TWI448418B - Method for manufacturing nanowires with micro-structure - Google Patents

Description

Method for manufacturing nanowire with micro structure at the tip

The invention relates to a method for manufacturing a nanowire, in particular to a method for manufacturing a horizontal field emission device.

The field emission component has the advantages of small size, light weight, and can help release the electron beam and increase the amount of current emitted, so it can be widely used in the manufacture of high frequency high radiation amplifier, low noise amplifier, wireless RF oscillator, and light emitting diode. Body, solar cell, field emission display and various types of detectors.

In the current field emission components, vertical and horizontal field emission elements can be classified according to the structure of the field emission source. In general, the distance between the cathode and the field emission source of the vertical field emission device and the anode is 60 to 200 μm, so that it has the disadvantage of operating in a vacuum environment and a high operating voltage (≧100 V). Therefore, horizontal field emission elements have also been developed to improve the shortcomings of vertical field emission elements. Among them, in the process of the horizontal field emission element, since the distance between the anode and the cathode and the field emission source can be effectively controlled and shortened, the horizontal field emission element has the advantages of not requiring operation under high vacuum or high operating voltage. Therefore, if horizontal field emission components are applied to high-speed components, wireless RF oscillators, and various types of detectors, the value of field emission components can be improved.

In the manufacturing method of the nanowire (or nano tube) of the field emission source of the field emission element, such as metal organic chemical vapor deposition (MOCVD), thermal evaporation, vapor solid solution (VLS) or electroplating Electrophoretic deposition (EPD), etc., generally require the use of expensive catalysts to participate in the reaction or process equipment, and the process steps are complicated, resulting in high cost of components, which does not meet economic effects. In addition, the general method for producing nanowires needs to be carried out under high temperature. When the nanowires are grown in such an environment, the characteristics of the components are disturbed, and the difficulty in fabricating the components is increased.

In addition, the field emission characteristics of the field emission element depend on the shape of the tip of the nanowire, so the current research also attempts to improve the tip microstructure of the nanowire, in order to improve the component characteristics of the field emission element.

Accordingly, there is an urgent need to develop a method for fabricating a nanowire, especially for a nanowire of a field emission device, in order to produce a tip structure having an improved nanowire in a simple and inexpensive process. The field emits components, which in turn enhance the component characteristics of the field emission components.

The main object of the present invention is to provide a method for producing a nanowire which can produce a nanowire having a tip microstructure at the end of the nanowire.

Another object of the present invention is to provide a method of fabricating a field emission element that enhances the element characteristics of the field emission element.

To achieve the above object, the nanowire manufacturing method and the field emission device manufacturing method of the present invention comprise the following steps: (A) providing a substrate; (B) forming a seed layer on the substrate, and the seed layer has a a first sidewall; (C) forming an electrode layer on the seed layer, wherein the electrode layer has a second sidewall and completely covering the seed layer; (D) placing the substrate in a first growth solution, and Forming a plurality of nanowires, and the nanowires extend from the first sidewall of the seed layer; and (E) placing the substrate in a second growth solution and continuing to grow the nanowire under disturbance A plurality of needle tips are formed at the ends of the nanowires.

In the method for producing a nanowire of the present invention and the method for producing a field emission device, by growing the nanowire in two steps (step (D) and step (E)), the microstructure of the end portion of the nanowire can be improved. More specifically, in the production method of the present invention, after the nanowire is first grown through the step (D), and the interference nanowire is further grown through the step (E), a plurality of needle tips can be formed at the end of the nanowire. . By the speed of the second growth solution, the tip shape of the end of the nanowire can be adjusted, including the thickness of the tip, the density of the tip, and the like. Since the nanowire prepared by the invention has a micro structure of a plurality of needle tips, the number of field emission sources for emitting electrons can be increased, thereby improving the component characteristics of the field emission elements.

In the production method of the present invention, the term "resting" means forming a nanowire in a growing solution without flowing; and the term "disturbing" means forming a nanowire in a flowing growing solution, and is not limited thereto. How to provide a growing solution that flows or disturbs. For example, the disturbed growth solution can be stirred to grow a solution through a magnet, circulated into a growth solution, or provided as a growth solution by a jet flow. Further, in the step (E), the direction of the disturbance is not particularly limited, and may be formed vertically or horizontally in the longitudinal direction of the nanowire or in the direction of the length of the nanowire. Preferably, the disturbance direction is perpendicular to the length of the nanowire.

In addition, in the manufacturing method of the present invention, in the step (B) and the step (C), the region where the seed layer and the electrode layer are formed on the substrate can be respectively defined by the yellow lithography process. Further, a patterned seed layer and an electrode layer may be separately formed by a deposition method commonly used in the art, such as an electron evaporation method, an ion sputtering method, or the like. Wherein, the pattern of the patterned electrode layer and the pattern of the patterned seed layer correspond to each other, and the patterned electrode layer comprises a cathode and an anode, and the nanowires are respectively formed on the sidewalls of the cathode and the anode.

In the preparation method of the present invention, in the step (D) and the step (E), the nanowire is formed by hydrothermal method, and the hydrothermal growth temperature and time can be according to the structure of the desired nanowire and its tip. Adjust the length, density, and thickness. Therefore, the manufacturing process of the present invention has a low process temperature (<100 ° C), and can reduce deterioration of device characteristics due to a high temperature process.

The hydrothermal growth temperature of the step (D) and the step (E) may be 30-100 ° C. Preferably, the hydrothermal growth temperature of step (D) and step (E) may be from 70 to 100 °C. More preferably, the growth temperature of the step (D) is 70-80 ° C, and the growth temperature of the step (E) is 90-100 ° C. Further, the hydrothermal growth time of the step (D) and the step (E) may be 60 to 300 minutes (min), and preferably 60 to 200 minutes. In addition, the first growth solution of the step (D) may be directly used as the second growth solution of the step (E); or the first growth solution of the step (D) may be replaced with a new nanowire growth solution. (ie, the new second growth solution) continues to grow the nanowire.

Furthermore, in the manufacturing method of the present invention, after the step (C), a step (C1) may be further included: etching the seed layer such that the second sidewall of the electrode layer protrudes from the first sidewall of the seed layer. Thereby, it is possible to selectively limit the growth of the nanowires in the horizontal direction and avoid the growth of the nanowires in the vertical direction. The etching solution for etching the seed layer may be phosphoric acid, hydrochloric acid or a mixed solution thereof, and is preferably a phosphoric acid solution. Further, the etching depth is 10 to 200 nm, preferably 10 to 100 nm. Therefore, the second sidewall of the electrode layer may protrude from the first sidewall of the seed layer by about 10 to 200 nm, and preferably 10 to 100 nm.

In the manufacturing method of the present invention, the material of the seed layer may be zinc aluminum oxide (AZO), indium zinc oxide (IZO), gallium zinc oxide (GZO), or zinc oxide (ZnO), and is preferably. It is AZO or ZnO, and more preferably AZO. Further, the material of the electrode layer may be a metal which can be used as an electrode material commonly used in the art, such as platinum, tungsten, nickel, zinc, gold, tin, or gallium, preferably platinum or tungsten, more preferably platinum. Wherein, the thickness of the seed layer is preferably from 90 to 500 nm, more preferably from 90 to 200 nm, most preferably from 90 to 120 nm; and the thickness of the electrode is preferably from 50 to 150 nm, more preferably from 50 to 100 nm. .

Furthermore, in the manufacturing method of the present invention, the substrate may be a substrate, a glass substrate, a quartz substrate, a semiconductor substrate, a metal substrate, or a plastic substrate. When the substrate is a germanium substrate, a semiconductor substrate, or a metal substrate, after step (A), a step (A1) is further included: forming an insulating layer on the substrate. The material of the insulating layer may be an insulating material commonly used in the art, and is preferably cerium oxide or tantalum nitride.

Further, in the production method of the present invention, the nanowire may be a metal oxide nanowire, wherein the material of the metal oxide nanowire is preferably ZnO, TiO ₂ or SnO ₂ , and more preferably ZnO.

The embodiments of the present invention are described by way of specific examples, and those skilled in the art can readily appreciate the other advantages and advantages of the present invention. The present invention may be embodied or applied in various other specific embodiments. The details of the present invention can be variously modified and changed without departing from the spirit and scope of the invention.

real Example 1

Please refer to FIG. 1A to FIG. 1E , which are schematic diagrams showing the manufacturing process of the field emission device of the embodiment.

First, as shown in FIG. 1A, a substrate 11 is provided, which is first washed with deionized water for 5 minutes, and then successively mixed with sulfuric acid and hydrogen peroxide (H ₂ SO ₄ :H ₂ O ₂ =3: 1) Soak for 10 minutes, then immerse in a hydrofluoric acid mixed solution (HF: H ₂ O = 1:100) for 20 seconds, and then a mixed solution of ammonium hydroxide and hydrogen peroxide (NH ₄ OH: H ₂ O ₂ : H ₂ O= :1:5) Soak for 10 minutes, then soak for 10 minutes in a mixed solution of hydrochloric acid and hydrogen peroxide (HCl: H ₂ O ₂ : H ₂ O = 1:1:6), and finally in a hydrofluoric acid mixed solution (HF :H ₂ O=1:100) Soak for about 15-20 seconds. After soaking each of the above mixed solutions, the substrate 11 is washed with deionized water for 5 minutes, and then the substrate 11 is immersed in another mixed solution to complete the step of immersion washing. Finally, it was blown dry with nitrogen to obtain a clean substrate 11. In the embodiment, the substrate 11 is a germanium substrate.

Then, the clean substrate 11 is placed in the center of the high temperature furnace tube, and cerium oxide is deposited on the substrate 11 at a growth temperature of 900 ° C and a water vapor atmosphere. After the deposition process, an insulating layer 12 can be formed on the substrate 11, as shown in FIG. 1A. In the present embodiment, the insulating layer 12 is a germanium dioxide insulating layer, and the insulating layer 12 has a thickness of 500 nm.

The deposition area of the subsequent seed layer and electrode layer is defined by the photoresist AZ 5214E using a yellow light lithography process. Among them, the deposition conditions of the seed layer are as follows: using a DC/RF sputtering system or an evaporation system at a power of 60 W, a vacuum of 7.6 x 10 ^-3 torr, an argon flow rate of 25 sccm, and a deposition rate of 0.4. AZO was deposited under the deposition conditions of /sec. A first seed layer 131 and a second seed layer 132 are formed on the substrate 11 via the yellow lithography and deposition process, as shown in FIG. 1B. The first seed layer 131 and the second seed layer 132 respectively have a first sidewall 1311, 1321; and the distance between the first seed layer 131 and the second seed layer 132 is L _M , which is a field emission element. The distance between the anode and the cathode. In the present embodiment, the first seed layer 131 and the second seed layer 132 have a thickness of 90 nm, and the pitch L _M is 8 μm.

Next, the same use of DC / RF sputtering system or evaporation system, power 90W, vacuum 5x10 ^-3 torr, argon flow rate 30 sccm, and deposition rate of 0.4 A first electrode layer 141 and a second electrode layer 142 are formed on the first seed layer 131 and the second seed layer 132, respectively, as shown in FIG. 1C. The first electrode layer 141 and the second electrode layer 142 respectively have a second sidewall 1411, 1421, and the first electrode layer 141 and the second electrode layer 142 completely cover the first seed layer 131 and the second crystal. The layer 132 is on the surface. In this embodiment, the thickness of the first electrode layer 141 and the second electrode layer 142 is 100 nm, the width between the first electrode layer 141 and the second electrode layer 142 is 500 μm, and the material is platinum (Pt).

Thereafter, a first growth solution is provided to form a nanowire on the substrate 11. In the present embodiment, the first growth solution is prepared by dissolving 3 g of zinc nitrate (Zinc Nitrate) and 3 g of hexamethylenetetramine (HMT) in 800 ml of deionized water. The substrate 11 was placed in a closed container, and the first growth solution was allowed to stand at a constant temperature of 75 ° C for 180 minutes to form a nanowire 15 on the substrate 11, as shown in Fig. 1D. The nanowires 15 extend from the first sidewalls 1311 and 1321 of the first seed layer 131 and the second seed layer 132, and the nanowires 15 are ZnO nanowires.

As shown in FIG. 1E, a second growth solution 21 is placed in the open container 20. In the present embodiment, the second growth solution 21 is prepared by dissolving 1 g of zinc nitrate and 1 g of cyclohexamethylenetetramine in 800 ml of deionized water. Then, the substrate 11 is placed in the open container 20, and the solution is stirred by the magnet 22 of the heating plate at a constant temperature of 95 ° C to continue the growth of the nanowire 15 (please refer to FIG. 1D). In this embodiment, the magnet rotation speed is 300 RPM.

After the above process, the field emission element of this embodiment can be obtained. It was confirmed by electron micrograph results that the end portion 151 of the nanowire 15 of the field emission element of the present embodiment was formed with a plurality of needle tips 1511 as shown in Figs. 1D and 2 . In addition, in the present embodiment, the diameter and length of the nanowire 15 are 40 to 100 nm and 1 to 4 μm, respectively, and the end portion 151 of the nanowire 15 extending from the first sidewall 1311 of the first seed layer 131 is 151. The distance from the end 151 of the nanowire 15 extending from the second side wall 1321 of the second seed layer is about 1.2 μm.

Example 2

The manufacturing method of this embodiment is the same as that of Embodiment 1, except that the magnet rotation speed is 600 RPM. It was confirmed by electron micrograph results that the end portions of the nanowires of the field emission device of the present embodiment were also formed with a plurality of needle tips, and the nanowire needle tip of the present embodiment was thinner than the needle tip of the first embodiment.

Example 3

The manufacturing method of this embodiment is the same as that of Embodiment 1, except that the magnet rotation speed is 900 RPM. It was confirmed by electron micrograph results that the end portions of the nanowires of the field emission element of the present embodiment were also formed with a plurality of needle tips, and the nanowire needle tip of the present embodiment was thinner than the needle tip of the second embodiment.

Example 4

The manufacturing method of this embodiment is the same as that of Embodiment 1, except that the magnet rotation speed is 1150 RPM. It was confirmed by electron micrograph results that the end portions of the nanowires of the field emission element of the present embodiment were also formed with a plurality of needle tips, and the nanowire needle tip of the present embodiment was thinner than the needle tip of the third embodiment.

The results of the comprehensive examples 1-4 show that as the magnet rotation speed increases, that is, the disturbance speed increases, the formed nanowire needle tip becomes thinner.

Comparative example 1

The production method of this example is the same as that of the first embodiment, except that after the first growth solution is grown to the nanowire, the step of growing the nanowire with the second growth solution is not performed. It was confirmed by electron micrograph results that since the comparative example did not perform the step of growing the nanowire under the disturbance, the end portion of the nanowire formed in the comparative example did not have the microstructure of the needle tip.

Comparative example 2

The manufacturing method of this embodiment is the same as that of Embodiment 1, except that the magnet rotation speed is 0 RPM. It was confirmed by electron micrograph results that even if the second growth solution was used to continue to grow the nanowire, the growth of the nanowire formed by the comparative example did not have the microstructure of the needle tip because the growth was not carried out under disturbance. .

Evaluation of ZnO nanowire characteristics

As shown in FIG. 3, this is a nanowire lattice diffraction analysis chart of Examples 1-4 and Comparative Example 1-2. The analysis results showed that the ZnO nanowires prepared in Examples 1-4 and Comparative Examples 1-2 had a main lattice orientation of ZnO (002) and ZnO (103). This result shows that even if the nanowires (the nanowires of Examples 1-4) continue to grow under disturbance, a nanowire having a good crystal structure can be produced, and in addition, photoluminescence is enhanced by light (Photoluminescence, PL). In order to analyze the material properties of the nanowire, the peak waveform signals of 380 nm and 520 nm are the main waveform signals of the ZnO material. As shown in Fig. 4, the nanowires prepared in Examples 1-4 and Comparative Examples 1-2 were indeed ZnO nanowires. In addition, the 520 nm peak waveform signal is related to the oxygen vacancies inside the ZnO material. As the tip of the ZnO nanowire is thinner, the measured signal strength is significantly enhanced.

Field emission component characterization

In the field emission device of Embodiment 1-4, the width between the first electrode layer 141 and the second electrode layer 142 is 500 μm, and the end portion 151 of the nanowire 15 of the first seed layer 131 extends from the second crystal. The distance between the ends 151 of the nanowires 15 of the seed layer 132 is about 1.2 μm (please refer to FIG. 1D). Fig. 5 is a graph showing measurement results of current-voltage (I-V) characteristics of field emission elements of Examples 1-4 and Comparative Example 1-2.

As shown in Figure 5, the equivalent measurement environment is maintained at a pressure of 5x10 ^-6 torr, and the applied voltage range is 0-10 V. The field emission IV characteristics of the field emission elements of Examples 1-4 are up to 0.05 mA. The operating voltage required and the corresponding electric field strength are shown in Table 1 below.

From the results of Fig. 5 and Table 1, the field emission elements produced in Example 2 have the best field emission characteristics.

In addition, FIG. 6 is a Folwer-Nordheim (FN) characteristic diagram corresponding to the field emission IV characteristic of FIG. The results show that the field emission elements of Examples 1-4 are linear in the high electric field strength region, indicating that the field emission element current system follows the field emission tunneling mechanism. Wherein, the field emission element of Embodiment 1 has a V _{on of} about 3.84 V, the field emission element of Embodiment 2 has a V _{on of} about 2.08 V, and the field emission element of Embodiment 3 has a V _{on of} about 3.07 V, and the embodiment The V _on of the field emission component of 4 is about 3.44 V.

Example 7

The fabrication method of this embodiment is the same as that of the first embodiment, except that after forming the first electrode layer 141 and the second electrode layer 142 (as shown in FIG. 7C), the first sidewall 1311 of the first seed layer 131 and The first sidewall 1321 of the second seed layer 132 is etched. Among them, the conditions and steps for etching the seed layer are as follows.

First, a mixed solution of monophosphoric acid (H ₃ PO ₄ :H ₂ O = 1:100) was provided, and the substrate 11 was placed in the phosphoric acid mixed solution for 10 seconds to etch the seed layer. Thereafter, it was washed with deionized water for 5 seconds and dried with nitrogen. Since the phosphoric acid mixed solution can selectively etch the seed layer without etching the electrode layer, the second sidewall 1411 of the first electrode layer 141 can be protruded from the first sidewall 1311 of the first seed layer 131, and the second The second sidewall 1421 of the electrode layer 142 protrudes from the first sidewall 1321 of the second seed layer 132. After the etching process is performed, the protruding first electrode layer 141 and the second electrode layer 142 can be used as a barrier layer for the subsequent grown nanowires 15 (as shown in FIG. 7E), and the nanowires 15 are selected. The lateral growth is horizontal, and the nanowire 15 is inhibited from growing in the vertical direction.

The above-mentioned embodiments are merely examples for convenience of description, and the scope of the claims is intended to be limited to the above embodiments.

11. . . Substrate

12. . . Insulation

131. . . First seed layer

132. . . Second seed layer

1311, 1321. . . First side wall

141. . . First electrode layer

142. . . Second electrode layer

1411, 1421. . . Second side wall

15. . . Nanowire

151. . . Ends

1511. . . Tip

20. . . sealed container

twenty one. . . Second growth solution

twenty two. . . magnet

L _M . . . spacing

1A to 1E are schematic views showing a manufacturing process of a field emission device according to Embodiment 1 of the present invention.

Figure 2 is a schematic illustration of the end of the nanowire of Example 1 of the present invention.

Fig. 3 is a diagram showing the diffraction diagram of the nanowire lattice of Examples 1-4 and Comparative Example 1-2 of the present invention.

Fig. 4 is a photo-excited fluorescence diagram of the field emission elements of Examples 1-4 and Comparative Examples 1-2 of the present invention.

Fig. 5 is a graph showing the results of current-voltage (I-V) characteristics of the field emission element of Embodiment 1-4 of the present invention.

Fig. 6 is a graph showing the result of F-N characteristics of the field emission element of Embodiment 1-4 of the present invention.

7A to 7E are schematic diagrams showing the manufacturing process of the field emission device of Embodiment 5 of the present invention.

15. . . Nanowire

151. . . Ends

1511. . . Tip

Claims (17)

A method for fabricating a nanowire includes the steps of: (A) providing a substrate; (B) forming a seed layer on the substrate, wherein the seed layer has a first sidewall; and (C) forming an electrode Layered on the seed layer, wherein the electrode layer has a second sidewall and completely covers the seed layer; (C1) etching the seed layer such that the second sidewall of the electrode layer protrudes from the seed layer a first sidewall; (D) placing the substrate in a first growth solution and forming a plurality of nanowires upon standing, and wherein the nanowires extend from the first sidewall of the seed layer; (E) placing the substrate in a second growth solution and continuing to grow the nanowires under disturbance to form a plurality of needle tips at the ends of the nanowires. The manufacturing method according to claim 1, wherein in the step (D), the nanowires are formed by a hydrothermal method. The production method according to claim 2, wherein the hydrothermal method has a growth temperature of 70 to 100 °C. The manufacturing method according to claim 3, wherein the hydrothermal method has a growth time of 60-300 min. The production method according to claim 1, wherein in the step (E), the nanowires are continuously grown by hydrothermal method. The production method according to claim 5, wherein the hydrothermal method has a growth temperature of 70 to 100 °C. The manufacturing method according to claim 6, wherein the hydrothermal method has a growth time of 60-300 min. The production method according to claim 1, wherein the etching solution for etching the seed layer is phosphoric acid, hydrochloric acid or a mixed solution thereof. The manufacturing method according to claim 1, wherein the material of the seed layer is AZO, IZO, GZO, or ZnO. The manufacturing method of claim 1, wherein the substrate is a substrate, a glass substrate, a quartz substrate, a semiconductor substrate, a metal substrate, or a plastic substrate. The manufacturing method according to claim 1, wherein the material of the electrode layer is platinum, tungsten, nickel, gold, tin or gallium. The manufacturing method of claim 1, wherein the substrate is a glass substrate, a quartz substrate, or a plastic substrate. The manufacturing method according to claim 1, wherein the substrate is a germanium substrate, a semiconductor substrate, or a metal substrate. The manufacturing method of claim 13, wherein the step (A) further comprises a step (A1) of forming an insulating layer on the substrate. The manufacturing method according to claim 14, wherein the material of the insulating layer is cerium oxide or cerium nitride. The production method according to claim 1, wherein the nanowires are metal oxide nanowires. The production method according to claim 16, wherein the material of the metal oxide nanowire is ZnO, TiO ₂ or SnO ₂ .