KR20150032279A - Preparing method of metal-doped gallium iron oxide thin film and metal-doped gallium iron oxide thin film using the same - Google Patents

Abstract

The present invention 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. According to the present invention, a metal-doped gallium iron oxide thin film is able to markedly reduce leakage of current from the metal-doped gallium iron oxide thin film, and is able to control a property of a carrier at the same time. These results show a possibility of developing a new type of substance capable of room temperature magnetization and representing a controllable transfer characteristic. According to a first aspect of the present invention, a method of producing a metal-doped gallium iron oxide thin film includes steps of: reacting iron oxide, gallium oxide, and metal oxide to form GaxFeyM2-yO3 (0<x<2, 0<y<2, 0<x+y<2) as a target for forming a thin film; and using the target for forming a thin film to form a metal-doped gallium iron oxide thin film by a physical vapor deposition (PVD).

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal-doped gallium-iron oxide thin film and a metal-doped gallium-

The present invention relates to a method of preparing a metal-doped gallium-iron oxide thin film and to a metal-doped gallium-iron oxide thin film produced by the method.

Magnetoelectric materials can be used in many applications due to their ability to control magnetic polarization and electric polarization by their respective electric and magnetic fields. For this reason, there is considerable interest in the potential application of electro-magnetic materials in new electronic devices [Hur, S. Park, PA Sharma, JS Ahn, S. Guha, SW Cheong; Nature London 429, 392 (2004)]. Oxides of Ga _{2 - x} Fe _x O ₃ (0.8 ≤ x ≤ 1.4) (hereinafter referred to as "GFO") provide all the necessary properties to become promising candidates for such applications [GT Rado, Phys. Rev. Lett. 13, 335 (1964)]. The GFO oxides form crystals in an orthorhombic structure (SG: Pc 2 ₁ n ) with a? 8.7 A, b? 9.4 A and c? 5.1 A. The material has a ferrimagneticity with a Curie temperature of up to 350 K for x = 1.4. Electro-electric effects have been observed in bulk materials by the paper by Rado (GT Rado, Phys. Rev. Lett. 13, 335 (1964)]. If the bulk properties of the compounds were already well established in the 1960's, high quality thin films essential for applications were recently 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)). Though these films show the same crystallographic and magnetic characteristics as the bulk, as shown in Fig. 1, the unsaturated PE hysteresis curve does not exhibit ferroelectricity, which is known to be due to a larger leakage current than other ferroelectric materials [ ZH Sun et al., Appl. Phys. A 91, 97 (2008), VB Naik, and R. Mahendira, J. Appl. Phys. 106, 123910 (2009)). The leakage current hinders the electrical characteristics of the electro-magnetic material. This leakage current appears to be due to the substoichiometry 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 prevents the polarization-electric field (PE) signal from being exerted and can lead to misinterpretation of the ferroelectric curve [JF Scott; J. Phys .: Condens. Matter 20, 021001 (2008)]. These aspects include the use of BiFeO ₃ , YMnO ₃ or Ni ₃ V ₂ O ₈ Gt; [G. &lt; / RTI &gt; Lawes, G. Srinivasan; J. Phys. D: Appl. Phys. 44, 243001 (2011)). The leakage current problem needs to be carefully studied and resolved for the thin film to be inserted into the functional device to utilize the magneto-electric property of the magneto-electric material [4M. Dawber, KM Rabe, and JF Scott, Rev. Mod. Phys. 77, 108 (2005). There is a lot of literature on the understanding of the leakage mechanism in ferroelectric thin films [JF Scott, J. Phys. Condens. Matter 18, R361 (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 provides a method for fabricating a metal-doped gallium-iron oxide thin film by a simple process and 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 invention provides a method of making a metal-doped gallium-iron oxide thin film comprising:

Forming a _{y O 3 (0 <x <} 2, 0 <y <2, 0 <x + y <2) - iron oxide, gallium oxide, and reacting the metal oxide for a thin-film formation target Ga _x Fe _y M ₂ ; And

Forming a thin film of gallium iron oxide (GaFeO: M) doped with the metal by physical vapor deposition (PVD) using the target for thin film formation;

According to one embodiment of the present invention, the metal oxide is at least one selected from the group consisting of Mg, Co, Mn, Ni Bi, Ca, Sr, Sc, V, Cr, Pb, Pt, Au, Al, Cu, Mo, , W, U, Zr, Ge, Ru, Ir, and combinations thereof, but is not limited thereto.

According to one embodiment of the present invention, the physical vapor deposition may be performed by a pulsed laser deposition (PLD) method, an E-beam evaporation method, a thermal evaporation method, an ion cluster beam ) Method, a sputtering method, and combinations thereof. The present invention is not limited thereto.

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

According to one embodiment of the present invention, the pulsed 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 an embodiment of the present invention, the pulsed 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 GaFeO: M thin film may contain about 0.1 atomic percent (atomic percent) to about 20 atomic percent of the metal, but is not limited thereto .

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

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

According to an embodiment of the present invention, the metal may be doped by substituting a part or all of the Fe ^{2 +} , but is not limited thereto.

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

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

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

According to the above-described task solution of the present invention, the leakage current generated from the metal-doped gallium-iron oxide thin film can be largely reduced, and at the same time, the properties of the carrier can be controlled. These results suggest possibilities for the development of a new class of materials that exhibit room temperature magnetization, controllable transport 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 embodiment of the present invention.
3 is an XRD pattern of an Mg-doped GFO thin film according to an embodiment of the present invention.
4 is a lattice structure of a Mg-doped GFO thin film according to an embodiment of the present invention.
FIG. 5 is a graph illustrating a change in lattice constant of an Mg-doped GFO thin film according to an embodiment of the present invention.
6 is a topographic image of an Mg-doped GFO thin film according to one embodiment of the present application.
7 is a graph showing the RMS roughness of the Mg-doped GFO thin film according to one embodiment of the present invention.
8 is a current-voltage curve of an Mg-doped GFO thin film according to an embodiment of the present invention.
9 is a lattice structure of a Mg-doped GFO thin film according to an embodiment of the present invention.
10 is a graph showing changes in leakage current according to the doping concentration of the Mg-doped GFO thin film according to an embodiment of the present invention.
11 is a PFM image of an Mg-doped GFO thin film according to one embodiment of the present application.
12 is a local PE hysteresis curve (at 1 Hz frequency) obtained using PFM of Mg-doped GFO thin film according to one embodiment of the present application.
13 is an XRD pattern of a Mn-doped GFO thin film according to an embodiment of the present invention.
14 is a graph showing RMS roughness of a Mn-doped GFO thin film according to an embodiment of the present invention.
15 is an image of a Mn-doped GFO thin film according to an embodiment of the present invention.
16 is a current-voltage curve of a Mn-doped GFO thin film according to an embodiment of the present invention.
17 is a PFM image of an Mn-doped GFO thin film according to one embodiment of the present application.
18 is a local PE hysteresis curve (at 1 Hz frequency) obtained using PFM of a Mn-doped GFO thin film according to one embodiment of the present application.
19 is a PE hysteresis curve of an Mn-doped GFO thin film according to one embodiment of the present invention.
20 is an XRD pattern of a Ni-doped GFO thin film according to an embodiment of the present invention.
21 is a graph showing RMS roughness of a Ni-doped GFO thin film according to an embodiment of the present invention.
22 is an image of a Ni-doped GFO thin film according to an embodiment of the present invention.
23 is a current-voltage curve of a Ni-doped GFO thin film according to one embodiment of the present invention.
24 is an XRD pattern of a Co-doped GFO thin film according to an embodiment of the present invention.
25 is a graph showing RMS roughness of a Co-doped GFO thin film according to an embodiment of the present invention.
26 is an image of a Co-doped GFO thin film according to an embodiment of the present invention.
27 is a current-voltage curve of a Co-doped GFO thin film according to an embodiment of the present invention.
28 is a Piezoresponse Force Micrograph (PFM) image of a Co-doped GFO thin film according to one embodiment of the present application.
29 is a local PE hysteresis curve (at 1 Hz frequency) obtained using PFM of a Co-doped GFO thin film according to one embodiment of the present application.
30 is an XRD pattern of a Bi-doped GFO thin film according to an embodiment of the present invention.
31 is a graph showing the RMS roughness of a Bi-doped GFO thin film according to an embodiment of the present invention.
32 is an image of a Bi-doped GFO thin film according to an embodiment of the present invention;
33 is a graph illustrating an amount of leakage current according to a metal doping concentration of a metal-doped GFO thin film according to an embodiment of the present invention.

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 "on " 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 thereof" included in the expression of the machine form means one or more combinations or combinations selected from the group consisting of the constituents described in the expression of the machine form, And the like.

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

Throughout this specification, "atomic percent" can be described as "at% &quot;, and in the absence of special mention, the content of metal atoms means" atomic% &quot;.

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

Iron oxide, to form a gallium oxide, and reacting the metal oxide for a thin-film formation target _{Ga y Fe 2 -yx M x O} 3 (0 <x <2, 0 <y <2, 0 <x + y <2) ; And

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

In the case of gallium iron oxide (GaFeO, hereinafter referred to as "GFO"), Fe coexists in the Fe ^{2 +} and Fe ^{3 +} states in the GFO. When the oxygen deficiency is as large as? In the GFO, the GFO has a structure of the following formula 1:

[Chemical Formula 1]

_{^{Ga y Fe 2 + 2δ e 3}} + 2-y-2δ3-δ

Electron transfer as shown in Equation (1) below occurs between Fe ^{2 +} and Fe ^{3 +} , and the electron transfer causes a leakage current in the GFO thin film.

[Formula 1]

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

By doping the GFO with a divalent metal, all or a part of Fe ^{2 +} contained in the GFO can be replaced with the metal (M ^{2 +} ), whereby the metal-doped gallium iron oxide (GaFeO 2: M) Has a structure represented by the following formula (2), even if oxygen defects are generated by delta, the amount of leakage current can be reduced as compared with that of GFO, and further ferroelectricity can be exhibited.

(2)

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

According to one embodiment of the present invention, the metal oxide may be an oxide of a metal having a valence of +2 valence, and may be an oxide of a metal having various valences including + valence valence, no. The metal oxide may be at least one selected from the group consisting of Mg, Co, Mn, Ni Bi, Ca, Sr, Sc, V, Cr, Pb, Pt, Au, Al, Cu, Mo, Rh, Si, U, Zr, Ge, Ru, Ir, and combinations thereof. However, the present invention is not limited thereto.

According to one embodiment of the present invention, the y value may be, for example, 0.6, but is not limited thereto, and 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 may be performed by a pulsed laser deposition (PLD) method, an E-beam evaporation method, a thermal evaporation method, an ion cluster beam ) Method, a sputtering method, and combinations thereof. The present invention is not limited thereto.

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

According to one embodiment of the present application, the pulsed laser deposition method may be performed at a temperature of from about 300 캜 to about 1,000 캜, from about 400 캜 to about 900 캜, from about 500 캜 to about 800 캜, from about 600 캜 to about 800 캜, About 650 ° 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, At a temperature of from about 700 ° C to about 800 ° C, from about 700 ° C to about 760 ° C, from about 700 ° C to about 720 ° C, or from about 750 ° C to about 800 ° C.

According to an embodiment of the present invention, the pulsed 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 10 atom%, about 0.1 atom% to about 5 atom% About 1 atom% to about 10 atom%, about 3 atom%, about 0.5 atom% to about 7.5 atom%, about 2 atom% To about 5 atom%, to about 5 atom%, to about 3 atom%, to about 5 atom%, to about 10 atom%, or from about 5 atom% to about 8 atom%. Depending on the type of the metal that is doped, if the content of a certain level or less, the amount of the metal to replace the Fe ²⁺ sufficient to have 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 one 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 by using a laser. The method is simple in structure, It can be easily deposited, and materials with high melting points can also be deposited. It is possible to produce an epitaxial thin film using the PLD deposition method. For example, it is known that the polarization direction of the GFO thin film is b axis, and when the PLD deposition method is used, a thin film which is epitaxially grown on the b axis can be formed, and the switching characteristics of the polarization can be improved. In addition, when a chemical method such as a solid state reaction, a sol-gel method or the like is used, it is possible to produce GFO in powder form, but it can not be manufactured in a thin film form, PLD deposition is advantageous in that a more uniform and epitaxial thin film can be produced than in the case of using a chemical method.

Specifically, 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, 0 < x + y < 2) is produced by first reacting iron oxide, gallium oxide and metal oxide to form Ga _y Fe _{2- y x} M _x O ₃ 2, 0 <y <2, 0 <x + y <2).

The target Ga _y Fe _{2 -yx} M _x O ₃ (0 <x <2, 0 <y <2, 0 <x + y <2) may be, for example, a high purity Ga ₂ O ₃ powder and Fe ₂ O ₃ In order to add about 0.1 atom% to about 20 atom% of the metal dopant in the powder, high purity metal oxide powder in the ammonia solution is uniformly mixed with the Ga ₂ O ₃ powder and Fe ₂ O ₃ powder in the milling system, To form a target mixture for forming. 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 A dry type dispersing machine such as a mill, a cutter mill, a hammer mill or a jet mill, or an ultrasonic dispersing machine or a high pressure homogenizer may be used. The grinding process through the milling system can be used to further atomize the iron oxide, gallium oxide, and metal oxide powder.

In forming the metal-doped gallium-iron oxide thin film using the pulsed laser deposition method, Ga _y Fe _{2 -yx} M _x O ₃ (0 <x <2, 0 <y <2, 0 <x + y < (0 < x < 2, 0 < y < 2, 0 < x + y < 2) can be formed by using Ga _x Fe _{2- yx} M _x O ₃ May be used in combination with an undoped Ga _{y '} Fe _2-y' O ₃ (0 <y '<2) target to form a doped gallium-iron oxide thin film. Moreover, the _{Ga y Fe 2 -yx M x O} 3 (0 <x <2, 0 <y <2, 0 <x + y <2) target, or a _{Ga y 'Fe 2 -y' O} 3 (0 < y &lt; 2) target and a 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.

After the target mixture for thin film formation is pulverized, an organic binder is added to compress the target mixture for thin film formation and sintered at a predetermined temperature to form the target.

The organic binder may be selected from, for example, polyvinyl alcohol, polyamide, polyvinyl acetate, polyvinyl butyral, polyvinyl pyrrolidone, polyester polyvinyl chloride, polyacryl, polyurethane, polycarbonate, But are not limited to, those selected from the group consisting of ethylene vinyl acetate, ethylene glycol, and combinations thereof.

The sintering process of the mixture may be carried out at a sintering temperature range of, for example, from about 1,100 캜 to about 1,500 캜, or from about 1,200 캜 to about 1,450 캜 for about 10 hours to about 20 hours, no.

Then, the energy density of the laser was set to be constant, and then the prepared thin film forming Ga _y Fe _{2 -y x} M _x O ₃ (0 <x <2, 0 <y <2, 0 <x + y < using a _{Ga y Fe 2 -yx M x O} 3 (0 <x <2, 0 <y <2, 0 <x + y <2) target material onto a substrate using a target by the metal under specific laser conditions A doped gallium iron oxide (GaFeO: M) thin film can be deposited. The substrate temperature to be deposited is between about 300 ° C. and about 1,000 ° C., and the specific deposition conditions are, for example, the wavelength of the laser of about 248 nm (KrF excimer laser), the repetition frequency of about 1 Hz to about 5 Hz, Instant 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 approximately 3 J / cm ² can be a road, and from about 3 cm to the substrate and a target distance of about 7 cm. In addition, since the oxygen deficiency of the thin film may cause leakage current, the deposition can be performed under background O ₂ pressure conditions of about 90 mTorr to about 110 mTorr to reduce leakage current.

The substrate _{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. The present invention is not limited thereto.

The metal-doped gallium-iron oxide (GaFeO: M) thin film forms a thin film having improved surface uniformity and denseness by a pulsed laser deposition process, so that the leakage current generated from the metal-doped gallium- have.

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

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

According to an embodiment of the present invention, the metal may be doped by substituting a part or all of the Fe ^{2 +} , but is not limited thereto.

In the case of gallium iron oxide (GaFeO, GFO), Fe coexist in the Fe ^{2 +} and Fe ^{3 +} states in the GFO. When the oxygen deficiency is as much as? In the GFO, the GFO has the structure of the following formula (3): &lt; EMI ID =

(3)

Ga _y Fe ^{2 + 2} _delta e ^{3 +} _{2-y-2 delta} O _{3- delta}

Electron transfer as shown in the following formula 2 occurs between Fe ^{2 +} and Fe ^{3 +} , and the electron transfer causes a leakage current in the GFO thin film.

[Formula 2]

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

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

[Chemical 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 invention, the electrical type as a semiconductor may be changed depending on the concentration of the doped metal. For example, the metal-doped gallium-iron oxide thin film of the present invention causes the movement of charge (e ^- ) or hole (h ^? ) By the mechanism of the following formula 3 or formula 4:

[Formula 3]

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

[Formula 4]

xAO? x (A ' _Fe + h? + 1 / 2O ₂ ).

In the above formulas 3 and 4, 隆 means oxygen deficiency amount, X means doped metal amount, A is a dopant, A 'is a cation state of a dopant, A' _Fe Means an A cation substituted in the Fe ^{2 +} site.

Combining the above-mentioned formula (3) and the above formula (4), the charge (e ^- ) or the hole (h˙) movement is caused by the mechanism of formula (5)

[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 an electrical carrier of the metal-doped gallium-iron oxide thin film. Accordingly, the electrical type of the metal-doped gallium-iron oxide thin film varies depending on the magnitude of the 2? And x values. For example, when 2?> X, the electrons e ^- become an electrical carrier and the metal-doped gallium-iron oxide thin film has an n-type electrical type, and when 2? Becomes an electrical carrier so that the metal-doped gallium-iron oxide thin film has a p-type electrical type.

FIG. 33 is a graph showing an 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 from FIG. 33, depending on the concentration of the doped metal, the metal-doped gallium-iron oxide thin film exhibited an n-type electrical type or a p-type electrical type. As described above, the metal-doped gallium-iron oxide thin film according to one embodiment of the present invention can change the electrical type according to the metal doping concentration, and by using this characteristic, the metal-doped gallium- It is possible to apply.

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

The metal-doped gallium-iron oxide thin film of the present invention 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 embodiment, Fe is replaced by Mg. It is known that Fe can be +2 or +3, while Mg is +2. The goal of this embodiment is to replace all +2 Fe cations induced by the oxygen approximation stoichiometry with Mg ^{2 +} cations. The Mg ^{2 +} radius is close to the Fe ^{2 +} radius. Then, a decrease in leakage current is expected, which is associated with a decrease in Fe ^{2 +} content and hence a decrease in the Fe ²⁺ / Fe ³⁺ hopping phenomenon.

A thin film was precisely fabricated by Pulsed Laser Deposition (PLD) using a KrF excimer laser with a λ = 248 nm repetition rate of 5 Hz. 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. The GFO: Mg layer, which is about 200 nm thick, is then heated to 200 mbar O ₂ Lt; / RTI &gt; 2 is a perspective view illustrating a structure of a memory device using a Mg-doped GFO thin film according to an embodiment of the present invention. After deposition of the 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 in the synthesis was formed by the reaction of Fe ₂ O ₃ , Ga ₂ O _3, and MgO. Stoichiometric milling was performed in an attritor mill for one hour in an ammonia solution (pH = 9). The solution was then placed in a drying oven until the liquid portion was completely evaporated. The resultant powder was manually pulverized. An organic binder (polyvinyl alcohol) was added in an amount of about 3 wt% to improve the mechanical behavior of the sample. The powder was finally compressed 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). The θ-2θ scan, φ-scan and reciprocal lattice mappings were measured using a Rigaku Smart Lab diffractometer equipped with rotating anode monochromatic copper radiation (Kα1 = 0.154056 nm). The surface morphology was measured by atomic force microscopy (AFM) using n-Tracer (Nanofocus Inc.). For electrical characterization, a platinum dot top electrode with a diameter of 0.2 mm was deposited by magnetron sputtering using a shadow mask on a GFO thin film at a pressure of 5 mTorr at room temperature. Then, the IV curve at room temperature was measured using a HP4145B semiconductor parameter analyzer in a voltage range of -10 V to 10 V.

The XRD measurement confirmed that the GFO: Mg thin film was epitaxially grown on the STO / SRO (111) substrate. Fig. 3 shows the &amp;thetas;-2&amp;thetas; pattern of the Mg-doped GFO thin film and shows the b -axis oriented epitaxial structure of the GFO. In fact, all predicted (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 surface cell parameter is shown in Figure 5 and shows a b value that is smaller than the bulk material (b _bulk = 9.3993 (3) A) [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 the average of at least 5 measurements performed at different locations on the samples and the standard deviation is less than 1% Wt.

[Table 2]

(a) composition by EDX

(b) Measurement in the θ-2θ pattern

The content of the metal atom (M) is an atomic amount measured by EDX, which means atomic percent, and M (%) = 100 x [M] / (M) + [Fe] + [Ga] . According to this definition, M (%) means the atomic% of the metal M contained in the GFO thin film, and thus the samples are referred to as GFO: Mg (0%), GFO: Mg (0.5% ) And GFO: Mg (7.5%). An image image at a scan area of 5 x 5 탆 ² or more is shown in Fig. FIG. 7 is a graph showing the RMS roughness of the Mg-doped GFO thin film, and the surface morphology shows that the crystal grains decrease uniformly as the Mg content increases. This surprising result was confirmed by the value of root mean square (rms) roughness of the GFO: Mg thin film. In fact, GFO: Mg (2.8%) and GFO: Mg (7.5%) exhibit somewhat higher values of rms (10.75 nm and 12.05 nm, respectively) %) Were 8.68 nm and 2.71 nm, respectively. The (204) lattice planes of STO and SRO and the (680) lattice planes of the GFO: Mg thin films were measured to determine the in-plane epitaxial relationship. All layers (STO, SRO and GFO) showed a 6-fold peak that exists every 60 °. These results can be explained by considering the following epitaxial relationships: SrTiO ₃ Forms a crystal with a cubic structure with a = 3.905 A, thereby forming a hexagonal pattern structure along [111]. At room temperature, SrRuO ₃ Form crystals with an orthorhombic structure, which can be described as somewhat twisted quasi-cubic perovskite cells with a = 3.92 A lattice parameter generally. As a result, the pattern following [111] is also a hexagon having apothem equal to 3.2 Å. The mismatch between STO and SRO is less than 1%. The different arrangements of the GFO crystals can be accounted for in terms of different matching possibilities between the GFO and the SRO lattice: on the other hand c _GFO ≈ 5.1 Å ≈ a _SRO × 2 ^0.5 (8% mismatch) and on the other hand a _GFO ? 8.7?? 3.2 3.2 (9% mismatch). The angle between the two GFO cells is about 60 degrees, which allows for the presence of three deformations. Measurements of in-plane cell parameters were measured by reciprocal space mapping (RSM). Measurements were performed on the (062) and (570) diffraction peaks and the results are shown in FIG. 5 and Table 2. Both the b- cell and c- cell parameters remained constant regardless of the Mg content. The a- cell parameters were increased for Mg content up to GFO: Mg (2.8%), and then remained constant.

Figure 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 by about 5 digits, from GFO: Mg (0.5%) to GFO: Mg (2.8%). This behavior, as a result of the substitution of Fe ^{2 +} for Mg ^{2 +} , reduced the likelihood of hopping between Fe ^{2 +} and Fe ^{3 +} in the structure. At higher Mg concentrations, an increase in leakage current was observed again: when the Mg content increased from 2.8% to 7.5%, the leakage current increased again by about three orders of magnitude. FIG. 9 shows a lattice structure of the Mg-doped GFO thin film, and the change in leakage current as a function of doping concentration is shown in FIG. As described above, this aspect is characterized by a strong decrease in leakage current up to GFO: Mg (2.8%) and an increase in leakage current for higher doping content. This behavior can be interpreted using the Kroger-Vink notation. In fact, the production of delta oxygen defects during the growth process can usually occur 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 shows the formation of holes:

Where Mg ' _Fe means Mg in the Fe site with apparent negative charge, and h˙ denotes the hole. Then, according to the above notation, the decrease in leakage current up to GFO: Mg (2.8%) may be due to recombination, which increases between holes and electrons. Therefore, the charge carriers responsible for the leakage current are electrons (i.e., n-type electrical types with d> x). For higher content doping, the observed behavior should be related to the increasing presence of holes (i.e., p-type electrical type with x> d).

11 is a Piezoelectric Force Microscopy (PFM) image of a Mg-doped GFO thin film. This is the PFM image of the Mg 2.5% sample with the smallest leakage current.

Figure 12 is a local P-E hysteresis curve (at 1 Hz frequency) obtained using PFM of Mg-doped GFO thin films. The local P-E hysteresis curves obtained from Pt-coated AFM probes show that ferroelectric properties may appear in Mg-doped GFO films.

As a result, Mg-doped GFO thin films were prepared by pulsed laser deposition with Mg contents of up to 7.5 at%. X-ray measurements showed complete epitaxial growth of Mg-doped GFO thin films on the SRO buffer layer with parasitic phase. This example demonstrated an optimum Mg content of 2.8 at%, which shows a sharp decrease in leakage current by 5 digits. This reduction in leakage current is very promising for future possible self-electrical characterization of elaborate thin films. The aspect of the leakage current suggests an evolution from n-type to p-type electrical type with increasing doping content. These results suggest the possibility of developing a new class of materials of materials exhibiting non-zero magnetization at room temperature, controllable transfer characteristics and magnetostatic properties.

[ 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 Except that a GFO: Mn layer was formed using a Fe _{1 .4 - x} Mn _x O ₃ target.

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

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

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

16 is a current-voltage curve of the Mn-doped GFO thin film according to this embodiment. Leakage current was also reduced when Mn was doped and the smallest leakage current was measured when 2% doped. When 10% Mn was doped, the leakage current slightly increased, which was the same tendency in the 7.5% Mg doped GFO thin film but the amount of increasing leakage current was smaller.

17 is a Piezoelectric Force Microscope (PFM) image of an Mn-doped GFO thin film according to this embodiment. It is the PFM image of the sample with the lowest leakage current of Mn 2%.

18 is a local P-E hysteresis curve (at 1 Hz frequency) obtained using the PFM of the Mn-doped GFO thin film according to this embodiment. The graph shows that the local PE hysteresis curve obtained by using Pt-coated AFM probe of 2% Mn sample with the smallest leakage current shows that ferroelectric characteristics can be exhibited as well as Mg doping in Mn-doped GFO thin films Respectively.

19 is a PE hysteresis curve of the Mn-doped GFO thin film according to this embodiment. In the 10% Mn doped GFO thin film, the nonlinear PE hysteresis curves were shown but the polarization was relaxed.

[ Example  3] Ni - Doped GFO  pellicle

A SrRuO ₃ (SRO) conductive layer is deposited on a SrTiO ₃ (111) substrate (Crystec), and a Ga ₀ .05 layer 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 ₃ target to form a GFO: Ni layer.

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

21 is a graph showing the RMS roughness of the Ni-doped GFO thin film according to this embodiment. The Ni-doped GFO thin films showed remarkably reduced RMS roughness and the smallest value in the Ni doped thin films.

22 is a video image of a Ni-doped GFO thin film according to this embodiment.

23 is a current-voltage curve of the Ni-doped GFO thin film according to this embodiment. Ni-doped GFO thin films also showed a decrease in leakage current. A small leakage current was also measured in a sample with a second phase peak in XRD than in an undoped GFO thin film. The smallest leakage current was measured in a 0.5% Ni doped thin film without any secondary peak.

[ Example  4] Co - Doped GFO  pellicle

SrTiO ₃ (111) was deposited ₃ (SRO) conductive layer SrRuO on a substrate (Crystec), on the SrRuO ₃ (SRO) conductive layer _{Fe 2 O 3, Ga 2 O} 3 and Ga ₀ formed by the reaction of _{CoO. 6} Fe _{1 .4 - x} Co _x O ₃ target to form a GFO: Co layer.

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

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

26 is a video 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 Microscope (PFM) image of a Co-doped GFO thin film according to this embodiment. This is the PFM image of the Co 2% sample with the smallest leakage current.

29 is a local PE hysteresis curve (at 1 Hz frequency) obtained using the PFM of a Co-doped GFO thin film according to this example. This is the PE hysteresis curve of the Co 2% sample with the smallest leakage current. The local PE hysteresis curves obtained with Pt-coated AFM probes indicate that ferroelectric properties may be present as well as Mn or Mg doping in Co-doped GFO films.

[ Example  5] Bi - Doped GFO  pellicle

SrTiO ₃ (111) was deposited ₃ (SRO) conductive layer SrRuO on a substrate (Crystec), on the SrRuO ₃ (SRO) conductive layer _{Fe 2 O 3, Ga 2 O} 3 and Ga ₀ formed by the reaction of _BiO. Except that a GFO: Bi layer was formed using a ₆ Fe _{1 .4 - x} Bi _x O ₃ target.

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

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

32 is an image of a Bi-doped GFO thin film according to this 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 (6)

As iron oxide, gallium oxide, and by reacting a metal oxide formed mixed powder for thin film deposition target by adding an organic binder to the _{Ga y Fe 2-yx M x} O 3 (0 <x <2, 0 <y <2, 0 < x + y &lt;2); And
Forming a metal-doped gallium iron oxide (GaFeO: M) thin film by depositing by epitaxial growth on the substrate using the pulse laser deposition method using the target for thin film formation;
/ RTI &gt;
The metal oxide may be selected from the group consisting of Co, Mn, Ni, Bi, Ca, Sr, Sc, V, Cr, Pb, Cu, Mo, Si, Ta, Ti, W, Zr, Ge, And an oxide of a metal to be oxidized,
Wherein the metal-doped gallium-iron oxide thin film comprises Fe ²⁺ or Fe ³⁺ , or Fe ²⁺ and Fe ³⁺ ,
The metal is doped by substituting a part or all of the Fe &lt; ^{2 +} &gt;
Wherein the metal-doped gallium-iron-oxide (GaFeO: M) thin film contains 0.1 atomic percent (atomic percent) to 10 atomic percent of the metal,
A method for manufacturing a metal-doped gallium-iron oxide thin film.
The method according to claim 1,
Wherein the pulsed laser deposition method is performed at a temperature of 750 ° C to 1,000 ° C.
The method according to claim 1,
Wherein the pulsed laser deposition method is performed in an oxygen atmosphere.
As a metal-doped gallium iron oxide (GaFeO: M) thin film,
Wherein the metal-doped gallium-iron oxide thin film comprises Fe ²⁺ or Fe ³⁺ , or Fe ²⁺ and Fe ³⁺ ,
^Wherein the metal is doped by substituting a part or all of the Fe ²⁺ ,
Wherein the metal is selected from the group consisting of Co, Mn, Ni, Bi, Ca, Sr, Sc, V, Cr, Pb, Cu, Mo, Si, Ta, Ti, W, Zr, Ge, &Lt; / RTI &gt;
The metal-doped gallium-iron-oxide (GaFeO: M) thin film contains 0.1 atomic percent to 10 atomic percent of the metal to reduce the leakage current,
Wherein said metal-doped gallium &lt; RTI ID = 0.0 &gt; iron oxide &lt; / RTI &gt; thin film is produced by the process according to any one of claims 1 to 3,
Metal-doped gallium-iron oxide thin films.
5. The method of claim 4,
Wherein the metal-doped gallium-iron oxide thin film is ferroelectric.
A memory element comprising the metal-doped gallium-iron oxide thin film according to claim 4.

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