into an integrated circuit. Furthermore, an electronic apparatus comprising any of the above electronic devices can be provided.  
         [0017]     Silicon oxide (described as SiO 2  hereafter), aluminum nitride (described as AlN hereafter), glass, amorphous silicon or the like can be used for the inorganic amorphous layer. Among these, the use of SiO 2  is preferable because, in many cases, an electronic device of the present invention is formed on a silicon substrate, on which SiO 2  is easily formed, or it is often already formed thereon.  
         [0018]     Thermosetting resins such as urea resins, melamine resins, phenolic resins, polyimides or the like; or thermoplastic resins such as polyesters (for example, polyethylene terephthalate), polyamides, rigid polyvinyl chlorides, polystyrenes or the like can be used as the organic solid layer.  
         [0019]     It is preferable that the oxide thin layer comprise at least one of strontium oxide (described as “SrO” hereafter), magnesium oxide (described as “MgO” hereafter), cerium oxide (described as “CeO 2 ” hereafter), zirconium oxide (described as “ZrO 2 ” hereafter), yttrium stabilized zirconium oxide (described as “YSZ” hereafter), barium oxide (described as “BaO” hereafter), and calcium oxide (described as “CaO” hereafter). These oxide materials permit a high quality perovskite-type oxide thin film to be formed thereon.  
         [0020]     The perovskite-type oxide thin film can comprise KNbO 3 , barium titanate (described as “BaTiO 3 ” hereafter), PZT, SrBi 2 Ta 2 O 9 , Bi 4 Ti 3 O 12 , strontium ruthenate oxide (described as “SrRuO 3 ” hereafter), or SrTiO 3  or the like. It is preferable that these have piezoelectric, ferroelectric or electrically conductive characteristics, and that they exhibit characteristics as an interlayer to form a layer having piezoelectric, ferroelectric, or electrically conductive characteristics. For example, SrTiO 3  can form an interlayer on which a layer having piezoelectric, ferroelectric, or electrically conductive characteristics is formed.  
         [0021]     In particular, the present invention provides an electronic device wherein the perovskite-type oxide thin film exhibits piezoelectric characteristics.  
         [0022]     Furthermore, an electronic device of the present invention includes a piezoelectric device, a surface acoustic device, a surface acoustic wave oscillator, a ferroelectric memory element, a ferroelectric memory device having a ferroelectric memory cell array and the like.  
         [0023]     Furthermore, the present invention also provides an electronic device comprising the above electronic device.  
         [0024]     According to the present invention, by including a suitable inorganic amorphous layer or an organic solid layer, as well as an oxide thin layer formed on the inorganic amorphous layer or the organic solid layer, and furthermore, by including a perovskite-type oxide thin film grown epitaxially on the oxide thin layer, and by using a suitable substrate including an inorganic amorphous layer or an organic layer, it is possible to provide an electronic device having a perovskite-type oxide thin film grown epitaxially in a desired direction on the inorganic amorphous layer or the organic solid layer. Furthermore, a high performance electronic device such as a surface acoustic device, a ferroelectric memory device, or a piezoelectric device can be provided by further incorporating such a device into an integrated circuit. Further, according to the present invention, a high performance electronic apparatus comprising any of the above electronic devices is provided. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  is a cross sectional view of a surface acoustic device in Embodiment 1 of the present invention.  
         [0026]      FIG. 2  is a schematic plan view of a ferroelectric memory device in Embodiment 2 of the present invention.  
         [0027]      FIG. 3  is a schematic cross sectional view of the portion along A-A in  FIG. 2 .  
         [0028]      FIG. 4  is a schematic cross sectional view of a surface acoustic wave (SAW) oscillator in Embodiment 3 of the present invention.  
         [0029]      FIG. 5  is a schematic cross sectional view of a piezoelectric device in Embodiment 4 of the present invention.  
         [0030]      FIGS. 6A, 6B  and  6 C are perspective views showing embodiments of electronic apparatuses of the present invention containing a ferroelectric memory device provided with an electronic device of the present invention, where  6 A shows a mobile phone,  6 B shows a wristwatch type electronic apparatus, and  6 C shows a mobile information processing device. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]     The hereinafter described embodiments 1 to 4 are examples of the electronic devices according to the present invention, and the hereinafter described embodiments 5 to 7 are examples of the electronic apparatuses according to the present invention.  
       Embodiment 1  
       [0032]      FIG. 1  is a cross sectional view of a surface acoustic device  10  in Embodiment 1 of the present invention. This device comprises a substrate  1 , an inorganic amorphous layer  2  formed on the substrate  1 , an oxide thin layer  3  formed on the inorganic amorphous layer  2 , a perovskite-type oxide layer  4  grown epitaxially on the oxide thin layer  3 , a piezoelectric thin film  5  of a perovskite-type oxide layer grown epitaxially on the perovskite oxide layer  4 , a thin film  6  comprised of an oxide or a nitride as a protective layer formed on the piezoelectric thin film  5 , and an electrode  7  formed on the thin film  6  as a protective layer.  
         [0033]     The substrate  1  can comprise a single silicon crystal, a silicon single crystal having a polycrystalline diamond thin film formed on the silicon or the like.  
         [0034]     The amorphous layer  2  can comprise SiO 2 , AlN or the like. It is preferable that the thickness of each amorphous layer be 5 to 50 nm in order to utilize high sound velocity through the substrate. These amorphous layers can be formed by a method such as a laser ablation method, a CVD method or the like. For example, when SiO 2  is formed by a laser ablation method, the oxygen partial pressure is set to 1.3 Pa (1×10 −2  Torr) and the substrate temperature is set between room temperature (20° C.) and 300° C. When forming AlN, N 2  is used.  
         [0035]     The oxide thin layer  3  can be formed by SrO, MgO, CeO 2 , Zro 2 , YSZ, BaO, CaO or the like. It is preferable that the thickness of the oxide thin layer  3  be 1 to 50 nm, because obtaining good epitaxial growth is difficult with a value of less than 1 nm. On the other hand, a thickness of more than 50 nm is not necessary since it is only required that a perovskite-type oxide layer  4  be grown epitaxially on an oxide thin film. The range of 1 to 5 nm is more preferable.  
         [0036]     These oxide thin layers can be formed by a method such as a laser ablation method, or the like. For example, when SrO is formed by a laser ablation method, the oxygen partial pressure is set to 1.3×10 −4  Pa (1×10 −6  Torr) and the substrate temperature is set to 200° C. while assisting the film formation by an ion beam.  
         [0037]     The oxide thin layer  4  can be formed by SrTiO 3 , SrRuO 3  or the like. It is preferable that the thickness of the oxide thin layer  4  be not less than 1 nm, because obtaining good epitaxial growth is difficult with a value of less than 1 nm.  
         [0038]     This perovskite-type oxide thin film  4  is obtained by growing it epitaxially, and can be formed by a method such as a laser ablation method or the like. For example, the perovskite-type thin film can be formed by a laser ablation method with an oxygen partial pressure of 1.3 Pa (1×10 −2  Torr) and a substrate temperature of 500 to 650° C.  
         [0039]     The piezoelectric thin film  5  of a perovskite-type oxide layer can be formed by KNbO 3 , PZT, BaTiO 3 , or the like. It is preferable that the thickness of the piezoelectric thin film of the perovskite-type oxide layers be 1 μm or more, because a high electromechanical coupling factor can be obtained.  
         [0040]     The piezoelectric thin film of a perovskite-type oxide layer is obtained by epitaxially growing the same, and can be formed by a laser ablation method, a CVD method, sol-gel method or the like. For example, when forming a KNbO 3  thin film by a laser ablation method, a substrate temperature of 500 to 650° C. and an oxygen partial pressure of 1.3 Pa (1×10 −2  Torr) are applicable.  
         [0041]     The thin film  6  of an oxide or a nitride as a protective layer can comprise SiO 2 , AlN or the like. These thin films of oxides or nitrides as protective layers can be formed by a method such as a laser ablation method, a CVD method or the like. For example, when forming SiO 2  by a laser ablation method, the oxygen partial pressure is set to 1.3 Pa (1×10 −2  Torr) and the substrate temperature is set between room temperature (20° C.) and 300° C. When AlN is formed, N 2  is utilized.  
         [0042]     The electrode  7  can comprise aluminum, copper, Al—Cu—Si alloy or the like. These electrodes can be formed by a method such as a sputtering method, an evaporation method, or the like.  
       Embodiment 2  
       [0043]      FIG. 2  is a schematic plan view of a ferroelectric memory apparatus  2000  in Embodiment 2 of the present invention.  FIG. 3  is a schematic cross sectional view of the portion along A-A of  FIG. 2 .  
         [0044]     In these drawings, reference numeral  100  refers to a matrix type memory cell array, and reference numeral  200  refers to a peripheral circuitry containing MOS transistors for selecting a memory cell. The top end of the peripheral circuitry  200  is an amorphous layer  201  of an interlayer insulating film acting as a protective layer at the same time. The reference numeral  21  refers to an oxide thin layer; reference numeral  22  refers to a first signal electrode of a perovskite-type oxide thin film grown epitaxially on the oxide thin layer  21 ; reference numeral  31  refers to a ferroelectric thin film of a perovskite-type oxide thin film grown epitaxially on the first signal electrode  22 ; reference numeral  23  refers to a second signal electrode formed on the ferroelectric thin film  31 ; and reference numeral  32  refers to a protective layer formed on the ferroelectric thin film  31  and the second signal electrode  23 .  
         [0045]     The peripheral circuitry  200  essentially comprises of a single crystal silicon substrate and integrated circuits formed on the single crystal silicon substrate.  
         [0046]     The amorphous layer  201  can comprise SiO 2 .  
         [0047]     The amorphous layer  201  can be formed by a method such as a CVD method, a laser ablation method or the like. For example, when SiO 2  is formed by a laser ablation method, the oxygen partial pressure is set to 1.3 Pa (1×10 −2  Torr) and the substrate temperature is set to between room temperature (20° C.) and 300° C. When forming AlN, N 2  is utilized.  
         [0048]     The oxide thin layer  21  can be formed by SrO, MgO, CeO 2 , ZrO 2 , YSZ, BaO, CaO or the like. It is preferable that the thickness of each oxide thin layer be 1 to 50 nm. It is preferable that the thickness be more than 1 nm in order to grow a good perovskite-type oxide layer  22  epitaxially on the oxide thin layer. On the other hand, it is not necessary to have a thickness of more than 50 nm since the only requirement is that the perovskite-type oxide layer  22  be grown epitaxially on the oxide thin layer. The range of 1 to 5 nm is more preferable.  
         [0049]     These oxide thin layers can be formed by a method such as a laser ablation method or the like. For example, when SrO is formed by a laser ablation method, the oxygen partial pressure is set to 1.3×10 −4  Pa (1×10 −6  Torr) and the substrate temperature is set to 200° C. with an ion beam assisting the film formation.  
         [0050]     The first signal electrode  22  of a perovskite-type oxide thin film can comprise SrRuO 3  or the like. The thickness of the perovskite-type oxide thin film  22  may be about 100 nm since it is only required to function as an electrode.  
         [0051]     The oxide electrode layer  22  comprising perovskite-type oxide layers can be formed by a method such as a laser ablation method or the like. For example, when a laser ablation method is used, these perovskite-type oxide layers can be fabricated at a substrate temperature of 500 to 650° C. and an oxygen partial pressure of 1.3 Pa (1×10 −2  Torr).  
         [0052]     The ferroelectric thin film  31  of a perovskite-type oxide thin film can comprise BaTiO 3 , PZT, SrBi 2 Ta 2 O 9 , Bi 4 Ti 3 O 12  or the like. It is preferable that the thickness of these perovskite-type oxide thin film  31  be 10 to 200 nm.  
         [0053]     These piezoelectric thin films of perovskite-type oxide layers can be formed by a method such as a laser ablation method, a CVD method, a sputtering method, a sol-gel processing or the like. For example, when BaTiO is used, the piezoelectric thin film can be formed at a substrate temperature of 500 to 650° C. and an oxygen partial pressure of 1.3 Pa (1×10 −2  Torr).  
         [0054]     The electrode  23  can comprise SrRuO 3 , Pt, Ir, Al, Cu or the like.  
         [0055]     These electrodes can be formed by a method such as a laser ablation method, a sputtering method, an evaporation method or the like.  
         [0056]     The protective layer  32 , formed on the ferroelectric thin film  31  and the second signal electrode  23 , can comprise SiO 2 .  
         [0057]     These thin films of oxides or nitrides as protective layers can be formed by a method such as a laser ablation method, a CVD method or the like.  
       Embodiment 3  
       [0058]      FIG. 4  is a schematic cross sectional view of a surface acoustic wave (described as SAW hereafter) oscillator  3  in Embodiment 3 of the present invention. The SAW oscillator comprises an oscillation circuit  300  including MOS transistors and a SAW resonator  301 . The top end of the oscillation circuit  300  is an amorphous layer  303  of an interlayer insulating film acting as a protective layer at the same time. The reference numeral  310  refers to an oxide thin layer formed on this amorphous layer  303 ; reference numeral  311  refers to a perovskite-type oxide thin film grown epitaxially on the oxide thin layer  310 ; reference numeral  312  refers to a perovskite-type oxide piezoelectric thin film grown epitaxially on the perovskite-type oxide thin film  311 ; reference numeral  313  refers to a thin film of a protective layer formed on the piezoelectric thin film  312 ; and reference numeral  314  refers to an electrode formed on the protective layer  313 .  
         [0059]     The oscillation circuit  300  essentially comprises a single crystal silicon substrate and integrated circuits formed on the single crystal silicon substrate.  
         [0060]     The amorphous layer  303  can comprise SiO 2 , AlN or the like.  
         [0061]     This amorphous layer  303  can be formed by a method such as a laser ablation method, a CVD method or the like. For example, when SiO 2  is formed by a laser ablation method, the oxygen partial pressure is set to 1.3 Pa (1×10 −2  Torr) and the substrate temperature is set to between room temperature (20° C.) and 300° C. When forming AlN, N 2  is utilized.  
         [0062]     The oxide thin layer  310  can be formed by SrO, MgO, CeO 2 , ZrO 2 , YSZ, BaO, CaO or the like.  
         [0063]     These oxide thin layers can be formed by a method such as a laser ablation method or the like. For example, when SrO is formed by a laser ablation method, the oxygen partial pressure is set to 1.3×10 −4  Pa (1×10 −6  Torr) and the substrate temperature is set to 200° C. with an ion beam assisting the film formation.  
         [0064]     The perovskite-type oxide thin film  311  can comprise SrTiO 3  or the like. This perovskite-type oxide thin film  311  is required for epitaxially growing a perovskite-type oxide piezoelectric thin film. It is preferable that the perovskite-type oxide thin film  311  be thicker in order to prevent leakage of electromagnetic waves and to increase the speed of sound waves.  
         [0065]     This perovskite-type oxide thin film can be formed by a method such as a laser ablation method or the like. For example, the perovskite-type thin film can be formed by a laser ablation method with an oxygen partial pressure of 1.3 Pa (1×10 −2  Torr) and a substrate temperature of 500 to 650° C. 
        a. The perovskite-type oxide piezoelectric thin film  312  can comprise KNbO 3 , PZT, BaTiO 3  or the like. It is preferable that the thickness of the perovskite-type oxide piezoelectric thin film  312  be 1 μm or more because a high electromechanical coupling factor can be obtained.        
 
         [0067]     The perovskite-type oxide piezoelectric thin film  312  can be formed by a method such as a laser ablation method, a CVD method, a sputtering method, a sol-gel processing or the like. For example, this thin film can be formed, in the case of the laser ablation method, with an oxygen partial pressure of 1.3 Pa (1×10 −2  Torr) and a substrate temperature of 500 to 650° C.  
         [0068]     The protective layer  313  formed on the perovskite-type oxide piezoelectric thin film  312  can comprise SiO 2 , AlN or the like.  
         [0069]     These thin films of oxides or nitrides as protective layers can be formed by a method such as a laser ablation method, a CVD method or the like. For example, when SiO 2  is formed by a laser ablation method, the oxygen partial pressure is set to 1.3 Pa (1×10 −2  Torr) and the substrate temperature is set to between room temperature (20° C.) and 300° C.  
         [0070]     The electrode  314  is an IDT electrode comprising Al, Cu, Al—Cu—Si alloy, SrRuO 3  or the like.  
         [0071]     These electrodes can be formed by a sputtering method, a evaporation method, a laser ablation method or the like.  
       Embodiment 4  
       [0072]      FIG. 5  is a schematic cross sectional view of a piezoelectric device in Embodiment 4 of the present invention. In this drawing, the reference numeral  401  refers to a substrate; reference numeral  402  refers to an inorganic amorphous layer formed on the substrate  401 ; reference numeral  403  refers to an oxide layer formed on the inorganic amorphous layer  402 ; reference numeral  404  refers to a perovskite-type oxide layer as a lower electrode grown epitaxially on the oxide layer  403 ; reference numeral  405  refers to a perovskite-type oxide piezoelectric thin layer grown epitaxially on the lower electrode  404 ; and reference numeral  406  refers to an upper electrode formed on the piezoelectric thin layer  405 .  
         [0073]     The substrate  401  comprises a silicon single crystal.  
         [0074]     The amorphous layer  402  can comprise SiO 2  or the like.  
         [0075]     These amorphous layers  402  can be formed by a method such as thermal oxidation, a CVD method, a laser ablation method or the like.  
         [0076]     The oxide thin layer  403  can be formed by SrO, MgO, CeO 2 , ZrO 2 , YSZ, BaO, CaO or the like.  
         [0077]     These oxide thin layers can be formed by a method such as a laser ablation method, a CVD method or the like. For example, when SrO is formed, the oxygen partial pressure is set to 1.3×10 −4  Pa (1×10 −6  Torr) and the substrate temperature is set to 200° C. with an ion beam assisting the film formation.  
         [0078]     The perovskite-type oxide thin film  404  as the lower electrode can comprise SrRuO 3 , SrTiO 3  made conductive by adding dopants such as Nb, or the like.  
         [0079]     These perovskite-type oxide thin films as the lower electrodes can be formed by a method such as a laser ablation method, a CVD method, a sputtering method, a sol-gel processing or the like. For example, the thin film can be formed with an oxygen partial pressure of 1.3 Pa (1×10 −2  Torr) and a substrate temperature of 500 to 650° C.  
         [0080]     The perovskite-type oxide piezoelectric thin film  405  can comprise BaTiO 3 , PZT, SrBi 2 Ta 2 O 9 , Bi 4 Ti 3 O 12  or the like.  
         [0081]     The perovskite-type oxide piezoelectric thin film  405  can be formed by a method such as a laser ablation method, a CVD method, a sputtering method, a sol-gel processing, or the like.  
         [0082]     The upper electrode  406  can comprise Al, Pt, Ir, perovskite-type oxides such as SrRuO 3 , or the like.  
         [0083]     These electrodes can be formed by a method such as a sputtering method, an evaporation method, a laser ablation method, a sol-gel processing or the like.  
         [0084]     Next, electronic apparatuses having a ferroelectric memory device of Embodiment 2 will be explained.  
       Embodiment 5  
       [0085]      FIG. 6A  is a perspective view of an example of a cellular phone. In  FIG. 6A , reference numeral  1000  refers to a main unit of the cellular phone having a memory section  1001  containing the ferroelectric memory device.  
       Embodiment 6  
       [0086]      FIG. 6B  is a perspective view of an example of a wrist watch type electronic apparatus. In  FIG. 6B , reference numeral  100  refers to a main unit of the watch having a memory section  1101  containing the ferroelectric memory device.  
       Embodiment 7  
       [0087]      FIG. 6C  is a perspective view of a mobile information processing device such as a word processor or a personal computer, for example. In  FIG. 6C , the reference numeral  1200  refers to an information processing device; the reference numeral  1202  refers to an input section such as a keyboard; and the reference numeral  1204  refers to a main unit of the information processing device having a memory section  1206  containing the ferroelectric memory device.  
         [0088]     Also, as an example of other electronic apparatuses, even though not shown, the present invention can be applied to a so-called IC card having a memory section containing the ferroelectric memory device.  
         [0089]     Each electronic apparatus (including an IC card) shown in  FIGS. 6A  to  6 C contains a ferroelectric memory device according to the embodiments described above, and thereby a compact electronic apparatus having a high reliability can be realized.  
         [0090]     The technological scope of the present invention is not limited to the embodiments described above and various modifications can be added within the scope of the gist of the present invention.  
         [0091]     For example, the above ferroelectric memory device can be applied to a so-called 1T1C type memory cell configured by one MOS transistor and one capacitor, or a so-called 2T2C type memory cell configured by two MOS transistors and two capacitors.  
         [0092]     The present invention is explained in detail in the following examples.  
       EXAMPLE 1  
       [0093]      FIG. 1  is a cross sectional view of a surface acoustic device  10  in Example 1 of the present invention. The device  10  is comprised of a substrate  1 , an amorphous layer  2 , an oxide thin layer  3 , an oxide thin layer  4 , a piezoelectric thin film  5 , a thin film  6  of an oxide or a nitride as a protective layer, and an electrode  7 .  
         [0094]     Fabrication processing of the surface acoustic device having the configuration above of the present invention is specifically described. A silicon substrate, on which a polycrystalline diamond thin film of thickness of 20 μm is formed, is used as a substrate  1 . First, a SiO 2  amorphous layer  2  is formed on the substrate  1  by using a laser ablation method. Next, a CeO 2  thin film as an oxide thin layer  3  is formed similarly on the amorphous layer  2  by using a laser ablation method with an ion beam assist. With an oxygen plasma of 0.13 Pa (10 −4  Torr) and a substrate temperature of 500° C., a CeO 2  thin film of (100) orientation was formed. By examining in-plane orientation of the CeO 2  thin film obtained through an X-ray diffraction pole figure, it was verified that the film has an in-plane orientation as well. That is, it was verified that a CeO 2  thin film of (100) orientation was grown epitaxially on the SiO 2  amorphous layer  2 .  
         [0095]     Again, a SrTiO 3  thin film as an oxide thin layer  4  was formed similarly on the CeO 2  oxide thin layer  3  by a laser ablation method. Multiple targets can be loaded in the laser ablation device and several films of different materials can be formed consecutively in the same chamber. After a film was formed in the oxygen plasma of 0.13 Pa (10 −4  Torr) at a substrate temperature of 600° C., it was verified that a perovskite-type oxide SrTiO 3  thin film of (110) orientation was grown epitaxially on the CeO 2  thin film of (100) orientation. This orientation relationship seems to be due to the relationship of the crystal structure and the lattice constant between CeO 2  of the fluorite (CaF 2 ) structure and SrTiO 3  of the perovskite-type structure.  
         [0096]     Next, a KNbO 3  piezoelectric thin film  5  was similarly formed consecutively in the same chamber by a laser ablation method. At this time, since K is easily evaporated, it is better to supply a high dosage of K for target formation. After a film was formed in the oxygen plasma of 0.013 Pa (10 −4  Torr) at the substrate temperature of 600° C., it was verified that a KNbO 3  thin film  5  of (010) orientation was grown epitaxially on the perovskite-type oxide SrTiO 3  thin film of (110) orientation. SrTiO 3  and KNbO 3  have the same perovskite-type structure, which orientation relationship was influenced by the lattice constant and was identical to the one described in the Japanese Unexamined Patent Application, First Publication No. Hei 10-65488.  
         [0097]     As described above, by forming a SiO 2  amorphous layer  2  on a substrate  1  having a polycrystalline diamond thin film with a thickness of 20 μm formed on the silicon substrate, a (100) orientation CeO 2  thin film as an oxide thin layer  3  and a (110) orientation SrTiO 3  thin film as an oxide thin layer  4  were grown epitaxially, and by making the SrTiO 3  thin film in (110) orientation, a KNbO 3  thin film was grown epitaxially on the SrTiO 3  thin film in (010) orientation. The &lt;010&gt; direction of KNbO 3  is the direction of the polarization axis.  
         [0098]     When a CeO 2  thin film was formed on the substrate  1  directly without having a SiO 2  amorphous layer  2 , a CeO 2  thin film, a SrTiO 3  thin film and a KNbO 3  thin film all became polycrystalline thin films due to lattice mismatch; therefore, desired characteristics could not be obtained, as will be described later. Also, when a KNbO 3  thin film was formed on the substrate  1  directly, the KNbO 3  thin film became a polycrystal thin film due to lattice mismatch; therefore, desired characteristics could not be obtained, as will be described later.  
         [0099]     Consequently, with the configuration described above, a high quality KNbO 3  piezoelectric thin film  5  was successfully grown epitaxially for the first time.  
         [0100]     Furthermore, here, even though silicon oxide was used as an amorphous layer, the same effect could be obtained by using AlN.  
         [0101]     Even though a CeO 2  thin film was used as an oxide thin layer  3 , the same effect could be obtained by using a ZrO 2  thin film or a YSZ thin film.  
         [0102]     When SrO, CaO, BaO or MgO is used for an oxide thin layer  3 , each epitaxial thin film is formed in (100) orientation for SrO, MgO or the like, in (100) orientation for an oxide thin layer  4  (SrTiO 3  thin film) grown on the oxide thin layer  3 , in (001) orientation for a piezoelectric thin film  5  (KNbO 3  thin film) grown on the oxide thin layer  4 ; therefore, orientations which differ from the configuration above can be obtained as well.  
         [0103]     Next, a SiO 2  amorphous thin film as the thin film  6  of a protective layer comprised of an oxide or a nitride is formed similarly on the KNbO 3  thin film  5  consecutively in the same chamber by using a laser ablation method. Since K in KNbO 3  is prone to react with water and deteriorates over time, a protective layer  6  is required. Since the sign of the temperature coefficient of SiO 2  is opposite to that of KNbO 3 , the protective layer also plays a role in controlling the temperature characteristics. One of the materials playing the same role as SiO 2  is AlN; therefore, an AlN thin film may be used as a protective layer.  
         [0104]     Finally, a surface acoustic device as shown in  FIG. 1  is fabricated by forming an aluminum thin film on the SiO 2  and by forming an IDT electrode  7  by the use of patterning.  
         [0105]     The reason for using a silicon substrate, having a polycrystalline diamond thin film formed thereon as a substrate  1  is that the diamond is the material having the highest sound velocity among known materials and is most suitable for high frequencies in the GHz band which will be required for the surface acoustic devices in the future. On the other hand, the reason for using KNbO 3  as a piezoelectric thin film  5  is that high performance can be expected since it has a high electromechanical coupling factor (k 2 ) of 50% or higher.  
         [0106]     Evaluation on the characteristics of the surface acoustic wave (SAW hereafter) device fabricated showed that a value for k 2  of 10% or higher was obtained with a good repeatability. However, since the k 2  value depends on the quality and film thickness of the KNbO 3  thin film  5 , a film forming technique to obtain high quality film is required for the KNbO 3  thin film  5  as well as the oxide thin layers  3  and  4 ; furthermore, the film thickness must be correct. Regarding sound speed, it was verified that the substrate caused excitation of Sezawa waves with a high sound velocity of over 10000 m/s. That is, obtaining high frequency in the GHz band can be achieved by normal photolithographic processing.  
         [0107]     As a comparison, k 2  of approximately 1% was obtained for a test sample forming a CeO 2  thin film on a substrate  1  directly without having a SiO 2  amorphous layer  2 , and for another test sample forming a KNbO 3  thin film directly on a substrate  1 . The results were considerably inferior to the results obtained in the epitaxially grown layer.  
         [0108]     Even though a silicon substrate, having a polycrystalline diamond thin film formed thereon, is used as a substrate  1  in Example 1, the substrate may be any material as long as the material can withstand the substrate temperature where oxide layers  3  and  4 , and the piezoelectric thin film  5 , are grown epitaxially, and satisfies the sound velocity requirement. Also, even though KNbO 3  was used as a piezoelectric thin film  5 , it is not necessary to be limited to this material. The materials for each thin film, fabrication methods and fabrication conditions are also not limited to these.  
       EXAMPLE 2  
       [0109]      FIG. 2  is a schematic plan view of a ferroelectric memory device (a type of electronic device of the present invention) in Example 2 of the present invention.  FIG. 3  is a partial schematic cross sectional view along A-A of  FIG. 2 .  
         [0110]     The ferroelectric memory devices of the Example 2 of the present invention having a matrix type memory cell array  100  with superior integration have a structure of forming the memory cell array  100  on a peripheral circuitry  200  containing MOS transistors for selecting a memory cell. The peripheral circuitry  200  contains various circuits in order to write or read data selectively from or to a memory cell. As shown in  FIG. 3 , the memory cell array  100  was formed on and in contact with the peripheral circuitry  200 . Here, the top section of the peripheral circuitry  200  was a SiO 2  amorphous layer of an interlayer insulating film acting as a protective layer at the same time. Consequently, the memory cell array  100  must be formed on the SiO 2  amorphous layer; however, since a superior square-loop P-V characteristic is required for a ferroelectric memory device using a memory cell array, a ferroelectric thin film  31  must be grown epitaxially. Furthermore, in  FIG. 2 , the ferroelectric thin film  31  is placed between a first signal electrode  22  and a second signal electrode  23 .  
         [0111]     Specific fabrication processes for the memory array  100  are described by referring to  FIG. 3 . First, a SrO thin film as an oxide thin layer  21  was formed on the peripheral circuitry  200  having the uppermost section terminated by a SiO 2  amorphous layer by using a laser ablation method with an ion beam assist. At this time, it was verified through X-ray diffraction that SrO was an epitaxial thin film of (100) orientation. Next, a SrRuO 3  thin film of a conductive perovskite-type oxide was formed as the first signal electrode  22  by using a laser ablation method. As expected, it was verified that SrRuO 3  was also an epitaxial thin film with pseudo-cubic crystal (100) orientation.  
         [0112]     Next, as shown in  FIG. 2 , a prescribed shape of SrRuO 3  was obtained by patterning, and then BaTiO 3  was formed as the ferroelectric thin film  31  by using a laser ablation method. Here, it was verified that BaTiO 3  on SrRuO 3  was an epitaxial thin film of (001) orientation. Then, similarly to the first signal electrode  22 , SrRuO 3  was formed, and then a prescribed shape was obtained by patterning to form the second signal electrode  23 . Finally, a protective layer  32  comprised of an insulating film of, for example, SiO 2 , AlN or the like was formed on the ferroelectric thin film  31 , on which the second signal electrode  23  had been formed.  
         [0113]     Even though a configuration of placing a memory array and a peripheral circuitry on separate planes can be used, the configuration of the Example 2 of the present invention is superior in integration of high capacity memory cells.  
         [0114]     Here, an example of write and read operation for a memory cell is described. First, a read out voltage Vo is applied to a selected cell during a read-operation. This operation also performs a write-operation of “0” at the same time. At this time, a current flowing in the selected bit lines or a potential when the bit lines are placed in a high impedance state is read out by a sense amplifier. Also, at this time, a prescribed voltage is applied to unselected cells in order to prevent cross talk during the read operation. When “1” is written during a write operation, a voltage of Vo is applied to a selected cell. When “0” is written, a voltage not inverting the polarization of the selected cell is applied and the “0” state written during the read operation is held. At this time, a prescribed voltage is applied to the capacitors of unselected cells in order to prevent cross talk during the write operation.  
         [0115]     Furthermore, the materials, fabrication methods and fabrication processing used here are also not limited to those described. Even though silicon oxide (SiO 2 ) was used as an amorphous layer here, the same effect can be obtained by using AlN and glass.  
         [0116]     Even though a SrO thin film was used as an oxide thin layer  3 , the same effect can be obtained by using a CeO 2  thin film, a ZrO 2  thin film, a MgO thin film, a CaO thin film, a BaO thin film or a YSZ thin film.  
       EXAMPLE 3  
       [0117]      FIG. 4  is a schematic cross sectional view of a SAW oscillator in Example 3 of the present invention. The SAW oscillator comprises an oscillation circuit  300  and a SAW resonator  301 . The reference numeral  310  refers to an oxide thin layer; reference numeral  311  refers to a perovskite-type oxide; reference numeral  312  refers to a piezoelectric thin film; reference numeral  313  refers to a thin film as a protective layer; and reference numeral  314  refers to an electrode. The uppermost section of the oscillation circuit  300  is a SiO 2  amorphous layer  303  of an interlayer insulating film acting as a protective layer at the same time. Consequently, the SAW resonator  301  must be formed on the SiO 2  amorphous layer  303 ; however, a piezoelectric thin film  312  must be grown epitaxially in order to obtain a SAW resonator  301  having good performance.  
         [0118]     The fabrication process of the SAW resonator  301  is described by referring to  FIG. 4 , which is similar to the one described in Example 1. First, a SrO thin film as the oxide layer  310  was formed on the oscillation circuit  300  having the uppermost section terminated by a SiO 2  amorphous layer  303 . As described in Example 1, SrO was an epitaxial thin film of (100) orientation at this time. Then, a SrTiO 3  thin film of an oxide thin layer  311  was formed on the SrO oxide thin layer  310 . The SrTiO 3  thin film of (100) orientation was grown epitaxially on the SrO thin film of (100) orientation. Next, a KNbO 3  piezoelectric thin film  312  was formed. The KNbO 3  thin film  312  with (001) orientation was grown epitaxially on the SrTiO 3  thin film of (100) orientation. A thin film  313  of a protective layer comprised of an oxide or a nitride was formed on the KNbO 3  thin film  312 . Finally, an aluminum thin film was formed on the protective layer  313 , the electrode  314  was formed by patterning the layer  313 , and the SAW oscillator shown in  FIG. 4  was fabricated.  
         [0119]     Evaluation on the characteristics of the SAW resonator  301  showed that a value of k 2  of 10% or higher was obtained with a good repeatability. However, the k 2  value depends on the quality and film thickness of the KNbO 3  thin film  312 , a film forming technology to obtain high quality film is required for the KNbO 3  thin film as well as the oxide thin layers,  310  and  311 , and the film thickness must be correct.  
         [0120]     A SAW oscillator usually has a configuration of placing a SAW resonator and an oscillation circuit separately on the same plane within a package. A SAW oscillator which is extremely miniaturized and with higher performance compared to the conventional unit can be obtained by using the configuration of the present invention.  
         [0121]     Furthermore, even though KNbO 3  was used as the piezoelectric thin film  312 , this is not limited thereto.  
       EXAMPLE 4  
       [0122]      FIG. 5  is a schematic cross sectional view of a piezoelectric device in Example 4 of the present invention. In this drawing, the reference numeral  401  refers to a single crystal substrate; reference numeral  402  refers to a SiO 2  amorphous layer; reference numeral  403  refers to an oxide layer; reference numeral  404  refers to a perovskite-type oxide layer as a lower electrode; reference numeral  405  refers to a perovskite-type oxide piezoelectric thin layer; and reference numeral  406  refers to an upper electrode. Specific fabrication processing is described by referring to  FIG. 5 .  
         [0123]     First, a SiO 2  amorphous layer  402  is formed on the surface of Si (110) single crystal substrate  401  by using thermal oxidation. Next, a SrO oxide layer  403  is formed, and then a SrRuO 3  thin film of a perovskite-type oxide is formed as a lower electrode  404 . Then, on top of that, BaTiO 3  as a piezoelectric thin film  405  and SrRuO 3  as an upper electrode  406  are formed consecutively. A cavity is formed at the rear side of the Si (110) single crystal substrate  401  by etching. At this time, the SiO 2  amorphous layer  402  plays a role of etching stopper. Consequently, a piezoelectric device as shown in  FIG. 5  is formed. An actual result was that each of the SrO oxide layer of (100) orientation, the lower electrode SrRuO 3  with pseudo-cubic crystal (100) orientation, the piezoelectric thin film BaTiO 3  with (001) orientation, and the upper electrode SrRuO 3  with pseudo-cubic crystal (100) orientation was an epitaxial thin film.  
         [0124]     Evaluation on the performance index of this element showed that the performance index ((piezoelectric constant)×(Young&#39;s modulus)) had an improvement of 50% compared with the case of using polycrystal BaTiO 3  piezoelectric thin film.  
         [0125]     Furthermore, the materials for the lower electrode, the piezoelectric thin film and the upper electrode are not limited to the ones described above. Also, MgO, CaO or BaO may be used as an oxide layer  403  and when CeO 2 , ZrO 2  or YSZ is used, the orientation of the piezoelectric thin film  405  can be changed, and thereby, the characteristics can be controlled.  
         [0126]     Instead of a SiO 2  amorphous layer  402 , an organic solid layer can be used. For example, an organic solid layer can be formed by applying a melamine resin layer or a polyimide precursor liquid on a substrate for hardening or by using nylon 66 or polyethylene terephthalate for thermobonding. Each of an oxide layer  403 , a perovskite-type oxide thin film  404 , a piezoelectric thin film  405 , and an upper electrode  406  can be formed or grown by a laser ablation method at a substrate temperature of 200 to 350° C. with an ion beam assist.