KR20130118147A - Preparing method of metal-doped gallium iron oxide thin film and metal-doped gallium iron oxide thin film using the same - Google Patents

Abstract

PURPOSE: A method for manufacturing a metal-doped gallium iron oxide thin film by a physical vapor deposition method and a metal-doped gallium iron oxide thin film by the same are provided to significantly reduce the leakage current generated from a metal-doped gallium iron oxide thin film, thereby controlling the property of the carrier at the same time. CONSTITUTION: A method for manufacturing a metal-doped gallium iron oxide thin film by a physical vapor deposition method and a metal-doped gallium iron oxide thin film by the same forms GayFe2-y-xMxO3(0<x<2, 0<y<2, 0<x+y<2) as a thin film forming target by reacting iron oxide, gallium oxide, and metal oxide. A doped gallium iron oxides (GaFeO:M) thin film doped by the metal by physical vapor deposition (PVD) is formed by the metal by using the thin film forming target.

Description

PREPARING METHOD OF METAL-DOPED GALLIUM IRON OXIDE THIN FILM AND METAL-DOPED GALLIUM IRON OXIDE THIN FILM USING THE SAME

The present application relates to a method for producing a metal-doped gallium iron oxide thin film and a metal-doped gallium iron oxide thin film produced by the method.

Magnetoelectric materials can be used in many applications because of their ability to control magnetic and electrical polarization by their own electric and magnetic fields, respectively. For this reason, considerable attention is being paid to the potential application of magnetoelectric materials in new electronic devices [Hur, S. Park, PA Sharma, JS Ahn, S. Guha, SW Cheong; Nature London 429, 392 (2004). Ga _{2 − x} Fe _x O ₃ (0.8 ≦ x ≦ 1.4) (hereinafter referred to as “GFO”) oxide provides all the necessary properties to be a promising candidate for such applications [GT Rado, Phys. Rev. Lett. 13, 335 (1964). GFO oxide forms crystals in a tetragonal structure (SG: Pc 2 ₁ n ) having a ≒ 8.7 Å, b 9.4 Å and c ≒ 5.1 Å. The material is ferrimagnetic with Curie temperature up to 350 K for x = 1.4. Magneto-electric effects have been observed in bulk materials by Rado's paper [GT Rado, Phys. Rev. Lett. 13, 335 (1964). If the bulk properties of the compound were well established in the sixties, high quality thin films essential for the application have recently been produced [M. Trassin, N. Viart, G. Versini, S. Barre, G. Pourroy, JH Lee, W. Jo, K. Dumesnil, C. Dufour, S. Robert; J. Mat. Chem 19 (2009) 8876 M. Trassin, N. Viart, G. Versini, S. Barre, G. Pourroy, JH Lee, W. Jo, K. Dumesnil, C. Dufour, S. Robert; J. Mat. Chem 19, 8876 (2009). These thin films show the same crystallographic and magnetic properties as bulk, but as shown in FIG. 1, the unsaturated PE hysteresis curves do not exhibit ferroelectricity, which is known to be due to greater leakage current than other ferroelectrics [ ZH Sun et al., Appl. Phys. A 91, 97 (2008), VB Naik, and R. Mahendira, J. Appl. Phys. 106, 123910 (2009)]. Leakage currents hinder the electrical properties of the magnetoelectric material. This leakage current appears to be due to the approximate stoichiometry of the thin film in oxygen. The reduction of the Fe ^{2 +} in Fe ^{3 +} intended to balance the charge defect is consequently through a hopping mechanism (hopping mechanism) to reduce the electrical resistance of the thin film GFO. This leakage current renders the polarization-electric field (PE) signal impaired and can lead to misinterpretation of the ferroelectric curve [JF Scott; J. Phys .: Condens. Matter 20, 021001 (2008). This behavior can be attributed to BiFeO ₃ , YMnO ₃ or Ni ₃ V ₂ O ₈ It has also been observed in other oxide systems such as [G. Lawes, G. Srinivasan; J. Phys. D: Appl. Phys. 44, 243001 (2011)]. The leakage current problem needs to be carefully studied and solved for thin films to be inserted into functional devices in order to exploit the magnetoelectric properties of magnetoelectric materials [4M. Dawber, KM Rabe, and JF Scott, Rev. Mod. Phys. 77, 108 (2005)]. There are many literatures on the understanding of leakage mechanisms in ferroelectric thin films [JF Scott, J. Phys .: Condens. Matter 18, R 361 (2006) / KH Yoon, JC Lee, J. Park, DH Kang, CM Song, YG Seo; Jpn J. Appl. Phys. 40, 5497 (2001) / N. Wakiya, Y. Kimura, N. Sakamoto, D. Fu, T. Hara, T. Ishiguro, T. Kiguchi, K. Shinozaki, H. Suzuki; J. Ceram. Soc. Jap. 117, 1004 (2009).

The present invention is to solve the above-mentioned problems of the prior art, to provide a method for producing a metal-doped gallium iron oxide thin film by a simple process, and to provide a metal-doped gallium iron oxide thin film produced by the method. .

However, the problems to be solved by the present invention are not limited to the above-mentioned problems, and other matters not mentioned can be clearly understood by those skilled in the art from the following substrates.

A first aspect of the present disclosure provides a method of making a metal-doped gallium iron oxide thin film comprising:

Iron oxide, gallium oxide, and metal oxide are reacted to form Ga _x Fe _y M _{2 - y} O ₃ (0 <x <2, 0 <y <2, 0 <x + y <2) as targets for thin film formation. Making; And

Forming a gallium iron oxide (GaFeO: M) thin film doped by the metal by physical vapor deposition (PVD) using the thin film forming target.

According to one embodiment of the present application, the metal oxide is Mg, Co, Mn, Ni Bi, Ca, Sr, Sc, V, Cr, Pb, Pt, Au, Al, Cu, Mo, Rh, Si, Ta, Ti , W, U, Zr, Ge, Ru, Ir, and may include an oxide of a metal selected from the group consisting of, but is not limited thereto.

According to one embodiment of the present invention, the physical vapor deposition method is a pulsed laser deposition (PLD) method, E-beam evaporation method, thermal evaporation method (thermal evaporation) method, ion cluster beam (ion cluster beam) ) Method, sputtering method, and a method selected from the group consisting of combinations thereof, but is not limited thereto.

According to one embodiment of the present application, the physical vapor deposition method may include a pulse laser deposition method, but is not limited thereto.

According to the exemplary embodiment of the present application, the pulse laser deposition method may be performed at a temperature of about 300 ° C. to about 1,000 ° C., but is not limited thereto.

According to one embodiment of the present application, the pulse laser deposition method may be performed under an oxygen atmosphere, but is not limited thereto.

According to an embodiment of the present disclosure, the metal-doped gallium iron oxide (GaFeO: M) thin film may contain about 0.1 atomic% to about 20 atomic% of the metal, but is not limited thereto. .

A second aspect of the present application provides a metal-doped gallium iron oxide thin film (GeFeO: M) prepared by the method according to the first aspect of the present application.

According to one embodiment of the invention, the metal-gallium iron oxide thin film is doped, but can be to include Fe ^{2 +} and / or Fe ^{+ 3,} but is not limited thereto.

According to one embodiment of the present application, the metal may be doped by substituting some or all of the Fe ^{2 +} , but is not limited thereto.

According to one embodiment of the present application, the metal-doped gallium iron oxide thin film may be to include a ferroelectric, but is not limited thereto.

According to one embodiment of the present application, the metal-doped gallium iron oxide thin film may be to reduce the leakage current, but is not limited thereto.

A third aspect of the present disclosure provides a memory device comprising the metal-doped gallium iron oxide thin film according to the second aspect of the present disclosure.

According to the above-described problem solving means of the present application, it is possible to greatly reduce the leakage current generated from the metal-doped gallium iron oxide thin film, and at the same time control the properties of the carrier. These results suggest the possibility for the development of a new class of materials that exhibit room temperature magnetization, controllable delivery properties.

1 is a PE hysteresis curve of a GFO thin film.
2 is a perspective view illustrating a structure of a memory device according to an exemplary embodiment of the present application.
3 is an XRD pattern of an Mg-doped GFO thin film according to one embodiment of the present disclosure.
4 is a lattice structure of an Mg-doped GFO thin film according to an embodiment of the present disclosure.
5 is a graph showing the lattice constant change of the Mg-doped GFO thin film according to an embodiment of the present application.
6 is a topographic image of an Mg-doped GFO thin film according to one embodiment of the present disclosure.
7 is a graph showing the RMS roughness of an Mg-doped GFO thin film according to an embodiment of the present disclosure.
8 is a current-voltage curve of an Mg-doped GFO thin film according to one embodiment of the present disclosure.
9 is a lattice diagram of an Mg-doped GFO thin film according to an embodiment of the present disclosure.
10 is a graph showing a change in leakage current according to the doping concentration of the Mg-doped GFO thin film according to an embodiment of the present application.
11 is a piezoelectric force microscope (PFM) image of an Mg-doped GFO thin film according to one embodiment of the present disclosure.
12 is a local PE hysteresis curve (@ 1 Hz) obtained using PFM of an Mg-doped GFO thin film according to one embodiment of the present disclosure.
13 is an XRD pattern of a Mn-doped GFO thin film according to an embodiment of the present disclosure.
14 is a graph showing the RMS roughness of the Mn-doped GFO thin film according to an embodiment of the present application.
15 is an image image of a Mn-doped GFO thin film according to an embodiment of the present disclosure.
16 is a current-voltage curve of an Mn-doped GFO thin film according to one embodiment of the present disclosure.
17 is a piezoelectric force microscopy (PFM) image of a Mn-doped GFO thin film according to one embodiment of the present disclosure.
FIG. 18 is a local PE hysteresis curve (@ 1 Hz) obtained using PFM of an Mn-doped GFO thin film according to one embodiment of the present disclosure.
19 is a PE hysteresis curve of an Mn-doped GFO thin film according to an embodiment of the present disclosure.
20 is an XRD pattern of a Ni-doped GFO thin film according to an embodiment of the present disclosure.
21 is a graph showing the RMS roughness of the Ni-doped GFO thin film according to an embodiment of the present application.
22 is an image image of a Ni-doped GFO thin film according to an embodiment of the present disclosure.
23 is a current-voltage curve of a Ni-doped GFO thin film according to an embodiment of the present disclosure.
24 is an XRD pattern of a Co-doped GFO thin film according to one embodiment of the present disclosure.
25 is a graph showing the RMS roughness of a Co-doped GFO thin film according to an embodiment of the present disclosure.
26 is an image image of a Co-doped GFO thin film according to an embodiment of the present disclosure.
27 is a current-voltage curve of a Co-doped GFO thin film according to an embodiment of the present disclosure.
FIG. 28 is a piezoelectric force microscopy (PFM) image of a Co-doped GFO thin film according to one embodiment of the present disclosure.
FIG. 29 is a local PE hysteresis curve (@ 1 Hz) obtained using PFM of a Co-doped GFO thin film according to one embodiment of the present disclosure.
30 is an XRD pattern of a Bi-doped GFO thin film according to an embodiment of the present disclosure.
31 is a graph showing the RMS roughness of a Bi-doped GFO thin film according to an embodiment of the present disclosure.
32 is an image image of a Bi-doped GFO thin film according to an embodiment of the present disclosure.
33 is a graph measuring the amount of leakage current according to the metal doping concentration of the metal-doped GFO thin film according to an embodiment of the present application.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. It should be understood, however, that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, the same reference numbers are used throughout the specification to refer to the same or like parts.

Throughout this specification, when a part is referred to as being "connected" to another part, it is not limited to a case where it is "directly connected" but also includes the case where it is "electrically connected" do.

Throughout this specification, when a member is &quot; on &quot; another member, it includes not only when the member is in contact with the other member, but also when there is another member between the two members.

Throughout this specification, when an element is referred to as "including " an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise. The terms "about "," substantially ", etc. used to the extent that they are used throughout the specification are intended to be taken to mean the approximation of the manufacturing and material tolerances inherent in the stated sense, Accurate or absolute numbers are used to help prevent unauthorized exploitation by unauthorized intruders of the referenced disclosure. The word " step (or step) "or" step "used to the extent that it is used throughout the specification does not mean" step for.

Throughout this specification, the term "combination of these" included in the expression of the mark of the form refers to one or more mixtures or combinations selected from the group consisting of the elements described in the mark of the form of Markus, wherein the component It means to include one or more selected from the group consisting of.

Throughout this specification, description of "A and / or B" means "A, B, or A and B."

Throughout this specification, "atomic percent" may be described as "at%", and the content of metal atoms means "atomic%" unless otherwise specified.

A first aspect of the present disclosure provides a method of making a metal-doped gallium iron oxide thin film comprising:

Iron oxide, gallium oxide, and metal oxide are reacted to form Ga _y Fe _{2 -y- x} M _x O ₃ (0 <x <2, 0 <y <2, 0 <x + y <2) as targets for thin film formation. Forming a; And

Forming a gallium iron oxide (GaFeO: M) thin film doped by a metal by physical vapor deposition (PVD) using the thin film forming target.

In the case of gallium iron oxide (GaFeO, hereinafter referred to as "GFO"), Fe coexists in the Fe ^{2 +} and Fe ^{3 +} state in the GFO. When there are oxygen defects in the GFO by δ, the GFO has the structure of Formula 1:

[Formula 1]

Ga _y Fe ^{2 +} _2δ Fe ^{3 +} _2-y-2δ O _{3 -δ}

The Fe ^{2 +,} and the Fe ^{3 +} to be displayed between the electron mobility, such as formula 1, the electron mobility becomes a cause of the leakage current in the thin film GFO.

[Formula 1]

^{Fe 2 + - e - → Fe} 3 +, Fe 3 + + e - → Fe 2 +

By divalent doping a metal to the GFO, it is possible to replace all or a portion of the Fe ^{2 +} contained in the GFO as the metal (M ^{2 +),} whereby a metal-doped gallium iron oxide (GaFeO: M) By having the structure of Formula 2, even if oxygen defects occur as much as δ can reduce the amount of leakage current compared to the GFO, it can further exhibit ferroelectricity.

(2)

Ga _y M ^{2 +} _x Fe ^{2 +} _{2δ- x} Fe ^{3 +} _2-y-2δ O _{3 -δ}

According to the exemplary embodiment of the present disclosure, the metal oxide may be an oxide of a metal having a valence of +2, and may be an oxide of a metal having various valences including a valence of +2, but is not limited thereto. no. The metal oxide is, for example, Mg, Co, Mn, Ni Bi, Ca, Sr, Sc, V, Cr, Pb, Pt, Au, Al, Cu, Mo, Rh, Si, Ta, Ti, W, It may include, but is not limited to, an oxide of a metal selected from the group consisting of U, Zr, Ge, Ru, Ir, and combinations thereof.

According to the exemplary embodiment of the present application, the y value may be, for example, 0.6, but is not limited thereto. The x value may vary depending on the content of the metal oxide.

According to one embodiment of the present invention, the physical vapor deposition method is a pulsed laser deposition (PLD) method, E-beam evaporation method, thermal evaporation method (thermal evaporation) method, ion cluster beam (ion cluster beam) ) Method, sputtering method, and a method selected from the group consisting of combinations thereof, but is not limited thereto.

According to one embodiment of the present application, the physical vapor deposition method may include a pulse laser deposition method, but is not limited thereto.

According to one embodiment of the invention, the pulsed laser deposition method is about 300 ℃ to about 1,000 ℃, about 400 ℃ to about 900 ℃, about 500 ℃ to about 800 ℃, about 600 ℃ to about 800 ℃, about 600 ℃ to About 750 ° C, about 600 ° C to about 700 ° C, about 600 ° C to about 650 ° C, about 650 ° C to about 800 ° C, about 650 ° C to about 760 ° C, about 650 ° C to about 720 ° C, about 650 ° C to about 680 ° C ℃, about 700 ℃ to about 800 ℃, about 700 ℃ to about 760 ℃, about 700 ℃ to about 720 ℃, or may be performed at a temperature of about 750 ℃ to about 800 ℃, but is not limited thereto.

According to one embodiment of the present application, the pulse laser deposition method may be performed under an oxygen atmosphere, but is not limited thereto.

According to an embodiment of the present invention, the metal-doped gallium-iron (GaFeO: M) thin film comprises about 0.1 atom% to about 20 atom%, about 0.1 atom% to about 15 atom% To about 10 atomic percent, about 0.1 atomic percent to about 5 atomic percent, about 0.1 atomic percent to about 3 atomic percent, about 0.5 atomic percent to about 7.5 atomic percent, about 2 atomic percent to about 7.5 atomic percent, about 2.8 atomic percent, About 1 atom% to about 15 atom%, about 1 atom% to about 10 atom%, about 1 atom% to about 5 atom%, about 1 atom% From about 5 atom% to about 10 atom%, from about 5 atom% to about 8 atom%, from about 5 atom% to about 20 atom%, from about 5 atom% About 10 atomic percent to about 14 atomic percent, about 10 atomic percent to about 12 atomic percent, about 15 atomic percent, about 20 atomic percent, about 10 atomic percent to about 18 atomic percent, about 10 atomic percent to about 16 atomic percent, To about 20 atomic%, or about 1 atomic% But is not limited to, from 5 atomic% to about 18 atomic%. Depending on the type of the metal that is doped, if the content is if a certain level or less, the amount of the metal to replace the Fe ^{2 +} insufficient and the ability to reduce the electron transfer that occurs between Fe ^{2 +} and Fe ^{3 +} off leak The effect of decreasing the current is weak. If the content of the metal is higher than a certain level, the leakage current increases due to other electron movements due to the excess dopant.

According to an embodiment of the present invention, the pulsed laser deposition (PLD) method is a method of depositing a thin film on a substrate by vaporizing a target material in a chamber with a laser, the structure is simple, even a complex composition of materials It is easy to deposit and even high melting point materials can be deposited. It is possible to produce an epitaxial thin film using the PLD deposition method. For example, the GFO thin film is known to have a b-axis polarization direction, and when the PLD deposition method is used, an epitaxial thin film may be formed on the b-axis to improve switching characteristics of the polarization. In addition, when using a chemical method, for example, solid state reaction, sol-gel method, etc., it is possible to prepare GFO in powder form, but not in thin film form. In the case of using the PLD deposition method, there is an advantage in that a more uniform and epitaxial thin film can be manufactured than in the case of using the chemical method.

Specifically, pulsed laser deposition (pulsed laser deposition; PLD) method using a metal-doped gallium iron oxide thin film _{(Ga y Fe 2 -y- x M} x O 3, where 0 <x <2, 0 < y < 2, the method for producing a 0 <x + y <2) is, first, an iron oxide, gallium oxide, and for thin film deposition target by reacting a metal oxide _{Ga y Fe 2 -y- x M x} O 3 (0 < x <2, 0 <y <2, 0 <x + y <2), but is not limited thereto.

The Ga _y Fe _{2 -yx} M _x O ₃ (0 <x <2, 0 <y <2, 0 <x + y <2) target is, for example, high purity Ga ₂ O ₃ powder and Fe ₂ O ₃ In order to add about 0.1 atomic% to about 20 atomic% metal dopant in the powder, a high purity metal oxide powder in ammoniacal solution was uniformly mixed with the Ga ₂ O ₃ powder and Fe ₂ O ₃ powder in a milling system to form a thin film The target mixture for formation can be formed. As the milling system, for example, a ball mill, a roller mill, a vibrating ball mill, an attritor mill, a planetary ball mill, a sand mill Dry mill or cutter such as a cutter mill, a hammer mill, a jet mill, or an ultrasonic disperser or a high pressure homogenizer. Grinding processes through milling systems can be used to further atomize iron oxide, gallium oxide, and metal oxide powders.

Ga _y Fe _{2 -yx} M _x O ₃ (0 <x <2, 0 <y <2, 0 <x + y <2) target when forming a metal-doped gallium iron oxide thin film using the pulse laser deposition method May be used alone to form a doped gallium iron oxide thin film, or Ga _y Fe _{2 -yx} M _x O ₃ (0 <x <2, 0 <y <2, 0 <x + y <2) target May be used together with an undoped Ga _{y '} Fe _{2 -y'O 3} (0 <y'<2) target to form a doped gallium iron oxide thin film, but is not limited thereto. Also, the Ga _y Fe _2-yx M _x O ₃ (0 <x <2, 0 <y <2, 0 <x + y <2) target or the Ga _{y '} Fe _{2 -y'O 3} (0 < The y '<2) target and the pure dopant target in the form of _a metal oxide (M _a O _b ) may be used together to form a doped gallium iron oxide thin film, but is not limited thereto.

Subsequently, the target mixture for forming a thin film may be pulverized, and then an organic binder may be added to compress the thin film forming target mixture and sintered at a predetermined temperature to form the target.

The organic binder is, for example, polyvinyl alcohol, polyamide, polyvinylacetate, polyvinyl butyral, polyvinylpyrrolidone, polyester polyvinylchloride, polyacryl, polyurethane, polycarbonate, polymethacryl, Ethylene vinyl acetate, ethylene glycol, and combinations thereof may be selected from the group consisting of, but is not limited thereto.

The sintering process of the mixture, for example, may be performed for about 10 hours to about 20 hours in the sintering temperature range of about 1,100 ℃ to about 1,500 ℃, or about 1,200 ℃ to about 1,450 ℃, but is not limited thereto. no.

Subsequently, after setting a constant energy density of the laser, the Ga _y Fe _{2 -yx} M _x O ₃ (0 <x <2, 0 <y <2, 0 <x + y <2) Ga _y Fe _{2 -yx} M _x O ₃ (0 <x <2, 0 <y <2, 0 <x + y <2) by a metal under specific laser conditions using a target material A doped gallium iron oxide (GaFeO: M) thin film may be deposited. The substrate temperature to be deposited is about 300 ° C. to about 1,000 ° C., and the specific deposition conditions are, for example, the wavelength of a laser of about 248 nm (KrF excimer laser), a repetition frequency of about 1 Hz to about 5 Hz, Instantaneous pulse width less than about 1 ms, about 0.1 J / cm ² per pulse To about 1,000 J / cm ² , or about 2 J / cm ² To radiation of from about 3 J / cm ² , and a distance between the substrate and the target of about 3 cm to about 7 cm. In addition, since the oxygen deficiency of the thin film may cause leakage current, the deposition may be performed under a background O ₂ pressure condition of about 90 mTorr to about 110 mTorr to reduce the leakage current.

The substrate is AlO _y , TiO _y , TaO _y , HfO _y , BaO _y , VO _y , MoO _y , SrO _y , NbO _y , MgO _y , SiO _y , FeO _y , CrO _y , NiO _y , CuO _y , ZrO _{y , BO y, TeO y, ZnO} y, BiO y, WO y, CdO y, CoO y, LaO y, MgO y, GaO y, GeO y, SrTiO 3, BaTiO 3, Al x Ti 1 -x O y, Hf _x Si _{1 - x} O _y , Hf _x Al _{1 - x} O _y , Hf _x Al _{1 - x} O _y , Ti _x Si _{1 - x} O _y , Ta _x Si _{1 - x} O _y , LaTiO ₃ , Zn _x Ti _{1 - x} O _y and combinations thereof may be included, but is not limited thereto.

The metal-doped gallium iron oxide (GaFeO: M) thin film can greatly reduce the leakage current generated from the metal-doped gallium iron oxide thin film because it forms a thin film having improved surface uniformity and density by a pulse laser deposition process. have.

A second aspect of the present application provides a metal-doped gallium iron oxide thin film produced by the method according to the first aspect.

According to one embodiment of the invention, the metal-gallium iron oxide thin film is doped, but can be to include Fe ^{2 +} and / or Fe ^{+ 3,} but is not limited thereto.

According to one embodiment of the present application, the metal may be doped by substituting some or all of the Fe ^{2 +} , but is not limited thereto.

In the case of gallium iron oxides (GaFeO, GFO), Fe coexists in the Fe ^{2 +} and Fe ^{3 +} state in the GFO. When there are oxygen defects in the GFO by δ, the GFO has a structure of Formula 3:

(3)

Ga _y Fe ^{2 +} _2δ Fe ^{3 +} _2-y-2δ O _{3 -δ}

It is the electron mobility, such as the following equation 2 between the Fe ^{2 +,} and the Fe ^{3 +} appears, the electron mobility becomes a cause of the leakage current in the thin film GFO.

[Formula 2]

^{Fe 2 + - e - → Fe} 3 +, Fe 3 + + e - → Fe 2 +

The metal-doped gallium iron oxide thin film is doped with a divalent metal (M ^{2 +} ) in the GFO, thereby replacing all or part of the Fe ^{2 +} contained in the GFO with M ^{2 +} , thereby Since the metal-doped gallium iron oxide thin film has a structure of Formula 4, even if oxygen defects occur by δ, the amount of leakage current may be reduced compared to GFO, and further, ferroelectricity may be exhibited.

[Formula 4]

Ga _y M ^{2 +} _x Fe ^{2 +} _{2δ- x} Fe ^{3 +} _2-y-2δ O _{3 -δ}

In the case of the metal-doped gallium iron oxide thin film of the present application, the electrical type as a semiconductor may be changed according to the concentration of the metal to be doped. For example, the metal-doped gallium iron oxide thin films of the present application generate charge (e ⁻ ) or hole (h ^· ) transfer by the mechanism of the following Equation 3 or 4:

[Equation 3]

δO ₀ ^{X _{→ δ (V 0 ‥ + 1}} / 2O 2 + 2e -)

[Formula 4]

xAO → x (A ′ _Fe + h ^· + 1 / 2O ₂ ).

In Equations 3 and 4, δ means oxygen defect amount, X means doped metal amount, A is a dopant, A 'is a cationic state of the dopant, A' _Fe Means A cation substituted at the Fe ²⁺ site.

Combining the mechanisms of Equation 3 and Equation 4, the transport of charge (e ⁻ ) or hole (h ^· ) occurs by the mechanism of Equation 5 below:

[Formula 5]

δO ₀ ^{X _{+ XAO → δV 0 ‥ + xA}} 'Fe + (x + δ) / 2O 2 + 2δe - + xh ·.

Therefore, 2δe- and xh ^· in the above formula 5 become electrical carriers of the metal-doped gallium iron oxide thin film. Accordingly, the electrical type of the metal-doped gallium iron oxide thin film is changed according to the size of the 2δ and x value. For example, when 2δ> x, electrons (e ⁻ ) become electrical carriers, and the metal-doped gallium iron oxide thin film has an n-type electrical type, and when 2δ <x, holes (h ^· ) This electrical carrier causes the metal-doped gallium iron oxide thin film to have a p-type electrical type.

33 is a graph measuring the amount of leakage current according to the metal doping concentration of the metal-doped gallium iron oxide thin film according to an embodiment of the present invention. As can be seen in FIG. 33, the metal-doped gallium iron oxide thin film according to the concentration of the metal to be doped exhibited an n-type electrical type or a p-type electrical type. As such, the metal-doped gallium iron oxide thin film according to an embodiment of the present application can change the electrical type according to the metal doping concentration, and by using this property, the metal-doped gallium iron oxide thin film may be applied to a new device. It is possible to apply.

A third aspect of the present application provides a memory device, comprising the metal-doped gallium iron oxide thin film according to the second aspect of the present application.

The metal-doped gallium iron oxide thin film of the present disclosure can greatly reduce the leakage current, thereby improving the electrical characteristics of the memory device including such a metal-doped gallium iron oxide thin film.

The description of the method according to the first aspect of the present application can be applied to both the second and third aspects of the present invention, and duplicate description thereof is omitted for the sake of convenience.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

[ Example  One] Mg - Doped GFO  pellicle

In this example, Fe was substituted with Mg. It is only known that Fe may be +2 or +3, while Mg is +2. In this embodiment the goal is to have all +2 induced by oxygen approximate stoichiometry by replacing Fe cations Mg ^{+ 2} cations. Mg ^{2 +} Fe ^{2 +} radius is close to the radius. And then it is expected the reduction of the leakage current, which is related to the reduction and its Fe ^{2 +} / Fe ^{3 +} reduction of the hopping phenomenon according to the content of Fe ^{2 +.}

Thin films were precisely prepared by pulsed laser deposition (PLD) using a λ = 248 nm KrF excimer laser at a 5 Hz repetition rate. The energy density of the laser on the target was adjusted to 2.5 J / cm ² and the distance between the target and the substrate was fixed at 5 cm. First, a SrRuO ₃ (SRO) conductive layer was deposited on a SrTiO ₃ (111) substrate (Crystec) at 655 ° C. under 250 mbar O ₂ . The substrate was previously cleaned in an ultrasonic cleaner with acetone, isopropanol, distilled water and ethanol. Then about 200 nm thick GFO: Mg layer is 200 mbar O ₂ at 750 ° C. Was deposited under. 2 is a perspective view showing the structure of a memory device using the Mg-doped GFO thin film according to the present embodiment. After deposition of a GFO: Mg layer, the sample was cooled to room temperature under the process gas. The _{Ga 0 .6 Fe 1 .4- x Mg} x O 3 target used for the synthesis was formed by the reaction of _{Fe 2 O 3, Ga 2 O} 3 and MgO. Stoichiometric milling was carried out in an attritor mill for one hour in ammonia solution (pH = 9). The solution was then placed in a drying oven until the liquid phase completely evaporated. The resulting powder was ground manually. An organic binder (polyvinyl alcohol) was added about 3 wt% to improve the mechanical behavior of the sample. The powder was finally compacted into pellets and sintered in a platinum crucible at 1400 ° C. for 20 hours under air. The crystal structure of the thin film was measured by X-ray diffraction (XRD). θ-2θ scans, φ-scans, and reciprocal lattice mappings were measured using a Rigaku Smart Lab diffractometer with rotating anode monochromatic copper radiation (Kα1 = 0.154056 nm). Surface morphology was measured by atomic force microscopy (AFM) using n-Tracer (Nanofocus Inc.). For electrical characterization, platinum dot top electrodes with a diameter of 0.2 mm were deposited by magnetron sputtering using a shadow mask on a GFO thin film under a pressure of 5 mTorr at room temperature. The IV curve at room temperature was then measured using the HP4145B semiconductor parameter analyzer in the voltage range of -10 V to 10 V.

XRD measurements confirmed that the GFO: Mg thin film was epitaxially grown on the STO / SRO (111) substrate. 3 shows the θ-2θ pattern of the Mg-doped GFO thin film and shows the b -axis oriented epitaxial structure of the GFO. In fact, all expected (0k0) harmonic peaks of the GFO compound were observed and no impurities were detected.

Table 1 below shows the lattice constant relationship between the SRO / STO 111 and the GFO thin film, and FIG. 4 shows the lattice structure of the Mg-doped GFO thin film.

[Table 1]

The improvement by the cotton cell parameter is shown in FIG. 5 and shows smaller b values than the bulk material (b _bulk = 9.3993 (3) iii) [SC Abrahams, JM Reddy, and JL Bernstein, The Journal of chemical physics 42]. (11), 3957 (1965). The chemical composition of the thin film was evaluated by scanning electron microscopy (SEM-EDX) coupled with energy dispersive X-ray analysis. The values shown in Table 2 below are averages of at least five measurements performed at different locations on the samples, with a standard deviation of less than 1% Wt.

[Table 2]

(a) Composition by EDX

(b) Measure with θ-2θ pattern

The content of the metal atom (M) is the atomic weight measured by EDX, which means atomic percent, and M (%) = 100 x [M] / (M) + [Fe] + [Ga]). Was defined by. According to this definition, M (%) refers to the atomic% of the metal M contained in the GFO thin film, so that the samples are GFO: Mg (0%), GFO: Mg (0.5%), GFO: Mg (2.8%). ) And GFO: Mg (7.5%). An image of the image above the scanning area of 5 × 5 μm ² is shown in FIG. 6. 7 is a graph showing the RMS roughness of the Mg-doped GFO thin film, the surface morphology showed that the grain size decreases to a uniform size as the Mg content is increased. This surprising result was confirmed by the value of the root mean square (rms) roughness of the GFO: Mg thin film. In fact, GFO: Mg (0%) and GFO: Mg (0.5%) show somewhat higher values of rms (10.75 nm and 12.05 nm, respectively), while GFO: Mg (2.8%) and GFO: Mg (7.5). %) Were 8.68 nm and 2.71 nm, respectively. Φ-scan on the (204) lattice plane of STO and SRO and the (680) lattice plane of the GFO: Mg thin film was measured to elucidate the in-plane epitaxial relationship. All layers (STO, SRO and GFO) showed 6-fold peaks present every 60 °. These results can be explained by considering the epitaxial relationship as follows: SrTiO ₃ The crystal forms a cubic structure with a = 3.905 Å, thereby showing a hexagonal pattern structure along [111]. SrRuO ₃ at room temperature Is crystallized into a tetragonal structure, which can generally be described as a somewhat twisted quasi- cubic perovskite cell with a = 3.92 Å lattice parameter. As a result, the pattern along [111] is also a hexagon with an apothem equal to 3.2 Å. The mismatch between STO and SRO is less than 1%. Different arrangements of GFO crystals can be described by considering different matching possibilities between the GFO and SRO grids: c _GFO ≒ 5.1 Å ≒ a _SRO × 2 ^0.5 (8% mismatch) and a _{GFO on the} other hand ≒ 8.7 Å ≒ 3.2 × 3 (9% mismatch). The angle between two GFO cells is about 60 ° allowing the presence of three variants. Measurement of in-plane cell parameters was measured by X-ray reciprocal space mapping (RSM). Measurements were performed on (062) and (570) diffraction peaks and the results are shown in FIG. 5 and Table 2. Both b cell and c cell parameters remained constant regardless of the Mg content. a Cell parameters increased for Mg content up to GFO: Mg (2.8%) and then remained constant.

8 shows the change in leakage current for different Mg-doped thin films. The leakage current density for the GFO: Mg thin film was greatly reduced from GFO: Mg (0.5%) to GFO: Mg (2.8%) by approximately five orders of magnitude. This behavior is reduced, the structure within the hopping between Fe ^{+ 2} and Fe ^{+ 3} at the (hopping) potential as a result of the substitution of Fe ^{2 + 2} for Mg ^+. At higher Mg concentrations, an increase in leakage current was observed again: upon increasing the Mg content from 2.8% to 7.5%, the leakage current increased again by about three orders of magnitude. FIG. 9 shows a lattice diagram of a Mg-doped GFO thin film, and the change of leakage current as a function of doping concentration is shown in FIG. 10. As described above, this aspect is characterized by a strong reduction in leakage current up to GFO: Mg (2.8%) and an increase in leakage current for higher doping contents. This behavior can be interpreted using the Kroger-Vink notation. In fact, the generation of δ oxygen defects during the growth process can usually be expressed as follows:

Here, V ₀ is the attacker ^‥ point in the oxygen site with a double positive charge (double positive charge). At the same time, the substitution of Fe for Mg indicates the formation of holes:

Here, Mg ' _Fe means Mg at the Fe site having an apparent negative charge, and h ^· indicates a hole. Then, according to the above notation, the decrease in leakage current generated up to GFO: Mg (2.8%) may be due to the increasing recombination between holes and electrons. Therefore, the charge carriers that cause the leakage current are electrons (ie n-type conduction with d> x). For higher content doping, the observed behavior should be related to the increasing presence of holes (ie, p-type conduction with x> d).

11 is a piezoelectric force microscopy (PFM) image of Mg-doped GFO thin film. PFM image of Mg 2.5% sample with lowest leakage current.

12 is a local P-E hysteresis curve (@ 1 Hz) obtained using PFM of Mg-doped GFO thin film. The local P-E hysteresis curve obtained using a Pt-coated AFM probe confirms the possibility of ferroelectric properties in Mg-doped GFO thin films.

In conclusion, in the present example, Mg-doped GFO thin films were prepared by pulsed laser deposition with an Mg content of up to 7.5 at%. X-ray measurements showed perfect epitaxial growth of Mg-doped GFO thin films on SRO buffer layer with parasitic phase. This example demonstrated an optimal Mg content of 2.8 at% showing a sharp decrease in leakage current by five orders of magnitude. This reduction in leakage current is very promising for future possible magnetoelectric characterization of sophisticated thin films. This aspect of leakage current suggests a progression from n-type to p-type electrical conduction with increasing doping content. These results offer the potential for the development of a new class of materials that exhibit non-zero magnetization, controllable transfer properties and magnetoelectric properties at room temperature.

[ Example  2] Mn - Doped GFO  pellicle

Ga _{0 .6} formed by the reaction of _{Fe 2 O 3, Ga 2 O} 3 and MnO in SrTiO SrRuO ₃ on the _third (111) substrate (Crystec) (SRO) and then depositing a conductive layer and a SrRuO ₃ (SRO) conductive layer using a Fe _{1 .4- x} Mn _x O ₃ target to GFO: except for forming the layer, and Mn were produced in the same manner as in example 1.

13 is an XRD pattern of a Mn-doped GFO thin film according to the present embodiment. It was found that the Mn-doped GFO thin film was deposited epitaxially on the b axis as a whole.

14 is a graph showing the RMS roughness of the Mn-doped GFO thin film according to the present embodiment. The smallest RMS roughness value was obtained when 2% Mn was doped.

15 is an image image of a Mn-doped GFO thin film according to the present embodiment.

16 is a current-voltage curve of the Mn-doped GFO thin film according to the present embodiment. The leakage current decreased even when Mn was doped, and the smallest leakage current was measured when 2% was doped. Leakage current increased slightly when Mn 10% was doped, which showed the same tendency in GFO thin films doped with 7.5% Mg but the amount of leakage current increased less.

17 is a piezoelectric force force microscope (PFM) image of a Mn-doped GFO thin film according to the present embodiment. PFM image of Mn 2% sample with the lowest leakage current.

18 is a local P-E hysteresis curve (@ 1 Hz) obtained using PFM of an Mn-doped GFO thin film according to the present embodiment. The graph shows the possibility of ferroelectric properties as Mg doped in Mn-doped GFO thin films with local PE hysteresis curves obtained using a Pt-coated AFM probe of 2% Mn sample with the lowest leakage current. Showed.

19 is a PE hysteresis curve of the Mn-doped GFO thin film according to the present embodiment. The GFO thin film doped with 10% Mn showed a nonlinear PE hysteresis curve, but with reduced polarization.

[ Example  3] Ni - Doped GFO  pellicle

After depositing a SrRuO ₃ (SRO) conductive layer on an SrTiO ₃ (111) substrate (Crystec), Ga _0. Formed by reaction of Fe ₂ O ₃ , Ga ₂ O ₃ and NiO on the SrRuO ₃ (SRO) conductive layer _{. 6} Fe _{1 .4- x} Ni _x O by using the _three target GFO: was prepared in the same manner as in example 1 except for forming the Ni layer.

20 is an XRD pattern of a Ni-doped GFO thin film according to the present embodiment. Ni-doped GFO thin films were also deposited epitaxially throughout the b axis.

21 is a graph showing the RMS roughness of the Ni-doped GFO thin film according to the present embodiment. Ni-doped GFO thin films have significantly reduced RMS roughness, with the smallest values for thin films doped with 1% Ni samples.

22 is an image image of a Ni-doped GFO thin film according to the present embodiment.

23 is a current-voltage curve of the Ni-doped GFO thin film according to the present embodiment. Ni-doped GFO thin film was also found to reduce the leakage current. Smaller leakage currents were also measured in the sample showing the secondary phase peak in XRD than the undoped GFO thin film. The smallest leakage currents were measured on thin films doped with Ni 0.5% without any secondary phase peaks.

[ Example  4] Co - Doped GFO  pellicle

After depositing a SrRuO ₃ (SRO) conductive layer on a SrTiO ₃ (111) substrate (Crystec), Ga _0. Formed by the reaction of Fe ₂ O ₃ , Ga ₂ O ₃ and CoO on the SrRuO ₃ (SRO) conductive layer _{. 6} by using the Fe _{1 .4- x} Co _x O ₃ target GFO: was prepared in the same manner as in example 1 except for forming a Co layer.

24 is an XRD pattern of a Co-doped GFO thin film according to the present embodiment. Co-doped GFO thin films were also deposited epitaxially throughout the b axis.

25 is a graph showing the RMS roughness of the Co-doped GFO thin film according to the present embodiment. RMS roughness tended to decrease with increasing doping concentration of Co.

26 is an image image of a Co-doped GFO thin film according to the present embodiment.

27 is a current-voltage curve of a Co-doped GFO thin film according to the present embodiment.

28 is a piezoelectric force force microscope (PFM) image of a Co-doped GFO thin film according to the present embodiment. PFM image of the Co 2% sample with the lowest leakage current.

FIG. 29 is a local PE hysteresis curve (@ 1 Hz) obtained using PFM of a Co-doped GFO thin film according to the present example. FIG. PE hysteresis curve of the Co 2% sample with the lowest leakage current. Local PE hysteresis curves obtained using Pt-coated AFM probes show that there is a possibility that ferroelectric properties may appear as Mn or Mg doped in Co-doped GFO thin films.

[ Example  5] Bi - Doped GFO  pellicle

After depositing a SrRuO ₃ (SRO) conductive layer on a SrTiO ₃ (111) substrate (Crystec), a Ga ₀ formed by the reaction of Fe ₂ O ₃ , Ga ₂ O ₃ and BiO on the SrRuO ₃ (SRO) conductive layer _{. 6} by using the Fe _{1 .4- x} Bi _x O ₃ target GFO: was prepared in the same manner as in example 1 except for forming the Bi layer.

30 is an XRD pattern of a Bi-doped GFO thin film according to the present embodiment. Bi-doped GFO thin films were also deposited epitaxially on the b axis.

31 is a graph showing the RMS roughness of the Bi-doped GFO thin film according to the present embodiment. Bi-doped GFO thin films have significantly reduced RMS roughness values. The smallest value was found in the Bi 0.5% sample and a slightly larger value was obtained in the Bi 2% sample showing the secondary phase peak.

32 is an image image of a Bi-doped GFO thin film according to the present embodiment.

It will be understood by those of ordinary skill in the art that the foregoing description of the embodiments is for illustrative purposes and that those skilled in the art can easily modify the invention without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

Claims (13)

Iron oxide, gallium oxide, and metal oxide are reacted to form Ga _y Fe _{2 -yx} M _x O ₃ (0 <x <2, 0 <y <2, 0 <x + y <2) as targets for thin film formation. Making; And
Forming a gallium iron oxide (GaFeO: M) thin film doped with a metal by physical vapor deposition (PVD) using the thin film forming target;
A method of producing a metal-doped gallium iron oxide thin film comprising a.
The method of claim 1,
The metal oxide is Mg, Co, Mn, Ni Bi, Ca, Sr, Sc, V, Cr, Pb, Pt, Au, Al, Cu, Mo, Rh, Si, Ta, Ti, W, U, Zr, Ge A method of making a metal-doped gallium iron oxide thin film comprising an oxide of a metal selected from the group consisting of Ru, Ir, and combinations thereof.
The method of claim 1,
The physical vapor deposition method is a pulsed laser deposition (PLD) method, an E-beam evaporation method, a thermal evaporation method, an ion cluster beam method, a sputtering method, and these Method of producing a metal-doped gallium iron oxide thin film comprising a method selected from the group consisting of.
The method of claim 1,
The physical vapor deposition method comprises a pulsed laser deposition method, a method of producing a metal-doped gallium iron oxide thin film.
5. The method of claim 4,
The pulsed laser deposition method is carried out at a temperature of 300 ℃ to 1,000 ℃, the method of producing a metal-doped gallium iron oxide thin film.
5. The method of claim 4,
The pulsed laser deposition method is performed under an oxygen atmosphere, the method of producing a metal-doped gallium iron oxide thin film.
The method of claim 1,
And the metal-doped gallium iron oxide (GaFeO: M) thin film contains 0.1 atomic percent to 20 atomic percent of the metal.
A metal-doped gallium iron oxide (GaFeO: M) thin film prepared by the method according to any one of claims 1 to 7.
The method of claim 8,
Wherein the metal-doped gallium-iron oxide thin film comprises Fe &lt; ^{2 +} & ^{gt ;} and / or Fe &lt; ^{3 + &} gt ;.
The method of claim 9,
Wherein the metal is doped with some or all of the Fe &lt; ^{2 + & gt ;} substituted.
The method of claim 8,
Wherein said metal-doped gallium iron oxide thin film comprises a ferroelectric one.
The method of claim 8,
Wherein said metal-doped gallium iron oxide thin film reduces leakage current.
A memory device comprising the metal-doped gallium iron oxide thin film according to claim 8.

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