JP6032597B2 - Functionally graded film and method for manufacturing the same - Google Patents

Description

  The present invention relates to a functionally graded film and a method for manufacturing the same.

  Research and development of a transmissive thin film transistor using a semiconductor thin film formed over a substrate having an insulating surface has been conducted. Thin film transistors are widely applied to electronic devices such as ICs and electro-optical devices, and are attracting attention as switching elements for image display devices such as liquid crystal televisions and organic EL televisions. For example, a method of forming an yttria-stabilized zirconia thin film as an insulating film on the gate electrode of a thin film transistor has been proposed (see Patent Document 1).

JP 2009-170896 A

  However, an apparatus for performing a method such as a plasma CVD method, a sputtering method, an MBE method, a PLD method, or an atomic layer epitaxy method, which is employed as a method for forming a highly crystalline insulating film, is very expensive. . In addition, preparation for film formation is complicated, for example, it is necessary to achieve a high degree of vacuum in the film formation chamber.

  Accordingly, an object of the present invention is to provide a functionally graded film in which electrical characteristics change in the film thickness direction by a simple and inexpensive method and a manufacturing method thereof.

The present inventor considered that the silica (SiO ₂ ) thin film has high transparency but low dielectric constant, and that the titania (TiO ₂ ) thin film is chemically stable and has high dielectric constant but high leakage current. An attempt was made to form a zirconia (ZrO ₂ ) thin film that has a high dielectric constant, a small leakage current, and is chemically stable. We also considered using the spray pyrolysis (SPD) method as an inexpensive and simple film formation method.

  However, since a zirconia inorganic salt is used as a solute and hardly dissolved in alcohol as a solvent, it is very difficult to prepare a raw material solution.

  The present inventor has found that a zirconia inorganic salt can be dissolved in an alcohol by adding a ketone compound as a first auxiliary agent to the solution. In addition, when the boiling point of the ketone compound is high, the present inventor has difficulty in vaporizing the ketone compound, and the carbon constituting the ketone compound combines with oxygen in the atmosphere when a combustion reaction occurs. Depending on the amount of oxygen in the atmosphere, oxygen defects in the thin film are induced, ketone compounds are expensive, and depending on the amount of ketone compounds added, it is difficult to mist the raw material solution. In view of the fact that the viscosity of the solution is increased, it has been found that it is important to adjust the amount of the first auxiliary agent added.

  Furthermore, the present inventor repeats the process of supplying the mist of the raw material solution to the substrate, evaporating the solvent by controlling the atmospheric temperature, and oxidizing the zirconium constituting the solute, whereby the zirconia is formed on the substrate. In addition to being able to form a thin film, it has been found that the electrical characteristics such as the electrical conductivity of the zirconia thin film differ depending on the temperature of the atmosphere at the time of film formation.

The method of the present invention based on this knowledge is a method for producing a functionally gradient film in which electrical characteristics change in the film thickness direction, using zirconium inorganic salt as a solute, alcohol as a solvent, and a ketone compound as a first auxiliary agent. And adjusting the raw material solution in which the concentration of the first auxiliary agent is adjusted, supplying the mist of the raw material solution to the substrate, evaporating the solvent by heating the atmosphere, and forming zirconium that constitutes the solute In the process of repeating the process of oxidizing, the temperature of the atmosphere is intermittently changed from a high temperature to a low temperature in a temperature range of 400 to 600 ° C., and a plurality of functional layers having different electrical characteristics are sequentially stacked on the substrate. The functionally gradient film is manufactured by the following.

  Furthermore, the present inventor has found that the electrical characteristics of the zirconia thin film as an oxide film can be adjusted by adding a metal compound as a second auxiliary agent to the solution and adjusting the amount of the second auxiliary agent added. . This is presumably because the metal compound functions as a dopant and changes at least one of the crystallinity in the oxide film, the band structure, or the concentration and mobility of carriers such as electrons derived from zirconia.

  Based on this knowledge, a plurality of types of raw material solutions having different concentrations of the second auxiliary agent are prepared using a metal compound as a second auxiliary agent, and in the process of repeating the process, in addition to the temperature of the atmosphere, the mist It is preferable to manufacture the functionally gradient film on the substrate by changing the type of the raw material solution that constitutes the substrate.

  It is preferable that the functionally gradient film is heat-treated in an oxygen atmosphere during or after the process is repeated.

  According to this method, the amount of oxygen defects in at least a part of the functionally graded film can be reduced by a simple method of realizing an oxidizing atmosphere (or oxygen atmosphere). A situation in which it is difficult to adjust the electrical characteristics of the layer of the functional film is avoided.

Explanatory drawing of the procedure of the manufacturing method of a functionally gradient film as 1st Embodiment of this invention. Explanatory drawing regarding the manufacturing method of the functionally gradient film of this invention. Explanatory drawing regarding the growth process of a functionally gradient film. BRIEF DESCRIPTION OF THE DRAWINGS Structure explanatory drawing of the functionally gradient film as 1st Embodiment of this invention. Explanatory drawing regarding the electrical property of the functionally gradient film of 1st Example group of this invention. Explanatory drawing of the procedure of the manufacturing method of the functionally gradient film as 2nd Embodiment of this invention. Structure explanatory drawing of the functionally gradient film as 2nd Embodiment of this invention. Explanatory drawing regarding the electrical property of the functionally gradient film of 2nd Example group of this invention. Explanatory drawing regarding the film thickness dependence of the electric current characteristic of the functionally gradient film of 2nd Example group of this invention. Explanatory drawing regarding the electrical property of the functionally gradient film of 2nd Example group of this invention.

(Configuration of Film Formation Method as First Embodiment of the Present Invention)
A method of forming a functionally graded film as the first embodiment of the present invention will be described.

  First, a raw material solution is prepared using a zirconium inorganic salt as a solute, alcohol as a solvent, and a ketone compound as a first auxiliary agent (FIG. 1 / STEP 102). In preparing the raw material solution, the concentration of the first auxiliary agent is adjusted.

  Here, the “zirconium inorganic salt” includes a zirconium compound having a β-diketone group such as tetrakis (acetylacetonato) zirconium, zirconium nitrate, zirconium sulfate, zirconium chloride, zirconium chloride oxide, zirconium fluoride, zirconium fluoride oxide, Zirconium bromide, zirconium bromide oxide, zirconium iodide, zirconium iodide oxide, metal salts such as zirconium acetate, zirconium formate and zirconium oxalate, and complex compounds such as zirconium EDTA complex are included.

  “Alcohol” includes monohydric alcohols such as ethanol, methanol, propanol, isopropanol and tert-butanol, polyhydric alcohols such as ethylene glycol and glycerin, phenols having a hydroxyl group, amines and amino acids.

  “Ketone compounds” include β-diketones such as acetylacetone, dipivaloylmethane, diisobutyrylmethane, isobutyrylpivaloylmethane, 2,2,6,6-tetramethyl-3,5-octanedione, etc. And compounds having a ketone group, such as a similar compound, acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, and cyclohexanone.

  An index “i” representing the number of repetitions of the process of mist generation (raw material solution spraying) and vapor phase growth of the zirconia thin film and an index “j” representing the number of times the film formation atmosphere temperature T is switched are both set to “1”. (FIG. 1 / STEP 104).

  It is determined whether or not the index i is Nj or less (FIG. 1 / STEP 106). This determination corresponds to the determination as to whether the film formation atmosphere temperature T needs to be switched.

  If the determination result is affirmative (FIG. 1 / STEP 106... YES), the film formation atmosphere temperature T is controlled to Tj (FIG. 1 / STEP 110). That is, in this case, the current value of the film formation atmosphere temperature T is maintained at the same value as the previous value.

On the other hand, when the determination result is negative (FIG. 1 / STEP 106... NO), the index j is increased by 1 (FIG. 1 / STEP 108), and a heater is used to set the film formation atmosphere temperature T to be 1. It is controlled to T _j (FIG. 1 / STEP 110). That is, in this case, the current value of the film formation atmosphere temperature T is changed to a value different from the previous value. The operation of the heater may be controlled by a control device configured by a computer.

  For example, as shown in FIG. 2, the deposition atmosphere temperature T is controlled by using a hot plate as a heater on which the substrate is placed and heating the substrate. In addition, the film forming atmosphere temperature may be controlled by various methods on the condition that the solvent in the current layer of the raw material solution can be vaporized or evaporated and the zirconium constituting the solute can be oxidized. For example, the film formation atmosphere temperature T may be controlled by a heater disposed in a chamber in which the substrate is accommodated.

  Further, a mist of the raw material solution is generated using a sprayer (FIG. 1 / STEP 112). For example, as shown in FIG. 2, a plunger pump is used as a sprayer, and the raw material solution is sprayed toward the substrate. Since the spray method by the plunger pump is a pressurization type or a one-fluid type, unlike the two-fluid type, it is possible to generate a mist of a raw material solution without using a carrier gas. For example, the spray amount is adjusted to 15 to 20 [ml] per 100 times of the raw material solution. The operation of the sprayer may also be controlled by a control device configured by a computer, similar to the operation of the heater. Note that a mist of the raw material solution may be generated using a sprayer different from the plunger pump, such as a two-fluid sprayer.

  By controlling the atmospheric temperature T, the solvent in the current layer of the raw material solution is vaporized or evaporated, and the zirconium constituting the solute is oxidized to gradually grow the zirconia thin film.

  In the initial stage where the index i is small, as shown in FIG. 3A, seeds of zirconia thin films dispersed in islands (see shaded areas) are formed on the surface of the substrate. By subsequently supplying the raw material solution, the seeds grow in a direction parallel to the substrate surface, thereby forming a zirconia thin film covering the entire surface of the substrate as shown in FIG. Is done. Thereafter, as the index i increases, and as the layer is deposited, the zirconia thin film or functionally graded film grows in a direction perpendicular to the surface of the substrate as shown in FIG. It gradually increases.

Thereafter, it is determined whether or not the index i is equal to the target number of times N (N _j ≦ N) (FIG. 1 / STEP 114).

  When the determination result is negative (FIG. 1 / STEP 114... NO), the value of the index i is increased by “1” (FIG. 1 / STEP 116). After that, it is determined whether or not the index i is Nj or less (FIG. 1 / STEP 106), and a process of controlling the film formation atmosphere temperature T (see FIG. 1 / STEP 110) and mist generation (see FIG. 1 / STEP 112). Is repeated. By adjusting the number of times N, the thickness of the functionally graded film is adjusted.

  On the other hand, when the determination result is affirmative (FIG. 1 / STEP 114... YES), the functionally gradient film is heat-treated at a higher temperature than when the solvent of the material solution is evaporated in an oxidizing atmosphere using ozone (FIG. 1). 1 / STEP 118). In addition, instead of or in addition to the subsequent heat treatment of the zirconia thin film (see FIG. 1 / STEP 118), the film formation atmosphere temperature T in the oxidizing atmosphere is provided on condition that the index i matches or falls within the specified range. The processes of control (see FIG. 1 / STEP 110) and mist generation (see FIG. 1 / STEP 112) may be repeated.

Thereby, for example, as shown in FIG. 4, a functionally graded film composed of _n functional layers A ₁ to An is manufactured on the substrate. The functionally graded zirconia thin film can be epitaxially grown or quasi-epitaxially grown in the film thickness direction using the same raw material. Accordingly, zirconia crystals are continuous rather than discontinuous at the boundary between the functional layers adjacent to each other in the film thickness direction.

The j-th functional layer A _j is formed by repeating the processes of mist generation and zirconium oxidation for N _j −N _j−1 (N ₀ = 0) at the ambient temperature T = T _j . The j-th functional layer A _j has a thickness t (A _j ) corresponding to the number of repetitions N _j −N _j−1 of the process and electric characteristics corresponding to the ambient temperature T = T _j .

(Example)
Example 1
0.01 [mol] tetrakis (acetylacetonato) zirconium is used as the solute, ethanol is used as the solvent, acetylacetone is used as the first auxiliary agent, and the zirconium ion concentration is 0.05 [mol / l]. A 200 [ml] raw material solution was prepared. The concentration of the first auxiliary agent is 20 [vol. %].

  The concentration of acetylacetone as the first auxiliary agent is 0.02-2 [vol. 2] from the viewpoint of stably forming a thin film regardless of the elapsed time after the preparation of the raw material solution. %] Or 20-40 [vol. %].

The process of N ₁ = 80 was repeated at the film formation atmosphere temperature T ₁ = 550 [° C.], and the process of N ₂ −N ₁ = 320 was repeated at the film formation atmosphere temperature T ₂ = 400 [° C.]. In the oxidizing atmosphere using ozone, the functionally graded film was heat-treated at T = 600 [° C.], which is a higher temperature than when the solvent of the material solution was evaporated. Thus, the first functional layer having a thickness of 0.05 [μm] and the second functional layer having a thickness of 0.2 [μm] are sequentially laminated on the substrate. A functionally graded film was formed.

(Example 2)
The process of N ₁ = 80 was repeated at the film formation atmosphere temperature T ₁ = 550 [° C.], and the process of N ₂ −N ₁ = 320 was repeated at the film formation atmosphere temperature T ₂ = 400 [° C.]. Thereby, the first functional layer having a thickness of 0.05 [μm] and the second functional layer having a thickness of 0.2 [μm] are sequentially stacked on the substrate in the second embodiment. A functionally graded film was formed.

Example 3
N ₁ = 80 processes were repeated at the film formation atmosphere temperature T ₁ = 600 [° C.], and N ₂ −N ₁ = 320 processes were repeated at the film formation atmosphere temperature T ₂ = 450 [° C.]. In the oxidizing atmosphere using ozone, the functionally graded film was heat-treated at T = 600 [° C.], which is a higher temperature than when the solvent of the material solution was evaporated. Thereby, the first functional layer having a thickness of 0.05 [μm] and the second functional layer having a thickness of 0.2 [μm] are sequentially stacked on the substrate in the third embodiment. A functionally graded film was formed.

Example 4
N ₁ = 80 processes are repeated at the deposition atmosphere temperature T ₁ = 550 [° C.], and N ₂ −N ₁ = 80 processes are repeated at the deposition atmosphere temperature T ₂ = 500 [° C.]. N ₃ -N ₂ = 80 processes are repeated at the film atmosphere temperature T ₃ = 450 [° C.], and N ₄ −N ₃ = 160 processes are repeated at the film formation atmosphere temperature T ₄ = 400 [° C.]. It was. Thereby, a first functional layer having a thickness of 0.05 [μm], a second functional layer having a thickness of 0.05 [μm], and a third functional layer having a thickness of 0.05 [μm] are formed on the substrate. Thus, the functionally graded film of Example 4 formed by sequentially stacking the fourth functional layer having a thickness of 0.1 [μm] was formed.

  In each of FIGS. 5A to 5D, voltage-current characteristics of each functionally graded film of Examples 1 to 4 and each functional layer constituting the functionally graded film are shown (solid line: functionally graded film, Dash-dotted line: 1st functional layer, 2-dot chain line ... 2nd functional layer, 1-dot chain line (thick) ... 3rd functional layer, 2-dot chain line (thick) ... 4th functional layer).

FIGS. 5B and 5D show that the functional conductivity σ of the functionally graded films of Examples 2 and 4 is relatively high. This is obtained at the film formation atmosphere temperature T ₁ = 550 [° C.]. This is because the crystallinity and mobility μ of the first functional layer were followed. Furthermore, it can be seen from FIGS. 5A and 5C that the electrical conductivity σ of the functionally gradient films of Examples 1 and 3 is relatively low. This is because heat treatment is performed in an oxidizing atmosphere using ozone. This is because the second functional layer and subsequent layers were oxidized while the crystallinity of the first functional layer was followed.

(Configuration of Film Formation Method as Second Embodiment of the Present Invention)
A method for forming a functionally graded film as a second embodiment of the present invention will be described.

  First, a plurality of types of raw material solutions having different concentrations of the second auxiliary agent are prepared using zirconium inorganic salt as a solute, alcohol as a solvent, a ketone compound as a first auxiliary agent, and a metal compound as a second auxiliary agent. (FIG. 6 / STEP 202).

  Here, "metal compound" includes metal nitrates such as aluminum nitrate, aluminum sulfate, aluminum chloride, aluminum bromide, aluminum fluoride, aluminum iodide, aluminum phosphate, aluminum hydroxide, aluminum acetate, aluminum formate, Shu Metal salts such as aluminum acid, metal compounds having a β-diketone group such as tris (acetylacetonato) aluminum, complex compounds such as tris (8-quinolinolato) aluminum, aluminum EDTA, and the like are included.

  An index “i” representing the number of repetitions of the process of mist generation (raw material solution spraying) and vapor phase growth of the zirconia thin film, an index “j” representing the number of times of film formation atmosphere temperature T switching, and an index “ k ”is set to“ 1 ”(FIG. 6 / STEP 204).

  It is determined whether or not the index i is Nj or less (FIG. 6 / STEP 206). This determination corresponds to the determination as to whether the film formation atmosphere temperature T needs to be switched.

  If the determination result is affirmative (FIG. 6 / STEP 206... YES), the film formation atmosphere temperature T is controlled to Tj (FIG. 6 / STEP 210). That is, in this case, the current value of the film formation atmosphere temperature T is maintained at the same value as the previous value.

On the other hand, when the determination result is negative (FIG. 6 / STEP 206... NO), the index j is increased by 1 (FIG. 6 / STEP 208), and a heater is used so that the film-forming atmosphere temperature T is increased. It is controlled to T _j (FIG. 6 / STEP 210). That is, in this case, the current value of the film formation atmosphere temperature T is changed to a value different from the previous value. The operation of the heater may be controlled by a control device configured by a computer.

It is determined whether or not the index i is N _k or less (FIG. 6 / STEP 212). This determination corresponds to the determination of whether or not switching of the raw material solution that is the mist source is necessary.

  If the determination result is affirmative (FIG. 6 / STEP 212... YES), a mist of the k-th raw material solution is generated (FIG. 6 / STEP 216). That is, in this case, the mist generated this time is generated from the same raw material solution as the mist generated last time.

  On the other hand, when the determination result is negative (FIG. 6 / STEP 212... NO), the index k is increased by 1 (FIG. 6 / STEP 214), and a mist of the k-type raw material solution is generated ( FIG. 6 / STEP 216). That is, in this case, the mist generated this time is generated from a raw material solution of a different type from the mist generated last time, that is, a raw material solution having a different content of the second auxiliary agent. A separate sprayer may be prepared for each raw material solution having a different content of the second auxiliary agent, and the operation of each sprayer may be controlled by a control device configured by a computer.

  By controlling the atmospheric temperature T, the solvent in the current layer of the raw material solution is vaporized or evaporated, and the zirconium constituting the solute is oxidized to gradually grow the zirconia thin film.

  Thereafter, it is determined whether or not the index i is equal to the target number N (Nj ≦ N) (FIG. 6 / STEP 218).

If the determination result is negative (FIG. 6 / STEP 218... NO), the value of the index i is increased by “1” (FIG. 6 / STEP 220). After that, it is determined whether or not the index i is N _j or less (FIG. 6 / STEP 206), which is referred to as control of the film formation atmosphere temperature T (see FIG. 6 / STEP 210) and mist generation (see FIG. 6 / STEP 216). The process is repeated. By adjusting the number of times N, the thickness of the functionally graded film is adjusted.

  On the other hand, when the determination result is affirmative (FIG. 6 / STEP 218... YES), the functionally graded film is heat-treated at a higher temperature than when the solvent of the material solution is evaporated in an oxidizing atmosphere using ozone (FIG. 6). 6 / STEP 222). In addition, in place of or in addition to the subsequent heat treatment of the zirconia thin film (see FIG. 6 / STEP 222), the film formation atmosphere temperature T in the oxidizing atmosphere is provided on condition that the index i matches or falls within the specified range. The process of control (see FIG. 6 / STEP 210) and mist generation (see FIG. 6 / STEP 216) may be repeated.

Thereby, for example, as shown in FIG. 7, a functionally graded film composed of _m functional layers B _{1 to} B _m is manufactured on the substrate. Since the raw materials are almost the same except for the content of the second auxiliary agent, the functionally graded film of the zirconia thin film can be epitaxially grown in the film thickness direction. Accordingly, zirconia crystals are continuous rather than discontinuous at the boundary between the functional layers adjacent to each other in the film thickness direction.

The k-th functional layer B _k is formed by repeating processes of generating mist of the k-th type raw material solution and oxidizing zirconium. The k-th functional layer L _k has electrical characteristics corresponding to the atmospheric temperature T when the k-type raw material solution is produced, in addition to the content of the second auxiliary agent in the k-th raw material solution. Further, when the k-th functional layer L _k is formed at the same atmospheric temperature T, the k-th functional layer L _k has uniform electrical characteristics. Meanwhile, if the ambient temperature T is changed in the course formation of the k functional layer L _k, a k-th functional layer L _k is formed in the front the change of the atmospheric temperature T moiety, after the change of the ambient temperature T The formed portion has different electrical characteristics.

(Example)
(Example 5)
0.01 [mol] tetrakis (acetylacetonato) zirconium is used as a solute, ethanol is used as a solvent, acetylacetone is used as a first auxiliary agent, aluminum nitrate is used as a second auxiliary agent, zirconium ion A 200 [ml] raw material solution having a concentration of 0.05 [mol / l] was prepared. The concentration of the first auxiliary agent is 20 [vol. %], And the additive amount of the second auxiliary agent was adjusted so that aluminum was 0 [atm%], 1 [atm%], or 2 [atm%].

Using a solution of aluminum 2 [atm%], the process was repeated N ₁ = 80 times at a film formation atmosphere temperature T ₁ = 550 [° C.], and using a solution of aluminum 1 [atm%], the film formation atmosphere temperature T N ₂ −N ₁ = 80 processes were repeated at ₂ = 550 [° C.], a solution of aluminum 0 [atm%] was used, a film formation atmosphere temperature T ₃ = 550 [° C.], and N ₃ −N ₂ = The process was repeated 80 times, and N ₄ −N ₃ = 80 processes were repeated at a film formation atmosphere temperature T ₄ = 450 [° C.], and N ₅ −N at a film formation atmosphere temperature T ₅ = 400 [° C.]. ₄ = 80 processes were repeated. Thereby, a first functional layer having a thickness of 0.05 [μm], a second functional layer having a thickness of 0.05 [μm], and a third functional layer having a thickness of 0.05 [μm] are formed on the substrate. The functional gradient film of Example 5 is formed by sequentially stacking a fourth functional layer having a thickness of 0.05 [μm] and a fifth functional layer having a thickness of 0.05 [μm]. It was done.

(Example 6)
Using a solution of aluminum 2 [atm%], the process was repeated N ₁ = 80 times at a film formation atmosphere temperature T ₁ = 550 [° C.], and using a solution of aluminum 1 [atm%], the film formation atmosphere temperature T _{2 = 550 [℃] N 2} -N 1 = 160 times in the process is repeated by using a solution of aluminum 0 [atm%], deposition atmosphere temperature T ₃ = 550 [℃] at N ₃ -N ₂ = 160 processes were repeated. Thereby, a first functional layer having a thickness of 0.05 [μm], a second functional layer having a thickness of 0.10 [μm], and a third functional layer having a thickness of 0.10 [μm] are formed on the substrate. The functionally graded film of Example 6 configured by sequentially stacking layers was formed.

(Example 7)
The process of N ₁ = 160 was repeated using a solution of aluminum 2 [atm%] at a film formation atmosphere temperature T ₁ = 550 [° C.], and a film formation atmosphere temperature T using a solution of aluminum 0 [atm%]. _{2 = 400 [℃] N 2} -N 1 = 80 times the process is repeated by using a solution of aluminum 2 [atm%], deposition atmosphere temperature T ₃ = 550 [℃] at N ₃ -N ₂ = 160 processes were repeated. Accordingly, the first functional layer having a thickness of 0.10 [μm], the second functional layer having a thickness of 0.05 [μm], and the third functional layer having a thickness of 0.10 [μm] are formed on the substrate. The functionally graded film of Example 7, which is configured by sequentially stacking layers, was formed.

  8A to 8C show voltage-current characteristics of the functional layers constituting the functionally gradient films of Examples 5 to 7, respectively. FIG. 9 shows the film thickness dependence of the current characteristics of each functionally graded film of Examples 5 to 7 (solid line... Example 5, dashed line. Example 6, one-dot chain line... Example 7). From FIG. 9, it can be seen that a portion with a high electric conductivity σ and a portion with a low electric conductivity σ can be formed in the film thickness direction by inclining the addition amount of the second auxiliary agent and controlling the film formation atmosphere temperature T.

(Relationship between ambient temperature and electrical characteristics of functional layer)
In FIG. 10, the solid line shows the dependence of the electric conductivity σ of the zirconia thin film constituting the functional layer on the ambient temperature T during film formation. The electrical conductivity σ is proportional to each of the carrier density n and mobility μ in the zirconia thin film. In FIG. 10, the T dependency of the carrier density n is indicated by a one-dot chain line, and the T dependency of the carrier mobility μ is indicated by a two-dot chain line.

As shown in FIG. 10, the carrier mobility μ (T) of the zirconia thin film shows a low value in the range of T = 350 to 400 [° C.]. This is because the zirconia thin film formed in the range of T = 350 to 400 [° C.] is in an amorphous state and has a low crystallinity. On the other hand, the carrier density n (T) of the zirconia thin film is ensured in the range of T = 350 to 400 [° C.]. This is because _x of ZrO _2-x is not 0 (oxygen defects exist). The electrical conductivity σ is proportional to the product of the carrier mobility μ (T) and the carrier density n (T), but since the carrier mobility μ (T) is low, the electrical conductivity of the zirconia thin film is around T = 350 [° C.]. The conductivity σ indicates a minimum value.

As shown in FIG. 10, the carrier mobility μ (T) of the zirconia thin film increases in the range of T = 400 to 575 [° C.]. This is because as the T increases, the crystallinity of the zirconia thin film gradually increases. On the other hand, in the range of T = 400 to 550 [° C.], the carrier density n (T) of the zirconia thin film decreases. This is because _x of ZrO _2-x approaches 0 (oxygen defects are reduced). As a result, the electric conductivity σ of the zirconia thin film shows a maximum value in the vicinity of T = 400 [° C.]. This is because both the carrier density n (T) and the sufficient carrier mobility μ (T) are provided.

As shown in FIG. 10, the carrier mobility μ (T) of the zirconia thin film further increases in the range of T = 575 to 600 [° C.]. This is because as the T increases, _x of ZrO _2-x becomes almost 0, oxygen defects are almost eliminated, and crystal densification progresses. On the other hand, in the range of T = 550 to 600 [° C.], the carrier density n (T) of the zirconia thin film is substantially constant. This is because oxygen defects are almost eliminated. As a result, in the vicinity of T = 550 [° C.], the electric conductivity σ of the zirconia thin film shows a minimum value. This is because the carrier density n (T) is sufficiently reduced to cause a steep rise in the carrier mobility μ (T).

(Other embodiments of the present invention)
As another embodiment of the present invention, a functionally graded film having cracks or defects may be repaired according to the same method as the film forming method. Specifically, the mist of the raw material solution is supplied to the zirconia thin film, and the process of evaporating the solvent and oxidizing the zirconium constituting the solute by controlling the atmospheric temperature is repeated. Thereby, the said crack etc. are repaired with the zirconia derived from the mist which entered the crack or adhered to the defect | deletion location.

Claims (3)

A method of manufacturing a functionally gradient film in which electrical characteristics change in the film thickness direction,
Zirconium inorganic salt as solute, alcohol as solvent, ketone compound as first auxiliary agent, and adjusting the raw material solution in which the concentration of the first auxiliary agent is adjusted,
In the process of supplying the mist of the raw material solution to the substrate, evaporating the solvent by heating the atmosphere and oxidizing zirconium constituting the solute, the temperature of the atmosphere is set to a temperature of 400 to 600 ° C. A method of manufacturing the functionally graded film by intermittently changing a range from a high temperature to a low temperature and sequentially laminating a plurality of functional layers having different electrical characteristics on the substrate . The method of claim 1, wherein
Using a metal compound as a second auxiliary agent, preparing a plurality of types of the raw material solutions having different concentrations of the second auxiliary agent,
In the process of repeating the process, the functionally graded film is manufactured on the substrate by changing the kind of the raw material solution constituting the mist in addition to the temperature of the atmosphere. The method according to claim 1 or 2, wherein
A method of heat-treating the functionally gradient film in an oxygen atmosphere during or after the process is repeated.

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