DE2549848C3 - Information storage device using elastic waves - Google Patents

Description

characterized in that the device further comprises means for reading the information which consist of second means (2, 3) for exciting a second electromagnetic field across the substrate (1), the second electromagnetic field interacting with the areas, in order to generate a second elastic wave (P) for reading with the same characteristics as the first elastic wave (S) , but which I propagate in the opposite direction to the transducer (5) ·

2. Device according to claim 1, characterized in that the first Anrcjmgseinrichtungen two electrodes (2, 3) which are attached to both sides of the substrate (I), wherein at least one of the electrodes is separated from the substrate by an insulating layer (4) and a pulse-shaped electrical signal (P) with the same angular frequency as the elastic wave ^ is applied to the electrodes.

3. Apparatus according to claim I or 2, characterized in that the first devices (2, 3) for exciting a first electromagnetic field and the second devices (2, 3) for Exciting a second electromagnetic field are identical.

4. Device according to one of claims I to 3, characterized in that the converter (5) emits elastic surface waves.

5. Apparatus according to claim 4, characterized in that the transducer (5) is one Converter type with interdigitally arranged combs (51, 52), which are odd, parallel Have tines (53).

6. Device according to one of claims I to 3, characterized in that the converter (50) emits elastic bulk waves.

7. Apparatus according to claim 6, characterized in that the transducer (50) electrodes (54, 56) with non-planar surfaces.

8. Device according to one of claims I to 7, characterized in that the elastic Lcsewel-Ic (P) is exposed to an interaction with a third elastic wave for writing, which by the same transducer (5) and mil the same circular frequencies / as the first elastic wave is generated, whereby by this Weehsclwir-

kung, second areas can be 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 devices for Defining the areas consist of a dielectric layer (41) opposite the Transducer (5) bearing surface of the substrate (1) and arranged without contact with the surface is and successively with at least one semiconductor layer (42) and one with an outer Bias potential connected metallic layer (43) is covered.

10. Device according to claims 2 and 9, characterized in that one (3) of the electrodes is applied to the metallic layer (43) by means of an electrical insulator (44).

11. The device according to claim 9, characterized in that it also has a second Semiconductor layer, the conductivity of which differs from that of the first semiconductor layer (42), contains, which is arranged between the first layer (4i) and the metallic layer (43).

12. Device according to one of claims 1 to 8, characterized in that the devices for Defining the areas formed by the substrate (1) made of piezoelectric ceramic are, whereby the determination is made by the ferroelectric effect.

13. Device according to one of claims 1 to 8, characterized in that the means for defining the areas are made of cadmium sulfide produced substrate (1) are formed, the definition by a trap effect for the Load carrier takes place.

14. Device according to one of claims 1 to 8, characterized in that the fixing devices are formed by the substrate (I), which is made of ceramic from Yt'.rium-Aluminum-Garnet.der Yttrium iron cranate type is made. being fixed by magnetoelastic Effect occurs.

15. Device according to one of claims 1 to 14, characterized in that there are several contains independent electromechanical transducers (5; 50).

V) f) ic invention relates to a device of the type specified in the preamble of patent claim 1 ^- Jr information storage using elastic waves.

Various devices are already in place

-, -, have been suggested, in which the interactions between elastic waves, d. H. between pressure or shear vibration movements of different frequencies for the purpose of amplitude and frequency analysis of optical or electrical images that are stored in

M) elastic waves have been converted, exploited which, however, work without memory will. Examples of these devices are in particular in German patent applications P 24 51 590.9 and P 25 13 166.2.

There is also a mechanical tensioning mechanism working magnetic storage device known (DE-AS 14 74 455), which contains a magnetic material. One elastic wave or sound wave is known to change the

magnetic properties of the magnetic material. The writing in this material takes place through the simultaneous action of an electric current pulse and an elastic wave, the effects of which add up and change the state of the material, ie reverse the direction of the magnetic flux. The amplitude of the electrical current pulse is sufficient on its own, ie not sufficient without the elastic wave. to the magnetic flux to reverse while it is where the magnetic material under mechanical chip w voltage, that is, where the elastic wave is present, is sufficient to reverse the magnetic flux. This known memory device can only store binary signals and for this purpose requires a number of discrete memory elements in the form of bars. The bits are written serially into these bars. Each rod consists of three elements, namely a magnetic material, a material that can conduct the elastic waves (e.g. glass or quartz), and an electrical conductor that transmits the electrical current pulse.

The object of the invention is to provide a device of the im To train the preamble of claim I specified type so that they are both binary and analog Can store signals without the need for discrete storage elements.

This object is achieved according to the invention by the features indicated in the characterizing part of claim 1 Features solved.

The memory device according to the invention works jo instead of a magnetic material with a piezoelectric material, on the surface of a elastic wave is generated, which represents a signal to be stored, which can be binary or analog. This Due to the piezo effect, the signal is generated by mechanical stresses and an electrical potential relief expressed. A pulsed electromagnetic field is generated that is non-linear with it Potential of piezoelectric origin interacts and a spatial one that is independent of time Distribution of electrical potential, which is independent of the shape of the elastic wave, during the the entire duration of the interaction. The spatially distinct, periodic areas that present at the end of the interaction represent the information obtained by modifying the physical Properties, for example with the help of ferroelectric, semiconductor or magnetoeiasticchen Effects, the medium of propagation of the elastic waves is stored in these areas. The reading the information stored in this way is carried out by emitting an electromagnetic field in the substrate, this field interacting in a non-linear manner with the areas around the to regenerate the initial elastic wave received by the transducer that sent it. the Storage device according to the invention has the advantage that it can also store analog Signals allowed and no elongated storage elements in the form of rods required, but with bo one continuous medium gets by completely.

Several exemplary embodiments of the invention are illustrated in the drawings and are described below described in more detail. It shows

F i g. I the scheme of a device according to the v> Invention, in which elastic surface waves are used, the

F i g. Figures 2 and 3 show the shape of the electrical used in the operation of the device according to the invention Signals,

F i g. 4 shows a modified embodiment of part of the device from FIG. 1,

F i g. 5 shows an embodiment of the scheme of FIG. I. and

6 shows the diagram of a device according to the invention, in which elastic bulk waves be exploited.

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

The diagram of FIG. 1 shows: a piezoelectric substrate t, for example in the form of a plate, on the surface of which elastic waves can propagate; a plurality of electromechanical transducers such as the transducer 5 applied to the surface of the substrate 1: t; one or more in total with the reference zdi! 4 and made of a material, the nature and function of which will be explained in more detail below, consisting of layers that are applied to the substrate 1 on the side of the transducer 5 and around them; Electrodes 2 and 3 which completely or partially cover the large sides of the substrate 1, openings being provided in the electrode 3 as in the layer 4 at the location of the transducers 5. Pie electrodes 2 and 3 are connected to a generator 6 which generates an electrical signal P , the form of which is shown in FIG. 3 is specified.

The transducers 5 are, for example, interdigitally arranged combs. In the case (shown in Fig. 1), in which the various layers are isotropic in planes parallel to the plane of the plate these transducers are arranged with any orientation on the surface of the substrate verder die The transducers 5 are each excited by amplitude-modulated electrical signals 5 of the angular frequency λ. A Example for such a signal is given in FIG. These electrical signals represent the information to be stored. The transducers excited in this way generate elastic waves on the surface of the substrate 1, which propagate in such a way that they have a certain Time after their emission, occupy essentially circular areas with their center in their Original converter lies.

It should be noted that the various transducers can be energized simultaneously and that the the aforementioned surfaces can overlap and interfere without any adverse effect on the correct operation of the device, as set out in the following description.

For the sake of simplicity, those sent from a transducer such as transducer 5 are elastic Waves denoted by 5 and by the pair (λ, £)

where k is the wave number k = -

is assigned wave vector and where ν is the speed of propagation of the elastic wave on the substrate 1.

After a time T. at the end of which the area occupied by a signal S around its output transducer (for example transducer 5) is sufficiently large, a very short pulse P of angular frequency λ is applied to electrodes 2 and 3. The electromagnetic wave that is in the substrate

spreads, is - also for the sake of simplicity - denoted by P and characterized by the pair (\. O), whereby the second term represents the wave vector of the wave / ', which is assigned to its wave number and is viewed as negligible compared to Ar, since the - The speed of light is very large compared to the speed of deflection in elastic waves.

This pulse generates an electric field on the entire surface of the piezoelectric substrate I. which lies under the electrode 3, which interacts in a non-linear manner with the field that is created by the piezoelectric effect in the grid caused by the elastic wave S. of mechanical stresses. This interaction induces surface waves, which can be characterized by the pairs (angular frequency, wave vector) that result from the sum and the difference of the pairs that characterize the interacting waves. This is how you get:

(2.Λ. V) (0. V) (0. - k) ^: "

The physical interpretation for this is:

- the first case corresponds to the formation of a non-progressive oscillation (where k equals>">

jrist). i.e. an oscillation that only occurs during the

Duration of interaction is present. is limited to the interaction zone and changes over time with twice the angular frequency 2 \ of the signals S and P m. It can therefore be neglected.

- The second case corresponds to a state of discrete potentials that are independent of time, are spatially periodic with step 2.17Ar and during the interaction period of the signals .S "and P in the above-mentioned area around the output transducer of the signal 5 are available around:

- the third case is identical to the previous one, because we know that an ^ .rhrpihu. php P: i: irpf \ Ic) iinrl I - λ - jl ·) Hip alpirhp

Represent surface waves that are in the same Direction spreads.

Thus, in the second case, periodic and .alpha. "Differentiated" areas "have been created which represent the signal S. However, because they are only present during the interaction period, it is necessary. Provide means for modifying the physical activation of the propagation medium to store these areas. These changes of state must have a time constant which is small compared to the duration of the pulse P. For this purpose, ferroelectric. Magnetoelastic or semiconductor effects are used, depending on the type of substrate I and the composition of the layers 4. Embodiments are given below.

To read the information stored in this way, an electromagnetic wave to interact with the stored areas. The electromagnetic wave is generated by applying a pulse such as pulse P to electrodes 2 and 3 as before.

The non-linear interaction is characterized by the pairs ^ (angular frequency, wave vector), which result from the sum and the difference of the pairs ^. which interact, namely (0.Ar ^ for the stored areas and (λ. 0) for the signal / '. Mai gets so:

Λ. k)

- X. k)

- The first case represents an elastic wave that fell at a distance from the output transducer 5 zi the periphery of the substrate, where it 11 the structure is attenuated: if there are several linear movements around it, it only induces signals without phascnko harshness that may possibly reach the converter

- The second and d ¹ correspond Ute pair ir fact, one and the same case and are eiiu elastic wave propagating in a coherent manner the back surface of the substrate ar / u output transducer propagates and is then used to readers.

One can therefore see that the transducer 11, arranged on the substrate 1, receives the non-linear reading interaction in a coherent manner only because the signal S transmitted by itself, while the other signals that it can receive do not have any coherence with one another and thus only represent a noise factor. This return of the stored signal to its transmission transducer has the advantage of allowing a transducer of any desired shape (an example of wcvhem is shown in FIG. 4) and of allowing the simultaneous operation of several transducers zi.

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

With a modified use of the device of FIG. I, it is possible to store the signal S on its return to its output transducer 5, that is to say after it has been stored for the first time. For this purpose, the returning signal S, which is characterized by the pair (λ, - / ^. And an elastic surface wave, interact, which is sent by the output transducer 5 of the signal 5 in the form of an "ImniiUp" Hpr pulse frequency * \ aiif the form of which is given in Fig. 3 and which is characterized by the pair (a. V) . As before, mar receives three possible cases:

(2 '<. 0) (0.2 *) (0.-2A)

the first of which can be neglected and the other two of which have the same condition discrete, time-independent potentials of spatial periodicity 2.T / 2A;

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

The information is read through non-linear interaction between the stored area ( 0.2V) and one in FIG. 3 shown pulsed elastic surface wave (α, k), which is emitted by the transducer 5._The interaction ran a first expression (α, 3ϊ), the. since it is not progressive. is neglected, and two more expressions (- <x. k) and (α, -k), for which e; are un "two equivalent expressions of the same surface wave which represents the signal S on its return to the transducer 5. which sent it first.

F i g. 4 shows a modified embodiment of the transducers, such as the transducer 5 Surface of the substrate 1 (F i g. 1) are arranged.

It is also of the interdigital type, that is to say it

contains two combs 51 and 52. their prongs 53 parallel and are pushed into one another, the prongs 51 but even take the form of a curve with a turning point.

The irregular shape of the prongs 53 is intended for the eventual coherence, the elastic We! ^ -: n to destroy which in their spread to the substrate I use parasitic paths after reflection.

Fig. 5 / Eigt an embodiment read in Fig. I. shown, working with elastic surface waves storage, in which the storage of by Non-linear interactions generated potential areas by MOS (metal-oxide-semiconductor) effect takes place.

F i g. 5 show! again the substrate 1, which is covered by the electrodes 2 and 3 connected to the generator 6 , where ^f i * ^p FlpktrmHp "i vrm ftptii S ^ bstr ^3. '. by a thin layer of air 40 and by a group of in their entirety with the reference number 4. The transducers, such as the transducer 5, which are arranged on the surface of the substrate 1, are not visible in FIG. 5 for the sake of clarity.

The substrate! consists of a piezoelectric material such as lithium niobate or LiNbOj Lead zirconate titanate PZT. The intermediate space 40 has the task of closing the layers 4 away from the substrate 1 separate 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; a layer 42 of silicon or of an amorphous semiconductor; a metallic electrode 43, which over a terminal 45 is connected to an external bias potential (not shown); and one Insulating layer 44.

When the silicon layer 42 is N-conductive, it is used to store the regions. the electrode 43 on brought positive potential. It then creates a majority carrier depletion in the silicon layer 42. There is some threshold potential difference between the two sides of the dielectric 41. above which minority charge carrier (in In this example positive minority charge carriers) in the silicon layer 42 are located at the interface 41-42 accumulate. This phenomenon is used to store the areas by placing the electrode 43 in this way (positive) is biased when the surface of the substrate 1 is at a uniform potential that it is just brought below the threshold potential. If the distribution of the potential on the surface of the substrate 1 represents a positive region, the remains Potential difference between the two sides of the layer 41 is below the threshold value and it takes place no change in occupation of the load carriers. On the other hand, the potential difference is opposite to a negative area between the two sides of layer 41 is greater than the threshold and it finds one Accumulation of (positive) minority charge carriers takes place at the interface 41-42, which leads to the (negative) Potential of the area concerned and, more generally, the distribution of the potential on the surface of the Substrate 1 holds, in this way after the termination of the non-linear interaction of the it has been created persists.

It should be noted that the silicon layer 42 is divided into two superimposed layers of different sizes

specific resistance of, for example, ΙΟΟΟΟΩςτη or 1ΟΩο * ιτι / can be imposed.

Of course, the areas generated by the interactions between elastic waves and clektromagnetic waves can be stored by other devices and in particular by the substrate itself. It should be noted that the layer 4 is always required to isolate the surface of the substrate 1 from the electrode 3. As an example, the use of ferroelectric effects can be cited, which cause a local shift in the centers of gravity of the positive or negative charges, which in this way holds the relevant potential area in place, the substrate then being made of piezoelectric ceramic. The use of magnetoelastic effects can also be cited, which cause a local tilting of the 7ii "tanHp" Ae.r atoms, in particular the alignment of their spin at the location of the areas to be stored, the substrate 1 being a ceramic of the YAG type (yttrium Aluminum garnet) or of the YIG type (yttrium iron garnet), or the exploitation of the effects of generating trapping points for the charge carriers in a piezoelectric and semiconducting substrate I _1, for example made of cadmium sulfide, where the exploited phenomenon is then the The transition of the conscious charge carriers into the forbidden energy bands is what causes these charge carriers to be trapped.

The surface elastic wave memory device described above has other advantages, one of which is a relatively high degree of efficiency for the nonlinear interactions due to the fact that the energy is concentrated on the surface of the device, and also the possibility of carrying out various processing of the signals can also be mentioned which, since they reproduce on the surface, are thus available and accessible.

It is also possible to create a storage system that works with elastic, volume waves, which, if it does not have the advantages mentioned above, it allows a larger capacity. The scheme such a memory is shown in FIG. 6 specified.

The device includes a piezoelectric substrate 10, transducer 50 for bulk elastic waves and two electrodes 20 and 30 covering the surface of the substrate 10 around the transducers 50 without to be in touch with each other. 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 placed on the substrate 10 applied and covered with a piezoelectric layer 55, which in turn with an electrode 56 is covered. The electrical signal to be stored, referred to as signal 5 as before, is sent to the both electrodes 54 and 56 applied

This signal is stored in an analog manner, that is, after the generation of areas by a non-linear interaction between the elastic bulk wave generated by the transducer 50 and the electromagnetic wave, which has the same angular frequency and is pulse-shaped ( designated P above) and between the Electrodes 20 and 30 is generated. Reading takes place in the same way as with the device working with surface waves.

This device, of course, has the same characteristics as that of FIG. 1 on: The

The stored signal is recovered by the transmitting transducer with the associated ones Advantages.

There is, however, a difference from the device using surface water. the Areas created are namely three-dimensional and can therefore be nitni through one or more surface layers, such as layer 4 in FIG. I. be saved. They must therefore be in the substrate 10 itself can be stored by, for example, magnetoelastic or ferroelectric effects or use is made of the effects of generating trapping points for the charge carriers that have been described above.

It should be noted that for the same reasons as above, that is, to destroy any eventual Coherence of the elastic interference waves, the transducers, such as the transducer 50, preferably an irregular one To have form, that is, to be non-flat.

The invention is not limited to the above merely as Example given and not to be understood as a limitation description is limited. So also educates a modification of part of the invention in which the medium / to hold the areas is separated from the sound propagation path. Such a variation can be realized by a piezoelectric and conductive medium (CdS) which the storage takes place by catchers and which with the path of propagation of the sound waves is coupled by conductor tracks. which are disordered parallel to each other with a pitch, the opposite half the wavelength of the elastic waves used is small.

For this purpose 2 sheets of drawings

Claims (1)

Patent claims: 1. Device for information storage using elastic waves, comprising: - a piezoelectric substrate; - At least one electromechanical transducer which is applied to a surface of the substrate is applied that receives information in the form of an electrical signal and a first emits elastic wave; - First means for exciting a first electromagnetic field across the Substrate, where the electromagnetic field interacts with the elastic wave, in order to generate spatially distinct areas representing the information, which distributions are electrical potential; - facilities for defining the areas;