KR101192095B1 - A method for preparation of periodic arrays of organic crystals, and a method for preparation of organic electronic devices comprising the periodic arrays of organic crystals - Google Patents

Abstract

The present invention relates to a method for producing an organic crystal periodically arranged, and to a method for manufacturing an organic electronic device comprising the organic crystal, and more particularly, using an organic semiconductor or a blend of the organic semiconductor and a polymer using a capillary tube. A method of producing highly oriented n -type or p-type organic semiconductor crystals by a simple method through the solution process used, and the low-voltage field effect transistor and complementary inverter, or photosensitive field effect, comprising the highly oriented organic semiconductor crystals A method for manufacturing organic electronic devices such as transistors and complementary inverters.

Description

A method for preparation of periodic arrays of organic crystals, and a method for preparation of organic electronic devices comprising the periodic arrays of organic crystals}

The present invention relates to a method for producing an organic crystal periodically arranged, and to a method for manufacturing an organic electronic device comprising the organic crystal, and more particularly, using an organic semiconductor or a blend of the organic semiconductor and a polymer using a capillary tube. A method of producing highly oriented n -type or p-type organic semiconductor crystals by a simple method through the solution process used, and the low-voltage field effect transistor and complementary inverter, or photosensitive field effect, comprising the highly oriented organic semiconductor crystals A method for manufacturing organic electronic devices such as transistors and complementary inverters.

Organic semiconductors are an interesting development that has attracted worldwide attention over the past two decades because of their possible applications in molecular electronics and are expected to have advantages in both cost and size over conventional silicon devices. In addition to their low manufacturing costs and ease of use, organic materials have the added advantage of including an effective range of large areas compatible with plastic substrates, low processing temperatures and mechanical flexibility. Significant advances have been made in organic electronics in recent years. Notable examples include organic field effect transistors (OFETs) ( p − and n − types) (H. Sirringhaus, Adv. Mater. , 2005, 17, 2411-2425; A. Hepp et al, Phys. Rev. Lett. , 2003, 91, 157406; J. Cornil et al, Adv. Mater. , 2007, 19, 1791-1799; B. Crone et al, Nature , 2000, 403, 521-523; PF Baude et al, Appl. Phys. Lett. , 2003, 82, 3964-3966; Y. Choi et al, Org.Elect . , 2009, 10, 1209-1216; K. Sim et al, Org.Elect . , 2009, 10, 506-510; JP Hong et al, Angew. Chem., Int. Ed. , 2009, 48, 3096-3098; H. Yan et al, Nature , 2009, 457, 679-687; C. Piliego et al, Adv. Mater. , 2009 , 21, 1573-1576), organic solar cells (SR Forrest, Nature , 2004, 428, 911-918; CD Dimitrakopoulos et al, Adv. Mater. , 2002, 14, 99-117), organic light emitting diodes (CD Muller et al, Nature , 2003, 421, 829-833; Y. Fukuda et al, Synth.Met. , 2000, 111, 1-6), sensors (J. Janata et al, Nat. Mater. , 2003, 2, 19-24;... L. Wang et al, Appl Phys Lett, 2004, 85, 6386-6388), and organic / inorganic hybrid Stable memory device; and the like (B. Mukherjee et al, Adv Mater , 2007, 19, 717-722..... B. Mukherjee et al, Appl Phys Lett, 2009, 94, 173510-173512). OFETs are used in display devices (JA Rogers et al, Proc. Natl. Acad. Sci. USA , 2001, 98, 4835-4840; Y. Fujisaki et al, Jpn. J. Appl. Phys. , 2005, 44, 3728-3732 ), Sensors (J. Janata et al, Nat. Mater. , 2003, 2, 19-24), and electronic barcodes (B. Crone et al, Nature , 2000, 403, 521-523; PF Baude et al, Appl Phys. Lett. , 2003, 82, 3964-3966), of particular interest in the printed electronics industry.

One of the major problems with these OFETs is their large operating voltage, often above 20V. In general, low voltage operation can be achieved through a high capacitive gate dielectric layer having either a reduced thickness or an increased dielectric constant (A. Facchetti et al, Adv. Mater. , 2005, 17, 1705-1725; H Klauk et al, Nature , 2007, 445, 745-748). However, reducing the thickness of the dielectric layer below the critical level results in significant current leakage due to direct tunneling to control the device's performance, leading to unstable operation and unsatisfactory power loss levels (SH). Lo et al, IEEE Electron Device Lett. , 1997, 18, 209-211). Therefore, a delicate balance between dielectric layer thickness, dielectric constant and film quality is essential to obtain a stable low voltage OFET. Devices with thick gate dielectric layers of such a suitable dielectric constant will be able to operate stably and avoid leakage of current and high power consumption (M. Yamagishi et al, Appl. Phys. Lett. , 2009, 94, 053305-053307). .

Although OFETs in which an organic semiconductor layer is formed by solution (spinning) casting or vacuum evaporation can obtain high current gains, the device performance is greatly reduced by trapping carriers that induce grain boundaries and defects in polycrystalline films. Recently, single crystal arrays of organic semiconductors have been patterned from a bottom-up approach for high performance OFET devices (AL Briseno et al, Nature , 2006, 444, 913-917).

In view of the above, the present inventors have been able to produce highly crystallized crystallized arrays whose orientation is controlled from highly oriented n -type, p-type organic semiconductors, or polymer blend solutions thereof through a solution process. The present invention was completed by confirming that it can be used for fabricating organic electronic devices such as low voltage OFETs and complementary inverters, photosensitive OFETs, and complementary inverters.

It is an object of the present invention to provide a method for producing highly oriented n -type, p-type organic semiconductor crystals through a solution process.

Another object of the present invention is to provide a method for manufacturing an organic electronic device comprising highly oriented n -type, p-type organic semiconductor crystals formed through a solution process.

Another object of the present invention is to provide an organic electronic device manufactured by the above method.

In order to solve the above problems, the present invention provides a method for producing a periodically arranged organic crystal comprising the following steps.

1) disposing a capillary on top of the dielectric layer formed on the gate electrode;

2) forming an organic semiconductor droplet by adding an organic semiconductor solution to the capillary; And

3) evaporating the solvent from the organic semiconductor droplets to form periodically arranged organic crystals.

Step 1 is a step of disposing a capillary on top of the dielectric layer formed on the gate electrode, a step of disposing a capillary for inducing the preferential crystal orientation of the organic crystal using the capillary force.

In the present invention, the capillary tube preferably has an outer wall diameter of 0.5 mm to 5 mm. If the diameter of the capillary tube is smaller than the lower limit, there is a disadvantage that the capillary force is difficult to form crystals, and if the capillary tube is larger than the upper limit, it is difficult to grow a crystal at a desired position.

As the capillary in the present invention, a glass capillary may be used, but is not limited thereto.

The material which can be used as the gate electrode in the present invention is a metal oxide semiconductor. Specific examples of the metal oxide semiconductor include indium tin oxide (ITO) and fluorine doped tin oxide (FTO), but are not limited thereto.

Dielectrics usable in the present invention include, but are not limited to, SiO ₂ , cross-linked poly (4-vinyl phenol), or combinations thereof.

Step 2 is a step of forming an organic semiconductor droplet by adding an organic semiconductor solution to the capillary, wherein a solution containing an organic semiconductor crystal is added to the capillary to form an organic semiconductor droplet covering the capillary periphery.

In the present invention, the organic semiconductor is pentacene such as 7,7,8,8-tetracyanoquinomimethane (TCNQ), TIPS-pentacene [6,13-bis (triisopropylsilylethynyl) pentacene] and the like. Derivatives or perylenediimide (PTCDI) derivatives of the general formula (1).

Where

R ₁ and R ₂ are H or C _1-4 alkyl group,

R ₃ is H or a C _1-18 straight or branched chain alkyl group.

Preferably, in Chemical Formula 1,

R ₁ and R ₂ are H,

R ₃ is H or a C _1-18 straight chain alkyl group.

More preferably, in Chemical Formula 1,

R ₁ and R ₂ are H,

R ₃ is H or a C _5-13 straight chain alkyl group.

Most preferably, in Chemical Formula 1,

R ₁ and R ₂ are H,

R ₃ is H, a straight chain alkyl group of C ₅ , a straight chain alkyl group of C ₈ , or a straight chain alkyl group of C ₁₃ .

In the present invention, the organic semiconductor may be used as a blend with a polymer.

In the present invention, the polymer may be poly (alpha-methylstyrene) or the like, but is not limited thereto.

In the present invention, the organic semiconductor solution may be prepared using toluene, xylene, dichlorobenzene, chloroform, tetrahydrofuran, chlorobenzene, or a combination thereof as a solvent, but is not limited thereto.

In the present invention, the concentration of the organic semiconductor solution is preferably 0.00001 to 1 mg ml ^-1 . If the concentration of the organic semiconductor solution is lower than the lower limit, the number of crystals produced is too small to be difficult to apply the device, and if it is higher than the upper limit, it is difficult to make a uniform solution because the solute is not completely dissolved.

Step 3 is a step of evaporating the solvent from the organic semiconductor droplets to form periodically arranged organic crystals, and inducing the organic crystals to self-assemble in a periodic arrangement as the solvent in the organic semiconductor droplets is evaporated. . In the present invention, in step 3, while the solvent of the organic semiconductor droplet is evaporated, the organic semiconductor is preferentially moved toward the line contacted by the particles in the evaporating droplet due to the capillary force between the capillary tube and the organic semiconductor droplet, that is, the line formed by the capillary tube. The self-assembly of crystals eliminates the need to orient the organic semiconductor crystals in a periodic array through a separate additional process.

In the present invention, the evaporation temperature is preferably 70 to 150 ℃. If the evaporation temperature is lower or higher than the lower limit, no crystallization occurs. Even if a crystal is formed, there is a disadvantage in that direction and crystallinity cannot be adjusted.

The present invention also provides a method of manufacturing an organic electronic device comprising the periodically arranged organic crystals produced by the above method.

In the present invention, the organic electronic device is a ring consisting of a low voltage field effect transistor, a complementary inverter consisting of a low voltage field effect transistor, a photosensitive field effect organic thin film transistor, a complementary inverter consisting of a photosensitive field effect organic thin film transistor, or a combination thereof. Oscillators, sensors including them, and the like, but are not limited thereto.

In one embodiment, the present invention provides a method of manufacturing a low voltage field effect transistor comprising periodically arranged organic crystals comprising the following steps.

1) disposing a capillary on top of the dielectric layer formed on the gate electrode;

2) forming an organic semiconductor droplet by adding an organic semiconductor solution to the capillary;

3) evaporating the solvent from the organic semiconductor droplets to form periodically arranged organic crystals; And

4) depositing gold on the periodically arranged organic crystals.

Steps 1 to 3 are steps for preparing the periodically arranged organic crystals, the specific method is the same as described in steps 1 to 3 of the periodically arranged organic crystal production method.

Step 4 is depositing gold on the periodically arranged organic crystals, and depositing gold on the periodically arranged organic crystals to form an upper contact source-drain electrode.

The present invention also provides a low voltage field effect transistor comprising periodically arranged organic crystals prepared by the above manufacturing method.

In another embodiment, the present invention provides a method of manufacturing a complementary inverter consisting of a low voltage field effect transistor comprising a periodically arranged organic crystal comprising the following steps.

1) disposing a capillary on top of the dielectric layer formed on the gate electrode;

2) forming an organic semiconductor droplet by adding an organic semiconductor solution to the capillary;

3) evaporating the solvent from the organic semiconductor droplets to form periodically arranged organic crystals;

4) depositing gold on the periodically arranged organic crystals; And

5) depositing a pentacene thin film on top of a dielectric layer located on a separate gate electrode disposed in parallel with the gate electrode.

Steps 1 to 4 are as described in the method of manufacturing the low voltage field effect transistor.

The step 5 is a step of depositing a pentacene thin film on top of a dielectric layer located on a separate gate electrode disposed in parallel with the gate electrode, in addition to the n -channel OFET transistor to form a p -channel transistor of the OFET transistor A step of depositing a pentacene thin film on a dielectric layer disposed on a separate gate electrode disposed in parallel with the gate electrode.

The present invention also provides a complementary inverter consisting of a low voltage field effect transistor comprising periodically arranged organic crystals prepared by the above manufacturing method.

In still another embodiment, the present invention provides a method of manufacturing a photosensitive field effect organic thin film transistor including periodically arranged organic crystals comprising the following steps.

1) disposing a capillary on top of the dielectric layer formed on the gate electrode;

2) forming an organic semiconductor droplet by adding an organic semiconductor solution to the capillary;

3) evaporating the solvent from the organic semiconductor droplets to form periodically arranged organic crystals; And

4) depositing gold on the periodically arranged organic crystals.

Steps 1 to 4 are as described in the method of manufacturing the low voltage field effect transistor.

The present invention also provides a photosensitive field effect organic thin film transistor comprising periodically arranged organic crystals prepared by the above method.

In still another embodiment, the present invention provides a method of manufacturing a complementary inverter composed of a photosensitive field effect organic thin film transistor including periodically arranged organic crystals comprising the following steps.

1) disposing a capillary on top of the dielectric layer formed on the gate electrode;

2) forming an organic semiconductor droplet by adding an organic semiconductor solution to the capillary;

3) evaporating the solvent from the organic semiconductor droplets to form periodically arranged organic crystals;

4) depositing gold on the periodically arranged organic crystals; And

5) depositing a pentacene thin film on top of a dielectric layer located on a separate gate electrode disposed in parallel with the gate electrode.

Steps 1 to 5 are the same as described in the method of manufacturing the complementary inverter consisting of the low voltage field effect transistor.

In addition, the present invention provides a complementary inverter consisting of a photosensitive field effect organic thin film transistor including a periodically arranged organic crystal produced by the above manufacturing method.

In the embodiment of the present invention, highly oriented n -type organic, viz , 7,7,8,8-tetracyanoquinodimethane (TCNQ) crystals were prepared and used in the fabrication of low voltage OFETs and complementary inverters. The device was then analyzed to evaluate the intrinsic properties of the material and to observe the minimal impact of grain boundaries and film form. Further, in the present invention, TCNQ crystals on the polymer gate dielectric are considered to be disadvantageous for n -type devices as SiO ₂ having the -OH group, the most commonly used inorganic gate dielectric, prevents the accumulation of electrons near the boundary. An OFET based on an array of is provided. In addition, SiO ₂ is not suitable for transparent or flexible devices. OFETs based on TCNQ crystals fabricated by complex physical vapor transport and laminating methods have been reported to have mobility of 0.2-0.5 cm ² V ^-1 s ^-1 (M. Yamagishi et al, Appl. Phys. Lett. , 2009, 94, 053305-053307; H. Alves et al, Nat. Mater. , 2008, 7, 574-580). In addition, when using a specific device structure (vacuum-spatial structure) has been reported to have a mobility value of 1.6 cm ² V ^-1 s ^-1 (E. Menard et al, Adv. Mater. , 2004, 16 , 2097-2101). However, the mobility decreased by three times with the use of polymer gate dielectrics (E. Menard et al, Adv. Mater. , 2004, 16, 2097-2101). Even after tremendous efforts to produce atmospheric stable, n -channel, high mobility, low voltage OFETs on polymer dielectrics, reports of OFETs with V _Th of less than 5 V are very few. The present invention provides a novel approach to fabricate a periodic array of highly oriented π-conjugated organic crystals from solution and then use them in low voltage OFETs. This method provides a very simple and efficient high performance low cost OFET on the polymer dielectric without any further modification. The highest observed field effect mobility was 0.03 cm ² V ^-1 s ^-1 . This value is two times higher than previous results for single crystal TCNQ OFETs (B. Crone et al, Nature , 2000, 403, 521-523).

The mobility of the TCNQ crystal OFETs provided by the present invention is the highest among the TCNQ crystal OFETs processed by any solution process using a polymer gate dielectric. To confirm that this n -type OFET can be used as a component of a logic device, an organic complementary inverter is fabricated using a TCNQ crystal array ( n -type) and a vacuum evaporated pentacene thin film ( p -type). Operated at low voltage.

In conclusion, the present invention provides a method of forming an array of highly oriented TCNQ crystals in an OFET with a polymer gate dielectric, which can achieve n -type characteristics that are unprecedentedly stable at low operating voltages. The maximum mobility of 0.03 cm ² V ⁻¹ s ⁻¹ and a low threshold voltage below 0.5 V were measured in the saturation region. An organic complementary inverter was fabricated comprising solution processed, well oriented TCNQ crystals and vacuum evaporated pentacene thin films. This showed good response at low operating voltages. These results show that high performance OFETs and logic devices can be fabricated through an easy solution process at low cost for low voltage, low power operation. Their performance can also be further improved through proper device design. This single step solution process, which combines the growth and self-assembly of organic nano / micro-structures in such a large area, can be applied to fabricate ordered structures of other soluble organic materials and is quite useful in providing a variety of large scale low cost future electronic devices. Gives the possibility.

The present invention is capable of producing highly oriented organic crystals in a simple manner through a solution process using capillary tubes, and by operating organic electronic devices such as low voltage field effect transistors and complementary inverters including the highly oriented organic crystals. There is an effect that can provide an organic electronic device showing excellent performance even at voltage.

1 is a view showing a process of preparing a highly oriented organic crystal by the method according to the present invention, and fabricating a low voltage field effect transistor comprising the highly oriented organic crystal.
FIG. 2 is a diagram illustrating a process of preparing a highly oriented organic crystal by a method according to the present invention and fabricating a complementary inverter of a low voltage field effect transistor including the highly oriented organic crystal.
3A shows a polarizing microscope image of a highly oriented, long, rod-shaped crystal between source-drain electrodes.
3B shows the GIXD pattern of TCNQ crystals measured with vertical geometry.
3C shows the GIXD pattern of TCNQ crystals measured in parallel geometry.
4A is a diagram showing the results of measuring output ( I _DS - V _DS ) characteristics of a low voltage TCNQ OFET having a gate dielectric having a thickness of 375 nm.
4B is a diagram showing the results of measuring transport ( I _DS - V _G ) characteristics for a low voltage TCNQ OFET having a gate dielectric having a thickness of 375 nm.
Figure 4c is a diagram showing the results of measuring the transport characteristics for the low voltage TCNQ OFET at V _DS = 2V with different dielectric layer thickness.
4D is a diagram showing the results of measuring the leakage current of the CL-PVP gate dielectric in a metal-insulator-metal (MIM) sandwich structure having ITO as a base and Au as an upper electrode.
FIG. 5 is a diagram illustrating a result of measuring output characteristics of a low voltage OFET including a periodically arranged TIPS-pentacene.
FIG. 6 is a diagram illustrating a result of measuring output characteristics of a low voltage OFET including PTCDI-C5 arranged periodically.
7 is a diagram illustrating a result of measuring output characteristics of a low voltage OFET including a periodically arranged PTCDI-C8.
FIG. 8 is a diagram showing results of measuring output characteristics of a low voltage OFET including a periodically arranged PTCDI-C13.
9A is a diagram illustrating a result of measuring output characteristics of a photosensitive field effect organic thin film transistor including TCNQ arranged periodically.
FIG. 9B is a diagram illustrating a result of measuring transport characteristics of a photosensitive field effect organic thin film transistor including a TCNQ arranged periodically. FIG.
FIG. 10 shows field effect mobility of 15 low voltage OFETs using periodically arranged TCNQ crystals grown directly on a CL-PVP gate electrode with a thickness of 375 nm.
Figure 11 shows the results of measuring the transport characteristics of the device at different temperatures (left) and extracting the mobility and threshold voltage ( V _TH ) of the OFETs to ensure that the OFETs operate in a low voltage situation, and plot these changes. It is a graph (right) shown as a function of temperature.
12a shows the static transport characteristics of the inverter at different drive voltages V _DD .
12b shows the voltage gain of the inverter at different V _DD .

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

Example 1 Fabrication of Low Voltage OFETs and Complementary Inverters Including Periodically Arranged Organic Crystals of the Present Invention Using TCNQ

OFETs were fabricated on a cleaned, patterned indium tin oxide (ITO) coated glass substrate that acts as a gate electrode. TCNQ, an active organic semiconductor, was used as received from Aldrich Chemical. Crosslinked poly (4-vinyl phenol) (CL-PVP) was used as the gate dielectric. Its precursor solution was poly (4-vinylphenol) (PVP) (M w = 20000 g mol ^-1 ) (10% by weight) crosslinker, poly (melamine- co -formaldehyde) (M n = 511 g

mol- ¹ ) (5 wt.%) and propylene glycol monomethyl ether acetate (PGMEA) (85 wt.%) with stirring overnight. The dielectric precursor solution was spun cast onto an ITO substrate to form an insulating layer covering the gate electrode. The spin cast film was soft baked at 90 ° C. on a hot plate for 10 minutes and (hard) baked at 175 ° C. in a vacuum oven for 30 minutes. The crystal arrangement of TCNQ was grown on top of the dielectric film using capillaries.

For this purpose, a 3 cm long glass capillary with an outer wall diameter of 1.0-1.1 mm was placed on top of the dielectric film to be parallel to the patterned underlying ITO (2 mm × 10 mm) gate electrode. A solution of TCNQ (1 mg ml ⁻¹ ) in 5-10 μl of toluene was added dropwise to the capillary. As soon as the TCNQ solution was placed in the capillary, it immediately spread along the length of the capillary to cover both capillaries to form droplets. The droplets formed in the capillary were then placed on a hot plate (110 ° C.) and baked for 1 hour under atmospheric conditions. After the solvent was completely evaporated, crystals grew in a direction perpendicular to its length on both sides of the capillary.

To complete the OFET fabrication, a high vacuum (5 × 10 ^-6 ) of gold (Au) at a rate of 0.3 μs ⁻¹ was deposited on a TCNQ crystal with a periodic array grown on the dielectric film coated / ITO substrate prepared above. torr) to make an upper contact source-drain electrode (40 nm). The shadow mask, used during Au deposition, defined the channel length L and the channel width W to 50 μm and 1000 μm, respectively. For fabrication of complementary inverters, pentacene thin films were also deposited via a vacuum thermal deposition method.

1 and 2 show the growth of highly oriented TCNQ crystals and the accompanying OFET and complementary inverter fabrication process. Capillary forces between the capillary and the TCNQ solution may result in preferential crystal orientation perpendicular to the capillary. As solvent evaporation increases, the density of the crystals increases. In addition, as the area of the solid / liquid interface continues to shrink during evaporation, compressive forces are induced on the nano / micro crystal rods, aligning them in a more compact and orderly manner to maximize the entropy of the self-assembled structure (L. Onsager, Ann.NY Acad.Sci . , 1949, 51, 627-659. In general, particles / molecules in the evaporating droplets preferentially move towards the contact line (liquid, vapor, solid interface), thereby allowing capillary controlled particle assembly (L. Malaquin et al, Langmuir). , 2007, 23, 11513-11521).

In addition, quantitative solid state leakage current through the polymer gate dielectric was recorded using a metal-insulator-metal (MIM) sandwich structure with ITO and Au as the base and top electrodes, respectively. For complementary inverters, n -type OFETs and vacuum deposited (5 × 10 ^-6 torr) pentacene thin films (15 nm, 0.3 μs ⁻¹ ) deposited based on solution processed, highly oriented TCNQ crystals Based p -type OFETs were used.

3A shows a polarizing microscope image of a highly oriented, long, rod-shaped crystal between source-drain electrodes. It can be seen that the microrods are clearly well oriented and in contact with the two electrodes parallel to each other in the channel region.

Example 2 Fabrication of Low Voltage OFETs and Complementary Inverters Incorporating Periodically Arranged Organic Crystals of the Present Invention Using TIPS-pentacene

A low voltage OFET and a complementary inverter were fabricated in the same manner as in Example 1 except that TIPS-pentacene was used instead of TCNQ as the organic semiconductor.

Example 3 Fabrication of Low Voltage OFETs and Complementary Inverters Including Periodically Arranged Organic Crystals of the Present Invention Using PTCDI-C5

A low voltage OFET and complementary inverter were fabricated in the same manner as in Example 1, except that PTCDI-C5 (R ₃ = 5) was used instead of TCNQ as the organic semiconductor.

Example 4 Fabrication of Low Voltage OFETs and Complementary Inverters Including Periodically Arranged Organic Crystals of the Present Invention Using PTCDI-C8

A low voltage OFET and complementary inverter were fabricated in the same manner as in Example 1 except that PTCDI-C8 (R ₃ = 8) was used instead of TCNQ as the organic semiconductor.

Example 5 Fabrication of Low Voltage OFETs and Complementary Inverters Including Periodically Arranged Organic Crystals of the Present Invention Using PTCDI-C13

A low voltage OFET and complementary inverter were fabricated in the same manner as in Example 1, except that PTCDI-C13 (R ₃ = 13) was used instead of TCNQ as the organic semiconductor.

Example 6 Fabrication of Photosensitive Field Effect Organic Thin Film Transistor and Photosensitive Complementary Inverter Including Periodically Arranged Organic Crystals

OPT was fabricated on a cleaned, patterned indium tin oxide (ITO) coated glass substrate that acts as a gate electrode. TCNQ, an active organic semiconductor, was used as received from Aldrich Chemical. Crosslinked poly (4-vinyl phenol) (CL-PVP) was used as the gate dielectric. CL-PVP precursor solution was added poly (4-vinylphenol) (PVP) (M w = 20000 g mol ^-1 ) (10 wt%) crosslinker, poly (melamine- co -formaldehyde) (M n = 511 g mol ^-1 ) (5 wt.%) And propylene glycol monomethyl ether acetate (PGMEA) (85 wt.%) With stirring overnight. The dielectric precursor solution was spun cast onto an ITO substrate to form an insulating layer covering the gate electrode. The spun cast film was soft baked at 90 ° C. for 10 minutes on a hot plate and further baked at 175 ° C. in a vacuum oven (10 ⁻³ torr) for 30 minutes. The thickness of the dielectric was adjusted to about 375 nm. On top of the dielectric, an oriented crystal array of TCNQ was grown using capillaries.

For this purpose, a 3 cm long glass capillary with an outer wall diameter of 1.0-1.1 mm was placed on top of the dielectric film to be parallel to the patterned underlying ITO (2 mm × 10 mm) gate electrode. A solution of TCNQ (1 mg ml ⁻¹ ) in 5-10 μl of toluene was added dropwise to the capillary. As soon as the TCNQ solution was placed in the capillary, it immediately spread along the length of the capillary to cover both capillaries to form droplets. The droplets formed in the capillary were then placed on a hot plate (110 ° C.) and baked for 1 hour under atmospheric conditions. After the solvent was completely evaporated, crystals grew in a direction perpendicular to its length on both sides of the capillary.

To complete the OPT fabrication, gold (Au) was deposited on a TCNQ crystal with a periodic array grown on the dielectric film coated / ITO substrate prepared above at a high vacuum (5 × 10 ⁻⁶ ) at a rate of 0.3 μs ⁻¹ . torr) to make an upper contact source-drain electrode (40 nm). The shadow mask, used during Au deposition, secured rod-shaped TCNQ crystals lying in the channel region and defined the channel length L and channel width W to 50 μm and 1000 μm, respectively. For fabrication of complementary inverters, pentacene thin films were also deposited via a vacuum thermal deposition method.

Experimental Example 1: Confirming the Orientation of TCNQ Crystals

The low voltage OFET and the complementary inverter of Example 1 were tested as follows.

To confirm the preferred orientation of the TCNQ crystals, grazing angle X-ray diffraction analysis (GIXD) was performed. Grazing angle X-ray diffraction analysis (GIXD) was performed on the 4C2 beamline of the Pohang Accelerator Laboratory (J. Yoon et al, Macromol. Res. , 2008, 16, 575-585).

Diffraction patterns were collected using a two-dimensional charge coupled device (2-D CCD) detector (Rayonix SX165, Evanston, IL; 165 mm diameter, 2048 × 2048 pixels). The sample-to-detector distance was 166 mm. X-rays of 8.979 keV (λ = 1.381 kHz, λ is the wavelength) were used for data collection. TCNQ crystals with periodic arrangements grown on dielectric film coated / ITO substrates were immobilized on motorized sample stages located inside the vacuum chamber. The angle of incidence of the X-rays was set to 0.14 ° below the critical angle of TCNQ. Diffraction patterns were collected for 60 seconds. The diffraction angle was calibrated using precalibrated silver behenate (TIC, Japan).

In general, the random crystal-plane scattering of GIXD mosaic pattern having a property (mosaicity) on the substrate vector (q _∥) is to be represented by the equation (1).

In the above formula, q _∥ is the scattering factor on the plane, q _x is the scattering factor on the x-axis, q _y is the scattering factor on the y-axis.

However, if the direction of crystal growth (or mosaicism) is well controlled, the q _x and q _y components can be separated through parallel or vertical measurement geometries, where the incident X-rays are parallel or perpendicular to the reference axis, respectively. Thus, two distinct GIXD patterns obtained from orthogonal measurement geometries can confirm the highly oriented preferred crystal orientation. TCNQ is known to form orange-red monoclinic crystals belonging to the C _{2 / c} space group with a = 8.906, b = 7.060, c = 16.395 Hz, β = 98.54 ° (RE Long et al, Acta Crystallogr ., 1965, 18, 932-939). Peak indexing was performed based on the reported crystal structure and unit cell parameters. In Figures 3B and 3C, the reference axis was chosen parallel to the initial growth direction of the needle-shaped TCNQ crystals parallel to the c -axis. The 2D GIXD pattern contains most of the diffraction peaks except those located near the q _z axis because the Bragg condition cannot be satisfactory for q values reflecting the curvature of the Ewald sphere. In the vertical measurement geometry was a series of [02 l] diffraction peak is observed (Fig. 3b), which a - indicates that the axis is incident parallel to the X- ray beam. In the parallel measurement geometry, only strong (110) peaks were seen, other peaks are insignificant (FIG. 3C). As a result, these GIXD results clearly demonstrate that perfect, long, needle-shaped TCNQ crystals grown through the capillary method exhibit highly desirable crystal orientation along the c -axis.

Experimental Example 2: Investigation of output and transport characteristics of OFET and OPT

The low voltage OFET including the periodic arrangement of TCNQ of Example 1 was tested as follows.

Electrical properties were investigated under pressure at room temperature using the HP Semiconductor Parameter Analyzer (HP 4145B). Gate dielectric layer thickness was measured using a surface profiler (AMBIOS XP-100).

The output ( I _DS - V _DS ) and transport ( I _DS - V _G ) characteristics for an OFET with a TCNQ crystal array and a 375 nm thick gate dielectric are shown in FIGS. 4A and 4B, respectively. Output characteristics at different gate biases show a typical n -type behavior with dominant electron transport (FIG. 4A). As the gate bias V _G increases, the drain current I _DS is increased by allowing more charge carriers to accumulate at the TCNQ crystal / CL-PVP interface near the channel region. 4A also shows a reasonably good saturation behavior of I _DS at low gate and drain biases, indicating that the device can be operated at significantly lower voltages lower than 2V. The transport ( I _DS - V _G ) characteristics of the OFET show no hysteresis in the forward and reverse sweeps of the gate bias (FIG. 4B). The maximum charge carrier mobility (μ) and threshold voltage ( V _TH ) of the _OFETs were determined to be ˜0.03 cm ² V ⁻¹ s ⁻¹ and 0.5 V, respectively. This mobility is twice as high as previously reported for TCNQ thin-polycrystalline film transistors (AR Brown et al, Synth. Met. , 1994, 66, 257-261; M. Lizuka et al, Appl. Surf. Sci. , 1998, 130, 914-918). This indicates that due to external influences such as grain boundaries, these OFETs cannot be fully realized through the inherent capabilities of TCNQ.

As described above, the low voltage OFET including the periodically arranged TIPS-pentacene, PTCDI-C5, PTCDI-C8, or PTCDI-C13 of Examples 2 to 5 showed the same output characteristics as shown in FIGS. A graph was obtained.

First, the output curve of the field effect organic thin film transistor fabricated using TIPS-pentacene periodically arranged in FIG. 5 is shown. 5 shows that as the negative gate bias V _G increases, the drain current I _DS is increased by accumulating more charge carriers at the TIPS-pentacene crystal and the CL-PVP interface in the channel region. there was. In addition, it can be seen that the linear drainage behavior is shown in the low drain bias region and the current saturation region is well seen in the relatively high bias region.

6 to 8 show output curves of the field effect organic thin film transistors fabricated using the periodically arranged PTCDI-C5, PTCDI-C8, or PTCDI-C13, respectively. 6 through 8, as the positive gate bias ( V _G ) increases, drain current is increased by accumulating more charge carriers at the CL-PVP interface with the PTCDI-C5, PTCDI-C8, or PTCDI-C13 crystals in the channel region. It was found that ( I _DS ) was increased. In addition, linear behavior is shown in the low drain bias region and current saturation region is shown in the relatively high bias region.

The low voltage OPT and the photosensitive complementarity inverter of Example 6 were tested as follows.

The photoreaction properties of the OPT were measured by shining light directly on top of the device as shown in the device diagram inserted in FIG. 9A. The difference in output characteristics (I _DS vs. V _DS ) of TCNQ OPT under dark and white light illumination is shown in FIG. 9A. The characteristics for the other gate voltage (V _G ) show typical n-type characteristics with predominant electron transport with a clear change from linear to saturated. As V _G increases, more charge carriers accumulate in the polymer gate dielectric near the interface and channel region of the TCNQ crystal, resulting in an increase in drain current (I _DS ).

9A also shows a fairly good saturation behavior of I _DS at low gate and drain bias (V _DS ), indicating that the device can be operated with significantly lower voltages of 2 V or less. After illumination, the I _DS increased to a much higher value than the same V _G without illumination. Many excitons, accompanied by electrons and holes, absorbed photons of energy equal to or higher than the band-gap energy of TCNQ, resulting in an increase in I _DS . Device control is complemented by light, which is regarded as the fourth terminal with conventional three terminals: source, drain and gate electrodes.

The transport (I _DS -V _G ) properties of OPT under darkness and illumination are shown in FIG. 9B. Properties in the dark were measured in both the front and back sweeps of the gate bias, but no hysteresis behavior was observed. 9B shows the enhancement of the drain current under illumination. The ratio between light and dark current (I _light / I _dark ) at a very low gate bias of V _G = 0.3 V was calculated to be 31. 9B shows that the device can be controlled by both light illumination and gate voltage. The photoreactivity of the device, typical of the advantages of photosensitive transistors, has been found to be> 1 mA W ⁻¹ at an optimum power of 5.98 mW cm ⁻² and a gate bias as low as 0.3 V. This value can be further improved by using monochromatic light having photon energy corresponding to the maximum absorption of TCNQ. The maximum charge carrier mobility (μ) and threshold voltage (V _Th ) of OPT under dark conditions were determined to be ˜0.03 cm ² V ⁻¹ s ⁻¹ and 0.5 V, respectively. The mobility is two times higher than that reported for TCNQ thin film transistors (AR Brown et al., Synth. Met. , 1994, 66, 257-261; M. Lizuka et al., Appl. Surf. Sci ., 1998, 130, 914-918), which indicates that the performance of the intrinsic material TCNQ, due to external influences, such as grain boundaries, has the TCNQ OFET of the above document has the amorphous / polycrystalline film is not sufficiently achieved.

However, under illumination, the mobility of the OPT has not changed substantially. Since the crystal size is much larger than the particles of a conventional organic film and even larger than the channel length, the boundary density is minimized and high device performance is achieved.

Experimental Example 3: Investigation of the Effect of Gate Dielectric Thickness on the Performance of OFET

In order to investigate the influence of the gate dielectric thickness, OFETs having dielectric layers of different thicknesses (120, 260, 375, 510 nm) were fabricated. Devices with dielectrics with a thickness of 510 nm show no field effect performance at low voltages, while devices with 120 nm dielectric layers have high leakage currents and run very poorly. This indicates that the dielectric thickness between these two values will have optimized performance. 4C shows that an OFET with a dielectric thickness of 375 nm performs best in low voltage situations. In a metal-insulator-metal (MIM) sandwich structure with ITO as the base and Au as the top electrode, it has been shown that as the gate dielectric thickness increases, the quantitative solid state leakage current decreases and thus the performance is improved (FIG. 4D). ). As the thickness of the polymer gate dielectric film increased from 120 nm to 375 nm, the leakage current density decreased from 9 × 10 ⁻⁶ to 4.3 × 10 ⁻⁸ A cm ⁻² at an applied voltage of 2V. The performance of OFETs derived from these transport properties is shown in Table 1 below, which shows that the device having a dielectric thickness of 375 nm is the best in terms of performance.

Dielectric thickness
(nm) J at 2 V
(A cm ^-2 ) V _TH
(V) On / Off ss
(V decade ^-1 ) Mobility
(cm ² V ^-1 s ^-1 ) 510 1.5 × 10 ^-9 - - - - 375 4.3 × 10 ^-8 0.5 ± 0.1 (1-5) × 10 ² 0.7 ± 0.1 0.025-0.03 260 4.1 × 10 ^-7 0.2 ± 0.2 (0.16-1) x 10 ² 1.5 ± 0.3 0.028-0.03 120 9 × 10 ^-6 0.5 ± 0.1 3-20 - 0.01-0.019

The high performance of the OFETs is due to the much larger crystals than both the particle and channel length of the organic film, which minimizes the boundary density. The negligible threshold voltage indicates that there is almost no trap level of effective depth at the boundary between the crystal surface and the dielectric (M. Yamagishi et al, Appl. Phys. Lett. , 2009, 94, 053305-053307). Data from 15 devices show consistent performance with an average field effect mobility of 0.025 cm ² V ⁻¹ s ⁻¹ (FIG. 10). However, since the calculated mobility used the channel width as the width of the Au electrode, the actual (corrected) mobility of the devices would be higher than the calculated value. Since TCNQ crystals do not occupy the full width of the channel and empty spaces exist between adjacent crystals, the actual channel width is much smaller than the width of the electrode, resulting in higher carrier mobility.

Experimental Example 4: Investigating the Effect of Temperature on the Performance of OFET

To ensure that the OFET is operating in a low voltage situation, the transport characteristics of the device at different temperatures were measured (FIG. 11, left). OFETs did not show any noticeable difference in their properties at various temperatures except for slightly higher currents at higher temperatures due to the thermally generated carriers.

The mobility and threshold voltage ( V _TH ) of the _OFETs were extracted and their changes are shown in FIG. 11 (zip) as a function of temperature. In the measured temperature range of −30 ° C. to 80 ° C., V _TH showed some change. Nevertheless, these results confirm that the OFETs of the present invention can operate in low voltage situations at high as well as low temperatures. In addition, the calculated mobility of the device at different temperatures did not show any appreciable difference.

Experimental Example 5 Investigation of Transport Characteristics and Voltage Gain at Different Voltages of Complementary Inverters

The ability of these OFETs to operate at low voltages enables the fabrication of low voltage complementary logic devices. Using a shadow mask, a low voltage organic complementary inverter was fabricated by combining a vacuum deposited thin pentacene film as a p -channel transistor and a TCNQ crystal based OFET as an n -channel transistor (FIG. 2). Conventional gates applied an input voltage. In order to match the current levels between the p − and n − channel OFETs, the channel length L and the channel width W of the two transistors were varied. The n -channel OFET was thus L = 50 μm and W = 4000 μm, whereas the p -channel OFET was L = 250 μm and W = 200 μm. A circuit diagram of the complementary inverter is shown in FIG. 12A. Switching between logic levels of the inverter was clearly observed with little hysteresis (Figure 12a).

12A also shows the static transport characteristics of the inverter at different drive voltages V _DD . The variation range of V _OUT is equal to V _DD , which ensures a "zero" static power consumption in the digital logic circuit. When V _DD = 2 V, the low and high voltage noise tolerances are 1.0 V and 0.3 V, respectively. V _IN is a logic threshold equal to V _OUT , which is 1.3 V when a maximum gain of 4 (-dV _OUT / d V _IN ) is achieved. 12b shows the voltage gain of the inverter at different V _DD . The observed gains of 4-6 suggest that these devices can be used to switch the steps involved in more complex logic circuits. In order to enable applications that require even greater effort, higher mobility of the n -type material and optimization of the device geometry enable immediate improvement.

Claims (15)

A method of making organic crystals arranged in one direction comprising the following steps:
1) disposing a capillary tube parallel to the gate electrode on top of the dielectric layer formed on the gate electrode;
2) dropping an organic semiconductor solution on a dielectric layer including an upper portion of the capillary to form organic semiconductor droplets; And
3) evaporating the solvent from the organic semiconductor droplets to form organic crystals arranged in one direction.
The method of claim 1, wherein the capillary tube is arranged in one direction having an outer wall diameter of 0.5 to 5 mm.
The method of claim 1, wherein the material used as the gate electrode is indium tin oxide or fluorine-doped tin oxide.
The method of claim 1, wherein the material used as the dielectric layer is SiO ₂ , crosslinked poly (4-vinyl phenol), or a combination thereof.
The method of claim 1, wherein the organic semiconductor is 7,7,8,8-tetracyanoquinomimethane, 6,13-bis (triisopropylsilylethynyl) pentacene, or perylene diimide of formula Process for preparing organic crystals arranged in one direction which are derivatives:
[Formula 1]

In this formula,
R ₁ and R ₂ are H or C _1-4 alkyl group,
R ₃ is H or a C _1-18 straight or branched chain alkyl group.
The method of claim 5, wherein in Chemical Formula 1,
R ₁ and R ₂ are H,
R ₃ is H or a C _1-18 straight chain alkyl group.
The method of claim 6, wherein in Formula 1,
R ₁ and R ₂ are H,
R ₃ is H or a C _5-13 straight chain alkyl group.
According to claim 7, In Chemical Formula 1,
R ₁ and R ₂ are H,
R ₃ is H, a straight chain alkyl group of C ₅ , a straight chain alkyl group of C ₈ or a straight chain alkyl group of C ₁₃ A method for producing organic crystals arranged in one direction.
The method of claim 1, wherein the organic semiconductor is arranged in one direction used as a blend with a polymer.
The method of claim 9, wherein the polymer is poly (alpha-methylstyrene).
The organic semiconductor solution of claim 1, wherein the organic semiconductor solution is prepared by using toluene, xylene, dichlorobenzene, chloroform, tetrahydrofuran, chlorobenzene, or a combination thereof as a solvent. Way.
The method of claim 1, wherein the concentration of the organic semiconductor solution is 0.00001 to 1 mg ml ⁻¹ .
The method of claim 1, wherein the evaporation temperature is in the range of 70 to 150 ° C.
An organic electronic device comprising organic crystals arranged in one direction produced by the method of any one of claims 1 to 13.
15. The organic electronic device of claim 14, wherein the organic electronic device is a complementary inverter consisting of a low voltage field effect transistor, a low voltage field effect transistor, a photosensitive field effect organic thin film transistor, a photosensitive field effect organic thin film transistor, or a combination thereof. An organic electronic device comprising a ring oscillator or a sensor comprising the same.

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