JPH0383291A - Switching memory composite function element - Google Patents

Abstract

PURPOSE:To obtain a highly economical composite function element with simple material constitution by impressing a voltage more than a threshold on a necessary thin film and changing a resistance state for prescribed time. CONSTITUTION:When the voltage is impressed on an organic thin film 4 such as lead phthalocyanine through upper and lower electrodes 2 and 3 and the voltage is set to be more than the threshold, the thin film 4 changes from a high resistance state to a low resistance state, and a switching function is realized by a state change. The changed state continues for prescribed time, and a memory function is realized. Then, the film 4 is restored to the original state by the impression of a reverse voltage and the highly economical switching memory composite function element can be obtained with simple material constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention is particularly applicable to devices that can perform switching and memory using optical signals, such as memory devices, switching devices, visual pseudo devices, electrophotographic photoreceptors, etc. The present invention relates to a switching/memory multifunctional device that can be used in the industrial field.

Conventional technology Elements that have a switching function using optical signals include:
Phototransistors are well known, but they do not have a memory function.

Recently, an optical switching element has been proposed in which a conductive layer (or semiconductor layer) is sandwiched between insulating organic thin film layers and provided between a pair of electrodes (Japanese Patent Application Laid-Open No. 1983-1999-1).
160385). However, this element also does not have a memory function, has a complicated structure, is expensive to manufacture, is difficult to manufacture, and is impractical.

On the other hand, organic photoreceptors such as polyvinylcarbazole/trinitrofluorenone and phthalocyanine are conventionally known as electrophotographic photoreceptors.

These photoreceptors take advantage of the fact that the area exposed to light is in a low resistance state only during light irradiation (image projection). However, if the light irradiation is stopped, the low resistance state is canceled, so the latent image is not stored in memory. By projecting the image once, it becomes possible to copy the image over and over again. Recently, a method has been proposed for the above-mentioned electrophotographic photoreceptor that combines the memory function of Cu/T CN Q to memorize the latent image so that multiple copies can be made with one image projection. (
Journal of the Electrophotography Society, Vol. 24, p. 86, 1986).

Problems to be Solved by the Invention However, the proposed electrophotographic photoreceptor
It has a complicated structure, is difficult to manufacture, and is expensive, making it impractical.

In view of the above circumstances, the present invention has both switching and memory functions using optical signals, has a simple material composition, has a simple structure, is easy to manufacture, and has a low manufacturing cost. The object of the present invention is to provide a switching memory multifunctional device.

Means for Solving the Problems In order to solve the above problems, a switching/memory composite element according to claim 1 is provided, in which a thin film having a switching function and a memo 11 function is sandwiched between a pair of opposing electrodes, is exerted by the thin film changing from a high resistance state to a low resistance state when a voltage equal to or higher than the threshold voltage is applied to the electrode, and the threshold voltage is lower in the light irradiation state than in the non-light irradiation state. In addition, the memory function is exerted when the thin film maintains a low resistance state for at least a certain period of time, and is released by returning the low resistance state to a high resistance state by applying a reverse voltage. It looks like this.

A thin film having such characteristics is, for example, an organic thin film, specifically, as in the invention of claim 2, a thin film made of lead phthalocyanine, which has a crystal structure particularly containing a large amount of monoclinic system, and It is suitable that the C-axis is oriented parallel to the electrode surface.

The organic thin film described above basically has photoconductivity, has crystal axes aligned (orientated) in a specific direction, and has anisotropy in electrical conduction. The thin film is formed on the surface of the electrode (which may also serve as the substrate), with the highly conductive crystal axes oriented primarily parallel to the electrode surface. Of course, the voltage (electric field) will be applied in a direction perpendicular to the highly conductive crystal axis.

Operation In this invention, although the mechanism is not fully detailed, it is possible to perform switching and memorize the switch state using an optical signal, and it is also possible to release the memory state.

EXAMPLES Below, examples of the present invention will be described in detail with regard to switching functions and memory functions, taking the case of a lead phthalocyanine thin film as an example.

In the state without light irradiation (dark state), as shown by the solid line in FIG. 1, when the applied voltage is V and the threshold voltage vth, the thin film maintains a high resistance R,1 state, but when the applied voltage ≧threshold voltage vth When , the thin film changes from the high resistance R state to the low resistance R3 state. In other words, the switching function is demonstrated. -And when it changes to the low resistance R13 state,
This state continues for at least a certain period of time. In other words, the memory function is demonstrated. However, as shown in FIG. 1, by applying a reverse voltage, the low resistance R3 state can be forcibly returned to the original high resistance R3 state. The memory state is released.

In the light irradiation state, the value of the threshold voltage at which the thin film changes from the high resistance state to the low resistance state is lower than in the non-light irradiation state. As shown by the broken line in FIG.
th', the thin film is in a high resistance R2 state. However, the resistance value of this high-resistance R2 state is lower than the previous high-resistance R state. This is because carriers are generated along with light irradiation. Then, in the light irradiation state,
Applied voltage V≧threshold voltage V 1. When h' is reached, the thin film (the region hit by the light) changes from the high resistance R2 state to the low resistance hole 4 state. - Once the resistance changes to the low resistance R4 state, this state continues for a certain period of time. However, as shown in FIG. 1, the low resistance R4 state can be forcibly returned to the high resistance state by applying a reverse voltage. Of course, here,
Threshold voltage V ih' is a voltage lower than threshold voltage Vth.

As can be seen from the above, the switching of this invention
In a memory element, a pair of electrodes has a voltage of at least v th' to vth
If a voltage lower than that is applied and an optical signal is applied, a change from a high-resistance state to a low-resistance state occurs and at the same time this change is sustained, that is, an optical switch function and a memory function are exhibited.

Note that the resistance value in the low resistance R4 state is the same or lower than that in the low resistance R3 state.

Thin films with such characteristics can be found, for example, in thin films formed from metal complexes, charge transfer complexes, etc. that have low-dimensional conductive anisotropy, but it goes without saying that they are not limited to these. . More specifically, the organic substance is formed of a metal complex of a polymer compound such as a metal complex of phthalocyanine or a metal complex of porphyrin, or a combination of various donors and acceptors, but is not limited thereto.

The thin film thickness is about 0.01 to 10 μm, preferably 0.01 to 10 μm.
The range is approximately 1 to 6 μm, but is not limited thereto.

The organic thin film in this invention can be made by a conventional thin film method such as vacuum evaporation or sputtering.
Film formation is controlled so that the crystals are oriented so that the low-dimensional (preferably one-dimensional) conductive direction is parallel to the electrode direction.

For example, as shown in FIG. 3, the switching memory multifunctional device of the present invention is arranged on a substrate 4 such that the upper electrode 2 is on the front side of the organic thin film 1 and the lower electrode 3 is on the back side. There is. 8.9 is a lead wire.

The substrate 4 is made of glass, ceramics, plastic, metal, or the like. Of course, it is not limited to these.

Electrode 2.3 is made of Au, iAg, C'u, Cr5Pts
Ni.

It is made of a single substance such as Pb, Zn, Sn, or a transparent conductor such as I'rO or a semiconductor, or an alloy or a laminated structure in which a plurality of them are used together. Of course, it is not limited to these. Further, the electrodes 2.3 may be formed of the same material or may be formed of different materials. Note that in order to irradiate the thin film with an optical signal, for example, at least one of the electrodes 2 and 3 is made of a transparent conductive material and has a voltage, or is made of a thin electrode that is effectively transparent.

In this invention, although the mechanism of changing from a high resistance state to a low resistance state as described above is not sufficiently detailed, for example,
We speculate that the mechanism is as follows. Of course, the present invention is not limited in any way by this explanation of the mechanism.

As shown in FIG. 2(a), the low-dimensional conductive organic thin film 1 has highly conductive columns 7 parallel to the surface of the substrate 4. For example, if A is an acceptor and B is a donor, these columns are Although this is an alternately laminated charge transfer complex, A may be a metal complex and B may be an axial ligand, or both A and B may be metal complexes. Of course, the direction perpendicular to column 7 is sufficiently electrically insulated (high resistance). Note that electrodes (not shown) are formed on both sides of the thin layer M1.

However, if there is a defect in the column 7 or if there is an interaction between the columns 7, if a voltage is applied in the direction perpendicular to the column 7, the electric field exists in the region E. As shown in FIG. 2(b), the interaction of the column 7 is induced, and the resistance value in this region becomes low. The interaction is thought to be based on the formation of new charge transfer complexes due to charge transfer due to the electric field, or the formation of new low-dimensional columns between columns due to molecular rotation due to the electric field. .

These conditions are maintained for a certain relaxation time (eg, several hours to a day or more) and the low resistance state is memorized. If the relaxation time passes or a reverse electric field (reverse voltage) is applied, it returns to its original high resistance state.

In addition, when performing light irradiation, the resistance value in the insulation direction decreases due to the presence of carriers generated by light, and as a result, the resistance value in the insulation direction decreases.
It is surmised that this results in a decrease in threshold voltage.

This will be explained in more detail below.

Example 1 A striped lower electrode having a width of 1 inch was formed on a cleaned glass substrate. This lower electrode has a two-layer laminated structure, and the lower layer is formed by vacuum evaporation and has a thickness of 3.
The upper layers are A and U layers having a thickness of about eooX formed by a vapor deposition method.

Then, a lead phthalocyanine thin film having a thickness of approximately 5000' was laminated on this lower electrode. This thin film was formed at a deposition rate of 1'h7SEc in a vacuum atmosphere of 10 Torr with the glass substrate kept at approximately room temperature. Then, a striped upper electrode with a width of 1 mm is formed on the lead phthalocyanine thin film so as to intersect with the lower electrode. This upper electrode has a single layer structure of an Au layer with a thickness of about 600 mm formed by vapor deposition.

X-ray diffraction analysis of the lead phthalocyanine thin film of the switching memory multifunctional device thus completed confirmed that the C-axis was oriented parallel to the electrode surface.

Next, we applied a voltage to the upper and lower electrodes of this switching memory multifunction device to examine its operation, and the following results were obtained.

Regarding the switching function, the non-light irradiation state (dark state)
Then, the specific resistance in the high resistance state is about 109Ω-α, the threshold voltage is about 20V, and the specific resistance at t:l in the low resistance state is about 1.
The resistance became 0Ω, and under light irradiation, as shown in FIG. 1, it became a low resistance state (ON state) with a threshold voltage of about 10V. This low resistance state lasted for more than 24 hours, and when a reverse bias was applied, it returned to its original OFF (high resistance) state.

<Example 2> Next, other embodiments will be described.

As in Example 1, a cleaned glass substrate was used, and a striped lower electrode having a width of 11,110 mm was formed thereon. This lower electrode has a two-layer laminated structure, with the lower layer being an 0" layer with a thickness of 300 mm formed by vacuum evaporation, and the upper layer being an Au layer with a thickness of about 6 ooX formed by evaporation.

Then, this glass substrate with a lower electrode was placed on top of an L-shaped glass tube with a diameter of 10 (1 m), and p-chloranil powder and tetrathiofulvalene powder were placed in the bottom of an H-shaped glass tube, respectively, and a rotary pump was applied to the glass substrate. 50 to 100℃ in a reduced pressure atmosphere and nitrogen gas introduced
heated to. While visually observing the substrate surface, the nitrogen gas and heating temperature were adjusted to form a 1 μm thick thin film on the electrode surface. Thereafter, the substrate was placed in a vacuum Pelger, and an upper electrode was formed in the same manner as in Example 1.

When we investigated the operation by applying a DC voltage to the upper and lower electrodes of this switching memory complex function element in the same manner as in Example 1, we found that in the non-light irradiation state (dark state), the specific resistance in the high resistance state was approximately 10Ω. -1, the threshold voltage was about 66V, and the specific resistance in the low resistance state was about 10Ω. In addition, in the light irradiation state, the specific resistance in the high resistance state is approximately 10Ω.
-α, the threshold voltage was about 60V and the switch was 1~. In this case as well, the low resistance state duration was 24 hours or more, and the original high resistance state was restored by applying a reverse bias.

Reference example> Next, reference examples will be explained. In the switching memory multifunctional device of the present invention, a pair of electrodes sandwich a thin film. In this reference example, the electrodes do not sandwich the thin film from both sides, but are arranged on the same side of the thin film.

Using the same cleaned glass substrate as in Example 1, two striped electrodes with a width of 1 inch intertwined in a comb-teeth shape were formed on the surface with an interval of 0.02 mm. As in Example 1, this electrode consisted of a C lower layer and A and U upper layers. Then, in the same manner as in Example 1, a lead phthalocyanine thin film was laminated.

Similarly to Example 1, this lead phthalocyanine thin film also had its C-axis oriented parallel to the electrode surface.

However, this switching memory composite function element did not change to a low resistance state even when a voltage of 100V was applied. Although light was irradiated with a voltage of 100 V applied, the conductivity was still about an order of magnitude higher, and as soon as the light irradiation was stopped, the resistance returned to its original value. It merely exhibits photoconductivity and has neither a switching function nor a memory function. Effects of the Invention The switching/memory complex function device of the present invention can perform switching using optical signals and memorize the switch state, and , it is also possible to release the memory state, making it an excellent high-performance device. Moreover, it is extremely practical because it requires a simple material composition and a simple structure, such as a lead phthalocyanine thin film sandwiched between a pair of electrodes, and can be manufactured easily and at low cost using ordinary thin film forming technology. rich in

[Brief explanation of drawings]

FIG. 1 is a graph showing the applied voltage-current characteristics in the switching memory complex function element of the present invention, and FIG.
Figures (a) and (b) are schematic cross-sectional views for explaining the conductive mechanism in the thin film of this switching memory complex functional element, and FIG. 3 is an embodiment of the switching memory complex functional element of the present invention. FIG. DESCRIPTION OF SYMBOLS 1... Organic thin film, 2... Upper electrode, 3... Lower electrode, 4... Base material, 11 R2... High resistance, R3, R4... Low resistance.

Claims (1)

[Claims] (1) A thin film having a switching function and a memory function is sandwiched between a pair of opposing electrodes, and the switching function is achieved by changing the thin film from a high resistance state to a low The threshold voltage is lower in the light irradiation state than in the non-light irradiation state, and the memory function is achieved by the thin film maintaining the low resistance state for at least a certain period of time. A switching memory complex function element that is activated by applying a reverse voltage to the low resistance state and released by returning the low resistance state to the high resistance state by applying a reverse voltage. (2) The switching memory multifunctional device according to claim 1, wherein the thin film is a lead phthalocyanine thin film.