JPH0794681A - Oxide electrode - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a lower electrode capable of easily forming a highly oriented dielectric thin film used in a superconducting device, a DRAM and a nonvolatile RAM. [Constitution] A conductive perovskite type oxide 3 is epitaxially formed on a single crystal substrate 1 or is epitaxially formed on a buffer epitaxially formed on the single crystal substrate 1 to form a lower electrode 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode for forming a dielectric thin film thereon, and more particularly to a superconducting device, DRA.
The present invention relates to an electrode for forming a highly oriented dielectric thin film used in a nonvolatile RAM using M and a ferroelectric.

[0002]

2. Description of the Related Art A lower electrode for forming a highly oriented dielectric thin film formed on a single crystal substrate is made of MgO.
An electrode in which Pt is epitaxially formed on a single crystal substrate is a Japanese Journal of Applied Physics 199.
It was reported on September 2nd, pp. 2985-2988.

Further, in a nonvolatile RAM capacitor in which a ferroelectric thin film is used for a capacitor of a memory cell and information is recorded according to the direction of spontaneous polarization, Pt or RuO _x is used for a lower electrode forming the ferroelectric thin film. Nikkei Microdevice May 1992 p.72-73.

[0004]

In the prior art, Pt epitaxially formed on a MgO single crystal substrate is used as a lower electrode for forming a highly oriented dielectric thin film formed on a substrate in the prior art. When used, the orientation of the dielectric thin film thereon tends to vary, and it is difficult to control the orientation. An object of the present invention is to provide an electrode which is formed on a substrate and on which a highly oriented dielectric thin film can be easily formed.

Further, in a memory cell of a DRAM, when a metal such as Pt is used for a lower electrode of a capacitor according to a conventional technique, it is difficult to control the orientation of a dielectric thin film formed on the lower electrode and a defect having a high orientation. It is difficult to obtain a film having a small amount of charge and there is a problem that the leakage current of the capacitor is large. An object of the present invention is to provide a memory cell suitable for high integration by forming a capacitor having a highly oriented and low defect dielectric thin film with improved insulation and dielectric properties on a Si substrate.

Further, in a non-volatile RAM memory cell using a ferroelectric substance, deterioration due to polarization reversal of the ferroelectric substance becomes a problem. Deterioration can be reduced by controlling the orientation of the ferroelectric thin film and aligning the crystal orientations. However, when a conventional Pt electrode is used as the lower electrode for manufacturing the ferroelectric thin film, the ferroelectric thin film formed is Orientation control is difficult. Also, Ru
When O _x is used as an electrode, the lattice matching with Si is poor due to the difference in lattice constant, and it is difficult to epitaxially form it on a Si substrate.

An object of the present invention is to provide a capacitor which has a highly oriented ferroelectric thin film and which is less deteriorated in characteristics due to polarization reversal.
It is to provide a non-volatile memory cell formed on an i substrate and capable of achieving a high rewriting frequency.

[0008]

A feature of the present invention is that a conductive perovskite oxide having a specific resistance of 500 mΩcm or less is epitaxially formed directly on a single crystal substrate, or is formed epitaxially on the single crystal substrate. And to form an electrode on the buffer layer epitaxially.

A feature of the present invention is that the specific resistance is 500 mΩ.
An oxide electrode made of a conductive oxide having a size of cm or less is formed on the substrate with the crystal orientations in the direction perpendicular to the substrate surface aligned.

Another feature of the present invention is that the oxide electrode is used as the lower electrode in the superconducting device. More specifically, the lower electrode of the chemical formula 2, the dielectric thin film of the chemical formula 3, the oxide magnetic layer of the chemical formula 4, and the superconductor layer of the chemical formula 5 are sequentially formed epitaxially on the single crystal substrate of the chemical formula 1 shown below. It is to form an element.

[0011]

Embedded image MgO, Al ₂ O ₃ , CaF ₂ , SrTiO ₃ and perovskite type oxide LnAO ₃ (Ln is La, Ce, P
r, Nd, Sm, Eu, Gd, Ho, Er, Dy, T
Any one of m, Yb and Lu, A is one of Al and Ga), and one of LaSrGaO ₄ single crystal

[0012]

Embedded image Perovskite type compounds A _1-X B _X MO _z (where A is Pb, Bi, Sc, Y, La, Ce, Pr, Nd,
Sm, Eu, Gd, Ho, Er, Dy, Tm, Yb, L
u is any one, B is any one of Ca, Sr and Ba, M is Ti, V, Cr, Mn, Fe, Co,
Any one of Ni, Ru, and Rh, 0 ≦ x ≦ 1, and 2.2 ≦ z ≦ 3.2)

[0013]

## STR00003 ## Perovskite type compound Sr _1-x Ba _x TiO ₃
(Where 0 ≦ x ≦ 1), Pb 1-y La y Zr x Ti
_{One of 1-x} O ₃ (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1)

[0014]

## STR00004 ## Perovskite type compound A _1-X B _X MO _z (where A is Y, La, Ce, Pr, Nd, Sm, Eu, Gd,
One of Ho, Er, Dy, Tm, Yb, and Lu, B is one of Ca, Sr, and Ba, and M is C
Any one of r, Mn, Fe, Co, Ni, Ru, and Rh, 0 ≦ x ≦ 1, and 2.2 ≦ z ≦ 3.2)

[0015]

Embedded image LnBa ₂ Cu ₃ O _y (where Ln is Y, La,
Ce, Nd, Sm, Eu, Gd, Ho, Er, Dy, T
m, Yb, any one of _{Lu), Ln 2-x B} x CuO y ( provided that Ln is Y, La, Ce, Pr, Nd, Sm, Eu,
Gd, Ho, Er, Dy, Tm, Yb, or Lu, and B is any one of Ca, Sr, or Ba,
0 ≦ x ≦ 1), Bi ₂ Sr ₂ CaCu ₂ O _y , Bi ₂
Any one of Sr ₂ Ca ₂ Cu ₃ O _{y Further} , a feature of the present invention is that an oxide electrode is used as a lower electrode in a capacitor of a memory cell. More specifically, the insulating buffer shown in Chemical formula 6, the lower electrode of Chemical formula 2, and the dielectric thin film are epitaxially formed in this order on a single crystal Si substrate, and an upper electrode is further formed to form a capacitor.

[0016]

Embedded image YSZ (yttrium-stabilized zirconia), C
_{aF 2, SrF 2, BaF 2} , CeO 2, PrO 2, Y 2 O 3, G
Any one of d ₂ O ₃ , MgAl ₂ O ₄ , LaAlO ₃ , and LaGaO ₃ or the capacitor of the memory cell is formed on the source of the field-effect transistor formed on the surface of the single crystal Si substrate. Buffer, the lower electrode of the chemical formula 2 and the dielectric thin film are epitaxially formed in this order, and the upper electrode is further formed to form a capacitor.

[0017]

Embedded image MSi ₂ (where M is Co, Ni, Ti, Zr,
Hf, V, Nb, Ta, W, Mo, Cr, Pt, Ir,
Os, Ru, Rh, or Pd) or the capacitor of the memory cell, the lower electrode of Chemical formula 2 or Chemical formula 8 on the source of the field effect transistor, and the crystal orientation in the direction perpendicular to the substrate surface is aligned. Then, a dielectric thin film is epitaxially formed thereon, and an upper electrode made of Chemical formula 2 or Chemical formula 8 is further formed to form a capacitor.

[0018]

Embedded image A _x B _y O _z (where A is Rh, Re, Mo, C
At least one element of r, W, Sn, Zn, Nb and In, B is at least one element of Sn, Te, Cd, Al, Ga, Bi and Pb, and 1 ≦ x ≦ 2, 0 ≦ y ≦
When the memory cell including any of the capacitors is used as the memory cell of the DRAM, the following chemical formula 9 is used as the dielectric thin film.

[0019]

Embedded image Sr _1-x Ba _x TiO ₃ (where 0 ≦ x ≦ 0.
5), Pb _1-y La _y Zr _x Ti _1-x O ₃ (where 0 ≦ x ≦
1,0 ≦ y ≦ 1), PbMg _{x / 3} Nb _2/3 O ₃ (however, 0.
9 ≦ x ≦ 1.2) Also, when the memory cell including any one of the above capacitors is used as a memory cell of a non-volatile RAM, the ferroelectric film of Chemical formula 10 below is used as the dielectric thin film.

[0020]

Embedded image BaTiO ₃ , Pb _1-y La _y Zr _x Ti _1-x O ₃
(However, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), BaMgF ₄ , KN
bO ₃ , LiNbO ₃ , LiTaO ₃ , Pb _1-x Ba _x Nb _2-y Ta _y O
₆ (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 2), Bi ₄ Ti ₃ O ₁₂ ,
One of LaBGeO ₅ .

[0021]

Most of the dielectrics expected to be applied to a non-volatile memory using a superconducting element, a DRAM, and a ferroelectric substance are conductive such as SrTiO ₃ which constitutes the oxide electrode of the present invention. It has a good lattice matching with the perovskite oxide, on which the dielectric is easily formed epitaxially. When the oxide electrode is epitaxially formed on the buffer layer formed directly or epitaxially on the single crystal substrate thereunder, it is a highly oriented film in which the crystal directions are aligned, and a dielectric layer is formed on top of this. By forming the body thin film epitaxially, a dielectric thin film having the same high orientation as that formed on the single crystal substrate is formed. Further, even if the oxide electrode is not formed epitaxially, if the crystal orientation perpendicular to the substrate surface of the oxide electrode is aligned, a dielectric thin film of considerably good quality can be formed. Further, since both the electrode and the dielectric are oxides, defects such as oxygen vacancies in the formed dielectric thin film are reduced as compared with the case where a metal electrode such as Pt is used.

Further, in a superconducting device using an oxide superconductor, the oxide magnetic layer and the superconducting electrode are required to be a highly oriented film in which the crystal orientations are almost the same as a single crystal. .
When the orientation is disturbed, the superconducting characteristics of the superconducting electrode are deteriorated or the characteristics of the element are deteriorated. The highly-oriented normal conductor layer and superconducting electrode can be formed by orienting the underlying dielectric layer and sequentially epitaxially forming it. For this purpose, it is necessary to form a dielectric thin film having high orientation. By using the oxide electrode of the present invention as a lower electrode of a superconducting device, a dielectric thin film is formed on the lower electrode.
By sequentially epitaxially forming the oxide layer and the superconducting electrode layer, it is possible to obtain a device having good characteristics in which the orientation of the entire device is uniform.

Defects such as grain boundaries and oxygen vacancies in the dielectric deteriorate the dielectric and insulating properties of the dielectric. By forming a highly oriented dielectric thin film to reduce grain boundaries and using the same oxide as the dielectric for the electrodes to reduce oxygen vacancies, the dielectric and insulating properties of the capacitor are improved.
The conductive perovskite type oxide forming the oxide electrode of the present invention has good lattice matching with Si, and is directly epitaxially formed on a single crystal Si substrate or on a buffer epitaxially formed on the single crystal Si substrate. Can be formed. By using the oxide electrode of the present invention as the lower electrode of a capacitor of a memory cell, a highly oriented thin dielectric thin film is formed, and the dielectric and insulating properties of the capacitor are improved.

Further, the ferroelectric substance has anisotropy, and by forming the ferroelectric thin film having a uniform crystal orientation, it is possible to improve the deterioration of the characteristics such as the decrease of the spontaneous polarization due to the reversal of the spontaneous polarization. In a memory cell of a non-volatile memory using a ferroelectric substance, by using the oxide electrode of the present invention as the lower electrode of the capacitor of the memory cell, a highly oriented ferroelectric thin film is formed and the spontaneous polarization of the capacitor is reversed. Deterioration of characteristics due to

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a lower electrode using the oxide electrode of the present invention and a dielectric thin film epitaxially formed thereon. A dielectric thin film 3 composed of the lower electrode 2, SrTiO ₃ containing the perovskite type oxide conductor La _0.8 Ca _0.2 MnO _z on the MgO single crystal substrate 1 are sequentially formed. The formation was performed by RF magnetron sputtering. From the X-ray diffraction of the formed laminated film, La _0.8 Ca _0.2
MnO _z and SrTiO ₃ are below MgO and La, respectively.
Oriented along the crystal orientation of _0.8 Ca _0.2 MnO _z ,
It was found that a highly oriented SrTiO ₃ thin film can be obtained.

(Embodiment 2) FIG. 2 shows an example of a superconducting device using the present invention. A lower electrode 2, a dielectric thin film 3, an oxide magnetic layer 4, and a superconductor layer 5 are sequentially and epitaxially formed on a substrate 1. A gap 6 was formed in the superconductor layer 5 by using electron beam drawing and ion milling to form superconducting electrodes 7 and 8.

For the substrate 1, a MgO single crystal is used.
An element was formed on the (00) plane. Perovskite type oxide conductor La _0.8 Ca _0.2 MnO _z is used as the lower electrode 2, SrTiO ₃ is used as the dielectric thin film 3 thereon, and perovskite type oxide magnetic substance La _0.6 Ca _{0.4 is} used as the oxide magnetic layer 4.
MnO _z is added to the superconductor layer 5 as an oxide superconductor YBa ₂ Cu ₃ O _y.
Was used. A superconducting current flows between the superconducting electrodes 7 and 8 through the oxide magnetic layer 4 in the gap 6 due to the proximity effect. This superconducting current is controlled by the voltage applied to the lower electrode 2 and the electromagnetic wave, magnetic field, and light applied to the gap portion 6.

From X-ray diffraction, it was found that each layer was formed epitaxially and an element in which the crystal orientation of the entire element was uniform was obtained. The superconducting transition temperature of the superconductor layer 5 is 60.
It was K. For comparison, when epitaxially formed Pt is used for the lower electrode 2, SrTiO _{3 of the} dielectric layer 3 is used.
Was disordered, and the orientations of the oxide magnetic layer 4 and the superconductor layer 5 thereon were also disordered. Further, the superconducting transition temperature of this superconductor layer was 30 K, and the superconducting characteristics were deteriorated. As described above, according to the present invention, an element having good orientation and an element having good characteristics can be obtained.

(Embodiment 3) FIG. 3 shows an example of a capacitor using the present invention.

The lower electrode 2 made of La _0.8 Ca _0.2 MnO _z on the (100) plane of the MgO single crystal used as the substrate 2 and Sr.
Dielectric thin film made of TiO ₃ , La _0.6 Ca _0.4 MnO _z
The upper electrode 9 composed of was sequentially formed. All R for formation
F magnetron sputtering was used. When X-ray diffraction was performed, each layer was epitaxially formed and had uniform alignment. As described above, the upper electrode can also be formed by epitaxially forming the conductive perovskite type oxide according to claim 2 to reduce defects at the electrode interface,
Insulation characteristics can be improved. When the leak current of this capacitor was measured, the leak current of SrTiO _{3 having} a film thickness of 280 nm was 10 ⁻⁸ A / cm ² or less in the range of ± 10V. The relative dielectric constant was about 250. On the other hand, in the capacitor having Pt as the lower electrode 1 and Au as the upper electrode 9 instead of La _0.8 Ca _0.2 MnO _z , the maximum leakage current was ± 10 V and the maximum value was 10 ⁻⁴ A / cm ² or more.
Further, the relative permittivity is about 200, which shows that the present invention improves the dielectric properties and insulating properties. Generally, the leakage current increases as the thickness of the dielectric thin film decreases,
Since the capacitor of the present invention has a small leak current, the film thickness can be reduced and the capacitance of the capacitor per unit area can be increased.

FIG. 4 shows an example of a memory cell using the present invention. Buffer 12 made of CaF ₂ on a single-crystal Si substrate 11, La _0.8 Ca _0.2 dielectric thin film 3 composed of the lower electrode 2, SrTiO ₃ consisting of MnO _z is formed.
Si, CaF ₂ , and La _0.8 Ca _0.2 MnO _z have close lattice constants and are sequentially formed epitaxially. Further, the upper electrode 13 is formed as a capacitor, and the source 21 of the field effect transistor also formed on the substrate 11 and the lower electrode 2 are connected by the wiring 25 to form a memory cell. Since the capacitor of the present invention can have a large capacitance per unit area, the memory cell can be miniaturized and is suitable for a highly integrated RAM.

Further, by forming the dielectric thin film 3 with the ferroelectric substance Pb _1-x La _x Zr _1-y Ti _y O ₃ instead of SrTiO ₃ , the information is recorded as the direction of its spontaneous polarization. Of memory cells are obtained. The ferroelectric thin film formed on the lower electrode of the present invention is an alignment film in which the crystal orientations are uniform,
Since the deterioration due to the reversal of the spontaneous polarization is small, a memory cell having a large number of rewritable times can be obtained.

Further, in the embodiment, the lower electrode 2 and the source 21
The wiring 25 is used to obtain the electrical coupling of the above, but as shown in FIG. 5, the buffer 12 made of a conductor is epitaxially formed on the source, and the lower electrode is formed on the buffer 12 to directly establish the electrical coupling. You can also

Further, without using the buffer 12, the lower electrode 2
Can also be formed directly on the source 21.

[0036]

According to the present invention, a highly oriented dielectric thin film can be formed on a lower electrode formed on a substrate.

Further, superconducting elements having the same crystal orientation of the entire element can be electrically separated and formed on the same substrate, and a superconducting element having good characteristics suitable for integration can be provided.

Further, since a highly oriented dielectric thin film having few defects can be formed on the Si substrate and the leak current can be reduced, the dielectric thin film can be thinned and the capacitance per unit area of the capacitor can be increased. As a result, the memory cell can be downsized and a highly integrated DRAM can be provided.

Further, a highly-oriented ferroelectric thin film with little characteristic deterioration due to polarization reversal can be formed on a Si substrate, and a nonvolatile RAM with a high rewritable frequency can be provided.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a lower electrode and a dielectric thin film.

FIG. 2 is an explanatory diagram of a superconducting element.

FIG. 3 is an explanatory diagram of a capacitor.

FIG. 4 is a cross-sectional view of a memory cell.

FIG. 5 is a cross-sectional view of a memory cell.

[Explanation of symbols]

 1 ... Substrate, 2 ... Lower electrode, 3 ... Dielectric thin film.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuzo Kozono 1-1-1, Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory

Claims (13)

[Claims] 1. An oxide electrode formed of a perovskite type oxide having a specific resistance of 500 mΩcm or less, which is epitaxially formed on a substrate. 2. The structure according to claim 1, which is represented by Ln _1-x A _x BO _z , where Ln is Bi, Pb or a rare earth element Y, La, C.
e, Pr, Nd, Sm, Eu, Gd, Tb, Dy, H
At least one element of o, Er, Tm, Yb, and Lu, A is at least one element of Ca, Sr, and Ba, and B is at least one of Ti, V, Cr, Mn, Fe, Co, and Ni. An oxide electrode made of a conductive perovskite oxide, which is one element and x is in the range of 0 ≦ x ≦ 1. 3. The oxide electrode according to claim 2, wherein the conductive perovskite oxide is formed at 600 ° C. or lower. 4. An oxide electrode, which is made of an oxide having a specific resistance of 500 mΩcm or less, and in which the crystal orientation in the direction perpendicular to the substrate surface is uniform in the electrode formed on the substrate. 5. The method of claim _{4, A x B y O z} ( where A is Rh, Re, Mo, Cr, W, Sn, Zn, Nb, In
At least one element, B is Sn, Te, Cd, A
at least one element of l, Ga, Bi and Pb, x is 1
≤x≤2, y is 0≤y≤0.5, and z is 2≤z≤3)
An oxide electrode made of an oxide having a specific resistance of 50 mΩcm or less. 6. The oxide electrode according to claim 2, a dielectric thin film formed on the oxide electrode, an oxide magnetic layer formed on the dielectric thin film, and the oxide magnetic layer. It is composed of two superconducting electrodes arranged in the same plane with a gap formed on the body layer, and the dielectric thin film, the oxide magnetic layer, and the superconducting electrode are formed epitaxially. Light with a superconducting current that flows between the two superconducting electrodes through the magnetic material layer to the gap,
A superconducting device controlled by a magnetic field, an electromagnetic wave and a voltage applied to the oxide electrode. 7. The capacitor according to claim 2, 3, 4 or 5, comprising the oxide electrode, a dielectric thin film epitaxially formed thereon, and an upper electrode formed on the dielectric thin film. . 8. The dielectric thin film according to claim 7, wherein the dielectric thin film is Sr.
_1-x Ba _x TiO ₃ (where 0 ≦ x ≦ 0.5), Pb _1-y La
_y Zr _x Ti _1-x O ₃ (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1),
A capacitor made of any one dielectric selected from PbMg _{x / 3} Nb _2/3 O ₃ (where 0.9 ≦ x ≦ 1.2). 9. The dielectric thin film according to claim 7, wherein the dielectric thin film is Ba.
TiO ₃ , Pb _1-y La _y Zr _x Ti _1-x O ₃ (where 0 ≦ x ≦
1,0 ≦ y ≦ 1), BaMgF ₄ , KNbO ₃ , LiNb
O ₃ , LiTaO ₃ , Pb _1-x Ba _x Nb _2-y Ta _y O ₆ (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 2), Bi ₄ Ti ₃ O ₁₂ , LaB
A capacitor made of any one ferroelectric material selected from GeO ₅ . 10. A source and drain formed on a substrate surface through a channel, an insulating film formed on the channel, and a gate formed on the source and drain, wherein: A field effect transistor for controlling the resistance of the channel between them by an electric field applied to the gate, a lower electrode formed on the substrate, a dielectric thin film formed on the lower electrode, and an upper electrode formed on the dielectric thin film. A memory cell for writing and reading information by controlling electric charges stored in the capacitor by the field effect transistor. 11. A DRAM using the memory cell according to claim 10. 12. A source and drain formed on a surface of a substrate via a channel, an insulating film formed on the channel, and a gate formed on the insulating film. A field effect transistor for controlling the resistance of the channel between them by an electric field applied to the gate, a lower electrode formed on the substrate, a dielectric thin film formed on the lower electrode, and an upper electrode formed on the dielectric thin film. A memory cell for writing and reading information by controlling the direction of spontaneous polarization of the dielectric thin film made of a ferroelectric substance of the capacitor by the field effect transistor. 13. A nonvolatile RAM using the memory cell according to claim 12.