JPS62222669A - Organic thin-film element - Google Patents

Abstract

PURPOSE:To improve the efficiency of charge transfer by using an organic conductor as an electrode applying voltage to an organic thin-film in an organic thin-film element in which the organic thin-film is employed and charge transfer among donor molecules and acceptor molecules by applying voltage is used. CONSTITUTION:A first organic thin-film (a donor molecular film) 3 containing donor molecules and a second organic thin-film (an acceptor molecular film) 4 containing acceptor molecules are laminated on an Al electrode 1 in succession through an insulating organic thin-film 2, and an organic conductor electrode 6 is shaped onto the organic thin-film 4 through an insulating organic thin-film 5. Accordingly, charges transfer among donor molecules and acceptor molecules by applying voltage to the organic thin-films, thus controlling the absorptivity, conductivity characteristics, etc. of the organic thin-films.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an element using an organic thin film, and particularly relates to improvement of an electrode portion thereof.

(Prior Art) In recent years, with the progress of ultra-thin film formation technology of organic molecules represented by the Langmuir Project method (hereinafter referred to as L, B method), the development of applied technology to organic thin film elements has become active. Loparts of Durham University (
G, G, Roberts) 1, lf machine using thin film gold 7?
-This type of research is being conducted in various places, with research on MIS devices being a representative example. However, at present, the properties of organic thin films5ij
A device with a new function that makes effective use of this has not yet been realized.

From the perspective of device applications, the phenomenon of charge transfer between five molecules is particularly noteworthy among the properties of organic materials6. Organic materials have donor molecules that have a small ionization potential and easily become a positive ion state by supplying electrons to other molecules, and donor molecules that have a high electron affinity and receive electrons from other molecules and turn themselves into a negative ion state. There are some acceptor molecules that are easy to become.

It is well known that a compound collectively called a charge transfer complex is formed between these two types of molecules. For example, the compound between irelin and tetracyanoquinodimethane (TCNQ) is a compound consisting of neutral molecules that do not transfer charge, but tetramethylphenylenediamine (4Mpn)
TCNQ becomes an ionic compound with positive and negative molecules, respectively. ti, tetrathiafulvalene (TTF
) (!: It is also known that, as in the case of chloranil, the transition from neutrality to ionicity can be observed depending on temperature and pressure.

When applying this phenomenon of charge transfer in organic materials to device operation, the efficiency of charge transfer.

It is required that the characteristics of charge transfer itself, such as response speed and controllability, be excellent, and that materials and elements that cause charge transfer can be easily formed. Charge transfer complex crystals have problems such as extremely difficult crystal preparation and difficulty in externally controlling charge transfer. In addition, attempts have been made to control charge transfer between metals and organic molecular films using sources or electric fields and use them in switching elements or memory devices, but the efficiency of charge transfer, response speed, lifespan, etc. has a big problem. Although the phenomenon of charge transfer is expected to have potential for device applications, it has not yet been put to practical use.

Further, as a problem specific to organic thin film elements, there is the problem of 1JL pole formation. Organic thin films have a lower density than inorganic thin films, so when metal electrodes are formed using normal vapor deposition methods, metal vapor easily enters the organic thin film, often forming metal particles and metal filaments in the organic thin film. Ru. As a result, when a voltage is applied to the organic thin film, the electric field within the film becomes non-uniform, resulting in a decrease in the efficiency of charge transfer within the organic thin film. The IJ current increases, causing deterioration of the characteristics of the element.

(Problems to be Solved by the Invention) As described above, although organic thin films are expected to be applied to devices with new functions, such devices have not yet been realized. There are also problems with the electrode formation method.

The present invention was made in view of the above points, and uses the charge transfer phenomenon of organic thin films as an operating principle to improve the efficiency of charge transfer, and suppresses leakage current of organic thin films to improve characteristics and reliability. The purpose is to provide an organic thin film device.

[Structure of the invention]

(Means for Solving the Problems) The organic thin film element according to the present invention is an element that utilizes a charge transfer phenomenon between organic molecules of an organic thin film containing donor molecules and acceptor molecules. Specifically, changes in absorbance, conductivity characteristics, dielectric constant, potential distribution within the film, etc. when a voltage is applied to an organic thin film are utilized. In such an element, the present invention is characterized in that at least a part of the electrode for applying a voltage to the organic thin film is made of an organic conductor.

Here, the organic thin film may have a laminated structure of a first organic thin film containing donor molecules and a second organic thin film containing acceptor molecules, or may be a mixed thin film containing both donor molecules and acceptor molecules. . Further, in the present invention, preferably, a monomolecular film formed by the LB method or an ultra-thin film obtained by stacking a plurality of layers thereof is used as the organic thin film. The speed of electrons or holes moving in organic materials is generally slower than that in inorganic semiconductors, but by using ultra-thin films of several to several tens of times, it is possible to transfer charges at a sufficiently high speed. c It is actually possible to form such a film using the LB method.

Further, as the organic conductive film serving as the electrode, for example, a vapor-deposited film of a charge transfer complex or a film formed by the LB method is used.

(Function) According to the configuration of the present invention, by applying a voltage to the organic thin film, charge transfer occurs between the sider molecules and the acceptor molecules, thereby controlling the absorbance, conductivity characteristics, etc. of the organic thin film. Ru. At this time, since an organic conductor is used for at least a portion of the electrode, metal fine particles or metal filaments are not formed within the organic thin film, and a uniform electric field is applied to the organic thin film, allowing donor molecules to interact with each other. The probability (efficiency) of charge transfer between acceptor molecules becomes high. For the same reason, the leakage current of organic thin films is small, and therefore highly reliable device characteristics can be obtained.

(Example) Embodiments of the present invention will be described below with reference to all the drawings.

FIG. 1 shows an organic, thin film device according to one embodiment. In the figure, 1 is Ati[, and a first organic thin film (donor molecular film) containing donor molecules is formed thereon via an insulating organic thin film 2. A second organic thin film (acceptor molecule film) 4 containing acceptor molecules is sequentially laminated, and an organic conductor electrode 6 is further formed on this with an insulating organic thin film 5 interposed therebetween. The organic conductor electrode 6 is a deposited film of a charge transfer complex in this embodiment.

A specific example of the fabrication process for this element is as follows. Poly L-7 enylalanine el: LB membrane development m solution was prepared by dissolving in a dichloroacetic acid-chloroform bath solution having a volume ratio of 5 (7) to a concentration of about 11n9/-. It was known from the surface pressure-molecule occupied area curve that this film-forming molecule forms a condensed film at a surface pressure of 13 dyne/cm or more. L
A commercially available vertical pulling type device was used for film formation B.

Aqueous phase prior to accumulation? The pH was set to -6.0, about 0.05 mM of divalent cadmium salt was added as a coexisting salt, and the water was maintained at 20°C. A glass substrate on which an At film, which will become At'ill pole 1, is formed is placed in this aqueous phase, and the above-mentioned film-forming molecule t-
600 μJ) was developed using the Ranit method, and the surface pressure was increased to 20 μJ.
The monolayer was stabilized by setting dyne/cm.

Then, this substrate was pulled up at a pulling speed of 70 μm/min to accumulate a monomolecular LB film. The cumulative number of layers was 10. This is the insulating organic thin film 2.

As the donor molecular film 3, a single layer of a 1:1 mixture of para-phenylene diamine and poly-L-phenylalanine was formed in the same manner as above. As the acceptor molecular film 4, a single layer of a mixture of tetracyanoquinodimethane and poly-L-phenylalanine in a ratio of 1:1 may be formed in the same manner. The above accumulation of the donor molecular film and the acceptor molecular film was repeated 10 times, and an insulating organic thin film 5 similar to the above insulating organic thin film 2 was formed thereon.

As the organic conductor electrode 6 on the top of the nine LB film superlattice formed in this way, a charge transfer complex of tetrathiafurparene (TTF), which is a donor molecule, and tetracyanoquinodimethane (TCNQ), which is an acceptor molecule, is used. TTF-
After forming TCNQ to a thickness of 2000× by vacuum evaporation, an Au film of 1000× was deposited on its surface.

FIG. 2 shows the results of measuring the current-voltage characteristics of the LB film when a voltage such that the organic conductor electrode 6 side is positive and the kA electrode 1 side is negative is applied to the device configured as described above. The figure is shown as a comparative example.

The characteristics of an element in which an Au electrode is directly formed in the organic conductor electrode 6 portion of FIG. 1 without using an organic conductor are also shown.

As is clear from the figure, in the element of this example, a large current change is observed at a predetermined ground pressure value.

This is a result of less leakage of the organic thin film than in the comparative example and efficient control of charge transfer between donor molecules and acceptor molecules.

FIG. 3 shows an organic thin film device of another example.

The difference from the embodiment shown in FIG.
This is achieved by using the aAs substrate 2 as an electrode. Ga
The As substrate 1 was a 9n type substrate doped with St at I x 1016/cm''.

In this MxsW element, a rapid change in capacitance was observed at a reverse bias of about 2 V, and it was confirmed that the surface of the GaAs substrate 7 was inverted.

In FIG. 4, a mixed thin film 34 containing both donor molecules and acceptor molecules is used in the laminated portion of the donor molecule membrane 3 and acceptor molecule membrane 4 in the configuration shown in FIG. Even in an element having such a configuration, characteristics similar to those of the element shown in FIG. 1 can be obtained by using the organic conductor electrode 6 as the upper electrode.

In the above embodiments, a similar effect can be obtained by using a vapor-deposited film of a charge transfer complex as an organic conductor electrode and using an LB film as an electrode. Further, in the above embodiments, an organic conductor was used for one of the electrodes sandwiching the organic thin film, but an organic conductor may be used for both electrodes.

In the present invention, the donor molecules used in the donor molecular film and the organic conductor electrode include the following.

(1) Fullvalene type donor with the following structure (2) S-containing heterocyclic fox donor with the following structural formula ≧ −S Here, φ represents a phenyl group.

(3) Amine type donor H with the following structural formula
3CH3 H2 (4) A metal compound type donor having the structural formula as shown below. N-containing heterocyclic donor with the structural formula (7) Donor polymer with the following structural formula... Noah N〆ゝ9'\... Polyacetylene (1)
The donor molecule shown in (7) can be used as its structural formula or as a skeleton.

CH3(-CH2+n, CH,+cH2YCH2-C
Derivatives with a hydrophobic group consisting of H2YCH23H (n and p + q + 1 are 8 or more), or -〇〇OH, -OH.

-8o3H, -COOR', -NH3,-&(R'
), Y- (where Y is an abbreviation), or a derivative having both a hydrophobic group and a hydrophilic group.

As the acceptor molecule, the following molecules can be used.

(8) Acceptor NL for a cyanide compound having the following structural formula: (9) To a quinone group accessor having the following structural formula Q Nitro compound substituted acceptor (8) having the following structural formula (The acceptor molecule shown in 11 can be used as its structural formula or as a skeleton.

CH, (0M2 leakage, Ckl, +CH25CH2-CM
2QCH2-)z (n and p + q + L are 8
Derivatives with hydrophobic groups consisting of the above) or -
〇〇〇H, -OH, -8o, H.

It may be a derivative having a hydrophilic group consisting of -coon', -NH2, -$(R'), y- (y is /%C!)f7), or a derivative having both of these hydrophobic and hydrophilic groups.

In the donor molecular film or acceptor molecular film in the present invention, the insulating molecules used in the mixture with the donor molecules and acceptor molecules, the insulating molecules used in the film or the insulating molecular film, are as follows. Such molecules are used.

αBu Substitutable saturated and unsaturated hydrocarbon derivatives represented by the following general formula -X Here, R is substitutable CH3(CH2)n- or CHs(-CH2,000)12=CH2early CH2)2
(However, n and p + q + 1 are 8 or more).

Examples include.

(6) Various polymerizable molecules, such as substitutable acrylates, methacrylates, t
'Vinyl polymers such as vinyl ether, styrene, vinyl alcohol, acrylamide, and acrylic. Alternatively, α- such as alanine, glutamate, asnoglutate, etc.
amino acids, amino acids other than α-amino acids such as ε-aminocaproic acid. Cyamine such as hexamethylene diamine,
A polyamide polymer consisting of a 1:1 mixture of socaldic acid such as hexamethylene dicarboxylic acid.

These molecules can be used alone if they themselves can be accumulated. C11) Molecules that cannot be used alone to form a film are mixed with insulating molecules that can be formed into a film independently, such as those shown in ~.

〔Effect of the invention〕

As described above, according to the present invention, an organic thin film element that uses an organic thin film containing donor molecules and acceptor molecules and utilizes charge transfer between the donor molecules and the acceptor molecules upon application of a voltage. By using an organic conductor as an electrode to which a voltage is applied, the efficiency of charge transfer due to voltage application can be completely improved, and reliability can be improved by reducing current.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an organic thin film device according to an embodiment of the present invention, FIG. 2 is a diagram showing its characteristics together with a comparative example, and FIGS.
The figure shows an organic thin film element of another example. 1... A/, - pole, 2... Insulating organic thin film, 3...
・Donor molecular film, 4... Acceptor molecular film, 5.
...Insulating organic thin film, 6...Organic conductor electrode, 7...
- GaAa substrate, 34...mixed thin film.

Claims (6)

[Claims] (1) An organic thin film element having an organic thin film containing donor molecules and acceptor molecules, characterized in that at least a part of an electrode for applying a voltage to the organic thin film is made of an organic conductor. (2) The organic thin film element according to claim 1, wherein the organic thin film has a laminated structure of a first organic thin film containing donor molecules and a second organic thin film containing acceptor molecules. (3) The organic thin film element according to claim 1, wherein the organic thin film is a mixed thin film containing both donor molecules and acceptor molecules. (4) The organic thin film element according to claim 1, wherein the organic thin film is a film formed by the Langmuir-Prodgett method. (5) The organic thin film device according to claim 1, wherein the electrode made of the organic conductor is a vapor deposited film of a charge transfer complex. (6) The organic thin film device according to claim 1, wherein the electrode made of the organic conductor is a thin film formed by the Langmuir-Prodgett method.