JPH09208305A - Thin film of dielectric and ceramic condenser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thin film of a dielectric high in relative permittivity not only at 1kHz but also at high frequency like 100MHz and excellent in characteristics to a DC bias, by using an oxide containing a specific metal. SOLUTION: This thin film of a dielectric comprises a perovskite type compound oxide containing Ba, Ti and Sn as metal elements in which these components are shown as BaTi1-x Snx O3 , (x) and an average crystal particle diameter (d) (μm) exist in a range enclosed by lines A ((x) 0.02, (d) 0.90)-B ((x) 0.02, (d) 0.185)-C ((x) 0.04, (d) 0.185)-D ((x) 0.10, (d) 0.160)-E ((x) 0.16, (d) 0.100)-F ((x) 0.20, (d) 0.080)-G ((x) 0.10, (d) 0.045)-H ((x) 0.07, (d) 0.045)-A in the figure 1. The thin film has >=1,000 relative permittivity at 100MHz measuring wavelength (at room temperature). This thin film is provided with electrodes at both sides to form a ceramic condenser and used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric thin film and a ceramic capacitor, for example, 1
The present invention relates to a dielectric thin film made of a perovskite type complex oxide and a ceramic capacitor used for a high frequency multilayer ceramic capacitor having a film thickness of 5 μm or less per layer.

[0002]

2. Description of the Related Art In recent years, as electronic devices have become smaller and thinner, there has been a demand for smaller and thinner electronic components. In particular, miniaturization and thinning of capacitors, which are passive components, are essential. In addition, electronic devices such as computers using high-speed digital circuits are in the trend of higher frequencies, and the operating frequency band of several tens of MHz to several hundreds of MHz is important. Along with this, it has become essential that passive components such as capacitors also exhibit excellent characteristics with respect to high frequency or high speed pulses.

In order to make a capacitor small and have a high capacity, it is most effective to thin the dielectric material sandwiched between a pair of electrodes to make it thinner. Further, in recent years, integration of electronic devices, that is, incorporation of electronic components has progressed, and thinning is the most effective.

On the other hand, due to the thinning, the characteristics under the application of DC bias voltage become a problem.

That is, since the capacitor is used in the state where a DC voltage of several volts or less is applied, the dielectric property under the application of a DC bias voltage is important. Since the electric field strength increases in inverse proportion to the thickness of the dielectric with respect to the applied voltage, a material having a small decrease in the relative dielectric constant with respect to the DC bias electric field is required.

BT which is a typical capacitor material
Also, a relaxor material such as PMN exhibits a large relative permittivity in a low frequency region of about 1 KHz and is an excellent material as a capacitor material, but since the frequency dispersion is large, the relative permittivity greatly decreases in the high frequency region. Therefore, it has been considered that it cannot be used as a high dielectric constant material in a high frequency region (see Japanese Patent Laid-Open No. 6-77083).

Therefore, as a conventional thin film capacitor material,
Although the relative permittivity is small, the rate of temperature change of the relative permittivity is small,
Paraelectric materials such as Ta ₂ O ₅ and SrTiO ₃ which have a small DC bias dependency due to spontaneous polarization and a small decrease in relative permittivity in a high frequency region have been mainly studied.

[0008]

However, these Ta ₂ O ₅ and SrTiO ₃ thin film materials have a relative dielectric constant of several hundreds at the maximum even at a low frequency of about 1 KHz. It was difficult to convert.

[0009]

Means for Solving the Problems As a result of repeated studies on the above-mentioned problems, the present inventors have found that the B-site element T
Substituting 2 to 20 mol% of i atom with Sn atom, the average crystal grain size of the perovskite crystal is 0.045 to
Controlled to 0.185 μm, that is, BaTi _1-x Sn _x
The average crystal grain size d (μm) of x and the perovskite crystal when expressed as O ₃ is represented by the line segment ABCD in FIG.
By setting it within the range surrounded by -E-F-G-H-A, the relative dielectric constant becomes large not only at 1 kHz but also at a high frequency such as 100 MHz even in a dielectric thin film having a small grain size, and DC The inventors have found that the characteristics with respect to bias are also good and have reached the present invention.

That is, the dielectric thin film of the present invention is a dielectric thin film composed of a perovskite type complex oxide containing Ba, Ti and Sn as metal elements, and these components are BaTi _1-x Sn _x O ₃ X and the average crystal grain size d (μm) of the perovskite crystal are within the range surrounded by the line segment A-B-C-D-E-F-G-H-A in FIG. is there. The dielectric thin film of the present invention has a relative dielectric constant of 1000 or more at a measurement frequency of 100 MHz (room temperature).

Further, the ceramic capacitor of the present invention comprises:
Electrodes are formed on both surfaces of the above-mentioned dielectric thin film.

[0012]

[Function] In the BaTiO ₃ system dielectric material, 12
Phase transition points exist at 0 ° C., 10 ° C., and −70 ° C., and the relative dielectric constant is high in the vicinity thereof. That is, around room temperature exists in the middle of this phase transition point, and the temperature characteristics are good, but the relative dielectric constant is not so large.

In the dielectric thin film of the present invention, by substituting Sn atoms for Ti atoms of BaTiO ₃ , the three phase transition points are shifted to near room temperature, and three kinds of ferroelectric phases exist at room temperature. By doing so, a high relative dielectric constant is realized.

When the average crystal grain size in the thin film is made finer, the dielectric constant is somewhat lowered because the paraelectric property appears in the ferroelectric property, but the DC voltage is applied. The decrease in relative permittivity is suppressed, and the DC bias characteristic becomes good.

Further, even in a high frequency region such as 100 MHz, the spontaneous polarization which is the origin of the ferroelectric property disappears, so that the frequency dispersion of the dielectric constant due to the spontaneous polarization becomes small, and a large relative dielectric constant is obtained even in the high frequency region. Show.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, BaTi _{1-x is used.}
When expressed as Sn _x O ₃ , x satisfies 0.02 to 0.20 and the average crystal grain size d satisfies 0.045 to 0.185.

The value of x is set to 0.02 to 0.20 because
When x is smaller than 0.02, the relative permittivity becomes small due to the size effect of BaTiO ₃ , and when x is larger than 0.20, the temperature at which the relative permittivity becomes maximum is room temperature or lower, and near room temperature. This is because the relative dielectric constant of is small.
When expressed as BaTi _1-x Sn _x O ₃ , x is 0.04 to
0.13 is desirable from the viewpoint that the relative dielectric constant becomes large at room temperature.

The average crystal grain size d is 0.045 to 0.
The reason why 185 is set is that when the average crystal grain size d is smaller than 0.045, the relative dielectric constant becomes small, and when d is larger than 0.185, the relative dielectric constant with respect to the DC bias is changed. This is because the rate of change becomes large.

The range of x and the average grain size d when expressed as BaTi _1-x Sn _x O ₃ are surrounded by points A, B, C, D, E, F, G and H in FIG. It must be within the line segment.

That is, points A (0.02, 0.09), B (0.02, 0.0.2) represented by (value of x, average crystal grain size d).
185), C (0.04, 0.185), D (0.1
0, 0.16), E (0.16, 0.10), F (0.
20, 0.08), G (0.10, 0.045), H
It must be within the range of the line segment surrounded by (0.07, 0.045). The reason for setting this range is that the relative permittivity becomes small in the above-mentioned reason and in the portion below the line segment AHGF in FIG. Line segment CDE
This is because the rate of change of the relative permittivity with respect to the DC bias becomes large in the portion above F.

The range of x and the average grain size d when expressed as BaTi _1-x Sn _x O ₃ are the points I, J, and
It is desirable to be within the range of the line segment surrounded by D and L from the viewpoint of improving the relative dielectric constant and the DC bias characteristics. Here, I (0.02, 0.115), J (0.0
2,0.160), D (0.10,0.160), L
(0.10, 0.115).

First, the dielectric thin film of the present invention is a perovskite type complex oxide containing Ba, Ti and Sn as metal elements, and these components are mixed with BaTi _1-x Sn _x O 2.
_A raw material solution in which x when expressed as ₃ is 0.02 to 0.20 is prepared, and the solution is applied onto a substrate, then dried, and heat treatment is repeated to form a film having a desired thickness, followed by baking. It is obtained by doing.

That is, the perovskite type oxide used in the present invention is represented by BaTi _1-x Sn _x O ₃ , and the range of x is 0.02 to 0.20 as shown in FIG. In the case of a dielectric thin film satisfying a value of 0.045 to 0.185 μm, it is relatively easy to control the composition of each component, the film thickness, and the crystal grain size in the fine grain region (0.045 to 1 μm). However, it is desirable to form by the following method.

First, an organic acid salt, an inorganic salt, or an organometallic compound containing a metal ion of Ba, Ti, or Sn, or an organometallic compound such as a metal alkoxide is used as a starting material, and BaTi _{1-x is used.}
A raw material solution is prepared by mixing so that the composition of x in Sn _x O ₃ satisfies 0.02 to 0.20.

Next, this raw material solution is applied onto the substrate.
The solution can be applied by various methods such as spin coating and dip coating. Next, in order to degrease the coating film thus coated on the substrate, a heat treatment for degreasing is performed at 200 to 600 ° C. for 1 to 2 minutes in the atmosphere,
Then, for crystallization, a heat treatment for crystallization is performed at 700 to 900 ° C. for 30 seconds to 10 minutes in the atmosphere. A dielectric thin film having a desired film thickness is obtained by repeating a series of processes from coating to heat treatment for crystallization, and finally 0.045 to
To obtain an average crystal grain size of 0.185 μm, firing is performed at 900 to 1140 ° C. for 10 minutes to 3 hours in an oxygen-containing atmosphere to obtain a dielectric thin film of the present invention having a thickness of 5 μm or less.
The particle size was controlled by the firing temperature. In the present invention, the thickness of the dielectric thin film is 0.
It is preferably 3 to 2 μm.

In the dielectric thin film of the present invention, Sr, Ca, Na, etc. may be mixed as unavoidable impurities in an amount of 1% by weight or less, but the characteristics are not affected.

In the dielectric thin film of the present invention, electrodes are formed on the upper and lower surfaces of the dielectric thin film to form a thin film capacitor, or a dielectric thin film and electrode layers are alternately laminated to form a laminated capacitor. It is also used.

As electrodes sandwiching the dielectric thin film, oriented platinum (Pt) and gold (A) with a thickness of 0.05 μm or more are used.
u), palladium (Pd) thin films, and the like, and of these, oriented platinum (Pt) and gold (Au) thin films are most suitable. This is because Pt and Au have low reactivity with the film and are less likely to be oxidized, so that a low dielectric constant phase is less likely to be formed at the interface with the film. The thickness is 0.05μm or more is 0.05μ
This is because if it is less than m, the equivalent series resistance in the high frequency region becomes large. An oriented platinum (Pt) thin film is an oriented or single crystal platinum (Pt) thin film, and an oriented Pt thin film has one of three crystal axes approximately perpendicular to the film surface. The single crystal Pt thin film is a film in which all three crystal axes are aligned. Such an electrode is obtained by setting the temperature of the substrate on which the electrode is formed to 450 ° C. or higher in physical vapor deposition such as sputter vapor deposition or laser vapor deposition. Among these, among these,
Sputter deposition with a substrate temperature of 450 ° C. or higher is desirable.

Further, as the substrate on which the metal thin film is deposited,
Alumina, sapphire, MgO single crystal, SrTiO ₃ single crystal, titanium-coated silicon, or copper (Cu), nickel (Ni), titanium (Ti), tin (Sn), stainless steel (Fe) thin films or thin plates are desirable. In particular, it has low reactivity with thin films, is inexpensive, has high hardness,
Alumina and sapphire are preferable from the viewpoint of the crystallinity of the metal thin film, and copper (C
u) A thin plate or a copper (Cu) thin film is desirable.

[0030]

EXAMPLE Tetra-iso-propoxytitanium and tetra-n-propoxytin were used as starting materials, and the solvent was 2-
It was dissolved in methoxyethanol to prepare a titanium solution and a tin solution, respectively. In addition, metal barium is used as a solvent 2
-Dissolved in methoxyethanol to make a barium solution. These three solutions were mixed with BaTi _1-x Sn _x O ₃
A raw material solution was prepared by mixing so that x when represented by the above was the value of Table 1.

Next, each of these raw material solutions was treated with platinum (Pt).
Each of the substrates was spin-coated, and the obtained coating film was subjected to a degreasing heat treatment at 300 ° C. for 1 minute in the air, and then a crystallization heat treatment at 750 ° C. for 5 minutes in the air.
A series of processes from the application of the solution by spin coating to the heat treatment for crystallization are repeated 30 times to form a thin film having a thickness of 0.8 μm, and the thin film having a thickness of 900 to 900
The average crystal grain size d shown in Table 1 was obtained by firing at 1140 ° C. for 1 hour.
A dielectric thin film of

The obtained dielectric thin film was measured by X-ray diffraction (XR
As a result of the analysis according to D), a peak of a perovskite oxide was confirmed in each case. The dielectric thin film was observed with a scanning electron microscope (SEM), and the average crystal grain size was measured. Further, the evaluation of the dielectric properties was performed by depositing Au on the dielectric thin film to form an upper electrode, and forming a Pt layer as a lower electrode and a plate capacitor. Measurement is L
CR Meter (Huret Packer 4284A)
Measurement frequency f = 1 kHz, applied voltage Vrm
s = 100 mV. The relative permittivity (K) and the dielectric loss (DF) at room temperature were measured. Assuming that the DC bias characteristic is the relative permittivity K ₀ when no voltage is applied and the relative permittivity K ₁ when a voltage of 5 MV / m is applied, (K ₀ −K ₁ )
It was determined by the rate of change of the relative dielectric constant represented by / K ₀ × 100.

Further, characteristic evaluation at 1 MHz to 1.8 GHz was performed using an impedance analyzer (HP4291A, fixture HP16092A manufactured by Hulett Packard). By measuring the impedance-frequency characteristics, the equivalent series capacitance at 100 MHz (room temperature) was evaluated, and the relative permittivity was determined.

[0034]

[Table 1]

As can be seen from Table 1, points A, B, and B in FIG.
The dielectric thin film of the present invention surrounded by the line segments C, D, E, F, G and H has a measurement frequency of 1 kHz (room temperature) and 100 M.
Has a high dielectric constant of 1000 or more at 1 Hz and is 1k
It can be seen that the dielectric loss at Hz is as small as 1.38 to 2.70%. Further, in the present invention, the rate of change of the relative dielectric constant with respect to the DC bias is a decrease of less than 40% even when 5 MV / m is applied. Particularly, in the range surrounded by the line segment connecting the points I, J, D, and K, the measurement frequencies of 1 kHz and 100
It can be seen that the relative permittivity is 1350 or more at MHz.

On the other hand, in the comparative examples, each is 1 kHz.
The relative permittivity at z and 100 MHz is 100, respectively.
It can be seen that it may be lower than 0 or the change rate of the relative dielectric constant with respect to the DC bias may be higher than 40%.

Further, in the case of a conventional BaTiO ₃ system material having a particle size of 10 μm or more prepared from powder as a raw material, the rate of change of the relative dielectric constant with respect to the DC bias is 70% when a 5 MV / m voltage is applied. This is a decrease, and it can be seen that the present invention has excellent dielectric properties.

[0038]

As described above in detail, the dielectric thin film of the present invention has excellent DC bias characteristics and temperature characteristics, and has a large relative dielectric constant even at a high frequency such as 100 MHz. Can be achieved and I
It can be widely applied as a capacitor used at high frequency such as a decoupling capacitor around C.

[Brief description of drawings]

FIG. 1 shows the average crystal grain size d of the dielectric thin film of the present invention on the vertical axis,
It is the figure which described x in the composition formula of the dielectric thin film of this invention on the horizontal axis.

Claims (3)

[Claims] 1. A dielectric thin film comprising a perovskite type complex oxide containing Ba, Ti and Sn as metal elements, wherein x and perovskite are expressed when these components are expressed as BaTi _1-x Sn _x O _3. Average crystal grain size d
(Μm) is the line segment A-B-C-D-E-F in FIG.
-A dielectric thin film characterized by being in a range surrounded by -GHA. 2. The dielectric thin film according to claim 1, which has a relative dielectric constant of 1000 or more at a measurement frequency of 100 MHz (room temperature). 3. A ceramic capacitor comprising electrodes formed on both surfaces of the dielectric thin film according to claim 1.