JPS6070595A - Photochemical hole burning optical memory - Google Patents

Abstract

PURPOSE:To shorten signal writing time by applying an external electric field or an internal electric field to a recording substance. CONSTITUTION:Although the photochemical hole burning phenomenon is generated by turning stable molecules to semi-stable state through excited state by photochemical reaction, the phonomenon is usually generated by the positional change of protons in the molecules. If proper molecules are selected, an energy wall under the excited state is sufficiently low as compared to the energy wall of basis state and switching is made possible, so that only the molecules excited by light when applying an electric field with proper intensity to the molecules can be selectively switched. Thus, the switching speed of protons can be increased by combining selective excitation by light and switching operation by the excited electric field.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field to which the Invention Pertains] The present invention relates to a high-density optical memory using the PHB (photochemical hole burning) method, which is expected to be applied as an external storage device for computers.

[Prior art and its problems] As the information processing ability of computers has improved, storage devices that can temporarily store large amounts of information that can be processed in a short period of time and output it as needed, that is, external storage devices, have become popular. It is desired to improve the storage density of

The upper limit of the storage density of ordinary magnetic disks, which are currently widely used, is 107 bits/c due to interaction between magnetic poles.
It is thought to be about 11 bits/d, and for magnetic disks using the perpendicular magnetization method, it is thought to be about 108 bits/d.

On the other hand, in an optical disk memory, a digital signal is recorded by irradiating a substrate with on/off laser light to create bits of 1 μm in size.

For reading, a low-intensity laser is irradiated, and changes in the intensity and phase of the light are detected. The limit of the recording density of this method is determined by the phenomenon of light diffraction and is approximately 108 bits/d.

One method of increasing the density of optical memory is currently researching optical memory that utilizes a phenomenon called photochemical hole blocking (PHB).

The idea for PHB optical memory came from IBM8a in 1978.
It was announced by the JOse Research Institute and is thought to be capable of zero-high density recording, which is about 1000 times that of normal optical memory.The principle and problems are outlined below.

Consider a case in which the optical absorption spectrum of a certain substance consists of a collection of absorption lines with a narrow linewidth IMh. The width Δωl of the entire spectrum arises from the fact that the environments of individual molecules exhibiting absorption are slightly different from each other9. When light is irradiated using a laser that can be tuned to any wavelength in this spectrum, molecules that absorb light at that wavelength may shift to a metastable state different from the ground state via an excited state. Therefore, after this substance is irradiated with intense laser light, the absorption of light at that wavelength decreases or disappears, resulting in a hole in the spectrum.

Utilizing this phenomenon, it is possible to write a binary code on a wavelength scale depending on the presence or absence of holes in a material. For reading, the absorption spectrum can be measured using a weak tunable laser. A high-density recording element can be obtained by arranging a large number of these materials two-dimensionally. The recording density is
It depends on the ratio between the width of the hole created and the width of the spectrum Δωi, but this ratio is about 10 to 10.

The first functional substance used was porphyrin,
Recording was performed using a 100 μm/7 laser beam for about 1 second. The efficiency is extremely low at about 1 inch. Various materials have since been tried, and a system in which 7-thalocyanine is dispersed in a polymer has attracted attention as the most efficient.

The disadvantages of PHB optical memory are that in order for the holes to exist stably, the material that is irradiated with the laser must be kept at a low temperature close to the temperature of liquid helium, and its efficiency is extremely low, so it takes a long time to write the signal. It takes a while.

[Object of the Invention] An object of the present invention is to shorten the signal writing time of an optical memory using the photochemical hole burning method.

[Summary of the Invention] As mentioned above, the phenomenon of photochemical hole burning occurs when molecules in a stable state transition to a metastable state via an excited state due to a photochemical reaction. is caused by a change in the position of protons in the molecule. Figures 1(a) and 1(b) show diagrams of its principle.

Although the detailed mechanism by which the proton position changes through the excited state is currently not well understood, it is shown in Figure 1 (
In the excited state of b), the proton changes from 5itel to Bi
When transitioning to te 2 , the process via singlet Sl is extremely slow due to a large energy barrier;
*ripple To, thought to be due to a process mediated by Tl.

On the other hand, the movement of protons is possible not only by photochemical reactions but also by electric fields. For example, hemtqui shown in FIG.
nove K
It is predicted that switching will be possible with an electric field on the order of 'V/2.

Furthermore, if a suitable molecule is selected, the energy barrier in the excited state is sufficiently small compared to the energy barrier in the ground state, and switching in the ground state requires 1
Even if an electric field of 0.6 V/cWL or more is required, switching may be possible in an excited state with an electric field of 10' V 7 cm or less.

Therefore, by applying an electric field of appropriate strength, only molecules excited by light can be selectively switched.

That is, instead of switching the proton position of a molecule by a photochemical reaction, it is expected that the switching speed will be increased by combining selective excitation by light and switching by an electric field of the molecule in the excited state.

The present invention increases the proton switching speed by combining selective excitation by light and switching by gLm in the excited state, instead of proton switching by photochemical reaction in the conventional PHB method. be.

The electric field referred to here may be not only an externally applied electric field but also an internal electric field generated by a Schottky heterojunction, a homojunction, or the like.

When applying an external electric field, it can be done, for example, by forming a polymer film with a dye melted on it to a thickness of several microns on the Nesa glass electrode, and then depositing aluminum on the other surface to form the other electrode. can.

Further, as the internal electric field, for example, an electric field in a Schottky barrier generated at the boundary between the polymer film in which the dye is melted and the substrate metal can be used. The magnitude of the Schottky electric field is
Although it depends on the difference in work function between the metal and the dye, the amount of impurities present in the dye, and the concentration of the dye in the polymer,
It is possible to generate an electric field on the order of 'V/cm.

[Effects of the Invention] According to the new photochemical hole-burning optical memory method of the present invention, it is possible to increase the sensitivity, that is, the writing speed, while keeping the recording density at the same level as that of a normal photochemical hole-burning optical memory.

[Example of the invention: Cometal-free phthalocyanine and PMMA l:10
The MBK melted at a ratio of 0 was spin-coded onto a Nesa glass electrode with a thickness of 100 μm to form a film with a thickness of about 1 μm, and aluminum was further vapor-deposited thereon as the other electrode.

This sample has a wavelength of 690 nm at 4.2K.

By irradiating a laser beam of 1 mW, △6) h-0,3
A 5 cyt hole was observed.

When the voltage across the membrane is IOV and O
When measured twice, the average time was 22.6 seconds when the voltage was 10V, and 25.2 seconds when the voltage was OV, indicating the effect of the electric field.

[Brief explanation of the drawing]

Figure 1 (→ is 9-hydroxy phenalen
Figure 1 (b) is a conceptual diagram of the energy levels involved in photochemical hole burning, the horizontal axis is a diagram showing the position coordinates of protons, and Figure 2 is a diagram showing the stable and metastable configurations of the OVE U conductor. FIG. 4 shows two stable arrangements of four conductors. Figure 1 Figure 2 Figure 1

Claims (1)

[Claims] A photochemical hole-burning optical memory for recording digital signals in the absorption spectrum of a substance, which is characterized by applying an external electric field or an internal electric field to the recording substance.