JPH0543398A - Ferroelectric single crystal thin film and its production - Google Patents

Abstract

PURPOSE:To provide a high-quality ferroelectric single crystal thin film composed of a ferroelectric single crystal body expressed by the formula LiTayNbpO3 (wherein O<=y<=1 and p=1-y) and being uniform in whole film and composed of a single crystal by using a laser ablation technique. CONSTITUTION:The present invention is characterized by forming a single crystal thin film expressed by the formula LiTayNbpO3 (y and p are same as mentioned above) on a substrate 4 of LiTaxNbwO3 (wherein 0<=x<=1 and w=1-x) by a laser abrasion 2 using LiTayNbpO3 (y and p are same as mentioned above) or Li2O, Nb2O5 and Ta2O5 as a target.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention is in the field of a ferroelectric single crystal thin film and a method for manufacturing the same.

[0002]

2. Description of the Related Art LiNbO ₃ , LiTaO ₃ , and Li (N
The following are conventional methods for producing an oxide single crystal thin film of b, Ta) O ₃ etc. RF sputtering method A LiNbO ₃ single crystal thin film of 1 μm or more was prepared on a sapphire substrate. The substrate temperature is 500 ° C. (Appl. Phys. Lett. Vo
l. twenty four. No. 10.1974 pp490~492) prepared LiNbO ₃ single crystal thin film in the CVD method LiTaO ₃ substrate. (M
at. Res. Bull. Vol. 10.1975 pp515-520) LPE method A ₃ μm LiNbO ₃ single crystal thin film was epitaxially grown on a LiTaO ₃ substrate. (Appl. Phys. Lett. Vol.
26. No. 1.1975 pp8-10) Laser ablation method Bi ₂ Sr ₂ Can ₁ Cun ₂ On ₃ (n ₁ =
n ₂ -1, n ₃ = 2n ₂ +4) superconducting thin film was prepared. (The Bulletin of the Japan Institute of Metals, Vol. 29, No. 9, 1990) The above-mentioned conventional techniques have the following problems. RF Sputtering Method Since the sputtering efficiency varies depending on the element, it is difficult to obtain a high-quality film having a uniform composition over the entire film and a single crystal over the entire film. CVD method For example, in the case of Li, 2,2,6,6-tetramethylheptane-
An organometallic compound of 3,5-dione and Li is used, and in the case of Nb, for example, niobium pentamethylate (Nibiumpe
Since ntamethylate) is used, mixing of carbon etc is unavoidable, the crystallinity is lowered, and it is difficult to obtain a uniform composition over the entire film. LPE method The crystallinity is excellent, but the controllability of the film thickness is poor, and further, a problem of etc in which impurities are mixed from the flux occurs. Further, the laser ablation method is known to be used for manufacturing a superconducting thin film, but LiNbO ₃ , LiT
aO ₃ or its mixed crystal LiTayNbpO
₃ (y and p are the same as above) It is not known to be used in a method for producing a single crystal thin film.

[0003]

[Objective] The present invention aims to provide a high quality ferroelectric single crystal thin film by using a laser ablation method.

[0004]

[Structure] The present invention uses, for example, a laser ablation device as shown in FIG. 1 to collect laser light with a lens,
By irradiating the target, plasma (plume) as shown in the figure is generated in a direction perpendicular to the target surface. As a result, LiTaxNbwO ₃ (0 ≦ x ≦ 1,
w = 1-x) LiTayNbpO ₃ (0 ≦ y ≦
1, p = 1-y) is formed without the inclusion of impurities. At this time, the film thickness can be precisely controlled by changing the laser conditions, that is, the laser energy density, the number of shots, and the irradiation time etc.

The thin film formation by laser ablation used in the present invention means that when intense pulsed laser light is focused on a solid, evaporation due to absorption heat and ablation due to multiphoton absorption process occur near the surface, and constituent elements are scattered. Are released in the form of atoms, molecules and ions. By this process, the atoms, molecules, and ions jumping out from the surface are deposited on the substrate at the opposite positions to form a thin film.
This film forming method is a method called a laser ablation method, a pulse laser deposition method, or the like. This method has long been called laser sputtering or laser evaporation,
Amorphous silicon, semiconductor thin films such as CdTe,
It has been applied to the formation of ceramic thin films of Al ₂ O ₃ , Si ₃ N ₄ , TiN and the like.

The type of laser light used in the present invention is not particularly limited as long as it can cause ablation, but the absorption of the target is increased to 400 n.
It is preferable to use one having a wavelength of m or less, and from that point, an excimer laser is preferable.

As the substrate, LiNbO ₃ , LiTaO ₃
Alternatively, the formula LiTaxNbwO showing the mixed crystal may be used.
_The material shown by ₃ (x and w are the same as above) is used. The substrate, like the thin film formed by laser ablation on it, must have an ilmenite structure, but the substrate and the thin film need not have the same composition. In addition, when the substrate temperature is lower than 0 ° C., the formed thin film becomes amorphous, so that a single crystal thin film cannot be obtained.
TaxNbwO ₃ (x and w are the same as above) L from the substrate
When i or Li ₂ O diffuses out, the substrate is altered and a high quality film cannot be obtained. Therefore, in order to form a high quality single crystal thin film, the substrate temperature is 0 ° C to 1100 ° C.
It is necessary to control at ℃.

The laser ablation target is composed of LiTayNbpO ₃ (y and p are the same as above) or a combination of Li ₂ O and an oxide of Nb ₂ O ₅ and / or Ta ₂ O ₅ . When the resulting single crystal thin film is doped with impurities, a metal oxide of MOz (M and z are the same as above) may be used as a target in addition to the target. By appropriately selecting and setting the power of the laser for irradiating these targets, the number of shots, the irradiation time, etc., the film thickness, the generation rate, the composition or the doping amount of the single crystal thin film can be appropriately controlled.

When the single crystal thin film is formed in an oxidizing gas atmosphere (O ₂ , O ₃ , NO, NO _2, etc.), O-Vacancy generated during film formation can be reduced,
A thin film with excellent crystallinity can be obtained. Further, by performing annealing after forming the single crystal thin film, a thin film having excellent crystallinity and no distortion can be formed.

The structure of the thin film thus formed is a combination of crystal units as shown in FIG. However, FIG. 2 is simplified for convenience of explanation. The ilmenite structure is characterized by, for example, LiN
Taking bO ₃ as an example, the first layer is a Li ₂ O layer and the second layer is Nb ₂
This is a combination of a layered structure of oxide such as an O ₅ layer and a Li ₂ O layer as the third layer. Therefore LiTayN
When a mixed crystal of bpO ₃ (y and p are the same as above) is formed,
For example, when y = 0.5, the second layer is Nb ₂ in the thickness direction.
The layers of O ₅ and Ta ₂ O ₅ may be sequentially laminated. Further, when impurities are doped, for example, when Mg is desired to be doped, Mg may be laminated on the first layer or the second layer. The doping amount is determined by how many layers containing Mg are stacked in the thickness direction. In the above description, the case where a single crystal thin film having an ilmenite structure is formed is taken as an example, but when a single crystal thin film having a perovskite structure is formed, the single crystal thin film is formed by the same laser ablation method manufacturing process can do.

[0011]

【Example】

To form a _{LiTa 0. 1 Nb 0. 9} O 3 single crystal thin film by laser ablation method on Example 1 LiTaO ₃ single crystal substrate (Z-cut). The conditions for laser ablation are KrF (24
With 8 nm) excimer laser, LiTa ₀ a laser beam. ₁
Nb _0. Irradiates the ₉ O ₃ target having a composition, when the laser energy density is set to 0.2 J / cm ² per pulse on the target surface, the rate of ablation became 20Å per pulse .. The laser repetition frequency was 10 Hz. Substrate temperature is 650 ° C, atmosphere is O
₂ (gas pressure: 100 mTorr),
The film thickness is 3 μm, and the composition is Li
Ta _0. Was ₁ Nb _0. Can form a single crystal thin film ₉ O _{3. LiTa 0. 5 Nb 0. 5} O 3 to form a single crystal thin film by laser ablation method on Example 2 LiTaO ₃ single crystal substrate (Z-cut). Targets are Li ₂ O, Nb ₂ O ₅ and Ta ₂ O ₅
The KrF (248 nm) excimer laser is used, the laser energy density is 0.2 J / cm ² per pulse on the target surface, and the ablation rate per pulse is 0.1 Å for each target. It was By controlling the target by computer, Li ₂ O, Nb ₂ O ₅ , Li ₂ O, and Ta ₂ O ₅ are deposited in this order for a total of 100 pulses, that is, 10 Å, and the film thickness is repeated. It was 3 μm. The substrate temperature is 300 ° C., the atmosphere is O ₂ (gas pressure: 1
00 mTorr). Also after forming, further subjected to annealing at 650 ° C. 2 hours in an O ₂ atmosphere, film thickness and a 3μm in total film performs improvement of crystallinity, the composition of LiTa throughout film _{0. 5} Nb _{0. 5} A single crystal thin film of O ₃ could be formed. Example 3 A LiNbO ₃ : MgO-doped single crystal thin film was formed on a LiTaO ₃ single crystal substrate (Z-cut) by a laser ablation method. Targets are Li ₂ O, Nb ₂ O ₅ and Mg
A KrF (248 nm) excimer laser is used as three types of O, the laser energy density is 0.2 J / cm ² per pulse on the target surface, and the ablation rate per pulse is Li ₂ O and Nb ₂ O ₅ Both 0.1
It became Å. By controlling the target with a computer, each of Li ₂ O and Nb ₂ O ₅ has a total of 1
00 pulses, that is, 10 Å each is formed, and this is repeated to form 100 Å each, and then MgO
The target is irradiated with a laser to form a 10 Å MgO layer, and then Li ₂ O and Nb ₂ O ₅ are repeated to obtain a LiNbO ₃ : MgO-doped 4.8% thin film having a thickness of 3 μm.
Formed. The substrate temperature was 300 ° C., and the atmosphere was O ₂ (gas pressure: 100 mTorr). After the film is formed, further O
Annealing was performed at 650 ° C. for 2 hours in _two atmospheres to improve the crystallinity, and a single crystal thin film having a film thickness of 3 μm and a constant composition throughout the film could be formed.

[0012]

【effect】

(1) By using the laser ablation technique, a high quality ferroelectric single crystal thin film having a uniform composition throughout the film and a single film throughout the film was obtained. (2) By using the laser ablation technique, a ferroelectric single crystal thin film having an arbitrary composition ratio can be formed while precisely controlling the film thickness. Also, any dopant can be added in any amount. (3) By using laser ablation technology, the pulse repetition frequency of the laser can be increased to improve the deposition rate of the ferroelectric single crystal, which is excellent in mass productivity.

[Brief description of drawings]

FIG. 1 shows a schematic view of a laser ablation device.

FIG. 2 shows an ilmenite structure or a perovskite structure of a substrate and a single crystal thin film.

[Explanation of symbols]

 1 Target 2 Laser Light 3 Plasma 4 Substrate 5 Substrate Heating Heater 6 Shows A Element such as Li 7 Oxygen Atom 8 Shows B Element such as Nb and Ta 9 First Layer 10 Second Layer 11 Third Layer

Claims (8)

[Claims] 1. LiTaxNbwO ₃ (where x is 0 ≦
a single crystal represented by LiTayNbpO ₃ (in the formula, 0 ≦ y ≦ 1, p = 1-y) formed on the substrate by a laser ablation method, or A ferroelectric single crystal thin film with a substrate provided with a thin film formed by doping a metal element. 2. LiTayNbpO ₃ (y and p are the same as above) or the oxide and MOz (in the formula, M and z).
Means any metal and number, respectively. ) Irradiates a target with laser light to cause ablation, whereby a single crystal represented by LiTayNbpO ₃ (y and p are the same as above) on a LiTaxNbwO ₃ (x and w are the same as above) substrate, Alternatively, the method for producing a ferroelectric single crystal thin film according to claim 1, wherein a thin film composed of a metal element doped therein is formed. 3. Li ₂ O, Nb ₂ O ₅ as a target
3. A method for producing a ferroelectric single crystal thin film according to claim 2, wherein a combination of oxides of Ta ₂ O ₅ and / or a combination of these oxides with an oxide of MOz (z is the same as above) is used. 4. The method for producing a ferroelectric single crystal thin film according to claim 2 or 3, wherein the film thickness or the production rate of the single crystal thin film is controlled by controlling the laser power, the number of shots or the irradiation time. 5. The method for producing a ferroelectric single crystal thin film according to claim 3, wherein the film thickness, the production rate or the composition of the single crystal thin film is controlled by controlling the laser power, the number of shots or the irradiation time. 6. The method for producing a ferroelectric single crystal thin film according to claim 2, 3, 4 or 5, wherein ablation is performed in an oxidizing gas atmosphere. 7. The method for producing a ferroelectric single crystal thin film according to claim 2, 3, 4, 5 or 6, wherein annealing is performed in an oxidizing gas atmosphere after forming the single crystal thin film. 8. The method for producing a ferroelectric single crystal thin film according to claim 2, 3, 4, 5, 6 or 7, wherein the substrate temperature is controlled at 0 ° C to 1100 ° C.