Method of manufacturing thermochromic substrate

Abstract

A method of manufacturing a thermochromic substrate, with which transmittance can be increased. The method includes the steps of forming a first thin film as a coating on a base substrate, the refractive index of the first thin film being different from that of a VO.sub.2 thin film; forming a pre-thermochromic thin film by coating the first thin film with pure vanadium; forming a second thin film as a coating on the pre-thermochromic thin film, the refractive index of the second thin film being different from that of a VO.sub.2 thin film; and heat-treating a resultant stack that includes the base substrate, the first thin film, the pre-thermochromic thin film and the second thin film.

Claims

1. A method of manufacturing a thermochromic substrate, comprising: coating a base substrate with a first thin film; coating the first thin film with a pre-thermochromic thin film, the pre-thermochromic thin film comprising a composition having a formula A.sub.xB.sub.z, where A is a metal, and B is oxygen, and x and z are relative molar proportions of the metal A and of oxygen, respectively, wherein z can be zero or greater; coating the pre-thermochromic thin film with a second thin film, wherein each of the first thin film and the second thin film comprises at least one of a transparent oxide thin film or a transparent nitride thin film, the transparent oxide thin film or the transparent nitride thin film comprises at least one selected from the group consisting of silicon dioxide (SiO.sub.2), niobium pentoxide (Nb.sub.2O.sub.5), aluminum oxide (Al.sub.2O.sub.3), titanium dioxide (TiO.sub.2), and silicon nitride (Si.sub.3N.sub.4), and at least one of the first thin film and the second thin film comprises an oxide thin film; and modifying the pre-thermochromic thin film into a thermochromic thin film having a formula A.sub.xB.sub.y, where x and y are relative molar proportions of the metal A and of oxygen, respectively, wherein a ratio of y to x in the formula for the thermochromic thin film is greater than a ratio of z to x in the formula for the pre-thermochromic thin film, the thermochromic thin film being one selected from the group consisting of vanadium dioxide (VO.sub.2), titanium oxide (III) (Ti.sub.2O.sub.3) and niobium oxide (NbO.sub.2), by heat-treating a resultant stack that includes the base substrate, the first thin film, the pre-thermochromic thin film and the second thin film, wherein heat-treating the resultant stack makes oxygen diffuse from at least one of the first thin film and the second thin film into the pre-thermochromic thin film, so that the pre-thermochromic thin film is modified into the thermochromic thin film, wherein each refractive index of the first thin film and the second thin film is different from that of the thermochromic thin film.

2. The method of claim 1, wherein z is 0.

3. The method of claim 1, wherein the pre-thermochromic thin film is formed by coating the first thin film with vanadium (V) while providing oxygen.

4. The method of claim 1, wherein the pre-thermochromic thin film comprises pure vanadium, which is to be converted into vanadium dioxide (VO.sub.2) by heat-treating the resultant stack.

5. The method of claim 1, wherein each thickness of the first thin film, the pre-thermochromic thin film and the second thin film ranges from 30 nm to 80 nm.

6. The method of claim 1, wherein heat-treating the resultant stack is performed in an argon (Ar) or vacuum atmosphere.

7. The method of claim 1, wherein heat-treating the resultant stack is performed at a temperature ranging from 400 C. to 500 C.

8. The method of claim 7, wherein heat-treating the resultant stack is performed for 20 to 120 minutes.

9. The method of claim 1, wherein coating with the first thin film and coating with the second thin film are performed via reactive sputtering deposition.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flowchart schematically depicting a method of manufacturing a thermochromic substrate according to an exemplary embodiment of the invention;

(2) FIG. 2 is a graph comparatively depicting the transmittance of thermochromic substrates having a multilayer film structure, each of which is manufactured according to an example of the invention, and the transmittance of a thermochromic substrate having only a vanadium dioxide (VO.sub.2) thin film;

(3) FIG. 3 is a graph depicting the thermochromic characteristics of a thermochromic substrate having a multilayer structure, which is manufactured by a method of the related art; and

(4) FIG. 4 is a graph depicting the thermochromic characteristics of a thermochromic substrate having a multilayer structure, which is manufactured according to an example of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(5) Reference will now be made in detail to a method of manufacturing a thermochromic substrate according to the present invention, embodiments of which are illustrated in the accompanying drawings and described below.

(6) In the following description of the present invention, detailed descriptions of known functions and components incorporated herein will be omitted when they may make the subject matter of the present invention unclear.

(7) FIG. 1 is a flowchart schematically depicting a method of manufacturing a thermochromic substrate according to an exemplary embodiment of the invention.

(8) Referring to FIG. 1, the method of manufacturing a thermochromic substrate according to an exemplary embodiment of the invention may include the step of forming a first thin film, forming a pre-thermochromic thin film, forming a second thin film, and heat-treating the resultant structure.

(9) In order to manufacture the thermochromic substrate, at step S100, a glass substrate is coated with a first thin film, the refractivity of the first thin film being different from that of a vanadium dioxide (VO.sub.2) thin film.

(10) The glass substrate is a transparent or colored substrate that has a predetermined area or thickness. It is preferred that the glass substrate be a sodalime glass.

(11) The first thin film acts as a sodium diffusion barrier to prevent sodium (Na) ions in the glass substrate from diffusing into the pre-thermochromic thin film or VO.sub.2 thin film, which will be described later, at a temperature of 350 C. or higher in the process of manufacturing the thermochromic substrate. Otherwise, the VO.sub.2 thin film would lose the thermochromic characteristics thereof due to the sodium diffusion.

(12) The first thin film is a thin film, the refractive index of which is different from that of the VO.sub.2 thin film. The first thin film may be implemented as a transparent oxide thin film or a transparent nitride thin film. It is preferred that the first thin film be made of one material selected from among, but not limited to, silicon dioxide (SiO.sub.2), niobium pentoxide (Nb.sub.2O.sub.5), aluminum oxide (Al.sub.2O.sub.3), titanium dioxide (TiO.sub.2), and silicon nitride (Si.sub.3N.sub.4).

(13) Although it is preferred that the thickness of the first film range from 30 nm to 80 nm, the thickness may vary depending on the type of coating materials, the refractivity of coating materials, and the like.

(14) The first thin film may be formed on the glass substrate as a coating via reactive sputtering deposition.

(15) After that, at step S200, the first thin film is coated with pure vanadium.

(16) The first thin film can be coated with pure vanadium via a variety of deposition methods, such as sputtering deposition, including direct current (DC) sputtering deposition and radio frequency (RF) sputtering deposition.

(17) The thickness of the pre-thermochromic thin film ranges, preferably, from 30 nm to 80 nm in consideration of the transmittance of visible light.

(18) In addition, when the first thin film is coated with pure vanadium, a faint amount of oxygen may be provided in order to increase reactivity in the following heat treatment step.

(19) Afterwards, at step S300, the pre-thermochromic thin film is coated with a second thin film, the refractive index of which is different from that of the VO.sub.2 thin film.

(20) The second thin film acts as a protective film that protects the thermochromic thin film from scratches or soiling.

(21) The second thin film is a thin film, the refractive index of which is different from that of the VO.sub.2 thin film, and may be implemented as a transparent oxide thin film or a transparent nitride thin film. It is preferred that the second thin film be made of one material selected from among, but not limited to, SiO.sub.2, Nb.sub.2O.sub.5, Al.sub.2O.sub.3, TiO.sub.2 and Si.sub.3N.sub.4. The first thin film and the second thin film may be made of the same material.

(22) In particular, when the second thin film is provided as an oxide or nitride coating, the surface of the pre-thermochromic thin film may be oxidized or nitrified, and the phase of vanadium may be changed into V.sub.2O.sub.5 or VN instead of VO.sub.2 in the heat treatment step, which will be described later, if oxygen or nitrogen is abundant. Therefore, it is required to provide a minimum amount of oxygen or nitrogen within the limits in which the second thin film maintains the characteristics thereof as an oxide thin film or a nitride thin film.

(23) In addition, when oxygen is provided during the step of coating with the second thin film in order to increase the reactivity of the pre-thermochromic thin film in the following heat treatment step, it is preferred that a minimum amount of oxygen be provided.

(24) Although it is preferred that the thickness of the second thin film range from 30 nm to 80 nm, the thickness may vary depending on the type of materials to be coated, the refractivity of coating materials, or the like.

(25) The second thin film may be applied as a coating on the glass substrate via reactive sputtering deposition.

(26) Finally, at step S400, the resultant stack, which includes the glass substrate, the first thin film, the pre-thermochromic thin film and the second thin film, is heat-treated, thereby producing a thermochromic substrate.

(27) When the stack that includes the glass substrate, the first thin film, the pre-thermochromic thin film and the second thin film is heat-treated, oxygen in the first and second thin films diffuses into the pre-thermochromic thin film, so that pure vanadium undergoes phase change into VO.sub.2.

(28) The heat treatment may be performed in an argon (Ar) or vacuum atmosphere, preferably at a temperature ranging from 400 C. to 500 C., and more preferably at a temperature ranging from 400 C. to 500 C. for 20 to 120 minutes.

(29) In this way, the thermochromic substrate is manufactured by the method according to an exemplary embodiment of the invention. Since the refractive index of light incident on the glass substrate is changed by the multilayer film structure that includes the first thin film, the VO.sub.2 thin film and the second thin film, which is formed on the glass substrate, the thermochromic substrate has thermochromic characteristics while exhibiting improved transmittance.

(30) That is, when the first thin film is formed on the glass substrate, the VO.sub.2 thin film is formed on the first thin film, and the second thin film is formed on the VO.sub.2 thin film in order to increase the transmittance of the thermochromic substrate as in the related art, the VO.sub.2 undergoes a phase change into V.sub.2O.sub.3. V.sub.2O.sub.5, or the like due to an oxidation reaction in the VO.sub.2 thin film, whereby the VO.sub.2 thin film loses the thermochromic characteristics thereof, which is problematic. In contrast, the present invention has solved the problem of the related art, since pure vanadium is used and the VO.sub.2 thin film is formed by diffusing oxygen into the pre-thermochromic thin film due to the heat treatment.

(31) FIG. 2 is a graph comparatively depicting the transmittance of thermochromic substrates having a multilayer film structure, each of which is manufactured according to an example of the invention, and the transmittance of a thermochromic substrate having only a vanadium dioxide (VO.sub.2) thin film.

(32) As shown in FIG. 2, it can be appreciated that the transmittance of the thermochromic substrates having the multilayer film structure, each of which is manufactured according to an example of the invention, is improved such that it is higher than that of the thermochromic substrate having only the VO.sub.2 thin film.

(33) FIG. 3 is a graph depicting the thermochromic characteristics of a thermochromic substrate having a multilayer structure, which is manufactured by a method of the related art, and FIG. 4 is a graph depicting the thermochromic characteristics of a thermochromic substrate having a multilayer structure, which is manufactured according to an example of the invention.

(34) Comparing FIG. 3 and FIG. 4, it can be appreciated that the thermochromic substrate manufactured by the method of the related art exhibits no change in transmittance at temperatures ranging from 20 C. to 90 C.

(35) Accordingly, in the thermochromic substrate manufactured by the method of the related art, which is intended to increase the transmittance of the thermochromic substrate, VO.sub.2 undergoes phase change into V.sub.2O.sub.3, V.sub.2O.sub.3, or the like in the process of manufacturing the thermochromic substrate, whereby the VO.sub.2 thin film loses its thermochromic characteristics. In contrast, the thermochromic substrate manufactured according to an embodiment of the invention, can have increased transmittance while maintaining the thermochromic characteristics thereof.

(36) The foregoing descriptions of specific exemplary embodiments of the present invention have been presented with respect to the certain embodiments and drawings. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible for a person having ordinary skill in the art in light of the above teachings.

(37) It is intended therefore that the scope of the invention not be limited to the foregoing embodiments, but be defined by the Claims appended hereto and their equivalents.