WO2014148830A1 - Method for manufacturing zinc oxide precursor, zinc oxide precursor obtained thereby, and zinc oxide thin film - Google Patents

Abstract

Disclosed are a method for manufacturing high-purity crystals of zinc hydroxide, which is a zinc oxide precursor used for oxide semiconductors, and an invention for manufacturing a ZnO thin film transistor device which is spin-coated using the zinc hydroxide manufactured by the method.

Description

Method for producing zinc oxide precursor, zinc oxide precursor and zinc oxide thin film obtained therefrom

This application claims priority based on Korean Patent Application No. 10-2013-0029569, filed March 20, 2013, and all the contents disclosed in the specification and drawings of the application are incorporated in this application.

In addition, the present application claims priority based on Korean Patent Application No. 10-2013-0164867, filed December 27, 2013, all the contents disclosed in the specification and drawings of the application are incorporated in this application.

The present invention relates to a method for preparing a zinc oxide precursor, to a zinc oxide precursor and a zinc oxide thin film obtained therefrom, and more particularly to a method for producing zinc hydroxide, which is a kind of zinc oxide precursor, with high purity crystals and It relates to an invention for forming a zinc oxide thin film that can be used for use in oxide semiconductors and the like by low temperature firing using the prepared zinc hydroxide.

The next-generation display is to use the printing process in an effort to achieve a low price, in order to achieve this, the backplane by the semiconductor must also be formed by a solution process. In particular, in manufacturing a semiconductor, efforts to use an oxide semiconductor capable of solution processing in a method using silicon are accelerating. As such a method, there is a method of forming a semiconductor in a vacuum by using a target material such as indium-gallium-zinc oxide (IGZO), and a predetermined result has been obtained. However, this method is still carried out under vacuum and is still a departure from the future of printed electronics.

In order to apply the printing method, the process of liquefying an oxide semiconductor is essential, and in order to become a semiconductor required for a flexible display, it is necessary to show certain characteristics such as electrical characteristics required in a thin film transistor (TFT) even after low temperature firing. do.

As known to date, even a solution process is known to be calcined at a high temperature of at least 200 ° C., and methods known as presently preferred methods employ a process of spin coating a solution in a nitrogen atmosphere.

Zinc oxide (ZnO), on the other hand, has a wide optical bandgap of about 3.3 eV and is a material used for semiconductor manufacturing. Zinc oxide thin films have strong piezoelectric and photoelectric effects, and have similar optical properties to GaN, which is a material of conventional ultraviolet / blue light emitting diode (LED) and laser diode (LD) devices. In particular, it has an excitation binding energy that is three times higher than GaN at room temperature, which enables high-efficiency light emission, and has a very low threshold energy when stimulated spontaneous emission by laser pumping.

The zinc oxide thin film has excellent transparency in the infrared and visible light region, electrical conductivity, and durability against plasma, and has a low raw material price, so that thin film transistors (TFTs), doped transparent electrodes, photocatalysts, energy-saving glazing coating materials, Acoustic optical devices, ferroelectric memories, solar cells, reducing gas detection sensors and the like have a wide range of applications.

Zinc hydroxide is a kind of zinc oxide precursor that is transformed into zinc oxide by firing. Zinc hydroxide is precipitated by dissolving zinc salt in water and adding a basic substance. This method has the advantage of obtaining zinc hydroxide by a simple process, but the basic material used in the process reacts with carbon dioxide in the air to easily form carbonates to generate impurities and precipitate anions in zinc salts together. As a possibility, zinc hydroxide obtained by this method is not suitable for use in oxide semiconductors that require high purity.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and is intended to provide a method for preparing a zinc oxide precursor for an oxide semiconductor, which is easy to manufacture, has high purity, and is calcinable even at low temperatures, and a zinc oxide precursor and a zinc oxide thin film formed therefrom.

According to one aspect of the invention, dissolving zinc salt in water to obtain a zinc salt solution; Adding a basic substance to the zinc salt solution to form a zincate salt solution; And separating the precipitate formed from the zinc salt solution.

The zinc salt may be one or a mixture of two or more selected from the group consisting of zinc chloride, zinc sulfate, zinc nitrate, zinc acetate, zinc phosphate, zinc fluoride, zinc bromide, and zinc iodide.

The basic substance may be one selected from the group consisting of ammonia water, sodium hydroxide, potassium hydroxide and lithium hydroxide.

The basic substance may be added so as to have 5 to 12 moles of hydroxy ions per mole of zinc ions.

The basic substance may be a solution portion separated from a supersaturated basic solution.

According to another aspect of the present invention, there is provided a zinc oxide precursor prepared according to the method described above.

In another aspect of the invention there is provided a method for producing a zinc oxide thin film comprising the step of heat-treating the zinc oxide precursor at a temperature range of 50 to 200 ℃.

The heat treatment may be carried out in a temperature range of 100 to 150 ℃.

The heat treatment may be performed for 1 to 90 minutes.

The heat treatment may be performed in air or Ar / H ₂ .

In another aspect of the present invention, there is provided a method for producing a zinc oxide thin film comprising the step of ultraviolet treatment heat treatment of the zinc oxide precursor at a temperature range of room temperature (25 ℃) to 200 ℃.

The heat treatment may be carried out in a temperature range of room temperature to 150 ℃.

The heat treatment and ultraviolet treatment may be performed for 1 second to 30 minutes.

The ultraviolet light treatment may be performed in the wavelength range of 100 to 1000 nm, which may include visible light.

According to another aspect of the invention, there is provided a zinc oxide thin film obtained by the above production method.

The zinc oxide thin film may be used for a transparent electrode, a solar cell, an optical sensor, a thin film transistor (TFT), zinc oxide nanowires, or a light emitting material.

Zinc hydroxide obtained according to the present invention is characterized by high purity and high crystalline structure.

In addition, the zinc hydroxide obtained in accordance with the present invention can be dissolved in a high solubility to form a zinc oxide precursor solution can be easily applied to the thin film process by the coating method.

The zinc oxide precursor solution applied to the substrate by the printing method may form a ZnO thin film having desirable physical properties by low temperature firing, and the ZnO thin film transistor according to an embodiment of the present invention may be further improved by passivation. .

In addition, the thin film transistor made of the zinc precursor solution may be manufactured to have improved quality and improved device performance within a short processing time.

This time reduction in the present invention is not only comparable to the microwave annealing method, but also has a simpler advantage over the microwave annealing method because it is better in saturation field effect mobility and can be adapted to actual industrial use. have.

The zinc oxide thin film according to the present invention is widely applicable to various applications such as not only an oxide semiconductor but also a transparent conductive thin film and a gas sensor.

1 is a graph showing the results of TGA (Thermogravimetric Analysis) thermal analysis of zinc hydroxide obtained in Example 1-1.

Figure 2 is a photograph taken with zinc hydroxide obtained in Example 1-1 with a Field Emission Scanning Electron Microscope (FE-SEM).

Figure 3a is an X-ray diffraction (XRD) graph (black) of zinc hydroxide obtained in Example 1-1, Figure 3b is an XRD graph (black) of zinc oxide obtained in Example 2-1, the figure The gray graph in the field is for zinc hydroxide standard.

4 is an XRD graph of the zinc hydroxide obtained in Example 1-1 after heat treatment at 100 ° C. for 1 hour or 3 hours.

5 is an XRD graph of the zinc hydroxide obtained in Example 1-1 after treatment with different annealing times at 150 ° C.

6a is a photograph of a solution in which zinc hydroxide prepared according to Example 1-1 was dissolved in 25% ammonia water, 1% by weight, 2% by weight, 3% by weight, 4% by weight, and 5% from left to right, respectively. Solution by weight concentration.

Figure 6b is a photograph for comparison with Figure 6a, shows the result of dissolving zinc hydroxide of Junsei in 25% ammonia water. From the left, a picture of 0.9% by weight and 1.2% by weight of the solution is shown and the maximum solubility is about 0.9%, showing a solubility lower than that shown in Figure 6a.

7 is a photograph of a solution obtained by dissolving zinc oxide obtained in Example 2-1 at 150 ° C. for 3 minutes and then dissolved in 25% ammonia water, and 0.45% by weight, 0.90% by weight, and 1.35% by weight from left to right, respectively. %, 1.8% by weight solution.

FIG. 8 is a photograph of a solution in which commercially available zinc oxide is heat-treated at 150 ° C. for 3 minutes and then dissolved in 25% ammonia water. The solution is 0.45% by weight, 0.90% by weight, and 1.35% by weight, respectively, from left to right.

9A and 9B show the output curves and the transfer curves of transistors using Zn (OH) ₂ and ZnO thin films obtained in this example using various conditions, respectively.

10A to 10D are FE-SEMs of ZnO thin films obtained in Examples 2-1, 2-2, 2-3, and 2-6, and the thin film thicknesses are described in each of the images.

11 is a graph showing an X-ray diffraction pattern of the ZnO thin film obtained in Example 2-1 and a graph (B) showing an X-ray diffraction pattern of the ZnO thin film obtained in each of Examples 2-3. .

12A to 12C are graphs showing XPS spectra of the ZnO thin films obtained in Examples 2-1, 2-3, and 2-6.

Hereinafter, the present invention will be described in detail. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention.

According to one aspect of the invention, dissolving zinc salt in water to obtain a zinc salt solution; Adding a basic substance to the zinc salt solution to form a zincate salt solution; And separating the precipitate formed from the zinc salt solution. Provided is a method for preparing a zinc oxide precursor, which method is based on the following Scheme 1.

Scheme 1

As shown in Scheme 1, when zinc salt is dissolved in water and an appropriate amount of basic substance is added, insoluble zinc hydroxide is precipitated. However, when an excess amount of basic substance is added, zinc hydroxide is converted into zincate ion. It forms and dissolves in the solvent. Since the formed zincate ions are in chemical equilibrium with the intermediate stage, as the zinc hydroxide is formed and precipitated, the equilibrium is gradually shifted to the left side, and pure zinc hydroxide crystals are formed in the process and precipitate.

The zinc hydroxide thus obtained is in a pure state with almost no impurities, and may be pyrolyzed at a low temperature of 50 to 200 ° C., more preferably 100 to 150 ° C., to be changed to zinc oxide. At this time, the heat treatment represents an embodiment performed without ultraviolet irradiation, the heat treatment time may be 1 minute to 90 minutes. Embodiments in which the heat treatment is carried out simultaneously with ultraviolet irradiation are described below, and the zinc oxide precursor firing can be made in a shorter time at a lower temperature than the method of firing only by heat treatment.

Compounds containing zinc that can be used in the present invention are water-soluble zinc salts. Non-limiting examples of zinc salts that can be used in the present invention include zinc nitrate, zinc chloride, zinc acetate, zinc sulfate, zinc phosphate, zinc fluoride, zinc bromide, zinc iodide, and the like, or may be used by mixing one or two or more of them. Can be. Among the zinc salts, zinc nitrate is preferred in view of thermal decomposition by low temperature firing.

As the basic material usable in the present invention, various basic materials which can be easily dissolved in water to form a basic solution may be used. Examples thereof include NaOH, KOH, LiOH, ammonia water, but are not limited thereto.

Since the basic material reacts with carbon dioxide in the air to easily form carbonate, in the present invention, in order to prevent the formation of carbonate, the basic material is supersaturated in water and separated from the solution part by focusing on the low water solubility of the carbonate. Can be used. This can minimize the incorporation of unnecessary carbonates into zinc hydroxide. In this way, the formation of zinc carbonate can also be prevented.

In the present invention, the basic substance is used in excess with respect to zinc ions. Specifically, more than theoretical hydroxy ions 5 per mol of zinc ions To 12 Basic materials are used to molar. If used less than 5 moles, the formation of ginkects is not easy and The use of more than mole is insignificant because it inhibits the formation of zinc hydroxide in proportion to it.

The temperature and pressure conditions of the reaction is not particularly limited as long as it meets the object of the present invention, can be carried out at room temperature and atmospheric pressure and can be heated to a temperature of 50 ℃ or less to increase the reaction rate, but at higher temperatures Zinc oxide may be formed.

The zinc hydroxide obtained by the above reaction is separated, washed and dried by conventional methods in the art.

Zinc hydroxide is added to distilled water, C ₁ -C ₃ alcohol, ammonia or a mixture thereof to form a zinc oxide precursor solution.

Zinc hydroxide is doped with one or more metals selected from the group consisting of aluminum (Al), tin (Sn), indium (In), gallium (Ga), iron (Fe), antimony (Sb), and lithium (Li) ( doping). To this end, a doped metal may be added to the zinc oxide precursor solution in which zinc hydroxide is dissolved.

The zinc concentration in the zinc oxide precursor solution is preferably 0.1 to 5% by weight, but is not necessarily limited thereto. When the concentration is lower than 0.1% by weight, the thickness of the zinc oxide thin film to be formed cannot be easily adjusted, and when higher than 5% by weight, it is difficult to obtain a transparent and uniform precursor solution.

The zinc oxide precursor solution of the present invention may contain no or less stabilizer or modifier because of its high solubility in solvents. Since the zinc oxide precursor through the conventional synthesis method has a low solubility in solvents, the solution can be made in a limited range (0.9% or less), but according to the present invention, even without adding a stabilizer or a modifier or a small amount, Clear and homogeneous zinc hydroxide precursor solutions can be prepared.

Examples of stabilizers include, but are not limited to, amine stabilizers such as monoethanolamine, diethanolamine, and triethanolamine. However, the condition of not adding a stabilizer is best because of the specificity of the semiconductor precursor.

When stabilizers are used, their concentration is controlled according to the zinc concentration in the precursor solution for zinc oxide thin film, but may be accompanied by a deterioration after the formation of the semiconductor, so it is preferably included 5 wt% or less based on 100 parts by weight of zinc. .

The coating method of the zinc oxide precursor solution on the substrate is spin coating, dip coating, roll coating, screen coating, spray coating, spin casting ( spin casting, flow coating, screen printing, ink jet, drop casting, and the like, but are not necessarily limited thereto.

The substrate to which the zinc oxide precursor solution is coated may be at least one selected from the group consisting of a wafer substrate, an ITO substrate, a quartz glass substrate, and a plastic substrate, but is not limited thereto.

When the zinc hydroxide solution obtained according to one embodiment of the present invention is low temperature deposited on a substrate, the purity of the compound and the homogeneous and dense morphology of the formed thin film play a particularly important role in high performance semiconductor thin films.

The influence of grain morphology and thin film density on the operational parameters of the thin film transistor is a main factor due to the grain boundary effect. Thus, if large scale sintering and grain growth at low temperatures are not advantageous at low temperatures, the morphology of the coated surface should be as dense as possible at low temperature processed device performance. In particular, porous agglomeration is generated on the surface of the thin film, which is the main interface state in the low temperature firing method, which not only restricts carrier mobility but also subthreshold slope and off current. In view of the negative effect on the electrical properties of the thin film transistor, such as switching voltage (switching voltage), it is noteworthy that low-temperature firing of 200 ° C or less, in particular 150 ° C or less.

According to another embodiment of the present invention, a zinc oxide thin film can be formed in a short time by simultaneously treating the solution containing zinc hydroxide with heat and ultraviolet rays at 50 to 200 ° C, more preferably at 100 to 150 ° C or lower. Ultraviolet treatment can be performed in the wavelength range of 100-1000 nm which may contain visible light, More preferably, it is 180-400 nm wavelength range. Rapid dehydration kinetics can occur during ultraviolet and heat treatment, followed by condensation of Zn-O-Zn bonds. At relatively low temperatures, the crystallization process is difficult mechanically and the rearrangement of Zn-O-Zn bonds is hindered. In the present invention, by treating with ultraviolet light to generate photolysis of the surrounding oxygen to generate reactive oxygen species reacting with the Zn dangling bond to form a metal-oxygen bond, to fill the oxygen vacancies, Attack Zn-O-Zn bonds. This bond-forming / deforming process at relatively low temperatures is caused by calcinations using ultraviolet light, resulting in dense thin films with larger grains. Thus, for high performance devices, simultaneous heat and ultraviolet treatment at 50 to 200 ° C., preferably 100 to 150 ° C., in an ambient atmosphere is completed within 1 second to 30 minutes, preferably 3 minutes. A ZnO thin film having a denser and larger grain can be formed efficiently and time-saving by using a Zn (OH) ₂ / NH ₄ OH solution of 5 wt% or less.

Another aspect of the invention relates to an electronic component comprising a zinc oxide thin film obtained by the method according to one aspect of the invention. Such electronic components include, but are not necessarily limited to, transparent electrodes, solar cells, optical sensors, TFTs, zinc oxide nanowires, and light emitting materials.

In the following Examples, the present invention will be described in more detail in detail, but the following examples are provided for illustrative purposes, and the scope of the present invention is not limited to the following examples.

Example 1-1: Synthesis of Zinc Hydroxide

Sodium hydroxide (NaOH) was dissolved in water to prepare a carbonate-free 50% NaOH solution. The clear solution portion was separated and titrated with potassium hydrogen phthalate (KHP) to prepare a 2.4 M NaOH solution containing no carbonate.

An aqueous zinc solution was prepared by dissolving 49.8 g of zinc nitrate hexahydrate in a 5 L two-necked round flask in 900 ml of tertiary distilled water. 600 ml of a 2.4 M NaOH solution without carbonate was added to the aqueous zinc solution. The solution was slowly heated and stirred at 50 ° C. for 2 hours. Particles were formed while Zn (OH) ₂ was formed during stirring heating. The produced Zn (OH) ₂ was filtered under reduced pressure using a paper filter, and the filtered material was again dispersed in distilled water and washed. In the last step, the mixture was washed with methanol and dried naturally to obtain zinc hydroxide.

Example 1-2 Synthesis of Zinc Hydroxide

In the method of Example 1-1, the heating temperature was lowered to 40 ° C. and the stirring time was about 3 hours to obtain desired zinc hydroxide.

Example 1-3 Synthesis of Zinc Hydroxide

In the method of Example 1-1, the heating temperature was lowered to 25 ° C. and the stirring time was about 10 hours to obtain desired zinc hydroxide.

Example 1-4: Synthesis of Zinc Hydroxide

In the method of Example 1-1, the desired heating temperature was lowered to 15 ° C. and stirring time was about 24 hours to obtain desired zinc hydroxide.

Example 1-5: Synthesis of Zinc Hydroxide

The desired zinc hydroxide was obtained in the same manner using zinc chloride instead of zinc nitrate in Example 1-1.

Example 1-6 Synthesis of Zinc Hydroxide

In Example 1-1, zinc zinc was used instead of zinc nitrate to obtain desired zinc hydroxide in the same manner.

Example 1-7: Synthesis of Zinc Hydroxide

In Example 1-1, desired zinc hydroxide was obtained in the same manner using potassium hydroxide instead of sodium hydroxide.

Example 1-8: Synthesis of Zinc Hydroxide

In Example 1-2, desired zinc hydroxide was obtained in the same manner using potassium hydroxide instead of sodium hydroxide.

Example 1-9: Synthesis of Zinc Hydroxide

In Examples 1-1 to 1-6, desired zinc hydroxide was obtained in the same manner using 25% ammonia water instead of sodium hydroxide.

Example 2-1 Preparation of Zinc Oxide Thin Films and Devices

Zinc hydroxide (Zn (OH) ₂ ) synthesized above was dissolved in aqueous NH ₄ OH (Duksan, 25-30%) to prepare a 2% by weight precursor stock solution to prepare a ZnO layer. The Zn (OH) ₂ / NH ₄ OH solution was filtered through a 0.2 μm PVDF filter and spin coated at 4000 rpm for 30 seconds on a 100 nm SiO ₂ / p-doped Si substrate. The coated thin film was baked to cure for 1 hour on a hot plate preheated to 150 ° C. in air. Subsequently, a source and drain electrode was fabricated by depositing an aluminum layer on the ZnO thin film using a metal evaporator (VPC-260) having a 50 μm channel width and 40 μm length to produce a bottom-gate in the fabrication of a ZnO base thin film transistor. And top-contact thin film transistor structures.

Example 2-2 Preparation of Zinc Oxide Thin Films and Devices

A zinc oxide thin film and a device were manufactured in the same manner as in Example 2-1, except that Ar / H ₂ was used instead of air as the firing condition. More specifically, the coated thin film was cured at 150 ° C. while flowing Ar / H ₂ at 100 cc / min in a tube furnace.

Example 2-3 Preparation of Zinc Oxide Thin Films and Devices

A zinc oxide thin film and a device were manufactured in the same manner as in Example 2-1, except that 150 ° C. heat treatment / ultraviolet light exposure was simultaneously performed in air under firing conditions. For ultraviolet treatment, a 1.1 kW medium pressure mercury UV lamp (Lichtzen, South Korea) with peak intensity at 365 nm was used and the distance from the sample to the lamp was set to 7 cm. During ultraviolet exposure the surface temperature of the hot plate increased to 10 ° C. and then settled to the desired temperature within 5 minutes.

Example 2-4 Preparation of Zinc Oxide Thin Films and Devices

A zinc oxide thin film and a device were manufactured in the same manner as in Example 2-3, except that the zinc hydroxide coating was performed twice.

Example 2-5 Preparation of Zinc Oxide Thin Films and Devices

After forming the Al gate electrode on a 100 nm SiO ₂ / p-doped Si substrate, Example 2-3 and Al ₂ O ₃ gate insulator having a thickness of 100 nm were further coated by atomic layer deposition. In the same manner, zinc oxide thin films and devices were prepared.

Example 2-6 Preparation of Zinc Oxide Thin Films and Devices

A zinc oxide thin film and a device were manufactured in the same manner as in Example 2-3, except that 4 wt% zinc hydroxide solution was used.

Example 2-7 Preparation of Zinc Oxide Thin Films and Devices

Zinc oxide thin film by the method described in Example 2-3 except for using a 4% by weight zinc hydroxide solution, and proceeding to the process described in Example 2-1 to the process described in Example 2-3 And devices.

Analysis / evaluation method

Zn (OH) ₂ powder or ZnO thin film after heat treatment or ultraviolet treatment was measured by XRD.

XRD data were collected using Bruker D8 Advance.

Thermogravimetric analysis of Zn (OH) ₂ powder was carried out at 2 ° C./min heat treatment rate using a TA instrument (Q50).

Fourier transform infrared spectroscopy (FT-IR) spectra were obtained on JASCO FT / IR 6100.

Field emission scanning electron microscopy (FE-SEM) images were obtained with Carl Zeiss LEO SUPRA 55.

The relative oxygen vacancies in the ZnO thin films were confirmed using X-ray photoelectron spectroscopy (XPS).

The electrical characteristics of the device were analyzed in ambient air using a semiconductor parameter analyzer (Agilent 4155B).

Evaluation Example 1: TGA Measurement

The result of heat-treating the zinc hydroxide obtained in Example 1-1 is shown in FIG. Referring to Figure 1, the zinc hydroxide obtained in Example 1-1 was changed to zinc oxide in one step at 130 ℃. In this process, as shown in the following reaction formula 2, one of the water powders from the white powder Zn (OH) ₂ exits and decomposes into ZnO. That's about 81.88%:

Scheme 2

Zn (OH) _2- > ZnO + H ₂ O

Depending on the amount of sample and the TGA scan rate, there was a slight variation in the final temperature of zinc hydroxide to zinc oxide, but it showed a weight content of 83% close to theory at about 150 ° C starting at 100 ° C. The pyrolysis reaction actually proceeds at lower temperatures because the rate is determined dynamically.

Evaluation Example 2: SEM Photograph of Zinc Hydroxide

The zinc hydroxide obtained in Example 1-1 was photographed by FE-SEM and shown in FIG. 2. Referring to FIG. 2, the zinc hydroxide obtained in Example 1-1 was obtained cleanly as crystals of one form.

Evaluation Example 3 XRD Results of Zinc Hydroxide and Zinc Oxide

XRD of the zinc hydroxide obtained in Example 1-1 was measured, and the result is shown in FIG. 3A.

According to FIG. 3A, the XRD (black graph) of zinc hydroxide obtained in Example 1-1 is consistent with the standard sample (gray graph) of zinc hydroxide having an orthorhomic structure, and the oxidation obtained in Example 2-1 according to FIG. 3B. The XRD graph of zinc (black graph) is consistent with the standard sample of zinc oxide (grey graph).

After the zinc hydroxide obtained in Example 1-1 was heat-treated at 100 ° C. for 1 hour or 3 hours, respectively, the XRD was measured and the graph is shown in FIG. 4. From the fact that XRD after heat treatment for 1 hour and 3 hours was almost identical, it was found that the zinc hydroxide obtained in Example 1-1 changed to zinc oxide even with a short time firing within 100 hours at 100 ° C.

Evaluation Example 4: Thermal Change Characteristics of Zinc Hydroxide by FT-IR

After firing the zinc hydroxide obtained in Example 1-1 at 150 ° C. for 1 minute, 3 minutes, 5 minutes, and 15 minutes, the FT-IR was measured for each, and the graph is shown in FIG. 5.

It can be seen from FIG. 5 that the OH group (about 3500 cm ⁻¹ peak) of zinc hydroxide disappears upon firing at 150 ° C. for 3 minutes. This means that the zinc hydroxide according to the present invention can be easily changed to zinc oxide by firing, thereby obtaining the characteristics of the semiconductor.

Evaluation Example 5 Solubility of Ammonia Water in Zinc Hydroxide

The zinc hydroxide obtained in Example 1-1 was dissolved in 25% aqueous ammonia at 1% by weight, 2% by weight, 3% by weight, 4% by weight and 5% by weight, respectively, and photographed.

According to FIG. 6A, the zinc hydroxide obtained in Example 1-1 was found to be completely transparent and homogeneously dissolved to form a solution even when dissolved in 25% ammonia water at a concentration of 5% by weight.

For comparison with Experimental Example 5, commercially available zinc hydroxide (Junsei) was dissolved in 25% ammonia water and photographed and shown in FIG. 6B. According to FIG. 6B, the zinc hydroxide in the market was found to have a solubility of 0.9%.

Evaluation Example 6: Solubility of Ammonia in Calcined Zinc Oxide

Zinc oxide obtained in Example 1-1 was calcined at 150 ° C. for 3 hours to dissolve zinc oxide formed in 25% ammonia water at a concentration of 0.45% by weight, 0.90% by weight, 1.35% by weight, and 1.8% by weight. 7 is shown.

According to FIG. 7, the zinc oxide was completely dissolved in ammonia water even at a concentration of 1.35 wt%.

For comparison, commercially available zinc oxide (Aldrich, 99.9% by weight) was dissolved in 25% aqueous ammonia at 0.45% by weight, 0.90% by weight, and 1.35% by weight, and photographed and shown in FIG. 8. According to FIG. 8, the concentration of zinc oxide purchased on the market was 0.9%, in which a transparent solution was dissolved in 25% ammonia water.

Evaluation Example 7 Evaluation of Thickness and Grain Boundary of the Zinc Oxide Thin Film

The zinc hydroxide synthesized in Example 1-1 was dissolved in 25% ammonia water to prepare a zinc oxide precursor solution having a concentration of 1% by weight, 2% by weight, 3% by weight, 4% by weight, and 5% by weight, respectively. The thickness change of the zinc oxide thin film obtained after spin coating the prepared zinc oxide precursor solution on a silicon wafer substrate and sufficiently baked at 150 ° C. was investigated using FE-SEM. As a result, the thickness of the zinc oxide thin film was found to vary almost linearly with the zinc oxide precursor concentration.

Table 1

Zinc Oxide Precursor Concentration	ZnO Thin Film Thickness
1 wt%	12.7 nm
2 wt%	17.6nm
3 wt%	27.4nm
4 wt%	36.7 nm

In addition, FE-SEM images of ZnO thin films prepared from the synthesized Zn (OH) ₂ solution using various firing conditions are shown in FIGS. 10A-10D.

Example 2-1 The thin film was 35.5 nm thick (FIG. 10A), similar to the thin film thickness (33.7 nm) of FIG. 10C, which was simultaneously treated with UV and heat for 3 minutes.

The size of grain boundaries in thin films is determined by firing methods such as ultraviolet or heat treatment. The grain boundaries of the UV treated thin film (FIGS. 10B and 10C) were larger than the thin film grain boundaries (FIG. 10A) by heat treatment without UV treatment.

In particular, the Example 2-6 thin film (FIG. 10D) has a larger grain than the Example 2-1 thin film (Example 10a) and uses a Zn (OH) ₂ solution at a concentration of at least 2 to 3 times higher than other samples. It had a thin film thickness of 48.5 nm thicker even though the coating was made once.

Evaluation Example 8: ICP-MS Analysis of Zinc Hydroxide

The amount of impurities present in the zinc hydroxide obtained in Example 1-1 was investigated by using ICP-MS. If the purity of the starting material is more than 99.50%, all impurities of other cations contained are negligible below ppm. Therefore, the purity of the zinc hydroxide produced in Example 1-1 is very excellent.

TABLE 2

Impurity	Impurity in Zn (OH) 2 / ppb
	Zn (NO 3 ) 2 99.50%	Zn (NO 3 ) 2 99.999%
Na	201.1	320.9
Mg	23.3	48
Al	47.5	52.2
K	156.8	276.7
Ca	22	41.2
Fe	134.4	110.1
Pb	1.6	4.8

Evaluation Example 9: Characterization of Oxide Semiconductors

The zinc hydroxide obtained in Example 1-1 was dissolved in 25% ammonia water to prepare a zinc oxide precursor solution at a concentration of 2% by weight. The solution was spin coated onto a p-doped silicon wafer made of 100 nm silicon oxide and then calcined to 110 ° C. After that, the source and drain electrodes were formed by depositing aluminum, and then TFT electrical characteristics were measured. The results are summarized in Table 3 below, and the transfer curve of the oxide semiconductor is shown in FIG. 9B:

Table 3 below shows the importance of thin film transistors such as field-effect mobility, subthreshold swing, I _on / I _off ratio and threshold voltage (V _th ) using various firing conditions. The electrical characteristics are summarized.

TABLE 3

Example	Zinc hydroxide concentration	Firing conditions	Mobility cm 2 / Vs	Subcritical Swing V / decade	I on / I off	V th (V)
2-1	2 wt%	150 ° C, 1h, air	0.6	1.1	About 10 5	8
2-2	2 wt%	150 ° C., 1 h, Ar / H 2	0.5	0.92	About 10 6	17
2-3	2 wt%	150 ° C., 3 minutes, UV	0.63	0.76	About 10 6	18
2-4	2 wt%	150 ° C, 3 minutes, UV, 2 layers	1.07	0.45	About 10 6	17
2-5	2 wt%	150 ° C., 3 minutes, UV, Al 2 O 3 (dielectric)	1.15	0.6	About 10 7	25
2-6	4 wt%	150 ° C., 3 minutes, UV	2.91	0.47	About 10 6	15
2-7	4 wt%	150 ° C, 1h, air-> 150 ° C, 3 minutes, UV	1.17	0.8	About 10 6	2

The zinc oxide thin film of Example 2-3 exhibited substantially similar electrical characteristics to the zinc oxide thin film of Example 2-1, which is different from ZnO grain (when UV irradiation and heat treatment are performed simultaneously). This means that the semiconductor channel in grains can be effectively activated even at shorter process times.

On the other hand, the electrical properties of the zinc oxide thin film of Example 2-2 did not change much.

In the zinc oxide thin film of Example 2-4, as a result of coating the same solution twice, the channel thickness was increased to improve the mobility performance twice.

ZnO thin-film transistors fabricated with patterned gates were modified to meet 100 nm thick Al ₂ O ₃ by UV irradiation at 150 ° C. for 3 minutes and atomic layer deposition (ALD) into the gate dielectric. Improved.

The transfer characteristics of the ZnO-TFTs of Examples 2-5 exhibited a low off-current of less than 10 ⁻¹² A and a higher on-off current ratio of about 10 ⁷ (see FIG. 9B). The measured saturation mobility was 1.15 cm ² / Vs at 40V gate voltage, and the threshold voltage (V _th ) and subcritical swing were 25V and 0.6V / dec, respectively.

The zinc oxide thin films of Examples 2-6 and 2-7 show typical field effect transistor embodiments according to FIG. 9B. In FIG. 9B the I _on / I _off current ratio is about 10 ⁶ and is expected to be further improved by the patterned active channel layer. Threshold voltage (V _th ) and subthreshold swing were 14.6 V and 0.47 V / dec, respectively. The field effect mobility extracted from the saturation regime was 2.91 cm ² / Vs at the gate voltage of 40V when irradiated with UV light at 150 ° C for 3 minutes.

The electrical properties of the thin film transistor are also affected by the thickness and grain size of the ZnO thin film. The zinc oxide thin film of Example 2-6 has an improved field effect mobility of 2.91 cm ² / Vs because of the large grain boundary and the thin film thickness. Indicated. Larger ZnO crystals due to simultaneous UV / heat treatment significantly improve the mobility of the ZnO thin film transistor because the migration length is reduced throughout the grain boundaries.

The graph of FIG. 11 shows the X-ray diffraction pattern (A curve) of the ZnO thin film heat-treated at 150 ° C. without UV treatment and the X-ray diffraction pattern (B curve) of the ZnO thin film heat-treated at 150 ° C. for 3 minutes under UV irradiation. .

In FIG. 11, the A curve does not show a ZnO diffraction pattern, while the B curve is based on three diffraction peaks of polycrystalline ZnO in the (100), (002), and (101) planes as shown in FIG. Represents a pattern. It was proved that the ZnO thin film annealed under UV treatment exhibited an increased XRD pattern than the ZnO thin film annealed without UV treatment. That is, UV / thermal co-treatment increases both the deposition of the zinc precursor and the thin film crystallization and greatly reduces the overall process time.

Another important point in the properties of oxide semiconductor materials is the bulk defect structure, and the general trend of the relative concentration of the internal ZnO thin film can be confirmed by XPS. The O 1s XPS spectrum of the ZnO thin film is shown in FIGS. 12A-12C, which are determined by the firing method.

12A to 12C, the zinc hydroxide thin film obtained in the present invention was converted to ZnO by heat treatment at 150 ° C. for 1 hour (see FIG. 12A). There is an intensive peak at 529.2 eV along the broad shoulder peak at 530.8 eV and 531.6 eV in the O 1s XPS spectrum. These peaks represent lattice oxygen, oxygen near the oxygen vacancies and hydroxy oxygen, respectively. There are minor differences in oxygen vacancies and hydroxy peaks generated during the firing process throughout the condensation and dehydration processes, but all three XPS results appear to be very similar. In addition, the oxygen vacancies are the source of charge carriers, while the hydroxy moiety slightly degrades device mobility. In addition, since the method of exposing the zinc hydroxide thin film to UV light at 150 ° C. for 3 minutes corresponds to 1 hour of heat treatment and the XPS results are very similar (see FIGS. 12A and 12B), simultaneous UV and thermal treatment is performed on a ZnO thin film transistor device. It can be seen that it is an effective method to prepare. Likewise, it can be seen that the method of heat / ultraviolet treatment by increasing the concentration of zinc hydroxide, for example, to 4% by weight, is an effective method for manufacturing a ZnO thin film transistor device (see FIG. 12C). In the case of UV / thermal co-treatment, Zn-OH-Zn is easily converted to Zn-O-Zn, and surface hydroxy groups are removed to influence other factors such as grain size and crystallinity as shown in Examples 2-6. The overall mobility then increased.

The zinc hydroxide prepared in the present invention can be dissolved in a solvent at a high concentration, so it can be expected to make an oxide semiconductor in the printing process in the future, and in particular, it can be used as a backplane semiconductor by being changed to zinc oxide at low temperature. It is expected to contribute to the industry or the sensor industry.

Claims (16)

1. Dissolving the zinc salt in water to obtain a zinc salt solution;

   Adding a basic substance to the zinc salt solution to form a zincate salt solution; And

   Separating the precipitate formed from the zinc salt solution

   Method for producing a zinc oxide precursor.
2. The method of claim 1,

   Zinc oxide, zinc sulfate, zinc nitrate, zinc nitrate, zinc acetate, zinc phosphate, zinc fluoride, zinc bromide and zinc iodide selected from the group consisting of one or two or more mixtures of zinc oxide precursors Manufacturing method.
3. The method of claim 1,

   And the basic substance is one selected from the group consisting of ammonia water, sodium hydroxide, potassium hydroxide and lithium hydroxide.
4. The method of claim 1,

   A method for producing a zinc oxide precursor, characterized in that a basic substance is added so as to have 5 to 12 moles of hydroxy ions per mole of zinc ions.
5. The method of claim 1,

   The basic material is a method for producing a zinc oxide precursor, characterized in that the solution portion is separated from the supersaturated basic solution.
6. Zinc oxide precursor, characterized in that prepared according to any one of claims 1 to 5.
7. A method of manufacturing a zinc oxide thin film comprising the step of heat-treating the zinc oxide precursor of claim 6 in a temperature range of 50 to 200 ℃.
8. The method of claim 7, wherein

   The heat treatment is a method for producing a zinc oxide thin film, characterized in that carried out at a temperature range of 100 to 150 ℃.
9. The method of claim 7, wherein

   The heat treatment is performed for 1 minute to 90 minutes, the method for producing a zinc oxide thin film.
10. The method of claim 7, wherein

    The heat treatment is carried out in air or Ar / H ₂ method for producing a zinc oxide thin film.
11. A method of manufacturing a zinc oxide thin film comprising the step of ultraviolet treatment while heat-treating the zinc oxide precursor of claim 6 at room temperature to 200 ℃ temperature range.
12. The method of claim 11,

    The heat treatment is a method of producing a zinc oxide thin film, characterized in that carried out in a temperature range from room temperature to 150 ℃.
13. The method of claim 11,

    The heat treatment and ultraviolet treatment is a method for producing a zinc oxide thin film, characterized in that performed for 1 second to 30 minutes.
14. The method of claim 11,

    The method of manufacturing a zinc oxide thin film, characterized in that the ultraviolet treatment is carried out in the 100 to 1000 nm wavelength range.
15. Zinc oxide thin film obtained by the manufacturing method of any one of Claims 7-14.
16. The method of claim 15,

    Zinc oxide thin film, characterized in that it is used in a transparent electrode, a solar cell, an optical sensor, a thin film transistor (TFT), zinc oxide nanowire (nanowire) or a light emitting material.

Images