DE3439283A1 - Process for reading signals in and out on the basis of electrically polarisable films - Google Patents

Abstract

An electrically polarisable polymer film provided with a system of electrodes is used as a data memory. The electric signals to be stored are recorded in the polymer film by remanent polarisation of individual domains. The reading-out operation is based on a pyroelectric activation of the polarised domains. The activation takes place by a multiplicity of the polarised domains simultaneously inducing electric signals in the system of electrodes, which are mutually arranged and interrogated in parallel and/or on the basis of a multiplex method. Electrode matrices are arranged on the upper side and underside of the polymer film. In the case of a data memory constructed in this way, the polarised domains assigned to a single conductor track of the strip matrix can be pyroelectrically activated simultaneously by a heating current pulse flowing in this conductor track, so that the domains assigned to the conductor track can be interrogated simultaneously and activated by changing over to other regions corresponding to a different conductor track. Alternatively, a dot matrix may also be used as the system of electrodes. In this case, the polarised domains are pyroelectrically activated globally by electromagnetic radiation or by a heating current pulse injected in the system of electrodes, and the induced signals are read out in parallel. The basic material for the polymer film preferably comprises a copolymer of ... Original abstract incomplete.

Description

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Patent department Process for reading in and reading out signals based on electrically polarizable layers The invention relates to a method for and reading out binary or analog electrical signals using a Data storage device based on an electrically polarizable and with an electrode system contacted polymer layer. The reading process is based on the fact that the polymer layer retentively polarized in accordance with the signals to be marked in local domains will. The readout process is based on a pyroelectric activation of the polarized Domains.

The current situation in the field of communication technology, in particular the field of data processing, is characterized by the development and the use of information stores with ever increasing data density. Currently Stationary electrical storage devices based on Si are primarily in use commercially (ROM, RAM, CCD) with storage densities around 106 bit cm-2 and movable magnetic memories (Tape, plate, drum) by 107 bit cm 2. In development are electrical sch Storage of higher density (production with the help of electron beam or X-ray lithography), higher density magnetic storage (replacement of pigment / binder systems by metallic layers, introduction of the "perpendicular recording" technique) as well as optical ones Storage, especially non-erasable opto-mechanical storage, e.g. optical disk, and erasable opto-magnetic memories based on the Kerr or Faraday effect. All these storages will - at least in the foreseeable future - not become greater storage densities than reach approx. 108 bit cm2; for example, the optical memory is through the maximum 2 Focusing of the laser beam of approx. 1 #m limited in its storage density.

However, memories are essential and are wanted and urgently needed higher storage densities than 108 bit / cm2.

In addition to the storage density, other important parameters are the access time, Data transfer rate, cost per bit, lifetime of the stored information and compatibility with existing computer systems. The following data are used as the target size Desired for memory from the 1990s: memory densities 1011 bit / cm2 access times 10 8 sec data transfer rates 108 bit / sec Permanence 10 years and erasable.

The main development goals are a higher storage capacity density and a shorter access time. Two development directions are currently being pursued: a) In the case of multi-dimensional storage "by means of laser holography or by means of "Photochemical hole burning" is the information with a laser beam in the storage medium enrolled. In the case of holographic systems, the information becomes spatially three-dimensional stored (e.g. in LiNbO2 or in polymers). With photochemical hole burning the information is read in by means of the laser, but additionally per surface element (approx. 1 Fm2) into a broadband solid-state IR absorption band (width approx. 500 GHz) up to 103 different narrow bands ("holes") with one bandwidth burned in at 50 MHz. In both cases there is the disadvantage that there is no bit for bit can be deleted and read in again, but the deletion always in packets, E.g. á 103 bit for photochemical hole burning.

b) The second direction of development is concerned with use of electron beams for reading in and out. The electron beam has opposite the laser has the advantage of a considerably smaller beam diameter (order of magnitude 0.005 #m). Accordingly, there is a higher spatial resolution and thus a higher one Storage density reached. With this method, a non-erasable and not re-inscribable Tiny memory by burning in Holes made in B-aluminum.

Memories based on electrically polarizable layers have been around since Developed in 1950. In U.S. Patent 2,698,928 the basic methods for described a movable memory. This is a tape / plate consisting of an electrically remanent polarizable material that is an electrically conductive Has lower layer moved past an electrode. By applying the Electrode with a voltage are areas of the electrically polarizable layer retentively polarized and thus information is stored. The electrode can become both in direct contact with the layer and a defined distance exhibit. Other methods of creating remanently polarized areas are Use of electron beams or ion resolution. To read out the saved Information is used the piezoelectric effect, i.e. on the electrical -polarizable layer gets a pull / push by moving it past a sharp one Edge or exerted by using ultrasound, so that the charges are released induce a voltage in the electrode that is proportional to that during the writing process is used in tension. Inorganic media are used as electrically polarizable media Ferroelectrics but also called electrically polarizable plastics.

In addition to the piezoelectric readout, at the end of the sixties the pyroelectric effect # is used for reading out the tape-shaped memories (H. Tanaka, R. Sato, Trans. I.E.C.J. 52-A, 436 (1969); H. Niitsuma, R. Sato, Ferroelectrics 34, 37 (1980)). This relieved stress from heating the electrically polarized layer in the abrasive grinding electrodes. Inorganic materials such as Pb (ZrTi) 03 were used as the electrically polarizable layer (= PZT) is used.

A further development to a high-density memory is not known. Such a further development should not be promising either, since ceramic Ferroelectrics, such as PZT, because of their high dielectric constants and their at the same time low coercive force not suitable, electrically polarizable Represent materials for storage of the highest density.

The high dielectric constant has a low readout signal result and the low coercive force leads to a low storage density. Using a method analogous to that proposed by Tanaka and Sato of drag electrodes and pyroelectric readout is disclosed in U.S. Patent 4,389 445 a polarizable macromolecular layer such as polyvinylidene fluoride (PVDF) used, which for the reasons given above are basically better than inorganic ones Materials is suitable. Also based on PVDF, a data memory was installed in the US Pat. No. 4,059,827 describes reading in directly with an electron beam and the readout via the expansion of the electron beam on polarized PVDF domains he follows. Reading in by means of an electron beam, however, carries the risk of that with electron bombardment with higher current densities a Spin-off of fluorine from the PVDF and thus irreversible destruction of the storage material takes place. Furthermore, in the method described above, the reading in of the Information by means of an electron beam only after the PVDF film has been heated via a certain temperature (800C) including cooling achieved after the reading process will. So are - because of the thermal inertia of the polymer material - only extreme low data transmission rates are possible, which are of no interest in practice. The data transfer rate is not a problem with the sliding electrode method The decisive disadvantage, which is inherent in all movable storage systems, is the access time, which due to the positioning process is always a few 10 3 sec. Will be.

This problem does not occur with stationary storage systems based on Si on. For this reason, stationary storage systems were also used in parallel to the Si-based storage systems developed on the basis of electrically polarizable media. Crawford (J.C. Crawford, Ferroelectrics 3, pp. 139-146 (1927)) discloses a ferroelectric memory device described which are compatible with the electrical storage devices based on Si at the time was. In this memory, electrode strips (so-called comb electrodes) were placed on the Top and bottom of a ceramic ferroelectric layer (PZT) at 900C against each other rotated vapor-deposited.

Information could be saved by creating a Voltage to corresponding electrodes on the top and bottom of the area at the intersection of these electrodes was polarized. Below the ferro- electrical Layer was applied an epoxy layer, on which in turn a piezoelectric Material was glued. This piezoelectric layer became selective by application a tension set in oscillation, so that the resulting sound wave over the epoxy adhesive exerts pressure / tension on the ferroelectric memory layer and thereby again by means of the piezoelectric effect a voltage in the corresponding Electrode pair was generated, depending on the sign of the in the polarized area present remanent polarization was positive or negative.

With this proposal, however, a high-density memory is not feasible because of the necessary thickness of the epoxy layer (at 10 MHz at least 0.5 mm) narrow electrodes (# 100 m), which enable large storage densities in the first place would not be selectively approachable and, moreover, those that inevitably occur Sound reflections also address unaddressed areas with a time delay, so that Spatial interference sometimes resulted in completely incorrect design data.

A similar comb electrode system applied to a polymer such as e.g. PVDF, is disclosed in U.S. Patent No.

3 772 518 presented. However, this patent does not address data storage thought, but exclusively of a light detection system similar to one VIDICON tube. A fine beam of light falls on a uniformly pre-polarized one organic film, so that taking advantage of the pyroelectric effect by means of Comb electrodes determine the position of the incident light beam detected can be. The currents registered here are approx. 10 11 A. By applying the applied comb electrodes with a voltage can be analogous to Crawford information are stored and read out by means of the fine light beam. It results but in turn the problem of positioning the light beam that leads to a undesirably long access times and the limitation of the storage density the maximum possible bundling of the laser light beam to approx.

1 cit2. A memory that also avoids this disadvantage would be ideal and thus has all the properties of silicon-based memories, but with storage densities of 1010 bit / cm2. The technological limit lies in the case of Si storage systems the storage density at approx. 106 2 bit / cm The invention is based on the object in combination with a data storage device based on a ferrcelectric polymer layer to develop a read-in and read-out process, the highest storage density and the shortest Allows access times.

This task is, starting from one with an electrode system contacted polymer layer using the remanent electrical polarization local domains when reading in and pyroelectric activation when reading out solved according to the invention in that the pyroelectric activation with or immediately takes place before the readout process in such a way that simultaneously a large number of the polarized Domains in the electrode system induce signals that are then parallel and / or after assigned to a multiplex method and queried.

When reading in, time-stable polarized domains are created in the polymer layer. The written remanent polarization is, however, caused by free charge carriers (Electrons and holes) shielded, so that almost no external electrical Field penetrates. For this reason, the system must be disrupted to temporarily cancel the shielding effect of the compensation charges. For this purpose, the polymer layer is briefly heated during the readout process Pyroelectrically activated. The spontaneous polarization decreases, so that due to the then existing overcompensation an external field against the polarization field occurs that is used as a signal field.

A strip matrix is preferred as the electrode system.

by a multitude of electrically conductive, parallel strips uaf the top and bottom of the polymer layer is formed. With one like that Built-up memories can advantageously be those of a single conductor track polarized domains of the polymer layer assigned to the strip matrix simultaneously pyroelectrically activated by a heating current pulse flowing in this conductor track will. In this way, the polarized regions assigned to the conductor track be queried at the same time and then by changing over to another conductor track the corresponding other areas are activated, so that a total of a selective parallel readout mode is enabled.

Surprisingly, it has been found that for pyroelectric activation of the polymer layer, extremely low thermal powers are sufficient. That's enough E.g. a heating output of 10 7 watts for global activation of the entire memory. The written information, i.e.

the polarization state of the polymer layer also remains during activation preserved unchanged. The remanently polarized polymer layer therefore sets Storage system with high time stability and high recording density. So exists For example, the known problem of j-radiation in Si memories and its influence in the form of bit errors is particularly noticeable with high storage density and requires complex correction procedures for the memory described here not. The memory can be deleted by applying a Alternating field of decreasing amplitude take place.

For pyroelectric activation when reading out, in principle the same electrode matrix can be used that is used to read in the information. Of course, separate conductor tracks can also be used for short-term global or local heating of the polymer layer is provided by means of a heating current pulse will.

Alternatively, the method according to the invention can also be carried out in this way that a dot matrix is used as the electrode system and all polarized Domains of the polymer layer globally by electromagnetic radiation or by one in the electrode system impressed heating current pulse pyroelectrically activated and the induced signals read out in parallel. pre-condition is, however, that all contacts of the dot matrix with individual connections are provided. The evaluation and assignment of the signals read out can then in turn done with a multiplexer. Another way of signal processing at global pyroelectric activation by means of electromagnetic radiation or Joule heat is that the induced signals using time of flight analysis read out in parallel and assigned to the storage elements (domains) of the polymer layer will. Has as a radiation source for brief heating of the polymer layer a commercially available flashlight has proven itself.

The storage materials used are advantageously polymers with easily polarizable atoms, for example polyolefins with fluorine atoms such as the polyvinylidene fluoride PVDF with the monomer formula or polymers with strongly polarizable end groups are used, for example polyolefins with cyano groups such as polyvinylidenecyanide with the monomer formula It turns out that an optimization of the technical storage parameters such as coercive force, polarization voltage, squareness of the hysteresis curve, among other things, can be achieved by copolymerization or by blending with other polymers. For example, instead of PVDF, copolymers of PVDF with PVF3 or blends with polymethyl methacrylate PMMA are more suitable; Instead of polyvinylidene cyanide, copolymers of polyvinylidene cyanide with polyvinyl acetate, among others, are more suitable

For the method according to the invention, films with a density between 0.1 and 2 #m preferred.

Films suitable for this purpose with high isotopic properties and a high degree of orientation the molecular chains are obtained when the polymer is taken from a solution between glass plates evaporated into films or the copolymer under the action of an electric field solidified from a melt or evaporated from a solution. Through appropriate The choice of process parameters can include the important data of the polymer film, such as the coercive force, the squareness of the hysteresis curve and the pyroelectric Constant, to be set.

The data memory required for the method according to the invention is characterized by a simple structure and a high level of operational reliability the end. The comb electrode system ensures adequate selectivity with regard to the storage elements defined by the intersection points of the strips. Likewise, only the addressed storage elements (domains) are read out. addressed. Interference phenomena between neighboring districts are avoided.

A further development of the data memory is characterized by that several polymer layers with their electrode systems on top of each other like a grid are arranged, optionally with insulating intermediate layers, so that a three-dimensional Memory block is formed.

The following advantages are achieved with the method according to the invention: - It has been shown that a very stable electrical polarization within Small volumes can be generated, i.e. high storage densities can be achieved with long Lifetime can be achieved.

- Even small temperature changes are sufficient for pyroelectric activation and i.e. low heating power in order to generate easily measurable readout potentials.

- Due to the small dielectric constant of the one described above Copolymers are given a high when read out by means of pyroelectric activation Output voltage and therefore a good signal-to-noise ratio.

- Thin, resistant films can be made from this copolymer whose data are physically optimized with regard to the intended use can (e.g. by stretching, by annealing, if necessary in an electric field, and by adjusting the layer thickness).

- The information can either be in the form of binary signals (polarization state 0 or 1 or also -1 and +1) or analogously. With analog storage a polarization is generated in each memory cell, the value of which corresponds to the respective Corresponds to the signal amplitude.

In the following the invention will be explained with reference to drawings and exemplary embodiments explained in more detail.

They show: FIG. 1 the reading-in and reading-out principle in one with one Electrode system provided polymer storage, Fig. 2 the time dependence of the the readout signal generated the pyroelectric effect.

The polymer memory according to FIG. 1 consists of a 1 .mu.m thick, largely uniaxially oriented film 1, made of a copolymer of polyvinylidenecyanide and Polyvinyl acetate, the molecular chains of which are largely parallel to surface are directed. The opposite surfaces of the film 1 are provided with an electrode system contacted.

The electrode system consists of an electrode matrix 2 and 3 on the top and bottom of the film 1. The electrode matrix 2 itself consists from a plurality of parallel strips 21 ... 2n, r the electrode matrix 3 from one analog strip system 31 3m ', however, with the strips 21 ... 2n an angle of 900C. The electrode system 2, 3 corresponds to an X-Y coordinate network in the film level. All strips are provided with connectors. Through a A memory cell 4 is defined in each case at the intersection of the strips. When reading all intersection points can either be addressed in parallel on one electrode or selectively only a few memory areas are occupied or changed.

The strips consist e.g. of gold, aluminum or nickel and are applied directly to the foils by vapor deposition, sputtering or photochemical means.

The strip width is approx. 1 m and the distance between the strips varies depending on the desired storage density between 1 µm and 1000 µm.

A signal is read in in such a way that, for example, the electrodes 24 and 33 a DC voltage U is applied. This will make the one at the intersection area 4 (dotted cuboid) lying on electrodes 24/33 is remanently polarized; i.e. the polarization is retained even after the voltage is switched off. the The electric field strength required for reading is in the Order of magnitude MV / cm, i.e. the required voltage U is one film thickness of 1 m in the order of 100 V. The spatial extent of area 4 is directly correlated with the stripe width, so that e.g. with a stripe width and a strip spacing of 1 µm, a storage density of 108 bits / cm2 in binary code is achieved. The binary code is generated by changing the sign of the remanent polarization, i.e. realized by reversing the polarity of the voltage U. However, it is also a record based on the polarization states O (no polarization) and 1 (full polarization) possible. In addition, it was found that a quasi-analog recording through Loading of the electroder.m! Atrices with variable voltage is possible. In this case, the individual memory cells become retentive to different degrees polarized.

For reading the stored in the form of polarization states Information, the same electrode system 2, 3 is used. However, it is not possible to determine the polarization states of the intersections of the strips 21 ... 2m, 31 ### 3m defined memory cells can be queried directly, since the polarization charges be shielded by free charge carriers (electrons and holes), so that after there is no external electric field. This equilibrium becomes polarized in a Domain disturbed by brief heating, this results in the relevant electrodes a potential different from 0. This effect is used for reading out. the thermal activation of a storage cell in a ferroelectric Recording medium is called pyroelectric activation. A sufficient one Pyroelectric activation is obtained at a temperature increase of just a few degrees C. For this purpose, as indicated in Fig. 1, the strip 33 is briefly covered with a Heating current pulse applied (heating circuit 5), so that through the length of the strip generated electrical power the entire area located above this strip is heated in the polymer film. Here, the Joule heating power is increased the film thickness and the distance between the electrodes so matched that exclusively the addressed areas are heated significantly. At the crossing points of the The strips 33 with the strips 21 to 2n are then those with the heating current pulse correlated signals induced in the relevant electrode pairs, which are parallel can be registered. In Fig. 1 is for the sake of clarity only for the memory cell 4 lying between the electrodes 24 and 33 is an evaluation circuit 6 drawn.

After the information that is generated in parallel has been sent to the central processing system 6 has been supplied, is switched to the strip 32 by means of a multiplexer 7, so that then the n-bits stored in the intersection of 32 with 21 to 2n can be queried.

To clarify the pyroelectric readout is in the upper part of Fig. 2 the heating current pulse (pulse duration tH) and in the lower Part of the resulting voltage (e.g. at memory cell 4) as a function depicted in time. In our example, the temperature increased with tH = 1.10 # 6 sec of approx. 30C is achieved and voltages of approx. 1 V are observed. The registered rise time is in the 10 ## 9 seconds range, so that from this time and the multiplexer time The resulting access time is also in the 10 ## 9 seconds range.

For pyroelectric activation by means of a heating current pulse the same electrode system was used here that was used to query the stored Information serves. Of course, the heating can also be carried out by separately applied Conductor tracks take place. In this case, the polymer data storage contains the Electrode matrices 2 and 3 still have a separate heating wire system.

Instead of a strip system 2, 3, a dot matrix can also be used individual connections can be vapor-deposited onto the polymer surface.

Another method of thermoelectric activation is to that the activation energy is not generated by Joule heat, but by electromagnetic radiation. In practice, one proceeds in such a way that one takes the entire Memory area illuminated with a flash and the stored signals parallel can be read out. In this case, if a polymer data Storage with a dot matrix used as the electrode system, the memory cells can with Using the multiplexer can be addressed selectively. When running the data store with a strip matrix as the electrode system is a direct assignment of the read out Signals to the individual storage elements not possible.

An assignment of the information content to the individual memory cells but can be achieved if the triggered signal pulses a transit time analysis be subjected.

In the case of excitation with light, in addition to thermal excitation, a direct photoelectric excitation take place due to an internal photo effect. However, it has not yet been clarified to what extent such an effect is technically decisive Role play.

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Claims (8)

Claims 1. Method for reading in and reading out binary or analog electrical signals using a data memory based on a electrically polarizable polymer layer contacted with an electrode system, the signals to be recorded in local domains during the reading process is remanently polarized and activated pyroelectrically during the readout process, characterized in that the pyroelectric activation with or immediately takes place before the readout process in such a way that simultaneously a large number of the polarized Domains in the electrode system induce signals that are then parallel and / or after assigned to a multiplex method and queried. 2. The method according to claim 1, characterized in that the one assigned to a single conductor track of the electrode system designed as a strip matrix polarized domains of the polymer layer simultaneously through one in this conductor track flowing heating current pulse are activated pyroelectrically, so that when switching through this conductor track a selectively parallel readout mode by means of a multiplex method is achieved. 3. The method according to claim 1, characterized in that the electrode system a dot matrix is used and all polarized domains of the polymer layer globally by electromagnetic radiation or by a heating current pulse in one conductive Layer or conductor path that is on the opposite of the dot matrix Side of the polymer layer is attached, pyroelectrically activated and the induced Signals are read out in parallel. 4. The method according to claim 1, characterized in that the electrode system a strip matrix is used and that the polymer layer is globally controlled by electromagnetic Radiation is activated pyroelectrically and the induced signals by means of time-of-flight analysis can be read out in parallel. 5. The method according to claim 1 to 4, characterized in that a Polymer layer made of a polymer with strongly polarizable end groups, preferably Polyolefins, containing cyano groups or fluorine atoms is used. 6. The method according to claim 1 to 5, characterized in that polymer layers with a thickness o ßm, preferably with a thickness between 0.1 and 2 to be used will. 7. The method according to claim 1 to 6, characterized in that the electrical signals read into the polymer layer by applying the Electrode system can be deleted with an alternating voltage of decreasing amplitude. 8. The method according to claim 1 to 7, characterized in that several electrically polarizable Polymer layers with their electrode systems Arranged one above the other and assembled into a three-dimensional memory block will.