JPH03285864A - Thin dielectric film - Google Patents

Abstract

PURPOSE:To obtain a thin dielectric film having a high dielectric constant by coating a substrate with a soln. contg. Pb-based metal ions satisfying a specified compsn. and calcining the coated substrate at a low temp. CONSTITUTION:A substrate such as an MgO single crystal is coated with a soln. contg. Pb-based metal ions satisfying a compsn. represented by formula I or II and the coated substrate is calcined at a relatively low temp. of about 700 deg.C to form a thin dielectric film made of a perovskite type oxide having a high dielectric constant. More than 70% of the oxide has a compsn. represented by the formula I or II. In the formulae I, II, each of M1 and M3 is at least one among Ba, Sr, Ca and lanthanides, M2 is at least one among Fe, Ni and Mg, M5 is at least one of Ti and Zr, M4 is at least one among Mg, Ni and Cd, M6 is at least one among Ti, Zr and Nb, 0.5<=n<=1.0, 0.5<=x<=1.0, y+x=1 and y and z show a ratio making (M2yNbz) and (M4yWz) tetravalent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a dielectric thin film made of a perovskite oxide.

(Prior Art) Dielectric materials are generally required to have a high dielectric constant, but they also need to satisfy various requirements such as low dielectric loss and high dielectric strength.

As a dielectric material that satisfies these various requirements,
Perovskite-type oxides have been reported for some time,
It is put into practical use. Among them, barium titanate Ba
T103 is widely applied as a typical dielectric material, and attempts have been made to make it thinner (for example, J, J,
uet, al, IEEE Transac-tron
on Ultrasonics, Ferroe
electrics and pre-quency
Control, vol, 3B, No, 3.1989
).

On the other hand, in recent years, as electronic devices have become smaller and faster, there has been an increasing demand for smaller circuit elements such as capacitors and higher density packaging. And in order to meet these demands,
There is also a need to use thinner dielectrics.

Ta203 has been known as a material with a high dielectric constant in the form of a thin film that has been put into practical use, but since its dielectric constant is not very high at 28, BaT10x, which is a material with a higher dielectric constant, has been used. Attempts are being made to make the film thinner.

(Problem to be solved by the invention) However, in the BaT103 system, although a perovskite structure film is formed at a low temperature of around 600°C, at that temperature the grain size is extremely small, less than 10 tv, and the dielectric constant is bulk-like. However, it had the disadvantage that it was extremely low at less than 1,710.

In addition, in order to increase the grain size to 0.1 μm or more and obtain properties equivalent to bulk ceramics, heat treatment at a high temperature of 1200°C or higher is required. This will lead to problems like this.

In other words, heat treatment at such high temperatures not only damages other parts to be bonded, such as capacitor electrodes, when the thin film is used as an element, but also induces reactions associated with diffusion, which can damage the film itself. It also causes a decline in the function of

The present invention was made to address these problems, and an object of the present invention is to provide a dielectric thin film that can be formed by low-temperature firing and has a high dielectric constant.

[Configuration of the Invention (Means and Effects for Solving the Problems) That is, in the dielectric thin film of the present invention, 70% or more of the oxide components in the thin film have the following general formula: % formula %) (1) ) ( ) (In the formula, Ml is at least one element selected from Fe, Ni, and Mg; M4 is at least one element selected from Mg, Ni, and Cd; Ml is Ba, Sr,
Ca, at least one element selected from the lanthanide elements, Mg, Bas 5rSCa, at least one element selected from the lanthanide elements, M5, TI,
M6 is at least one element selected from Zr, M6 is at least one element selected from Tl5Zr and Nb, and n, X, and YSZ are numbers that satisfy the following formula.

0.5≦n≦1.0 0.5≦X≦1.0 y+z■1 (However, y, z are (Ml Nb ) or (M
4° z V ) is shown as a composite 4-reef ratio. ) is characterized by being a perovskite-type oxide represented by (hereinafter the same).

The dielectric thin film of the present invention is mainly composed of an ABOn-type perovskite oxide containing PB as one of the main components, and this oxide can easily obtain a perovskite structure even when fired at a low temperature of 1000°C or less. , particle growth also progresses satisfactorily.

When such an oxide accounts for at least 70% of the oxide component in the thin film, the dielectric constant should be a high value of 30 or more, exceeding the dielectric constant of Ta203, which has been conventionally used as a high dielectric constant thin film. I can do it.

In the present invention, the composite oxide represented by the above formula (1) or (II) is a perovskite-type oxide whose basic composition is Pb(Ml, Nb2)03 or Pb(M4.W2)03. In order to obtain a high dielectric constant material, it is desirable that Ml be at least one element selected from Fe5NI%Mg, and M4 be at least one element selected from Mg5Nl and Cd.

Here, y%Z indicates the ratio set so that the component at the B site is synthetically tetravalent in the chemical formula ABO3 of the oxide.

In addition, in the above chemical formula ABO3, the component at the A site is Ml or Mg, and the component at the B site is M5, M6.
A partially substituted solid solution system can also be used.

Metal elements M1, M3, old, and M6 are added to obtain desired temperature characteristics and mechanical strength, but it is undesirable to add elements that prevent the formation of a perovskite structure. A suitable substitutional solid solution element is selected as appropriate.

For example, Ml and M3 include Ba, Sr, Ca
, lanthanides, etc., and M5 such as Tis Zr.
TI, Zr, Nb, etc. are selected as M6.

Each of X and n is 0.5≦X≦1.0.0.5≦
If n≦1.0, a high dielectric constant material can be obtained.
Moreover, firing at low temperatures is possible. If X is outside the above range, the grain size will not increase when fired at a low temperature of 1000°C or less, and if n is outside the above range, the grain size will not increase even if the grain size becomes sufficiently large. I can't get anything.

Furthermore, among the perovskite-type oxides constituting the dielectric thin film of the present invention, the oxide represented by the general formula: % formula %) is a high dielectric constant material and exhibits antiferroelectricity, Since the decrease in dielectric constant (decrease in bias characteristics) when a bias voltage is applied is small, it is useful as a thin film that is subjected to a high load compared to bulk materials.

The dielectric thin film of the present invention can be produced by sputtering method, vapor deposition method, C
Although it is possible to form by a vapor phase method such as a VD method, it is preferable to form by the method shown below because the composition and film thickness can be easily controlled and mass production is possible.

That is, a solution containing each desired metal ion and prepared in a molar ratio such that an oxide represented by the above formula (I) or (II) is produced is applied onto a substrate, and then baked. to obtain a dielectric thin film.

Here, as the starting material, organic acid salts, inorganic salts, or organic metal compounds such as alkoxides containing each metal ion can be used.

In addition, methods such as spin cord, spray coating, and dipping may be used for coating the substrate. For example, spray coating may be performed while the temperature of the substrate is raised.

Furthermore, in the heat treatment (baking) step after coating, 40%
A phase with a perovskite structure can be generated by heating to a temperature of 0°C or higher, but in order to increase the generation rate of the perovskite phase to 70% or higher and to increase the adhesion strength of the film to the substrate, the heat treatment temperature must be adjusted. It is desirable that the temperature be 500°C or higher.

(Example) Examples of the present invention will be described below.

Example 1 PbSFe, Nb metal alkoxides were mixed in l:0
．． A predetermined amount was weighed out so that the molar ratio was 5:0.5, and this was dissolved and mixed in 2-ethoxyethanol. Then,
The obtained solution was spin-coded onto a MgO single crystal substrate, and then heat-treated at a temperature of 700° C. for 30 minutes.

The thin film thus formed was subjected to X-ray diffraction.

As a result, a measurement chart is shown in FIG.

In the measurement chart shown in the figure, 0 indicates the indexing of the perovskite phase, and Δ indicates the diffraction peak from the substrate.

As is clear from the measurement results, a perovskite phase with good crystallinity was observed in the thin film, indicating that a perovskite-type oxide was formed.

Furthermore, when the surface of the formed thin film was observed by SEX, the particles had grown to a diameter of 15 μta - 0.2 μm, and the adhesion to the substrate was also good.

Comparative Example 1 A thin film was formed in the same manner as in Example 1 using a solution in which Ba5T+ metal alkoxides were dissolved and mixed in 2-ethoxyethanol at a molar ratio of 1:1.

When the obtained thin film was observed by SEX, the particle size was unobservable, and when the cross section was observed by TEN, it was found that it was composed of particles with a diameter of 0.05 μm or less.

Additionally, this thin film was easily scratched by the tip of the probe, causing a short circuit.

Example 2, Comparative Example 2 An oxide thin film was formed on the substrate in the same manner as in Example 1 and Comparative Example 1, except that the same solution was used and the heat treatment temperature was changed to 700°C, 800°C, and 900°C. formed respectively.

Next, interdigital electrodes of A1 were provided on each of the obtained thin films, and a method such as Parnel I (G, W, Fa
r-nell et, al, IEEE Trans, 5
onlcs Llltrason, SU-17 (197
The dielectric constant was determined according to 0)18g). The measurement results are shown in Figure 2.

As is clear from the graph in Figure 2, the dielectric constant of the thin film obtained in Example 2 was improved compared to the thin film obtained in Comparative Example 2 when heat treatment was performed at each temperature. I can see that

Example 3.4 Metal alkoxides of Pb, Fe, and Nb5Ti were dissolved and mixed in 2-ethoxyethanol at a molar ratio of 1:0.45:0.45:0.1 to prepare a solution. The substrate used was MgO sputtered with PT, and the above solution was coated on this substrate in the following manner, and then baked to form a thin film (Example 3)
.

In other words, the coating was done using a spin cord, and the baking was done at 750°C.
The test was carried out for 5 minutes. Then, such a spin cord and firing cycle was repeated eight times to form a thin film with a thickness of 1 μm, and Au was further deposited on top of the thin film.

Further, the solution prepared in Example 1 was applied onto a substrate and baked to form a thin film in the same manner as in Example 3 (Example 4).

The properties of the thin films obtained in Examples 3 and 4 are shown in Table 1.

Furthermore, when forming the thin film in Example 3, the firing temperature was varied from 400°C to 900°C, and X-ray diffraction was performed on the thin film fired at each temperature, and the formation of perovskite phase was observed from 400°C. The pyrochlore phase was also detected at this temperature. Perovskite ratio (-(perovskite (110) / (perovskite (110) + virochlore (222)) )
100) exceeds 70% when the firing temperature is 500℃.
That was the time.

Also, the dielectric constant is 20.500℃ when the firing temperature is 400℃.
So it was 50.

Example 5 Pb, Mg, and ν metal alkoxides were mixed in a ratio of 1:0.
A solution was prepared by dissolving and mixing in 2-ethoxyethanol at a molar ratio of 5:0.5, and a thin film was formed from this solution in the same manner as in Example 3.

When the electric field and dielectric polarization of the obtained thin film were measured and graphed, it showed a double hysteresis loop indicating antiferroelectricity. Further, when X-ray diffraction was performed in the same manner as in Example 1, it was found that a perovskite phase was formed in 70% or more of the obtained thin film.

The dielectric constant showed a high value of 150 or more in the range of 0 to 4 V/μ.

Examples 6 to 13 After coating a solution prepared to contain each metal ion with the composition shown in Table 2 on a substrate in the same manner as in Example 1,
After heat treatment at 00℃ x 30 minutes, 70% of the oxide component
A thin film of perovskite oxide was thus formed.

Next, the dielectric constant of the obtained thin film was measured using an AI interdigital electrode.

The measurement results are shown in Table 2.

(Left below) Also, IKHz, 0. [Effects of the Invention] As explained above, the dielectric thin film of the present invention has a high dielectric constant, so it can be applied to various devices as a high dielectric constant material.

In addition, this dielectric thin film can be obtained by applying a solution containing the desired metal ions and baking it at a low temperature, which not only suppresses reaction with the substrate material, but also
A homogeneous film can be continuously obtained over a large area, and mass productivity is high.

[Brief explanation of the drawing]

FIG. 1 is a chart showing the X-ray diffraction pattern of a dielectric thin film obtained in one example of the present invention, and FIG. 2 shows the heat treatment temperature and temperature of thin films obtained in other examples and comparative examples of the present invention. It is a graph showing the relationship with dielectric constant.

Claims (1)

[Claims] (1) More than 70% of the oxide components in the thin film have the general formula: (Pb_xM1_1_-_x)((M2_yNb_z)
_nM5_1_-_n)O_3 or (Pb_xM3_1_-_x)((M4_yW_z)_
nM6_1_-_n)O_3 (where M2 is Fe, Ni
, at least one element selected from Mg, M4 is M
At least one element selected from g, Ni, and Cd,
M1 contains at least one element selected from Ba, Sr, Ca, and lanthanide elements; M3 contains at least one element selected from Ba, Sr, Ca, and lanthanide elements;
5 is at least one element selected from Ti and Zr,
M6 is at least one element selected from Ti, Zr, and Nb, and n, x, y, and z are numbers that satisfy the following formula. 0.5≦n≦1.0, 0.5≦x≦1.0, y+z=1 (However, y, z are (M2_yNb_z) or (H
4_yW_z) is shown as a composite tetravalent. )) A dielectric thin film characterized by being a perovskite oxide.