Manufacturing method of spin-orbit torque array device

Abstract

The present invention provides a spin-orbit torque device array comprising a non-magnetic layer, a magnetic layer bonded to the non-magnetic layer, and an upper layer bonded to the magnetic layer and composed of an oxide, wherein each of the single elements has only two magnetization states, an up state or a down state. According to the present invention, a spin-orbit torque device array capable of driving at low power without an ADC using spin-orbit torque and a method for manufacturing the same can be provided.

Description

Technology Field

[0001] The present invention relates to a magnetic element array using spin-orbit torque and a method for manufacturing the same. Background Technology

[0002] With the mass production of autonomous vehicles approaching due to advancements in information and communication technologies such as the Internet of Things (IoT), security issues regarding autonomous driving systems are emerging in the context of V2X (vehicle to everything). If autonomous driving systems are not reliably protected from external attacks, it could pose a fatal threat to the lives of passengers or pedestrians.

[0003] Furthermore, there are reports of cases where the results of security keys generated through machine learning are predicted in existing software-based security systems.

[0004] To address this, hardware-based security solutions that surpass the stability of existing software-based security solutions have recently begun to gain attention.

[0005] Recently, a case was reported in which a hardware security device was implemented by utilizing the fact that the switching current of spin-orbit torque (SOT), a method for electrically controlling the perpendicular magnetization of magnetic thin films, varies from device to device.

[0006] This prior study suggests that by utilizing the fact that the SOT switching current differs for each device, if a pulse current of the same intensity is applied to all devices, the devices have a magnetic state between up and down, and since this intermediate state is random for each device, it can be used as a random element of a security device.

[0007] Therefore, through an Analog-Digital Converter (ADC), the Hall resistance value (R) of the component HBy converting ) into a digital value, the range of analog values ​​between up and down is divided into equal intervals and a digital bit is assigned to each cell, and a digital bitmap is obtained by verifying the digital value and position of each element in the element array.

[0008] However, the intermediate state between this up and down state is susceptible to degradation in magnetic fields of much lower strength than the material's coercivity, and preventing information loss in the security device is one of the critical issues when applying hardware security devices.

[0009] The matters described in the background technology above are intended to aid in understanding the background of the invention and may include matters that are not prior art already known to those skilled in the art to which this technology belongs. Prior art literature

[0010] Korean Patent Publication No. 10-2016-0133821 The problem to be solved

[0011] The present invention has been devised to solve the aforementioned problems, and the purpose of the present invention is to provide a spin-orbit torque device array capable of driving at low power without an ADC using spin-orbit torque, and a method for manufacturing the same. means of solving the problem

[0012] A spin-orbit torque element array according to one aspect of the present invention comprises single elements including a non-magnetic layer, a magnetic layer bonded to the non-magnetic layer, and an upper layer bonded to the magnetic layer and composed of an oxide, wherein each of the single elements has only two magnetization states: an up state or a down state.

[0013] Here, the magnetic layer is characterized as being one of CoFeB, CoFe, NiFe alloy, or Co.

[0014] In addition, the above non-magnetic layer is characterized by being either Pt (platinum) or Ta (tantalum).

[0015] Next, a method for manufacturing a spin-orbit torque device array according to one aspect of the present invention comprises the steps of: obtaining a switching curve according to an applied current of a spin-orbit torque device array composed of single devices including a non-magnetic layer, a magnetic layer bonded on the non-magnetic layer, and an upper layer bonded on the magnetic layer and composed of an oxide; setting a pulse current for obtaining a security device pattern from the switching current magnitude distribution of the single devices according to the switching curve; setting a saturation current from the SOT switching curve obtained by applying the pulse current to the single devices; and applying the saturation current to the single devices to saturate the magnetization state of the single devices.

[0016] And, by the step of saturating the magnetization state of the single elements, the magnetization state of each of the single elements is characterized by having only two states: an up state or a down state.

[0017] In addition, the step of setting the saturation current is characterized by setting the magnitude of the saturation current to a magnitude of current required for the magnetization state of the single elements to saturate from the SOT switching curve.

[0018] Furthermore, the step of setting the saturation current includes the step of applying the pulse current to the single elements and then checking the sign of the anomalous Hall effect (AHE) of each of the single elements.

[0019] And, the step of setting the saturation current is characterized by setting a (+) current for a single element among the single elements whose sign of the abnormal Hall resistance is (+), and setting a (-) current for a single element among the single elements whose sign of the abnormal Hall resistance is (-).

[0020] In addition, the step of setting the pulse current is characterized by setting the median value among the switching current values ​​of the single elements from the switching current magnitude distribution as the pulse current.

[0021] Meanwhile, after the step of setting the saturation current and before the step of saturating the magnetization state, the method may further include the step of applying the saturation current to the single elements to initialize the magnetization state and then applying the pulse current.

[0022] In addition, the magnetic layer is characterized as being one of CoFeB, CoFe, NiFe alloy, or Co, and the non-magnetic layer is characterized as being one of Pt (platinum) or Ta (tantalum). Effects of the invention

[0023] The present invention is a technology that improves resistance to an external magnetic field up to a value corresponding to the coercivity of the material by saturating the magnetic state of a single element forming a physically unclonable function (PUF) device into an up state or down state according to the sign of the anomalous Hall resistance of each single element through spin-orbit torque (SOT).

[0024] In the case of conventional PUF devices utilizing an unsaturated magnetization state, the expansion of magnetic domains by an external magnetic field occurs easily, so the magnetization state (information possessed by the PUF) can change at a magnetic field strength lower than the material's coercivity.

[0025] The method proposed in this invention imparts digital output characteristics to existing devices, and since an analog-digital converter (ADC) that converts abnormal Hall resistance values ​​of each device into digital bits is not required, low-power operation is possible.

[0026] In addition, the security device applying the present invention adopts a CoFeB / MgO structure, which makes it possible to apply it to SOT-MRAM, and it is expected that the sensing margin of the magnetic tunnel junction will significantly increase as the magnetization of the device becomes saturated. Brief explanation of the drawing

[0027] FIG. 1 schematically illustrates an example of a single device constituting a spin-orbit torque device array of the present invention. FIG. 2 schematically illustrates an example of a method for manufacturing a spin-orbit torque device array according to the present invention. Figure 3 shows the state before the magnetization saturation process according to the present invention, and Figure 4 shows the state after the magnetization saturation process according to the present invention. Figure 5 is an example of a SOT switching curve of an element array, and Figure 6 shows its switching current distribution. Figure 7 shows the sign and magnitude of the Hall resistance when magnetization is saturated. Figure 8 is a SOT switching curve showing the Hall resistance of the device according to the intensity of the pulse current applied under an in-plane magnetic field of a specific strength. Figure 9 illustrates the concept of digital bit allocation according to the present invention. FIG. 10 shows the magnetization state after exposure to an external magnetic field before the magnetization saturation process, FIG. 11 shows the magnetization state after exposure to an external magnetic field after the magnetization saturation process according to the present invention, and FIG. 12 shows the entropy change between the two. Figure 13 shows the state after the magnetization saturation process according to the present invention. Figure 14 shows the tunnel magnetoresistance ratio (TMR) according to the magnetic field, and Figure 15 shows the magnetization state of the magnetic tunnel junction in the corresponding state. Specific details for implementing the invention

[0028] In order to fully understand the present invention, the operational advantages of the present invention, and the objectives achieved by the implementation of the present invention, reference must be made to the accompanying drawings illustrating preferred embodiments of the present invention and the contents described in the accompanying drawings.

[0029] In describing preferred embodiments of the present invention, known technologies or repetitive descriptions that may unnecessarily obscure the essence of the invention will be shortened or omitted.

[0030] FIG. 1 schematically illustrates an example of a single device of the spin-orbit torque device array of the present invention, and FIG. 2 schematically illustrates an example of a method for manufacturing the spin-orbit torque device array of the present invention. FIG. 3 shows the state before the magnetization saturation process according to the present invention, and FIG. 4 shows the state after the magnetization saturation process according to the present invention.

[0031] Hereinafter, a spin-orbit torque element array according to an embodiment of the present invention and a method for manufacturing the same will be described with reference to FIGS. 1 to 4.

[0032] Among recent semiconductor devices, magnetic memory devices possess ideal conditions as memory devices because they have high speed, low operating voltage, and non-volatile characteristics.

[0033] Magnetic memory devices have a magnetic tunnel junction structure in which two ferromagnetic materials are separated by an insulating layer. Therefore, they store information based on magnetoresistance, which varies depending on the relative magnetization directions of the two magnetic materials.

[0034] The magnetization direction of the two magnetic layers can be controlled by the spin polarization current, which is called spin transfer torque, where the angular momentum of electrons is transferred to the magnetic moment to generate torque.

[0035] In order to control the direction of magnetization using spin transfer torque, spin polarization current must pass through the magnetic material. However, a technique called spin orbit torque has recently been proposed, which involves placing a heavy metal that generates spin current in close proximity to the magnetic material to achieve magnetization reversal of the magnetic material by applying a horizontal current.

[0036] The present invention relates to a physically unclonable (PUF) magnetic memory device capable of being used in security technology by utilizing such spin-orbit torque, and more specifically, to a spin-orbit torque device array capable of operating at low power without an analog-to-digital converter (ADC).

[0037] A single device of the spin orbit torque device array of the present invention may be formed into a triple-layer structure in which a non-magnetic layer (10), a magnetic layer (20), and an upper layer (30) are stacked as shown in FIG. 1.

[0038] The non-magnetic layer (10) may be a non-magnetic metal such as Pt (platinum) or Ta (tantalum), and the magnetic layer (20) may be a ferromagnetic material such as CoFeB, CoFe, NiFe alloy, or Co.

[0039] And, the upper layer (30) can be an example of MgO oxide.

[0040] To measure the anomalous Hall effect (AHE) of a device, a single device is fabricated in the shape of a cross-shaped Hall-bar, and the vertical component of the magnetization can be electrically measured through the AHE measurement of the device.

[0041] Single devices of Ta / CoFeB / MgO Hall-bar structure fabricated through the same process have slightly different SOT switching currents, and the degree of switching varies from device to device when a pulse current of the same intensity and an in-plane magnetic field are applied. Therefore, the magnetization direction of the magnetic layer becomes an unknown state as shown in S10 of Fig. 2.

[0042] The present invention saturates the magnetization state of the element array in a state like that of Fig. 3, thereby making it into a magnetization state like that of Fig. 4, so that it has digital characteristics.

[0043] That is, by obtaining the SOT switching curve of the Hall-bar devices and applying a pulse current of sufficient strength to saturate the magnetization state of the device through the abnormal Hall resistance of the SOT device, the magnetization state of the device is saturated to have digital characteristics.

[0044] Here, the abnormal Hall resistance R of each element H Saturate by applying a (+) current when the sign is (+) and a (-) current when the sign is (-).

[0045] This process of Hall resistance selection and magnetization saturation is called write-back, and through this, the magnetization state is made to have only two states: up state or down state.

[0046] Looking more closely, as referenced in FIGS. 5 and 6, the magnitude of the switching current of the devices is obtained from the switching curve according to the current applied to the device array, for example, composed of 32 Hall-bar devices.

[0047] The switching current of the device refers to the intensity of the pulse current at the point where the Hall resistance value becomes zero on the switching curve.

[0048] Among the switching current values ​​of the 32 elements in the example, a pulse current of the magnitude corresponding to the median value is selected.

[0049] It can be seen that among the total components, the switching current of 16 components, which is half, is less than -8.8 mA, and the switching current of the remaining 16 components is greater than -8.8 mA; the corresponding magnitude is the current (I) for obtaining the Hall resistance distribution. p Set to ).(S20)

[0050] Next, referring to FIG. 7, the abnormal Hall resistance (R H )-Perpendicular magnetic field(B z From the hysteresis curve, the sign and magnitude of the Hall resistance when magnetization is saturated can be determined.

[0051] The magnitude and sign of the Hall resistance are indicators that can be used to verify the normal magnetization state of the device. It can be confirmed that the Hall resistance of the device is + (-) 5 Ω when all magnetization is in the Up (Down) state.

[0052] The SOT switching curve of Fig. 8 is a graph showing the Hall resistance of the device according to the intensity of the pulse current applied under an in-plane magnetic field (x-axis direction) of a specific intensity.

[0053] That is, the current (I) required for the magnetization state of the device to saturate from the SOT switching curve s ), the strength of the saturation current can be determined. (S20)

[0054] In this embodiment, when an in-plane magnetic field of +10 mT and a pulse current of magnitude 15 mA required for SOT switching are applied, it can be confirmed through the Hall resistor that the magnetization is saturated.

[0055] That is, when saturated in the Up state, a pulse current + 15 mA and an in-plane magnetic field 10 mT are applied, and when saturated in the Down state, a pulse current - 15 mA and an in-plane magnetic field 10 mT are applied to saturate it.

[0056] When Is and Ip are determined in this way (S20), the magnetization direction is initialized to an up state or down state by applying -Is followed by +Ip or by applying +Is followed by -Ip (S30), and then a pulse current and an in-plane magnetic field (10mT) are applied to obtain a security element pattern.

[0057] Then, the abnormal Hall resistance (R) of the single devices is determined through the abnormal Hall effect (AHE), which allows verification of the normal magnetization component. H Check the sign of ) (S40).

[0058] By applying +Is to devices with positive abnormal Hall resistance and -Is to devices with negative abnormal Hall resistance, a device array saturated in a random magnetic layer magnetization direction is obtained (S60).

[0059] As described above, by saturating the magnetization, the present invention enables the fabrication of a security device capable of operating at low power without an ADC, and as a result, the robustness of the security device against external magnetic fields can be improved.

[0060] To verify this, digital bits of 0 or 1 can be assigned to extract the security element indicator as shown in Fig. 9.

[0061] The security element evaluation index (entropy) is an evaluation index for the ratio of the number of different bits that make up the security element, where 1 is the case where the number of bits 1 and the number of bits 0 are the same, and 0 is the case where all bits are the same.

[0062] FIG. 10 shows the state according to the magnetic field strength before write-back according to the present invention, and FIG. 11 shows the state after write-back.

[0063] As a result of the comparison, it can be seen that the security device evaluation index (entropy) appears as shown in Figure 12. Through this, it can be confirmed that the magnetic field strength increased, causing the security device index to decrease after write-back.

[0064] In order to generate such bits, conversion by an ADC was required due to the magnetic state between up and down, but after the write-back according to the present invention, the magnetic state has two states, up or down, as shown in FIG. 13.

[0065] Therefore, the PUF device according to the present invention can have digital signal characteristics and enables low-power operation as it does not require an ADC.

[0066] In addition, as referenced in FIGS. 14 and 15, the tunnel magnetoresistance (TMR) of a device having a magnetic state between Up and Down has a TMR smaller than the maximum TMR of the magnetic tunnel junction (MTJ).

[0067] The present invention saturates the magnetic domains of the magnetic layer through write-back, thereby enabling the use of the maximum TMR value by being composed of elements in a parallel state (①) and an anti-parallel state (②), and it can be seen that the TMR is larger than that of the intermediate state (③), making it easier to distinguish magnetic states (improved sensing margin).

[0068] Although the present invention has been described above with reference to the illustrated drawings, it is obvious to those skilled in the art that it is not limited to the described embodiments and can be modified and varied in various ways without departing from the spirit and scope of the invention. Accordingly, such modifications or variations should be deemed to fall within the scope of the claims of the present invention, and the scope of rights of the present invention should be interpreted based on the appended claims. Explanation of the symbols

[0069] 10: Non-stratified 20: Magnetic layer 30 : Upper layer

Claims

Claim 1 delete Claim 2 delete Claim 3 delete Claim 4 A method for manufacturing a spin orbit torque device array comprising: a step of obtaining a switching curve according to an applied current of a spin orbit torque device array composed of single elements including a non-magnetic layer, a magnetic layer bonded to the non-magnetic layer, and an upper layer bonded to the magnetic layer and composed of an oxide; a step of setting a pulse current for obtaining a security element pattern from the switching current magnitude distribution of the single elements according to the switching curve; a step of setting a saturation current from the SOT switching curve obtained by applying the pulse current to the single elements; and a step of saturating the magnetization state of the single elements by applying the saturation current to the single elements. Claim 5 A method for manufacturing a spin orbit torque device array according to claim 4, characterized in that, by the step of saturating the magnetization state of the single elements, the magnetization state of each of the single elements has only two states, up state or down state. Claim 6 A method for manufacturing a spin orbit torque device array according to claim 5, wherein the step of setting the saturation current is characterized by setting the magnitude of the saturation current to the minimum magnitude of the current at which the magnetization state of the single elements saturates from the SOT switching curve. Claim 7 A method for manufacturing a spin orbit torque device array according to claim 6, wherein the step of setting the saturation current includes the step of determining the sign of the anomalous Hall effect (AHE) of each of the single elements after applying the pulse current to the single elements. Claim 8 A method for manufacturing a spin orbit torque device array according to claim 7, wherein the step of setting the saturation current is characterized by setting a (+) current for a single device among the single devices in which the sign of the abnormal Hall resistance is (+), and setting a (-) current for a single device among the single devices in which the sign of the abnormal Hall resistance is (-). Claim 9 A method for manufacturing a spin orbit torque device array according to claim 8, wherein the step of setting the pulse current is characterized by setting the median value among the switching current values ​​of the single elements from the switching current magnitude distribution as the pulse current. Claim 10 A method for manufacturing a spin orbit torque device array according to claim 9, further comprising the step of applying the saturation current to the single elements to initialize the magnetization state and then applying the pulse current, after the step of setting the saturation current and before the step of saturating the magnetization state. Claim 11 A method for manufacturing a spin orbit torque device array according to claim 9, wherein the magnetic layer is one of CoFeB, CoFe, NiFe alloy, and Co, and the non-magnetic layer is one of Pt (platinum) and Ta (tantalum).

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