JPH0196368A - Manufacture of thin film of ferroelectric substance - Google Patents

Abstract

PURPOSE:To easily form a film of ferroelectric substance excellent in characteristics by using an MgO plane as a substrate and regulating film-forming velocity so that it is lower than a specific velocity at the time of forming a thin film of ferroelectric substance with a specific composition on a substrate by means of sputtering. CONSTITUTION:A single-crystal MgO cleaved along the (100) plane and subjected to mirror-finish polishing is used as a substrate and a compound having a composition represented by formula 1 (where Y means 0.05-0.4) is used as a sputtering target and, as a sputtering gas, a gaseous mixture of Ar and O2 is used under <=3Pa pressure, and further, the substrate is heated to 550-675 deg.C, so that a thin film of a ferroelectric substance having a chemical formula Pb(Zr1-xTix)O3 [where the symbol (x) stands for >0.46-<1] is formed by means of sputtering at <=50A/min film-forming velocity. By this method, the thin film of ferroelectric substance suitable for pyroelectric-type infrared detecting element, piezoelectric element, and electrooptical element can be easily manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a ferroelectric thin film used in pyroelectric infrared detection elements, piezoelectric elements, and electro-optical elements.

BACKGROUND ART There are various applications of ferroelectric materials in the electronics field, such as infrared detection elements, piezoelectric elements, light modulation elements, and memory elements. As electronic components become smaller due to advances in semiconductor technology in recent years, ferroelectric elements are also becoming thinner.

By the way, in pyroelectric infrared detection elements, piezoelectric elements, etc. that extract changes in the spontaneous polarization Ps of a ferroelectric material as an output, the largest output can be obtained when the Ps of the ferroelectric material is aligned in one direction. .

Problems to be Solved by the Invention Currently, the ferroelectric ceramics used in infrared detection elements, piezoelectric elements, etc. are polycrystalline, and there is no directionality in the arrangement of crystal axes, so if spontaneous polarization Ps occurs. Arranged in the eye.

In epitaxial ferroelectric thin films and oriented ferroelectric thin films, the crystal polarization axes are aligned, but the electrical spontaneous polarization Ps is 1.
80° domains are created and arranged alternately. Therefore, when these materials are used as electronic devices as mentioned above, the materials are subjected to a high electric field (~100 kV/cm
) is required to align the direction of Ps.

In addition, there are many reports on the production of thin films such as PbTiOs and PZT-PLZT, but for thin films in the ferroelectric phase region, thin films oriented along the C axis, which is the polarization axis, and even spontaneous polarization are unidirectional. The method for manufacturing thin films oriented in this direction has not yet been fully elucidated.

The following problems arise in the method of aligning Ps by applying a high electric field to a ferroelectric material.

(1) Dielectric breakdown may occur due to polarization treatment, resulting in lower yield.

(2) In a high-resolution array element in which many microscopic cavities (Q elements) are arranged at high density, it is difficult to uniformly polarize them.

(3) In an integrated device in which a ferroelectric thin film is formed on a semiconductor device, polarization itself may not be possible in some cases.

Means for Solving the Problem In the step of producing a ferroelectric thin film on a substrate by sputtering, the chemical formula is Pb(Zr, , , xTi,)03 and the composition range is 0, 46<x<l. niMg
In addition to using the O (too) plane, the film formation rate was set to 50
A/min, slower.

Effect When the ferroelectric material falls off due to the manufacturing method described above,
Natural polarization in which Ps is already aligned in one direction can be obtained, there is no need for polarization treatment, and a high-performance ferroelectric thin film can be realized with a high yield.

The MgO single crystal that had been mirror-polished in Example (100) was used as a substrate, and a 0.2 μm thick PT film was formed as a lower electrode by sputtering. Sputtering gas is Ar-02
It is a mixed gas. Next, a ferroelectric thin film Pb(Zr, -
xTix)0. (PZT) was grown to a thickness of 1 to 4 μm.

The method is high frequency magnetron sputtering, using a mixed gas of Ar and 02, and the sputtering target is + (
1-Y)・F'voice 4r x 3T+ O”Y4bO1
powder. Table 1 shows typical sputtering conditions.

Table 1 Next, an upper electrode was provided on this thin film, and the dielectric properties were measured.

FIG. 1 shows X-ray diffraction patterns of PZT thin films with different compositions. (001) and (100) of perovskite structure
Only reflections and their higher order reflections are observed. Also (00
1) Since the intensity of reflection is significantly higher than that of (100), it can be seen that it is a C-axis oriented film. The C-axis orientation rate α is defined by the following equation.

α-1(00+)/l'+(001)++(+0011
Here, l(o old) and +(+00) are respectively (0
It represents the diffraction intensity of 01) and (100) reflections. The composition was analyzed using an X-ray microanalyzer and was found to be almost the same as the target.

It has become clear that the C-axis orientation ratio α and crystallinity vary depending on the sputtering conditions: film formation rate, sputtering gas, gas pressure, substrate temperature, and target.

FIG. 2 shows the relationship between the C-axis orientation rate α and the film formation rate. As shown in the figure, as the film formation rate increases, the C-axis orientation rate α decreases. Target PbO MAY be 0.2 to 0°3, C
Axial orientation ratio α and 1 (oo+1 is almost the maximum. Also,
Substrate temperature: When T is 575 to 650°C, C-axis orientation rate α
shows a high value. FIG. 3 shows how the C-axis orientation rate α and 1(0011 change when the gas pressure is changed. However, this is when the substrate temperature is T-600°C.

As the gas pressure increases, the C-axis orientation rate α decreases.

Based on the above results, it has become possible to obtain a PZT thin film with a C-axis orientation ratio α of 972 or more in a composition range of 0.46<X<1.

Next, the pyroelectric coefficient γ and dielectric constant ε of the Pz thin film having a high C-axis orientation were measured. FIG. 4 shows the relationship between composition X, pyroelectric coefficient, and dielectric constant. The dielectric constant of each composition was equivalent to that of ceramics. Even without polarization treatment, pyroelectric current was detected and the pyroelectric coefficient was 4.5xlO-8C/c
A value as large as JK could be measured.

The value of this pyroelectric coefficient is based on the PbTiOs ceramics (γ-1
, 8x10'c/c+JK).

This means that natural polarization in which the polarization Ps is already aligned in one direction has been obtained. Note that PZT has a composition of o
, sj<x<t, the crystal structure is tetragonal, and the C axis is the polarization axis. In addition, polarization treatment (100kV at 200℃)
/c+J (applied for 10 minutes) and then measured. As a result, when the orientation rate was high, the values of the pyroelectric coefficient and dielectric constant hardly changed after the polarization treatment surface.

As described above, in the PZT thin film produced in this example, if the film is sufficiently oriented along the C-axis during production, the spontaneous polarization is uniform even without polarization treatment.

When the ferroelectric thin film produced in this example is used as a device, a large output can be obtained without any polarization treatment. This is useful not only for pyroelectric infrared sensors but also for piezoelectric elements, electro-optical elements, etc.

Effects of the Invention According to the present invention, the ferroelectric thin film manufactured does not require polarization treatment, has excellent characteristics, and is easy to produce, so it is extremely effective in practice.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the X-ray diffraction pattern of a ferroelectric thin film in an embodiment of the invention, and FIG. 2 is a diagram showing the C-axis orientation ratio and film formation rate of the ferroelectric thin film in an embodiment of the invention. FIG. 3 is a graph showing the relationship between C-axis orientation ratio and (001) intensity and gas pressure, and FIG. 4 is a graph showing the relationship between composition, pyroelectric coefficient, and dielectric constant. Name of agent: Patent attorney Toshio Nakao and one other person Fig. 1 29 (deg, 1 thread 2 Fig. Deposition speed 7 yen (A/mjIn) Fig. 3 Gas pressure (Pa)

Claims (4)

[Claims] (1) The chemical formula is Pb(Zr_1_-_xTi_x)O_
In the step of producing a ferroelectric thin film having a composition range of 0.46<x<1 on a substrate by sputtering in step 3,
A MgO (100) plane was used for the substrate, and the film formation rate was 50 A/min. A method for producing a ferroelectric thin film, characterized by slowing down the production process. (2) When producing a ferroelectric thin film by sputtering, the composition formula {(1-Y)
2. The method of manufacturing a ferroelectric thin film according to claim 1, wherein a material is used in which Y is in the range of 0.05 to 0.4 in PbZr_1_-_xTi_xO_3+YPbO}. (3) The method for producing a ferroelectric thin film according to claim 1, wherein the ferroelectric thin film is produced by sputtering at a substrate temperature in the range of 550 to 675°C. (4) The method for producing a ferroelectric thin film according to claim 1, characterized in that when the ferroelectric thin film is produced by sputtering, the sputtering gas pressure is lower than 3 Pa.