A multi-resistance magnetic device and its preparation method and application

Abstract

The present invention relates to a multi-resistance magnetic device and its preparation method and application, and the free layer of the magnetic device is specially processed: (1) the free layer is grown in a splicing manner, the splicing part is composed of different ferromagnetic materials, and the above-mentioned magnetic device is arranged at the splicing position; (2) the free layer is composed of a single ferromagnetic material, but impurities are uniformly added on the surface of the free layer and away from the barrier layer or the space layer, and the impurities are used to make the magnetic domains of the free layer autonomously divided. The two processing methods can realize the multi-resistance state characteristics of the device, which means that one device can store more than one bit of information, and multiple devices can realize more random number combinations. The present invention can be controlled by all electrical means, and has the advantages of multiple resistance values, randomness, strong scalability, low energy consumption, and compatibility with CMOS processes. It only needs to be slightly improved on the basis of the existing device preparation process, effectively reducing the manufacturing cost of devices, arrays and chips composed of them.

Description

Technical Field

[0001] The invention belongs to the field of information storage, and in particular relates to a multi-resistance magnetic device and a preparation method and application thereof. Background Art

[0002] In recent years, with the steady advancement of the information process, more and more production equipment, work accessories, and household appliances have become intelligent, and urgent problems have also emerged - how to quickly and stably store such a large amount of data information for a long time and how to protect the key technologies, core secrets, and personal privacy of this information from being leaked. In response to the requirements for information storage, people mainly change the original structure process or develop new storage technologies to obtain high-integration, stable storage, fast reading and writing, low energy consumption, strong erasing and writing capabilities, and non-volatile memories, such as MRAM (Magnetic Random Access Memory: magnetic random access memory), RRAM (Resistance Random Access Memory: resistance random access memory), etc. These memories are mostly used to store binary information. In response to the requirements of storage security, people have developed pseudo-random number generators generated by programming software, but the random numbers generated by this type of generator still have a certain predictable regularity and lack a safety factor. Although the safety factor of CMOS true random number generators based on natural random signal sources such as thermal noise, oscillator frequency jitter, and optical noise has been improved, they generally occupy a larger area and have low efficiency in random number generation.

[0003] Based on the above background, people have paid more attention to magnetic devices such as magnetic tunnel junction (MTJ) and spin valve. On the one hand, this is because such magnetic devices are the indispensable basic storage units of contemporary MRAM, and the preparation process is relatively mature. On the other hand, it is also because of the random characteristics of the devices themselves. First of all, starting with the structure of such devices, we will introduce them in detail. According to the different writing methods, the above magnetic devices can be mainly divided into STT (Spin Transfer Torque: spin transfer torque) magnetic devices and SOT (Spin Orbit Torque: spin orbit torque) magnetic devices, such as Figure 1. By comparison, it can be found that there are differences in the traditional manufacturing processes of the two. The STT magnetic device is composed of a lower electrode, a buffer layer, a pinned layer, a reference layer, a barrier layer or a space layer, a free layer, a covering layer, and an upper electrode grown on the substrate surface from bottom to top, while the SOT magnetic device uses the spin current generating layer as the lower electrode, and requires the free layer to be adjacent to the spin current generating layer, and then grows a barrier layer or a space layer, a reference layer, a pinned layer, a covering layer, an upper electrode and other parts thereon. However, the core components of this type of device are the same - the reference layer, the barrier layer or the space layer, and the free layer. The first part is composed of a single or multiple ferromagnetic layers and a coupling layer between the ferromagnetic layers. The magnetic moment of the ferromagnetic material is firmly fixed by the pinned layer; the second part can be composed of an insulating oxide or a conductive metal, which is closely related to the size of the magnetoresistance effect; the third part is often composed of a single or double ferromagnetic layer and a coupling layer between the ferromagnetic layers, and the direction of its magnetic moment is variable, such as Figure 2 (According to the different magnetic anisotropies of the free layer and the reference layer magnetic moments, the above devices are subdivided into STT magnetic devices with in-plane magnetic anisotropy, STT magnetic devices with perpendicular magnetic anisotropy, SOT magnetic devices with in-plane magnetic anisotropy, and SOT magnetic devices with perpendicular magnetic anisotropy).

[0004] The free layer and the reference layer are usually single domains, and remain consistent during the magnetic moment reversal of the free layer. Therefore, based on the giant magnetoresistance effect or tunnel magnetoresistance effect, this type of magnetic device has two main resistance states: when the magnetic moment directions of the free layer and the reference layer are consistent, the device presents a stable low resistance state, which can represent the binary logic state "0"; conversely, when the magnetic moment directions of the two are opposite, the device presents a stable high resistance state, which can represent the binary logic state "1", such as Figure 3 . It can be seen that a magnetic device has one bit of information storage capacity, which is the storage principle of this type of device. On the other hand, the free layer magnetic moment has a random flipping characteristic, that is, when the upper and lower electrodes of the STT magnetic device are applied (but less than its breakdown voltage), the free layer magnetic moment has a certain probability of flipping, such as Figure 4 The voltage (or current) pulse amplitude or polarity is regulated by a reciprocal external circuit to keep the probability of magnetic moment reversal of the free layer at 50%. That is, when the regulated pulse voltage or pulse current is input, the probability of the device resistance being in the high resistance state and the low resistance state is the same. This is the principle of generating true random numbers. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a multi-resistance magnetic device and a preparation method and application thereof, wherein a free layer is spliced ​​out by different magnetic materials or impurities are uniformly added to the surface of a free layer composed of a single magnetic material and away from a barrier layer or a space layer, and a preparation method for an array of such devices is provided, so as to reduce the preparation cost and writing energy consumption as much as possible; in addition, the device can be embedded in a traditional CMOS logic circuit or a probability control feedback circuit, so as to increase the information storage capacity of the memory or improve the quality of the random number sequence.

[0006] The present invention provides a first multi-resistance magnetic device, wherein the free layer thickness of the magnetic device is uniform and is composed of two or more ferromagnetic materials spliced ​​together; one or more of the magnetic moment size, damping coefficient or magnetocrystalline anisotropy of different ferromagnetic materials are different; the magnetic moments of different ferromagnetic materials are regarded as single domains, and they follow a consistent flip when flipped; the contact resistance at the joint of different ferromagnetic materials is greater than the contact resistance at other positions (at least 5 times the contact resistance at other positions), so that current flows through other positions.

[0007] The ferromagnetic material includes at least one of Co, Fe, Ni, Mn, Rh, Pd, Pt, Gd, Tb, Dy, Ho, Al, Si, Ga, Ge, Zr, Hf and B; different ferromagnetic materials can be selected from the above alloy materials with different atomic percentages, such as Co 40 Fe 40 B 20 、Co 60 Fe 20 B 20 、Co 20 Fe 60 B 20 Etc., different alloys can also be selected, such as FePt, FePd, CoPt, CoHf, CoTb, etc.

[0008] The thickness of the free layer is 1-2 nm and does not exceed 2.5 nm.

[0009] The magnetic device further includes a barrier layer, a spacer layer or a spin current generating layer.

[0010] The barrier layer may be made of AlO x , Al2O3, MgO and other insulating materials; the space layer can be composed of materials with a large spin diffusion length such as Cu; the spin current generating layer can be composed of materials with a large spin Hall angle such as Ta, W, Mo, Pt, Pd, Ir, Ru, Nb, FeMn, IrMn, PdMn, PtMn, Bi2Se3 and other materials.

[0011] The device may be in the shape of a cylinder, an elliptical cylinder, an irregular cylinder, a cube, a cuboid, etc.

[0012] The present invention also provides a method for preparing a first multi-resistance magnetic device and an array thereof, comprising the following steps:

[0013] The multi-resistance magnetic device is an STT multi-resistance magnetic device;

[0014] (1) According to the conventional magnetic device preparation process, the thin film parts of the lower electrode, buffer layer, pinning layer, reference layer, barrier layer or spacer layer are prepared by using magnetron sputtering technology, electron beam evaporation technology or pulsed laser deposition technology;

[0015] (2) Spin-coating a photoresist on the above-mentioned part, and then using photolithography technology to carve out a first area where the first type of magnetic material is to be grown, and then washing away the photoresist attached to the area with a developer, and covering the remaining part with the photoresist;

[0016] (3) growing the first type of magnetic material into the region using magnetron sputtering technology;

[0017] (4) using a stripping solution to clean the excess photoresist;

[0018] (5) Spin-coating a photoresist on the above-mentioned portion, and then using photolithography technology to carve out a second region where the second type of magnetic material is to be grown, and then washing away the photoresist attached to the region with a developer, and covering the first region with the photoresist;

[0019] (6) growing a second type of magnetic material into the region using magnetron sputtering technology;

[0020] (7) Using a stripping solution to wash away excess photoresist, the free layer growth is completed, and the thickness of the free layer in different areas is ensured to be the same;

[0021] (8) Using magnetron sputtering technology, continue to grow a cover layer film portion on the free layer film;

[0022] (9) performing annealing treatment on the multilayer film;

[0023] (10) etching a magnetic device and a device array at the junction of the first region and the second region through a micro-nano processing technology, and preparing a corresponding lower electrode;

[0024] (11) exposing the top of the device array by insulating dielectric filling, planarization or opening technology;

[0025] (12) growing the upper electrode thin film portion using magnetron sputtering technology;

[0026] (13) preparing the corresponding upper electrode through micro-nano processing technology;

[0027] Alternatively, the multi-resistance magnetic device is a SOT multi-resistance magnetic device, and the free layer film is prepared by referring to steps (2) to (7).

[0028] The present invention also provides a second multi-resistance magnetic device, wherein the free layer of the magnetic device is composed of a single ferromagnetic material, impurities are uniformly added to the surface of the free layer and away from the barrier layer or the space layer, and the impurities are used to make the magnetic domains of the free layer autonomously divided.

[0029] The impurities are magnetic particles, non-magnetic particles or clusters.

[0030] The device may be in the shape of a cylinder, an elliptical cylinder, an irregular cylinder, a cube, a cuboid, etc.

[0031] The present invention also provides a second method for preparing a multi-resistance magnetic device and an array thereof, comprising the following steps:

[0032] The multi-resistance magnetic device is an STT multi-resistance magnetic device;

[0033] (1) According to the traditional magnetic device preparation process, the thin film parts of the lower electrode, buffer layer, pinning layer, reference layer, barrier layer or space layer, and free layer are prepared by using magnetron sputtering technology, electron beam evaporation technology, or pulsed laser deposition technology;

[0034] (2) The impurities are uniformly attached to the surface of the free layer by lightly sputtering the impurities or wrapping the impurities with organic matter, and the spacing between the impurities is 5-500 nm;

[0035] (3) Using magnetron sputtering technology, continue to grow a cover layer film portion on the free layer film;

[0036] (4) annealing the multilayer film;

[0037] (5) Etching magnetic devices, device arrays, and preparing corresponding lower electrodes through micro-nano processing technology;

[0038] (6) exposing the top of the device array by insulating dielectric filling, planarization or opening technology;

[0039] (7) growing the upper electrode thin film portion using magnetron sputtering technology;

[0040] (8) preparing the corresponding upper electrode through micro-nano processing technology;

[0041] Alternatively, the multi-resistance magnetic device is a SOT multi-resistance magnetic device, and the impurities are prepared by referring to step (2).

[0042] The present invention also provides an application of a multi-resistance magnetic device in a multi-state memory.

[0043] The present invention also provides an application of a multi-resistance magnetic device in a random number generator.

[0044] Beneficial Effects

[0045] The present invention can realize the multi-resistance state characteristics of the device through two processing methods, which means that one device can store more than one bit of information, and multiple devices can realize more random number combinations. The present invention can be fully electrically controlled, and has the advantages of multiple resistance values, randomness, strong scalability, low energy consumption, and compatibility with CMOS processes. It only needs to make slight improvements on the existing device preparation process to effectively reduce the manufacturing cost of devices, arrays and chips composed of them. Therefore, its application is more extensive than traditional magnetic devices, especially for polymorphic memories and random number generators. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a schematic diagram of the structure of the STT magnetic device and the SOT magnetic device in the prior art;

[0047] Figure 2 It is a schematic diagram of the core part of the STT magnetic device and the SOT magnetic device in the prior art;

[0048] Figure 3 The resistance states of the STT magnetic device and the SOT magnetic device in the prior art;

[0049] Figure 4 The probability of reversal of the magnetic moment of the free layer when a voltage pulse is applied to the upper and lower electrodes of the STT magnetic device in the prior art;

[0050] Figure 5 This is a schematic diagram of the core part of the first multi-resistance magnetic device of the present invention (taking the splicing of two magnetic materials as an example, it can also be composed of more than two magnetic materials);

[0051] Figure 6 It is a schematic diagram of the connection of the test equipment for the electrical characteristics of the first multi-resistance magnetic device of the present invention;

[0052] Figure 7 A test schematic diagram for obtaining the relationship between the resistance and voltage pulse change of the first multi-resistance magnetic device of the present invention;

[0053] Figure 8 A schematic diagram of a current path generated when a write / read voltage is applied to the first multi-resistance magnetic device according to the present invention;

[0054] Fig. 9 It is a schematic diagram of equivalent resistance of the first multi-resistance magnetic device of the present invention;

[0055] Fig.10 The resistance characteristics of the first multi-resistance magnetic device under ideal conditions of the present invention;

[0056] Fig.11The magnetic moment states of the free layer and the reference layer corresponding to each resistance value of the first multi-resistance magnetic device of the present invention;

[0057] Fig.12 The resistance characteristics of the first multi-resistance magnetic device of the present invention under special circumstances;

[0058] Fig.13 It is a schematic diagram of testing the random reversal characteristics of magnetic moments in different regions of the free layer of the first multi-resistance magnetic device of the present invention;

[0059] Fig.14 The first multi-resistance magnetic device of the present invention has a magnetic moment reversal characteristic in different regions of the free layer;

[0060] Fig.15 It is a schematic diagram of the preparation of the first multi-resistance magnetic device and its array of the present invention;

[0061] Fig.16 A schematic diagram of a gap generated during the preparation of the first multi-resistance magnetic device of the present invention and a solution thereof;

[0062] Fig.17 A schematic diagram of overlap and a solution thereof during preparation of the first multi-resistance magnetic device of the present invention;

[0063] Fig.18 and 19 It is a schematic diagram of the first multi-resistance magnetic device of the present invention, in which the free layer is formed by splicing more kinds of magnetic materials;

[0064] Fig. 20 and 21 Schematic diagram of the core part of the second multi-resistance magnetic device of the present invention (the two have different perpendicular magnetic anisotropies, the former is in-plane magnetic anisotropy, and the latter is perpendicular magnetic anisotropy);

[0065] Fig. 22 is the resistance characteristic of the second multi-resistance magnetic device under ideal conditions of the present invention;

[0066] Fig.23 The magnetic moment directions of the reference layer corresponding to different resistances of the second multi-resistance magnetic device of the present invention;

[0067] Fig.24 The reversal characteristic of the magnetic moment of the free layer of the second multi-resistance magnetic device of the present invention;

[0068] Fig.25 A schematic diagram of the preparation of the second multi-resistance magnetic device and its array according to the present invention;

[0069] Figure 26-28 A method for controlling the number of resistance values ​​or the number of free layer magnetic domains of the second multi-resistance magnetic device of the present invention;

[0070] Fig.29 The invention relates to the application of the multi-resistance magnetic device in MRAM;

[0071] Fig.30 A schematic diagram of a core structural unit of an MRAM composed of a multi-resistance magnetic device of the present invention;

[0072] Fig.31 A voltage pulse implementation scheme for writing information into an MRAM composed of a multi-resistance magnetic device of the present invention;

[0073] Fig.32 A voltage pulse implementation scheme for reading MRAM information formed by a multi-resistance magnetic device of the present invention;

[0074] Fig.33 The invention relates to the application of the multi-resistance magnetic device in a random number generator;

[0075] Fig.34 This is a schematic diagram of the core structural unit of the random number generator composed of the multi-resistance magnetic device of the present invention. DETAILED DESCRIPTION

[0076] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0077] Example 1

[0078] The present embodiment provides a magnetic device that can realize multi-resistance states, wherein the free layer has uniform thickness and is composed of two or more ferromagnetic materials spliced ​​together, and the magnetic properties of each ferromagnetic material are not exactly the same, that is, at least one or more of the magnetic moment size, damping coefficient or magnetocrystalline anisotropy of different ferromagnetic materials are different; in the device, the free layer can be divided into many small parts according to different ferromagnetic materials, and the magnetic moment of each small part can be regarded as a single domain and follows the principle of consistent reversal when it is flipped, but the magnetic moments of different small parts do not interfere with each other during the reversal process; the magnetic moments of the free layer and the reference layer can have in-plane magnetic anisotropy or perpendicular magnetic anisotropy; the contact resistance at the joints of different magnetic materials is large, and it is difficult for current to flow from magnetic material 1 to magnetic material 2 in parallel, and it is also difficult to reach the reference layer from the joint through the barrier layer or space layer; the remaining components can be consistent with traditional magnetic devices. Taking the STT multi-resistance magnetic device as an example, its core structure and the magnetic moment of each part are as follows Figure 5 shown.

[0079] The ferromagnetic material can be made of at least one of Co, Fe, Ni, Mn, Rh, Pd, Pt, Gd, Tb, Dy, Ho, Al, Si, Ga, Ge, Zr, Hf and B. Different ferromagnetic materials can be selected from the above alloy materials with different atomic percentages, such as Co 40 Fe 40 B 20 、Co 60 Fe 20 B 20 、Co 20 Fe 60 B 20 etc., and different alloys can also be selected, such as FePt, FePd, CoPt, CoHf, CoTb, etc.; the thickness of the free layer does not exceed 2.5nm, generally between 1 and 2nm. The barrier layer can be made of AlO x , Al2O3, MgO and other insulating materials, the space layer can be composed of materials with large spin diffusion length such as Cu, and the spin current generating layer can be composed of materials with large spin Hall angle such as Ta, W, Mo, Pt, Pd, Ir, Ru, Nb, FeMn, IrMn, PdMn, PtMn, Bi2Se3, etc.

[0080] The connection diagram of the test equipment for the electrical characteristics of this type of device is as follows Figure 6 As shown in FIG. 1 , when a voltage pulse is applied to the upper and lower electrodes of the STT magnetic device through a pulse voltage source, or a current pulse is applied to the left and right ends of the spin current generating layer of the SOT magnetic device through a pulse current source, as the voltage / current pulse amplitude continues to increase, that is, increases in a positive direction or increases in a negative direction, the free layer magnetic moments of different regions will be successively reversed. During this period, after each pulse signal is sent, the total resistance of the device is measured by a DC voltage source to monitor the change of the total resistance of the device. The above test process is as follows: Figure 7 As shown. It is worth noting that the DC voltage source only needs to provide a small voltage (~mV level, such as 10mV), otherwise it will cause abnormal reversal of the free layer magnetic moment. For STT magnetic devices, during the application of pulse voltage or DC voltage, the pulse current or small DC current will be shunted when it flows through the free layer in different regions and its vicinity, and basically no shunting occurs at other locations; for SOT magnetic devices, during the application of pulse voltage, basically no pulse current flows through the free layer, and during the application of DC voltage, the small DC current will be shunted at the free layer in different regions and its vicinity, and basically no shunting occurs at other locations, such as Figure 8 As shown; in addition, an additional magnetic field can be applied to the device to assist the directional reversal of the free layer magnetic moments in different regions.

[0081] The resistance characteristics of the device are as follows. Taking two ferromagnetic materials as an example, the first region composed of the first material, the first region free layer, barrier layer or space layer, and reference layer can be regarded as variable resistor 1. According to whether the magnetic moment direction of the free layer is consistent with or opposite to that of the reference layer, variable resistor 1 specifically includes low resistance state R1 and high resistance state R2. Preferably, R2 is more than one times of R1. The second region composed of the second material, the second region free layer, barrier layer or space layer, and reference layer can be regarded as variable resistor 2. According to whether the magnetic moment direction of the free layer is consistent with or opposite to that of the reference layer, variable resistor 2 specifically includes low resistance state R3 and high resistance state R4. Preferably, R4 is R3. more than twice; in order to change the variable resistance value, a voltage pulse (or current pulse) higher than the reversal voltage (or reversal current) of the magnetic moment of the free layer in the first / second region must be applied to the device, and the reversal voltages (or reversal currents) of the variable resistor 1 and the variable resistor 2 are different; the constant resistor composed of the pinning layer, the buffer layer, the covering layer, the electrode and other parts, due to its mature preparation process and good conductivity, the constant resistor is much smaller than the variable resistor 1 and the variable resistor 2 (most preferably, more than ten times smaller), the voltage divider effect of this part can be ignored, that is, the total resistance of the device can be approximately regarded as the resistance of two variable resistors in parallel, such as Fig. 9 shown.

[0082] Taking the STT four-resistance magnetic device as an example, assuming that the absolute value of the flip voltage of variable resistor 1 is greater than that of variable resistor 2, and the initial state of the total resistance of the device is resistance value 1 (R1 / / R3: R1 and R3 are connected in parallel), when a negative voltage pulse is applied to the upper and lower electrodes of the device, as the amplitude increases negatively to V1, variable resistor 2 changes from R3 to R4. At this time, the total resistance of the device becomes resistance value 2 (R1 / / R4); as the amplitude continues to increase negatively to V2, variable resistor 1 changes from R3 to R4. R1 changes to R2, at this time, the total resistance of the device changes to resistance value 3 (R2 / / R4); then when the voltage pulse increases in the positive direction to V3, the variable resistor 2 changes from R4 to R3, at this time, the total resistance of the device changes to resistance value 4 (R2 / / R3); as the amplitude continues to increase in the positive direction to V4, the variable resistor 1 changes from R2 to R1, at this time, the total resistance of the device changes back to resistance value 1 (R1 / / R3); as the amplitude continues to decrease in the reverse direction to 0V, the total resistance of the device will not change, such as Fig.10 Correspondingly, taking the in-plane anisotropic STT four-resistance magnetic device as an example, the magnetic moment states of the free layer and the reference layer corresponding to each resistance value are given, as shown in Fig.11 The SOT four-resistance magnetic device also exhibits the above characteristics. Although the interlayer design of its free layer and reference layer is different from that of the STT device, the corresponding relationship between the magnetic moment state and resistance value of the free layer and reference layer is consistent with that of the STT device, which will not be elaborated here.

[0083] From the above, it can be seen that under ideal conditions, the multi-resistance device can exhibit four different resistance states. If the coupling between the free layer and the reference layer is not zero or the free layer is affected by the stray field generated by other ferromagnetic layers, the device resistance may show an abnormal state. In a certain flipping direction (i.e., from high resistance state to low resistance state, or from low resistance state to high resistance state), there will be no intermediate state, such as Fig.12 shown.

[0084] In the process of testing the reversal characteristics of magnetic devices, a single voltage pulse is applied to the device and then the resistance state of the multi-resistance magnetic device is tested. When voltage pulses of the same amplitude and width are repeatedly applied to the device, due to the randomness of the reversal of the magnetic moment of the free layer, it cannot be guaranteed that the magnetic moments of different regions of the free layer will be reversed every time. It should be noted that in the above process, before each voltage pulse is issued, the initial resistance state of the device is the same. For example, the initial state of the multi-resistance magnetic device always remains at a resistance value of 1. After applying a voltage pulse of V1 to the device 10,000 times, the final state of the device may only change to a resistance value of 2 5,000 times, while the remaining 5,000 times remain at a resistance value of 1. At this time, it can be considered that under the action of the V1 pulse voltage, the probability of magnetic moment reversal in the second region of the free layer is 50%. In order to obtain the relationship between the probability of random reversal of magnetic moments in different regions of the free layer in a multi-resistance magnetic device and the voltage pulse amplitude, the following test process is designed, such as Fig.13 As shown in the figure, two voltage pulses (reset pulse + drive pulse) are applied to the upper and lower electrodes of the STT magnetic device through a pulse voltage source, or two current pulses (reset pulse + drive pulse) are applied to the two ends of the spin current generating layer of the SOT magnetic device through a pulse current source, wherein the reset pulse is used to reset the state of the free layer device to the same initial state (resistance value 1 or resistance value 3), and the drive pulse is used to drive the magnetic moments of different regions of the free layer of the device to flip; one cycle includes a reset pulse and a drive pulse, and there is a certain time interval (optionally ~μs order of magnitude) between the two; by applying N cycles (N reset pulses with the same pulse width and amplitude + N drive pulses with the same pulse width and amplitude) to the device, and testing the device resistance with a DC voltage source, or monitoring the device resistance with a current amplifier and an oscilloscope, the probability of magnetic moment flipping in different regions of the free layer under a certain fixed drive pulse voltage or pulse current can be calculated; then, by changing the pulse width, amplitude or polarity of the drive pulse voltage or pulse current, the probability of magnetic moment flipping in different regions of the free layer under another fixed drive pulse voltage or pulse current can be obtained.

[0085] The random reversal characteristics of the free layer magnetic moment of the device are as follows. Taking the STT four-resistance magnetic device as an example, its reversal characteristics are as follows Fig.14As shown. When the initial resistance is always the resistance value 1, as the driving voltage pulse increases negatively to near V1, the magnetic moment of the second region of the free layer begins to flip, that is, the probability that the total resistance of the device is at a resistance value of 2 gradually increases; when the driving voltage pulse increases negatively to a certain value V1 (50%), the probability of the resistance value 2 reaching 50%; when the driving voltage pulse increases negatively to a certain value V1 (100%), the maximum probability of the resistance value 2 reaching a certain value (most preferably, 100%); as the voltage pulse continues to increase negatively to near V2, the magnetic moment of the first region of the free layer begins to flip, that is, the probability that the total resistance of the device is at a resistance value of 3 gradually increases, during which the probability of the resistance value 2 gradually decreases; as the voltage pulse continues to increase negatively to V2 (50%), the probability of the resistance value 3 reaching 50%; as the voltage pulse continues to increase negatively to V2 (100%), the maximum probability of the resistance value 3 reaching 100%, as shown Fig.14 When the initial resistance is always 3, as the voltage pulse increases in the positive direction, the magnetic moment of the second region of the free layer begins to flip first, and then the magnetic moment of the first region of the free layer begins to flip. The whole process is similar to the negative pulse case and will not be described in detail here.

[0086] The preparation method of the magnetic device and array thereof is as follows.

[0087] For STT multi-resistance magnetic devices and arrays thereof, (1) according to the conventional magnetic device preparation process, the thin film parts of the lower electrode, buffer layer, pinning layer, reference layer, barrier layer or space layer are prepared by using magnetron sputtering technology, electron beam evaporation technology or pulsed laser deposition technology; (2) photoresist is spin-coated on the above parts, and then the photolithography technology is used to carve out the first area where the first type of magnetic material is to be grown, and then the photoresist attached to the area is washed away with a developer, and the remaining parts are covered with photoresist; (3) the first type of magnetic material is grown to the area by using magnetron sputtering technology; (4) the excess photoresist is washed away with a stripping solution; (5) photoresist is spin-coated on the above parts, and then the photolithography technology is used to carve out the second area where the second type of magnetic material is to be grown, and then the photoresist attached to the area is washed away with a developer, and the first area is covered with photoresist; (6) magnetron sputtering technology is used to (7) Use a stripping solution to clean the excess photoresist and complete the free layer growth. During this period, the thickness of the free layer in different regions must be the same; (8) Use magnetron sputtering technology to continue growing the cover layer film on the free layer film; (9) Anneal the above multilayer film; (10) Use photolithography technology, ion beam etching, reactive ion etching and other micro-nano processing techniques to etch magnetic devices and device arrays at the junction of the first region and the second region and prepare the corresponding lower electrode; (11) Use insulating medium filling, flattening, opening and other technologies to expose the top of the above device array; (12) Use magnetron sputtering technology to grow the upper electrode film; (13) Use photolithography technology, ion beam etching, reactive ion etching and other micro-nano processing techniques to prepare the corresponding upper electrode, such as Fig.15 Among them, only the free layer film part ((2)-(7)) of the device is different from the traditional free layer preparation method, and the rest is consistent with the traditional magnetic device preparation process.

[0088] For SOT multi-resistance magnetic devices and their arrays, (1) the thin film portion of the spin current generation layer is prepared by magnetron sputtering technology; (2) the thin film growth process is completed by the preparation method of the free layer thin film portion of the above-mentioned STT multi-resistance magnetic device (steps (2)-(7)); (3) the thin film portion of the barrier layer or space layer, reference layer, pinning layer, and covering layer is prepared by magnetron sputtering technology, electron beam evaporation technology, or pulsed laser deposition technology; (4) the above-mentioned multilayer thin film is annealed; (5) through micro-nano processing techniques such as photolithography technology, ion beam etching, reactive ion etching, etc., the magnetic device, the device array, and the lower electrode formed by the spin current generation layer are etched at the joint of the first area and the second area; (6) the top of the above-mentioned device array is exposed by insulating medium filling, flattening, opening, etc.; (7) the upper electrode thin film portion is grown by magnetron sputtering technology; (8) the corresponding upper electrode is prepared by micro-nano processing techniques such as photolithography technology, ion beam etching, reactive ion etching, etc. Among them, only the free layer film part of the device (step (2)) is different from the traditional free layer preparation method, and the rest is consistent with the traditional magnetic device preparation process.

[0089] During the free layer growth process, two situations may occur:

[0090] The first is that gaps appear at the joints. In this case, two steps need to be added to the above growth process. After filling the gaps with insulating material, the insulating material is flattened to expose the free layer plane. Fig.16 As shown; the second type - overlap occurs at the joint, and the overlap is higher than other plane positions, that is, the contact resistance is large, and it is necessary to use flattening technology to remove the raised part to make it consistent with the thickness of other free layer parts, such as Fig.17 shown.

[0091] The method for regulating the resistance value of a multi-resistance magnetic device is as follows: the free layer is composed of more magnetic materials, such as Fig.18 (six-resistance type: 6 resistance values) and Fig.19 (Eight-resistance type: 8 resistance values) as shown.

[0092] Example 2

[0093] This embodiment provides another magnetic device that can achieve multi-resistance states. The free layer is composed of a single ferromagnetic material. Impurities are uniformly added on the surface of the free layer and away from the barrier layer or the space layer. The impurities are used to make the magnetic domains of the free layer autonomously divided into domains. The magnetic moment in each magnetic domain region can be regarded as a single domain. The magnetic moments in different magnetic domain regions are flipped, and the magnetic moments in adjacent regions are less affected. The magnetic moments of different magnetic domain regions are pinned to different degrees by impurities. The magnetic moments of magnetic domain regions close to impurities are more easily pinned, which means that the greater the degree of pinning, the more difficult it is for the magnetic moment to flip. The magnetic moments of the free layer and the reference layer can have in-plane magnetic anisotropy or perpendicular magnetic anisotropy. The remaining components can be consistent with traditional magnetic devices. The device shape can be a cylinder, an elliptical cylinder, an irregular cylinder, a cube, a cuboid, etc. Taking the STT magnetic device as an example, the pinning strength of the magnetic moment of the third magnetic domain region>the pinning strength of the magnetic moment of the second magnetic domain region>the pinning strength of the magnetic moment of the first magnetic domain region, such as Fig. 20 and Fig.21 shown.

[0094] The resistance characteristics of this device are similar to those of the first multi-resistance device in Example 1. Taking the in-plane magnetic anisotropic STT magnetic device as an example, if the initial state of the total resistance of the device is a resistance value of 5, when a voltage pulse with a negative polarity is applied to the upper and lower electrodes of the device, as the amplitude increases negatively to V5, the magnetic moment of the first magnetic domain region is first reversed, and at this time, the total resistance of the device becomes a resistance value of 6; as the amplitude continues to increase negatively to V6, the magnetic moment of the second magnetic domain region is reversed, and at this time, the total resistance of the device becomes a resistance value of 7; as the amplitude continues to increase negatively to V7, the magnetic moment of the third magnetic domain region is reversed, and at this time, The total resistance of the device becomes a resistance value of 8; then, when the voltage pulse increases positively to V8, the magnetic moment of the first magnetic domain region flips, and at this time, the total resistance of the device becomes a resistance value of 9; as the amplitude continues to increase positively to V9, the magnetic moment of the second magnetic domain region flips, and at this time, the total resistance of the device becomes a resistance value of 10; as the amplitude continues to increase positively to V10, the magnetic moment of the third magnetic domain region flips, and at this time, the total resistance of the device returns to a resistance value of 5; as the amplitude continues to decrease in the reverse direction to 0V, the total resistance of the device will not change. The direction of the free layer magnetic moment corresponding to each resistance value of the device is as follows Fig.23 shown.

[0095] In the above process, the STT effect on the magnetic moment of each magnetic domain region is not exactly the same. The larger the angle with the magnetic moment of the reference layer, the stronger the STT effect. But at the same time, the magnetic moment is also more strongly pinned by impurities. Generally speaking, the pinning effect is dominant. Therefore, it is more difficult to flip the magnetic moment of the third magnetic domain region than that of the first magnetic domain region.

[0096] The random reversal characteristics of the free layer magnetic moment of this device are similar to those of the first multi-resistance device, and the analysis can be analogized. Taking the STT magnetic device as an example, Fig.24 shown.

[0097] The preparation scheme of the magnetic device and its array is as follows.

[0098] The only difference from the traditional magnetic device preparation process is that for STT devices, impurities can be manufactured after the free layer film is grown and before the cover layer is grown. Impurities (which can be magnetic / non-magnetic particles or clusters, etc.) are evenly attached to the surface of the free layer by lightly sputtering impurities or wrapping impurities with organic matter to ensure that the distance between impurities is constant, ranging from 5 to 500nm; for SOT devices, impurities can be manufactured after the spin current generation layer is grown and before the free layer is grown. The manufacturing method is as above. It is worth noting that when the micro-nano processing is completed to prepare the device and its array structure, it should be carried out near the impurities, such as Fig.25 shown.

[0099] The method for controlling the number of resistance values ​​of the magnetic device is as follows: (1) changing the position or number of impurities; (2) changing the ambient temperature; (3) changing the width of the driving pulse, such as Fig.26 , 27 and 28.

[0100] The above two magnetic device solutions are conducive to reducing the device's operating energy consumption. The reason is that when the device size and free layer thickness are the same, it is easier to flip the magnetic moment of each small area of ​​the free layer of the above multi-resistance magnetic device one by one than to flip the overall magnetic moment of the free layer of the traditional device. (1) The volume of the free layer of each small area is reduced; (2) The magnetic anisotropy of each small area is different and may be smaller than that of the traditional device.

[0101] Example 3

[0102] By embedding the multi-resistance magnetic device of Example 1 or Example 2 into a conventional CMOS logic circuit, a MRAM with large storage capacity, high integration, non-volatility, fast read / write speed, and low energy consumption can be formed. Taking the STT multi-resistance magnetic device as an example, the specific implementation scheme of its application in MRAM is as follows: Fig.29 As shown. The MRAM circuit design also includes address decoding circuits, storage arrays, timing / pulse control circuits, reference parts, and sensitive amplifiers. The core structural unit of the memory is composed of a multi-resistance magnetic device and a metal-oxide-semiconductor field-effect transistor. The former is mainly used to store information, and the latter mainly acts as a switch circuit. Fig.30As shown. A storage array can be formed by regularly arranging many of the above basic structural units and setting word lines, bit lines and source lines - the word lines and source lines are parallel and arranged orthogonally to the bit lines; the crisscrossing bit lines and source lines can be used as the upper and lower electrodes of the core structural unit, and near the intersection of the two is the location of the multi-resistance magnetic device; the word line can control the opening and closing of the metal-oxide-semiconductor field effect transistor; the material of the word line, bit line and source line can be Cu, Au, Al and other high-conductivity metal materials for room temperature and high temperature MRAM, or Nb, NbN, NbTi, NbTiN, Nb3Sn, high-temperature superconductors and other superconducting materials for low temperature and ultra-low temperature MRAM.

[0103] (1) Information writing: input row address signal and column address signal, select the word line, source line and bit line corresponding to the address through the address row decoding circuit and column decoding circuit, and do not energize other word lines, source lines and bit lines. Based on timing and voltage control, voltage pulses with different amplitudes and longer widths are applied to the selected bit line (or source line), the selected source line (or bit line) is grounded (i.e. 0V), and voltage pulses with the same amplitude and width (the voltage must be higher than the threshold of the metal-oxide-semiconductor field-effect transistor) are applied to the selected word line, and the pulse width is short, so that the magnetic moments of different regions of the free layer of the STT multi-resistance magnetic device are reversed, and the information writing is completed. Among them, the pulse width applied to the word line determines the speed of information writing, which in turn affects the writing energy consumption. Taking the STT four-resistance magnetic device as an example, "resistance value 1", "resistance value 2", "resistance value 4" and "resistance value 3" can represent "00", "01", "10" and "11" respectively, that is, one device can carry two bits of binary logic information. A voltage pulse implementation scheme for information writing is given, as follows: Fig.31 shown.

[0104] (2) Information reading: The main purpose is to detect the resistance of the multi-resistance magnetic device and determine the storage information carried by the device. However, considering that the resistance of the magnetic device will drift with factors such as ambient temperature and relative position, in general, the readout circuit needs to include some magnetic devices that have been pre-written as high-resistance, intermediate, and low-resistance states as reference parts. The specific readout process is as follows: the word line, source line, and bit line corresponding to the address are selected and energized through the address row decoding circuit and the column decoding circuit, and the other word lines, source lines, and bit lines are not energized. Based on timing and voltage control, a voltage pulse with an amplitude far less than the device flip voltage is applied to the selected bit line, the selected source line is grounded (i.e., 0V), and a voltage pulse higher than the threshold of the metal-oxide-semiconductor field-effect transistor is applied to the selected word line. The resistance of the selected magnetic device can be obtained, and then a sensitive amplifier is used to compare the resistance of the selected magnetic device with the reference part to determine which state the resistance of the selected magnetic device is in. Finally, the binary information carried by the selected magnetic device is output. Among them, the pulse width of the word line determines the speed of information reading, which in turn affects the readout energy consumption. Taking the STT four-resistance magnetic device as an example, a voltage pulse implementation scheme for information reading is given, such as Fig.32 shown.

[0105] Example 4

[0106] By utilizing the random reversal characteristics of the free layer magnetic moment of multi-resistance magnetic devices and using them as the core components of random number generators, higher quality random number sequences can be obtained, and information security can be guaranteed. Taking the STT multi-resistance magnetic device as an example, the specific implementation plan for its application in the random number generator is as follows: Fig.33 The random number generator is provided with an address decoding circuit, a random number generation array, a voltage control circuit and the like, wherein each multi-resistance magnetic device in the random number generation array is equipped with a sensitive amplifier, a probability calculation circuit, a voltage feedback circuit, and a bit line and a source line are also provided, as shown in FIG. Fig.34As shown. Due to the slight differences between the devices caused by the manufacturing process, the above configuration circuit is mainly used to adjust the probability of magnetic moment reversal of the free layer in each magnetic device to 50%. Taking the STT four-resistance magnetic device as an example, the multi-resistance magnetic device can have four modes through the above voltage feedback circuit - the first one, the initial state of the device resistance is a resistance value of 1, and the probability of magnetic moment reversal in the second region of the free layer is adjusted to 50%, that is, near V1 (50%); the second one, the initial state of the device resistance is a resistance value of 3, and the probability of magnetic moment reversal in the second region of the free layer is adjusted to 50%, that is, near V3 (50%); the third one, the initial state of the device resistance is a resistance value of 2, and the probability of magnetic moment reversal in the first region of the free layer is adjusted to 50%, that is, near V2 (50%); the fourth one, the initial state of the device resistance is a resistance value of 4, and the probability of magnetic moment reversal in the first region of the free layer is adjusted to 50%, that is, near V4 (50%). This means that by adjusting the initial state of the device resistance and the working mode of the voltage feedback circuit, a device can output 4 different results. If there are N-bit sequences in the random number generator array (e.g. N>10), the output result can reach 4 N The output of the random number generator composed of traditional magnetic devices is much better than that of the random number generator (2 N If the number of random number sequence bits is required to be higher, the number of column address bits (i.e., the magnetic devices and their matching circuits in the random number generation array) or the number of row address bits and row address decoding circuits can be increased.

Claims

1. A multi-resistance magnetic device, characterized in that: The free layer thickness of the magnetic device is uniform and is composed of two or more ferromagnetic materials spliced ​​together; one or more of the magnetic moment size, damping coefficient or magnetocrystalline anisotropy of different ferromagnetic materials are different; the magnetic moments of different ferromagnetic materials are regarded as single domains, and they follow a consistent flip when flipped; the contact resistance at the joint of different ferromagnetic materials is at least 5 times the contact resistance at other positions, so that current flows through other positions; the multi-resistance magnetic device is an STT multi-resistance magnetic device; (1) According to the conventional magnetic device preparation process, the thin film parts of the bottom electrode, buffer layer, pinning layer, reference layer, barrier layer or spacer layer are prepared by using magnetron sputtering technology, electron beam evaporation technology or pulsed laser deposition technology; (2) Spin-coating a photoresist on the above-mentioned portion, and then using photolithography technology to carve out a first region where the first type of magnetic material is to be grown, and then washing away the photoresist attached to the region with a developer, and covering the remaining portion with the photoresist; (3) growing a first type of magnetic material into the region using magnetron sputtering technology; (4) Using a stripping solution to remove excess photoresist; (5) Spin-coating a photoresist on the above-mentioned portion, and then using photolithography technology to carve out a second region where the second type of magnetic material is to be grown, and then washing away the photoresist attached to the region with a developer, and covering the first region with the photoresist; (6) growing a second type of magnetic material into the region using magnetron sputtering technology; (7) Using a stripping solution to wash away excess photoresist, the free layer growth is completed, and the thickness of the free layer in different areas is ensured to be the same; (8) Using magnetron sputtering technology, continue to grow a cover layer film portion on the free layer film; (9) performing annealing treatment on the multilayer film; (10) etching a magnetic device and a device array at the junction of the first region and the second region and preparing a corresponding lower electrode through a micro-nano processing technology; (11) exposing the top of the device array by insulating dielectric filling, planarization or opening technology; (12) growing the upper electrode thin film portion by using magnetron sputtering technology; (13) The corresponding upper electrode is prepared through micro-nano processing technology.

2. The multi-resistance magnetic device according to claim 1, characterized in that: The ferromagnetic material includes at least one of Co, Fe, Ni, Mn, Rh, Pd, Pt, Gd, Tb, Dy, Ho, Al, Si, Ga, Ge, Zr, Hf and B; different ferromagnetic materials select alloys of the above ferromagnetic materials with different atomic percentages.

3. The multi-resistance magnetic device according to claim 1, characterized in that: The thickness of the free layer is 1-2 nm.

4. The multi-resistance magnetic device according to claim 1, characterized in that: The magnetic device further includes a barrier layer, a spacer layer or a spin current generating layer.

5. A method for preparing the multi-resistance magnetic device and array thereof as claimed in claim 1, comprising the following steps: The multi-resistance magnetic device is an STT multi-resistance magnetic device; (1) According to the conventional magnetic device preparation process, the thin film parts of the bottom electrode, buffer layer, pinning layer, reference layer, barrier layer or spacer layer are prepared by using magnetron sputtering technology, electron beam evaporation technology or pulsed laser deposition technology; (2) Spin-coating a photoresist on the above-mentioned portion, and then using photolithography technology to carve out a first region where the first type of magnetic material is to be grown, and then washing away the photoresist attached to the region with a developer, and covering the remaining portion with the photoresist; (3) growing a first type of magnetic material into the region using magnetron sputtering technology; (4) Using a stripping solution to remove excess photoresist; (5) Spin-coating a photoresist on the above-mentioned portion, and then using photolithography technology to carve out a second region where the second type of magnetic material is to be grown, and then washing away the photoresist attached to the region with a developer, and covering the first region with the photoresist; (6) growing a second type of magnetic material into the region using magnetron sputtering technology; (7) Using a stripping solution to wash away excess photoresist, the free layer growth is completed, and the thickness of the free layer in different areas is ensured to be the same; (8) Using magnetron sputtering technology, continue to grow a cover layer film portion on the free layer film; (9) performing annealing treatment on the multilayer film; (10) etching a magnetic device and a device array at the junction of the first region and the second region and preparing a corresponding lower electrode through a micro-nano processing technology; (11) exposing the top of the device array by insulating dielectric filling, planarization or opening technology; (12) growing the upper electrode thin film portion by using magnetron sputtering technology; (13) The corresponding upper electrode is prepared through micro-nano processing technology.

6. Use of the multi-resistance magnetic device according to claim 1 in a multi-state memory.

7. Use of the multi-resistance magnetic device as claimed in claim 1 in a random number generator.

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