DE2549848B2 - - Google Patents

Description

characterized in that the device also includes 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, to generate a second elastic wave (P) for reading with the same characteristics as the first elastic wave (S) , but which propagates in the opposite direction 5: u to the transducer (5)

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

3. Apparatus according to claim 1 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 1 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 1 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 1 to 7, characterized in that the elastic reading wave (P) is exposed to an interaction with a third elastic wave for writing, b5 by the same transducer (5) and with the same angular frequency as the first elastic Wave is generated, whereby second areas are generated by this interaction, which are held 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 characterized in that they also have a second semiconductor layer, the conductivity of which is different from the the first semiconductor layer (42) differentiates between the first layer (41) and the metallic layer (43) is arranged

12. Device according to one of claims 1 to 8, characterized in that the means for defining the areas by the piezoelectric Ceramic-made substrate (1) are formed, the definition by ferroelectric Effects: follows.

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 fastening devices are formed by the substrate (1), which is made of ceramics of the yttrium-aluminum-garnet or yttrium-iron-garnet type, whereby the fixing takes place through the magnetoelastic effect.

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

The invention relates to a device of the type specified in the preamble of claim 1 for information storage using elastic waves.

Various devices have been proposed 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 elastic waves have been converted, are exploited, but which worked without a memory effect will. Examples of these devices are in particular in German patent applications P 24 51 590.9 and P 25 13 166.2.

A magnetic storage device using mechanical stress waves is also known (DE-AS 14 74 455), which contains a magnetic material. It is well known that an elastic wave or sound wave changes them

magnetic properties of the magnet material. This material is registered by the Simultaneous action of an electrical current pulse and an elastic wave, their effects add up and change the state of the material, d. H. reverse the direction of the magnetic flux. the The amplitude of the electric Suom impulse is sufficient d. H. without the elastic wave does not work to reverse the magnetic flux while it is there where the magnetic material is under mechanical tension, ii h. where the elastic wave is present, sufficient to reverse the magnetic flux. This known memory device can only be binary Store signals and require a number of discrete storage elements in the form of Rods. The bits are written serially into these bars. Each staff consists of three Elements, namely a magnetic material, a material that can guide the elastic waves (e.g. glass or quartz), and an electrical conductor, which transmits the electrical current impulse

The object of the invention is to provide a device of the type specified in the preamble of claim 1 train that it can store both binary and analog signals without using discrete storage elements to need.

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 with a instead of a magnetic material Piezoelectric material, on the surface of which an elastic wave is generated, which is to be stored Represents signal that can be binary or analog. This signal is due to the piezo effect by mechanical Expressed voltages and an electrical potential relief It becomes a pulse-shaped electromagnetic The field generates the non-linear interaction with this potential of piezoelectric origin occurs and a time-independent spatial distribution of the electrical potential that depends on the shape of the elastic wave is independent, generated during the entire duration of the interaction. the spatially different, periodic areas that are 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 magnetoelastic effects, the medium of propagation is elastic Waves in these areas is stored. The information stored in this way is read by emitting an electromagnetic field in the substrate, this field being in a non-linear manner interacts with the areas to regenerate the initial elastic wave generated by the Converter who sent it is received. The memory device according to the invention has the Advantage that it also allows the storage of analog signals and no elongated storage elements in the form of rods, but gets along completely with a continuous medium.

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 invention, in which elastic surface waves be exploited that

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. and

6 shows the scheme of a device according to the Invention in which elastic bulk waves are used.

ίο In the different figures the same references Reference numerals to the same parts and the device and the signals are for better clarity of the Drawing has been shown on an arbitrary and overall enlarged scale.

The diagram of FIG. 1 shows: a piezoelectric substrate 1, 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; one or more layers, denoted as a whole by the reference number 4 and made of a material, the nature and function of which will be explained in more detail below, which are applied to the substrate 1 on the side of the transducers 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. The 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),

J5 in which the various layers are isotropic in planes parallel to the plane of the wafer, these transducers can be arranged with any orientation on the surface of the substrate. The transducers 5 are each excited by amplitude-modulated electrical signals S of the angular frequency λ. An example of such a signal is shown in FIG. 2 specified. 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 occupy essentially circular surfaces a certain time after their transmission, the center of which is in their original transducer lies.
It should be noted that the various converters

so can be excited at the same time and that the aforementioned surfaces overlap and interfere can without adversely affecting the correct operation of the device, such as is set out in the following description.

For the sake of simplicity, the elastic waves emitted by a transducer, such as transducer 5, are denoted by 5 and are represented by the pair («, It)

where k is the wave number k = -

bo is associated 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 signals from a signal 5 to its output converter (for example

If the area occupied around the transducer 5) is sufficiently large, a very short pulse P of the angular frequency α is applied to the 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 (a, O), the second term representing the wave vector of the wave P , which is assigned to its wave number and is considered negligible compared to k , since the speed of light is compared to the velocity of propagation v of the elastic waves is very high.

This pulse generated on the entire surface of the piezoelectric substrate 1, which is below the Electrode 3 is an electric field which interacts in a non-linear manner with the field occurs, which is caused by the elastic wave 5 due to the piezoelectric effect Results grid of mechanical stresses. This interaction induces surface waves, which can be characterized by the pairs (angular frequency, wave vector), which result from the sum and the difference between the pairs that characterize the interacting waves. This is how you get:

(2a, t) (Q, t) (0, -t)

The physical interpretation for this is:

- the first case corresponds to the formation of a non-progressive oscillation (where k is equal to

pst), d. H. a vibration that only occurs during the

Duration of the interaction is present, is limited to the interaction zone and changes over time with double the angular frequency 2oc of the signals 5 and P. It can therefore be neglected.

The second case corresponds to a state of discrete potentials which are independent of time, are spatially periodic with step 2nlk and are present during the interaction period of the signals S and P in the abovementioned area around the output transducer of the signal 5;

- the third case is identical to the previous one, because we know that Jjei the notation used here pairs (λ, Around (- α, - k) d \ e represent the same surface wave, which propagates in the same direction: jus.

Thus, in the second case, periodic and different "regions" have been achieved which Represent signal 5. However, because they are only present during the interaction period, it is required facilities for modifying the physical properties of the propagation medium to be provided so that these areas are saved. 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 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 allowed 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) that result from the sum and the difference of the pairs that interact, namely (Ο, ϊζ) for the stored areas and (λ, 0) for the signal P. One obtains:

The first case represents an elastic wave that moves away from the output transducer 5 spreads out the periphery of the substrate, being attenuated in the structure; with several outward and backward It only induces signals without phase coherence, which may possibly reach the converter;

- The second and third pair actually correspond to one and the same case and constitute one elastic wave, which is reflected in a coherent manner on the surface of the substrate back to the Output wandier and then used for reading.

It is therefore found that each of the transducers arranged on the substrate 1 after the non-linear Read interaction in a coherent manner only receives the signal S sent by itself while the other signals that it can receive do not have any coherence with one another and thus only one Represent noise factor. This return of the stored signal to its transmission transducer provides the Advantage of allowing a transducer of any shape (an example of which is shown in FIG. 4) and to allow the simultaneous operation of several converters.

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

In a modified use of the device from FIG. 1 it is possible to store the signal 5 on its return to its output transducer 5, that is to say after a first storage. For this purpose, the returning signal 5, which is characterized by the pair (, -jy, is allowed to interact with an elastic surface wave emitted by the output transducer 5 of the signal S in the form of a pulse of the angular frequency, whose Form is given in Fig. 3, and which is characterized by the pair (a, k) . As before, three possible cases are obtained:

(2λ, 0) (0.2 *) (0, -2t)

of which the first can be neglected and of which the other two represent the same state of discrete, time-independent potentials of spatial periodicity Tztllk .

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, 2k) and one in FIG. 3, the pulsed elastic surface wave (pi, kj emitted by the transducer 5JMe interaction ran a first expression («, Sk *), which, since it is not progressive, is neglected, and two further expressions (-ac, k) and (α , -K), which are two equivalent expressions of the same surface wave which represents the signal S on its return to the transducer 5, which it first sent out

Fi g. 4 shows a modified embodiment of the dei Transducers, such as transducer 5, disposed on the surface of substrate 1 (Fig. 1).

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

contains two combs 51 and 52, the prongs 53 of which are parallel and nested, the prongs 53 but even take the form of a curve with a turning point.

The irregular shape of the prongs 53 is intended to reduce the possible coherence of the elastic Destroying the waves as they propagate on the substrate! parasitic paths after reflection use.

F i g. 5 shows an embodiment of the in FIG. 1, working with elastic surface waves Storage in which the storage of the potential areas generated by non-linear interactions by means of the MOS (metal-oxide-semiconductor) effect.

F i g. 5 again shows the substrate 1, which is formed by the electrodes 2 and 3 connected to the generator 6 is covered, the electrode 3 from the substrate by a thin layer of air 40 and by a group is separated by layers designated in their entirety by the reference number 4. The converters like For example, the transducers 5, which are arranged on the surface of the substrate 1, are shown in FIG 5 not visible.

The substrate 1 consists of a piezoelectric material such as lithium niobate or LiNbO3 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.

To store the regions, when the silicon layer 42 is N-conductive, the electrode 43 is brought to a positive potential. It then creates a depletion of majority charge carriers in the silicon layer 42. There is a certain welding potential difference between the two sides of the dielectric 41, above which minority charge carriers (in this example positive minority charge carriers) in the silicon layer 42 collect at the interface 41-42. This phenomenon is used to store the areas in that the electrode 43 is biased (positive) in such a way when the surface of the substrate 1 is at a uniform potential that it is brought just below the threshold potential. If the distribution of the potential on the surface of the substrate 1 represents a positive region, the potential difference between the two sides of the layer 41 remains below the threshold value and there is no change in the occupation of the charge carriers. In contrast to a negative area, the potential difference between the two sides of the layer 41 is greater than the threshold value and there is an accumulation of (positive) minority charge carriers at the interface 41-42 , which increases the (negative) potential of the area concerned and, more generally, maintains the distribution of the potential on the surface of the substrate 1, which thus persists after the termination of the non-linear interaction which produced it

It should be noted that the silicon layer 42 can be divided into two superimposed layers with different resistivities of, for example, 10,000 Ωcm and 10 Dem.

Of course, the areas generated by the interactions between the elastic wave and electromagnetic ^r) shear wave by other devices and are stored 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 an example

κι the exploitation of ferroelectric effects can be cited, which cause a local shift in the The focus of the positive or negative charges, which in this way causes the relevant Holds potential range, wherein the substrate is then made of piezoelectric ceramic. Can continue the exploitation of magnetoelastic effects, 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 cause, the substrate 1 a ceramic of the YAG type (yttrium aluminum garnet) or the YIG type (Yttrium-iron-garnet) is, or the exploitation of the effects of the creation of trapping sites for the Charge carriers in a piezoelectric and semiconducting substrate 1, for example made of cadmium sulfide, where the exploited phenomenon is the transition from the conscious charge carriers to the forbidden ones Energy bands are what traps these charge carriers.

jo The surface elastic wave storage 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 bulk waves that, 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

so 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, which is 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 operating with surface waves. the Areas created are namely three-dimensional and therefore cannot be covered by one or more surface layers, such as layer 4 in FIG. 1, can 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 to be limited to the above given by way of example only understanding description limited. So a modification also forms part of the invention in which the medium for capturing the areas is separated from the sound propagation path. Such a variation can by a piezoelectric and

ίο semiconducting medium (CdS) can be realized with which the storage takes place through trapping and which with the propagation path of the sound waves is coupled by conductor tracks which are arranged parallel to one another with a pitch that is 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 under Use of elastic waves, with: - a piezoelectric substrate; - At least one electromechanical transducer which is applied to a surface of the substrate is applied, receives the information in the form of an electrical signal and a ersne 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;