KR20070088226A - Method of manufacturing pentacene organic thin film transistor - Google Patents

Abstract

A method of manufacturing a pentacene organic TFT is provided to improve the crystallinity of an organic thin film without additional processes by using a cluster beam deposition and to improve the uniformity of the organic thin film by using a surfactant. A substrate(110) is loaded at an inner upper side of a vacuum chamber. Pentacene stored in a crucible is heated, wherein the crucible is arranged at an inner lower side of the vacuum chamber. The pentacene is sublimated and passed through a nozzle, wherein the nozzle is installed at an upper portion of the crucible. At this time, a pentacene cluster of a beam type is formed. An organic thin film is uniformly deposited on the substrate while the substrate is kept in room temperature. A surfactant made of HMDS(HexaMethylDiSilazane) is deposited on the substrate.

Description

Method of manufacturing pentacene organic thin film transistor

1 is a schematic cross-sectional view of an organic thin film transistor according to an exemplary embodiment of the present invention.

2 is an atomic force microscope (AFM) photograph of the pentacene organic thin film prepared by Comparative Example 1. FIG.

3 is an atomic force micrograph of the pentansene organic thin film prepared according to Examples 1 and 2.

4 is an X-ray diffraction graph of the pentacene organic thin film prepared according to Examples 1 and 2. FIG.

5 is a graph measuring electrical characteristics of the pentacene organic thin film transistors manufactured according to Examples 1 and 2. FIG.

6 is a graph measuring electrical characteristics of the pentacene organic thin film transistors manufactured by Comparative Examples 1 and 2. FIG.

The present invention relates to a method for manufacturing a pentacene organic thin film transistor, and more particularly, to increase the crystallinity of the organic thin film by using a cluster beam deposition method, and to form an organic layer on the surface of the gate dielectric layer on which the organic thin film is grown using a surfactant. The present invention relates to a method for manufacturing a pentacene organic thin film transistor in which a thin film can be uniformly deposited.

In general, a flat panel display panel is a device having a flat surface using visible light, and when a strong voltage is applied between two electrodes, a gas discharge is generated between the electrodes. PDP (plazma display panel) using the phenomenon of emitting light, electrons emitted from a plane formed cathode (Cathode) hit the phosphor and emits heat electrons by applying a voltage to the field emission display (FED), filament (Filament) The electrons are accelerated in the grid to reach the anode, and the current flows through a thin film of a fluorescent fluorescent display (VFD), a fluorescent or phosphorescent organic material, which displays information by hitting a patterned phosphor and emitting light. Organic light emitting diodes (OLEDs), which emit light when the electrons and holes combine in the organic layer, Liquid crystal display device that displays the information using the principle of transmitting or blocking light in response to the switching of voltage by the liquid crystal acting as a shutter. (liquid crystal display).

Thin film transistors (hereinafter referred to as TFTs) used in flat panel displays such as liquid crystal displays and OLEDs are used as switching elements for controlling the operation of each pixel and as driving elements for driving the pixels.

The TFT includes a gate electrode having a semiconductor layer having a source / drain region and a channel region formed between the source / drain regions, the semiconductor layer being insulated from the semiconductor layer and located in a region corresponding to the channel region. And source / drain electrodes in contact with the source / drain regions, respectively. The polysilicon thin film was used for the said semiconductor layer conventionally. However, it can be used in place of silicon substrates due to the characteristics of conductive organic materials that require easy molding, flexible properties, and low cost of manufacturing, and active research is being conducted in a wide range of fields. Organic thin film transistors (OTFTs) using such conductive organic materials can be formed by printing at atmospheric pressure instead of chemical vapor deposition (CVD) using plasma for forming conventional silicon thin films. It is possible to perform a roll to roll using a plastic substrate and to realize a low-cost transistor. The organic thin film transistor has the crystallinity of the organic active layer, the charge characteristics of the interface between the substrate and the organic active layer, the source / drain electrode and The quality can be determined by the carrier injection ability of the organic active membrane interface and the like.

Although the organic thin film transistor is dependent on the crystallinity of the organic thin film, there is a problem in that the crystallinity is low. In order to solve this problem, Korean Patent Publication No. 0399283 discloses a technique for improving the crystallinity by liquefying an organic thin film by vacuum depositing pentacene and applying a pressure at a high temperature with a pressurizing device, but there is a question whether the crystallinity is improved. In addition, in addition to vacuum deposition, there was a problem involving a separate pressurization process and a secondary process of high temperature treatment.

In addition, in order to increase the crystallinity, Korean Laid-Open Patent Publication No. 2005-0049837 deposits pentacene using an organic molecular beam deposition (OMBD) method, but the OMBD method has a wide range of organic molecules in an effusion cell. It is difficult to secure the uniformity of the organic thin film due to partial or small accumulation of organic molecules because it is directed to the deposits at various angles with the kinetic energy of the distribution, and when heating the substrate for the uniformity of the organic thin film. There was a problem that a separate heating means is required.

Therefore, the technical problem to be achieved by the present invention is to increase the crystallinity of the organic thin film without heating the deposit using the cluster beam deposition method, and without any additional process, while the gate dielectric layer on which the organic thin film is grown by using a surfactant It is to provide a method for manufacturing an organic thin film transistor that can be uniformly deposited organic material having a high crystallinity on the surface.

The present invention to achieve the above technical problem,

Fixing the substrate on the inner upper side of the vacuum chamber and heating pentacene in the crucible disposed on the inner lower side of the vacuum chamber (step S1);

Subliming the heated pentacene to form a cluster while passing through a nozzle provided on the crucible (step S2); And

The substrate is maintained at room temperature and at the same time the cluster collides thereunder and is deposited uniformly (step S3); provides a method of manufacturing an organic thin film transistor comprising a.

According to another embodiment of the present invention,

The cluster may have a maximum kinetic energy in a direction toward the substrate.

In addition, the cluster may have a uniform kinetic energy toward the substrate.

In addition, the substrate may not be heated.

In addition, the method may further include laminating a surfactant on the surface of the substrate.

Here, the surfactant may be hexamethyldisilazane (HMDS).

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

However, embodiments of the present invention illustrated below may be modified in many different forms, and the scope of the present invention is not limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art. In the drawings, the size or thickness of films or regions is exaggerated for clarity.

1 is a schematic cross-sectional view of an organic thin film transistor according to an exemplary embodiment of the present invention.

Referring to FIG. 1, a pentacene thin film transistor according to an exemplary embodiment of the present invention includes a dielectric layer 120 formed on the substrate 110 and a pentacene thin film 130 formed on the dielectric layer. . In addition, as a commonly used electrode, the gate 100, the source 141, and the drain electrode 140 are stacked on the lower portion of the substrate and the upper portion of the pentacene, respectively.

First, looking at the vacuum deposition equipment used in the present invention, the substrate to be deposited is placed on the inner upper side of the vacuum chamber, and the inner and lower sides arrange a crucible with a heating wire as a heating means and a nozzle on the top of the crucible. A cover having a cover is formed so that the crucible has a sealed shape except for a nozzle at an upper portion thereof, and the organic material to be deposited is positioned therein. In addition, the thickness monitor installed in order to measure the thickness of the deposited organic thin film is completed, the deposition rate and the thickness of the deposition organic material in Å / s and k Å unit respectively to monitor the thickness of the thin film and to adjust the appropriate thickness. In addition, the shutter is positioned between the substrate and the crucible so that the shutter can be opened and closed from the outside, and is initially closed to prevent the deposition of unpurified impurities and to rotate outside when a constant deposition rate is reached. It is arranged to open.

On the other hand, the dielectric layer is not particularly limited as long as it is a material commonly used in the art, but may be preferably formed by vacuum deposition of silicon dioxide (SiO ₂ ) on the surface of the substrate.

The substrate 110 may be an n-type silicon substrate or a plastic material. Here, the plastic material is polyethersulphone (PES, polyethersulphone), polyacrylate (PAR, polyacrylate), polyetherimide (PEI, polyetherimide), polyethylene naphthalate (PEN, polyethyelenen napthalate), polyethylene terephthalate (PET, polyethyeleneterepthalate) ), Polyphenylene sulfide (PPS), polyallylate, polyimide, polycarbonate (PC), cellulose triacetate (TAC), cellulose acetate propinonate (CAP) ) May be one of.

Hereinafter, a method of manufacturing a pentacene thin film transistor according to the present invention will be described.

Here, the present invention is a step of fixing the substrate on the inner upper side of the vacuum chamber, heating the pentacene in the crucible disposed on the inner lower side of the vacuum chamber, and the heated pentacene is sublimed to the Forming a cluster while passing through a nozzle of a cover provided at an upper portion thereof, and the substrate is maintained at room temperature, and at the same time, the cluster is collided and uniformly deposited at a lower portion thereof, and an interface is formed on the surface of the substrate. The active agent can be laminated.

First, to fix the substrate on the inner upper side of the vacuum chamber, and to look at the step of heating the pentacene in the inside of the crucible disposed on the inner and lower sides of the vacuum chamber, first, the heating method is a method commonly used in the art Although it does not specifically limit, For example, the electrical resistance heating system which digitalizes easily in temperature control is preferable.

In addition, the material of the crucible is not particularly limited as long as the material is not adsorbed or reacted when the pentacene is heated. However, the crucible is capable of heating at a high temperature and has little thermal deformation even at a high temperature. Is preferred. In addition, the form of the crucible is not particularly limited as long as it is sealed and a cover having a nozzle thereon may be provided.

In addition, the pentacene is conjugated as an organic material in which double bonds and single bonds are alternately bonded to each other, thereby having electrical conductivity, and excellent in that the dielectric layer formed on the substrate in the step of depositing on a substrate to be described later. It can have a bonding force.

Moreover, it is preferable that the temperature to heat is 227-247 degreeC. If the heating temperature is lower than 227 ° C, pentacene is difficult to vaporize, and sufficient kinetic energy is required to find an empty spot even if it is difficult or breaks the weak intermolecular attraction of the cluster after the impact on the substrate. It may be difficult to obtain a uniform thin film, and if it exceeds 247 ° C., the organic molecules may be pyrolyzed, and thus the chemical composition of the deposited organic molecules may change.

Next, when the heated pentacene is sublimed to form a cluster and passes through a nozzle provided at the top of the crucible, the pentacene is sublimed into gas by a phase change when the pentacene is heated in a vacuum state. Sublimed pentacene particles will flow inside the crucible. The pentacene particles flowing through the nozzle formed in the upper portion of the crucible. The pentacene particles move upward through the small holes of the nozzle, i.e., the pentacene in a state having kinetic energy in one direction. Only particles can pass through this nozzle. Therefore, the vaporized particles in the crucible flow in the crucible and collide with each other to form clusters with weak intermolecular attraction, and only the clusters having an upward direction have uniform and constant kinetic energy. It passes through the nozzle in the form of a beam and proceeds toward the inner upper side of the vacuum chamber. In this way, the clusters having the direction toward the top and at the same time having uniform and constant kinetic energy collide with the lower part of the substrate arranged on the inner side of the vacuum chamber, and the weak intermolecular attraction of the cluster is broken by the collision and the remaining motion at the same time. The pentacene thin film formed by finding and vacancies around the impingement by energy is uniformly formed, resulting in excellent crystallinity.

On the contrary, according to the conventional physical vapor deposition (PVD) method or the OMBD method, the organic molecules to be deposited are heated in a plate-like or vessel-like boat rather than moving in a vacuum chamber with a specific orientation. Evaporation occurs directly into the vacuum environment. This is different from the cluster in the cluster beam deposition according to the present invention, the organic molecules are aggregated with a weak attraction force to form a cluster. In other words, organic molecules having various directions of directional energy and kinetic energy having a wide distribution size are sublimated to the surroundings in a vacuum state. Thus, particles with a wide range of kinetic energies are deposited more or less from various directions so that the surface of the substrate has a rough island shape. Therefore, the surface of the organic molecules to be deposited is roughened and the crystallinity is reduced to reduce the mobility of the charge (mobility).

Next, the step of uniformly depositing the cluster collides with the lower portion of the substrate, the cluster sublimated through the nozzle of the crucible proceeds to the inner upper side of the vacuum chamber and collides with the lower portion of the substrate. The impingement clusters break the weak intermolecular bonding force and become original sublimated organic particles, which move to the surrounding voids and bond with the substrate.

Referring to the combination of the organic particles and the substrate, as the dielectric layer 120 applied to the substrate, silicon dioxide (SiO ₂ ) is partially negatively charged (δ +) to silicon (Si) and partially negatively charged to oxygen (O). δ−), the pentacene particles to be deposited are conjugated to single bonds and double bonds, and the electron density of the π-bonds is high to form partial positive charges (δ +) of the silicon and a bonding force.

In addition, a surfactant may be deposited on the surface of the substrate prior to depositing pentacene particles. The surfactant is not particularly limited as long as it is commonly used in the art as a material for solidifying the bonding force between the dielectric layer and the pentacene particles to be deposited, but hexamethyldisilazane (HMDS) may be used. The hexamethyldisilazane is composed of a polar portion and a non-polar portion, and the polar portion faces the dielectric layer and the non-polar portion faces the pentacene particles, thereby providing excellent bonding strength to the organic particles and the dielectric layer.

Here, the method of applying the surfactant is not particularly limited as long as it is a method commonly used in the art, spin coating is easy to form a thin film is preferred.

In addition, when using the pentacene may have a thickness of 400 to 600 kPa. If it is less than 400 GPa, there is a risk of physical damage such as cracking due to handleability through various processes in the actual manufacturing process, and if it is more than 600 GPa, electrical characteristics may be deteriorated. In addition, the deposition rate of the pentacene is preferably 0.8 to 1.2 Å / S, when the deposition rate is less than 0.8 Å because the deposition rate of the thin film is too slow to form a pentacene thin film properly and exceeds 1.2 에는 Roughness of the manufactured pentacene thin film may be poor.

On the other hand, it is preferable not to heat the substrate during cluster beam deposition. If the substrate is heated, not only the production cost required for heating is increased but also the size of the substrate is difficult to establish the temperature uniformity as a process condition.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments of the present invention, but the present invention is not limited thereto.

Example 1

1- (1) Dielectric  formation

First, silicon dioxide (SiO ₂ ) was deposited to a thickness of 3000 기 on the cleaned n-type silicon substrate by thermal oxidation.

1- (2) Gate electrode  formation

Next, a gate electrode was formed to have a thickness of 2000 kPa using aluminum (Al) on the lower portion of the n-type silicon substrate on which silicon dioxide (SiO ₂ ) was deposited by vacuum deposition.

1- (3) Organic thin film  deposition

A 10-inch diffusion pump with a baffle is used to maintain the vacuum in the vacuum chamber at an average of 1 × 10 ^-6 Torr, and graphite with a cover with a nozzle 1 mm in diameter on top. ) The crucible of the material was placed on the inner side of the vacuum chamber and placed on the inner side of the vacuum chamber with the silicon dioxide laminated surface of the n-type silicon substrate stacked downward. At this time, the distance between the n-type silicon substrate and the crucible was 190 mm. Next, pentacene was introduced into the crucible, and a pentacene thin film having a thickness of 500 kPa was deposited under a condition of a heating temperature of 237 ° C. and a deposition rate of 1 kW / sec. Here, the temperature of the substrate temperature was maintained at 20 ℃.

1- (4) source and drain electrode formation

Next, an organic thin film transistor was manufactured by simultaneously forming a source and a drain electrode using a vacuum deposition method using a gold (Au) electrode material as a thin film thickness of 500Å and a channel length of 200 μm and a channel width of 1 mm.

Example 2

In Example 1- (3), spin-coated hexamethyldisilazane (HMDS) (manufactured by Aldrich) before drying the n-type silicon substrate on which silicon dioxide (SiO ₂ ) was deposited into the deposition chamber was dried. An organic thin film transistor was manufactured in the same manner as in Example 1 except that the organic thin film transistor was manufactured.

Comparative Example 1

The degree of vacuum in the vacuum chamber is maintained at an average of 2 × 10 ^-6 Torr, the pentacene is placed on the top of a dish-shaped boat without a cover, and the substrate temperature is 190 ° C. using a conventional vacuum deposition method. An organic thin film transistor was manufactured in the same manner as in Example 1, except that the pentacene thin film was formed while maintaining the surrounding at a high pressure of 10 atm.

Comparative Example 2

An organic thin film transistor was manufactured in the same manner as in Comparative Example 1 except for spin-coating HMDS (hexamethydisilazane) (manufactured by Aldrich) on a surface where silicon dioxide of an n-type silicon substrate was stacked in a vacuum chamber and dried.

      Test Example 1

Atomic force microscope  ( Atomic Force Microscopy , AFM )

The roughness of the surface can be determined by atomic force microscopy. The atomic force microscope shows the image of the surface while the silicon probe scans the surface of the thin film and numerically represents the degree of roughness from the baseline. The organic thin film transistor manufactured by Comparative Example 1 can be seen through FIG. 2, wherein the n-type silicon substrate is treated at high pressure and high temperature with the size of the crystallized pentacene particles being non-uniformly stacked. have.

In contrast, an atomic force microscope was measured on the surface of pentacene of the organic thin film transistors prepared in Examples 1 and 2, and the results are shown in FIG. 3. Referring to Figure 3, it can be seen that the pentacene particles of uniform size are uniformly stacked.

Test Example 2

X-ray diffraction analysis XRD )

XRD was measured on the surface of pentacene of the organic thin film transistors prepared in Examples 1 and 2, and the results are shown in FIG. 4. Referring to FIG. 4, it can be seen that the inherent peak of the deposited pentacene is formed and a thin film is formed in a single crystalline phase. In addition, it can be seen that the pentacene of the organic thin film transistor manufactured by Example 2 has an excellent signal-to-noise ratio.

Test Example 3

Electrical property measurement

The current transfer characteristics of the pentacene thin film transistors prepared according to Examples 1 and 2 and Comparative Examples 1 and 2 were measured by a semiconductor characteristic analyzer (HP4155A, manufactured by Hewlett Packard), and are shown graphically in FIGS. 5 and 6, respectively. 5 and 6 show charge mobility using the current formula of the saturation region of Equation (1) based on the electrical characteristic values and are shown in Table 1 below.

(1)

(One)

In Equation (1), I _SD is the source-drain current and μ _FET Or μ is charge mobility, C ₀ is the capacitance of the insulating layer, W is the width of the channel, L is the length of the channel, V _G is the gate voltage, and V _T is the threshold voltage.

In addition, it is shown in Table 1 to calculate the current flashing ratio using the following formula 2.

(2)

(2)

In Equation (2), I _on is the maximum current value, I _off is the blocking leakage current, μ is the charge mobility, σ is the conductivity of the organic thin film, q is the charge amount, N _A is the charge density, t is The thickness of the semiconductor film, C ₀ is the capacitance of the insulating layer, and V _D is the drain voltage.

Charge mobility (㎠ / Vs) Current blink ratio (I _{on / off} ) Example 1 0.19 1 × 10 ⁵ Example 2 0.31 1 × 10 ⁵ Comparative Example 1 0.00058 5 × 10 ³ Comparative Example 2 0.04 1 × 10 ⁵

Referring to Table 1, the organic thin film transistors manufactured according to Examples 1 and 2 have a larger or similar current flashing ratio than the organic thin film transistors prepared according to Comparative Examples 1 and 2, in particular, the charge mobility of at least 3 It can be seen that more than doubled. The charge mobility is an important indicator that affects the response speed of an image in a display device as an indicator of how fast charge moves when the same voltage is applied, and depends on the crystallinity of the organic particles and the uniformity of the organic thin film. Therefore, it can be seen that the crystallinity of the transistor of the organic thin film manufactured by the manufacturing method of the present invention is improved and excellent in uniformity.

According to the present invention, the crystallinity of the organic thin film is increased by heating the deposited material without using a cluster beam deposition method and without any additional process, and the crystallinity is high on the surface of the gate dielectric layer on which the organic thin film is grown using a surfactant. An organic thin film transistor capable of uniformly depositing an organic material may be manufactured.

Claims (6)

Fixing the substrate on the inner upper side of the vacuum chamber and heating pentacene in the crucible disposed on the inner lower side of the vacuum chamber (step S1); Subliming the heated pentacene to form a cluster while passing through a nozzle provided on the crucible (step S2); And The substrate is maintained at room temperature and at the same time the cluster is collided and uniformly deposited thereunder (S3 step); manufacturing method of an organic thin film transistor comprising a. The method of claim 1, The cluster is a method of manufacturing an organic thin film transistor, characterized in that the maximum kinetic energy in the direction toward the substrate. The method of claim 1, Wherein the cluster has a uniform kinetic energy directed toward the substrate. The method of claim 1, The method of manufacturing an organic thin film transistor, characterized in that the substrate is not heated. The method of claim 1, The method of manufacturing an organic thin film transistor comprising the step of laminating a surfactant on the surface of the substrate. The method of claim 5, The surfactant is a method for manufacturing an organic thin film transistor, characterized in that hexamethyldisilazane (HMDS).

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