JPS63142543A - Optical reversible memory - Google Patents

Abstract

PURPOSE:To realize an optical reversible memory by dispersing org. compd. molecules exhibiting nonlinear optical responsiveness into a high-polymer material and controlling the orientation of the nonlinear org. compd. molecules in the high-polymer material to create a difference in the generation intensity of SHG. CONSTITUTION:A recording layer 15 and an upper electrode 17 are provided on a substrate 11 on which a lower electrode 13 is formed. The memory is so formed that a voltage is impressed between the electrode 13 and the electrode 17. The layer 15 is formed by dispersing the org. compd. molecules exhibiting the nonlinear responsiveness as a guest particle into the high-polymer material as a host matrix. Recording and reproduction of information are executed by heating the substrate to the glass transition temp. of the high-polymer material or above in, for example, a selected position and impressing an electric field to the electrodes at this time to increase the orientability of the molecules and to create the two different states of the oriented part and nonoriented part. The oriented part and nonoriented part are fixed when the substrate is cooled down to the glass transition point or below. The two different states are read out fro the difference in the intensity of the SHG.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optically reversible memory using a nonlinear optical material.

Ever since it was discovered that organic nonlinear optical materials have high nonlinear performance, various organic molecules have been proposed as nonlinear optical materials and their physical properties have been measured. Application to functional devices has been proposed (magazine "Functional Materials Enclosure" October 19985 issue, pages 21-34).

Nonlinear response is a phenomenon in which light components other than the input light are generated in response to input light from outside the system.

Among them, second-order optical harmonic generation (SHG: Second
dHarmonic Generation), it is known that the orientation of molecules shows a large dependence on the nonlinear response, such as when the crystal structure has central symmetry, it is no longer observed macroscopically. Therefore, a method is known in which the orientation of the guest molecules is controlled by forming a guest-host composite material using an organic molecule exhibiting a nonlinear optical response as a guest molecule and a transparent molecule whose orientation can be controlled as a host molecule (Appl.
, Phys., Lett., Vol.

49, Nα5 (1986) p248-250, JP-A-61-186942).

Summary of the Invention The present invention realizes an optical reversible memory using nonlinear optical materials.

The optically reversible memory of the present invention disperses organic compound molecules exhibiting a nonlinear optical response in a polymeric material, controls the orientation of the nonlinear organic compound molecules in the polymeric material, and forms an alignment part and It is characterized by creating a difference in the second harmonic generation intensity between the non-oriented portion and the non-oriented portion.

The present invention will be explained in more detail below.

It is known that many organic molecules with unbounded electrons exhibit highly nonlinear responses. However, even for materials that exhibit a nonlinear response in the molecular state, if the molecules are arranged in a centrally symmetrical arrangement, the second-order nonlinear response will not be observed macroscopically, and the macroscopic nonlinear optical response depends on the orientation of the molecules. is large. The present invention makes use of this property to arbitrarily create oriented regions and non-oriented regions by controlling the orientation of molecules, creating two states with different SHG intensity ratios, and by reading these states, a reversible memory is created. This has been achieved.

In order to record and reproduce information using the optically reversible memory of the present invention, for example, nonlinear organic compound molecules are dispersed in a polymeric material, and the glass transition point (g183g) of the polymeric material is placed at a selected position. -rubber transition temperature) or higher;
By applying an electric field at this time, the orientation of the molecules is increased, while the orientation of the molecules remains low in the unheated part, resulting in two different states: an oriented part and a non-oriented part. By cooling below the glass transition temperature,
The oriented part and the non-oriented part are fixed, and two different states can be read out from the difference in SHG intensity.

FIG. 1 is a sectional view showing an example of the structure of the optically reversible memory of the present invention, in which a recording layer 15 is formed on a substrate 11 on which a lower electrode 13 is formed, and an upper electrode 17 is further provided thereon. There is. A voltage is applied between the lower electrode 13 and the upper electrode 17.

The recording layer 15 is formed by dispersing organic compound molecules exhibiting a nonlinear response as guest molecules in a polymeric substance as a host matrix. At this stage, the host matrix-guest molecules are in an amorphous state (
(Fig. 1A), the dipole of the guest molecule exists in a disordered manner as indicated by the arrow in the figure. Therefore, even if light were incident, no macroscopic nonlinear response would be observed.

Next, the writing process will be explained (Figure 1B).
. A voltage is applied between the upper electrode 17 and the lower electrode 13. The host matrix-guest molecules are fixed and cannot move when voltage is applied alone, but when high-power density light is irradiated and this promotes a rise in the temperature of the irradiated area, the host matrix rises above the glass transition temperature point. Rise.

When the host matrix becomes rubbery, guest molecules can move freely within the host matrix.
As shown in FIG. 1B, the orientation of the guest molecules only in the irradiated area is aligned in the direction of electrolysis.

At this time, the direction of the voltage applied to the recording layer 15 is not particularly limited. However, when a bias opposite to the voltage direction shown in the figure is applied, the orientations of the guest molecules are aligned so that the dipoles are opposite.

Thereafter, even if the applied voltage is removed after the light irradiation is stopped and the irradiated part is cooled to below the glass transition point temperature, the oriented part is preserved as it is (FIG. 1C).

Reading is performed by irradiating weak light that does not cause a temperature rise above the glass transition temperature of the polymeric material, and the light source used for writing can be weakened. When light is irradiated for reading, the incident light 31 is simply transmitted (or reflected) in the non-aligned portion 21, but in the aligned portion 23, second harmonic generation (SHG), which is one of the nonlinear responses, is generated. is observed in transmitted light (or reflected light). Note that there is no particular need to apply a voltage between the electrodes 13 and 17 during this time (FIG. 1D).

When erasing the memory, the recording layer 15 may be heated to a temperature above the glass transition temperature by irradiating light without applying a voltage to break the orientation of the oriented portion (FIG. 1E). At this time, the state of the memory returns to the initial state (FIG. 1A), so that this memory can be written to again.

Regarding the irradiation light, coherent light with a single wavelength is desirable, so laser light is preferable. In particular, when considering the light transmission region of memory materials, etc., lasers having suitable emission wavelengths, such as semiconductor lasers, Nd'':YAG lasers, Nd'' Nigaras lasers, He-Ne lasers, etc., can be used.

In addition, since the orientation of guest molecules is perpendicular to the electrode, if the x and y axes are taken in the guest-host matrix layer, that is, the recording layer 15, and the two axes are taken perpendicular to the guest-host matrix layer, the orientation region The SHO tensor of is d 3'
J becomes maximum. Therefore, it is desirable that the incident light at the time of reading be a P wave having an appropriate incident angle θ with respect to the Z axis.

In addition, in the above description, the heating method is not particularly limited in selectively heating with high power density light.

Next, the components of the optical reversible memory of the present invention will be explained.

The guest molecule is not particularly limited as long as it is an organic nonlinear optical material, but β, which is the second-order nonlinear susceptibility of the molecule, is particularly large, regardless of d, which is the SHG tensor in the normal crystalline state. Something is desirable. This is because, in the present invention, the value of β is important because the nonlinear material exists in the polymer in an individually independent molecular state.

On the other hand, in a normal crystalline state, the arrangement and packing density of a single molecule are determined by interactions between molecules, so even if a molecule has a large β, if it has central symmetry in the crystalline state, d will be small.
There were also materials that did not macroscopically exhibit a second-order nonlinear response and could not be used until now. In this way, the present invention can also effectively utilize materials that have central symmetry in the crystalline state.

Specific examples of nonlinear organic compounds having a large β and suitable for the present invention are shown below.

H2N+N0234.5 UH3 (hereinafter blank) As the polymer substance used as the host matrix, a translucent polymer material having an appropriate glass transition point temperature is used from the standpoint of heating temperature during recording and stability during storage. Specific examples of such polymeric substances include polymethyl methacrylate, polyacrylic acid, and polyacrylic acid-2-
Naphthyl, polyphenyl methacrylate, polyt-butyl methacrylate, polyacrylamide, polymorpholyl acrylamide, poly-4-carboxyphenylmethacrylamide, polymethylchloroacrylate, polyvinyl alcohol, polyvinyl chloride, poly-4-trimethylsilyl Benzoyloxyethylene, polystyrene, polyphenylacetylene, poly-1,4-phenyleneethylene, polyethylene terephthalate, bisphenol A polycarbonate, polyoxyethyleneoxycarbonylimino-1,4-phenylenetetramethylene-1,4-
Examples include phenyleneiminocarbonyl.

The recording layer 15 is formed by coating the lower electrode 13 with nonlinear organic molecules dispersed in a polymer material. Application methods include spin code method, dip method,
The method is not particularly limited as long as it is a method such as a blade coating method in which host molecules and guest molecules are uniformly mixed and applied. After coating, the recording layer 15 is formed by performing appropriate processing such as drying.

The optimal guest molecule-host matrix dispersion ratio is determined depending on the thickness of the recording layer and the characteristics of the guest molecules; for example, for an azo dye, a weight ratio of 50:50 is appropriate.

The optimal thickness of the recording layer is selected depending on the refractive index characteristics of the guest molecule-host matrix, but it is usually desirable to have a thickness of several tens of micrometers to about 0.1 micrometer in order to obtain good resolution.

As shown in FIG. 2A, in the transmission reading method in which light is irradiated and SHG in the transmitted light is detected, the upper electrode 1
It is desirable that the recording layer 7 and the recording layer 15 have high translucency at the wavelength of the irradiated light, and the recording layer 15, the lower electrode 13, and the substrate 11 have high translucency at the wavelength of the second harmonic (SH).

In addition, in the reflection reading method that detects SHG in reflected light as shown in FIG. Alternatively, it is necessary that the SH wave be reflected by the substrate 11. Moreover, a reflective layer can also be provided separately.

Regarding writing, it is necessary to absorb incident light and generate heat to heat the recording layer. This is, for example, the lower electrode 1
As 3, a material that selectively absorbs the irradiation light and transmits the SH light is used, or a material that selectively absorbs the irradiation light and transmits the SH light (
Alternatively, an absorbing layer for reflection) may be provided. Third
The figure is a cross-sectional view showing an example of the configuration of such an optical reversible memory, in which an absorption layer 19 is provided between the lower electrode 13 and the recording layer 15.

Furthermore, if a substrate material that functions as a lower electrode is used, the lower electrode can be omitted.

According to the present invention, organic compound molecules exhibiting a nonlinear optical response are dispersed in a polymeric material, the orientation of the nonlinear organic compound molecules in the polymeric material is controlled, and the orientation portion By creating a difference in SHG strength between the
Two different states can be read from the G intensity ratio,
It can be used as an optical memory.

Example 1 IT○ (Indium Tio 0x) was placed on a glass substrate.
A lower transparent electrode consisting of ide) is formed, and a 4μ
A recording layer was formed to have a thickness of about 1.0 m.

The recording layer uses equal amounts of 2-methyl-4-nitroaniline (MNA) as a guest molecule and polymethyl methacrylate (PMMA) as a host molecule, which are dissolved in tetrahydrofuran and coated, then heat-treated to form tetrahydrofuran. It was created by evaporating.

Next, gold is deposited on the recording layer to form an upper transparent electrode,
An optical reversible memory according to the present invention was created.

As a light source, a continuous wave semiconductor laser with an emission wavelength of 1.5 μm and an output of 5 mW was used.

Laser light is focused on the optically reversible memory in the initial state created above using a lens to a diameter of approximately 1 μm, and the transmittance is 2 at a wavelength of 1.5 μm.
．． Passed through a 6% attenuation filter.

When the light was irradiated, S with a wavelength of 750 nm was detected in the transmitted light.
No HG was observed.

Next, a voltage of 240 V was applied between the upper electrodes, and laser light was irradiated without passing through the attenuation filter (writing).

Since IT○ has absorption in the wavelength region of 1.5 μm, it absorbs strong laser light and generates heat, promoting a rise in temperature of PMMA, and the electric field forms a portion of PMMA with uniform orientation.

The existence of the alignment region was confirmed by the observation of SHG with a wavelength of 750 nm in the transmitted light when the applied voltage was later cut off and the laser light that had passed through the attenuation filter was irradiated again.

After cutting off the applied voltage, the sample was left for several days and then irradiated with attenuated laser light again, and SHG was observed.

When an unattenuated laser beam was irradiated with the applied voltage cut off, the SHG intensity attenuated and finally reached the zero level, confirming that erasing had taken place.

Example 2 The same procedure as in Example 1 was performed except that the guest molecule and dimethylaminonitrostilbene were used.

Created optical reversible memory.

When this optically reversible memory was subjected to writing, storage, readout, and erasure processing in the same manner as in Example 1, similar effects were confirmed.

Dimethylaminonitrostilbene has central symmetry in its crystalline state, and is a material in which no SHG is normally observed, but strong SHG has been observed by arranging the orientation of the molecules.

Example 3 A photoreversible memory was prepared in the same manner as in Example 1 except that merosinian was used as a guest molecule, and writing, storage, reading, and erasing processes were performed, and similar effects were confirmed.

Like the dimethylaminonitrostilbene used in Example 2, merocyanine is also a material in which SHG is not observed because it has central symmetry in a normal crystalline state.

Example 4 A photoreversible memory was produced in the same manner as in Example 1 except that an aluminum vapor deposition film was used as the lower electrode and an absorption layer was provided thereon.

The absorbent layer is made of polyimide resin and 1'1-diethyl-6'
6-dichloro-4-41-quinotricarbocyanine
- It was prepared by dissolving it in methyl-pyrrolidone and applying it.

A continuous emission semiconductor with an oscillation wavelength of 1.2 μm and an output of n+W was used as a light source, and reading was performed by observing the reflected light, and the same results as in Example 1 were confirmed.

[Brief explanation of the drawing]

FIGS. 1A to 18 are explanatory diagrams showing an example of the configuration of the optical reversible memo of the present invention and its operation, and respectively show the initial state (FIG. 1A), writing (FIG. 1B), and storage (FIG. 1B). 1C), reading (Fig. 1D) and erasing (Fig. 1E)
shows. FIGS. 2A and 2B are explanatory diagrams showing transmission type and reflection type readout states. FIG. 3 is a sectional view showing an example of the structure of the optical reversible memory of the present invention. 11... Substrate 13... Lower electrode 15...
Recording layer 17... Upper electrode 19... Absorption layer Figure 1A Figure 8 Figure 1D Figure 2A Figure 2B Figure 3 Old figure

Claims (1)

[Claims] 1. Disperse organic compound molecules exhibiting a nonlinear optical response in a polymeric material, control the orientation of the nonlinear organic compound molecules in the polymeric material, and generate second-order harmonics between oriented and non-oriented regions. An optical reversible memory characterized by creating a difference in generated intensity.