A sot-based non-volatile peak current measurement system and method

Abstract

The application discloses a non-volatile peak current measurement system and method based on SOT. The system comprises a plurality of vertical magnetic tunnel junctions with different flip threshold values integrated on a heavy metal conductor layer. The heavy metal conductor layer is connected to a circuit to be measured. Under the action of an external current, the flip state of the MTJ on the heavy metal conductor layer is changed, thereby changing the equivalent resistance value of the plurality of MTJs. A pull-up resistor and a standard voltage are applied to one end of the heavy metal conductor layer. The voltage drop across the pull-up resistor is collected by an A / D module, the equivalent resistance value of the MTJ is calculated, and the current measurement value stored in the MTJ is calculated. Since the MTJ is passive and non-volatile, no external driving power source is required when the system is used for current measurement. Moreover, the system can save the measured current peak value until the next initialization. The system has the advantages of simple structure, high practicability and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of measurement circuit design, and relates to a current measurement system, in particular to a non-volatile peak current measurement system and method based on SOT. BACKGROUND

[0002] Traditional ammeters include a pointer type ammeter and a digital ammeter. The pointer type ammeter is based on mechanical principles and internally includes structures such as a coil, a permanent magnet, a spring and a dial. The greater the input current, the stronger the magnetic force generated by the coil, and the greater the angle at which the pointer is driven to rotate, thereby indicating the size of the input current through the scale on the dial. The digital ammeter is based on the pointer type ammeter and internally includes a high-precision analog-to-digital conversion sampling chip, which can be read by a microprocessor to accurately measure a small voltage drop and convert the voltage drop into a current to display the measurement result. Although most simple ammeters can meet the daily current measurement task, the disadvantage is that the measured current data disappears after leaving the measurement environment, and the ammeters do not have a storage function. Those ammeters with a data storage function are often complex in structure, large in size and not easy to carry.

[0003] A magnetic tunnel junction is a device affected by the SOT (spin orbit torque) effect and has two resistance states of a high resistance state and a low resistance state. The resistance state depends on the polarization direction of the reference layer and the free layer in the magnetic tunnel junction. The heavy metal layer has perpendicular magnetic anisotropy. By using the strong spin orbit interaction of the heavy metal, the spin Hall effect or the Rashha effect of the interface is used to convert the charge flow into pure spin flow and inject it into the free layer, so as to exert a spin orbit torque on the magnetic moment or the magnetic domain wall to drive the magnetic moment to flip or the magnetic domain wall to move to change the polarization direction. If the polarization direction is parallel, the possibility of electron tunneling through the insulating layer is greater, and its macroscopic performance is that the resistance is small. If the polarization direction is anti-parallel, the possibility of electron tunneling through the insulating layer is smaller, and its macroscopic performance is that the resistance is extremely large. Therefore, under the action of an external current, the magnetic tunnel junction can be converted between the high resistance state and the low resistance state. For magnetic tunnel junctions with different threshold current sizes, when a steady current with the same size is input, some magnetic tunnel junctions will flip, and some will not. Based on this characteristic of the magnetic tunnel junction, different sizes of currents can be detected. In addition to the storage of measurement results, the magnetic tunnel junction also has the advantages of non-volatility, radiation resistance, wear resistance, high speed and the like, can adapt to harsh working environments, prolong the service life and improve the use efficiency. Moreover, due to the small size of the SOT-MTJ, the volume of the detection device can be further reduced, and the detection device is easy to carry. SUMMARY

[0004] In view of the deficiencies of the prior art, the application provides a non-volatile peak current measurement system and method based on SOT, which quantifies the peak value of the measured current by using the parallel resistance of a plurality of spin-orbit torque magnetic tunnel junctions, and realizes a passive current measurement mode.

[0005] A non-volatile peak current measurement system based on SOT comprises a plurality of magnetic tunnel junctions, a heavy metal conductor, a single-chip microcomputer control system, an A / D module, a transistor and a pull-up resistor R.

[0006] The free layers of the plurality of magnetic tunnel junctions are fixed on the surface of the heavy metal conductor, and the flipping threshold values are different. The two ends of the heavy metal conductor on the opposite side are used as current input ports. The collector of the transistor is connected with one of the current input ports on the heavy metal conductor, the base is connected with the single-chip microcomputer control system, and the emitter is connected with the ground. The single-chip microcomputer system is connected with the other current input port on the heavy metal conductor through the A / D module. One end of the pull-up resistor R is connected with the reference layer of the magnetic tunnel junction, and the other end is connected with a standard voltage.

[0007] Preferably, the plurality of magnetic tunnel junctions have the same material and height but different diameters.

[0008] Preferably, the plurality of magnetic tunnel junctions have the same material and diameter but different heights.

[0009] The magnetic tunnel junction comprises, from top to bottom, a reference layer, a tunneling barrier layer and a free layer. The reference layer and the free layer are ferromagnetic materials, the magnetization direction of the reference layer is fixed and unchangeable, the magnetization direction of the free layer is affected by the SOT effect, the magnetic tunnel junction shows a low resistance state when the magnetization directions of the two layers are the same, and shows a high resistance state when the magnetization directions of the two layers are opposite. The tunneling barrier layer is a non-magnetic insulating material.

[0010] Preferably, the heavy metal conductor is one of platinum (Pt), tantalum (Ta) and tungsten (W) or a combination thereof.

[0011] A non-volatile peak current measurement method based on SOT, specifically comprising the following steps:

[0012] Step 1: Construct the above measurement system.

[0013] Step 2: Make the transistor in the amplification state by the single-chip microcomputer control system, input the flipping current to the heavy metal conductor, make the magnetic tunnel junctions on the surface all flip to the low resistance state, and then remove the flipping current.

[0014] Step 3: Apply different sizes of current to the current input end of the heavy metal conductor, so that the state of the magnetic tunnel junction changes. After removing the input current, disconnect the transistor from the heavy metal conductor. A standard voltage is applied to the other end of the pull-up resistor, and a test voltage is applied to the other end of the heavy metal conductor. The voltage drop across the pull-up resistor is collected using an A / D module, and the equivalent resistance R of the multiple magnetic tunnel junctions under different input current sizes is calculated S , and a resistance-current peak value table is established.

[0015] Step 4: Initialize the system using the method of Step 2, and then connect the measurement system in series to the circuit to be measured. After the measurement is complete, disconnect the transistor from the heavy metal conductor. A standard voltage is applied to the other end of the pull-up resistor, and a test voltage is applied to the other end of the heavy metal conductor. The voltage drop across the pull-up resistor is collected using an A / D module, and the equivalent resistance R of the multiple magnetic tunnel junctions at this time is calculated t .

[0016] Step 5: Using the resistance-current peak value table obtained in Step 3, find the current peak value corresponding to the resistance Rt as the current value in the current to be measured.

[0017] The present application has the following beneficial effects:

[0018] 1. The measured current data will not be lost due to power failure, and has storage function.

[0019] 2. The measurement system proposed in the present application has small size, simple structure and is easy to carry.

[0020] 3. The non-volatile characteristics of the measurement system can be used to make sensors with storage function BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a schematic diagram of a non-volatile peak current measurement system based on SOT in the embodiment;

[0022] Figure 2 is a flow chart of a non-volatile peak current measurement method based on SOT;

[0023] Figure 3 is a schematic diagram of a measurement circuit in the embodiment. DETAILED DESCRIPTION

[0024] The present application will be further explained and described below in conjunction with the accompanying drawings;

[0025] As shown in Figure 1 , a non-volatile peak current measurement system based on SOT includes multiple magnetic tunnel junctions, a heavy metal conductor, a single-chip microcomputer control system, an A / D module, a transistor, and a pull-up resistor R.

[0026] The magnetic tunnel junction is sequentially composed of a reference layer, a tunnel barrier layer and a free layer from top to bottom, wherein the reference layer and the free layer are ferromagnetic materials, the magnetization direction of the reference layer is fixed, the magnetization direction of the free layer is affected by the SOT effect, and the magnetic tunnel junction is in a low resistance state when the magnetization directions of the two are the same, and is in a high resistance state when the magnetization directions are opposite. The tunnel barrier layer is a non-magnetic insulating material. The free layers of a plurality of magnetic tunnel junctions are fixed on the surface of the heavy metal conductor, and the flip threshold values are different. By changing the material, height or diameter of the magnetic tunnel junction, the flip threshold value can be changed.

[0027] The two ends of the heavy metal conductor on the opposite side are used as current input ports, the heavy metal conductor layer is one of platinum, tantalum T and tungsten, or includes two or more of them, and is mixed in a stacked manner.

[0028] The collector of the transistor is connected with one current input port on the heavy metal conductor, the base is connected with the single-chip microcomputer control system, and the emitter is connected with the ground. The single-chip microcomputer system is connected with the other current input port on the heavy metal conductor through an A / D module. One end of an upper pull resistor R is connected with the reference layer of the magnetic tunnel junction, and the other end is connected with a standard voltage.

[0029] Embodiment 1

[0030] The embodiment provides a SOT-based non-volatile peak current measurement system, which includes three magnetic tunnel junctions with the same material and height and different diameters, and the resistance value of the tunnel magnetoresistance of the magnetic tunnel junctions is:

[0031]

[0032] R ap =R p (1+TMR)

[0033]

[0034] In the formula, d represents the diameter of the magnetic tunnel junction, R p represents the resistance when the magnetization directions of the two ferromagnetic layers are the same, i.e., in a low resistance state, and R ap represents the resistance value when the magnetization directions of the two ferromagnetic layers are opposite, i.e., in a high resistance state. P l and P2 represent the spin polarization rates of the reference layer and the free layer respectively. RA represents the unit area resistance value. TMR represents the tunnel magnetoresistance. By changing the diameter d of the magnetic tunnel junction, the tunnel magnetoresistance value can be changed.

[0035] Suppose that the diameters of the three magnetic tunnel junctions MTJ0, MTJ1 and MTJ2 are d0, d1 and d2 from small to large. The relationship between the equivalent resistance and the flip state of the magnetic tunnel junction is shown in Table 1.

[0036]

[0037] Table 1

[0038] Therefore, the equivalent resistance values R1, R2, R3, and R4 can all be expressed as functions related to d0, d1, and d2. To improve the measurement accuracy, during the selection of magnetic tunnel junctions, the difference in the equivalent resistance of the magnetic tunnel junctions corresponding to different input currents should be made as large as possible, that is, the value of min(R4 - R3, R3 - R2, R2 - R1, R1 - R0) needs to be as large as possible. Set the value range of d0, d1, and d2 to be 50 - 200 nm, and use Matlab to solve. The optimal solutions for the diameters of the 3 magnetic tunnel junctions that meet the conditions are 50 nm, 68 nm, and 95 nm respectively.

[0039] As Figure 2 shown, a non - volatile peak current measurement method based on SOT specifically includes the following steps:

[0040] Step 1: Construct the above - mentioned measurement system. The low - resistance state resistance values of MTJ0, MTJ1, and MTJ2 are Rp0, R p1 , R p2 respectively, and the high - resistance state resistance values are R ap0 , R ap1 , R ap2 respectively. The current thresholds for flipping are ITH0, ITH1, and ITH2 respectively.

[0041] Step 2: Initialize the measurement system. Control the base current of the triode through the single - chip microcomputer to make the triode in the amplification state. At this time, the collector is reverse - biased, and the initialization flipping current is passed through the heavy metal layer to set all magnetic tunnel junctions to the low - resistance state uniformly, and then remove the base current of the triode.

[0042] Step 3: As Figure 3 shown, apply input currents I1, I2, I3, and I4 with magnitudes on the current input end of the heavy - metal conductor, where 0 < I1 < ITH0, ITH0 < I2 < ITH1, ITH1 < I3 < ITH2, ITH2 < I4, and the direction is opposite to the initialization flipping current applied in Step 2. The flipping states, that is, the equivalent resistance values, of MTJ0, MTJ1, and MTJ2 under different input currents are shown in Table 2:

[0043] input current MTJ0 MTJ1 MTJ2 equivalent resistance value ​ [R p0 ]]> [R p1 ]] [R p2 ]]> [R1 = 1 / (1 / R p0 +1 / R p1 +1 / R p2 )]]> [I2] [R ap0 ]]> [R p1 ]]> [R p2 ]]> [R2 = 1 / (1 / R ap0 +1 / R p1 +1 / R p2 )]]> [I3] [R ap0 ]]> [R ap1 ]]> [R p2 ]]> [R3 = 1 / (1 / R ap0 +1 / R ap1 +1 / R p2 )]]> [I4] [R ap0 ]]> [R ap1 ]]> [R ap2 ]]> [R4 = 1 / (1 / R ap0 +1 / R ap1 +1 / R ap2 )]]>

[0044] Table 2

[0045] After the input current is removed, a standard voltage V1 is applied to one end of the pull-up resistor, and the A / D module collects the voltage value V0 at the other end of the pull-up resistor and the reference layer of the magnetic tunnel junction. A test voltage V2 is applied to one end of the heavy metal conductor, and the parallel resistance of the multiple magnetic tunnel junctions under different input current magnitudes is calculated through the resistance value of the pull-up resistor and the voltage drop across the two ends, thereby establishing a resistance-current peak value relationship table.

[0046] Step 4: The system is initialized using the method of step 2, and then the heavy metal conductor is connected in series to the circuit to be tested. After the measurement is completed, the equivalent resistance R of the multiple magnetic tunnel junctions at this time is calculated according to the voltage value V0 collected by the A / D module. t :

[0047]

[0048] Step 5: The resistance-current peak value relationship table shown in Table 2 is used to find the resistance value R corresponding to the current peak value, as the current value in the current to be tested, by using the table lookup method. t

[0049] Example 2

[0050] In this embodiment, multiple magnetic tunnel junctions with the same diameter and material but different heights are selected, and the tunnel magnetoresistance value can be represented as a function related to the height. The range of input magnetic tunnel junctions is solved by Matlab, and the height of the magnetic tunnel junction that satisfies the condition can be obtained by min(R N +1-R N ,..., R1-R0).​

Claims

1. A non-volatile peak current measurement system based on SOT, characterized in that: It includes multiple magnetic tunnel junctions, heavy metal conductors, a microcontroller control system, an A / D module, transistors, and pull-up resistors; The free layers of the multiple magnetic tunnel junctions are fixed on the surface of the heavy metal conductor, and the flip thresholds are different. The two ends opposite to the heavy metal conductor serve as current input ports. The collector of the transistor is connected to one current input port on the heavy metal conductor, the base is connected to the microcontroller control system, and the emitter is connected to ground. The other current input port on the heavy metal conductor is connected to the test voltage. The microcontroller control system is connected to the reference layer of the magnetic tunnel junction through an A / D module. One end of the pull-up resistor R is connected to the reference layer of the magnetic tunnel junction, and the other end is connected to the standard voltage.

2. The non-volatile peak current measurement system based on SOT as described in claim 1, characterized in that: The heavy metal conductor is one or a combination of platinum, tantalum, and tungsten.

3. The non-volatile peak current measurement system based on SOT as described in claim 1, characterized in that: The multiple magnetic tunnel junctions are made of the same material and have the same diameter, but differ in height.

4. The non-volatile peak current measurement system based on SOT as described in claim 1, characterized in that: The multiple magnetic tunnel junctions are made of the same material and have the same height, but different diameters.

5. The non-volatile peak current measurement system based on SOT as described in claim 4, characterized in that: When different input currents are applied to the current input port of a heavy metal conductor, the equivalent resistance Rs of N magnetic tunnel junctions has N+1 possible values: Among them, R n This represents the resistance of the nth magnetic tunnel junction; when the magnetic tunnel junction is in a low-resistance state, In the high-resistivity state, P l P1 and P2 represent the spin polarization of the reference layer and the free layer, respectively; RA represents the resistivity per unit area, and d represents the diameter of the magnetic tunnel junction; N diameter ranges for the magnetic tunnel junctions are defined, and the maximum [min(R]] is solved using Matlab. N+1 -R N , ..., R2-R1, R1-R0)], to obtain the diameters of N magnetic tunnel junctions.

6. A non-volatile peak current measurement method based on SOT, characterized in that: Specifically, the following steps are included: Step 1: Construct the measurement system as described in any one of claims 1 to 5; Step 2: The transistor is put into amplification state by the microcontroller control system. A switching current is passed into the heavy metal conductor to make the magnetic tunnel junction on the surface switch to a low resistance state. Then the switching current is removed. Step 3: Apply different currents to the current input terminal of the heavy metal conductor to change the state of the magnetic tunnel junction; after removing the input current, disconnect the transistor from the heavy metal conductor, and apply a standard voltage V1 to the other end of the pull-up resistor. The A / D module collects the voltage V0 at one end of the pull-up resistor and the test voltage V2 at the end of the heavy metal conductor. By using the resistance value of the pull-up resistor and the voltage drop across it, calculate the equivalent resistance Rs of multiple magnetic tunnel junctions under different input current magnitudes, and establish a table of resistance and peak current relationship. Step 4: Initialize the system using the method in Step 2, and then connect the measurement system in series with the circuit under test; after the measurement is completed, calculate the equivalent resistance R of the multiple magnetic tunnel junctions using the method in Step 3. t : Step 5: Using the table lookup method, find the resistance value R using the resistance-current peak value relationship table obtained in Step 3. t The corresponding peak current is taken as the current value in the current to be measured.

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