JPS6369104A - Manufacture of ferrodielectric thin film element - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

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

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 (therefore, there is no spontaneous polarization Ps). They are arranged in a row.

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 described above, it is necessary to apply a high electric field (~1ookV/c+m) to the materials to perform polarization treatment to align the directions of Ps.

In addition, there are many reports regarding the production of thin films such as PbTiO3 and PLZT, but for thin films in the ferroelectric phase region of these thin films, thin films oriented along the C axis, which is the polarization axis, and even spontaneous polarization are unidirectional. The method for producing oriented thin films has not 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 devices such as high-resolution array devices in which many microelements are arranged at high density, it is difficult to polarize them uniformly.

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

Means to solve the problem The chemical formula is Pb1-1 (La) (Tit-o, 7sx 0
3, the composition range is 0<x<0.15, and the polarization axis is 75
When producing a ferroelectric thin film in which one or more elements are oriented in one direction on a substrate by sputtering, the sputtering target has a compositional formula (%) in which Y is in the range of 0.05 to 0.4.

Function: In the ferroelectric thin film manufactured by the above-mentioned manufacturing method,
Natural polarization in which Ps is already aligned can be obtained, there is no need for polarization treatment, and a high-performance ferroelectric element can be realized with 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 PL thin film was formed as a lower electrode by sputtering. The sputtering gas is Ar
02 mixed gas. Next, a ferroelectric thin film Pb+-
x Lax Tit-o7sx 03 (PLT) from 1 to
It was grown 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) Pb+-x Lax Tit-o, 7s
x 03 "Y Pb0) powder. Table 1 shows the sputtering conditions.

Next, a Ni--Cr electrode was deposited as an upper electrode on this thin film to produce a ferroelectric thin film element. Furthermore, an opening was provided in the substrate below the ferroelectric thin film.

(Margin below) Table 1 Figure 1 shows the X-ray diffraction pattern of a typical thin film. Only the (001) and (100) reflections of the perovskite structure and their higher-order reflections are observed. Furthermore, since the intensity of the (001) reflection is significantly larger 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(001)/+1(001)+1(+00)1 where l (oo+) and IC100) are respectively (
represents the diffraction intensity of (001) and (100) reflections.

It has become clear that the C-axis orientation ratio α changes depending on the sputtering conditions, such as the deposition rate, sputtering gas, gas pressure, substrate temperature, and target.

X-0,1, substrate temperature: T-600℃, other conditions are Table 1
In the case of , the C-axis orientation rate α and +(00+
) is shown in Figure 2.

α becomes thicker as V increases, and becomes saturated from Y-0, 2. On the other hand, 1 (ooH becomes maximum at Y-0, 2).

Figure 3 shows α and 1(oo+) at T-650°C.
shows the relationship between and Y. α shows the same tendency as at T-600°C. 1(oo+)Y=0.3te is the maximum. Further, when T-, 575°C, 1(00+> becomes maximum at Y-0,1.

From the above results, Y-2,050-1612+(T+2
73) It has become clear that when the following relationship is satisfied, a ferroelectric thin film with a high C-axis orientation rate and good crystallinity can be obtained.

As the substrate temperature: ■ increases, the amount of PbO that re-evaporates increases, so it is thought that adding an excessive amount of PbO to the target in advance will bring about good results.

Figure 4 shows the pyroelectric coefficient of the PLT thin film with respect to the C-axis orientation rate: γ
Figure 5 shows the change in dielectric constant: ε. The pyroelectric coefficient increases in proportion to the orientation of the spontaneous polarization Ps.

The pyroelectric coefficient becomes thicker as the orientation rate increases, and the dielectric constant becomes smaller. Figures 4 and 5 show the results when polarization treatment (l 00 kV/cd l 0 minutes applied at 200°C) is performed. The results are also shown. When the orientation rate is small, the values of pyroelectric coefficient and permittivity change greatly before and after polarization treatment. When the orientation rate becomes 75z, the pyroelectric coefficient becomes 5.0xl.
O-8C/cdK, and this value is 100 at 200℃.
It is considerably larger than PbTiO3 ceramics (γ-1,8X10-8C/c+J) which was polarized by applying kV/voltage.

When the orientation rate is 90N, the pyroelectric coefficient is 6.8xlO=C/ci
It is K. In addition, the dielectric constant is almost the same as the value after polarization treatment (it is larger than the value after polarization when the orientation rate is small). It is.

As mentioned above, in a PLT thin film, if the thin film is sufficiently oriented along the C-axis during production, the spontaneous polarization will be uniform even without polarization treatment, and this effect is particularly large for thin films with an orientation rate of 75% or more. It became clear.

When the ferroelectric thin film element produced in this example is used as an infrared sensor, the figure of merit as a pyroelectric material is [
The value of pyroelectric coefficient/permittivity 1 increases. 10 at 200℃
PbT subjected to polarization treatment by applying 100 kV/cm for minutes
Compared to the value of i0a ceramics, the PLT thin film shows a value more than three times as large. In other words, it can be seen that by using the ferroelectric thin film according to the present invention, an infrared sensor with excellent characteristics can be produced without any polarization treatment.

As can be seen from the above example, the device using the ferroelectric thin film of the present invention can produce a large output even without polarization treatment.This is applicable not only to infrared sensors but also to electro-optical devices such as piezoelectric elements and optical switches. The same is true.

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

[Brief explanation of drawings]

FIG. 1 is a diagram showing an X-ray diffraction pattern of a ferroelectric thin film in an embodiment of the present invention, and FIGS. 2 and 3 are diagrams showing the C-axis of a ferroelectric thin film in an embodiment of the present invention. Orientation rate and (
001) A graph showing the relationship between the strength and the PbO molar ratio; 4゛;;Ii; It is a graph showing the relationship between dielectric constants. Name of agent: Patent attorney Toshio Nakao 1st person? θ 2nd θ ? 040 PbO molar ratio (/, J 3rd core a40 PbO molar ratio [%] Fig. 406o, 8 7.0 Cht orientation only, required

Claims (3)

[Claims] (1) The chemical formula is Pb_1_-_xLa_xTi_1_-
＿0＿． _7_5_xO_3 and the composition range is 0<x<0.
15, and when producing a ferroelectric thin film in which 75% or more of the polarization axis is oriented in one direction on a substrate by sputtering, the sputtering target has the composition formula {(1-Y)Pb_1_-_xLa_xTi_1_-_
0__. _7_5_xO_3+YPbO}, Y is in a range of 0.05 to 0.4. (2) A method for manufacturing a ferroelectric thin film element according to claim 1, characterized in that the substrate temperature is in the range of 575 to 650° C. when the ferroelectric thin film is produced by sputtering. (3) When the ferroelectric thin film is produced by sputtering, the substrate temperature: T and Y satisfy the following relationship: Y-2.050-1612÷(T+273) A method for manufacturing a ferroelectric thin film element.