DE2222920A1 - Information store - Google Patents

Description

Information store

The invention relates to an information memory.

There are already different types of information stores that are known and have a wide range of applications, especially in electronic computers. Of particular interest are the types that use "write", "read", and "erase" processes can be used during the operating cycles. One "write" method is to change a specific one Property of the information store during an "erase" process is to restore this property to its original form. A "read" method consists in determining whether or not information is stored

293- (JXJD2 / 04) -HdHp

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(i.e. in determining whether or not the property of the memory has changed) (and if so, then the Type of information usually also determined). The "read" process can be carried out simultaneously with the "delete" process (destructive reading) or independently of the "erasure" method (non-destructive reading). The memory can also store information indefinitely without rewriting it, or only for very short periods, which is why a new registered letter is necessary.

Information storage can be done in facilities using certain materials in which Parb Centers may exist. Parb centers are vacancies or traps that are introduced into the materials and where electrons are trapped. The existence of color centers in a material causes the material to show a strong absorption of radiation in a specific wavelength band and also to appear colored with a typical color of the given material. One particular type of Parb center that traps a single electron is known as an "F center". A P-center strongly absorbs radiation in a band called the P-wavelength band (P-light or P-radiation). Information can be written into materials in which P-centers can be created, either by creating P-centers at the time of the "writing" process or by changing the properties of a material that already contains P-centers. In such materials it is also usually possible that other parabolic centers known as P 'centers exist. F ¹ centers are vacancies or traps where two electrons are trapped. The existence of P centers causes the material to show a strong absorption of radiation from a band (the P 'band) which is different from the F band and which also appears colored with a different typical color.

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The invention specifies an information store, which is characterized by a piece of material in which F-centers can be generated and the concentration of the F-centers can be changed is, by means of changing the concentration of the F-centers in at least a part of the piece of material with an irradiation device for irradiation at least a part of the piece of material with radiation in the F-band for the piece of material and with a device for applying an electric field on the piece of material while the material is irradiated with radiation from the irradiation device is, by a device for reading information in at least a part of the piece of material with a further Irradiation device for irradiating at least a part of the piece of material with radiation in the F-band of the piece of material, and a device for detecting the size of the radiation from the further irradiation device, the is absorbed by at least a portion of the piece of material.

According to a preferred embodiment of the invention, the comprises Store a piece of material, in which F centers and F 'centers can be generated and in which the concentration of F centers and F 'centers changeable, a means of writing of information in at least a portion of the piece of material, means for reading information in at least a part of the piece of material, a device for erasing information from at least a part of the piece of material, wherein the device for reading has a first irradiation device for irradiating at least a part of the piece of material with radiation in the F-band or F'-band for the piece of material, wherein the device for reading has a second irradiation device for irradiating at least one Part of the piece of material with radiation in the F-band for the piece of material and also a device for detecting the size the radiation from the second irradiation device, the

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absorbed by at least part of the material and wherein the means for erasing information from the piece of material is a third irradiating means has for irradiating at least a part of the piece of material with radiation in the F-band or P'-band for the piece of material and also means for applying an electric field to the piece of material while treating the material with F-band radiation is irradiated by either the first irradiation device or the third irradiation device.

If the radiation from the first irradiation device is in the F-band for the piece of material, the radiation from the third irradiation device in the F 'band for the piece of material lie. Similarly, if the radiation from the first irradiation device is in the F 'band for the piece of material, then the radiation from the third irradiation device must lie in the F-band for the piece of material.

The first, second and third irradiation devices can have lasers. The piece of material can be a crystal of a Alkali metal halide such as potassium chloride.

For a potassium chloride crystal, the first and second irradiation devices can be a single argon laser or a be a single ruby laser, both of which emit radiation in the KCl-F band, and the third irradiation device can be a Be a helium / neon laser, the radiation of which is in the KCl-F 'band.

The invention is explained in more detail with reference to the drawing. Show it:

Fig. 1 is a graphical representation of the quantum yield of the photochemical F- in-F ¹ conversion process and the photochemical F ¹ - in-F conversion pro-

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process depending on "the temperature for Potassium chloride; and

2 shows a cross section through an exemplary embodiment of the information memory according to the invention.

Various materials are already known in which P centers can be generated. Of these materials is one of the most important groups is that of the alkali metal halides. In materials of this group, P centers can be concentrated in

IQ 3

ions of up to 5 * 10 centers / cm by electron irradiation or by heating in alkali metal vapor. Colored alkali metal halide materials, the F centers may be lightened or bleached by the absorption of radiation in the F-band. Expressed differently, Although the absorption of F light is initially strong, it becomes weaker after exposure to F light as F light causes the destruction of F-centers. The F-band absorption is therefore reversible (i.e. it can be increased or decreased at a quantum efficiency that can be close to unity, and photochromic alkali metal halide crystals can can be made that last more than 10 color / bleach cycles without experience some decrease in quantum efficiency. It is also possible to use the F-band absorption without destroying any monitor larger number of F-centers, leaving alkali metal halides as reversible photochromic materials are suitable for use in information storage.

Potassium chloride is one of the most suitable alkali metal halides for use in information storage based on F centers is based. Samples of potassium chloride with F centers are relatively stable when illuminated with F light at temperatures below 80 ° K, but above this temperature there is an increasing probability of thermal ionization from the excited State after excitation with F light. Many of the so

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Generated free electrons are captured at other P centers to form ^ centers. If the temperature rises above 80 ° K, the efficiency for the conversion of two P centers into one P 'center (the photochemical F-in-F ¹ conversion process) increases, up to a temperature of about 170 K der Efficiency reaches its maximum, ie the quantum efficiency (quantum yield) is approximately 2 (since two P centers result in one P 'center). Similarly takes between these two temperatures, the quantum efficiency of the conversion of F 'centers in F-centers (the photochemical P'-in-P conversion) from a low value at 17O ⁰ C to about 2 at 80 K to. Light that is absorbed in the P 'band in this temperature range causes the ionization of an F' center, so that a P center and a free electron are released, which soon afterwards at another location to form a second P center is captured.

1 is a graph of the quantum yield of the F to P 'photochemical conversion process and the F' to F photochemical conversion process, plotted as a function of temperature, for potassium chloride. As already explained, the quantum yield of the photochemical F ¹ - to F conversion

o process from a value of about 2 at about 80 K to a low value at about 170 ⁰ K, and the quantum yield of the photochemical P to P 'conversion process changes from a low value at about 80 ⁰ K to a value of about 2 at about 170 ⁰ K. At a temperature of about 1; 55 ° Κ the quantum yields are the same for both processes.

An information store can be fabricated based on the P to P ¹ photochemical and P ^{1 to} P photochemical conversion processes. A colored KCl crystal with F centers and P 'centers is at a temperature of

about ο
135 K, the temperature at which the quantum

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exploit are the same for the two conversion processes. Information can then pass into the memory (KCl) crystal its illumination with red F light (which is strongly absorbed by the P 'centers) is inscribed in special areas will. The effect is to increase the number of F-Centers in these specific areas. the Information can be read by monitoring the absorption of F light by the crystal, this absorption being monitored is stronger in these specific areas. Alternatively, the information can be read by monitoring the absorption of F 'light through the crystal, this being absorption is weaker in these areas. The information can be erased by illuminating with F light that the F centers made while writing reshaped back into F 'centers.

Alternative storage can be obtained by using the Information is written with F light, read with either F or F 'light, and erased with F' light.

Long exposure to "read" light might be expected to result in too large a number of F centers in F 'centers or convert F 'centers to F centers, whichever one Case exists. This cannot occur in the case of exposure to F light because the equilibrium between the F light and F 'centers from the temperature and the intensity of the illumination light depends. The equilibrium F-center concentration always remains greater for illumination with weak F light than for lighting with strong F light. Information written into a crystal by a powerful beam of light is not destroyed by prolonged reading with a weak F light beam, although the signal-to-noise ratio becomes lower as the F-center concentration is repeated

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Cycles gets smaller.

The main disadvantage of an information store from the one described above Type consists in the need to keep the crystal at a constant temperature (even with repeated exposure with light bundles), and in that one caused by repeated exposure to "reading" light Bleaching often cannot be eliminated.

From Fig. 1 it can be seen that for temperatures of about 8O ⁰ K a colored crystal of KCl with P centers a quantum efficiency (quantum yield) of about 2 for the photochemical F'-in-F conversion process and a very small quantum efficiency for the brings photochemical F-in-F ^f conversion process with it. However, if a strong electric field is applied to the potassium chloride crystal when the F light shines on the crystal, the crystal will be bleached (ie, it will become more transparent to F light even at low temperatures). Effective optical bleaching is equivalent to high quantum efficiency for the F-to-F ¹ photochemical conversion process. The effects of a strong electric field and a temperature rise are similar, and the electric field greatly shifts the quantum yield curve for the F-to-F 'photochemical conversion process of FIG. 1 along the temperature axis to lower temperatures. This is the case because thermal ionization of electrons from the excited state of an F-center at low temperatures is supported by the applied electric field.

Fig. 2 shows a cross section through an embodiment of the information memory according to the invention. A crystal 1 from potassium chloride (prepared as described below)

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is mounted in a chamber 3, the temperatures below 100 K can be cooled. A common electrode 5 and a common electrode 7 are on opposite sides of the crystal 1 Faces of the crystal 1 attached. (The electrodes 5, 7 can be thin transparent films, e.g. made of tin oxide, such as is shown in Fig. 2, or they can optionally be a fine mesh gold net.) The electrodes 5 and 7 are on one Device 9 for applying voltages between the electrode 5 and the electrode 7 is connected. An argon laser 11 is so arranged that a laser beam 1J5 can strike the crystal 1 from it. A helium / neon laser 15 is arranged so that a laser beam 17 falls from him on the crystal 1 can. (The laser beam 17 is shown in phantom in Fig. 1 because it does not occur simultaneously with the laser beam 15. ') Between a conventional laser deflection system 19 (e.g. a series of electro-optic switches followed by birefringent crystals or Wollaston prisms) that can be used around the laser beam 13 and the laser beam 17 on any one Point on the crystal 1 to direct. A detector 21 is located on the side facing away from the lasers 11 and 15 Crystal 1 so that it faces the laser 11 and the laser 15.

The crystal 1 is initially prepared by growing one Potassium chloride crystal in the usual way (e.g. by pulling from the melt) and heat treatment with potassium metal vapor in a conventional device. This creates the "extra staining" or F-centers. The crystal is then treated like this (e.g. by splitting) to give it a thickness of about 100 / µm to 400 / to give, and heat-treated in the dark to ensure that only simple F centers are included and ' not so-called "aggregate centers" (the F 'centers and M centers that consist of two F-Centers).

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Information is stored in the crystal 1 in the memory of FIG. 2 in that the laser beam 13 is deflected onto the crystal 1 by the deflection system 19. An argon laser contains an emission line at 51 ^ * 5 nm and thus in the F-band for KCl. An electric field is applied between the electrode 5 and the electrode 7 during writing. The illumination of the crystal 1 by the laser beam 13 causes a photochemical F to F ¹ conversion process to take place in the areas where the laser beam 13 hits the crystal 1. Information can be written in the form of a series of dots in selected areas that represent a figure, letter or number or multiple figures, letters or numbers, or as a series of dots that represent an "1" state with areas where there are no dots representing an "O" state, or in the form of laser holograms, or in any other suitable manner.

Information in crystal 1 can be read by scanning the Crystal 1 with the laser beam 13, but without an electric field being applied between the electrode 5 and the electrode 7 is. In the areas where information is stored, the absorption of F light is small compared to that in other parts of the crystal 1 (since many F-centers are converted into F'-centers in the information-storing areas have been). Therefore, the areas where information is stored are detected by the detector 21 as an increased one The laser beam 13 passes through these areas and is detected by the detector 21.

The erasure is carried out by means of the laser beam 17 with the aid of the deflection system 19, but without using one electric field between the electrode 3 and the

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Electrode 5 is applied. A helium / neon laser contains an emission line - in the P 'band for KCl. Therefore, the laser beam 17 causes the P ^{1 to} P photochemical conversion process, and the P 'centers generated by the writing process using the laser beam 13 are converted back to P centers by the laser beam 17. The crystal 1 can then be subjected to a writing process again.

The temperature inside the chamber 3 is usually that of liquid nitrogen (77 ° K). The strength of the electric field that is applied between the electrode 5 and the electrode 7 is initially set and adjusted from time to time during operation in order to create the curve for the photochemical P to F ¹ conversion process (FIG. 1). to the appropriate point on the temperature scale. Normally, the electric field intensity is about / 2 · 10- be ⁵ V cm. The direction of the electric field in the crystal 1 is not critical with regard to the operation of the information memory.

The intensity of the reading beam that the laser beam 13 im 2 is not large, since the strength of the applied electric field (and thus the photochemical P-in-F 'conversion curve) is adjustable.

If necessary, a deflection system can be used by the deflection system 19 is separated, can be used to deflect the laser beam 17.

Instead of the detector 21, an arrangement of conventional detectors can be provided.

In a modified embodiment of the invention, the laser beam 17 can be used to provide information

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write, and the laser beam 1; 5, assisted by the strength of the applied electric field, can be used to capture information in a manner similar to that above
described to delete. (The laser beam 17 is again used, but without the electric field, to read information.)

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Claims (7)

Claims 1. Information storage with a piece of material in the F-centers can be generated and in which the concentration of F-centers can be changed, with a device for changing the concentration of F centers in at least a portion of the piece of material including an irradiation device for irradiating at least part of the piece of material with radiation in the F-band for the piece of material, characterized by a device (9) for applying an electric field to the piece of material (1), while the material with radiation (13) from the irradiation device (11) is irradiated, and by means for reading information in at least a part of the piece of material including a further irradiation device (15) for irradiating at least one part of the piece of material with radiation in the F-band for the piece of material and a device (21) for detecting the size of the Radiation from the further irradiation device, which is absorbed or transmitted through at least one part of the piece of material. 2. Information storage device according to claim 1, with a piece of material in which F-centers and F'-centers can be generated and in which the concentration of F centers and F 'centers is changeable is, with means for writing information in at least a part of the piece of material, with a Means for reading information in at least a portion of the piece of material, and having means for erasing of information from at least a portion of the piece of material and a first irradiation device for irradiating at least part of the piece of material with radiation 209 8 4 87 08 16 ... - i4 - development in the F-band or P'-band for the material piece, characterized in that the device for writing information the first irradiating means comprises that the means for reading from Information has a second irradiation device to at least a part of the piece of material with radiation in the P-band for irradiating the piece of material, as well as means for detecting the magnitude of the radiation from the second Irradiating device which is absorbed by at least a part of the piece of material, and that the device to erase information from the piece of material, a third irradiation device has at least one for irradiation a portion of the piece of material with radiation in the P-band or in the P'-band for the piece of material, and that either the device for writing or the device for erasing a device for applying an electric field to the Have piece of material while the material with F-band radiation is irradiated by either the first irradiation device or the third irradiation device. 3 information memory according to claim 1 or 2, characterized in that that each irradiation device has a laser (11, 15). 4. Information memory according to claim j5, characterized in that that the device for writing and the device for reading two lasers or a single laser with one Output emission in the P-band of the piece of material, and that en the means for erasing a / laser with an output emission in the F 'band of the piece of material. 5. Information memory according to claim j5 > characterized in that the means for erasing and the means for reading two lasers or a single laser with one 209848/0816 Have output emission in the F-band of the piece of material, and that the means for writing a single laser with an output emission in the F 'band for the piece of material Has. 6. · Information storage device according to one of the preceding claims, characterized by two electrodes (5 > 7) » which belong to the device (9) for applying an electric field each irradiation facility is transparent. 7. Information memory according to one of the preceding claims, characterized in that each irradiation device a deflection system (19) for deflecting the radiation from the irradiation device (11, 15) onto a given one Part of the piece of material (l). 209848/0816