Nano flake defect passivation method and electronic device manufactured using the same

Abstract

Provided is method of manufacturing a conductive film. The method includes forming a conductive film including a plurality of flakes on a substrate, wherein the conductive film is a semiconductor or a conductor, and forming a passivation region selectively on a boundary between the flakes adjacent to each other. The passivation region includes a metal compound selected from the group consisting of metal chalcogenide and transition metal chalcogenide. The forming of the passivation region includes providing a solution containing a first precursor including a cation of the metal compound and a second precursor including an anion of the metal compound on the conductive film. pH of the solution is between 7.0 and 10.0.

Claims

1. A method of manufacturing a conductive film, the method comprising: forming a conductive film including a plurality of flakes on a substrate, wherein the conductive film is a semiconductor or a conductor; and forming a passivation region selectively on a boundary between the flakes adjacent to each other, wherein the passivation region comprises a metal compound selected from the group consisting of metal chalcogenide and transition metal chalcogenide, wherein the forming of the passivation region comprises providing a solution containing a first precursor including a cation of the metal compound and a second precursor including an anion of the metal compound on the conductive film, wherein pH of the solution is between 7.0 and 10.0.

2. The method of claim 1, wherein the metal compound is represented by a formula of M.sub.aX.sub.b, where M comprises Zn or Cd, X comprises S, Se, O or Te, and a and b are independently an integer of 1 or more.

3. The method of claim 1, wherein a ratio of a molar concentration of an anion of the metal compound to a molar concentration of a cation of the metal compound in the solution is 9 to 20.

4. The method of claim 1, wherein the boundary is a grain boundary.

5. The method of claim 1, wherein each of the flakes comprises metal chalcogenide, transition metal chalcogenide, or graphene, wherein each of the flakes has a monolayer, or a multi-layer where two to ten monolayers are stacked.

6. The method of claim 1, wherein the forming of the conductive film comprises: exfoliating metal chalcogenide, transition metal chalcogenide, or graphene to form the flakes dispersed in a solution; and uniformly providing the flakes on the substrate.

7. The method of claim 1, wherein the passivation region is formed in a plurality and is arranged along the boundary.

8. The method of claim 1, wherein the passivation region is not formed on upper surfaces of the flakes.

9. The method of claim 1, wherein the flakes adjacent to each other are spaced apart from each other with the boundary therebetween, wherein the passivation region is formed to fill the boundary to connect the flakes adjacent to each other.

10. The method of claim 1, wherein the flakes adjacent to each other comprise a first flake and a second flake on the first flake, wherein the second flake covers at least a portion of an upper surface of the first flake, wherein the boundary is defined at an edge of the second flake on the upper surface of the first flake.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The accompanying drawings are included to provide a further understanding of the inventive concept, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the inventive concept and, together with the description, serve to explain principles of the inventive concept. In the drawings:

(2) FIGS. 1 and 3 are plan views illustrating a method of manufacturing a conductive film according to embodiments of the inventive concept;

(3) FIGS. 2 and 4 are cross-sectional views taken along the line A-A in FIGS. 1 and 3, respectively;

(4) FIG. 5 is a cross-sectional view schematically showing a system in which deposition is performed by a chemical reaction in a solution;

(5) FIGS. 6 and 8 are plan views illustrating a method of manufacturing a conductive film according to embodiments of the inventive concept;

(6) FIGS. 7 and 9 are cross-sectional views taken along the line A-A in FIGS. 6 and 8, respectively;

(7) FIG. 10 is a cross-sectional view taken along the line A-A in FIG. 8 for illustrating a conductive film according to an embodiment of the inventive concept;

(8) FIG. 11 is a cross-sectional view taken along the line A-A in FIG. 8 for illustrating a conductive film according to another embodiment of the inventive concept;

(9) FIG. 12 is a plan view for explaining an electronic device according to embodiments of the inventive concept;

(10) FIG. 13 is a cross-sectional view taken along a line A-A of FIG. 12; and

(11) FIG. 14 is a graph showing resistance according to channel lengths of a conductive film according to an embodiment of the inventive concept and a conductive film according to a comparative example.

DETAILED DESCRIPTION

(12) In order to fully understand the configuration and effects of the technical spirit of the inventive concept, preferred embodiments of the technical spirit of the inventive concept will be described with reference to the accompanying drawings. However, the technical spirit of the inventive concept is not limited to the embodiments set forth herein and may be implemented in various forms and various modifications may be applied thereto. Only, the technical spirit of the inventive concept is disclosed to the full through the description of the embodiments, and it is provided to those skilled in the art that the inventive concept belongs to inform the scope of the inventive concept completely.

(13) It will also be understood that when a layer (or film) is referred to as being on another layer or substrate, it may be directly on the other layer or substrate, or intervening layers may also be present. Additionally, in the drawings, the thicknesses of components are exaggerated for effective description. Like reference numerals refer to like elements throughout the specification.

(14) It will be understood that the terms first and second are used herein to describe various components but these components should not be limited by these terms. These terms are just used to distinguish a component from another component. Embodiments described herein include complementary embodiments thereof.

(15) The terms used in this specification are used only for explaining specific embodiments while not limiting the inventive concept. The terms of a singular form may include plural forms unless referred to the contrary. The meaning of comprises, and/or comprising in this specification specifies the mentioned component but does not exclude at least one another component.

(16) FIGS. 1 and 3 are plan views illustrating a method of manufacturing a conductive film according to embodiments of the inventive concept. FIGS. 2 and 4 are cross-sectional views taken along the line A-A in FIGS. 1 and 3, respectively. FIG. 5 is a cross-sectional view schematically showing a system in which deposition is performed by a chemical reaction in a solution.

(17) Referring to FIGS. 1 and 2, a conductive film 110 may be formed on a substrate 100. The substrate 100 may be a semiconductor substrate, a glass substrate, or a polymer substrate. However, the inventive concept is not limited thereto, and the type of the substrate 100 may be variously changed. The conductive film 110 may include a plurality of flakes NF. In other words, the flakes NF formed on the substrate 100 may constitute the conductive film 110. The conductive film 110 may be a semiconductor or a conductor.

(18) Each flake NF may include a metal chalcogenide, a transition metal chalcogenide, or a graphene. The metal chalcogenide or transition metal chalcogenide may be a metal compound represented by the formula M.sub.yX.sub.z (for example, y and z are an integer of 1, 2 or more). In the above formula, M is a metal or a transition metal atom, and may include, for example, W, Mo, Ti, Zn, V or Zr. X is a chalcogen atom and may include, for example, S, Se, O or Te. In one example, each flake NF may include one selected from the group consisting of graphene, MoS.sub.2, MoSe.sub.2, MoTe.sub.2, WS.sub.2, WSe.sub.2, WTe.sub.2, ReS.sub.2, ReSe.sub.2, TiO.sub.2, TiS.sub.2, TiSe.sub.2, TiTe.sub.2, ZnO, ZnS.sub.2, ZnSe.sub.2, WO.sub.3, VS.sub.2, VSe.sub.2, VO.sub.2, V.sub.2O.sub.5, and MoO.sub.3.

(19) Each flake NF may have a monolayer, or a multi-layer in which two to ten layers are stacked. In other words, each flake NF may have a two-dimensional structure. As an example, each flake NF may have a monolayer of metal chalcogenide or a transition metal chalcogenide. As an example, each flake NF may have a multi-layer having a first monolayer and a second monolayer stacked on the first monolayer. Here, a monolayer refers to a layer having a formula of MX.sub.2 when a metal decalcogenide is used as an example. In this case, the first monolayer and the second monolayer in the flake NF may be bonded to each other by a van der Waals force.

(20) The flakes NF may contain the same material. In other words, the flakes NF may have the same composition with each other. The flakes NF may have the same crystal structure or different crystal structures. For example, the crystal structure may include a hexagonal lattice structure, a triangular lattice structure, an orthorhombic lattice structure, and a modified tetragonal (monoclinal) lattice structure. Each of the flakes NF according to this embodiment may be a nanosheet. An air gap AG may be interposed between the flake NF and the substrate 100. Alternatively, the air gap AG may be interposed between the stacked flakes NF.

(21) A boundary defects BD may be defined between neighboring flakes NF. Since the nanosheet flakes may break off from the big chunk and break off along their edges, defects may occur. The boundary defect BD may be the edge of the flake NF. In the case of the flakes NF composed of several layers, the boundary defect BD may be a terrace. The boundary defects BD in the conductive film 110 may act as defects that interfere with the charge flow or that capture the charges before the charges are collected on the electrode. By the boundary defects BD as described above in the conductive film 110 composed of flakes, the charge mobility, electrical conductivity, and thermal conductivity of the film 110 may be reduced.

(22) In one embodiment, the liquid phase exfoliation method may be used to form the conductive film 110. Specifically, ultrasonic waves may be applied to a transition metal chalcogenide, a metal chalcogenide, or a graphite in a solution having a condition for liquid phase exfoliation. The raw materials are compounds which have a weak Van der Waals bonding force between single layers and are easily exfoliated by ultrasonic waves or the like. The metal chalcogenide, transition metal chalcogenide or graphene may be separated and dispersed in solution in the form of the flakes NF. The dispersion solution may be centrifuged to remove the precipitate and the flakes NF may be obtained from the remaining solution. The conductive film 110 may be formed by uniformly providing the obtained flakes NF on the substrate 100.

(23) Referring to FIGS. 3, 4 and 5, passivation regions PR may be formed on the boundary defects BD of the conductive layer 110. The passivation regions PR may be selectively provided only on the boundary defects BD of the conductive film 110. For example, the passivation region PR may not be formed on the upper surface having no boundary defects of the flake NF. Thus, the upper surface of each flake NF may be exposed.

(24) At least one passivation region PR may be formed on the boundary defect BD. A plurality of passivation regions PR may be arranged along the boundary defect BD. Neighboring flakes NF may be interconnected by at least one passivation region PR therebetween. The passivation region PR may be interconnected to neighboring another PR.

(25) Each of the passivation regions PR may include metal compounds selected from the group consisting of metal chalcogenides and transition metal chalcogenides. Each of the passivation regions PR may include a metal compound represented by the formula of M.sub.aX.sub.b. M is a metal or transition metal atom, and may include, for example, Zn or Cd. X is a chalcogen atom and may include, for example, S, Se, O or Te. a and b independently may be an integer of 1 or more. a and b independently may be an integer of 1 to 10. As an example, the passivation region PR may include transition metal chalcogenides such as ZnS, ZnO, ZnSe, CdSe, or CdS. The passivation region PR may include the same or different material than the flake NF of the conductive film 110.

(26) As described above, a two-dimensional defect occurs due to a boundary defect BD between adjacent flakes NF, so that the electrical conductivity and charge mobility between adjacent flakes NF may be reduced. Meanwhile, the passivation region PR according to the inventive concept may be provided on the boundary defect BD to electrically connect neighboring flakes NF. This may increase the electrical conductivity and charge mobility between adjacent flakes NF. Furthermore, since the passivation region PR is not provided on the upper surface of the flake NF except for the boundary defect BD, the electrical characteristics of the flake NF may not be impaired. As a result, the electrical characteristics of the conductive film 110 according to the inventive concept may be improved.

(27) The formation of passivation regions PR according to the present embodiment may use a chemical solution deposition method. The formation of passivation regions PR according to the present embodiment may use a chemical bath deposition (CBD), which is a kind of chemical solution deposition. Specifically, referring again to FIG. 5, a solution SOL may be provided in a bath BAT. The solution SOL may include precursors of a metal compound and a chalcogen compound. The substrate 100 fixed by a holder HO may be provided in the solution SOL. A deposition reaction occurs on the substrate 100, so that passivation regions PR may be formed. The deposition reaction may be performed at a temperature of 20 C. to 100 C.

(28) The solution SOL may include a first precursor and a second precursor. The first precursor may include M-cations for forming the metal compound (M.sub.aX.sub.b). In one example, the first precursor may be metal sulfate or metal acetate. As an example, the first precursor may include zinc sulfate or cadmium acetate. The second precursor may include X-anions for forming a metal compound (MaXb). In one example, the second precursor may include a thiourea. The solution SOL may further include ammonium acetate as a buffer.

(29) Reaction occurs between the first precursor and the second precursor in the solution SOL on the substrate 100 to form deposits so that passivation regions PR may be formed. According to embodiments of the inventive concept, the reaction rate of the deposition reaction may be lowered so that passivation regions PR are selectively formed only on the boundary defects BD of the conductive film 110. In other words, in relation to the formation of the passivation regions according to the inventive concept, it is possible to selectively form the passivation regions PR on the boundary defects BD by controlling the reaction rate of the deposition reaction.

(30) The upper surfaces of the flakes NF may be chemically stable sites, but the boundary defects BD between the flakes NF may be chemically unstable sites. In other words, the upper surfaces of the flakes NF may be less reactive sites, and the boundary defects BD of the flakes NF may be highly reactive sites.

(31) When the reaction rate of the deposition reaction is lowered, the reactivity of the deposition reaction may be lowered. Thus, the deposition reaction may not occur on the upper surfaces of the flakes NF, which are chemically stable sites. On the other hand, the deposition reaction may occur only on the boundary defects BD, which are chemically unstable sites. As a result, the passivation regions PR may be selectively formed only on the boundary defects BD of the conductive film 110.

(32) In one example, lowering the reaction rate of the deposition reaction may include adjusting the pH of the solution SOL close to neutral. pH of the solution SOL may be adjusted to 7.0 to 10.0. The solution SOL may include a pH adjusting agent for adjusting pH, and pH of the solution SOL may be adjusted by adjusting the content of the pH adjusting agent. The pH adjusting agent may include a compound containing a hydroxyl group (OH), for example, ammonium hydroxide (NH.sub.4OH).

(33) When pH of the solution SOL is high (for example, pH>10), the reaction rate of the deposition reaction may be relatively high. When pH of the solution SOL is high, the deposition reaction may occur nonselectively on the upper surfaces of the flakes NF, thereby forming a passivation film covering the upper surfaces of the flakes NF.

(34) On the other hand, when pH of the solution SOL is low (for example, pH is 7.0 to 10), the reaction rate of the deposition reaction may be relatively low. When pH of the solution SOL is low, the deposition reaction occurs only on the boundary defects BD so that passivation regions PR may be selectively formed only on the boundary defects BD. As a result, by adjusting pH of the solution SOL to 7.0 to 10, passivation regions PR may be selectively formed only on the boundary defects BD of the conductive film 110. When pH of the solution SOL is 7.0 to 9.0, a reaction having high selectivity occurs, and a passivation region may be selectively formed only on the boundary defect BD.

(35) As another example, lowering the reaction rate of the deposition reaction may include adjusting the ratio of the second precursor to the first precursor of solution SOL. The ratio (i.e., [X]/[M]) of the molar concentration of the X-anions to the molar concentration of the M-cations in the solution SOL may be 9 to 20. For example, when the concentration of M-cations in the solution SOL is 0.01 M, the concentration of X-anions may be 0.09 M to 0.2 M. When the ratio (i.e., [X]/[M]) of the molar concentration of the X-anions to the molar concentration of the M-cations in the solution SOL is 10 to 20, a reaction with high selectivity may occur.

(36) The concentration of the X-anions in the solution SOL may be inversely proportional to the reaction rate of the deposition reaction. When the ratio of the X-anion to the M-cation in the solution SOL is relatively small (e.g., 1 to 8), the reaction rate of the deposition reaction may be relatively high. When the ratio of the X-anion to the M-cation in the solution SOL is relatively small, the deposition reaction occurs on the upper surfaces of the flakes NF, thereby forming a passivation film covering the upper surfaces of the flakes NF.

(37) When the ratio of the X-anion to the M-cation in the solution SOL is relatively large (e.g., 9 to 20), the reaction rate of the deposition reaction may be relatively small. When the ratio of the X-anion to the M-cation in the solution SOL is relatively large, the deposition reaction occurs only on the boundary defects BD, so that passivation regions PR may be selectively formed only on the boundary defects BD. As a result, by adjusting the ratio of the X-anion to the M-cation in the solution SOL to 9 to 20, passivation regions PR may be selectively formed only on the boundary defects BD of the conductive film 110.

(38) In another embodiment of the inventive concept, formation of the passivation regions PR may be accomplished through dipping, drop casting, spray coating, or spin coating methods using the above-described solution SOL.

(39) FIGS. 6 and 8 are plan views illustrating a method of manufacturing a conductive film according to embodiments of the inventive concept. FIGS. 7 and 9 are cross-sectional views taken along the line A-A in FIGS. 6 and 8, respectively. In this embodiment, the detailed description of the technical features overlapping with those described with reference to FIGS. 1 to 5 will be omitted, and the differences will be described in detail.

(40) Referring to FIGS. 6 and 7, a conductive film 110 may be formed on a substrate 100. The conductive film 110 may include a plurality of flakes NF. The conductive film 110 may be a semiconductor or a conductor. Each of the flakes NF according to this embodiment may be a crystal grain. For example, the conductive film 110 may be formed through a vapor deposition method. In other words, the conductive film 110 may be deposited directly on the substrate 100.

(41) Specifically, the flakes NF may include first to third flakes NF1, NF2, and NF3. The first to third flakes NF1, NF2, and NF3 may be disposed adjacent to each other in one direction. The first flake NF1 and the second flake NF2 may be crystal grains having different orientations and the second flake NF2 and the third flake NF3 may be crystal grains having different orientations. A first boundary defect BD1 may be defined between the first and second flakes NF1 and NF2 and a second boundary defect BD2 may be defined between the second and third flakes NF2 and NF3. For example, the first boundary defect BD1 and the second boundary defect BD2 may be grain boundaries. In other words, the grain boundary may also act as a defect.

(42) Referring to FIGS. 8 and 9, at least one passivation region PR may be formed in the first boundary defect BD1 and at least one passivation region PR may be formed in the second boundary defect BD2. A plurality of passivation regions PR may be arranged along the first boundary defect BD1. A plurality of passivation regions PR may be arranged along the second boundary defect BD2. The first flake NF1 and the second flake NF2 may be connected to each other by at least one passivation region PR of the first boundary defect BD1. The second flake NF2 and the third flake NF3 may be connected to each other by at least one passivation region PR of the second boundary defect BD2. Formation of the passivation regions PR may be substantially the same as that described with reference to FIGS. 3 to 5 above.

(43) FIG. 10 is a cross-sectional view taken along the line A-A in FIG. 8 for illustrating a conductive film according to an embodiment of the inventive concept. FIG. 11 is a cross-sectional view taken along the line A-A in FIG. 8 for illustrating a conductive film according to another embodiment of the inventive concept. In this embodiment, the detailed description of the technical features overlapping with those described with reference to FIGS. 6 to 9 will be omitted, and the differences will be described in detail.

(44) Referring to FIGS. 8 and 10, at least a portion of the first flake NF1 and at least a portion of the second flake NF2 may be spaced apart from each other with the first boundary defect BD1 therebetween. At least a portion of the second flake NF2 and at least a portion of the third flake NF3 may be spaced apart from each other with the second boundary defect BD2 therebetween. The first boundary defect BD1 and the second boundary defect BD2 may expose a portion of the upper surface of the substrate 100.

(45) The passivation region PR may fill each of the first boundary defect BD1 and the second boundary defect BD2. The passivation region PR may cover a portion of the upper surface of the exposed substrate 100. By the passivation region PR, at least a portion of the first flake NF1 and at least a portion of the second flake NF2 may be electrically connected to each other. By the passivation region PR, at least a portion of the second flake NF2 and at least a portion of the third flake NF3 may be electrically connected to each other.

(46) Referring to FIGS. 8 and 11, the third flake NF3 may be provided on the second flake NF2. The third flake NF3 may cover at least a portion of the upper surface of the second flake NF2. The second boundary defect BD2 may be defined on one side of the third flake NF3. The second boundary defect BD2 may be defined on the upper surface of the second flake NF2.

(47) The passivation region PR may be provided on the second boundary defect BD2. The passivation region PR may cover one side of the third flake NF3 and a portion of the upper surface of the second flake NF2. By the passivation region PR, the second flake NF2 and the third flake NF3 may be electrically connected to each other.

Experimental Example

(48) MoS.sub.2 single crystals were put into an aqueous solution mixed with a surfactant or an alcohol, and ultrasonic waves were applied to exfoliate thin flakes composed of one or more layers. An organic solvent may be used instead of the aqueous solution. By using centrifugation, precipitates that are not exfoliated were removed and MoS.sub.2 flakes were separated from the remaining solution. The MoS.sub.2 flakes were uniformly provided on the glass substrate to form a MoS.sub.2 film. The MoS.sub.2 film is composed of a plurality of flakes.

(49) A solution SOL was prepared in the bath BAT shown in FIG. 5. The solution SOL was prepared by mixing zinc sulfate (ZnSO.sub.4) as the first precursor and thiourea as the second precursor. The concentration of zinc sulfate in the solution SOL was adjusted to 10 mM and the concentration of thiourea in the solution SOL was adjusted to 100 mM. By using NH.sub.4OH as the pH adjusting agent, pH of the solution SOL was adjusted to 7.5 to 9.5. The temperature of the solution SOL in the bath BAT was adjusted to about 70 C.

(50) The substrate on which the MoS.sub.2 film was formed was immersed in the solution SOL of the bath BAT and the deposition reaction of ZnS was performed. The solution SOL was continuously stirred through a stirrer SIT during the reaction time. The substrate where the ZnS deposition was completed was washed with ethanol and distilled water.

(51) As a result of examining the substrate washed with an AFM image, it was confirmed that ZnS particles (or patterns) were selectively formed at the boundary between MoS.sub.2 flakes as illustrated in FIG. 3. ZnS particles were not formed on the upper surfaces of the MoS.sub.2 flakes.

(52) FIG. 12 is a plan view for explaining an electronic device according to embodiments of the inventive concept. FIG. 13 is a cross-sectional view taken along a line A-A of FIG. 12. In this embodiment, the detailed description of the technical features overlapping with those described with reference to FIGS. 1 to 5 will be omitted, and the differences will be described in detail.

(53) Referring to FIGS. 12 and 13, a conductive film 110, a first electrode EL1, and a second electrode EL2 may be provided on a substrate 100. The conductive film 110 may be the same as the conductive film 110 described with reference to FIGS. 3 and 4 above. The conductive film 110 may include flakes NF and passivation regions PR selectively provided on the boundary defects BD of the flakes NF.

(54) The conductive film 110 is provided between the first electrode EL1 and the second electrode EL2 to electrically connect them. A carrier (e.g., an electron or a hole) may move between the first electrode EL1 and the second electrode EL2 through the conductive film 110. In relation to the conductive film 110 according to the present embodiment, since the grain boundaries are passivated through the passivation regions PR, a current may smoothly flow in proportion to a voltage difference between the first electrode EL1 and the second electrode EL2. An electronic device according to this embodiment may be used as a photoelectric device or a semiconductor device.

(55) FIG. 14 is a graph showing resistance according to channel lengths of a conductive film according to an embodiment of the inventive concept and a conductive film according to a comparative example. Resistance according to the length (i.e., channel length) of the conductive film 110 of the electronic device shown in FIGS. 12 and 13 was measured (Embodiment). Meanwhile, unlike the conductive film 110 of FIGS. 12 and 13, an electronic device using a conductive film where passivation regions PR are omitted is prepared. The resistance according to the length (i.e., the channel length) of the conductive film was measured (Comparative Example). The results are shown in FIG. 14.

(56) Referring to FIG. 14, it may be confirmed that the current flowing through the channel is more than twice as the electronic device according to the embodiment of the inventive concept is compared with the electronic device according to the comparative example which is not passivated.

(57) The method for manufacturing a conductive film according to the inventive concept may selectively passivate defects in a conductive film to improve its electrical characteristics. Selective passivation of defects in a conductive film may be achieved by adjusting the reaction rate of the deposition reaction in a solution without complex processes and reactors. In relation to selective defect passivation, the passivation region is formed only in the defective region and does not hinder the characteristics of the conductive film. Selective defect passivation passivates only defects, and the passivation material does not replace the properties of the conductive film.

(58) Although the exemplary embodiments of the inventive concept have been described, it is understood that the inventive concept should not be limited to these exemplary embodiments but various changes and modifications may be made by one ordinary skilled in the art within the spirit and scope of the inventive concept as hereinafter claimed.