KR101124545B1 - Organic thin film transistor and method of manufacturing the same - Google Patents

Abstract

The present invention provides a gate electrode, an organic semiconductor overlapping the gate electrode and including a first organic semiconductor material, a gate insulating layer positioned between the gate electrode and the organic semiconductor, and a source electrode electrically connected to the organic semiconductor; An organic thin film transistor comprising a drain electrode, wherein the source electrode and the drain electrode are surface treated with a second organic semiconductor material, and a method of manufacturing the same.

Organic thin film transistor, organic semiconductor, surface treatment, contact resistance

Description

Organic thin film transistor and its manufacturing method {ORGANIC THIN FILM TRANSISTOR AND METHOD OF MANUFACTURING THE SAME}

The present invention relates to an organic thin film transistor and a method of manufacturing the same.

Research into organic thin film transistors (O-TFTs) has been actively conducted as driving elements of next generation display devices.

The organic thin film transistor is formed by converting a semiconductor constituting the thin film transistor into an organic material instead of an inorganic material such as silicon (Si). Since the organic thin film transistor can be manufactured in a single process at low temperature, it has a large process advantage and a fiber or film ( Since it can be manufactured in a film-like form, it is attracting attention as a core element of a flexible display.

The organic thin film transistor array panel in which the organic thin film transistors are arranged in a matrix form has many differences in structure and manufacturing method compared with the conventional thin film transistor array panel.

In particular, since the organic semiconductor is made of an organic material unlike silicon, the energy level is different from the electrode made of an inorganic conductor such as metal. As a result, an energy barrier between the organic semiconductor and the electrode may increase, which hinders charge transfer, thereby degrading thin film transistor characteristics.

Therefore, the problem to be solved by the present invention is to improve the thin film transistor characteristics by reducing the energy barrier between the organic semiconductor and the electrode.

An organic thin film transistor according to an exemplary embodiment of the present invention includes a gate electrode, an organic semiconductor overlapping the gate electrode and including a first organic semiconductor material, a gate insulating layer positioned between the gate electrode and the organic semiconductor, and the organic semiconductor. And a source electrode and a drain electrode electrically connected to each other, wherein the source electrode and the drain electrode are surface treated with a second organic semiconductor material.

The energy level difference between the organic semiconductor and the surface treated source electrode and the energy level difference between the organic semiconductor and the surface treated drain electrode may be 0.4 eV or less, respectively.

The first organic semiconductor material and the second organic semiconductor material are tetracene, naphthalene, anthracene, pentanecene, thiophene, thiolanthracene, thiolpentanecene, 6,13-bis (triisopropylsilylethynyl) pentacene, respectively. (6,13-bis (triisopropylsilylethynyl) pentacene, TIPS pentacene), tris (8-oxoquinolato) aluminum (Alq3), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), at least one selected from bathophenanthroline (Bphen) and derivatives thereof.

The second organic semiconductor material may have an energy level control substituent.

The energy level controlling substituent may include an electrophilic functional group.

The first organic semiconductor material and the second organic semiconductor material may be the same material.

The source electrode and the drain electrode may include gold (Au), silver (Ag), nickel (Ni), copper (Cu), aluminum (Al), molybdenum (Mo), chromium (Cr), nickel (Ni), and titanium ( Ti), tantalum (Ta), ITO, and at least one selected from IZO.

The gate insulating layer may include an organic insulating material.

In the method of manufacturing an organic thin film transistor according to an embodiment of the present invention, forming a gate electrode on a substrate, forming a gate insulating film on the gate electrode, forming a source electrode and a drain electrode on the gate insulating film, Surface treating the source electrode and the drain electrode with an organic semiconductor material, and forming an organic semiconductor on the surface treated source electrode and the drain electrode.

The surface treatment may include coating the organic semiconductor material on the surface of the source electrode and the drain electrode by an electrochemical method.

The energy level difference between the organic semiconductor and the surface treated source electrode and the energy level difference between the organic semiconductor and the surface treated drain electrode may be 0.4 eV or less.

The organic semiconductor may include the same material as the organic semiconductor material used in the surface treatment.

By surface-treating the electrode surface with an organic semiconductor material, the mobility of charge can be increased by making the energy level between the electrode and the organic semiconductor the same or similar. In addition, by changing the substituent on the surface-treated organic semiconductor material can give a doping effect to the organic semiconductor to act as a resistive contact layer to lower the contact resistance.

In addition, since the organic semiconductor material on the surface of the electrode is formed into a stacking structure, the organic semiconductor formed thereon can also be led to the same structure on the organic semiconductor material, leading to the same crystal structure. Can increase.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like parts are designated by like reference numerals throughout the specification. When a part of a layer, film, region, plate, etc. is said to be "on" another part, this includes not only the other part being "right over" but also another part in the middle. On the contrary, when a part is "just above" another part, there is no other part in the middle.

Next, an organic thin film transistor according to an exemplary embodiment of the present invention will be described with reference to FIG. 1.

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

Referring to FIG. 1, a gate electrode 102 is formed on a substrate 101 made of glass, plastic, or silicon. The gate electrode 102 is connected to a gate line (not shown) extending along one direction of the substrate 101 and receives a gate signal.

The gate insulating film 103 is formed on the gate electrode 102. The gate insulating layer 103 may be made of an inorganic insulating material or an organic insulating material, and an organic insulating material such as poly vinyl phenol (PVP), polyimide, and derivatives thereof is preferable.

The source electrode 104 and the drain electrode 105 are formed on the gate insulating film 103. The source electrode 104 and the drain electrode 105 face each other with a predetermined distance around the gate electrode 102.

The source electrode 104 is connected to a data line (not shown) formed in a direction crossing the gate line and receives a data signal. The drain electrode 105 is separated from the data line and is island-shaped.

The source electrode 104 and the drain electrode 105 may be formed of gold (Au), silver (Ag), nickel (Ni), copper (Cu), aluminum (Al), molybdenum (Mo), chromium (Cr), and nickel (Ni). ), At least one selected from metals such as titanium (Ti), tantalum (Ta), and alloys thereof, or conductive oxides such as ITO and IZO.

The surface 104 'of the source electrode 104 and the surface 105' of the drain electrode 105 are each surface-treated with an organic semiconductor material. This is to reduce the energy level difference with the organic semiconductor 106, which will be described later, an ohmic contact between the source electrode 104 and the organic semiconductor 106 and between the drain electrode 105 and the organic semiconductor 106. Play a role. This will be described later.

The organic semiconductor material may be a p-type semiconductor material or an n-type semiconductor material, and the p-type organic semiconductor material may be, for example, tetracene, naphthalene, anthracene, pentanecene, thiophene, thianthracene, thiolpentanecene, 6,13-bis (Triisopropylsilylethynyl) pentacene (6,13-bis (triisopropylsilylethynyl) pentacene, TIPS pentacene), polymers thereof and derivatives thereof, and the like, and n-type semiconductor materials, for example, tris (8- Oxoquinolato) aluminum (Alq3), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, BCP ), Bashophenanthroline (bathphenanthroline, Bphen), polymers thereof and derivatives thereof, and the like, and may include one or more selected from these.

In addition, by using an organic semiconductor material in which a soluble substituent such as a thiophene compound is bonded to the above-described compound, solubility can be enhanced, and by using an organic semiconductor material in which an electrophilic substituent or a nucleophilic substituent is bonded to the above-mentioned compound. The doping effect can be imparted to the organic semiconductor.

For example, combining the thiophene substituents on anthracene or pentacene, as shown in formulas (1) and formula (2) and fluorine (F ^-) in the side chain direction (R ₁₎ of the substituent (s), chlorine (Cl ^-), bromine (Br ^-) electrophilic of something The organic semiconductor material which combined the sex substituent can be used.

Wherein n is 1 to 10 and R ₁ is an alkyl group or an alkoxy group.

The organic semiconductor 106 is formed on the source electrode 104 and the drain electrode 105.

The organic semiconductor 106 may be a p-type semiconductor material or an n-type semiconductor material, and examples of the p-type organic semiconductor material include tetracene, naphthalene, anthracene, pentanecene, thiophene, thiol anthracene, thiolpentanecene, 6,13 -Bis (triisopropylsilylethynyl) pentacene and derivatives thereof, and n-type semiconductor materials such as tris (8-oxoquinolato) aluminum (Alq3), 2,9-dimethyl-4 , 7-diphenyl-1,10-phenanthroline, vasophenanthroline and derivatives thereof, and the like, and may include one or more selected from these.

The organic semiconductor 106 may be the same material as or different from the organic semiconductor material that is surface-treated on the source electrode 104 and the drain electrode 105.

Next, the charge transfer between the organic semiconductor 106 and the source electrode 104 / drain electrode 105 in the above-described organic thin film transistor will be described with reference to FIGS. 1 and 2.

FIG. 2A is a schematic view illustrating an energy level between an organic semiconductor and an electrode in a p-type organic thin film transistor according to an embodiment of the present invention, and FIG. 2B is an organic diagram of an n-type organic thin film transistor according to an embodiment of the present invention. A schematic diagram showing energy levels between a semiconductor and an electrode.

As described above, the organic thin film transistor according to the exemplary embodiment of the present invention includes a source electrode 104 and a drain electrode 105 each surface-treated with an organic semiconductor material. As described above, when the source electrode 104 and the drain electrode 105 are surface treated with an organic semiconductor material, effective work functions are performed on the surfaces 104 'and 105' of the source electrode 104 and the drain electrode 105. function) can be matched to the energy level of the organic semiconductor 106 or the energy difference can be reduced to 0.4 eV or less.

In general, the smaller the difference between the effective work function of the electrode and the HOMO level of the organic semiconductor in the case of the p-type semiconductor, the easier the movement of holes due to the lower energy barrier.In the case of the n-type semiconductor, the effective work function of the electrode and the organic The smaller the difference in the LUMO level of the semiconductor, the lower the energy barrier and the easier the movement of electrons.

In FIG. 2A, in the p-type organic thin film transistor, the source electrode 104 and the drain electrode 105 include molybdenum (Mo) having a work function Φ (S) and Φ (D) of about 4.2 eV. 106 illustrates an example of pentacene having a lower unoccupied molecular orbital (LUMO) level of about 2.9 eV and a higher occupied molecular orbital (HOMO) level of about 5.0 eV. The source electrode 104 and the drain electrode 105 are surface-treated with pentacene, which is the same material as the organic semiconductor 106.

1 and 2A, when the source electrode 104 and the drain electrode 105 are surface treated with the same pentacene as the organic semiconductor 106, the source electrode 104 and the drain in contact with the organic semiconductor 106 are described. The surfaces 104 'and 105' of the electrode 105 exhibit an effective work function ((Φ '(S), Φ' (D)) of about 5.0 eV substantially equal to the HOMO level of the organic semiconductor 106. It can be seen that substantially no energy barrier exists between the surface 104 ′ of the source electrode 104 and the organic semiconductor 106 and between the surface 105 ′ of the organic semiconductor 106 and the drain electrode 105. Therefore, it can be seen that holes can easily move from the source electrode 104 to the organic semiconductor 106 and from the organic semiconductor 106 to the drain electrode 105. Similarly, in FIG. In the transistor, the source electrode 104 and the drain electrode 105 include molybdenum (Mo) having a work function Φ (S), Φ (D) of about 4.2 eV. The organic semiconductor 106 has an n-type organic semiconductor material having a predetermined HOMO level and LUMO level, and the surfaces 104 'and 105' of the source electrode 104 and the drain electrode 105 are formed of the organic semiconductor 106. It is surface treated with the same material as).

1 and 2B, when the source electrode 104 and the drain electrode 105 are surface treated with the same organic semiconductor material as the organic semiconductor 106 in the n-type organic thin film transistor, The surfaces 104 'and 105' of the contacting source electrode 104 and the drain electrode 105 have an effective work function substantially equal to the LUMO level of the organic semiconductor 106 ((Φ '(S), Φ' (D)). Whereby an energy barrier is substantially between the surface 104 'of the source electrode 104 and the organic semiconductor 106 and between the surface 105' of the organic semiconductor 106 and the drain electrode 105. Therefore, it can be seen that electrons can be easily moved from the source electrode 104 to the organic semiconductor 106 and from the organic semiconductor 106 to the drain electrode 105.

Here, since the surfaces 104 'and 105' of the source electrode 104 and the drain electrode 105 are surface treated with the same material as the organic semiconductor 106 as an example, the energy barrier is not substantially present. Even in the case of the surface-treated organic semiconductor material and a material different from the organic semiconductor 106, the energy barrier can be sufficiently lowered when the energy level difference is about 0.4 eV or less.

When the surface-treated organic semiconductor material and the organic semiconductor 106 are different materials, a doping effect may be imparted to the organic semiconductor by combining an electrophilic substituent or a nucleophilic substituent with the above-described organic semiconductor materials. In this case, since the effective work functions Φ '(S) and Φ' (D) may be adjusted by the doping effect of the organic semiconductor, the energy level with the organic semiconductor 106 may be adjusted as close as possible.

On the other hand, in the case where the source electrode 104 and the drain electrode 105 are surface treated with an organic semiconductor material and then the organic semiconductor 106 is formed thereon, the organic semiconductor materials of the electrode surfaces 104 'and 105' are formed. Since the film is formed into a stacking structure, the organic semiconductor 106 formed thereon may also be led to the same structure on the organic semiconductor material and formed into the same crystal structure. This is because the stacking structure of the planar benzene rings forms a pi-pi (π-π) stacking structure in the form of face-to-face, so that the organic semiconductor 106 formed thereon is also pi-pie. The stacking structure may be induced, thereby increasing charge mobility from the source electrode 104 to the drain electrode 105 through the organic semiconductor 106.

An embodiment of the present invention described above may be compared with the comparative example of FIGS. 3 to 5.

FIG. 3A is a cross-sectional view of a conventional organic thin film transistor in which both a source electrode and a drain electrode are not surface treated, and FIG. 3B is a cross-sectional view of the organic thin film transistor of FIG. 4A is a cross-sectional view of an organic thin film transistor in which only a source electrode is surface treated, and FIG. 4B is an organic semiconductor and an electrode in the organic thin film transistor of FIG. 5A is a cross-sectional view of an organic thin film transistor having only a drain electrode surface treated, and FIG. 5B is a cross-sectional view of an organic semiconductor in FIG. 5A. Schematic showing energy levels between electrodes.

3 to 5 illustrate p-type organic thin film transistors as in FIG. 2A.

Referring to FIG. 3, the work functions Φ (S) and Φ (D) of the source electrode 104 and the drain electrode 105 are about 4.2 eV, and the source electrode 104 and the drain electrode 105 are surface treated. The effective work functions? '(S) and?' (D) at the surfaces of the source electrode 104 and the drain electrode 105 are also about 4.2 eV. On the other hand, since the HOMO level of the organic semiconductor 106 is about 5.0 eV, an energy barrier L of about 0.8 eV between the source electrode 104 and the organic semiconductor 106 and between the organic semiconductor 106 and the drain electrode 105, respectively. ) Exists.

Meanwhile, referring to FIG. 4, when only the surface 104 ′ of the source electrode 104 is surface-treated with an organic semiconductor material, since there is almost no energy barrier between the source electrode 104 and the organic semiconductor 106, the source electrode Holes can easily migrate from 104 to organic semiconductor 106. On the other hand, since the surface 105 ′ of the drain electrode 105 is not surface-treated with an organic semiconductor material, the energy barrier L of about 0.8 eV between the organic semiconductor 106 and the drain electrode 105 is similar to that of the comparative example described above. This exists. In this case, although the charge mobility is not as high as that of the embodiment of the present invention, the charge mobility moving from the source electrode 104 to the organic semiconductor 105 is somewhat higher, so that the charge mobility is improved compared to the comparative example described above.

Meanwhile, referring to FIG. 5, when surface treatment is performed only on the surface 105 ′ of the drain electrode 105 with the organic semiconductor material, approximately 0.8 eV is already between the source electrode 104 emitting the holes and the organic semiconductor 106. Because of the existence of an energy barrier, the number of holes emitted from the source electrode 104 to the organic semiconductor 106 is small. Therefore, the number of holes moving through the source electrode 104, the organic semiconductor 106, and the drain electrode 105 is reduced.

This result can be confirmed with reference to FIG. 6.

6 is a graph illustrating current characteristics of the organic thin film transistor of FIGS. 3 to 5.

In FIG. 6, 'A' represents current characteristics when both the source electrode 104 and the drain electrode 105 are not surface treated, and 'B' performs surface treatment only on the source electrode 104 and the drain electrode ( 105 shows a current characteristic when no surface treatment is performed, and 'C' shows a current characteristic when the surface treatment is performed only on the drain electrode 105 and the surface treatment is not performed on the source electrode 104.

Referring to FIG. 6, when the charge mobility is calculated, when both the source electrode 104 and the drain electrode 105 are not surface treated (A), only the source electrode 104 is surface treated (B) and the drain The charge mobility in the case where only the electrode 105 was surface treated (C) was measured at about 0.005 cm 2 / Vs, about 0.002 cm 2 / Vs, and about 0.00005 cm 2 / Vs, respectively.

As shown here, the current characteristics are best when the surface treatment is performed only on the source electrode 104 (B), and when the surface treatment is performed only on the drain electrode 105 (C), the source electrode 104 and the drain electrode 105 It can be seen that current characteristics are deteriorated rather than the case where (A) is not surface treated in both cases.

This has the opposite effect when a bidirectional current is applied, so in practice it is most desirable to surface treat the organic semiconductor material on both the source electrode 104 and the drain electrode 105 as in the embodiment of the present invention described above. Do.

Next, the manufacturing method of the organic thin film transistor shown in FIG. 1 is demonstrated.

First, a conductive layer is stacked on the substrate 101 and photo-etched to form a gate line (not shown) including the gate electrode 102.

Next, an organic insulating material such as polyvinylphenol is formed on the gate line and the substrate 101 to form the gate insulating film 103.

Next, a conductive layer is stacked on the gate insulating layer 30 and photo-etched to form a data line (not shown) including the source electrode 104 and a drain electrode 105 spaced apart from the data line.

The source electrode 104 and the drain electrode 105 are then surface treated with an organic semiconductor material. Surface treatment may be performed by an electrochemical method, a dipping method, a printing method, etc. Of these, the electrochemical method is most preferred.

The electrochemical method can be performed by the following method. First, the substrate 101 on which the source electrode 104 and the drain electrode 105 are formed is immersed in an electrolyte solution. In this case, the electrolyte solution may be, for example, a mixed solution of tetrabutyl ammonium tetrafluoroborate (TBAB) and methylene chloride. In the electrolyte solution, a reference electrode (not shown) and a counter electrode (not shown) are disposed.

Next, the voltage is applied while controlling the intensity of the voltage between the source electrode 104 and the drain electrode 105 and the counter electrode while applying a constant voltage to the reference electrode using Epsilon CV (cyclic voltametry) equipment.

Next, when the substrate 101 is taken out of the electrolyte solution and dried, the source electrode 104 and the drain electrode 105 are surface treated.

Next, the organic semiconductor 106 is formed on the surface-treated source electrode 104 and the drain electrode 105.

As described above, according to the exemplary embodiment of the present invention, the surface of the electrode may be treated with an organic semiconductor material, such as an electrochemical method. Accordingly, an energy barrier between the effective work function of the electrode surface and the organic semiconductor may be reduced, thereby increasing charge mobility. have.

 Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of the invention.

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

2A is a schematic diagram illustrating an energy level between an organic semiconductor and an electrode in a p-type organic thin film transistor according to an embodiment of the present invention;

2B is a schematic diagram illustrating energy levels between an organic semiconductor and an electrode in an n-type organic thin film transistor according to an exemplary embodiment of the present invention.

3A is a cross-sectional view of a conventional organic thin film transistor in which both the source electrode and the drain electrode are not surface treated.

FIG. 3B is a schematic diagram showing energy levels between an organic semiconductor and an electrode in the organic thin film transistor of FIG. 3A.

4A is a cross-sectional view of an organic thin film transistor in which only a source electrode is surface treated.

FIG. 4B is a schematic diagram showing energy levels between an organic semiconductor and an electrode in the organic thin film transistor of FIG. 4A.

5A is a cross-sectional view of an organic thin film transistor having only a drain electrode surface treated;

FIG. 5B is a schematic diagram showing an energy level between an organic semiconductor and an electrode in the organic thin film transistor of FIG. 5A,

6 is a graph illustrating current characteristics of the organic thin film transistor of FIGS. 3 to 5.

Claims (12)

Gate electrode, A gate insulating film formed on the gate electrode, A source electrode and a drain electrode formed on the gate insulating layer and facing each other with respect to the gate electrode; An organic semiconductor disposed on the source electrode and the drain electrode and overlapping the gate electrode and including a first organic semiconductor material; and A second organic semiconductor material positioned between the source electrode and the organic semiconductor and between the drain electrode and the organic semiconductor and selectively surface-treated on the surfaces of the source electrode and the drain electrode Organic thin film transistor comprising a. In claim 1, And an energy level difference between the organic semiconductor and the surface treated source electrode and an energy level difference between the organic semiconductor and the surface treated drain electrode are each 0.4 eV or less. 3. The method of claim 2, The first organic semiconductor material and the second organic semiconductor material are tetracene, naphthalene, anthracene, pentanecene, thiophene, thiolanthracene, thiolpentanecene, 6,13-bis (triisopropylsilylethynyl) pentacene, respectively. (6,13-bis (triisopropylsilylethynyl) pentacene, TIPS pentacene), tris (8-oxoquinolato) aluminum (Alq3), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline An organic thin film transistor comprising at least one selected from (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), bashophenanthroline (Bphen) and derivatives thereof. 4. The method of claim 3, And the second organic semiconductor material has an energy level regulating substituent. In claim 4, The energy level regulating substituent is an organic thin film transistor comprising an electrophilic functional group. 4. The method of claim 3, And the first organic semiconductor material and the second organic semiconductor material are the same material. In claim 1, The source electrode and the drain electrode are gold (Au), silver (Ag), nickel (Ni), copper (Cu), aluminum (Al), molybdenum (Mo), chromium (Cr), nickel (Ni), titanium An organic thin film transistor comprising at least one selected from (Ti), tantalum (Ta), ITO, and IZO. In claim 1, The gate insulating layer includes an organic insulating material. Forming a gate electrode on the substrate, Forming a gate insulating film on the gate electrode; Forming a source electrode and a drain electrode on the gate insulating film, Selectively surface treating the surfaces of the source electrode and the drain electrode with an organic semiconductor material using an electrochemical method, and Forming an organic semiconductor on the surface-treated source electrode and drain electrode Method for manufacturing an organic thin film transistor comprising a. delete The method of claim 9, And a difference in energy level between the organic semiconductor and the surface-treated source electrode and a difference in energy level between the organic semiconductor and the surface-treated drain electrode are 0.4 eV or less. The method of claim 9, And the organic semiconductor comprises the same material as the organic semiconductor material used in the surface treatment step.

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