DE2549848A1 - INFORMATION STORAGE DEVICE - Google Patents

Description

THOMSON - CSF
173, vol. Haussmann
75008 Paris / France

Our reference: T 1878

Information storage device

The invention relates to the field of information storage and particularly relates to a device in which interactions between elastic Waves and electromagnetic waves can be exploited for storing electrical signals.

Various devices have already been proposed in which the interactions between elastic Waves, i.e. between pressure or shear vibration movements of different frequencies for the purpose of Amplitude and frequency analysis of optical or electrical images converted into elastic waves have been exploited, but without a memory effect. Examples of these devices are in particular in

609822/0656

German patent applications P 24 51 590.9 and P 25 13 166.2 described.

The invention relates to an information storage device in which such interactions are used, to make spatially different, periodic areas that represent the information appear, and which facilities are used to modify of the medium of propagation of the elastic waves at the level of these areas in order to convey the information to save.

For this purpose the device according to the invention contains:

- a piezoelectric substrate;

- At least one electromechanical converter that receives the information in the form of electrical signals and one on the surface or in the substrate propagating elastic wave supplies;

- Means for exciting an electromagnetic field in the substrate, this field interacting in a non-linear manner with the elastic wave steps to make areas representing the information appear;

and means for modifying the physical properties of the wave propagation medium on the Height of these areas with the help of for example ferroelectric, semiconductor or magnetoelastic effects.

Reading the information recorded in this way occurs through the emission of an electromagnetic field. in the substrate, this field being in a non-linear manner interacts with the areas to make the. elastic initial wave to regenerate that of the Converter who sent it is received.

609822/0656

7R49848

Several exemplary embodiments of the invention are illustrated in the drawings and are described below described in more detail. Show it:

Fig. 1 'the scheme of a memory according to the

Invention, in which elastic surface waves are used,

Figures 2 and 3 show the shape of the device used in the operation of the device according to the invention electrical signals,

Fig. 4 shows a modified embodiment of a

Part of the device of Fig. 1,

FIG. 5 shows an embodiment of the scheme of FIG

Fig. ■ 1, and

6 shows the diagram of a memory according to FIG

Invention in which elastic bulk waves are used.

In the various figures, the same reference symbols relate to the same parts and the device and For the sake of clarity in the drawing, the signals are arbitrary and enlarged overall Scale has been shown.

In the diagram of Fig. 1 are shown: a piezoelectric substrate 1, for example in the form of a Platelet, on the surface of which elastic waves can propagate; several electromechanical converters, such as the transducer 5 applied to the surface of the substrate 1; one or more in total denoted by the reference number 4 and made of a material, the nature and function of which will be explained in more detail below are, existing layers that are on the substrate 1 on the

609822/0658

Side of the transducer 5 and around these are applied; Electrodes 2 and 3, which completely or partially cover the large sides of the substrate 1, with openings are provided in the electrode 3 as in the layer 4 at the location of the transducers 5. Electrodes 2 and 3 are connected to a generator 6 which generates an electrical signal P, the form of which is shown in FIG is.

The transducers 5 are arranged, for example, interdigitally Combs. In the case (shown in Fig. 1) in which the various layers in to the plane of the platelet's parallel planes are isotropic, these transducers can point to any orientation the surface of the substrate are arranged. The transducers 5 are each amplitude-modulated electrical signals S of the angular frequency α excited. An example of such a signal is given in FIG. These electrical signals represent the information to be stored. The excited in this way Transducers generate elastic waves on the surface of the substrate 1 which propagate in such a way that for a certain time after their emission they occupy essentially circular areas, the center of which lies in their original converter.

It should be noted that the various transducers can be energized simultaneously and that the aforesaid Surfaces can overlap and interfere without adversely affecting the correct Operation of the device results as set forth in the following description.

For the sake of simplicity, the elastic waves transmitted from a transducer such as transducer 5 are denoted by S. and identified by the pair (a, Tc), where "k" is the wave vector assigned to the wave number k = ~ and where ν is the speed of propagation

609822/0656

of the elastic wave on the substrate 1.

After a time T, at the end of which the signals from a signal S around its output transducer (for example the transducer 5) is sufficiently large around, is to the Electrodes 2 and 3 a very short pulse P of the angular frequency α is applied. The electromagnetic wave that spreads in the substrate is - also for the sake of simplicity - denoted by P and by the pair (α, ο) characterized, wherein the second term represents the wave vector of the wave P associated with its wave number and is considered to be negligible compared to k, since the speed of light compared to The speed of propagation ν of the elastic waves is very large. .

This pulse is generated on the entire surface of the piezoelectric substrate 1, which lies under the electrode 3, an electric field which is in nonlinear Way with the field interacts, which is due to the piezoelectric effect from the through the elastic wave S results in the grid of mechanical stresses caused. This induces interaction Surface waves generated by the pairs (angular frequency, Wave vector) resulting from the sum and the difference of the pairs, which characterize the interacting waves. This is how you get:

(2a, Ic) (o, Tc) (o, -Ic)

The physical interpretation for this is: - the first case corresponds to the formation of a non-progressive one Oscillation (where k is equal to -), i.e. an oscillation that only occurs during the duration of the interaction is present, is limited to the interaction zone and temporally with double the angular frequency 2a of

60982 2/0656

⁶ "75498

Signals S and P changes. It can thus be neglected will.

- the second case corresponds to a state of discrete potentials that are independent of time, with step 2n / k are spatially periodic and during the interaction period of the signals S and P in of the above-mentioned area around the output transducer of the signal S.

- the third case is identical to the previous one, because we know that with the notation used here Pairs (a, k) and (-α, -k) represent the same surface wave propagating in the same direction.

In the second case, periodic and differentiated "areas" have thus been achieved which contain the signal S represent. However, because they are only present during the interaction period, it is necessary to To provide means for modifying the physical properties of the propagation medium therewith these areas are saved. These changes of state must have a time constant that is opposite the duration of the pulse P is small. For this purpose, ferroelectric, magnetoelastic or semiconductor effects can be used can be used, depending on the type of substrate 1 and the composition of the layers 4. Exemplary embodiments are given below.

To read the information stored in this way, an electromagnetic wave is left with the stored information Areas interact. As before, the electromagnetic wave is generated by applying a pulse, such as the pulse P to the electrodes 2 and generated.

6.0 9822/0656

" ⁷ " 7549848

The nonlinear interaction is given by the pairs (angular frequency, Wave vector), which result from the sum and the difference of the pairs that interact occur, namely (o, k) for the stored areas and (α, ο) for the signal P. This gives:

(α, t)

- The first case is an elastic wave propagating to remove from the output transducer 5 to the periphery of the substrate, whereby it is attenuated in the structure; with several outward and backward. It only induces signals without phase coherence, which can possibly reach the converter;

- The second and third pair correspond in reality to the same case and represent an elastic one Wave that is in a coherent manner on the surface of the substrate is propagated back to the output transducer and then used for reading.

It is therefore found that each of the transducers arranged on the substrate 1 according to the non-linear reading interaction receives in a coherent way only the signal S sent by itself, while the other signals, which it can receive do not have any coherence with one another and thus only represent a noise factor. These Returning the stored signal to its transmitting transducer has the advantage of using a transducer of any shape allow (an example of which is shown in Fig. 4) and the simultaneous operation of multiple converters to allow.

It should be noted that the signal read by its output transducer 5 after storage. S reversed in time is.

609822/0656

7 549848

With a modified use of the device of FIG. 1, it is possible to use the signal S on its return to its output transducer 5, that is to say after a first storage. For this purpose one leaves that returning signal S, identified by the pair (a, -k ") is, and an elastic surface wave interacting through the output transducer 5 of the signal S has been sent out in the form of a pulse of the angular frequency α, the form of which is shown in FIG and which is characterized by the pair (α, k). As before, you get three possible cases:

(2a, o)

(o, 2t) -

(o, -T

of which the first can be neglected and of which the other two have the same state of discrete, represent time-independent potentials of spatial periodicity 2 π / 2k.

This state, which consists of different areas, is saved in the same way, namely by Change of state of the propagation medium.

The information is read through non-linear interaction between the stored areas (o, 2k) and a pulse-shaped elastic shown in Fig. 3 Surface wave (α, k) emitted by the transducer 5. The interaction provides a first expression (α, 3k), which, because it is not progressive, is neglected, and two further expressions (-α, k) and (α, -k), at which are two equivalent expressions of the same surface wave that return to the Converter 5, which sent it out first, represents the signal S.

Fig. 4 shows a modified embodiment of the converter,

609822/0656

such as the transducer 5, which are arranged on the surface of the substrate 1 (Fig. 1).

It is also of the interdigital type, i.e. it contains two combs 51 and 52, the prongs 53 of which are parallel and pushed into one another, the prongs 53 themselves but take the form of a curve with a turning point.

The irregular shape of the prongs 53 is intended to destroy the possible coherence of the elastic waves, which use parasitic paths as they propagate on the substrate 1 after reflection.

FIG. 5 shows an embodiment of the one shown in FIG. 1 which operates with elastic surface waves Memory, in which the storage of the potential areas generated by non-linear interactions by MOS (Metal-oxide-semiconductor) effect takes place.

Fig. 5 shows again the substrate 1, which by the is covered with the generator 6 connected electrodes 2 and 3, the electrode 3 from the substrate by a thin air layer 40 and by a group of layers designated in their entirety by the reference number 4 is separated. The transducers such as the transducer 5 arranged on the surface of the substrate 1 are not visible in FIG. 5 for the sake of clarity.

The substrate 1 consists of a piezoelectric material such as lithium niobate LiNbO ₃ or lead zirconate titanate PZT. The intermediate space 40 has the task of separating the layers 4 from the substrate 1 so that the elastic waves can freely propagate on the surface of the substrate.

The group of layers 4 consists successively and outwardly of: a silicon oxide layer 41; one layer

609822/0658

7549848

made of silicon or an amorphous semiconductor; a metallic electrode 43, which via a connection 45 connected to an external bias potential (not shown); and an insulating layer 44.

To save the areas is when the silicon layer

42 is N-conductive, the electrode 43 to a positive potential brought. It then creates an impoverishment of majority carriers in the silicon layer 42. There is some threshold potential difference between the two sides of the dielectric 41, above which Minority charge carriers (in this example positive minority charge carriers) accumulate in the silicon layer 42 at the interface 41-42. This appearance will to save the areas exploited by the electrode

43 is biased (positive) in such a way when the surface of the substrate 1 is at a uniform potential is that it is being brought just below the threshold potential. If the distribution of the potential at the Surface of the substrate 1 represents a positive area, the potential difference remains between the two sides of the layer 41 below the threshold value and there is no change in occupation of the charge carriers. Against it the potential difference between the two sides of the layer 41 becomes greater than that of a negative region Threshold value and there is an accumulation of (positive) minority charge carriers at the interface 41-42, which shows the (negative) potential of the area in question and, more generally, the distribution of the Holds the potential on the surface of the substrate 1, which continues in this way after the termination of the nonlinear interaction that produced it.

It should be noted that the silicon layer 42 is divided into two superimposed layers with different resistivities of, for example, 10,000 Ωcm or 10 square centimeters can be dismantled.

609 8 22/06 56

25498A8

Of course, they can be caused by the interactions between elastic waves and electromagnetic waves generated areas are stored by other devices and in particular by the substrate itself. It should be noted that the layer 4 is always used to isolate the surface of the substrate 1 from the electrode 3 is required. As an example, the exploitation of ferroelectric effects can be cited, which have a local Shifting the centers of gravity of the positive or negative charges, which in this way causes the relevant potential area holds, wherein the substrate is then made of piezoelectric ceramic. Further the exploitation of magnetoelastic effects can be cited, which cause a local tilting of the state of the atoms, in particular the alignment of their spin at the location of the areas to be stored, wherein the substrate 1 is a ceramic of the YAG type (yttrium aluminum garnet) or the YIG type (yttrium iron garnet) is, or the use of the effects of creating trapping points for the load carriers in one piezoelectric and semiconducting substrate 1, for example made of cadmium sulfide, taking advantage of the phenomenon then the transition of the conscious charge carriers into the forbidden energy bands is what causes these charge carriers be captured.

The storage device working with elastic surface waves, which has been described above has other advantages, one of which is relatively high efficiency for the non-linear interactions due to the fact that the energy is concentrated on the surface of the device, and also called the possibility can be able to perform various processing operations on the signals as they are at the surface reproduce, are available and accessible in this way.

6098 2 2/0656

According to the invention it is also possible to have a to create elastic bulk waves working memory, which, if it does not have the advantages mentioned above, on the other hand, a larger capacity is allowed. The scheme of such a memory is given in FIG.

The device includes a piezoelectric substrate 10, bulk elastic wave transducer 50, and two electrodes 20 and 30, which cover the surface of the substrate 10 around the transducers 50 without interfering with each other To be touch. The electrodes 20 and 30 are connected to a generator 60.

The transducers 50 can consist, for example, of a counter electrode 54 which is applied to the substrate 10 and is covered with a piezoelectric layer 55, which in turn is covered with an electrode 56. The electrical signal to be stored, which is referred to as signal S as before, is sent to the two electrodes 54 and 56 created.

This signal is stored in an analog way, that is, after the generation of areas by a non-linear one Interaction between the elastic bulk wave generated by the transducer 50 and the electromagnetic one Wave that has the same angular frequency and is pulse-shaped (labeled P above) and between the electrodes 20 and 30 is generated. Reading takes place in the same way as in the case of the device operating with surface waves.

This device, of course, has the same characteristic as that of Fig. 1: the recovery of the stored signal is carried out by the transmitter converter with the associated advantages.

6098 2 2/0 658

" ¹³ " 7549848

There is, however, a difference from the device operating with surface waves. The generated Areas are namely three-dimensional and can therefore not go through one or more surface layers, such as for example layer 4 in FIG. 1, can be stored. They must therefore be stored in the substrate 10 itself are, for example, by magnetoelastic or ferroelek tr i see effects or by effects of the generation use is made of trapping points for the load carriers, which have been described above.

It should be noted that for the same reasons as above, that is, to destroy any possible coherence the elastic interference waves, the transducers, such as the transducer 50, preferably have an irregular shape, that is, are not flat.

The invention is not to be construed as being limited to that given above merely as an example Description limited. Thus, a modification also forms part of the invention in which the medium is used to hold onto Areas is separated from the sound propagation path. Such a modification can be made by a piezoelectric and semiconducting medium (CdS) can be realized, in which the storage takes place through trapping points and which is coupled to the path of propagation of the sound waves through conductor tracks that are parallel to each other with a pitch are arranged which is small compared to half the wavelength of the elastic waves used.

609822/0656

Claims (15)

₁₄ - 7549848 Claims Device for information storage using elastic waves, comprising: - a piezoelectric substrate; - At least one electromechanical converter that is on a surface of the substrate is applied which receives information in the form of an electrical signal and emits a first elastic wave; - First devices for exciting a first electromagnetic Field across the substrate, the electromagnetic field interacting with the elastic wave occurs to generate spatially distinct areas representing the information; - facilities for defining the areas; - characterized in that the device also Includes means for reading the information consisting of second means for exciting a second electromagnetic field across the substrate, the second electromagnetic field interacting with the Areas occurs in order to generate a second elastic wave with the same characteristics as the first elastic wave for reading, but which propagates in the opposite direction to the transducer. 2. Device according to claim 1, characterized in that that the first excitation devices contain two electrodes attached to either side of the substrate, wherein at least one of the electrodes is separated from the substrate by an insulating layer and wherein the Electrodes apply a pulse-shaped electrical signal with the same angular frequency as the elastic wave will. 609822/0856 ¹⁵ "75498A8 3. Device according to claim 1 or 2, characterized in that that the first means for exciting a first electromagnetic field and the second means for exciting a second electromagnetic field are identical. 4. Device according to one of claims 1 to 3, characterized characterized in that the transducer emits elastic surface waves. 5. Apparatus according to claim 4, characterized in that the transducer is a transducer type with interdigital arranged combs, which have odd parallel prongs. 6. Device according to one of claims 1 to 3, characterized in that the transducer is elastic bulk waves sends out. 7. Apparatus according to claim 6, characterized in that the transducer electrodes with non-planar surfaces contains. 8. Device according to one of claims 1 to 7, characterized in that the elastic reading wave of an interaction is exposed to a third elastic wave for writing, passed through the same transducer and with the The same angular frequency as the first elastic wave is generated, with second areas through this interaction are generated, which are recorded with the help of the fixing devices. 9. Device according to one of claims 1, 4, 5, characterized in that the means for setting the Areas consist of a dielectric layer facing the transducer-bearing surface of the substrate and is arranged without contact with the surface and 609822/0656 successively with at least one semiconductor layer and one connected to an external bias potential metallic layer is covered. 10. Arrangement according to claims 2 and 9, characterized in that that one of the electrodes is applied to the metallic layer by means of an electrical insulator .is. 11. The device according to claim 9, characterized in that it also has a second semiconductor layer / whose conductivity differs from that of the first semiconductor layer, that between the first layer and the metallic layer is arranged. 12. Device according to one of claims 1 to 8, characterized characterized in that the means for defining the regions are made of piezoelectric ceramic manufactured substrate are formed, the definition being carried out by the ferroelectric effect. 13. Device according to one of claims 1 to 8, characterized characterized in that the means for defining the areas by the CdS produced from cadmium sulfide Substrate are formed, the definition being carried out by a trap effect for the charge carriers. 14. Device according to one of claims 1 to 8, characterized characterized / that the fixing devices are formed by the substrate, which is made of ceramic from Yttrium-aluminum-garnet (YAG) - or yttrium-iron-garnet (YIG) type is manufactured, whereby the laying down by magnetoelastic effect takes place. 15. Device according to one of claims 1 to 14, characterized in that it has several independent electromechanical Includes converter. 609822/0656 Ah Blank page