KR20160055334A - Organic field-effect transistors, and method for preparing thereof - Google Patents

Abstract

The present invention relates to an organic field-effect transistor and a method for preparing the same, the organic field-effect transistor including an insulation layer which is surface-modified by forming a self-assembled monolayer using a silazane-based material in which a main chain has 1 to 12 alkyl groups. According to the present invention, the organic field-effect transistors can be manufactured, in which the self-assembled monolayers are formed by modifying the surface of the insulation layer using various silazane-based materials having different alkyl groups of the main chain. Additionally, by performing two-step self-assembled monolayer processing using the silazane-based materials with different alkyl groups of the main chain when the insulation layer is surface-modified, both mobility and bias stability which are in a trade-off relationship can be improved.

Description

[0001] The present invention relates to a method of manufacturing an organic field-effect transistor,

The present invention relates to a method of manufacturing an organic field effect transistor having high mobility and excellent bias stability.

Recently, interest is increasing due to excellent properties such as flexibility of organic field-effect transistors (hereinafter, referred to as 'OFETs'), solution stability and applicability in a wide area. OFET has been considered as a next-generation solution that can be used for flexible substrates such as RFID tags and backplanes of low-cost electronic devices, and its application areas are temperature, liquid, gas, pressure, optical , And biochemicals.

In order for OFET to be used in such a region, high mobility and excellent bias stability are required, and the organic-insulator coupling technique is one of the most effective ways to realize this. Various methods have been attempted to introduce organic semiconductor-insulator bonds.

On the other hand, self-assembled monolayer (SAM) has been frequently used because of its features including solution-process usability, thermal stability, and roll-to-roll processability. Various SAM materials and deposition methods have been introduced, and specialized studies have been conducted to improve the mobility or bias stability of OFET through SAM processing.

Many groups have reported studies that improve the mobility of OFETs using various SAMs with different characteristics. There have also been several studies that have improved the bias stability of OFETs through SAM-processing.

In view of the prior art for producing OFET using such SAM treatment, pentacene, oligothiophene derivatives and the like show good performance only when a thin film is formed mainly by a vacuum deposition process, and the solution process is easy It is possible to provide a novel polyether ring compound which can be easily synthesized, has good processability, can be used as a semiconductor or a charge transport material having a high charge mobility and a current flicker ratio, an organic electronic device using the same, And an electronic device including the organic electronic device.

In addition, in Patent Document 2, in order to provide a semiconductor thin film which not only increases the adhesion between the insulating layer and the semiconductor layer but also improves the crystallinity of the thin film, a self-assembled monolayer Monolayer); An inorganic seed layer formed on the self-assembled monolayer; And a semiconductor layer formed on the inorganic seed layer.

However, previous studies, including the foregoing literature, have focused primarily on either mobility or bias stability and have overlooked the correlation between mobility and bias stability with SAM-processing in OFET. Because of the high mobility and excellent bias stability in practical use, these two characteristics are basically required, and more systematic studies are needed to find out how the mobility and bias stability change simultaneously through SAM-processing.

Korean Patent Publication 2006-0021390 Korean Patent No. 10-0661695

The present invention also provides a method of manufacturing an organic field effect transistor capable of identifying mutual relations between mobility and bias stability in an OFET according to a SAM process and improving both characteristics in a tradeoff relationship .

A method of fabricating an organic field effect transistor according to an embodiment of the present invention includes forming an insulating layer on a substrate, modifying the insulating layer using at least two kinds of silane residual materials, assembled monolayer, and forming an organic semiconductor layer on the self-assembled monolayer.

The surface modification of the insulating layer may be performed continuously or stepwise.

The silazane material may be represented by the following chemical formula 1:

(Formula 1)

R ₂ -Si (CH ₃ ) ₂ -NH-Si (CH ₃ ) ₂ -R ₁

In the above formula, R ₁ and R ₂ are the same or different and each independently an alkyl group having 1 to 12 carbon atoms.

The surface modification may be performed using any one of a vaporization method, a liquid-phase solution immersion method, and a spin coating method.

The surface modification of the insulating layer may be carried out by using a silane residual material having an alkyl group having a main chain of 5 to 12 in the formula 1 and a silane residual material having a short alkyl group having an alkyl group of 1 to 4 in the main chain of the formula 1 Lt; / RTI >

The self-assembled monolayer is formed on the insulating layer by surface modification using an alkyl group having 5 to 12 carbon atoms in the main chain and a long silane residual material in the main chain in the formula 1, The surface of the silazane material may form a passivation layer that protects the hydroxyl group (-OH) remaining in the insulation layer with a coating through a surface modification using a short silazane residual material.

According to the present invention, it is possible to control the mobility and bias stability of the organic field effect transistor by forming the self-assembled monolayer by surface-modifying the insulating layer using various silane-based materials having different main chain alkyl groups.

In addition, in the present invention, mobility and bias stability in a tradeoff relationship are obtained by performing self-assembled monolayer treatment using two or more kinds of silane residual materials having different alkyl groups in the main chain at the time of surface modification of the insulating layer. stability can be improved.

1 illustrates a structure of an organic field effect transistor manufactured according to an embodiment of the present invention,
FIG. 2 is a graph showing the -I _DS and V _GS displacement characteristics of the OFETs of Examples 1 to 4 and the control group 1,
FIG. 3 is a graph showing (-I _DS ) ^1/2 and V _GS characteristics of Examples 1 to 4 and the control group 1,
4 is a graph showing average mobility and threshold voltage according to alkyl chain lengths of the main chains of Examples 1 to 4,
5 to 9 show the results of measurement of AFM surface characteristics of a 50 nm pentacene thin film (5 x ⁵ 탆 ² ) formed in Control 1 (SiO ₂ , 5) and Examples 1 to 4 (6 to 9)
10 is a graph showing the threshold voltage displacement of the OFETs according to the control group 1 and the EXAMPLES 1 to 4 under the processing conditions of gate bias stress -30 V for 2 hours,
11 is a graph showing displacement characteristics of OFETs with time according to the first embodiment,
12 is a graph showing displacement characteristics of OFETs with time according to the fourth embodiment, and FIG.
13 is a schematic diagram showing the structural change at the time of two-step surface modification (SAM-processing) according to Example 5 of the present invention,
14 is a graph showing threshold voltage displacements of Examples 1, 4 and 5 under a processing condition of gate bias stress of -30 V for 2 hours,
15 shows the drain source variation under on current of the fourth and fifth embodiments.

Hereinafter, the present invention will be described in more detail.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a,""an," and "the" include singular forms unless the context clearly dictates otherwise. Also, " comprise "and / or" comprising "when used herein should be interpreted as specifying the presence of stated shapes, numbers, steps, operations, elements, elements, and / And does not preclude the presence or addition of one or more other features, integers, operations, elements, elements, and / or groups.

The present invention relates to a method of manufacturing organic field-effect transistors (OFETs) having excellent mobility and bias stability characteristics.

The organic field effect transistor according to the present invention is characterized by using an insulating layer whose surface is modified by forming a self-assembled monolayer using two or more kinds of silane-based materials having different main chain alkyl groups.

1, an insulating layer 12 formed on a substrate 11, a self-assembled monolayer formed by surface-modifying the insulating layer 12 using a silane residual material, An organic semiconductor layer 14 formed on the self-assembled monolayer 13 and electrodes 15 and source and drain electrodes 15 formed on the organic semiconductor layer 14.

The substrate 11 according to the present invention may be made of a material such as plastic, glass, and silicon, and the type of the substrate 11 is not particularly limited. In addition, the substrate 11 may be provided as a gate electrode. The substrate 11 is preferably cleaned using a piranha solution, deionized water, acetone, isopropyl alcohol, or the like.

In the present invention, an insulating layer 12 is formed on the substrate 11. As the material of the insulating layer 12, an insulating film in the form of an oxide such as silicon dioxide (SiO ₂ ), Al ₂ O ₃ , HfO ₂ or the like can be preferably used, but the present invention is not limited thereto.

In particular, the present invention is characterized in that the insulating layer 12 is surface-modified by using various silane residual materials having different alkyl groups to form a self-assembled monolayer 13 to control charge transfer and bias stability of OFETs.

The SAM material used for forming the self-assembled monolayer may be represented by the following formula (1), which is a silane residual material having different alkyl groups in the main chain.

(Formula 1)

R ₂ -Si (CH ₃ ) ₂ -NH-Si (CH ₃ ) ₂ -R ₁

In the above formula, R ₁ and R ₂ are the same or different and each independently an alkyl group having 1 to 12 carbon atoms.

The mobility of the organic field effect transistor increases as the alkyl group of the main chain in the silazane-based material used in the present invention increases. However, when the number of alkyl groups in the main chain is too long and exceeds 12, the boiling point of the above-mentioned silane residual material becomes high, which causes a problem of poor process stability, which is not preferable.

When the self-assembled monolayer film is formed by SAM-treating the surface of the insulating layer as in the present invention, an excellent surface state can be provided for the subsequent growth of the organic semiconductor layer. That is, the organic semiconductor layer having a relatively large grain size is formed on the surface of the surface-modified insulating layer.

Considering grain size and charge transfer characteristics, it is known that the smaller the grain boundary, the more trapping state can be provided at the grain boundary, which is more effective for charge transfer. Thus, when the grains are large, the grain boundaries are formed less, so that a device with higher field-effect mobility can be obtained.

As in the present invention, the grains of the organic semiconductor layer formed on the surface-modified insulating layer are largely formed, and when the grain size is large, the grain boundary is smaller than in the case where the grain size is relatively small, It is possible to manufacture a field effect transistor. This effect tends to further increase the grain size of the pentacene used as the organic semiconductor layer as the alkyl chain length of the main chain increases in the silazane SAM material used for surface modification of the insulating layer.

In addition, when the silazane-based material is used for SAM formation as in the present invention, it is excellent in workability and contains only one active group, so that it is easy to control the process conditions. Therefore, it is easy to use for a large-area device, and it can be applied more easily than a silane-based material containing chlorine (Cl) which has been used in the roll-to-roll process.

The organic semiconductor layer 14 formed on the self-assembled monolayer 13 of the present invention is preferably a pentacene based material, but is not limited thereto. The organic semiconductor layer 14 may be formed by a vaporization method, a spin coating method using a liquid solution, or the like, but the method is not limited thereto.

The method for fabricating an organic field effect transistor according to the present invention includes the steps of forming an insulating layer on a substrate, surface-modifying the insulating layer using at least two kinds of silane residual materials, and forming a self-assembled monolayer forming a monolayer on the self-assembled monolayer, and forming an organic semiconductor layer on the self-assembled monolayer.

Particularly, in the present invention, the surface modification of the insulating layer using the self-assembled monolayer using the above-described silane residual material may be performed in a continuous process using two or more kinds of silane residual materials, or may be carried out in a stepwise manner. But is not limited thereto.

As the silane residual material, it is preferable to use two or more kinds of alkyl groups having different main chain lengths as shown in the following chemical formula 1:

(Formula 1)

R ₂ -Si (CH ₃ ) ₂ -NH-Si (CH ₃ ) ₂ -R ₁

In the above formula, R ₁ and R ₂ are the same or different and each independently an alkyl group having 1 to 12 carbon atoms.

In the present invention, when the surface modification of the insulating layer proceeds in a continuous process or stepwise, it is preferable that the surface modification is performed through the formation of a self-assembled monolayer using two or more kinds of silane-based materials having different alkyl groups in the main chain. That is, the two or more kinds of the silane residual materials include 1) a long silane residual material having an alkyl group of 5 to 12 in the main chain of the formula 1 and 2) an alkyl group of 1 to 4 in the main chain of the formula 1 And a short silazane residual material are sequentially used.

Therefore, the self-assembled monolayer is formed on the insulating layer through surface modification using an alkyl group having 5 to 12 alkyl groups in the main chain and a long silyl group-containing material in the main chain in the formula 1, and the alkyl group in the main chain is 1 to 4 (-O-Si (CH ₃ ) ₂ -R), which protects the hydroxyl group (-OH) remaining in the insulating layer with the silyl group-containing material through a surface modification using a short silanol group- passivation. < / RTI >

Next, referring to FIG. 13, first, when a first surface modification is performed using a relatively long silane residual material having an alkyl group of 5 to 12 as a main chain, a long SAM (long SAM) SiO ₂ ), a self-assembled monolayer film layer is formed.

Through the formation of the self-assembled monolayer film layer, it is possible to manufacture a device having high mobility by providing an environment favorable for the subsequent growth of an organic semiconductor layer (for example, a pentacene material) by increasing the intimacy with the organic semiconductor . However, when the long SAM (long SAM) is formed, gate bias instability may be more serious than a relatively short SAM process because the number of OH groups on the surface of a conventional insulating film is smaller than that of a short SAM (short SAM).

Accordingly, in the present invention, in order to further reduce the residual hydroxyl group on the surface of the SiO ₂ insulating layer that has been subjected to the first surface modification after the first surface modification of the insulating layer using the long silane residual material of the alkyl group, And a second SAM process is performed using a silane residual material having a relatively short alkyl group of ~4.

In this case, then, as shown in Figure 13, a short length of a SAM (SAM short) a first surface modification kept SiO ₂ (Passivation, -O-Si (CH ₃ ) ₂ -R) protecting the remaining hydroxyl group (-OH) in the insulating layer with a film.

Therefore, the finally fabricated organic field effect transistor can have a high mobility and a bias stability.

In order to achieve both of the above two effects in the two-step SAM treatment of the present invention, the insulating layer is surface-modified by using a silane residual material having a long alkyl group length, and then the silyl residual material having a short alkyl group is used It is more preferable to modify the surface of the insulating layer.

According to an embodiment of the present invention, the surface modification of the insulating layer may be performed by any one of a vaporization method, a liquid-phase solution immersion method, and a spin coating method.

According to the above-described vaporization method, the alkyl group is treated with the SAM using the long silane residual material, and then the SAM is treated with the short silane residual material. It is also vaporized and reacted with the SiO ₂ insulating layer surface. The above-described vaporization method is a method in which an alkyl group flows through a gas containing a long silane residual material, that is, a chamber in which a substrate is placed with a vapor containing a long SAM, and then there is a vacuum or an injection / , A continuous process in which the alkyl group contains a long silane residual material, that is, the vapor containing the short SAM is replenished. When such a continuous process is used, the process time can be shortened in an actual process, and the cost saving effect is excellent.

Further, according to the immersion liquid immersion method, the silazane-based material exists in a liquid phase, and the silazane-based material is diluted in a solvent such as hexane or toluene. Subsequently, the SiO ₂ insulating layer may be immersed in the diluted solution to modify the surface. The surface modification proceeds by immersing the alkyl group in a solution of the SAM material containing the long silane residual material, rinsing and then immersing the alkyl group in the SAM material solution containing the short silane residual material.

It is also possible to form a spin coating on the insulating layer using two or more kinds of silane residual materials to carry out surface modification. At this time, the spin-coating liquid may be a diluted solution obtained by diluting the above-mentioned silazane-based material in a liquid state as it is, or diluted in a solvent such as hexane or toluene. However, in the case of a SAM material using an alkyl group having a long silane residual material, it is preferable to use a diluted solution diluted with an organic solvent because the viscosity is high and the cost is high. Alternatively, the spin coating may be performed twice using two or more kinds of silane residual materials, or may be performed by spin coating the SAM material using a long silane residual material on the rotating substrate, It is also possible to apply continuous treatment in one process by spraying the used SAM material.

The organic field effect transistor according to the present invention manufactured through the above-described series of processes can solve both mobility and bias stability problems in a trade-off relationship, thereby achieving high mobility and ensuring bias stability. I have.

Hereinafter, preferred embodiments of the present invention will be described in detail. The following examples are intended to illustrate the present invention, but the scope of the present invention should not be construed as being limited by these examples. In the following examples, specific compounds are exemplified. However, it is apparent to those skilled in the art that equivalents of these compounds can be used in similar amounts.

Example  1 ~ 4 Organic Thin Film Transistor Manufacture

Silicon dioxide (SiO ₂ ) was thermally deposited on an n-doped silicon substrate to form a silicon dioxide (SiO ₂ ) insulating layer having a thickness of 100 nm. The substrate was washed with piranha solution, deionized water, acetone, and isopropyl alcohol for 30, 15, 10 and 10 minutes, respectively, and then dried in an oven at 120 ° C for 2 hours.

For the self-assembled monolayer (SAM) treatment, the substrate was placed in a crystallization dish containing small vials containing 15 mg of various silazane SAM materials with different alkyl groups in the main chain as shown in Table 1 below. The crystallization dish was covered with aluminum foil and placed in a vacuum oven. The pressure in the vacuum oven was suitably adjusted to the boiling point of the silazane SAM material used. The temperature of the vacuum oven was maintained at 100 DEG C for 2 hours and then slowly cooled to room temperature (r.t.). The substrate was then washed with toluene and isopropyl alcohol to remove the residual layer.

The pentacene-based organic field-effect transistor was formed on a surface-modified SiO ₂ substrate through vacuum evaporation. A 50 nm pentacene film was thermally evaporated at a rate of 0.5 A / s using a shadow mask. The substrate temperature was maintained at 60 占 폚 during the deposition.

Then, a 70 nm thick gold (Au) source electrode and a drain electrode were respectively formed using a shadow mask at a speed of 1 A / s. The device was removed from the vacuum chamber, exposed in air, and moved into a box in a nitrogen atmosphere.

Silazane SAM material Material name Number of main chain alkyl groups Example 1 Hexamethyldisilazane (HMDS) One Example 2 1,3-di-n-propyl-1,1,3,3-tetramethyldisilazane (DPDS) 3 Example 3 1,3-di-n-butyl-1,1,3,3-tetramethyldisilazane (DBDS) 4 Example 4 1,3-di-n-octyl-1,1,3,3-tetramethyldisilazane (DODS) 8

Example  5

In the above Examples 1 to 4, the first SAM-treatment was performed in which the SiO ₂ insulating layer was surface-modified by using a DODS-silane residual material having eight alkyl groups in the main chain to form a SAM film.

Then, the second SAM-treatment was carried out by surface modification again using HMDS-silane-based material having one alkyl group in the main chain.

The SAM-treatment conditions and other processes were carried out in the same manner as in Examples 1 to 4 to prepare organic field effect transistors.

Control 1

For comparison with the organic field effect transistor according to the present invention, a pure SiO 2 insulating layer which was not surface-modified was used as the control 1.

Experimental Example  1: Organic Field  Measure electrical characteristics of effect transistor

The electrical characteristics of the organic field effect transistor according to Examples 1 to 4 and the control group were measured using a semiconductor parameter analyzer (Agilent 4155C) in a box under a nitrogen atmosphere. The transfer curve was measured at a drain-source voltage (V _DS ) of -30 V and a saturation condition with channel length and width of 50 μm and 1000 μm, respectively.

For the gate bias stress test, the gate bias stress of -30V was applied for 2 hours and then the threshold voltage and the drain-source current (I _DS ) were measured. In order to reduce the contact resistance effect, the gate bias stress test used a relatively large device with a channel length of 200 μm and a width of 2000 μm.

Referring to FIGS. 2 to 4, SAM-treated organic field effect transistors (Examples 1 to 4) are compared with the SiO ₂ insulating layer (Control 1) The mobility is remarkably increased.

The embodiments of the invention the surface modification by the treatment SAM- Examples 1 ~ 4 SiO ₂ insulating layer is the average mobility 0.46㎠ / V, respectively as compared to the pure SiO ₂ that is not surface-modified according to the (example 1), 0.61㎠ / V (Example 2), 0.65 cm 2 / V (Example 3), and 0.84 cm 2 / V (Example 4).

In addition, most of the SAM-treated organic field effect transistors exhibited similar threshold voltages and showed excellent I _on / I _off ratios in all devices.

In particular, FIG. 4 is a graph showing mobility and threshold voltage values according to the alkyl chain length. Referring to FIG. 4, mobility increases proportionally as the alkyl chain length of the silazane compound used as the self-assembled monolayer material increases Able to know.

Experimental Example  2: Organic Field  Check the structure of effect transistor

AFM (Park system, XE-100) was used to confirm the surface structure of the organic field effect transistor and the control group 1 according to the SAM-treated Examples 1 to 4, and the results are shown in Figs.

5 to 9, it can be seen that the grain sizes are different in the surface images (6 to 9) of the pentacene-based thin films formed on the SiO ₂ (5) and the SAM-treated SiO ₂ , respectively. Considering the grain size and charge transfer characteristics, it is known that the smaller the grain boundary, the more effective the charge transfer because it can provide many trap states at the grain boundary. Thus, when the grains are large, the grain boundaries are formed less, so that a device with higher field-effect mobility can be obtained.

Further, in the SiO ₂ surface it is pentacene having a small grain size is formed, and (5), in the surface-treated SiO ₂ SAM- it can be seen that the pentacene having a relatively large grain size is formed. From this, it can be deduced that grain particles have the highest mobility in the case of the largest pentacene thin film, which is consistent with previous studies.

Comparing only self-assembled monolayers, the grain size of pentacene was the largest in DODS with 8 alkyl groups (Example 4) and the grain size of pentacene was lowest in the individual HMDS with 1 alkyl (Example 1) . That is, as the alkyl chain length increases, the grain size of the pentacene increases. This is in agreement with the results of Experimental Example 1 in which the mobility of the SAM-treated organic field effect transistor was measured, and it was shown that the self-assembled monolayer having a long alkyl chain length provides a better surface state for growth of the pentacene thin film Loses. The formation of pentacene with a large grain size on a self-assembled monolayer having a long alkyl chain length is one of the main reasons for improving mobility.

As a result of measuring the contact resistance (Rc) of each device, the mobility was improved and the contact resistance was also decreased. The RcW values of the devices were measured using the transmission line method and the RcW values were similar regardless of the SAM-treatment. (27 ~ 33kΩ at V _GS = -30V). From these results, it can be seen that the SAM-treatment has no significant influence on the contact resistance. Therefore, it can be seen that the improvement in mobility is mainly induced as the charge transfer occurs actively in a larger pentacene grain.

Experimental Example  3: Organic Field  Bias Stability of Effect Transistors ( bias stability ) Measure

The bias stability of the SAM-treated organic field effect transistor was measured. The threshold voltage variation was measured for 2 hours at a gate bias of -30 V (corresponding to an electric field of -3 MV / cm), and the results are shown in FIGS. 10 to 12.

Referring to FIGS. 10 to 12, it can be seen that the threshold voltage shift of the un-SAM-processed OFET reaches 50% of the gate bias stress applied for 2 hours. From these results, It can be seen that the bias stability is poor. However, it can be seen that the SAM-treated OFET undergoes a fine threshold voltage displacement and is more stable under a high electric field (3 MV / cm). In addition, devices that were SAM-treated with a material having a long alkyl group showed a tendency to have a greater change in threshold voltage than devices that had SAM-treated with a material having a short alkyl group. That is, the threshold voltage displacement of the DODS-processed device is 7.14 V, which is higher than 5.69 V of the HMDS-processed device.

Bias stability is caused by the trapping state, which is deeply related to the hydroxy group on the surface. Therefore, it can be said that the difference in the threshold voltage shift in each device depends on the content of the hydroxy group remaining on the surface of the SAM-treated SiO ₂ insulating layer.

Thus, from the result of the threshold voltage displacement of the SAM-treated device, alkyl groups can cover more SiO ₂ insulating layer surfaces than SAMs with longer alkyl groups in the case of shorter SAMs, thereby reducing more trapped states on the surface. Generally, silazane SAMs comprising three alkyl groups form amorphous structures that are disordered due to monofunctional reactions. Therefore, a long alkyl chain having an irregular structure in the SAM may interfere with high packing, and thus it is insufficient to act as a protective film of a hydroxyl group on the surface.

The threshold voltage displacement resulting from gate bias stress can be expressed as a stretched exponential function as: < RTI ID = 0.0 >

(1)

In Equation (1), VGS is an applied gate bias stress, Vth (0) is an initial threshold voltage,? Is a relaxation time, and? Is a dispersion index.

This is called an extended exponential function because the time response is faster than the exponential function before τ and then slower than the exponential function. The dispersion index β indicates how broad the distribution of time constants is. When β approaches a single value, it means that the time constant has a narrow distribution.

The threshold voltage displacement of the SAM-processed OFET fits in Equation 1 above. SAM- relaxation of the treated OFET time (~ 6x10 ⁵ 6x10 ⁶ s) and polydispersity index (0.16 ~ 0.20) is a value from a previous study was treated with a silane SAM SiO ₂ in a tilt phenethyl leakage (β = 0.19, τ = 1 to 7 x 10 ⁶ s). The relaxation time of the SAM-processed OFET is longer than that of the untreated device.

Experimental Example  4: Measurement of threshold voltage displacement

The threshold voltage displacements of the OFETs prepared by the two-step SAM process and the OFETs processed by the one-step SAM process in Example 5 were measured. The results are shown in Figs. 14 to 15.

Referring now to FIG. 14, the threshold voltage displacement of OFETs fabricated by two-step SAM treatment is 5.35 V, which is similar to 5.69 V of an HMDS-treated device (Example 1) with one alkyl group. In addition, OFETs prepared by two-step SAM treatment show improvement in bias stability and high mobility.

15 shows I _DS reduction under gate bias stress. Example 4 (OFET with 1-step SAM treatment with DODS) and Example 5 (OFET with 2-step SAM treatment) exhibit similar I _DS at the beginning, but with application of gate bias stress, OFET with 1-step SAM treatment) showed a sharp decrease in current as compared to Example 5 (2-step SAM-treated OFET).

That is, the electrical performance of the device according to Example 5 (2-step SAM processed OFET) exhibits a high value similar to that of Example 4, and the bias stability is similar to that of Example 1 (OFET with 1- , Respectively.

From these results, it was confirmed that both the high mobility and excellent bias stability can be obtained by using the two-step SAM-treatment method. This is an effective way to improve the problem of mobility and bias stability depending on the SAM process.

Table 2 summarizes the electrical characteristics of the organic field effect transistors using Examples 1 to 5 and the insulating layer (SiO ₂ ) as the control group 1.

Mobility
(Cm2 / Vs) V _th (V) I _on / I _{off Vth} after 2h (V) ^(a) Relaxation time τ (s) The dispersion index (?) Control 1 0.29 (0.03) -7.20 (+/- 0.48) ~ 10 ⁶ 12.19 2.58x10 ⁴ 0.24 Example 1 0.46 (0.03) -8.15 (+/- 0.59) ~ 10 ⁶ 5.69 2.38x10 ⁶ 0.20 Example 2 0.61 (+/- 0.03) -9.95 (+/- 0.51) ~ 10 ⁷ 5.93 6.25x10 ⁶ 0.16 Example 3 0.65 (0.03) -8.97 (+/- 0.76) ~ 10 ⁷ 6.52 5.57x10 ⁶ 0.16 Example 4 0.84 (0.03) -8.45 (+/- 0.76) ~ 10 ⁷ 7.14 6.22x10 ⁵ 0.20 Example 5 0.88 (0.03) -9.10 (+ -0.22) ~ 10 ⁷ 5.34 1.67x10 ⁷ 0.16 (a) Measured under gate bias stress of -30V.

11: substrate, 12: insulating layer
13: self-assembled monolayer (SAM), 14: organic semiconductor layer
15: source and drain electrodes

Claims (6)

Forming an insulating layer on the substrate,
Forming a self-assembled monolayer on the insulating layer by surface-modifying the insulating layer using at least two kinds of silane residual materials; and
And forming an organic semiconductor layer on the self-assembled monolayer.
The method according to claim 1,
Wherein the surface modification of the insulating layer is performed in a continuous process or stepwise.
The method according to claim 1,
Wherein the silane residual material is represented by the following chemical formula 1:
(Formula 1)
R ₂ -Si (CH ₃ ) ₂ -NH-Si (CH ₃ ) ₂ -R ₁
In the above formula, R ₁ and R ₂ are the same or different and each independently an alkyl group having 1 to 12 carbon atoms.
The method according to claim 1,
Wherein the surface modification uses any one selected from a vaporization method, a liquid phase solution immersion method, and a spin coating method.
The method according to claim 1,
The surface modification of the insulating layer may be carried out by using a long silane residual material having an alkyl group having an alkyl group of 5 to 12 in the main chain in the above formula
Wherein the alkyl group having an alkyl group of 1 to 4 in the main chain of the formula (1) is a short silane residual material.
6. The method of claim 5,
The self-assembled monolayer is formed on the insulating layer through surface modification using an alkyl group having a main chain of 5 to 12 in the formula (1)
In the above formula (1), the silane residual material may be passivated to protect the hydroxyl group (-OH) remaining in the insulating layer with a coating through a surface modification using a short silane residual material in which the alkyl group of the main chain is 1 to 4, Is formed on the surface of the substrate.

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