JP2005142233A - Orientation control method of liquid crystal compound thin film, film texture of liquid crystal compound thin film formed by using the same, tft, and organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means wherein arrangement is controlled arbitrarily without being based on rubbing of an orientation film, and conductivity of the direction of film thickness and conductivity of the specific direction parallel to a film surface are increased remarkably in cylindrical liquid crystal compound. <P>SOLUTION: After oblique evaporation of the cylindrical liquid crystal compound is performed on the surface of a substrate by a PVD method and an evaporated film is formed, the evaporated film is heat-treated in temperature region of smectic phase of this compound. Moreover, oblique evaporation is performed by vacuum vapor deposition as the PVD method. Further, the heat treatment is performed within temperature range which is one half of a high temperature level of the smectic phase temperature region of the liquid crystal compound for depositing. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a film structure of a liquid crystal compound thin film used for an organic thin film transistor and an organic electroluminescence element and a method for forming the same, and in particular, an alignment control method for controlling the alignment of a liquid crystal compound by selecting a vapor deposition method and heat treatment, and forming by this method The present invention relates to a film structure of a liquid crystal compound thin film, a thin film transistor, and an organic electroluminescence element.

  Organic semiconductor elements are attracting a great deal of attention because they are capable of forming elements that are flexible and can withstand impacts, can be formed at low cost by printing methods, etc., and are expected to have functionality specific to organic matter. The research is being actively conducted. Among organic semiconductor devices, the most advanced research is on organic electroluminescence (EL) devices, but research is also progressing on organic light-emitting diodes (LEDs) and organic thin-film transistors (TFTs). Much research has been conducted on field effect transistors (FETs) that are often used as devices.

  In order to realize such an organic semiconductor element, it is important to develop an organic material having high conductivity. Many efforts have been made to develop conductive organic materials, and various materials such as low molecular weight materials and high molecular weight materials have been studied. In recent years, among liquid crystal organic compounds, those having high charge transporting properties have been found, and much research has been conducted on their application. The present inventors have also conducted various studies on liquid crystal compounds with high conductivity for a long time, and have proposed many novel polymer compounds (Patent Documents 1 and 2 below).

  The liquid crystal compound that the present inventors are paying attention to is a rod-like compound having chain-like alkyl hydrocarbon branch portions on both sides (or one side) of a long linear conjugated structure portion (hereinafter referred to as “core portion”). It is. FIG. 6 is an explanatory diagram of the charge transport mechanism of this liquid crystal compound. This compound has a feature that the core portions 4 are easily oriented so as to be stacked in parallel by the interaction of the chain hydrocarbon portions 16. The core portion forms a conjugated system by an aromatic ring or multiple bonds so that π electrons can move. Therefore, as shown in FIG. 6, the charge transportability is remarkably increased by orienting the core portion 4 in parallel. Therefore, in order to use this compound as an organic semiconductor element, the orientation control is extremely difficult. It has become important.

JP 2002-356473 A JP 2003-055337 A JP 2001-167888 A

  The liquid crystal compound as described above has a property of a semiconductor that develops conductivity when an electric field is applied, and can be used as a thin film transistor. However, the charge transportability of organic materials is much smaller than that of silicon single crystals, and in recent years, organic materials having mobility close to that of amorphous silicon have become available. In general, as the mobility increases, the responsiveness as a switching element also increases. Therefore, it is desirable to improve the charge transportability of the liquid crystal compound as described above by controlling its orientation as much as possible.

Further, as is apparent from the charge transport mechanism shown in FIG. 6, this liquid crystal compound has anisotropy in charge transport. In the case of a field effect transistor, this anisotropy is utilized. Is a challenge. FIG. 7 is an explanatory diagram of the structure of a conventional field effect transistor (n-type MOS-FET). A part of the p-type silicon substrate 17 is doped n-type to form a channel portion 10, and a source electrode 7 and a drain electrode 8 are provided at both ends thereof. A gate electrode 6 is provided on the channel portion 10 via an insulating film 9 made of SiO ₂ . In the case of an organic FET, since a thin film of a liquid crystal compound is used for the channel portion 10, it is important to improve the charge transport property in a specific direction of the thin film, that is, the direction connecting the source electrode 7 and the drain electrode 8. is there. Therefore, it is necessary to control the orientation of the liquid crystal compound so that the core portion of the liquid crystal compound is stacked perpendicular to the line connecting the source and drain electrodes.

  Conventionally, in order to control the alignment of a liquid crystal material, a method of rubbing the surface of an alignment film of a polymer material such as polyimide in a certain direction and aligning liquid crystal molecules along the rubbing direction has been frequently used. . However, due to contamination caused by rubbing generated by rubbing, problems of static electricity, and the like, various studies have been made on orientation control methods that do not use rubbing. Even when the above liquid crystal compound is used as an organic semiconductor element, particularly an organic thin film transistor, it is desired to establish means for controlling the alignment of liquid crystal molecules without rubbing.

  Therefore, the present invention has an object to provide an alignment control means that can arbitrarily control the alignment of the conjugated structure portion in a rod-like liquid crystal compound having a long linear conjugated structure portion without rubbing the alignment film. . Accordingly, it is an object of the present invention to provide a means by which the charge transporting property between the source and drain electrodes can be selectively enhanced when the charge transporting property is greatly increased and the compound is used in the channel portion of a field effect transistor. And

The alignment control method of the liquid crystal compound thin film of the present invention includes:
A rod-like liquid crystal compound having a long linear conjugated structure portion and a linear hydrocarbon portion on both sides or one side thereof is obliquely deposited on the surface of the substrate by the PVD method to form a deposited film. The heat treatment is performed in the temperature range of the smectic phase.

  The oblique deposition is a method in which the surface of the base material is inclined with respect to the direction of the vapor flow, whereby the rod-like liquid crystal compound is stacked in an inclined state with respect to the base material surface. . By heat-treating the deposited film in such a state in the temperature range of the smectic phase of this compound, rearrangement of the liquid crystal molecules occurs, and the long linear conjugated structure portion (core portion) becomes parallel to the substrate surface. Laminated. At that time, since the oblique deposition is performed, the core portions are arranged in a certain direction. That is, since the core portion is arranged on the substrate in parallel with the vapor flow during vapor deposition (and the plane including the vapor deposition point), the charge transport property in the direction perpendicular to this can be remarkably improved.

  In this orientation control method, the PVD method is preferably a vacuum deposition method. The reason is that it is considered that it is more advantageous to align the rod-shaped molecules if the deposition is performed with the kinetic energy of about the thermal speed without giving excessive energy to the deposited particles. Is preferable.

  In this orientation control method, it is preferable that the heat treatment is performed within a temperature range that is 1/2 of the high temperature side of the smectic phase temperature range of the liquid crystal compound to be deposited. More preferably, it is performed within the temperature range of 1/3 of the high temperature side of the smectic phase temperature range. This is because the fluidity becomes excessive on the higher temperature side and the alignment of the core portion may be disturbed, and on the lower temperature side, the rearrangement of liquid crystal molecules may not sufficiently proceed due to insufficient fluidity. Note that this heat treatment is preferably performed in a vacuum or an inert gas atmosphere in order to avoid alteration of the liquid crystal compound. As shown in the examples described later, it has been confirmed that the voltage-current characteristics, particularly the rising characteristics, of the liquid crystal compound thin film are remarkably different depending on the presence or absence of heat treatment.

  The film structure of the liquid crystal compound thin film of the present invention is formed using any one of the above alignment control methods, wherein the linear conjugated structure portion of the liquid crystal compound is laminated in parallel with the substrate surface, and It is characterized by being laminated so that its longitudinal direction is parallel to the direction of vapor flow during vapor deposition. By adopting such a film structure, the liquid crystal compound thin film has not only conductivity in the film thickness direction (normal direction of the base material) but also a specific direction having a film surface (surface perpendicular to the film thickness direction). That is, the conductivity in the film surface direction perpendicular to the direction of the vapor flow during deposition is significantly increased. This latter conductivity is a characteristic suitable for utilizing this thin film as a conductive channel of a field effect transistor.

  The switching element of the present invention is characterized in that a liquid crystal compound thin film having the above film structure is used as a conductive channel between a pair of electrodes.

  The thin film transistor of the present invention includes a gate, a source, and a drain electrode, an insulating film formed so as to cover the gate electrode, and a channel portion that is formed outside the insulating film and conducts between the source and drain electrodes. A thin film transistor, wherein a liquid crystal compound thin film having the above film structure is used in the channel portion. According to the present invention, the orientation can be easily controlled so that the core portion of the rod-like liquid crystal compound forming the channel portion is laminated at right angles to the line connecting the source and drain electrodes. High-speed response can be remarkably improved.

  The first of the organic electroluminescence elements of the present invention is a plurality of layers including a light-emitting layer and a charge transport layer formed between a pair of electrodes, at least one of which is made of an electroconductive liquid crystal compound. A luminescence device is characterized in that a liquid crystal compound thin film having the above film structure is used for the liquid crystal compound layer.

  The second of the organic electroluminescent elements of the present invention is an organic electroluminescent element in which an anode layer, an anode buffer layer, a liquid crystal compound layer, and, if necessary, a cathode buffer layer and a cathode layer are sequentially laminated on a substrate. A liquid crystal compound thin film having the above film structure is used for the liquid crystal compound layer. In this element, the anode layer may be formed of ITO (Indium Tin Oxide), and the anode buffer layer may be formed of PEDOT-PSS (poly (ethylenedioxythiphene) -polystylene sulphonic acid).

  The organic electroluminescence device of the present invention has extremely high charge transportability because the orientation of the liquid crystal compound thin film is sufficiently controlled. Therefore, it is possible to reduce the operating voltage and the voltage gradient inside the element. Further, since the liquid crystal compound itself has a light emitting property and the charge transport layer and the light emitting layer can be integrated, the element structure can be simplified.

  According to the present invention, it is possible to provide an alignment control means that can arbitrarily control the alignment of the conjugated structure portion in the rod-like liquid crystal compound without rubbing the alignment film. As a result, the charge transportability can be greatly enhanced, and when this compound is used in the channel portion of a field effect transistor, the charge transportability between the source and drain electrodes can be selectively enhanced. It can be said that this technology greatly contributes to the realization of an organic thin film transistor used as a switching element.

In the method for forming a liquid crystal compound thin film of the present invention, a vapor deposition film of a rod-like liquid crystal compound is formed on the surface of a substrate by an oblique vapor deposition method, and then the vapor deposition film is heat-treated in a predetermined temperature range.
First, the liquid crystal compound used in the present invention will be described. This compound has a long linear conjugated structure portion and a paraffinic hydrocarbon portion on both sides or one side thereof. Examples of such a liquid crystal compound include those represented by the following formula (wherein R1 and R2 are alkyl groups). In this compound, three benzene rings are linearly connected with an ethylene group interposed between them, and alkyl groups are present at both ends thereof.

このベンゼン環とエチレン基との部分が直線的共役構造部分（コア部分）であり、この部分を前出の図６のように配列させることにより、共役電子がホッピングして高い導電性を示す。両側のアルキル基は、隣接する分子のアルキル基との相互作用によって、コア部分の配列を促進するもので、片側のみであってもよいが、両側にあることがより好ましい。アルキル基の炭素数はとくに限定を要しないが、５〜２０個程度でよい。

The portion of the benzene ring and the ethylene group is a linear conjugated structure portion (core portion). By arranging this portion as shown in FIG. 6 above, conjugated electrons hop and show high conductivity. The alkyl groups on both sides promote the arrangement of the core portion by interaction with the alkyl groups of adjacent molecules, and may be on one side only, but more preferably on both sides. The carbon number of the alkyl group is not particularly limited, but may be about 5 to 20.

  In forming the deposited film of the liquid crystal compound on the substrate surface, oblique deposition is performed by the PVD method (physical vapor deposition method). The oblique vapor deposition is a method in which the surface of the base material is inclined with respect to the direction of the vapor flow, and is often used for the production of alignment films such as magnetic recording media and liquid crystal SiO. However, the conventional oblique deposition is a technique mainly used for granular molecules, and in the case of a rod-like liquid crystal compound as in the present invention, there is no knowledge about what kind of characteristics a deposited film can be obtained. rare.

  The inventors of the present invention, when depositing a rod-like liquid crystal compound, moves so that its longitudinal direction is approximately parallel to the direction of the vapor flow. When this is obliquely deposited, the deposited film in which the rod-like compounds are regularly arranged It was found that can be obtained. The present invention is characterized by combining this technique and the subsequent heat treatment to control the alignment of the liquid crystal compound thin film, to remarkably increase its conductivity, and to form an alignment state suitable for a field effect transistor. Is.

  FIG. 1 is an explanatory diagram showing the principle of alignment control of a liquid crystal compound in the method of the present invention. FIG. 1 (a) is a schematic diagram showing a state in which liquid crystal molecules move in space, and FIGS. 1 (b) and 1 (c). Is a schematic diagram showing the arrangement of liquid crystal molecules in the deposited film, and is a view seen from the B direction and the A direction in FIG. 1A, respectively, and FIGS. It is the schematic diagram which shows these, and is the figure seen from the B direction and A direction of Fig.1 (a), respectively.

  The rod-shaped liquid crystal compound moves so that its long axis is generally coincident with the direction of the vapor flow so that the resistance is reduced in the vapor flow (since some gas molecules remain even in vacuum, It is thought that you will do a lot of exercise). Therefore, in oblique vapor deposition, as shown in FIG. 1B, the liquid crystal molecules are aligned and attached to the substrate so that the longitudinal direction of the liquid crystal molecules is substantially parallel to the direction of vapor flow. As shown in FIG. 1 (c) (side view as viewed from the direction A), the rod-like molecules may be attached to the substrate surface with a certain degree of inclination, and the inclination angle is not necessarily constant. Also good. The substrate temperature during vapor deposition is close to room temperature. In this state, the liquid crystal compound is in a solid phase, and the liquid crystal molecules on the substrate are attached with a certain amount of voids, so the density of the deposited film is small. .

  Next, the deposited film is heat-treated in the temperature range of the smectic state of the liquid crystal compound. As a result, rearrangement of the liquid crystal molecules occurs, and as shown in FIG. 1E, the core portions of the liquid crystal molecules adhering in an inclined manner are stacked in parallel on the substrate surface. At this time, since the core portions are arranged in parallel to the direction of the vapor flow, this parallel state is maintained as it is (FIG. 1 (d). Thereby, along with the film thickness direction (normal direction of the base material) The conductivity in the direction perpendicular to the axis of the aligned core portions (in the direction of arrow C in FIG. 1 (d)) is significantly increased.

  In the heat treatment in the temperature range of the smectic phase, it is considered that the main driving force for moving the molecule is due to the interaction between the alkyl groups on both sides of the core portion, that is, the intermolecular attractive force between the alkyl groups of adjacent molecules. As a result, the rod-like molecules are arranged in parallel, and the core portions are stacked so as to be stacked at regular intervals. If the length of the core part is constant, it is considered that the layers are laminated so that both ends thereof are almost aligned. This makes it very easy for the conjugate electrons to move between the cores, and the conductivity in the direction perpendicular to the laminated surface. Increases significantly.

  As shown in the above-mentioned Patent Document 3, it is known that when a liquid crystal compound is generally heat-treated up to the temperature of the liquid crystal region, the π-electron resonance structure surface is aligned in parallel with the electrode surface. However, when the rod-like liquid crystal compound is randomly deposited on the surface of the base material and then heat-treated, even if the core portions are stacked in parallel with the base material surface, the direction becomes random, as shown in FIG. 1 (d). The parts do not line up in a certain direction. Therefore, even if the conductivity in the film thickness direction increases, the conductivity in the direction parallel to the film surface does not increase. By forming the deposited film by oblique deposition, as shown in FIG. 1B, the rod-like liquid crystal compound is deposited in a substantially uniform direction. It is a feature of the present invention that the conductivity in a specific direction parallel to the film surface (the direction of arrow C in FIG. 1D) is increased.

  In the present invention, the base material for forming the vapor deposition film of the liquid crystal compound may be an organic material such as a polymer thin film, or an inorganic material such as a glass or silicon substrate or a metal electrode film formed thereon. There may be. As the vapor deposition method, it is considered that PVD methods such as vacuum vapor deposition, molecular beam epitaxy (MBE), ion plating, and sputter vapor deposition can be widely applied. However, according to the knowledge of the present inventors, if the vapor deposition is performed at a kinetic energy of about the thermal speed without giving excessive energy to the vapor deposition particles, the speed of moving through the space becomes slower, and the length of the rod-like molecule is reduced. It is considered that the direction is easily aligned in parallel with the vapor flow, and from this viewpoint, the vacuum deposition method is particularly suitable.

  The tilt angle in oblique deposition (angle between the normal of the substrate and the vapor flow) does not necessarily need to be strictly limited, but if this is too small, rod-shaped molecules are arranged at an angle close to a right angle to the substrate. It becomes difficult to lay this in a certain direction by heat treatment. Further, if the inclination angle is too large, uneven deposition tends to occur, which is not preferable. Therefore, it seems that the inclination angle is suitably in the range of about 10 to 70 degrees.

  In the method of the present invention, the temperature of the heat treatment is also important. When the temperature is raised to the temperature of the isotropic liquid, it goes without saying that the arrangement during oblique deposition is lost and inappropriate, but according to the knowledge of the present inventors, the fluidity is excessive even at the temperature of the nematic phase. It is not preferable. However, on the low temperature side of the temperature range of the smectic phase, there may be a case where the liquid crystal is insufficient and is not properly oriented. Therefore, the heat treatment temperature is preferably a temperature range that is a half on the high temperature side of the smectic phase temperature range of the liquid crystal compound of interest. More preferably, the temperature range is 1/3 on the high temperature side. The heat treatment time is not particularly limited, but it may be maintained for several minutes to several tens of minutes in the above temperature range.

  Next, the thin film transistor of the present invention will be described. FIG. 2 is a schematic cross-sectional view of a thin film transistor which is an embodiment of the present invention. This thin film transistor is a field effect transistor in which a source electrode 7 and a drain electrode 8 are formed on a substrate 5 with a gate electrode 6 interposed therebetween, and an insulating film 9 is formed so as to cover the gate 6. A channel portion 10 for conducting the source 7 and the drain 8 is formed outside the channel 9. The channel portion 10 is characterized in that a liquid crystal compound thin film whose orientation is controlled by the above-described method is used.

  In order to manufacture this thin film transistor, first, a gate electrode 6 is formed on a substrate 5 by a metal vapor deposition method or the like, and an insulating film 9 made of a polymer material or the like is formed thereon by a vapor deposition method or a spin coating method. . Furthermore, a source electrode 7 and a drain electrode 8 facing each other with the gate electrode 6 interposed therebetween are formed by a metal vapor deposition method or the like. Thereafter, the rod-like liquid crystal compound which is the object of the present invention is obliquely vapor-deposited on this substrate by vacuum vapor deposition. At this time, the substrate 5 is set so that the line connecting the source electrode 7 and the drain electrode 8 is substantially perpendicular to the direction of vapor flow (the line connecting the evaporation source and the vapor deposition point). When a vapor-deposited film having a predetermined film thickness is obtained, a heat treatment may be performed by holding it at a predetermined temperature in a vacuum or an inert gas atmosphere. As a result, the core portion of the rod-like liquid crystal compound is laminated at right angles to the line connecting the source and the drain, and the charge transport property in this direction is remarkably increased.

  Next, the organic electroluminescence (EL) element of the present invention will be described. FIG. 3 is a schematic cross-sectional view of an organic EL element which is an embodiment of the present invention. In this element, an anode 12, a buffer layer 13, a liquid crystal compound thin film 14, and a cathode 15 are sequentially laminated on a transparent substrate 11. The anode 12 is made of a transparent material having a high work function, for example, an ITO film, for extracting light. The cathode 15 is formed of a thin film of a metal having a low work function, such as Al, Ca, FLi (lithium fluoride), Mg, or an alloy thereof.

  Since the liquid crystal compound of this example has a light emitting property per se, the liquid crystal compound thin film 14 is a light emitting layer and has a function of a carrier transport layer. The buffer layer 13 is intended to lower the energy barrier for hole injection from the anode 12 and uses, for example, PEDOT-PSS (poly (ethylenedioxythiphene) -polystylene sulphonic acid). The buffer layer 13 may not be required, and a buffer layer for the purpose of electron injection may be provided on the cathode 15 side as necessary.

  The organic EL element of the present invention is characterized by the film structure / formation method of the liquid crystal compound thin film 14, and the other layers may be formed by a method similar to the conventional method. After the formation of the anode 12 and the buffer layer 13 on the transparent substrate 11, the rod-like liquid crystal compound that is the subject of the present invention is obliquely deposited by vacuum deposition. In this case, it is not necessary to specify the direction in which the substrate is set. When a vapor deposition film having a predetermined film thickness is obtained, heat treatment is performed to keep the vapor deposition film at a predetermined temperature in a vacuum or an inert gas atmosphere, and the cathode 15 may be formed thereon by vapor deposition or the like.

  In the case of the organic EL element of the present invention, unlike the case of the thin film transistor, it is not necessary to increase the conductivity in a specific direction perpendicular to the film thickness of the liquid crystal compound thin film 14. However, according to the knowledge of the present inventors, in the case where the deposited film is oblique deposition and non-oblique deposition (vertical deposition), the former has higher charge transportability after the heat treatment. The significance of applying the orientation control method to an organic EL element is sufficiently great. In the organic EL device of the present invention, the liquid crystal compound thin film 14 may be divided into two layers of a light emitting layer and a charge transport layer. In that case, both or one of these layers is formed by the alignment control method of the present invention. Any liquid crystal compound thin film may be used.

  A PEDOT-PSS thin film was formed on a transparent substrate, a liquid crystal compound thin film whose orientation was controlled by the method of the present invention was further formed thereon, and the polarization characteristics and voltage-current characteristics of the liquid crystal thin film were investigated. A glass substrate having a size of 4 × 4 mm was cleaned by ultrasonic cleaning liquid (cleaning liquid: isopropanol + acetone) and UV cleaning, and then a PEDOT-PSS thin film was formed by spin coating. The film forming conditions were a rotation speed of 2000 rpm and a film forming time of 30 sec. After the film formation, the PEDOT-PSS thin film was cured by heat treatment at 150 ° C. for 30 minutes.

A liquid crystal compound thin film was formed on the PEDOT-PSS thin film by the method of the present invention. In the liquid crystal compound used, the alkyl groups R ₁ and R _{2 of the} compound represented by Chemical Formula ₁ are both represented by C ₁₂ H ₂₅ . 30 mg of this compound was obliquely deposited by resistance heating vacuum deposition on a room temperature substrate inclined at 45 ° with respect to the direction of vapor flow. Thereafter, the substrate was heated to 200 ° C. in a nitrogen atmosphere, and heat treatment was performed for 2 minutes. In addition, the temperature range of the smectic phase of this compound is approximately 100 to 250 ° C.

  FIG. 4 shows an example of the result of observing the orientation of the liquid crystal compound thin film thus formed with a polarizing microscope. FIG. 4A shows a case where the direction of the polarizer of the polarization microscope and the alignment direction of the core portion of the liquid crystal compound (direction perpendicular to the arrow C in FIG. 1D) coincide with each other and the field of view is considerably dark. It has become. The reason for not being a complete dark field is thought to be that there is a slight disturbance in the alignment of the liquid crystal compound. On the other hand, FIG. 4B is an observation image when the sample is rotated by 45 ° and has a sufficiently bright field of view. From this, it can be seen that the liquid crystal compound thin film produced as described above is in an alignment state as shown in FIG.

  Moreover, the electroconductivity of the liquid crystal compound thin film (+ PEDOT-PSS thin film) produced as mentioned above was evaluated. An element composed of a base material-ITO electrode film-PEDOT-PSS thin film-liquid crystal compound thin film-metal cathode was prepared, and voltage-current characteristics between both electrodes were measured. The conditions for forming the PEDOT-PSS thin film and the liquid crystal compound thin film are the same as described above. The ITO electrode film and the metal cathode were formed by vacuum deposition. As a comparative example, a sample in which the liquid crystal compound thin film was not heat-treated was prepared, and the conductivity was compared with that of the heat-treated sample. An example of the measurement result is shown in FIG.

In the figure, the heat-treated material (circles) shows a sudden rise from the vicinity of the applied voltage of 4 V, and the current increases rapidly. On the other hand, in the comparative example without the heat treatment (marked with ●), the rise of the current is unclear and the increase in the current is extremely small. From this, it was clarified that the conductivity in the film thickness direction of the liquid crystal compound thin film is remarkably increased by the heat treatment at 200 ° C. It can be said that the rapid rise characteristic like this heat treatment material is suitable for use as a switching element.

It is explanatory drawing which shows the principle of the orientation control of the liquid crystal compound in the method of this invention. It is a cross-sectional schematic diagram of the thin-film transistor which is an Example of this invention. It is a cross-sectional schematic diagram of the organic electroluminescent element which is an Example of this invention. It is an example of the polarization micrograph of the liquid crystal compound thin film in a present Example. It is a figure which shows the example of the measurement result of the voltage-current characteristic in a present Example. It is explanatory drawing of the charge transport mechanism of the liquid crystal compound used for this invention. It is explanatory drawing which shows the structure of the conventional field effect transistor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rod-like liquid crystal compound 2 Vapor flow 3 Base material 4 Core part 5 Substrate 6 Gate electrode 7 Source electrode 8 Drain electrode 9 Insulating film 10 Channel part 11 Transparent substrate 12 Anode 13 Buffer layer 14 Liquid crystal compound thin film 15 Cathode 16 Chain hydrocarbon part 17 p-type silicon substrate

Claims (9)

  A rod-like liquid crystal compound having a long linear conjugated structure portion on a substrate surface is obliquely deposited by PVD method to form a deposited film, and then the deposited film is heat-treated in the temperature range of the smectic phase of the compound. For controlling the orientation of a liquid crystal compound thin film.   The orientation control method according to claim 1, wherein the PVD method is a vacuum deposition method.   3. The alignment control method according to claim 1, wherein the heat treatment is performed within a temperature range that is 1/2 of the high temperature side of the smectic phase temperature range of the liquid crystal compound to be deposited.   A film structure of a liquid crystal compound thin film formed by the alignment control method according to any one of claims 1 to 3, wherein a linear conjugated structure portion of the liquid crystal compound is laminated in parallel with a substrate surface, and the length thereof A film structure characterized by being laminated so that the direction is parallel to the direction of vapor flow during vapor deposition.   A switching element comprising a liquid crystal compound thin film having a film structure according to claim 4 as a conductive channel between a pair of electrodes.   A thin film transistor having three electrodes of a gate, a source and a drain, an insulating film formed so as to cover the gate electrode, and a channel portion formed outside the insulating film and conducting between the source and drain electrodes, 5. A thin film transistor comprising a liquid crystal compound thin film having a film structure according to claim 4 in a channel portion.   A plurality of layers including a light emitting layer and a charge transport layer are formed between a pair of electrodes, at least one of which is an organic electroluminescent element made of a conductive liquid crystal compound, and the liquid crystal compound layer is charged. Item 5. An organic electroluminescence device, wherein a liquid crystal compound thin film having the film structure of Item 4 is used.   An organic electroluminescence device comprising an anode layer, an anode buffer layer, a liquid crystal compound layer, and optionally a cathode buffer layer and a cathode layer laminated on a substrate, wherein the film structure according to claim 4 is provided on the liquid crystal compound layer. A liquid crystal compound thin film having an organic electroluminescence device is used. 9. The organic electroluminescence device according to claim 8, wherein the anode layer is made of ITO, and the anode buffer layer is made of PEDOT-PSS.

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