PHASE CHANGE STORAGE

Description

Technical area

[0001] The invention relates to a phase change memory for the non-volatile storage of binary contents, which stores the information electrically and / or optically non-volatilely by locally switching a material between an amorphous and a crystalline phase, wherein the state with respect to the electrical conductivity of the material and / or with respect to the reflection properties of the material determines the information content of the phase change memory.

[0002] Furthermore, the invention relates to a method for a phase change memory for the non-volatile storage of binary contents, which stores the binary contents electrically and / or optically non-volatilely by locally switching a material between an amorphous and a crystalline phase, wherein the state with respect to the electrical conductivity of the material and / or with respect to the reflection properties of the material determines the information content of the phase change memory. Description

[0003] Phase-change memories (PCMs) alternate between amorphous and crystalline structures. They can be used, for example, as energy or data storage devices. Here, phase-change memories are considered as data storage devices for binary content or digital information.

[0004] A distinction is made between volatile and non-volatile data or working memories in electronic units, such as microprocessor-controlled electronic data processing systems or computers. Volatile memories, such as semiconductor memories with direct access, also called RAM (Random Access Memory), have the property that they lose their stored contents as soon as the power is switched off. The memory contents are therefore only temporarily stored in the memory. A non-volatile memory such as ROM (Read-Only Memory), EPROM (Eraseable-Programmable ROM) or EEPROM (Electrically Eraseable Programmable ROM), on the other hand, retains its contents even after the power is switched off.

[0005] Non-volatile memory also includes magnetic data tapes, floppy disks, and hard disks, which store their data electromagnetically on a magnetizable storage medium. Optical storage media that store data in a non-volatile manner include CDs and DVDs. Flash memory is also worth mentioning as a non-volatile digital semiconductor component. Writing or saving information to such digital storage media always takes a certain amount of time.

[0006] The storage time depends particularly on the respective switching times of the storage media. These switching times are influenced not only by the material properties themselves but also by temperature, for example. The more or faster switching processes occur, the more heat is generated by the components, and the slower the switching processes of the storage device often become unless the heat is dissipated. Semiconductor components in particular are highly temperature-dependent and therefore usually require relatively intensive cooling.

[0007] To increase the speed of non-volatile storage media, new memory concepts have been developed, such as the phase-change memory (PCM) mentioned above. Phase-change memory, as mentioned above, is now in mass production and used in computers. Intel Corporation offers such phase-change memory under the name "Intel Optane®".

[0008] Phase-change memory takes advantage of the fact that a material exhibits different optical and / or electrical properties in its amorphous and crystalline phases. By applying two electrodes, a current pulse can be applied to the material of the phase-change memory. When the material is subjected to a relatively high current pulse, heat is generated, causing the crystalline material to change into the amorphous phase. After the pulse ends, the material cools very quickly. The material therefore remains in the amorphous state and does not revert to the crystalline phase. The conductivity is significantly poorer in the amorphous state than in the crystalline state of the material.

[0009] The crystalline state is often referred to as the "SET state." The material returns from the amorphous state to the set, crystalline state by being exposed to a longer, relatively low current pulse. The process from the amorphous to the crystalline state can thus be reversed by adjusting the duration and amplitude of the current pulse. This heats the amorphous material above the crystallization temperature and maintains it at this temperature until crystallization occurs. The material thus forms a memory cell whose phase state defines its binary content.

[0010] To read the information, a voltage is applied across such a resistive memory cell, resulting in such a low current that the temperature in the material does not reach the level necessary for a phase change. Depending on the state, a different current flows, which is used for reading. This allows a binary state to be defined via the resistance of the memory cell. In the crystalline state, the "SET state" is defined, a binary "one," and in the amorphous state, a binary "zero." Many such memory cells are used to form non-volatile digital memory for data processing systems with microprocessors. State of the art

[0011] DE 10 2008 016 522 A1 discloses a memory cell. The memory cell described therein comprises a first electrode and a second electrode. Furthermore, a composite material is provided, wherein the composite material electrically connects the first electrode to the second electrode and contains a phase-change material and a resistor material. At least a portion of the phase-change material is capable of responding to the application of a switching signal to the first and / or the second electrode, so that a switch can be made between a substantially crystalline phase and a substantially amorphous phase. The resistor material has a resistivity that is lower than that of the phase-change material when the phase-change material is in the substantially amorphous phase.

[0012] A switchable semiconductor component is known from US 3 271 591 A. The semiconductor materials used for the semiconductor elements can be constructed in various ways. Semiconductor materials that are amorphous in the off-state and in which at least one path serving for current flow is crystalline in the conducting state serve as storage types. Semiconductor materials that can be either crystalline or amorphous in the off-state serve as non-storage switching types. However, the semiconductor is in either the n-conducting or the p-conducting state. The solid-state semiconductor materials can be selected such that they have an intermolecular

[0013] Band structure with a large number of charge carrier traps thanks to disturbed chain or ring structures or disturbed atomic structures, which can be produced by treatment in the same or different ways, such as using impure materials, adding impurities, depositing on sublayers, incorporating oxides into the mass and / or into the surface or interfaces, mechanically by machining, sandblasting, beating, bending, etching or ultrasonic treatment or producing physical lattice deformations by metallurgical measures, such as heating and rapid quenching, etc.

[0014] DE 21 38 581 A1 discloses a storage material with an amorphous and crystalline structure. Typical shape, form, and position changes of the storage material can be included, e.g., changes from a generally amorphous state to a more ordered or crystalline state, which may include various crystalline states, or vice versa. The layer of storage material is equipped with a catalytic material capable of relatively increasing the internal prestressing forces (the crystallization forces) and reducing the internal inhibiting forces against the action of the prestressing forces (the crystallization-inhibiting factors) when the storage material is activated. When energy is supplied to the storage material layer, the catalytic material is activated in parts of the layer and changes these parts of the layer, transforming them from one of the detectable structural states to another.Some activated catalytic materials can primarily increase the internal prestressing forces, while others primarily reduce the internal inhibiting factors against the action of the internal prestressing forces. The catalyst material can also control the number of nuclei and the size of the crystals formed at them. The applied energy can be electrical energy, radiant energy, electron beam energy, electromagnetic energy (including heat), visible light or ultraviolet energy, acoustic energy, mechanical stress or pressure energy, chemical energy, or the like, as well as a combination of these energy forms.

[0015] US 2010 / 073997 A1 describes a piezoelectrically programmed, non-volatile memory cell structure. Phase-change material can be converted between two discrete states, amorphous (high electrical resistance) and crystalline (low electrical resistance), enabling data storage. The conversion or writing process for these exemplary materials is achieved by thermal cycling of the phase-change material. The memory cell structure includes a programmable piezoresistive hysteretic material (PRHM) that can be converted to a low-resistance and a high-resistance state. A piezoelectric material is mechanically coupled to the PHRM.

[0016] By applying a voltage to the piezoelectric material, either a tensile or compressive stress is exerted on the PRHM, depending on the polarity of the applied voltage. One or more electrodes are electrically connected to the PRHM. The one or more electrodes are configured to provide a write-programming current path through the piezoelectric material and a read current path through the PRHM.

[0017] DE 10 2017 208 205 A1 relates to a filter element with a variable filter area. The filter element comprises a filter layer embodied as a composite of a piezoelectric material acting as an acoustic resonator and a phase-change material. The phase-change material is designed to change between at least a first phase and a second phase depending on the temperature, wherein the filter layer has a different transmission characteristic in the first phase state than in the second phase state. Furthermore, the filter element comprises a heating layer for changing a temperature of the phase-change material.

[0018] The current phase-change memories have the disadvantage that, despite their advantages, they are still too slow. Non-volatile memories that are significantly faster than, for example, flash memory modules are desirable. While known phase-change memories, such as the 3D Xpoint "Intel Optane®<", are considerably faster, even this switching speed is insufficient for some applications. Phase-change memories are limited in their switching speed due to their crystallization speed. Disclosure of the invention

[0019] The object of the invention is therefore to avoid the disadvantages of the prior art and to provide a phase change memory for data processing systems whose switching times are considerably shortened.

[0020] The invention is defined in the appended claims 1 to 5.

[0021] According to the invention, the object is achieved in that, in a phase change memory configured for the non-volatile storage of binary contents of the type mentioned at the outset, an ultrasonic generator with a piezoelectric unit is provided which, at least during the switching process, exposes the phase change material to ultrasound and thus accelerates the switching process.

[0022] Furthermore, the object is achieved by a method for a phase change memory for the non-volatile storage of binary contents of the type mentioned at the outset, in which ultrasound is generated, with which the phase change material is acted upon at least during the switching process and thus accelerates the switching process, wherein the ultrasound is generated with a piezoelectric unit.

[0023] The invention is based on the principle that ultrasound, i.e., mechanical waves, can significantly accelerate the transition from the amorphous to the crystalline phase of a phase-change material. This exploits the phenomenon of beta relaxation in phase-change materials. This phenomenon of beta relaxation means that amorphous materials exhibit faster atomic or particle movements, which differ in timescale from typical relaxation processes. Current experiments show that the switching process can be accelerated by a factor of 10, i.e., by an order of magnitude. The influence of ultrasound thus significantly accelerates the switching process.

[0024] An advantageous embodiment of the phase-change memory according to the invention consists in providing control means for variably adjusting the frequency of the ultrasound. In this way, the frequency can be optimized, for example, for the material used. Preferably, the control means can adjust the frequency of the ultrasound depending on the temperature. The temperature of the phase-change material has a significant influence on the switching process. In this case, it may be necessary to coordinate the temperature and ultrasound frequency to optimize the switching process.

[0025] A particularly preferred embodiment of the phase change memory according to the invention for the non-volatile storage of binary contents consists in that several phase stages of the phase change material are provided between the amorphous and crystalline phases for multi-stage switching for storing contents.

[0026] This embodiment is explained in more detail below with reference to the accompanying drawings. The invention is not intended to be limited to this embodiment alone. It merely serves to explain the invention in more detail.

[0027] The scope of the present invention is defined by the appended claims 1-5. Short description of the drawing

[0028] Fig. 1 shows the structure of a phase change memory according to the invention with an ultrasonic generator. Preferred embodiment

[0029] In Fig. 1The phase-change memory according to the invention is designated by 10. The phase-change memory 10 comprises a first electrode 12 and a second electrode 14. A layer 16 of a phase-change material 18 is provided between the electrodes 12, 14. The electrode 12, the phase-change material 18, and the electrode 14 form a first functional region 20 of the phase-change memory 10 and is identified by a curly bracket. This first functional region 20 is arranged on an insulating layer 22 belonging to this functional region 20.

[0030] A second functional region 24, also indicated by a curly bracket, comprises an ultrasonic generator 26. This second functional region 24 borders the insulating layer 22 of the first functional region 20. The ultrasonic generator 26 consists of a piezocrystalline layer 28, which is controlled by two additional electrodes 30, 32. An insulating layer 33 and a third functional region 34 border the piezocrystalline layer 28.

[0031] The third functional region 34 comprises a heating layer 36 and two electrodes 38, 40. The third functional region is represented by another curly bracket. The heating layer 36 is operated via the two heating electrodes 38, 40. This third functional region contains a silicon oxide layer 42 and is closed by a substrate layer 44.

[0032] The electrodes 12, 14 switch the phase change material 18 depending on the current pulse and its duration.

[0033] The phase-change memory 10 takes advantage of the fact that the phase-change material 18 has different electrical properties in the amorphous and crystalline phases. The electrical resistance is considerably greater in the amorphous state than in the crystalline state of the phase-change material 18. A current pulse is applied to the phase-change material 18 of the phase-change memory 10 via the two electrodes 12, 14. When the phase-change material 18 is subjected to a relatively high and short current pulse, it changes from the crystalline to the amorphous phase. After the end of the current pulse, the phase-change material 18 cools very quickly. The phase-change material 18 remains in the amorphous state and does not revert to the crystalline phase.

[0034] The phase change material 18 returns from the amorphous state to the crystalline state by being exposed to a longer, relatively low current pulse. The process from the amorphous to the crystalline state can thus be reversed over the duration of the current pulse. As a result, the amorphous material is heated above the crystallization temperature and maintained at this temperature until crystallization occurs. The process is accelerated by subjecting the phase change material 18 to ultrasound, at least during the individual switching processes. The ultrasound generator 26, with the piezoelectric layer 28, generates an ultrasound field tailored to the phase change material 18, which acts on the phase change material 18 and stimulates it accordingly. The switching process of the phase change material 18 is thereby considerably accelerated.Since the switching process of the phase-change material 18 is particularly temperature-dependent, the ultrasound is picked up differently. Therefore, control means (not shown here) are provided to optimize the frequency of the ultrasound with respect to the temperature of the phase-change material 18.

[0035] The binary information contained in such a phase-change memory 10 is read out via a voltage applied, for example, across the electrodes. Depending on the state—amorphous or crystalline—of the phase-change material 18, a different current flows, which is then used for reading. This allows a binary state to be defined via the resistance of the phase-change memory 10. The crystalline state is assigned a binary "one," and the amorphous state a binary "zero." List of reference symbols

[0036] 10Phase change memory 12First electrode 14Second electrode 16Layer 18Phase change material 20First functional area 22Insulating layer 24Second functional area 26Ultrasonic generator 28Piezocrystalline layer 30Electrode for ultrasonic generator 32Electrode for ultrasonic generator 33Insulating layer 34Functional area 36Heating layer 38Electrode for heating layer 40Electrode for heating layer 42Silicon oxide layer 44Substrate

Claims

1. Phase-change memory (10) configured for non-volatile storage of binary contents, the phase-change memory storing the binary contents electrically and / or optically in a non-volatile manner by locally switching a phase-change material (18) between an amorphous and a crystalline phase, wherein the state with respect to the electrical conductivity of the phase-change material (18) and / or with respect to the reflection properties of the phase-change material (18) determines the information content of the phase-change memory (10), characterized in that an ultrasonic generator (26) with a piezoelectric unit (28) is provided, said ultrasonic generator exposing the phase-change material (18) to ultrasound at least during the switching process and thus accelerating the switching process.

2. Phase-change memory (10) for non-volatile storage of binary contents according to Claim 1, wherein a control means is provided for variably setting the frequency of the ultrasound.

3. Phase-change memory (10) for non-volatile storage of binary contents according to Claim 2, wherein the control means set the frequency of the ultrasound in a manner dependent on temperature and / or material.

4. Phase-change memory (10) for non-volatile storage of binary contents according to any one of Claims 1 to 3, wherein a plurality of phase stages of the phase-change material (18) are provided between the amorphous and crystalline phase for multi-stage switching for storing contents.

5. Method for a phase-change memory (10) for non-volatile storage of binary contents, the phase-change memory storing the binary contents electrically and / or optically in a non-volatile manner by locally switching a phase-change material (18) between an amorphous and a crystalline phase, wherein the state with respect to the electrical conductivity of the phase-change material (18) and / or with respect to the reflection properties of the phase-change material determines the information content of the phase-change memory (10), characterized in that ultrasound is generated, to which the phase-change material is exposed at least during the switching process and this thus accelerates the switching process, wherein the ultrasound is generated using a piezoelectric unit (28).