JP5597510B2 - Core-shell semiconductor fine particles - Google Patents

Description

  The present invention relates to a core-shell type particle and a method for producing the same. The present invention also relates to a thin film transistor manufactured using core-shell particles and a method for manufacturing the same.

  Field effect transistors are widely used as unit electronic elements, high frequency signal amplifying elements, liquid crystal driving elements and the like of semiconductor memory integrated circuits, and are the most widely used electronic devices at present.

  Among them, with the remarkable development of display devices in recent years, not only liquid crystal display devices (LCD) but also various display devices such as electroluminescence (EL) display devices and field emission displays (FED) are driven by display elements. Thin film transistors (TFTs) are frequently used as switching elements for driving a display device by applying a voltage.

As the material, a silicon semiconductor compound is most widely used. Generally, a silicon single crystal is used for a high-frequency amplifying element and an integrated circuit element that require high-speed operation, and a liquid crystal driving element or the like is used. Amorphous silicon is used because of the demand for large area.
Amorphous silicon has the advantage that it can be formed at a relatively low temperature, but its switching speed is slower than crystalline silicon, so when it is used as a switching element to drive a display device, it cannot follow high-speed video display There is. In addition, since the transmittance of visible light is low, if the semiconductor layer protrudes from the electrode section, the transmittance of the display section may decrease, the illumination efficiency by the backlight may decrease, and the screen may become dark, and the tolerance of processing accuracy is small. It contributed to the cost increase.

Under such circumstances, an oxide semiconductor has been proposed as a solution to the above problem. In recent years, a flexible thin film transistor using an amorphous oxide semiconductor manufactured by a vapor phase method has been reported. According to this, amorphous ZnGaInO ₄ is formed on the plastic substrate by a vapor phase method, and high rectification characteristics are obtained.

However, since the vapor phase method requires a vacuum system and the apparatus is large and complicated for a large area, wet processes such as coating have been studied. Further, high-performance ZnGaInO ₄ uses a large amount of rare and expensive Ga and In, which is a big problem in terms of energy saving and resource saving.

As a method of reducing the use of rare and expensive elements, there are cases where these high-functional elements are present only on the surface, and core-shell type particles using a large amount of inexpensive elements as the core are used.
As the core-shell type semiconductor particles, it is known that a quantum well structure is expressed and the movement of electrons is suppressed by the shell layer, so that the light emission efficiency is improved. Patent Document 1 discloses Si, Ge, InN, InP as cores. And examples using compound semiconductors are shown.

  Patent Document 1 describes a core-shell type particle having a metal element having a band gap (3 eV or less) below the energy gap of visible light as a core, but in the vicinity of visible light (350 to 1100 nm: 3.54 to 1). .13 eV) and does not transmit visible light, and cannot be used as transparent semiconductor particles.

JP 2009-132771 A

  An object of the present invention is to provide core-shell type fine particles that can be used in the manufacture of semiconductor devices by a wet process such as coating, have good electrical characteristics, and can be manufactured at low cost.

According to the present invention, the following core-shell type particles and the like are provided.
1. A core particle and a shell covering at least a part of the surface of the core particle;
The core particle is made of at least one metal oxide (A) having a band gap of 3 eV or more,
The shell is a core-shell type particle of 0.01 to 1 μm made of at least one metal oxide (B).
2. 2. The core-shell type particle according to 1, wherein the metal oxide (A) is a metal oxide selected from Sn, Zn, In, and Ga.
3. 3. The core-shell type particle according to 1 or 2, wherein the metal oxide (B) is an oxide of a metal selected from Sn, Zn, In, Ga, Al, Ti, Zr, Hf and Cu.
4). a) A core particle containing at least one metal oxide having a band gap of 3 eV or more is mixed with a solution in which at least one metal compound is dissolved or dispersed,
b) A method for producing 0.01 to 1 μm core-shell type particles in which the mixture is reacted at 200 to 800 ° C. and at least a part of the surface of the core particles is covered with a metal oxide of the metal compound.
5. 5. The method for producing core-shell particles according to 4, wherein the metal oxide is a metal oxide selected from Sn, Zn, In, and Ga.
6). 6. The method for producing core-shell particles according to 4 or 5, wherein the metal compound is a metal compound selected from nitrates, carbonates, acetates, hydroxides and halides.
7.4 Core-shell particles obtained by the method according to any one of 7.4 to 6.
8. Dispersion liquid containing core-shell type particle | grains in any one of 1-3, 7, and a dispersion medium.
9. 9. The dispersion liquid according to 8, wherein the dispersion medium is at least one selected from water or a non-aqueous solvent.
A coating liquid for forming a semiconductor film, comprising the dispersion liquid according to 10.8 or 9.
11. A thin film transistor having a channel layer made of core-shell particles according to any one of 11.1 to 3.
A method for producing a thin film, which is formed by applying and drying the dispersion according to 12.8 or 9.
13. A thin film transistor using a thin film obtained by the production method according to 13.12 as a channel layer.

  ADVANTAGE OF THE INVENTION According to this invention, it can be used in manufacture of the semiconductor device by wet processes, such as application | coating, and it can provide the core-shell type fine particle which has a favorable electrical property and can be manufactured cheaply.

It is a figure which shows one Embodiment of the thin-film transistor of this invention.

  The core-shell type particle of the present invention comprises a core particle and a shell covering at least a part of the surface of the core particle. The core particle contains at least one metal oxide (A) having a band gap of 3 eV or more, and the shell contains at least one metal oxide (B). The particle diameter of the core-shell type particles is 0.01 to 1 μm.

The particle diameter of the core-shell type particles is preferably 0.01 to 0.2 μm, more preferably 0.01 to 0.1 μm, and more preferably 0.01 to 0.05 μm. Transparent and stable FET operation can be obtained when the thickness is 0.01 to 0.2 μm.
The thickness of the shell is usually 0.1 to 3 nm.

  The core particle is composed of one or more metal oxides (A) having a band gap of 3.0 eV or more, preferably 3.1 eV or more. As a result, a transparent oxide semiconductor is obtained.

The band gap can be measured by UV-Vis spectrum. It is determined by the following equation from the absorption edge of the UV-Vis spectrum.
α · hν = A (hν−E _g ) ⁿ
α is the absorbance near the absorption edge, ν is the frequency, A is a constant, E _g is the bandgap energy, and n is a constant. From this equation, E _g is determined from the intercept by plotting (α · hν) ^1/2 against the light energy hν.

Examples of the metal oxide (A) having a band gap of 3 eV or more include SnO ₂ (3.8 to 4.0 eV), ZnO (3.3 to 3.6 eV), In ₂ O ₃ (3.6 to 4. 2eV) and Ga ₂ O ₃ (4.8 to 5.0 eV), but are not limited thereto.
Among these, SnO ₂ and ZnO are preferable from the viewpoint of manufacturing cost. SnO ₂ is preferable from the viewpoint of chemical stability. From the viewpoint of high mobility, SnO ₂ ,
ZnO and In ₂ O ₃ are preferred. Furthermore, it is preferable to use SnO ₂ or ZnO because the use of rare elements can be reduced.

  Preferably, the metal oxide (A) in the core portion is crystalline, and the metal oxide (B) in the shell portion covering the core metal is amorphous. In this way, it is possible to prevent the electron carrier from being scattered at the interface of the core-shell particles.

  The metal oxide (B) is not particularly limited, but an oxide of at least one selected from Sn, Zn, In, Ga, Al, Ti, Zr, Hf, and Cu, preferably 2 to 4 metals is preferable. .

When Sn, Zn, In, Ga, or Al is used, field effect mobility is improved, and when Ti, Zr, or Hf is used, oxygen is easily taken in, so oxygen vacancies in the core-shell type particles are reduced, and the carrier concentration is increased. It can reduce and it can be set as the favorable FET characteristic.
The carrier concentration can also be reduced by using an element such as Cu having a low valence with respect to other metal elements constituting the core-shell type particles.

  Transparent metal particles can be formed by selecting a transparent metal oxide that forms the core and shell. For example, tin oxide is selected as the core and indium-gallium-zinc amorphous oxide is selected as the shell.

The core-shell type particles of the present invention can be produced by a method including the following steps:
a) a step of mixing a solution in which at least one metal compound is dissolved or dispersed in core particles containing at least one metal oxide (A) having a band gap of 3 eV or more;
b) The process which makes the said mixture react at 200-800 degreeC, and covers at least one part of the surface of the said core particle with the metal oxide (B) of the said metal compound.

  As the core particles used in step a), those described above can be used.

The solution to be impregnated into the core particles is a solution in which a metal compound is dissolved or dispersed in a solvent such as water, and preferably a solution in which 2 to 4 kinds of metal compounds are dissolved or dispersed.
The metal compound is preferably a compound of Sn, Zn, In, Ga, Al, Ti, Zr, Hf or Cu, and is preferably a nitrate, carbonate, acetate, hydroxide or halide. Hydrates may also be used.

  The compounding ratio of the metal oxide (A) and the metal compound is preferably 0.001 to 0.1 mol of one or more metal compounds with respect to 1 mol of the metal oxide (A).

  When the above solution is mixed with the core particle, the surface of the core particle is impregnated with the solution. Mixing is performed, for example, for 1 to 20 hours using a ball mill.

Next, this mixture is reacted at 200 to 800 ° C., preferably 300 to 600 ° C., to produce a metal oxide (B) of the above metal compound. This metal oxide (B) covers at least part or all of the surface of the core particle.
This reaction is performed, for example, in an inert gas atmosphere (nitrogen or the like) or an air atmosphere, for example, for 0.1 to 10 hours.

As a method for producing composite oxide ultrafine particles, a method is generally used in which a plurality of metal salt aqueous solutions are co-precipitated by pH adjustment to obtain composite hydroxide, which is filtered, dried and then fired.
However, because of the ultrafine particles, filtration and composition control are difficult, and defects are likely to remain in the fine crystal due to the conversion from hydroxide to oxide. For this reason, it is difficult to increase the mobility of electrons, and it becomes difficult to develop the FET behavior.

In the present invention, when the shell of the surface layer is composed of two or more metal oxides, a composite oxide is formed.
By using existing oxide fine particles as core particles of raw materials and generating composite oxide particles only on the surface layer, high mobility can be achieved by utilizing the high crystallinity of the core particles, so that FET behavior can be easily achieved. Can be expressed.
As a method for coating the surface layer with the composite oxide, a plurality of kinds of metal salt aqueous solutions are impregnated into the oxide ultrafine particles serving as the core, followed by baking after drying.

In the method of the present invention, since a solid phase method is used instead of a liquid phase method in the process of coating the surface layer, a filtration step, a precipitation, a coprecipitation step are unnecessary, and it is not necessary to alkoxylate the raw material. Manufacturing cost can be reduced.
Further, since the contact resistance generated between the particles can be reduced while ensuring the crystallinity of the core particles, the high mobility and the on / off ratio of the obtained thin film transistor are expected.

The dispersion of the present invention contains the core-shell type particles of the present invention and a dispersion medium. The dispersion can be used as a coating liquid for semiconductor film formation.
A thin film can be easily formed by a coating method using the dispersion of the present invention. For example, the dispersion is discharged toward the substrate or the substrate by a printing method, an inkjet method, a dispenser method, or the like. Thereafter, it is dried by heating or the like to form a film.

The dispersion medium is preferably at least one selected from water or a non-aqueous solvent. Examples of the non-aqueous solvent include alcohols, ketones, ethers, esters, aromatic solvents, and the like, and non-aromatic solvents are preferable from the environmental viewpoint.
It is preferable to further improve the dispersibility of the powder by adding a dispersant such as a surfactant.

  The thin film transistor of the present invention has a channel layer manufactured using core-shell type particles. The configuration is not limited as long as the channel layer is made of core-shell type particles. FIG. 1 shows an embodiment.

The thin film transistor 1 has an insulating film 20 on a substrate (gate electrode) 10, and has a pair of a source electrode 30 and a drain electrode 40 formed on the insulating film 20 at a predetermined interval. A channel layer 50 is provided so as to cover the insulating film 20 between the drain electrodes 40.
The channel layer 50 is composed of the core-shell type particles of the present invention. The channel layer 50 can be formed by the above coating method.

  The substrate 10 also serves as a gate electrode, and the current flowing through the channel layer 50 between the source electrode 30 and the drain electrode 40 is controlled by a voltage applied to the substrate 10, whereby the thin film transistor 1 is turned on / off.

Example 1
(1) Production of fine particle oxide 19.611 g of tin oxide ultrafine particles (Mitsubishi Materials, trade name S-1) were weighed, and 0.185 g of indium nitrate trihydrate and 0.1258 g of gallium nitrate octahydrate were added thereto. Then, 0.078 g of zinc nitrate hexahydrate was mixed with 4 g of water, a dissolved aqueous solution was added, and the mixture was mixed for 2 hours with a planetary ball mill.

  The mixed powder was dried with a dryer for 3 hours and then calcined at 500 ° C. for 30 minutes while flowing nitrogen at 0.5 L / min in a tubular furnace to obtain pale yellow fine particle oxides. About this light yellow particle | grain, it measured by four-probe method using a particle-resistance measuring system (made by Dia Instruments Co., Ltd.), and it measured the electric conductivity in 9.81 MPa from the graph of pressure-electric conductivity ( σ) was obtained. Further, the element ratio of the elements constituting the core-shell type particles was measured by ICP-MS (inductively coupled plasma mass spectrometry). The particle size of the core particles was measured by the BET method. The results are shown in Table 1.

(2) Production of Fine Particle Dispersion Solution 0.4 g of the fine particles produced above were added to a solution of 3.56 g of methoxypropanol and 0.05 g of a dispersant (Chemie BYK-2000), and 1 was added using an ultrasonic cleaner. Dispersion was carried out over time to prepare a dispersion.

(3) Production of Thin Film Transistor The bottom contact type thin film transistor 1 shown in FIG. 1 was produced.
A conductive silicon substrate 10 with a thermal oxide film (SiO ₂ film) 20 having a thickness of 100 nm was used. The thermal oxide film functions as the gate insulating film 20, and the conductive silicon portion 10 functions as the gate electrode.

  A metal mask is installed on the gate insulating film 10, and the channel portion 50 having a source-drain electrode gap (L) of 200 μm and a width (W) of 3000 μm is formed in the vicinity of both ends of the channel portion. Gold was deposited to form the source electrode 30 and the drain electrode 40.

  Thereafter, the fine particle dispersion was taken in a microsyringe, dropped between the source and the drain, dried on a hot plate at 50 ° C. for 30 minutes, and then placed in a tubular furnace and heat-treated at 300 ° C. in a nitrogen stream to produce the thin film transistor 1.

Using the semiconductor parameter analyzer, the source-drain current Ids when the gate voltage was changed from -30V to + 30V was measured using the semiconductor parameter analyzer, and the maximum and minimum values were measured. As a result of calculating the drain current ratio (hereinafter referred to as on / off ratio) as a measure of characteristics, it was 2 × 10 ³ . The results are shown in Table 1.

Example 2
19.574 g of tin oxide ultrafine particles (Mitsubishi Materials, trade name S-1) was weighed, and 0.23 g of indium nitrate trihydrate, 0.157 g of gallium nitrate octahydrate, zinc nitrate hexahydrate 0 0.039 g was mixed with 4 g of water and a dissolved aqueous solution was added, and mixed for 2 hours with a planetary ball mill.
Other than this, a fine particle oxide, a fine particle dispersion and a TFT were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1. A large ON / OFF ratio was obtained.

Example 3
19.692 g of tin oxide ultrafine particles (Mitsubishi Materials, trade name S-1) was weighed, and 0.189 g of gallium nitrate octahydrate and 0.118 g of zinc nitrate hexahydrate were mixed and dissolved in 4 g of water. The aqueous solution was added and mixed for 2 hours in a planetary ball mill.
Other than this, a fine particle oxide, a fine particle dispersion and a TFT were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1. A large ON / OFF ratio was obtained.

Example 4
19.605 g of tin oxide ultrafine particles (Mitsubishi Materials, trade name S-1) were weighed, and 0.277 g of indium nitrate trihydrate and 0.118 g of zinc nitrate hexahydrate were mixed and dissolved in 4 g of water. The aqueous solution was added and mixed for 2 hours in a planetary ball mill.
Other than this, a fine particle oxide, a fine particle dispersion and a TFT were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1. A large ON / OFF ratio was obtained.

Example 5
A fine particle oxide, a fine particle dispersion and a thin film transistor were prepared and evaluated in the same manner as in Example 4 except that the firing atmosphere was changed to air. The results are shown in Table 1. A large ON / OFF ratio was obtained.

Example 6
19.457g of tin oxide ultrafine particles (Mitsubishi Materials, trade name S-1) were weighed, 0.183g of indium nitrate trihydrate, 0.2064g of gallium nitrate octahydrate, zinc nitrate hexahydrate 0 154 g was mixed with 4 g of water and dissolved in water, and the mixture was mixed for 2 hours with a planetary ball mill.
Other than this, a fine particle oxide, a fine particle dispersion and a TFT were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1. A large ON / OFF ratio was obtained.

Example 7
Weigh 59.38 g of indium oxide powder (manufactured by Asia Physical Properties Co., Ltd., purity 4N), impregnate it with an aqueous solution of 0.62 g of copper nitrate trihydrate dissolved in 12 g of water, and mix for 2 hours in a planetary ball mill And then dried with a dryer. The mixed powder was dried with a dryer for 3 hours and then calcined at 350 ° C. for 30 minutes while flowing nitrogen at 0.5 L / min in a tubular furnace to obtain a fine particle oxide.
Other than this, a fine particle dispersion and TFT were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1. A large ON / OFF ratio was obtained.

Comparative Example 1
A fine particle dispersion and a TFT were prepared and evaluated in the same manner as in Example 1 except that tin oxide ultrafine particles (manufactured by Mitsubishi Materials Corporation, trade name S-1) were used as the fine particle oxide. The results are shown in Table 1. The ON / OFF ratio was about 2, and almost no FET behavior was observed.

Comparative Example 2
A fine particle dispersion and a thin film transistor were prepared in the same manner as in Example 1 except that indium oxide powder (manufactured by Asia Physical Properties Co., Ltd., purity 4N) was used as the fine particle oxide. The results are shown in Table 1. The ON / OFF ratio was 1 or less, which resulted in a behavior as a simple resistor, and no FET behavior was observed.

  The core-shell type particles of the present invention can be used for thin film transistors.

1 Thin film transistor 10 Substrate (gate electrode)
20 Insulating film 30 Source electrode 40 Drain electrode 50 Channel layer

Claims (12)

A core particle and a shell covering at least a part of the surface of the core particle;
The core particle is made of at least one metal oxide (A) having a band gap of 3 eV or more,
The shell is an oxide of at least one metal selected from Sn, Zn, In, Ti, Zr, Hf and Cu, an oxide of Sn, Zn, In and Ga, or an oxide of Sn, Zn and Ga. 0.01-1 μm core-shell type particles comprising a metal oxide (B).   The core-shell type particle according to claim 1, wherein the metal oxide (A) is an oxide of a metal selected from Sn, Zn, In and Ga. a) A core particle containing at least one metal oxide having a band gap of 3 eV or more is mixed with a solution in which at least one metal compound is dissolved or dispersed,
b) A method for producing 0.01 to 1 μm core-shell type particles in which the mixture is reacted at 200 to 800 ° C. and at least a part of the surface of the core particles is covered with a metal oxide of the metal compound. The method for producing core-shell particles according to claim 3 , wherein the metal oxide is an oxide of a metal selected from Sn, Zn, In, and Ga. The method for producing core-shell particles according to claim 3 or 4 , wherein the metal compound is a metal compound selected from nitrates, carbonates, acetates, hydroxides and halides. Core-shell type particles obtained by the method according to any one of claims 3 to 5 . A dispersion comprising the core-shell type particles according to claim 1, 2 and 6 and a dispersion medium. The dispersion according to claim 7 , wherein the dispersion medium is at least one selected from water and a non-aqueous solvent. Semiconductor deposition coating liquid consisting of a dispersion according to claim 7 or 8. Thin film transistor having a channel layer composed of core-shell particles according to claim 1, 2 and 6. The manufacturing method of the thin film formed by apply | coating and drying the dispersion liquid of Claim 7 or 8 . A thin film transistor using the thin film obtained by the manufacturing method according to claim 11 as a channel layer.

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