CN114975770A - Current comparator and analog-to-digital converter based on spin orbit torque device - Google Patents

Current comparator and analog-to-digital converter based on spin orbit torque device Download PDF

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CN114975770A
CN114975770A CN202210524634.1A CN202210524634A CN114975770A CN 114975770 A CN114975770 A CN 114975770A CN 202210524634 A CN202210524634 A CN 202210524634A CN 114975770 A CN114975770 A CN 114975770A
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current
orbit torque
spin orbit
torque device
resistance
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游龙
陈镇江
张帅
李若凡
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Huazhong University of Science and Technology
Shenzhen Huazhong University of Science and Technology Research Institute
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Huazhong University of Science and Technology
Shenzhen Huazhong University of Science and Technology Research Institute
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N50/00—Galvanomagnetic devices
    • H10N50/10—Magnetoresistive devices
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K5/00—Manipulating of pulses not covered by one of the other main groups of this subclass
    • H03K5/22—Circuits having more than one input and one output for comparing pulses or pulse trains with each other according to input signal characteristics, e.g. slope, integral
    • H03K5/24—Circuits having more than one input and one output for comparing pulses or pulse trains with each other according to input signal characteristics, e.g. slope, integral the characteristic being amplitude
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
    • H03M1/12—Analogue/digital converters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D10/00—Energy efficient computing, e.g. low power processors, power management or thermal management

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Abstract

The invention belongs to the technical field of memory signal processing, and particularly relates to a current comparator and an analog-to-digital converter based on a spin orbit torque device. According to the relation that the resistance of a spin orbit torque device and a planar magnetic field change linearly within a certain range, a current wire is laid on the upper layer and/or the lower layer of the SOT device, the resistance RH of the device is in direct proportion to the current IDC on the current wire, the linear regulation of the IDC on the RH is realized, when a write current is applied, the hysteresis of the device is almost 0 due to the magnitude of the write current, and the device does not need to be initialized before working. When current comparison is carried out, current to be compared is input into a current lead to form a current difference delta I or a magnetic field difference delta H, the resistance delta R of a device is changed, the magnitude of the two currents is judged according to the magnitude of the resistance of the device, the current comparison function is realized, the comparison threshold is adjustable, the comparison result is stored in the resistance of the SOT device while the current is compared, and an additional storage circuit is not needed to store the comparison result.

Description

Current comparator and analog-to-digital converter based on spin orbit torque device
Technical Field
The invention belongs to the technical field of memory signal processing, and particularly relates to a current comparator and an analog-to-digital converter based on a spin orbit torque device.
Background
The comparator is a circuit that can compare two input Analog signals to generate a binary output, and is commonly used in Analog-to-Digital converters (ADCs), power chips, oscillators, etc., and is one of the basic units in the Analog circuit, and its speed, area, power consumption, offset, etc. are of great concern. As transistor dimensions shrink, CMOS comparators face challenges of high static power consumption, low power supply resulting in reduced speed, increased transistor mismatch resulting in increased offset.
In order to overcome the problems faced by the current CMOS comparators, current comparators based on spintronic devices are proposed in succession. At present, a current comparator based on a Spin transfer Torque effect faces a great challenge in the aspects of power consumption and durability, and in the current comparator based on a Spin Orbit Torque (SOT) effect, a magnetic hysteresis phenomenon exists in a magnetic device due to the action of a coercive force of the magnetic device. This means that the current comparator needs to perform an initialization operation to initialize the resistance state of the device to a specific resistance state before each operation, which is very disadvantageous for realizing high-speed signal comparison. When the current comparator is used to implement a complicated circuit such as an ADC, an oscillator, etc., an initialization process needs to be added before a normal duty cycle, which not only greatly limits the operating speed thereof, but also increases the complexity of operation. Meanwhile, the current comparator scheme based on the spin electronic device mostly utilizes external input to compare with a device overturning threshold value, the overturning current threshold value of the device is relatively fixed, and when current comparison is carried out, only current comparison in a specific range can be carried out, so that the current comparator has certain limitation in practical application.
Disclosure of Invention
In view of the defects and improvement requirements of the prior art, the invention provides a current comparator and an analog-to-digital converter based on a spin orbit torque device, and aims to provide a method for realizing memory signal processing by using the spin orbit torque device.
To achieve the above object, according to one aspect of the present invention, there is provided a current comparator based on a spin orbit torque device, having a double-layer structure, including: a first current lead and a spin orbit torque device which are arranged in a stacked manner; the first current lead is vertical to the direction of a plane write current input port of the spin orbit torque device;
two ends of the first current lead are respectively used for inputting two currents or voltages to be compared, a planar magnetic field is formed below the first current lead and acts on the spin orbit torque device; the resistance of the spin orbit torque device changes under the action of the magnetic field.
Further, the spin orbit torque device is a Hallbar heterojunction device or an MTJ device.
The invention also provides a current comparison method, which adopts the current comparator to execute the following steps:
two currents or voltages to be compared are respectively input to two ends of a first current lead in a current comparator, a planar magnetic field is formed below the first current lead and acts on a spin orbit torque device;
inputting a write current to a planar write current input port of a spin orbit torque device in the current comparator, wherein the magnitude of the write current enables the resistance of the spin orbit torque device to be in a linear relation with the current on the first current lead;
reading out the resistance of the spin orbit torque device, and determining the magnitude relation of two currents to be compared according to the magnitude of the resistance; when the spin orbit torque device is a Hallbar heterojunction device, determining the current magnitude relation according to the positive and negative of the resistor and the writing direction of the writing current; and when the spin orbit torque device is an MTJ device, determining the current magnitude relation according to whether the resistance is greater than the intermediate threshold value and the writing direction of the writing current.
The invention also provides a current comparator based on the spin orbit torque device, which is of a three-layer structure and comprises: the second current lead, the spin orbit torque device and the third current lead are sequentially stacked; the spin orbit torque device is arranged at the center between the two current leads, and the second current lead and the third current lead are parallel and are vertical to the direction of a plane write current input port of the spin orbit torque device;
the current or the voltage to be compared is respectively input into the same side port of the second current lead and the third current lead, and planar magnetic fields H in opposite directions are generated at the position of the spin orbit torque device 1 、H 2 The planar magnetic field acting on the spin orbit torque device has a magnitude of Δ H ═ H 2 -H 1 ；
The resistance of the spin orbit torque device changes under the action of Δ H.
Further, the spin orbit torque device is a Hallbar heterojunction device or an MTJ device.
The invention also provides a current comparison method, which adopts the current comparator to execute the following steps:
respectively inputting currents or voltages to be compared to the same side ports of the second current lead and the third current lead in the current comparator, and generating planar magnetic fields H in opposite directions at the position of the spin orbit torque device 1 、H 2 The planar magnetic field acting on the spin orbit torque device has a magnitude of Δ H ═ H 2 -H 1 ；
Inputting a write current to a planar write current input port of a spin orbit torque device in the current comparator, wherein the magnitude of the write current enables the resistance of the spin orbit torque device to be in a linear relation with the current on the second current lead and the current on the third current lead respectively;
reading out the resistance of the spin orbit torque device, and determining the magnitude relation of two currents to be compared according to the magnitude of the resistance; when the spin orbit torque device is a Hallbar heterojunction device, determining the current magnitude relation according to the positive and negative of the resistor and the writing direction of the writing current; and when the spin orbit torque device is an MTJ device, determining the current magnitude relation according to whether the resistance is greater than the intermediate threshold value and the writing direction of the writing current.
The present invention also provides an analog-to-digital converter comprising: a fourth current conductor, n spin orbit torque devices, n fifth current conductors, and n readout circuits; the n fifth current leads are correspondingly arranged on the other side, opposite to the fourth current leads, of the n spin orbit torque devices; each spin orbit torque device is arranged in the center position between the corresponding fifth current lead and the fourth current lead, and the fourth current lead and the n fifth current leads are parallel and vertical to the direction of the plane write current input ports of the n spin orbit torque devices;
one end of the fourth current lead is used for inputting current to be converted, ports of the n fifth current leads, which are on the same side as the fourth current lead, are used for inputting n reference currents, and planar magnetic fields delta H with different sizes are generated at the positions of the spin orbit torque devices i I is 1, …, n; resistance of each spin orbit torque device at Δ H i Is changed under the action of (1);
each reading circuit is formed by connecting a gating transistor and a plurality of inverters connected in series and is used for applying reading current to the corresponding spin orbit torque device and judging whether the reading voltage of the spin orbit torque device is greater than the overturning threshold value of the inverter of the reading circuit or not, wherein the overturning threshold value is equal to the voltage generated by applying equal reading current to the middle threshold value resistor of the spin orbit torque device; and determining the magnitude relation between the current to be converted and the reference current of the spin orbit torque device corresponding to the reading circuit according to the judgment result and the writing direction of the writing current.
Further, the spin orbit torque device is a Hallbar heterojunction device or an MTJ device.
The invention also provides an analog-to-digital conversion method, which adopts the analog-to-digital converter to execute the following steps:
of said fourth current conductorOne end of the current to be converted is input, n reference currents are respectively input into ports of the n fifth current leads, which are on the same side as the fourth current leads, and planar magnetic fields delta H with different sizes are generated at the positions of the spin orbit torque devices i I is 1, …, n; resistance of each spin orbit torque device at Δ H i Is changed under the action of (1);
inputting write currents in the same direction and the same magnitude to the planar write current input ports of the n spin orbit torque devices, wherein the magnitude of the write currents enables the resistance of each spin orbit torque device to be in a linear relation with the currents on the upper current lead and the lower current lead of each spin orbit torque device;
judging whether the read voltage of each corresponding spin orbit torque device is greater than the overturning threshold of the inverter of the read circuit through each read circuit; and determining the magnitude relation between the current to be converted and the reference current of the spin orbit torque device corresponding to the reading circuit according to the judgment result and the writing direction of the writing current.
Generally, by the above technical solution conceived by the present invention, the following beneficial effects can be obtained:
(1) the invention adopts a double-layer or three-layer structure formed by laminating a current lead and a spin orbit torque device, and when a write current is applied, the coercive force of the device is reduced to 0 due to the size of the write current, the magnetic hysteresis is almost 0, and the device does not need to be initialized before working, thereby overcoming the problem that the current implementation scheme of the current comparator based on the spin electronic device needs to be initialized, greatly increasing the working speed of the current comparator and reducing the working complexity.
(2) In the invention, the current to be compared can be directly input into the current lead, the comparison result is presented by the positive and negative of the device resistor, the comparison result can be stored in the resistor of the SOT device while the current is compared, the need of an additional storage circuit for storing the comparison result when the traditional comparator is applied to analog-to-digital conversion and the like is avoided, and the area overhead is reduced.
(3) The invention avoids the defect of fixed threshold caused by using the turnover current threshold of the device as the comparison threshold, the comparison threshold is adjustable, and the expansibility and the applicability of the current comparator are improved.
(4) Compared with the traditional comparator based on CMOS, the invention realizes the comparison function by using a single spin orbit torque device, and has more advantages in area.
(5) The spin electronic device has the advantages of nonvolatility, high durability, high speed and the like, and the comparator realized by the spin electronic device is expected to solve the problems of electric leakage, speed and the like in the traditional CMOS comparator at present.
Drawings
Fig. 1 is a schematic diagram of a current comparator structure and a device test of a current lead/SOT device double-layer structure provided in an embodiment of the present invention, wherein (a) is a test circuit structure, and (b) is a specific film structure of a half heterojunction of an SOT device;
fig. 2 is a comparison result diagram of a current comparator with a double-layer structure of a current conducting wire/sothialbar heterojunction device according to an embodiment of the present invention, where (a) is an input/output schematic diagram, and (b) is a fixed input current I 2 Lower device R H -I 1 Testing a curve;
fig. 3 is a schematic structural diagram of a current comparator of a current lead/sothialbar heterojunction device/current lead/three-layer structure provided in an embodiment of the present invention;
fig. 4 is a schematic diagram of a planar magnetic field distribution between two current wires in a current comparator of a current wire/sothialbar heterojunction device/current wire/three-layer structure provided in an embodiment of the present invention, where (a) to (c) represent a magnetic field parallel to a write current direction, a magnetic field perpendicular to the write current direction, and a magnetic field perpendicular to a device plane, respectively;
FIG. 5 shows the current conducting wire/SOTHALLBAR heterojunction device/current conducting wire/current comparator with three-layer structure according to the embodiment of the present invention 1 Magnetic field H parallel to write current direction at fixation 2 A variation graph;
FIG. 6 is a schematic diagram of a current comparator structure and a test circuit of a current lead/SOT-MTJ device/current lead tri-layer structure according to an embodiment of the present invention, wherein (a) is the comparator structure and (b) is the test circuit;
FIG. 7 is a current comparator Verilog-A modeling simulation result of the current lead/SOT-MTJ device/current lead tri-layer structure according to the embodiment of the present invention;
FIG. 8 is a schematic diagram of a 3-bitFlashADC structure based on a three-layer current comparator according to an embodiment of the present invention;
FIG. 9 is a diagram of the simulation results of the 3-bitFlashADC based three-layer current comparator according to the embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Example one
A current comparator based on a spin orbit torque device is of a double-layer structure and comprises: the first current conducting wire and the spin orbit torque device are arranged in a stacked mode; the first current lead is vertical to the direction of a plane write current input port of the spin orbit torque device; two ends of the first current lead are respectively used for inputting two currents or voltages to be compared, a planar magnetic field is formed below the first current lead and acts on the spin orbit torque device; the resistance of the spin orbit torque device changes under the action of the magnetic field.
Preferably, the spin orbit torque device is a Hallbar heterojunction device or an MTJ device.
As another embodiment of the present invention, a method for comparing currents by using the above current comparator is provided, and specifically, a method for comparing currents by using the current comparator according to the first embodiment of the present invention includes the following steps:
two currents or voltages to be compared are respectively input to two ends of a first current lead in a current comparator, a planar magnetic field is formed below the first current lead and acts on a spin orbit torque device;
inputting a write current to a planar write current input port of a spin orbit torque device in a current comparator, wherein the magnitude of the write current enables the resistance of the spin orbit torque device to be in a linear relation with the current on a first current lead;
reading the resistance of the spin orbit torque device, and determining the magnitude relation of two currents to be compared according to the magnitude of the resistance; when the spin orbit torque device is a Hallbar heterojunction device, determining the current magnitude relation according to the positive and negative of the resistor and the writing direction of the writing current; and when the spin orbit torque device is an MTJ device, determining the current magnitude relation according to whether the resistance is greater than the intermediate threshold value and the writing direction of the writing current.
In the embodiment, according to the relation that the abnormal Hall resistance of a spin orbit torque device (SOT device) and a planar magnetic field change linearly within a certain range, a current lead is laid on the upper layer or the lower layer of the SOT device, and the abnormal Hall resistance of the device is related to the current I on the current lead DC Proportional ratio, realize I DC To R H When the write current is applied, the coercive force of the device is reduced to 0 by the size of the write current, the magnetic hysteresis is almost 0, and the device does not need to be initialized before working. When current comparison is carried out, current to be compared is input into a current lead to form current difference (delta I) or magnetic field difference (delta H), device resistance (delta R) is changed, the magnitude of the two currents is judged according to the magnitude of the device resistance, and the current comparison function is realized.
The embodiment overcomes the problem that the current comparator implementation scheme based on the spin electronic device needs initialization operation, greatly increases the working speed of the current comparator, and reduces the working complexity; meanwhile, the current to be compared can be directly input into the current lead, and the comparison result is presented by the positive and negative of the AHE resistor, so that the defect that the device overturning current threshold is used as the comparison threshold is avoided, and the expansibility and the applicability of the current comparator are improved. In addition, the spin electronic device has the advantages of nonvolatility, high durability, high speed and the like, so that the comparator is realized by utilizing the spin electronic device, and the problems of electric leakage, speed and the like in the traditional CMOS comparator are hopefully solved.
To better illustrate the solution of the present embodiment, the following example is now given.
The current comparator structure and the test schematic diagram of the current comparison scheme of the current lead/SOT Hall bar heterojunction device double-layer structure shown in FIG. 1 are shown. The current comparator of the current lead/SOT Hall bar heterojunction device double-layer structure is shown in fig. 1 (a), and the film layer structure is a substrate/SOT Hall bar heterojunction device/insulating layer/current lead in sequence from bottom to top. The substrate is used as a carrier of the whole device, and the commonly used material is Si or SiO 2 (ii) a The SOT Hall bar heterojunction device structure is shown in fig. 1 (b); the current lead is used for generating a planar magnetic field, and Au, Ag and the like are generally adopted as growth materials of the current lead; the insulating layer is used for blocking the current conducting wire and the SOT device and preventing the SOT device from being influenced by electric leakage, and Al is generally selected 2 O 3 MgO, etc. U in FIG. 1 H Indicating an abnormal hall voltage.
The current comparator with double-layer structure comprises six ports, wherein the ports 1 and 2 are plane write currents (I) w ) Input/output terminals, ports 3 and 4 are abnormal Hall voltage (V +, V-) test terminals, and ports 5 and 6 are current in current conductor (I) DC ) And an input end and an output end. When comparing the currents, the currents I to be compared 1 、I 2 Current lines are fed from the ports 5 and 6, respectively, and a current difference Δ I (Δ I ═ I) is formed in the current lines 1 -I 2 ) An Oersted field Δ H is generated below the current conductors, and a write current I is applied to ports 1 and 2 w The magnetization state is changed under the combined action of Δ H. Applying a positive write current, i.e. I w Along the direction from port 2 to port 1, when Δ I is equal to 0, the planar magnetic field Δ H is equal to 0, the proportion of the magnetization direction in the SOT device is equal to the proportion of the magnetization direction in the SOT device to the direction from the upper part to the lower part, and the abnormal hall resistance R of the device is equal to H 0; when Δ I>0, plane magnetic field Δ H>0, the magnetization direction in the CoFeB layer is increased in proportion upwards, and the AHE resistance R of the device is increased H >0; when Δ I<0, plane magnetic field Δ H<0, the downward proportion of the magnetization direction in the CoFeB layer is increased, and the AHE resistance R of the device is increased H <0. The current I to be compared can be obtained by measuring the positive and negative of the AHE resistance of the device 1 、I 2 The magnitude relationship of (1).
For voltage comparison, the voltage V to be compared 1 、V 2 The ports 5 and 6 are accessed, respectively, and a voltage drop Δ V (Δ V ═ V) occurs in the Au wire 1 -V 2 ) The current Δ I (Δ I ═ Δ V/R, R is the resistance of the current lead) on the current lead also generates a magnetic field Δ H, so that the current comparator of the double-layer structure can also realize the voltage comparison function.
In order to prove the function of the current comparator with the double-layer structure, experimental tests were carried out. The test results are shown in FIG. 2, wherein I R Representing read current, current source I 1 And I 2 Are respectively connected with two ends of the current lead, and a current difference delta I (delta I ═ I) is formed in the current lead 1 -I 2 ) And passing a write current into the device to read the abnormal Hall voltage. During the test, the current I is fixed 2 Value of (1), measuring current I 1 Change from-80 mA to +80mA, R H A change in (c). As shown in FIG. 2 (b), when I 2 When the ratio is +/-20 mA, R H With I 1 Results of the varying tests, when I 2 If 20mA, if I 1 >20mA, then R H >0; if I 1 <At 20mA, then R H <0. Similarly, when I 2 When equal to-20 mA, if I 1 >-20mA, then R H >0; if I 1 <-20mA, then R H <0. The output result of the comparator is represented by the positive and negative of the resistance when I 1 >I 2 When the output of the comparator is 1, when I 1 <I 2 The comparator output is 0.
In this example, at write current I w At 31mA, the hysteresis of the device is almost 0, and the AHE resistance of the SOT device varies in real time with Δ I, regardless of the initial state of the device. Therefore, the current comparator with the double-layer structure does not need to carry out initialization operation before comparison, the speed of the comparator is greatly improved, the complexity of operation is reduced, meanwhile, the current to be compared can be directly input into a current lead, the comparison result is presented by the positive and negative of the abnormal Hall resistor, and the problem that the device overturning threshold value is used as the comparison threshold value in other current comparator schemes based on the spintronic device is solved.
Example two
A current comparator based on a spin orbit torque device is of a three-layer structure and comprises: the second current lead, the spin orbit torque device and the third current lead are sequentially stacked; the spin orbit torque device is arranged at the center between the two current leads, and the second current lead and the third current lead are parallel and are vertical to the direction of a plane write current input port of the spin orbit torque device; the current or the voltage to be compared is respectively input into the same side port of the second current lead and the third current lead, and planar magnetic fields H in opposite directions are generated at the position of the spin orbit torque device 1 、H 2 The planar magnetic field acting on the spin orbit torque device has a magnitude of Δ H ═ H 2 -H 1 (ii) a The resistance of the spin orbit torque device changes under the action of Δ H.
Preferably, the spin orbit torque device is a Hall bar heterojunction device or an MTJ device.
As another embodiment of the present invention, a current comparator using the three-layer structure described above may be provided, and in particular, a current comparison method may be provided, where the current comparator using the three-layer structure described above performs the following steps:
respectively inputting current or voltage to be compared to the same side port of a second current lead and a third current lead in a current comparator, and generating planar magnetic fields H in opposite directions at the position of a spin orbit torque device 1 、H 2 The planar magnetic field acting on the spin orbit torque device has a magnitude of Δ H ═ H 2 -H 1 ；
Inputting a write current to a planar write current input port of a spin orbit torque device in a current comparator, wherein the magnitude of the write current enables the resistance of the spin orbit torque device to be in a linear relation with the current on a second current lead and a third current lead respectively;
reading the resistance of the spin orbit torque device, and determining the magnitude relation of two currents to be compared according to the magnitude of the resistance; when the spin orbit torque device is a Hall bar heterojunction device, determining the current magnitude relation according to the positive and negative of a resistor and the writing direction of writing current; and when the spin orbit torque device is an MTJ device, determining the current magnitude relation according to whether the resistance is greater than the intermediate threshold value and the writing direction of the writing current.
In order to further improve the expansion capability of the current comparator with the double-layer structure in the first embodiment, a current comparator with a three-layer structure of current conducting wire/SOT device/current conducting wire is realized in the third embodiment, and the structure of the current comparator is shown in fig. 3.
The distance between the two current leads is 1 μm, and the SOT device is placed in the center between the two current leads (the distance from the center of the device to the two current leads is equal). When currents in the same direction are introduced into the two current leads, the upper and lower current leads generate plane magnetic fields (H) in opposite directions at the position of the device 1 、H 2 ) The planar magnetic field acting on the device has a magnitude Δ H (Δ H ═ H) 2 -H 1 ) When the SOT device is connected with a write current, the AHE resistor R of the SOT device in the current comparator H Will vary linearly with Δ H, therefore, when I 2 >I 1 When R is H >0, otherwise when I 2 <I 1 When R is H <0。
Similarly, for voltage comparison, the right ends of the two current wires are grounded, and the left ends are respectively connected with the voltage V to be compared 1 、V 2 Since the two current wires have the same size and the resistances are substantially equal, the current Δ I is equal 1 (ΔI 1 ＝(ΔV 1 ) /R) and Δ I 2 (ΔI 2 ＝(ΔV 2 ) /R) respectively generating a planar magnetic field acting on the device when V 2 >V 1 When R is H >0, otherwise when V 2 <V 1 When R is H <0。
As shown in the schematic diagram of the distribution of the planar magnetic field between the current conductors in FIG. 4, according to the COMSOL simulation test result, in the current comparator with three-layer structure, only the planar magnetic field H parallel to the write current direction acts, and when the current density J applied to the upper current conductor is fixed 1 ＝1×10 10 A/m 2 Current density J applied to the lower current conductor 2 From 1X 10 9 A/m 2 To 2X 10 10 A/m 2 When changed, SOT device placeThe variation curve of the magnitude of the planar magnetic field H at the position (coordinates are (0, 0, 0), black dots in fig. 4) parallel to the writing current direction is shown in fig. 5, Δ H is proportional to the current density difference Δ J, the variation range of Δ H is about-6 to +6Oe, and the variation range of AHE resistance of the current comparator is about-200 to +200m Ω calculated according to experimental data. In a three-layer current comparator, according to R H The positive and negative of (2) can judge the comparison result. When I is 2 >I 1 When R is H >0, the comparator output is 1; i is 2 ＝I 1 When R is H ＝0；I 2 <I 1 When R is H <0, the comparator output is 0. When a planar magnetic field is applied, the proportion of magnetization reversal is independent of its initial state, and the current comparator implemented also does not require an initialization operation.
In summary, the current comparator with the double-layer structure and the current comparator with the three-layer structure do not need an initialization process during working. For the current comparator with the double-layer structure, the area is minimum, but the application of the current comparator is limited by a single input channel, and the expansibility is relatively low; the current comparator with the three-layer structure adopts a vertical structure, the plane area cannot be increased, the input ends are separated by the upper current lead and the lower current lead, and the expansibility is stronger.
EXAMPLE III
An analog-to-digital converter comprising: a fourth current conductor, n spin orbit torque devices, n fifth current conductors, and n readout circuits; the n fifth current leads are correspondingly arranged on the other side, opposite to the fourth current leads, of the n spin orbit torque devices; each spin orbit torque device is arranged at the center position between the corresponding fifth current lead and the fourth current lead, and the fourth current lead and the n fifth current leads are parallel and vertical to the direction of the plane write current input ports of the n spin orbit torque devices;
one end of the fourth current lead is used for inputting current to be converted, ports of the n fifth current leads, which are on the same side with the fourth current lead, are used for inputting n reference currents, and a large current is generated at the position of each spin orbit torque deviceSmall different plane magnetic field deltah i I is 1, …, n; resistance of each spin orbit torque device at Δ H i Is changed under the action of (1);
each reading circuit is formed by connecting a gating transistor and a plurality of inverters connected in series and is used for applying reading current to the corresponding spin orbit torque device and judging whether the reading voltage of the spin orbit torque device is greater than the overturning threshold value of the inverter of the reading circuit or not, wherein the overturning threshold value is equal to the voltage generated by applying equal reading current to the middle threshold value resistor of the spin orbit torque device; and determining the magnitude relation between the current to be converted and the reference current of the spin orbit torque device corresponding to the reading circuit according to the judgment result and the writing direction of the writing current.
Preferably, the spin orbit torque device is a Hall bar heterojunction device or an MTJ device.
As another embodiment of the present invention, a method for comparing currents by using the above analog-to-digital converter is provided, and specifically, a method for converting an analog signal by using the above analog-to-digital converter performs the following steps:
one end of a fourth current lead is input with current to be converted, n reference currents are respectively input into ports of the n fifth current leads, which are on the same side as the fourth current lead, and planar magnetic fields delta H with different sizes are generated at the positions of the spin orbit torque devices i I is 1, …, n; resistance of each spin orbit torque device at Δ H i Is changed under the action of (1);
inputting write currents in the same direction and the same magnitude to the planar write current input ports of the n spin orbit torque devices, wherein the magnitude of the write currents enables the resistance of each spin orbit torque device to be in a linear relation with the currents on the upper current lead and the lower current lead of each spin orbit torque device;
judging whether the read voltage of each corresponding spin orbit torque device is greater than the overturning threshold of the inverter of the read circuit through each read circuit; and determining the magnitude relation between the current to be converted and the reference current of the spin orbit torque device corresponding to the reading circuit according to the judgment result and the writing direction of the writing current.
A method for realizing a Flash ADC based on a current comparator with a three-layer structure is provided. Take 3-bitFlashADC as an example:
first, as shown in fig. 6, the current wire/SOT-MTJ device/current wire tri-layer current comparator includes 7 ports, namely, current wire input current terminals TA0 and TA1, and TB0 and TB1, and three ports TA, TB and TC of the SOT-MTJ device.
The operation of the comparator is divided into two phases: a comparison stage in which a write current is applied to the heavy metal layer and an input current (I) in the same direction 1 ，I 2 ) Respectively applied to the two current leads to generate a planar magnetic field and change the resistance of the device; in the reading stage, the read signal is changed into high level, the switch tube is conducted, and the resistance value of the MTJ is at R due to TMR effect P And R AP (R AP ＝(1+TMR)×R P ) And (4) selecting proper reading current, and utilizing a pair of inverters to read out the state of the MTJ, namely the output of the current comparator, Vout. In order to verify the function of a single current comparator, a physical model is constructed by using a Verilog-A hardware description language and simulation verification is carried out, the simulation result is shown in FIG. 7, wherein the first row represents the input current I 1 And I 2 (ii) a The second row represents the resistance value RMTJ of the device, where R 1 The device resistance was 4.68K Ω, R, when Δ I ═ 20mA 2 The resistance of the device when Δ I ═ 20mA was expressed, and the value was 4.92K Ω; third row represents current comparator output V out . With input current I 1 Slowly changing, the resistance of the device changes, when I 1 <I 2 When Vout is 0V, when I 1 >I 2 The current comparator output Vout is inverted from 0V to 1V.
Then, a three-layer current comparator is used to implement a 3-bit Flash ADC, and a schematic diagram of a core structure thereof is shown in fig. 8, which includes: the device comprises a sampling and reference current generating circuit, a comparator core circuit based on a spin orbit torque device and a reading and encoding circuit. In the comparator circuit, 7 MTJs share the same heavy metal layer, and the write current is I w . Input current I in Applied to the upper current conductor and at the same time referenced to the current I ref_i (i-1, 2 … 7) applied to the underlying layerOn the flow conductor, a planar magnetic field Δ H is generated i (ΔH i ＝H Iin -H Iref_n I ═ 1, 2 … 7) acts on each MTJ. Each signal conversion comprises two phases: switching and reading, in the switching phase, the sampling signal SP is set to high level, the write current I w Applied to the heavy metal layer, and an input current and a reference current are respectively applied to the upper and lower current conductors to generate magnetic fields of different magnitudes, so that each MTJ exhibits a different resistance state (R); in the read phase, the read signal RE is set to high level and the read current I is set R (I R 0.1mA) is applied across the MTJ to form a voltage (V ═ I) R ×R MTJ ，R MTJ Representing the resistance of the MTJ), the comparison result of each current comparator is read out using a set of inverter strings, and the output signals of 7 MTJs constitute a set of temperature codes C7 to C1. After being processed by the temperature code-to-binary code encoding circuit, the digital output of the ADC can be obtained.
The simulation verification result of the ADC is shown in FIG. 9, I in For the input signal waveform, C7-C1 are output results of 7 current comparators, namely temperature codes, and B2, B1 and B0 are coded output digital codes. According to the simulation results, when the input current signal is less than 10mA, for example, Iin ═ 1mA, all comparator outputs are "0", and the output digital code B2B1B0 is "000"; when the input current signal is greater than 70mA, e.g. I in When the output of the comparator is 78mA, all the outputs of the comparators are 1, and the output digital code B2B1B0 is 111; when in an intermediate state, e.g. I in The comparator output is "0111111" and the encoded output is "110" at 63 mA. And changing the frequency of the input signal, wherein no code missing or error code occurs in the ADC in the 1-500 MHz simulation process.
In summary, the invention realizes two current comparators based on SOT devices, wherein the first is a current lead/SOT device double-layer structure, and the second is a current lead/SOT device/current lead three-layer structure. Meanwhile, a scheme for realizing FlashADC based on a current comparator with a current lead/SOT device/current lead three-layer structure is provided. The Flash ADC which is free of initialization, high in conversion rate and strong in expansibility is realized based on the proposed current comparator, and an idea is provided for the application of the spin electronic device in the field of in-memory signal processing.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (9)

1. A current comparator based on a spin orbit torque device is characterized by being of a double-layer structure and comprising: a first current lead and a spin orbit torque device which are arranged in a stacked manner; the first current lead is vertical to the direction of a plane write current input port of the spin orbit torque device;
two ends of the first current lead are respectively used for inputting two currents or voltages to be compared, a planar magnetic field is formed below the first current lead and acts on the spin orbit torque device; the resistance of the spin orbit torque device changes under the action of the magnetic field.
2. The current comparator of claim 1, wherein the spin-orbit torque device is a Hallbar heterojunction device or an MTJ device.
3. A current comparison method, characterized in that the following steps are performed with a current comparator according to claim 1 or 2:
two currents or voltages to be compared are respectively input to two ends of a first current lead in a current comparator, a planar magnetic field is formed below the first current lead and acts on a spin orbit torque device;
inputting a write current to a planar write current input port of a spin orbit torque device in the current comparator, wherein the magnitude of the write current enables the resistance of the spin orbit torque device to be in a linear relation with the current on the first current lead;
reading out the resistance of the spin orbit torque device, and determining the magnitude relation of two currents to be compared according to the magnitude of the resistance; when the spin orbit torque device is a Hallbar heterojunction device, determining the current magnitude relation according to the positive and negative of the resistor and the writing direction of the writing current; and when the spin orbit torque device is an MTJ device, determining the current magnitude relation according to whether the resistance is greater than the intermediate threshold value and the writing direction of the writing current.
4. A current comparator based on a spin orbit torque device is characterized by being of a three-layer structure and comprising: the second current lead, the spin orbit torque device and the third current lead are sequentially stacked; the spin orbit torque device is arranged at the center position between the two current leads, and the second current lead and the third current lead are parallel and vertical to the direction of a plane write current input port of the spin orbit torque device;
the current or the voltage to be compared is respectively input into the same side port of the second current lead and the third current lead, and planar magnetic fields H in opposite directions are generated at the position of the spin orbit torque device 1 、H 2 The planar magnetic field acting on the spin orbit torque device has a magnitude of Δ H ═ H 2 -H 1 ；
The resistance of the spin orbit torque device changes under the action of Δ H.
5. The current comparator as claimed in claim 4, wherein the spin-orbit torque device is a Hallbar heterojunction device or a MTJ device.
6. A current comparison method, characterized in that the following steps are performed using a current comparator according to claim 4 or 5:
respectively inputting currents or voltages to be compared to the same side ports of the second current lead and the third current lead in the current comparator, and generating planar magnetic fields H in opposite directions at the position of the spin orbit torque device 1 、H 2 The planar magnetic field acting on the spin orbit torque device has a magnitude of Δ H ═ H 2 -H 1 ；
Inputting a write current to a planar write current input port of a spin orbit torque device in the current comparator, wherein the magnitude of the write current enables the resistance of the spin orbit torque device to be in a linear relation with the current on the second current lead and the current on the third current lead respectively;
reading out the resistance of the spin orbit torque device, and determining the magnitude relation of two currents to be compared according to the magnitude of the resistance; when the spin orbit torque device is a Hallbar heterojunction device, determining the current magnitude relation according to the positive and negative of the resistor and the writing direction of the writing current; and when the spin orbit torque device is an MTJ device, determining the current magnitude relation according to whether the resistance is greater than the intermediate threshold value and the writing direction of the writing current.
7. An analog-to-digital converter, comprising: a fourth current conductor, n spin orbit torque devices, n fifth current conductors, and n readout circuits; the n fifth current leads are correspondingly arranged on the other side, opposite to the fourth current leads, of the n spin orbit torque devices; each spin orbit torque device is arranged in the center position between the corresponding fifth current lead and the fourth current lead, and the fourth current lead and the n fifth current leads are parallel and vertical to the direction of the plane write current input ports of the n spin orbit torque devices;
one end of the fourth current lead is used for inputting current to be converted, ports of the n fifth current leads, which are on the same side as the fourth current lead, are used for inputting n reference currents, and planar magnetic fields delta H with different sizes are generated at the positions of the spin orbit torque devices i I is 1, …, n; resistance of each spin orbit torque device at Δ H i Is changed under the action of (2);
each reading circuit is formed by connecting a gating transistor and a plurality of inverters connected in series and is used for applying reading current to the corresponding spin orbit torque device and judging whether the reading voltage of the spin orbit torque device is greater than the overturning threshold value of the inverter of the reading circuit or not, wherein the overturning threshold value is equal to the voltage generated by applying equal reading current to the middle threshold value resistor of the spin orbit torque device; and determining the magnitude relation between the current to be converted and the reference current of the spin orbit torque device corresponding to the reading circuit according to the judgment result and the writing direction of the writing current.
8. The analog-to-digital converter according to claim 7, characterized in that the spin-orbit torque device is a Hallbar heterojunction device or a MTJ device.
9. A method of analog-to-digital conversion, characterized in that the following steps are performed with an analog-to-digital converter according to claim 7 or 8:
one end of the fourth current lead is input with current to be converted, the ports of the n fifth current leads, which are on the same side as the fourth current lead, are respectively input with n reference currents, and planar magnetic fields delta H with different sizes are generated at the positions of the spin orbit torque devices i I is 1, …, n; resistance of each spin orbit torque device at Δ H i Is changed under the action of (1);
inputting write currents with the same direction and the same magnitude to the planar write current input ports of the n spin orbit torque devices, wherein the magnitude of the write currents enables the resistance of each spin orbit torque device to be in a linear relation with the currents on the upper current lead and the lower current lead of the spin orbit torque device;
judging whether the read voltage of each corresponding spin orbit torque device is greater than the overturning threshold of the inverter of the read circuit through each read circuit; and determining the magnitude relation between the current to be converted and the reference current of the spin orbit torque device corresponding to the reading circuit according to the judgment result and the writing direction of the writing current.
CN202210524634.1A 2022-05-13 2022-05-13 Current comparator and analog-to-digital converter based on spin orbit torque device Pending CN114975770A (en)

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