JPH0578200A - Synthesis of piezoelectric thin film - Google Patents

Abstract

PURPOSE:To obtain a film composed of Li(NbxTa1-x)O3 single phase and capable of providing a material for SAW devices and optics by the laser ablation method. CONSTITUTION:Laser ablation synthesis of a piezoelectric thin film, characterized by the ratio between target-constituting elements adjusted to 1.5<=Li/(NbxTa1-x)<=3.5 when synthesizing an Li(NbxTa1-x)O3 thin film (0<=x<=1).

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an optical device and elasticity.
Surface wave (Surface Acoustic Wave,
Li (Nb) suitable as a lower SAW device_xT
a_1-x) O ₃The present invention relates to a method for manufacturing a thin film.

[0002]

2. Description of the Related Art LiNbO ₃ single crystal or LiTaO
₃ Single crystal is a ferroelectric substance with a high Curie temperature, and has extremely excellent properties in terms of its large electromechanical coupling constant, electro-optical effect, nonlinear optical effect, etc., and is put to practical use as a material for SAW devices. On the other hand, it is a promising material for optical elements.

With the recent progress in semiconductor technology and the increasing integration and miniaturization of electronic components, ferroelectric elements and piezoelectric elements are also becoming smaller and thinner, and LiNbO ₃ single crystal or LiTaO ₃ single crystal is being used. The demand for thin films is strong, and many studies have been conducted. Conventionally, Li
As a method for producing the NbO ₃ thin film or the LiTaO ₃ thin film, a liquid phase epitaxial method, a CVD method, a vacuum vapor deposition method, a sol-gel method, a sputtering method and the like have been reported, but there is almost no report by the laser ablation method.

The laser ablation method is a new film-forming means that has recently been receiving attention. Compared with the sputtering method, the target composition and the composition of the obtained film are almost the same, the mixing of impurities is extremely small, and the film-forming rate. It is generally said that it has the advantage that it can be adjusted freely. Li (Nb by laser ablation method
_x Ta _1-x ) O ₃ thin film (0 ≦ x ≦ 1)
When the composition of the target is Li / (Nb _x Ta _1-x ) = 1, Li (Nb _x Ta _1-x ) O is obtained at any substrate temperature and pressure.
There is a problem that a film consisting of _three single phases cannot be obtained.

[0005]

In order to prepare a Li (Nb _x Ta _1-x ) O ₃ thin film by the laser ablation method,
First, it is necessary to find out the conditions under which a film composed of a Li (Nb _x Ta _1-x ) O ₃ single phase can be obtained.

[0006]

According to the present invention, Li (Nb _x
When synthesizing a Ta _1-x ) O ₃ thin film (0 ≦ x ≦ 1), the ratio of elements constituting the target is 1.5 ≦ Li / (Nb _x
Ta _1-x ) ≦ 3.5, in particular, the substrate for synthesizing the thin film is a sapphire substrate,
In particular, the present invention relates to a method for synthesizing a piezoelectric thin film by a laser ablation method, wherein the sapphire substrate is the C surface of the sapphire substrate.

In the laser ablation method, spatter is used.
Compared to the ring method, the target composition and the composition of the obtained film are
The target Li /
(Nb_xTa_1-x) Was predicted to be about 1, but
1.5> Li / (Nb_xTa _1-x) At any substrate temperature
Li (Nb_xTa_1-x) O₃Single-phase membrane
I couldn't get it.

As a result of the inventors' earnest studies, it was unexpected.
First by making Li in the target too large
Li (Nb_xTa_1-x) O₃Discovered that a single phase film can be obtained
did. That is, the target composition is 1.5 ≦ Li / (N
b_xTa_1-x) ≦ 3.5 only for Li (Nb_xTa_1-x)
O₃It was found that a film composed of a single phase was obtained. Target
Composition is 1.5 ≦ Li / (Nb_xTa_1-x) ≤ 3.5
And more preferably 1.75 ≦ Li
/ (Nb_xTa_1-x) ≦ 2.5. 1.5 ≦ Li /
(Nb_xTa_1-x) ≦ 3.5, Li (N
b_xTa_1-x) ₃O₈And Li₃(Nb_xTa_1-x) O_Four
It became a film with what seemed to coexist.

The laser apparatus used here is not particularly limited, but the following apparatus was used to synthesize under the following conditions. The laser is an excimer laser (A
rF193nm) and laser frequency is 1 to 10
The laser output was 0 Hz and the laser output was 80 to 800 mJ. Both targets made of alloy and ceramics can be used as the target, but Li ₂ CO ₃ , Nb ₂ O ₅ and Ta _{2 are used.}
Sintered body using O ₅ as a raw material (size 15 mmΦ × 1-5 m
m ^t ) is easy to manufacture and is a preferred means of practicing the invention. Pressure is oxidizing gas, 0.0001-0.05
torr, more preferably 0.001 to
A range of 0.05 torr is used. Pressure range 0.0
When the atmosphere gas is oxygen at 001 to 0.003 torr, the film tends to be colored, but if an atmosphere gas having a stronger oxidizing power such as ozone, N ₂ O, or NO ₂ is used in this pressure range, a colorless film is obtained. A film is obtained. These are preferred embodiments for carrying out the present invention. The substrate temperature was in the range of 500 to 850 ° C., and the film formation was performed in the range of 10 minutes to 450 minutes. However, the substrate temperature and the reaction time do not limit the implementation of the present invention.
The distance between the target and the substrate during the reaction is preferably in the range of 1 to 5 cm, but is not particularly limited. The substrate is not particularly limited, but a single crystal substrate (sapphire, S
i) and an amorphous substrate (such as quartz). Whatever substrate is used, it is preferable that the substrate surface used for film formation is mirror-polished.

An example using a sapphire substrate will be shown below as an example. It should be noted that this embodiment does not limit the present invention.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an outline of an apparatus used for carrying out the present invention. The sintered target was irradiated with laser light to form a film on the substrate in an oxidizing gas (oxygen and ozone) atmosphere. The conditions used in the synthesis are listed below. Synthesis conditions Target Sintered body composed of Li, (Nb _x Ta _1-x ), O Single crystal substrate Sapphire C surface Substrate temperature (T) 500 to 850 ° C Introduced gas Oxygen, ozone Reaction pressure (P) 0. A Li (Nb _x Ta _1-x ) O ₃ thin film was synthesized under the conditions of 0005 to 0.05 torr laser output 150 mJ laser frequency 15 Hz reaction time 50 minutes or more. The phase of the synthesized film was examined by X-ray diffractometry. The results are shown in Table 1. FIG. 2 shows an example of X-ray diffraction. Target composition 1.5 ≦ Li / (Nb _x Ta _1-x )
Li (Nb _x Ta _1-x ) in all cases where ≦ 3.5
It was an O ₃ single-phase film.

[0012]

Comparative Example As a comparative example, the target composition Li / (Nb
_x Ta _1-x ) <1.5, Li / (Nb _x Ta _1-x )>
A synthetic experiment at 3.5 was performed. The phases of the synthesized membrane are shown in Table 2. Examples of X-ray diffraction are shown in FIGS. 3 and 4, respectively. Li
/ (Nb _x Ta _1-x ) <1.5, Li (Nb _x Ta
_1-x ) ₃ O ₈ and Li / (Nb _x Ta _1-x )> 3.5, a phase of Li ₃ (Nb _x Ta _1-x ) O ₄ was observed and Li (Nb
_It can be seen that _x Ta _1-x ) O ₃ single phase cannot be obtained.

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

According to the present invention, a film composed of a Li (Nb _x Ta _1-x ) O ₃ single phase can be obtained by the laser ablation method, and it is possible to supply materials for SAW devices and materials for optical elements. Becomes

[Brief description of drawings]

FIG. 1 is a schematic view of a synthesizer used in the present invention.

FIG. 2 X-ray diffraction of a film synthesized with a target composition Li / Nb = 2.0

FIG. 3 X-ray diffraction of a film synthesized with a target composition Li / Nb = 1.4

FIG. 4 X-ray diffraction of a film synthesized with a target composition Li / Nb = 4.0.

[Explanation of symbols]

 1 ArF excimer laser 2 lens 3 window 4 target 5 substrate 6 film thickness measuring device 7 gas inlet

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication H01L 41/18

Claims (1)

[Claims] 1. A Li (Nb _x Ta _1-x ) O ₃ thin film (0 ≦
When synthesizing x ≦ 1), the ratio of the elements constituting the target is 1.5 ≦ Li / (Nb _x Ta _1-x ) ≦ 3.5, and the piezoelectric thin film by the laser ablation method is characterized. Method of synthesis.