JPS63266705A - Manufacture of ferroelectric thin film element - Google Patents

Abstract

PURPOSE:To make a polarization process needless by keeping a substrate's potential positive to a wall of an evaporation room to perform film formation when a ferroelectric thin film with prescribed compositions is manufactured by a sputtering evaporation method. CONSTITUTION:A ferroelectric thin film is made of a material which is expressed in a chemical formula PbxLayZrwTizO3 and has either of the following compositions:a) o.7<=x<=1, 0.9<=x+y<=1, 0.95<=z<=1, w=0, b) x=1, y=0, 0.45<=z<1, Z+w=1, c) 0.83<=x<=1, x+y=1, 0.5<=z<1, 0.96<=z+w<=1. When this ferroelectric thin film is manufactured on a conductive substrate by a sputtering evaporation method, a substrate's potential to a wall of an evaporation room is kept 30V or more to perform film formation. Even if the substrate is conductive, a ferroelectric thin film, in which Ps has already been naturally polarized, is obtained accordingly and so a polarization process can be made needless.

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. With the miniaturization of electronic components due to recent advances in semiconductor technology, ferroelectric elements are also becoming thinner.

By the way, in, for example, a pyroelectric infrared detection element or a piezoelectric element that extracts a change 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 Ferroelectric ceramics currently used for infrared detection elements, piezoelectric elements, etc. are polycrystalline bodies, and the arrangement of crystal axes has no directionality. Therefore, the spontaneous polarizations Ps are also arranged randomly. Although the crystal polarization axes of epitaxial ferroelectric thin films and oriented ferroelectric thin films are aligned, electrical spontaneous polarization Ps forms 180° domains and is arranged alternately. Therefore,
When these materials are used as electronic devices as described above, it is necessary to apply a high electric field (~100 kV/cw) to the materials to perform polarization treatment to align the directions of Ps.

In addition, there are many reports on the production of thin films such as P b Ti O3 and 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 have been reported. The method for producing thin films aligned in one direction is not entirely clear.

The following problem occurs with the method of aligning Ps by applying a high electric field to a ferroelectric material.

(1) Polarization treatment may cause dielectric breakdown, reducing yield.

■ 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 itself may not be possible in some cases.

In addition, when forming a PbTiOs thin film by sputtering deposition, if the substrate is conductive, the crystallinity will be poor (and the orientation to the C axis will be poor. This means that the spontaneous polarization will not be aligned, and the polarization No more processing.

Means for solving the problem The chemical formula is expressed as PbxLaZrwTi203, a)
0.7≦×≦L0.9≦x+y≦1, 0.95≦Z≦L
w=0b) x=1, y-0,0,45≦z<l
, z+w-1, or c) 0.83≦x≦Lx+y-
When producing a ferroelectric thin film having a composition of either 10,5≦zLo, 96≦z+w≦1 by sputtering deposition, the substrate is kept at a positive potential with respect to the wall of the deposition chamber. Deposit a dielectric thin film.

Effects According to the above manufacturing method, even if the substrate is conductive, a ferroelectric thin film with Ps already aligned and naturally polarized can be obtained, and there is no need for polarization treatment (, good yield (, high performance). ferroelectric thin film devices can be realized.

A platinum thin film having a thickness of 0.2 μI was formed by sputtering vapor deposition on the MgO single crystal that had been cleaved and mirror-polished in Example (100), and this was used as a substrate. On top of this, a ferroelectric thin film Pb,
9La. ,,Tio,,7503 (PLT) was deposited to a thickness of 2 um. The method is high-frequency magnetron sputtering, and the sputtering target is 0.8 Pb La.
TiO+0.2 PbO0.9G, 1
0.975 3 powder. Table 1 shows the film forming conditions.

(Left below) Table 1 Next, NiCr was applied as an upper electrode on this ferroelectric thin film.
Electrodes were deposited to form a ferroelectric thin film element.

Furthermore, an opening was provided in the substrate below the ferroelectric thin film.

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. Also, the intensity of the (001) reflection is significantly thicker than the intensity of the (100) reflection (,c
It can be seen that it is an axially oriented thin film. The C-axis orientation rate α is defined by the following equation.

α= 1(00+)/l I(001)+ 1<+o
o+) where 1(oo+) and 1(+001 represent the diffraction intensities of (001) and <100> reflections, respectively.

When depositing a ferroelectric thin film, the deposition chamber is grounded.
A voltage was applied to the substrate holder so that voltage was also applied to the lower electrode. As a result, the voltage applied to the substrate is 1(00
It became clear that the 11 and C axis orientation rates changed.

Figures 2 and 3 show the changes in I (00) and C-axis orientation ratios with respect to the bias voltage applied to the substrate, respectively.When the substrate is grounded (Ov), no sharp X-ray peaks appear; It was impossible to estimate the C-axis orientation rate.When a positive voltage was applied as a bias, it became 1 (00+).
It can be seen that the crystallinity increases and the crystallinity becomes good.It can be seen that the C-axis orientation rate also becomes thicker as the bias voltage is increased.

In a grounded state, argon ions and the like in the plasma collide with the substrate, hindering crystal growth of the ferroelectric integrated thin film. Therefore, by setting the substrate at a positive potential and performing ion bombardment, the C-axis orientation rate can be improved by eliminating interference with crystal growth.

Figure 4 shows the pyroelectric coefficient of the PLT thin film with respect to the C-axis orientation rate α:
Changes in γ and changes in dielectric constant: ε are shown in FIG. The pyroelectric coefficient increases in proportion to the orientation of the spontaneous polarization Ps. The pyroelectric coefficient increases as the orientation rate increases, and the dielectric constant decreases. Figures 4 and 5 show polarization treatment (200°C, 100°C).
(kV/cm applied for 10 minutes), the results are also shown. When the orientation rate is small, the values of the pyroelectric coefficient and permittivity become thick (change) before and after polarization treatment.
When the orientation rate is 75%, the pyroelectric coefficient is 5.0×10-”
C/cjK, and this value is changed by polarization treatment (10
PbTiO3 ceramic (0 kV/cm applied)
r = 1.8xlO-eC/cJK). Furthermore, when the orientation rate is 90%, the pyroelectric coefficient is 6.8×
10-8 C/cdK. This value is not only the same as the value after polarization treatment, but also larger than the value after polarization treatment when the orientation rate is small. When the orientation rate is 90%, the dielectric constant is approximately 200, which is approximately the same value as ceramic.

As mentioned above, in a PLTM film, if the C-axis is sufficiently oriented during film formation, polarization treatment is not necessary (although the spontaneous polarization is uniform, and it is clear that this effect is especially large for thin films with an orientation rate of 75% or more). Became.

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] becomes large. Pb
The value is more than three times that of TiOs ceramic. 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 fabricated even without polarization treatment. Also, according to FIG. When the C-axis orientation rate is 70%, a pyroelectric material exhibiting a higher figure of merit than ceramic can be obtained even without 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 processing. The same is true.

The example is about a ferroelectric thin film element using a typical PLT thin film, but the chemical formula is PbxLa, Zr2Ti20. a) 0.7≦x≦1, 0.9≦)
(+y≦110.95≦2≦l 1w-0b) x”l
s y-0,0,45≦z<l 1z"w-1c)
0.83≦x≦Lx+y=1, o, 5≦z<110.
A similar effect can be obtained with a ferroelectric thin film having a composition of 96≦20-≦1.

Effects of the Invention The ferroelectric thin film element produced by the production method of the present invention 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 present invention, and FIGS. 2 and 3 are diagrams showing the C-axis orientation ratio and (00
1) A diagram showing the relationship between intensity and bias voltage. FIGS. 4 and 5 are diagrams showing the relationship between the pyroelectric coefficient and the dielectric constant with respect to the C-axis orientation rate. Name of agent Patent attorney Toshio Nakao One idiot Figure 1 ze Figure 2 Bias voltage (VJ Figure 3 Og) 100 Byanu voltage (VJ Figure 4 C sleeve orientation: Me

Claims (3)

[Claims] (1) The chemical formula is Pb_xLa_yZr_wTi_zO
Represented by _3, a) 0.7≦x≦1, 0.9≦x+y≦
1, 0.95≦z≦1, w=0b) x=1, y=0, 0
．． 45≦z<1, z+w=1, or c) 0.83≦x≦
1, x+y=1, 0.5≦z<1, 0.96≦z+w≦
When producing a ferroelectric thin film having one of the compositions of 1 on a conductive substrate by sputtering deposition, the ferroelectric thin film is formed while keeping the substrate at a positive potential with respect to the wall of the deposition chamber. A method for manufacturing a ferroelectric thin film element, characterized by: (2) A method for manufacturing a ferroelectric thin film element according to claim 1, characterized in that the potential of the substrate is maintained at 30 V or higher. (3) A method for manufacturing a ferroelectric thin film element according to claim 1, characterized in that the substrate is a MgO single crystal with a platinum electrode formed on the (100) plane.