Sensor device

Abstract

Provided is a sensor device comprising: a plurality of sensor elements that each change from a first state to a second state according to temperature and the duration of exposure to the temperature; and a magnetic field application unit that applies a magnetic field in a prescribed direction to the plurality of sensor elements. The plurality of sensor elements each include a magnetic tunnel junction element having an energy barrier between the first state and the second state. The magnetic field application unit applies the magnetic field to the plurality of sensor elements, thereby increasing the asymmetry of each of the sensor elements between the potential in the first state and the potential in the second state with the energy barrier interposed therebetween.

Description

Sensor Device

[0001] The present disclosure relates to a sensor device.

[0002] In recent years, thanks to the dramatic development of various information devices and network technologies, as well as the explosive progress of machine learning technology, so-called IoT (Internet of Things) systems have become increasingly popular, which pursue safe and comfortable living by acquiring, processing, and utilizing all information from around the world or in outer space. Sensing devices (sensor apparatuses), which are one of the core technologies of IoT systems, detect images, sound, temperature, chemical substance concentrations, environmental electromagnetic fields, etc., and transmit the detected information to other devices, etc., via a network. Therefore, such sensing devices are required to efficiently acquire necessary information.

[0003] One type of sensing device is a magnetic field sensing device that uses a magnetic tunnel junction (MTJ) element. The MTJ element has a magnetic thin film and has the property that the magnetization direction of the magnetic thin film changes when it senses a magnetic field greater than or equal to the magnetic anisotropy.

[0004] JP 2023-050897 A

[0005] In recent years, it has been proposed to use a magnetic field sensing device (sensor apparatus) using the above-mentioned MTJ element as a measurement apparatus for measuring the time exposed to a predetermined temperature. However, in conventional techniques, it has been difficult to miniaturize the sensing device and to suppress an increase in the manufacturing cost of the device.

[0006] Therefore, the present disclosure proposes a technique that can provide a miniaturized sensor device while suppressing increases in manufacturing costs.

[0007] According to the present disclosure, there is provided a sensor device comprising: a plurality of sensor elements that change from a first state to a second state depending on temperature and the time that they are exposed to the temperature; and a magnetic field application unit that applies a magnetic field in a predetermined direction to the plurality of sensor elements, wherein each of the sensor elements is a magnetic tunnel junction element having an energy barrier between the first state and the second state, and the magnetic field application unit applies the magnetic field to each of the sensor elements, thereby increasing the asymmetry between the potential in the first state and the potential in the second state of each of the sensor elements across the energy barrier.

[0008] FIG. 1 is a block diagram showing an example configuration of a measurement device according to an embodiment of the present disclosure. FIG. 2 is a block diagram showing an example configuration of a sensor circuit according to an embodiment of the present disclosure. FIG. 3 is a diagram showing an example configuration of a sensor element according to an embodiment of the present disclosure. FIG. 4 is a diagram explaining the measurement principle of a sensor element according to an embodiment of the present disclosure. FIG. 5 is a diagram showing an example of a potential with respect to the magnetization direction of a free layer of a sensor element according to an embodiment of the present disclosure. FIG. 6 is a diagram showing an example of a potential with respect to the magnetization direction of a free layer of magnetic tunnel junction elements with different radii. FIG. 7 is a plan view showing an example configuration of a memory cell array and a sensor cell array. FIG. 8 is a schematic diagram showing an example configuration of a measurement device according to a comparative example. FIG. 9 is a schematic diagram showing an example configuration of an element according to a comparative example. FIG. 10 is a schematic diagram showing an example configuration of a measurement device according to a first embodiment of the present disclosure. FIG. 11 is a schematic diagram showing an example configuration of an element according to a first embodiment of the present disclosure. FIG. 12 is a schematic diagram showing an example configuration of an element according to a second embodiment of the present disclosure. FIG. 13 is a schematic diagram showing an example configuration of a measurement device according to a third embodiment of the present disclosure. FIG. 14 is a schematic diagram showing an example configuration of an element according to a third embodiment of the present disclosure. FIG. 15 is a schematic diagram showing an example configuration of a measurement device according to a fourth embodiment of the present disclosure. FIG. 16 is a schematic diagram showing an example configuration of an element according to a fourth embodiment of the present disclosure. Fig. 1 is a flowchart showing an example of operation of a measurement device according to an embodiment of the present disclosure; Fig. 2 is a diagram (part 1) showing an example of the configuration of a sensor circuit according to an embodiment of the present disclosure; Fig. 3 is a diagram (part 2) showing an example of the configuration of a sensor circuit according to an embodiment of the present disclosure; Fig. 4 is a block diagram showing an example of the configuration of a memory system; Fig. 5 is a block diagram showing an example of the configuration of a storage unit; Fig. 6 is a flowchart showing an example of operation of the memory system;

[0009] Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant description will be omitted. Furthermore, in this specification and the drawings, multiple components having substantially the same or similar functional configurations may be distinguished by adding different letters after the same reference numeral. However, when there is no particular need to distinguish between multiple components having substantially the same or similar functional configurations, only the same reference numerals will be used.

[0010] The drawings referred to in the following description are for explaining and facilitating understanding of one embodiment of the present disclosure, and for the sake of clarity, the shapes, dimensions, ratios, etc. shown in the drawings may differ from the actual ones. Furthermore, the design of the devices shown in the drawings can be modified as appropriate, taking into consideration the following description and known technologies.

[0011] Furthermore, when describing the magnetization direction and magnetic anisotropy, terms such as "perpendicular direction" (the direction perpendicular to the film surface, or the stacking direction of the stacked structure) and "in-plane direction" (the direction parallel to the film surface, or the direction perpendicular to the stacking direction of the stacked structure) may be used for convenience. However, these terms do not necessarily refer to the strict direction of magnetization. For example, terms such as "the magnetization direction is perpendicular" and "having perpendicular magnetic anisotropy" mean that the perpendicular magnetization is dominant over the in-plane magnetization. Similarly, terms such as "the magnetization direction is in-plane" and "having in-plane magnetic anisotropy" mean that the in-plane magnetization is dominant over the perpendicular magnetization.

[0012] The explanation will be given in the following order: 1. Configuration of the measurement device 1.1 Overview of the measurement device 1.2 Overview of the sensor circuit 1.3 Details of the sensor element 1.4 Size of the sensor element 2. Background 3. First embodiment 4. Second embodiment 5. Third embodiment 6. Fourth embodiment 7. Operation example 8. Example of the sensor circuit configuration 9. Summary 10. Application example 10.1 Various devices 10.2 Memory system 11. Supplementary information

[0013] <<1. Configuration of the Measuring Apparatus>> <1.1 Overview of the Measuring Apparatus> First, an overview of a measuring apparatus (sensor apparatus) 140 according to an embodiment of the present disclosure will be described with reference to Fig. 1. Fig. 1 is a block diagram showing an example configuration of the measuring apparatus 140 according to an embodiment of the present disclosure.

[0014] As described above, one type of magnetic field sensing device is a sensing device including an MTJ element. Such magnetic field sensing devices can be divided into two types: devices that utilize the phenomenon in which the magnetization direction of the magnetic thin film of the MTJ element changes abruptly by 180 degrees when the MTJ element senses a magnetic field greater than the magnetic anisotropy, and devices that utilize the phenomenon in which the magnetization direction of the magnetic thin film of the MTJ element changes linearly in proportion to the magnetic field. Furthermore, it is known that the magnetization direction of the former not only changes in response to the magnetic field, but also changes in response to the time elapsed since the element was initialized and the temperature of the ambient environment. This is equivalent to the data retention time of an MTJ element used in STT-MRAM (Spin Transfer Torque-Magnetic Random Access Memory) being affected by temperature and magnetic field. By utilizing these characteristics of the MTJ element, the magnetic field sensing device can measure temperature, magnetic field, and the elapsed time since initialization.

[0015] The measuring apparatus 140 according to the embodiment of the present disclosure is a magnetic field sensing device that uses the above-described MTJ element to measure the elapsed time from the initialization of the element at a predetermined temperature.

[0016] Specifically, the measuring device 140 detects at least one of the ambient temperature of the measurement target and the time (exposure time) that the measurement target is exposed to that temperature. For example, the measurement target of the measuring device 140 can be an electronic component (e.g., an integrated circuit (IC), memory, etc.), a rechargeable battery, etc.

[0017] In conventional measurement devices, depending on the number of elements functioning as sensors, it is possible to use a nonvolatile flip-flop (NVFF) circuit, a nonvolatile SRAM (Static Random Access Memory), or the like. The measurement device 140 according to this embodiment uses a structure in which MTJ elements functioning as sensors are arranged in an array.

[0018] 1 , a measuring device 140 according to an embodiment of the present disclosure includes a sensor 141, an acquisition unit 142, a determination unit 143, a storage (storage unit) 144, and an initialization unit 145. Each block of the measuring device 140 will be described below in order.

[0019] (Sensor 141) The sensor 141 has a plurality of sensor circuits (sensor circuit units) 10 that can detect the state of each sensor element 200 (see FIG. 3). Each sensor circuit includes a sensor element 200. The sensor element 200 has a stacked structure similar to that of a memory element made up of an MTJ element of an MRAM, as will be described later. In this embodiment, the sensor element 200 can be, for example, a magnetic field write type, toggle type, voltage reversal type (VC), spin orbit torque type (STT) or other MTJ element.

[0020] An initial value (bit value) is written to the sensor element 200 by the initialization unit 145, which will be described later. In detail, the initial value is written to the sensor element 200 by being controlled by the initialization unit 145 so that the sensor element 200 is in a specific state (for example, "0" or "1") as its initial state. The initial states of the sensor elements 200 may be the same or different from each other, and the initial value of each sensor element 200 may be "0" or "1". In this embodiment, it is preferable to select the more unstable state of the two states ("0" and "1") of the sensor element 200 as the initial value.

[0021] Furthermore, the sensor elements 200 transition (reverse) their states ("0" or "1") depending on the temperature and exposure time. Furthermore, the number of sensor elements 200 that reverse changes depending on the ambient temperature and exposure time of the sensor 141. Hereinafter, the ratio of the number of sensor elements 200 that reverse depending on the ambient temperature and exposure time to the total number of sensor elements 200 included in the sensor 141 will be referred to as the "reverse rate F" of the sensor 141.

[0022] Specifically, the sensor element 200 can maintain specific characteristics (initial values) when power is not supplied to the sensor circuit 10. Furthermore, the characteristics of the sensor element 200 change depending on the ambient temperature and exposure time when power is not supplied. Therefore, the sensor element 200 can measure the ambient temperature and exposure time without power being supplied. The sensor circuit 10 can then detect the state of the sensor element 200. Details of the sensor circuit 10 will be described later.

[0023] (Acquisition unit 142) The acquisition unit 142 acquires sensor information from the sensor 141. The sensor information includes information about the sensor element 200 whose state has changed. Specifically, for example, the sensor information includes a bit value ("0" or "1") of each sensor element 200. Furthermore, the acquisition unit 142 outputs the sensor information to the determination unit 143.

[0024] (Determination Unit 143) The determination unit 143 detects at least one of the ambient temperature of the sensor 141 (ambient temperature of the measurement target) and the exposure time based on the sensor information acquired by the acquisition unit 142.

[0025] The determination unit 143 calculates the reversal rate F based on, for example, the sensor information. For example, as described above, whether the state of the sensor element 200 is reversed depends on the ambient temperature and the time the sensor element 200 is exposed to that temperature. Therefore, the reversal rate F changes depending on the temperature and the exposure time.

[0026] For example, when one of the temperature and the exposure time is known, the determination unit 143 can detect the other according to the reversal rate F. In this case, the determination unit 143 can obtain, for example, one of the temperature and the exposure time from another sensor (not shown).

[0027] Note that the sensor 141 can detect both the temperature and the exposure time by including a plurality of sensor elements 200 that differ in their susceptibility to changes in state due to temperature and exposure time (sensitivity to temperature). If the plurality of sensor elements 200 differ in their sensitivity to temperature, whether or not the state is reversed depends on the characteristics of each individual sensor element 200. In other words, in this case, even if the plurality of sensor elements 200 are exposed to the same temperature for the same time (exposure time), the states of the plurality of sensor elements 200 do not change uniformly because of the different sensitivities to temperature. Therefore, the measuring device 140 can detect both the temperature and the exposure time by utilizing the differences in sensitivity of the sensor elements 200.

[0028] The method for detecting the temperature and exposure time described here is merely an example. The determination unit 143 only needs to detect at least one of the temperature and exposure time using the sensor information from the sensor 141, and the method is not limited to the above example.

[0029] The determination unit 143 outputs at least one of the detected temperature and the exposure time to a control unit (not shown). Alternatively, or in addition, the determination unit 143 may store at least one of the detected temperature and the exposure time in the storage 144.

[0030] (Storage 144) The storage 144 is, for example, a readable and writable storage device such as an MRAM. The storage 144 stores the initial values ​​of the sensor 141. The storage 144 also stores the determination results (for example, at least one of the temperature and the exposure time) by the determination unit 143. Note that in this embodiment, the storage 144 may be refreshed or otherwise processed in accordance with the determination results (details will be described later).

[0031] (Initialization Unit 145) The initialization unit 145 initializes the sensor element 200 of the sensor 141, for example, in accordance with an instruction from the determination unit 143. The initialization unit 145 instructs the initialization circuit 15 of the sensor circuit 10 to control the sensor element 200 to a specific state (for example, "0" or "1").

[0032] In this embodiment, for example, the determination unit 143 instructs the initialization unit 145 to initialize the sensor 141 after the acquisition unit 142 acquires sensor information. Alternatively, the determination unit 143 may instruct the initialization unit 145 to initialize the sensor 141 after detecting (determining) the temperature and exposure time. Note that in this embodiment, the timing at which the initialization unit 145 initializes the sensor 141 is not limited to the example described above. For example, the initialization unit 145 may initialize the sensor 141 at various times, such as when instructed by a control unit (not shown).

[0033] In this embodiment, the measuring device 140 is not limited to the form shown in FIG. 1, but can be modified into various forms.

[0034] 1.2 Overview of Sensor Circuit Next, an overview of the sensor circuit 10 according to the embodiment of the present disclosure will be described with reference to Fig. 2. Fig. 2 is a block diagram showing an example configuration of the sensor circuit 10 according to the embodiment of the present disclosure. As shown in Fig. 2, the sensor circuit 10 includes a sensor element 200, an initialization circuit 15, and a readout circuit 90. Each block of the sensor circuit 10 will be described below in order.

[0035] (Sensor element 200) The sensor element 200 changes state (for example, "0" or "1") depending on the temperature and the time it is exposed to that temperature. As described above, the sensor circuit 10 stores and outputs information (sensor information) related to the state of the sensor element 200. Details of the sensor element 200 will be described later.

[0036] (Initialization Circuit 15) The initialization circuit 15 controls the sensor element 200 so that the sensor element 200 maintains a specific state (initial state) (for example, an initial value of "0" or "1") by applying a current or voltage to the sensor element 200. The initialization circuit 15 initializes the sensor element 200 in response to an instruction from the initialization unit 145, for example.

[0037] (Readout Circuit 90) The readout circuit 90 reads out the state of the sensor element 200 and generates sensor information according to the readout result. The readout circuit 90 outputs the generated sensor information to the acquisition unit 142.

[0038] In this embodiment, the sensor circuit 10 is not limited to the form shown in FIG. 2, but can be modified into various forms.

[0039] <1.3 Details of the sensor element> Next, a detailed configuration of the sensor element 200 according to the embodiment of the present disclosure will be described with reference to Fig. 3. Fig. 3 is a diagram showing an example of the configuration of the sensor element 200 according to the embodiment of the present disclosure, and specifically corresponds to a cross-sectional view of the sensor element 200 cut along the stacking direction of the sensor element 200.

[0040] In this embodiment, as described above, the sensor element 200 has the same layered structure as the MTJ element, which is a memory element of an MRAM. Note that the memory element 300 (see FIG. 9B etc.) and the magnetic field application element 400 (see FIG. 12B) according to this embodiment, which will be described later, are also MTJ elements having the same layered structure as the sensor element 200.

[0041] 3, the sensor element 200 has a laminated structure in which fixed layers (first to third fixed layers) 201, a coupling layer 202, a reference layer 203, tunnel barrier layers (first to third nonmagnetic layers) 204, and free layers (first to third free layers) 205 are sequentially laminated. Furthermore, although not shown in FIG. 3, the sensor element 200 may have upper and lower electrodes that sandwich the laminated structure from above and below. These upper and lower electrodes can apply voltage and current to the laminated structure of the sensor element 200.

[0042] In this embodiment, the cross-sectional structure of the sensor element 200 when cut along the stacking direction is not particularly limited, and may be, for example, a rectangular shape, a trapezoidal shape (tapered shape / reverse tapered shape), a stepped shape, etc. Furthermore, in this embodiment, the cross-sectional structure of the sensor element 200 when cut perpendicular to the stacking direction is also not particularly limited, and may be, for example, a circular shape, an elliptical shape, a polygonal shape, etc.

[0043] The pinned layer 201 is a ferromagnetic layer having a fixed magnetization direction. The magnetization direction of the pinned layer 201 is controlled to be perpendicular to the film surface, for example, by magnetic anisotropy. The pinned layer 201 contains one or more elements selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), manganese (Mn), platinum (Pt), and palladium (Pd), and at least a portion of the pinned layer 201 is alloyed or composed of an artificial lattice of Co / Pt, Co / Ni, or Co / Pd.

[0044] The coupling layer 202 can align the magnetization directions of the two pinned layers 201 and the reference layer 203 sandwiching the coupling layer 202 by ferromagnetic coupling. The coupling layer 202 can be formed using, for example, magnesium (Mg), aluminum (Al), titanium (Ti), silicon (Si), zinc (Zn), zirconium (Zr), hafnium (Hf), tantalum (Ta), bismuth (Bi), chromium (Cr), gallium (Ga), lanthanum (La), gadolinium (Gd), strontium (Sr), barium (Ba), tungsten (W), rhenium (Re), iridium (Ir), gold (Au), niobium (Nb), molybdenum (Mo), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), vanadium (V), copper (Cu), osmium (Os), Mn, Ni, Pt, or the like.

[0045] Alternatively, in this embodiment, the coupling layer 202 can cause the magnetization directions of the two layers sandwiching the coupling layer 202, the pinned layer 201 and the reference layer 203, to be opposite to each other due to diamagnetic coupling. In this case, the coupling layer 202 can contain at least one element selected from the group consisting of, for example, ruthenium (Ru), iridium (Ir), and osmium (Os).

[0046] The magnetization direction of the reference layer 203 is controlled to, for example, a direction perpendicular to the film surface by the above-described coupling layer 202. The reference layer 203 is made of a ferromagnetic material and contains, for example, one or more elements selected from the group consisting of Fe, Co, Ni, and Mn.

[0047] The tunnel barrier layer 204 may contain at least one of an oxide, a nitride, and a fluoride containing one or more elements selected from the group consisting of calcium (Ca), lithium (Li), strontium (Sr), scandium (Sc), europium (Eu), carbon (C), boron (B), magnesium (Mg), yttrium (Y), Si, Al, Zr, Hf, Ti, Zn, La, Ta, Eu, Cu, Ba, Mo, W, V, Ni, Co, Mn, Cr, and Fe, or may be formed using a stacked structure of these.

[0048] The magnetization direction of the free layer 205 is reversed by applying a voltage or current (for example, a voltage or current is applied when the sensor element 200 is initialized). Furthermore, the magnetization direction of the free layer 205 of the sensor element 200 is reversed depending on the temperature and the time exposed to that temperature. The free layer 205 is made of a ferromagnetic material and contains, for example, one or more elements selected from the group consisting of Fe, Co, Ni, and Mn. Furthermore, in the memory element 300 and the magnetic field application element 400 according to this embodiment, the free layer 205 functions as a memory layer that stores data by applying a voltage or current.

[0049] In this embodiment, the sensor element 200 is not limited to the form shown in FIG. 3, but can be modified into various forms.

[0050] Here, the principle of data retention of the MTJ element in the MRAM will be explained. Data retention in the MRAM utilizes the bistability of the free layer 205 having uniaxial magnetic anisotropy, just like in a hard disk. For example, when the stacked structure of the MTJ element of the MRAM has uniaxial anisotropy in the direction perpendicular to the film surface (i.e., the stacking direction), the magnetization direction of the free layer 205 is stable in the vertical upward direction or the vertical downward direction, and is unstable in the intermediate direction (horizontal or oblique to the film surface) due to high energy. This property is called bistability, and there is an energy barrier E that separates the two stable states. Ｂ The height of the MTJ element (see FIG. 5) is determined by the characteristics of the materials constituting each layer of the MTJ element and the size of the MTJ element (determination by size will be described later).

[0051] Therefore, in the MTJ element of the MRAM that stores data nonvolatilely, a sufficiently high energy barrier E Ｂ In the MTJ element of the MRAM, for example, the state in which the magnetization direction of the free layer 205 is perpendicularly upward and the state in which it is perpendicularly downward correspond to "0" and "1," respectively, thereby enabling stable digital storage.

[0052] The stability of data stored in the MTJ element of the MRAM is called retention characteristic. The retention characteristic is expressed as the probability that, after a certain time has passed since writing, an external disturbance will overcome the energy barrier against the user's intention, causing the magnetization direction of the free layer 205 to reverse from "0" to "1" or from "1" to "0." The retention characteristic is also called a retention error rate, and the lower the retention error rate, the better the memory element 300.

[0053] One of the external disturbance factors is the ambient temperature. As the temperature increases, the thermal energy expressed as the product of the temperature and the Boltzmann constant also increases, so the effective energy barrier E ＢThe potential energy sensed by the magnetization of the free layer 205 varies depending on the direction of the external magnetic field, which reduces the stability of either the "0" or "1" state. In other words, the influence of the external magnetic field is asymmetric with respect to the retained data of "0" and "1."

[0054] As described above, in the MTJ element of an MRAM, there is a non-zero probability that data will be rewritten after a certain time has elapsed since writing due to temperature or an external magnetic field. Therefore, in the MRAM, it may be necessary to take measures such as clearly indicating the operating temperature range or providing a magnetic shielding structure. However, in this embodiment, the measurement device 140 measures the temperature and elapsed time by utilizing this characteristic of the MTJ element, i.e., the probability that data will be rewritten after a certain time.

[0055] FIG. 4 is a diagram illustrating the measurement principle of the sensor element 200 according to this embodiment. Specifically, as shown in FIG. 4 , the measurement device 140 according to this embodiment of the present disclosure includes a plurality of sensor elements 200. Here, as shown on the left side of FIG. 4 , the initial state (initial value) of the sensor elements 200 is, for example, a "0" state. In this embodiment, as shown on the right side of FIG. 4 , after a certain period of time, some or all of the sensor elements 200 are rewritten (reversed) to a "1" state due to temperature, which is one of the external disturbance factors. Therefore, in this embodiment, the temperature and elapsed time can be measured by detecting the ratio of the number of sensor elements 200 that have reversed depending on the ambient temperature and exposure time to the total number of sensor elements 200 in the measurement device 140.

[0056] In this embodiment, the initialization circuit 15 may include, for example, an external magnetic field application unit (not shown) that applies an external magnetic field to the plurality of sensor elements 200. The initialization circuit 15 initializes the plurality of sensor elements 200 by applying an external magnetic field to the plurality of sensor elements 200 using the external magnetic field application unit. Alternatively, in this embodiment, the initialization circuit 15 may be connected to, for example, a plurality of wirings (not shown) that are electrically connected to each of the plurality of sensor elements 200. The initialization circuit 15 initializes the plurality of sensor elements 200 by applying a current or a voltage to each of the plurality of sensor elements 200 via the wirings.

[0057] In addition, the energy barrier E Ｂ As explained above, the height of the energy barrier E is determined by the characteristics of the materials constituting each layer of the MTJ element and the size of the MTJ element. Ｂ On the other hand, in the measurement device 140 according to this embodiment, the MTJ element, which is the sensor element 200, is designed to have an energy barrier E Ｂ is set to a predetermined height, that is, the energy barrier E Ｂ Design it to be lower than

[0058] FIG. 5 is a diagram showing an example of potential with respect to the magnetization direction of the free layer 205 of the sensor element 200 according to an embodiment of the present disclosure. In this embodiment, for example, when the magnetization direction of the free layer 205 of the sensor element 200 is the same (parallel) as the magnetization direction of the fixed layer 201, this is called a low resistance state or a parallel state (hereinafter referred to as a P state). Also, in this embodiment, for example, when the magnetization direction of the free layer 205 of the sensor element 200 is opposite (anti-parallel) to the magnetization direction of the fixed layer 201, this is called a high resistance state or an anti-parallel state (hereinafter referred to as an AP state). Furthermore, in this embodiment, for example, when the sensor element 200 is in a low resistance state, this corresponds to stored data "0" (the "0" state in the figure). Also, in this embodiment, for example, when the sensor element 200 is in a high resistance state, this corresponds to stored data "1" (the "1" state in the figure).

[0059] In this embodiment, the initial state (initial value) of the sensor element 200 is, for example, a "0" state (low resistance state). Note that the above example is one example of the initial state (initial value) of the sensor element 200, and is not limited to this example. In other words, the initial state (initial value) of the sensor element 200 may be a "1" state (high resistance state). In this embodiment, it is sufficient that the sensor element 200 stores a specific initial state, and that changes in that state can be read out by the readout circuit 90.

[0060] Here, the sensor element 200 in the P state receives thermal energy k Ｂ T causes a transition (inversion) to the AP state, but the energy E Ｂ However, depending on the temperature and time (exposure time) to which the sensor element 200 is exposed, the thermal energy k Ｂ T is the energy barrier E Ｂ , the state of the sensor element 200 can transition from the P state to the AP state.

[0061] In this manner, in this embodiment, the state of the sensor element 200 changes from the initial value "0" state (low resistance state) to the "1" state (high resistance state) depending on the temperature and time of exposure. The determination unit 143 detects the temperature and exposure time in accordance with this change in the state of the sensor element 200.

[0062] Therefore, in this embodiment, the sensor element 200 is preferably an MTJ element that is more likely to invert from the "0" state (low resistance state) to the "1" state (high resistance state) depending on temperature than the memory element 300 of the MRAM. Alternatively, in this embodiment, the sensor element 200 is preferably an MTJ element that is more likely to invert from the initial state, which is the "1" state (high resistance state), to the "0" state (low resistance state) depending on temperature than the memory element 300. Such an MTJ element can be realized, for example, by changing the diameter of the MTJ element.

[0063] 1.4 Size of Sensor Element As described above, the sensor element 200 can be realized by changing the diameter of the MTJ element, for example. Therefore, the size (diameter) of the sensor element 200 will be discussed with reference to FIGS. 6 and 7. FIG. 6 is a diagram showing an example of the potential with respect to the magnetization direction of the free layer 205 of MTJ elements with different radii, and FIG. 7 is a plan view showing an example of the configuration of the memory cell array 146 and the sensor cell array 150.

[0064] The environmental temperature T, retention time t, and retention characteristic (here, the reversal probability P ｓｗ There is a relationship between the product quality and the defect rate, as shown in the following equation (1).

[0065] In equation (1), k Ｂ is the Boltzmann constant, E Ｂ corresponds to the energy barrier, and τ0 corresponds to a constant of, for example, about 1 ns.

[0066] Also, the energy barrier E Ｂ is proportional to the volume of the free layer 205, and can be expressed by the following formula (2) when the radius of the MTJ element is r.

[0067] In equation (2), a is a proportionality constant determined by the magnetic properties of the material.

[0068] Therefore, in an MTJ element having layers made of the same material and the same thickness, the energy barrier E Ｂ is different.

[0069] MTJ elements with different radii r have potentials and characteristics as shown in FIG. 6 according to the formulas (1) and (2). That is, as shown in the upper and middle parts of FIG. 6, when the radius r of the MTJ element is large, the energy barrier E Ｂ On the other hand, as shown in the lower part of FIG. 6, when the radius r of the MTJ element is small, the energy barrier E Ｂ is small, and it is relatively easy to transition from the P state to the AP state, for example.

[0070] Therefore, in the MRAM memory element 300 that stores data in a non-volatile manner, it is preferable to increase the radius r, for example, so that the memory element 300 has the potential and characteristics shown in the upper and middle rows of Fig. 6. On the other hand, in the sensor element 200 according to this embodiment, it is preferable to decrease the radius r, for example, so that the sensor element 200 has the potential and characteristics shown in the upper and middle rows of Fig. 6.

[0071] Therefore, when the MRAM memory element 300 (memory cell array 146) and the sensor element 200 (sensor cell array 150) are mounted on the same substrate, MTJ elements of different sizes are arranged side by side as shown in FIG.

[0072] The diameter of the MTJ element used as the memory element 300 and the sensor element 200 is not limited to the above example, depending on specifications such as temperature and retention period.

[0073] <<2. Background>> Next, the background that led the inventors to create the embodiments of the present disclosure will be described with reference to Figures 8A and 8B. Figure 8A is a schematic diagram showing an example configuration of a measurement device 140a according to a comparative example, and Figure 8B is a schematic diagram showing an example configuration of an element according to the comparative example. Here, the comparative example refers to the measurement device 140a that the inventors had studied extensively before creating the embodiments of the present disclosure.

[0074] 8A , the measuring device 140a according to the comparative example includes a sensor cell array 150 having a plurality of sensor elements 200a. Furthermore, the measuring device 140a includes a memory cell array 146 having a plurality of memory elements (storage elements) 300 that store the states of the plurality of sensor elements 200a or that are controlled in a predetermined manner according to the states of the plurality of sensor elements 200a. That is, in the measuring device 140a according to the comparative example, the sensor cell array 150 that performs measurements and the memory cell array 146 that stores data can be mounted on a single substrate. Furthermore, in the comparative example, the memory elements 300 and the sensor elements 200a are MTJ elements having the same stacked structure, which allows the sensor cell array 150 and the memory cell array 146 to be fabricated simultaneously, thereby suppressing increases in manufacturing time and manufacturing costs for the measuring device 140a.

[0075] The measuring device 140a according to the comparative example also has a sensor control unit 147 that controls the sensor cell array 150 according to data stored in the memory cell array 146 and reads out the state from the sensor cell array 150. The measuring device 140a according to the comparative example also has an MRAM control unit 148 that controls the memory cell array 146 according to sensor information from the sensor cell array 150 and reads out the state from the memory cell array 146.

[0076] 8B shows cross sections of the memory element 300 and the sensor element 200a mounted on the measuring device 140a according to the comparative example, and an example of the potential relative to the magnetization direction of the free layer 205. In the comparative example, the sensor element 200a is preferably an MTJ element that is more likely to switch from a "0" state (low resistance state) to a "1" state (high resistance state) depending on the temperature than the memory element 300. Therefore, in the comparative example, the sensor element 200a has a smaller radius r than the memory element 300, and therefore the sensor element 200a has a smaller energy barrier E than the memory element 300. Ｂ In addition, in the comparative example, the memory element 300 and the sensor element 200a have almost the same potential in the "0" state (low resistance state) and the "1" state (high resistance state), that is, they can be said to have high symmetry.

[0077] However, with such high symmetry, the sensor element 200a has an energy barrier E Ｂ Since this is small, for example, after a transition (inversion) from the initial value "0" state (low resistance state) to the "1" state (high resistance state) depending on the temperature and exposure time, there may be a transition (re-inversion) from the "1" state (high resistance state) to the "0" state (low resistance state).

[0078] Furthermore, because such re-inversion of the sensor element 200a occurs, the readout circuit 90 that reads out the state of the sensor element 200a reads out both the "0" state (low resistance state) and the "1" state (high resistance state), which makes the circuit complicated and large-scale. In other words, if the re-inversion of the sensor element 200a does not occur, the readout circuit 90 only needs to read out one of the "0" state (low resistance state) and the "1" state (high resistance state), which makes it possible to simplify and miniaturize the circuit.

[0079] In view of this situation, the present inventors have considered that it is necessary for the sensor element 200 to have different potentials in the "0" state (low resistance state) and the "1" state (high resistance state), that is, to enhance (increase) the asymmetry, and have come to create the embodiments of the present disclosure described below. In other words, the present inventors have created an embodiment of the present disclosure in which the potential with respect to the magnetization direction of the free layer 205 of the sensor element 200 can be made lower in the "1" state (high resistance state) than in the initial "0" state (low resistance state). Alternatively, the present inventors have created an embodiment of the present disclosure in which the potential with respect to the magnetization direction of the free layer 205 of the sensor element 200 can be made lower in the "0" state (low resistance state) than in the initial "1" state (high resistance state). In the embodiments of the present disclosure, a magnetic field application unit that applies a bias magnetic field in one direction (a predetermined direction) to the sensor element 200 is provided, thereby reducing the energy barrier E Ｂ The potential asymmetry between the "0" state (low resistance state) (first state) and the "1" state (high resistance state) (second state) sandwiching the "0" state (low resistance state) (first state) is enhanced. Hereinafter, details of the embodiments of the present disclosure created by the inventors will be sequentially described.

[0080] 9A and 9B, details of a measuring device 140 according to a first embodiment of the present disclosure will be described. Fig. 9A is a schematic diagram showing a configuration example of the measuring device 140 according to this embodiment, and Fig. 9B is a schematic diagram showing a configuration example of an element according to this embodiment.

[0081] As shown in FIG. 9A , the measuring device 140 according to this embodiment includes a sensor cell array 150 having a plurality of sensor elements 200, similar to the comparative example. Furthermore, the measuring device 140 includes a memory cell array 146 having a plurality of memory elements (storage elements) 300 that store the states of the plurality of sensor elements 200 or that are controlled in a predetermined manner according to the states of the plurality of sensor elements 200. For example, the memory cell array 146 corresponds to the storage 144 in FIG. 1 described above. That is, in the measuring device 140 according to this embodiment, the sensor cell array 150 that performs measurements and the memory cell array 146 that stores data can also be mounted on a single substrate. Furthermore, in this embodiment, the memory elements 300 and the sensor elements 200 are MTJ elements having a stacked structure of the same material, which allows the sensor cell array 150 and the memory cell array 146 to be fabricated simultaneously, thereby suppressing increases in manufacturing time and manufacturing costs for the measuring device 140.

[0082] Similarly to the comparative example, the measuring device 140 according to this embodiment also has a sensor control unit 147 (corresponding, for example, to the initialization circuit 15 and read circuit 90 in FIG. 2 ) that controls the sensor cell array 150 according to data stored in the memory cell array 146 and reads out the state from the sensor cell array 150. Furthermore, the measuring device 140 according to the comparative example has an MRAM control unit 148 (corresponding, for example, to the memory control unit 770 in FIG. 19 ) that controls the memory cell array 146 according to sensor information from the sensor cell array 150 and reads out the state from the memory cell array 146.

[0083] 9B shows cross sections of the memory element 300 and the sensor element 200 mounted on the measurement device 140 according to this embodiment, and an example of the potential relative to the magnetization direction of the free layer 205. In this embodiment as well, it is preferable that the sensor element 200 is an MTJ element that is more likely to switch from a "0" state (low resistance state) to a "1" state (high resistance state) depending on the temperature than the memory element 300. Therefore, in this embodiment, the sensor element 200 has a smaller radius r than the memory element 300, and therefore the sensor element 200 has a smaller energy barrier E than the memory element 300. Ｂis small.

[0084] Furthermore, in this embodiment, unlike the comparative example, as shown in FIG. 9B , the film thickness of the fixed layer 201 of the sensor element 200 is thicker than that of the fixed layer 201 of the memory element 300. By doing so, in the sensor element 200, a leakage magnetic field to the free layer 205, which is generated by the sum of the magnetizations of the fixed layer 201 and the reference layer 203, becomes large. Therefore, according to this embodiment, the leakage magnetic field increases (increases) the asymmetry of the potential between the "0" state (low resistance state) (first state) and the "1" state (high resistance state) (second state) of the sensor element 200. In detail, as shown in the lower part of FIG. 9B , in this embodiment, for example, the potential with respect to the magnetization direction of the free layer 205 of the sensor element 200 is lower in the "1" state (high resistance state) than in the initial "0" state (low resistance state).

[0085] Therefore, in this embodiment, the sensor element 200 can irreversibly reverse from the "0" state (low resistance state) to the "1" state (high resistance state) depending on the temperature and the time exposed to that temperature. As a result, according to this embodiment, after the sensor element 200 transitions (reverses) from the "0" state (low resistance state) which is the initial value to the "1" state (high resistance state) depending on the temperature and the exposure time, it does not transition (re-reverse) from the "1" state (high resistance state) to the "0" state (low resistance state).

[0086] That is, in this embodiment, the magnetic field application unit that applies a bias magnetic field in one direction to the sensor element 200 can be said to be the fixed layer 201 of the sensor element 200, which has a predetermined film thickness. Note that this embodiment is not limited to adjusting the film thickness of the fixed layer 201, as long as the function of the magnetic field application unit that can apply a leakage magnetic field of the sensor element 200 can be obtained by adjusting the film thickness of each layer of the sensor element 200.

[0087] As described above, in this embodiment, the film thickness of the fixed layer 201 of the sensor element 200 is made thicker than that of the fixed layer 201 of the memory element 300. This increases the leakage magnetic field to the free layer 205 in the sensor element 200, which is generated by the sum of the magnetizations of the fixed layer 201 and the reference layer 203. Therefore, according to this embodiment, the leakage magnetic field increases the potential asymmetry between the "0" state (low resistance state) (first state) and the "1" state (high resistance state) (second state) of the sensor element 200. Therefore, according to this embodiment, the sensor element 200 does not transition (re-invert) from the "1" state (high resistance state) to the "0" state (low resistance state) after transitioning (reversing) from the "0" state (low resistance state), which is the initial value, to the "1" state (high resistance state) depending on the temperature and exposure time.

[0088] Furthermore, in this embodiment, since re-inversion of the sensor element 200 does not occur, the readout circuit 90 only needs to be able to read out one of the "0" state (low resistance state) and the "1" state (high resistance state), which enables the readout circuit 90 to be simplified and miniaturized. As a result, according to this embodiment, the measuring device 140 can be miniaturized, and an increase in the manufacturing cost of the measuring device 140 can also be suppressed.

[0089] Additionally, in this embodiment, by using MTJ elements having a stacked structure of the same material for the memory element 300 and the sensor element 200, the sensor cell array 150 that performs measurements and the memory cell array 146 that stores data can be mounted on a single substrate. Therefore, according to this embodiment, the sensor cell array 150 and the memory cell array 146 can be fabricated simultaneously, which makes it possible to suppress increases in the manufacturing time and manufacturing costs of the measuring device 140.

[0090] In this embodiment, the measuring device 140 and the sensor element 200 are not limited to the forms shown in FIGS. 9A and 9B, but can be modified into various forms.

[0091] <<4. Second Embodiment>> Next, details of a second embodiment of the present disclosure will be described with reference to Fig. 10. Fig. 10 is a schematic diagram showing a configuration example of an element according to the second embodiment of the present disclosure.

[0092] In this embodiment, the basic configuration of the measurement device 140 is the same as that of the first embodiment. However, unlike the first embodiment, in this embodiment, as shown in FIG. 10 , the sensor element 200b has a tapered structure in which the diameter expands from the free layer 205 toward the fixed layer 201. This increases the leakage magnetic field to the free layer 205 in the sensor element 200b, which is generated by the sum of the magnetizations of the fixed layer 201 and the reference layer 203. Therefore, according to this embodiment, the leakage magnetic field increases the asymmetry of the potential between the "0" state (low resistance state) (first state) and the "1" state (high resistance state) (second state) of the sensor element 200b. Specifically, as shown in the lower part of FIG. 10 , in this embodiment, for example, the potential with respect to the magnetization direction of the free layer 205 of the sensor element 200b is lower in the "1" state (high resistance state) than in the initial "0" state (low resistance state).

[0093] As a result, in this embodiment, the sensor element 200b can irreversibly reverse from the "0" state (low resistance state) to the "1" state (high resistance state) depending on the temperature and the time of exposure to that temperature. That is, according to this embodiment, the sensor element 200b transitions (reverses) from the "0" state (low resistance state), which is the initial value, to the "1" state (high resistance state) depending on the temperature and the exposure time, and then does not transition (reverse) from the "1" state (high resistance state) to the "0" state (low resistance state).

[0094] In this embodiment, the magnetic field applying section that applies a bias magnetic field in one direction to the sensor element 200 can be said to have a tapered structure of the sensor element 200 b that expands in diameter from the free layer 205 toward the fixed layer 201 .

[0095] In this embodiment, the sensor element 200b is not limited to the form shown in FIG. 10, but can be modified into various forms.

[0096] 5. Third Embodiment Next, details of a measuring device 140c according to a third embodiment of the present disclosure will be described with reference to Fig. 11A and Fig. 11B. Fig. 11A is a schematic diagram showing an example of the configuration of the measuring device 140c according to this embodiment, and Fig. 11B is a schematic diagram showing an example of the configuration of an element according to this embodiment.

[0097] In the first and second embodiments described above, the sensor element 200 and the memory element 300 have different film thicknesses and shapes and therefore need to be fabricated separately, which may increase the manufacturing time and manufacturing costs of the measuring device 140. Therefore, in the third embodiment, a measuring device 140c is proposed that has a configuration that does not require such fabrication.

[0098] In this embodiment, the basic configuration of the measurement device 140c is the same as that of the first embodiment. However, unlike the first embodiment, this embodiment is different from the first embodiment in that, as shown in Fig. 11A, a magnet layer 152 is provided near the sensor cell array 150, more specifically, above or below the sensor cell array 150, as a magnetic field application unit that applies a bias magnetic field in one direction to the plurality of sensor elements 200c.

[0099] In this embodiment, as in the first embodiment, as shown in FIG. 11B, the sensor element 200c has a smaller radius r than the memory element 300. Therefore, the sensor element 200c has a smaller energy barrier E Ｂ11B , the potential of the sensor element 200c is highly asymmetric between the "0" state (low resistance state) (first state) and the "1" state (high resistance state) (second state) of the sensor element 200c. As shown in the lower part of FIG. 11B , the potential of the sensor element 200c relative to the magnetization direction of the free layer 205 of the sensor element 200c is lower in the "1" state (high resistance state) than in the initial "0" state (low resistance state).

[0100] As a result, in this embodiment, the sensor element 200c can irreversibly reverse from the "0" state (low resistance state) to the "1" state (high resistance state) depending on the temperature and the time of exposure to that temperature. That is, according to this embodiment, the sensor element 200c transitions (reverses) from the "0" state (low resistance state), which is the initial value, to the "1" state (high resistance state) depending on the temperature and the exposure time, and then does not transition (reverse) from the "1" state (high resistance state) to the "0" state (low resistance state).

[0101] In this embodiment, the measuring device 140c and the sensor element 200c are not limited to the forms shown in FIGS. 11A and 11B, but can be modified into various forms.

[0102] <<6. Fourth Embodiment>> Next, details of a measuring device 140d according to a fourth embodiment of the present disclosure will be described with reference to Fig. 12A, Fig. 12B, Fig. 13, and Fig. 14. Fig. 12A is a schematic diagram showing an example configuration of the measuring device 140d according to this embodiment, and Fig. 12B is a schematic diagram showing an example configuration of an element according to this embodiment. Furthermore, Fig. 13 and Fig. 14 are diagrams for explaining this embodiment.

[0103] In the third embodiment described above, there is a possibility that the manufacturing time and manufacturing cost of the measuring device 140c will increase due to the provision of the magnet layer 152. Furthermore, in the third embodiment, if the sensor cell array 150 and the memory cell array 146 are close to each other, the memory elements 300 of the memory cell array 146 may be affected by the magnet layer 152, and data may not be stored properly.

[0104] Therefore, in the fourth embodiment, as shown in FIG. 12A , a magnetic field application element 400 is provided in the sensor cell array 150 as a magnetic field application unit that applies a unidirectional bias magnetic field to the sensor element 200d. Specifically, in this embodiment, a plurality of magnetic field application elements 400 are provided adjacent to each of the plurality of sensor elements 200d. As shown in FIG. 12B , the magnetic field application element 400 is an MTJ element having the same layered structure as the sensor element 200d and the memory element 300. In this embodiment, by using the magnetic field application element 400, the memory element 300, and the sensor element 200 as MTJ elements having a layered structure made of the same material, these elements can be fabricated simultaneously, thereby suppressing increases in the manufacturing time and manufacturing costs of the measurement device 140d.

[0105] Furthermore, in this embodiment, as initialization, the same data ("0" or "1" state) is written to each magnetic field application element 400 so that the magnetic field application element 400 has a magnetization direction opposite to that of the initial state of the multiple sensor elements 200. In this way, the multiple magnetic field application elements 400 can generate a leakage magnetic field that applies a unidirectional bias magnetic field to the adjacent sensor element 200d. As shown in FIG. 13 , the sensor element 200d is subjected to, for example, a vertically downward magnetic field, which increases the asymmetry of the potential between the "0" state (low resistance state) (first state) and the "1" state (high resistance state) (second state). Specifically, as shown in the lower center of FIG. 12B , in this embodiment, for example, the potential with respect to the magnetization direction of the free layer 205 of the sensor element 200d is lower in the "1" state (high resistance state) than in the initial "0" state (low resistance state).

[0106] As a result, in this embodiment, the sensor element 200d can irreversibly reverse from the "0" state (low resistance state) to the "1" state (high resistance state) depending on the temperature and the time of exposure to that temperature. That is, according to this embodiment, the sensor element 200d transitions (reverses) from the "0" state (low resistance state), which is the initial value, to the "1" state (high resistance state) depending on the temperature and the exposure time, and then does not transition (reverse) from the "1" state (high resistance state) to the "0" state (low resistance state).

[0107] In this embodiment, it is preferable that the magnetic field application element 400 stably retains the magnetization direction (data) that was initially written, and therefore, similarly to the memory element 300, it is preferable that the radius r of the magnetic field application element 400 is large. Therefore, in this embodiment, the radius r of the magnetic field application element 400 is larger than that of the sensor element 200d. Note that, in this embodiment, when the sensor element 200d and the magnetic field application element 400 are converted into resistance values, it is preferable that the resistance value of the magnetic field application element 400 is about half that of the sensor element 200d.

[0108] The left side of FIG. 14 shows the initial state of the sensor cell array 150 in this embodiment. On the left side of FIG. 14, the sensor elements 200d and the magnetic field application elements 400 are initialized to the "0" state. Then, in this embodiment, as shown on the right side of FIG. 14, after a certain period of time, some or all of the sensor elements 200d are rewritten (reversed) to the "1" state depending on the temperature. On the other hand, the magnetic field application elements 400 stably maintain their initial state and are therefore not rewritten (reversed) to the "1" state. Therefore, in this embodiment, the measuring device 140d can measure the temperature and elapsed time by detecting the ratio (reversal rate F) of the number of sensor elements 200d that have been reversed depending on the ambient temperature and exposure time to the total number of sensor elements 200d.

[0109] In this embodiment, the initialization circuit 15 may include, for example, an external magnetic field application unit (not shown) that applies an external magnetic field to the plurality of sensor elements 200 and the plurality of magnetic field application elements 400. The initialization circuit 15 collectively initializes the plurality of sensor elements 200 and the plurality of magnetic field application elements 400 by applying an external magnetic field to the plurality of sensor elements 200 and the plurality of magnetic field application elements 400 via the external magnetic field application unit. Alternatively, in this embodiment, the initialization circuit 15 may be connected to, for example, a plurality of wirings (not shown) electrically connected to each of the plurality of magnetic field application elements 400. The initialization circuit 15 initializes the plurality of magnetic field application elements 400 by applying a current or a voltage to each of the plurality of magnetic field application elements 400 via the wirings.

[0110] As described above, in this embodiment, the magnetic field application element 400 is provided as a magnetic field application unit that applies a unidirectional bias magnetic field to the sensor element 200d. In this embodiment, the multiple magnetic field application elements 400 generate a leakage magnetic field that applies a unidirectional bias magnetic field to adjacent sensor elements 200d. Therefore, in this embodiment, a magnetic field in a predetermined direction is applied to the sensor element 200d, and the potential asymmetry between the "0" state (low resistance state) (first state) and the "1" state (high resistance state) (second state) becomes high (increased).

[0111] As a result, in this embodiment, the sensor element 200d can irreversibly reverse from the "0" state (low resistance state) to the "1" state (high resistance state) depending on the temperature and the time of exposure to that temperature. That is, according to this embodiment, the sensor element 200d transitions (reverses) from the "0" state (low resistance state), which is the initial value, to the "1" state (high resistance state) depending on the temperature and the exposure time, and then does not transition (reverse) from the "1" state (high resistance state) to the "0" state (low resistance state).

[0112] Furthermore, in this embodiment, since re-inversion of the sensor element 200d does not occur, the readout circuit 90 only needs to read out one of the "0" state (low resistance state) and the "1" state (high resistance state), which simplifies and reduces the size of the readout circuit 90. As a result, according to this embodiment, the measuring device 140d can be made smaller, and an increase in the manufacturing cost of the measuring device 140d can also be suppressed.

[0113] In addition, in this embodiment, the magnetic field application element 400, the memory element 300, and the sensor element 200d are MTJ elements having a stacked structure of the same material, so that they can be manufactured simultaneously, thereby suppressing increases in the manufacturing time and manufacturing costs of the measuring device 140d.

[0114] In this embodiment, the measuring device 140d, the sensor element 200d, and the magnetic field application element 400 are not limited to the forms shown in FIGS. 12A and 12B, but can be modified into various forms.

[0115] <<7. Operation Example>> Next, an operation example of the measuring device 140 according to an embodiment of the present disclosure will be described with reference to Fig. 15. Fig. 15 is a flowchart showing an operation example of the measuring device 140 according to this embodiment. This operation is started, for example, when the measuring device 140 is powered on.

[0116] The measuring device 140 initializes the sensor element 200 and the like (step S1). Next, the measuring device 140 is turned off, and the sensor element 200 starts measuring the temperature and elapsed time. Then, after a predetermined time has elapsed since the above-mentioned step S1 (step S2), the measuring device 140, which has been turned on, acquires (measures) information on at least one of the ambient temperature of the measurement target and the time (exposure time) that the measurement target has been exposed to that temperature based on the reversal rate F (step S3).

[0117] In this embodiment, the operation of the measuring device 140 is not limited to the flow shown in FIG.

[0118] <<8. Configuration Example of Sensor Circuit>> Next, a configuration example of the sensor circuit 10 according to an embodiment of the present disclosure will be described with reference to Fig. 16. Fig. 16 is a diagram showing a configuration example of the sensor circuit 10 according to an embodiment of the present disclosure. Fig. 16 shows the sensor circuit 10 using an SSR (Split Store / Restore)-NVFF circuit system.

[0119] The sensor circuit 10 shown in Figure 16 has a volatile memory unit 11, an initialization driver (initialization circuit) 15, a transistor 16, a transistor 17, a transistor 18, a transistor 19, a sensor element 200, an inverter 22, a control driver 23, an OR circuit 24, and a transistor 25.

[0120] Here, transistor 16 is a P-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor), and transistors 17, 18, 19, and 25 are N-channel MOSFETs. Although each transistor is represented as a single element in Fig. 16, in practice, each transistor may be configured as a group of transistor elements in which elements of the same type are connected in parallel according to current capacity.

[0121] The volatile memory unit 11 is configured as a flip-flop circuit that temporarily holds the state of a memory node, such as stored data (initial value), which is information supplied from the outside, more specifically, the voltage level corresponding to the stored data (initial value).

[0122] The volatile memory unit 11 includes an inverter 41, a transmission gate 42, a master latch 43, a transmission gate 44, a slave latch 45, and an inverter 46. The slave latch 45 is, for example, an example of the read circuit 90 (see FIG. 2 ) described above.

[0123] In the configuration of FIG. 16, the master latch 43 includes an inverter 51 , an inverter 52 and a transmission gate 53 .

[0124] The slave latch 45 also has an inverter 61, an inverter 62, a transmission gate 63, and a transistor (N-channel MOSFET) 64. The slave latch 45 also has a storage node N11 and a storage node N12.

[0125] In the volatile memory unit 11, the transmission gates 42 and 63 turn on when the clock signal C falls and turn off when the clock signal C rises. In other words, the transmission gates 42 and 63 turn off when the inverted clock signal CB rises and turn on when the inverted clock signal CB rises. In contrast, the transmission gates 53 and 44 turn off when the clock signal C falls and turn on when the clock signal C rises. In other words, the transmission gates 53 and 44 turn on when the inverted clock signal CB rises and turn off when the inverted clock signal CB rises.

[0126] In the volatile storage unit 11 , the input side of the inverter 41 serves as the input terminal of the volatile storage unit 11 , and the output side of the inverter 41 is connected to the input side of the inverter 51 via the transmission gate 42 .

[0127] The output side of the inverter 51 is connected to the storage node N11 of the slave latch 45 via the transmission gate 44, and the output terminal of the inverter 51 is also connected to the input side of the inverter 52.

[0128] Furthermore, the output side of the inverter 52 is connected to the input side of the inverter 51 via the transmission gate 53. That is, the output side of the transmission gate 53 is connected between the inverter 51 and the transmission gate 42 via the transmission gate 53.

[0129] The slave latch 45 has storage nodes N11 and N12 that temporarily hold a voltage level corresponding to input storage data. An inverter 61 is provided between the storage nodes N11 and N12.

[0130] The storage node N12 is connected to the input terminals of the inverter 46, the inverter 62, and the initialization driver 15. The output side of the inverter 46 serves as the output terminal of the volatile storage unit 11.

[0131] The output side of the inverter 62 is connected to the storage node N11 via a transmission gate 63. In addition, both ends of the transmission gate 63 are connected to a transistor 64, which is an N-channel MOSFET. In other words, one end of the transistor 64 is connected to the input side of the transmission gate 63, and the other end of the transistor 64 is connected to the output side of the transmission gate 63. A restore (read) control signal SR1 of a predetermined voltage level is supplied to the gate of the transistor 64.

[0132] The initialization driver 15 corresponds to, for example, the initialization circuit 15 (see FIG. 2 ) described above. The initialization driver 15 shown in FIG. 16 is configured as an inverter, which is an inverting element. That is, the initialization driver 15 has a transistor 81, which is a P-channel MOSFET, and a transistor 82, which is an N-channel MOSFET.

[0133] In the initialization driver 15, a transistor 82 is connected to one terminal of a transistor 81. The other terminal of the transistor 81 is connected to a power supply via a transistor 16.

[0134] The gate of the transistor 16 is supplied with an inverted signal of the initialization control signal SR 2 via an inverter 22 .

[0135] The terminal of the transistor 82 opposite to the terminal connected to the transistor 81 is connected to ground via the transistor 17. The gate of the transistor 17 is supplied with an initialization control signal SR2.

[0136] Furthermore, the output side end of the inverter formed by the transistors 81 and 82 is connected to the sensor element 200 via a node N14.

[0137] At the time of initialization, an initial value corresponding to the voltage level state at the storage node N11 and the storage node N12 is written to the sensor element 200. At the time of reading, the data held in the sensor element 200, i.e., the state of the voltage level held, is read out to the storage node N11 and the storage node N12.

[0138] In the sensor element 200, the free layer 205 is connected to the control line L11, and the opposite side of the free layer 205, that is, the fixed layer 201 of the sensor element 200, is connected to a node N14.

[0139] The node N14 is connected to the output end of the initialization driver 15 and is also connected to the storage node N11 via the transistor 18.

[0140] The gates of the transistors 18 and 19 are supplied with a restore control signal SR1.

[0141] A control driver 23 for controlling the voltage level of the control line L11 is connected to the control line L11 connected to the sensor element 200.

[0142] The control driver 23 includes an inverter, which is an inverting element, that is, a transistor 101 which is a P-channel MOSFET and a transistor 102 which is an N-channel MOSFET.

[0143] In the control driver 23, one terminal of the transistor 101 is connected to a power supply, and the other terminal of the transistor 101 is connected to the transistor 102 and the control line L11.

[0144] The terminal of the transistor 102 opposite to the terminal to which the transistor 101 and the control line L11 are connected is connected to ground via a transistor 25 .

[0145] A control signal CTRL is supplied to the input terminals of the control driver 23, that is, the gates of the transistors 101 and 102.

[0146] The gate of the transistor 25 is connected to the output terminal of the OR circuit 24, and the input terminal of the OR circuit 24 is supplied with the restore control signal SR1 and the initialization control signal SR2.

[0147] For example, one sensor circuit 10 may be one cell that constitutes the sensor 141, and multiple cells may be provided within the sensor 141. In this case, the transistor 25 in each sensor circuit 10 is set to an on state in the initialization mode and the readout mode.

[0148] In this case, as the OR circuit 24 for turning on the transistor 25, one OR circuit may be provided that is common to all the plurality of cells, that is, all the plurality of sensor circuits 10.

[0149] Next, a description will be given of an example of state transitions of the sensor circuit 10. The sensor circuit 10 operates in three modes: an initialization mode, a sensing mode, and a readout mode.

[0150] In the initialization mode, an initial value is stored in the sensor element 200 of the sensor circuit 10. In the sensing mode, the state of the sensor element 200 is inverted depending on the temperature and exposure time. In the readout mode, the state of the sensor element 200 is read out. The sensor circuit 10 transitions through the initialization mode, sensing mode, and readout mode in this order. The measuring device 140 can detect whether the characteristics (initial value) of the sensor element 200 have changed (inverted) depending on the output Q of the sensor circuit 10.

[0151] The sensor circuit shown in Fig. 16 may be modified as shown in Fig. 17. Fig. 17 is a diagram showing a configuration example of a sensor circuit 10 according to an embodiment of the present disclosure. In Fig. 17, elements similar to those in the sensor circuit 10 of Fig. 16 are denoted by the same reference numerals, and description of each element will be omitted here.

[0152] <<9. Summary>> As described above, in each embodiment of the present disclosure, by providing a magnetic field application unit that applies a unidirectional bias magnetic field to the sensor element 200, the potential asymmetry between the “0” state (low resistance state) (first state) and the “1” state (high resistance state) (second state) of the sensor element 200 is increased (increased). Therefore, according to this embodiment, after the sensor element 200 transitions (reverses) from the “0” state (low resistance state), which is the initial value, to the “1” state (high resistance state) depending on the temperature and exposure time, the sensor element 200 does not transition (reverse) from the “1” state (high resistance state) to the “0” state (low resistance state).

[0153] Furthermore, in this embodiment, since re-inversion of the sensor element 200 does not occur, the readout circuit 90 only needs to be able to read out one of the "0" state (low resistance state) and the "1" state (high resistance state), which enables the readout circuit 90 to be simplified and miniaturized. As a result, according to this embodiment, the measuring device 140 can be miniaturized, and an increase in the manufacturing cost of the measuring device 140 can also be suppressed.

[0154] Additionally, in this embodiment, by using MTJ elements having a stacked structure of the same material for the memory element 300 and the sensor element 200, the sensor cell array 150 that performs measurements and the memory cell array 146 that stores data can be mounted on a single substrate. Therefore, according to this embodiment, the sensor cell array 150 and the memory cell array 146 can be fabricated simultaneously, which makes it possible to suppress increases in the manufacturing time and manufacturing costs of the measuring device 140.

[0155] Furthermore, the sensor element 200 and the like according to the embodiment of the present disclosure can be manufactured using manufacturing methods, devices, and conditions that are used in the manufacture of general semiconductor devices.

[0156] Examples of the above-mentioned method include a PVD (Physical Vapor Deposition) method, a CVD (Chemical Vapor Deposition) method, and an ALD (Atomic Layer Deposition) method. Examples of PVD methods include vacuum deposition, EB (electron beam) deposition, various sputtering methods (magnetron sputtering, RF (radio frequency)-DC (direct current) combined bias sputtering, ECR (electron cyclotron resonance) sputtering, facing target sputtering, high frequency sputtering, etc.), ion plating, laser ablation, molecular beam epitaxy (MBE), and laser transfer. Examples of CVD methods include plasma CVD, thermal CVD, metal organic (MO) CVD, and photo CVD. Other methods include electroplating, electroless plating, spin coating, dipping, casting, microcontact printing, drop casting, various printing methods such as screen printing, inkjet printing, offset printing, gravure printing, and flexographic printing, stamping, spraying, and various coating methods such as air doctor coater, blade coater, rod coater, knife coater, squeeze coater, reverse roll coater, transfer roll coater, gravure coater, kiss coater, cast coater, spray coater, slit orifice coater, and calendar coater. Furthermore, patterning methods include chemical etching such as shadow mask, laser transfer, and photolithography, and physical etching using ultraviolet light or laser. Additionally, planarization techniques include CMP (Chemical Mechanical Polishing), laser planarization, and reflow.

[0157] <<10. Application Examples>> <10.1 Various Devices> For example, electronic devices such as computers and cameras have multiple electronic components (e.g., ICs, memory, batteries, etc.) densely packed together. Therefore, heat generated by each electronic component during operation may cause malfunctions in the electronic device. Even when the electronic device is not in operation, malfunctions may occur due to a rechargeable battery that generates heat during charging or exposure to high temperatures, such as the inside of a car in summer. Therefore, many electronic devices may be equipped with temperature sensors that detect the temperature of electronic components, or timers that detect a predetermined time, such as the time the device has been exposed to a predetermined temperature. Therefore, the measuring device 140 or sensor element 200 according to an embodiment of the present disclosure can be mounted in various electronic devices or electronic components as such sensors or timers.

[0158] Furthermore, the sensor element 200 according to the embodiment of the present disclosure can perform measurements without a power source, and therefore can be applied to IC tags attached to various products. For example, by mounting the sensor element 200 on an IC tag and attaching the IC tag to a product to be stored and managed, it is possible to measure, without a power source, the temperature and period for which the product has been stored.

[0159] <10.2 Memory System> The measurement device 140 according to the present disclosure can also be applied to a memory system. An example configuration of a memory system will be described below with reference to FIG. 18. FIG. 18 is a block diagram showing an example configuration of a memory system 1. As shown in FIG. 18, the memory system 1 includes a host computer 100 and a storage device 500.

[0160] The host computer 100 controls the entire memory system 1. Specifically, the host computer 100 generates commands and data and supplies them to the storage device 500. The host computer 100 can also receive data read from the storage device 500. Here, commands are used to control the storage device 500, and include, for example, a write command that instructs writing data and a read command that instructs reading data.

[0161] The storage device 500 has a memory controller 510 and a storage unit 700. The memory controller 510 controls the storage device 500. When the memory controller 510 receives a write command and data from the host computer 100, it generates an error detection and correction code (ECC) from the data. The memory controller 510 accesses the storage device 500 and writes the encoded data.

[0162] Furthermore, when the memory controller 510 receives a read command from the host computer 100, it accesses the storage device 500 and reads the encoded data. The memory controller 510 then converts (decodes) the encoded data back to the original data before encoding. During decoding, the memory controller 510 detects and corrects errors in the data based on the ECC. The memory controller 510 then supplies the corrected data to the host computer 100.

[0163] Furthermore, as shown in FIG. 18, the memory controller 510 includes a read / write processing unit 511, a refresh processing unit 512, and a measuring device 140.

[0164] The read / write processing unit 511 accesses the storage unit 700 in accordance with commands from the host computer 100 to read or write data. When writing data, the above-mentioned ECC is generated and the encoded data is written. When reading data, errors in the data are detected and corrected based on the ECC.

[0165] The refresh processing unit 512 performs refresh processing under the control of the measuring device 140. In the refresh processing, the refresh processing unit 512 reads data from the storage unit 700, corrects errors in the data using ECC, and writes the corrected data again.

[0166] The measurement device 140 detects the timing to refresh the storage unit 700. The measurement device 140 according to an embodiment of the present disclosure can be used as the measurement device 140. For example, the refresh processing unit 512 refreshes the storage unit 700 based on the ambient temperature and exposure time of the measurement target (here, the storage unit 700) based on the reversal rate F obtained by the measurement device 140.

[0167] The storage unit 700 stores data under the control of the memory controller 510. The storage unit 700 includes, for example, a non-volatile MRAM (memory element 300).

[0168] Next, a configuration example of the storage unit 700 will be described with reference to Fig. 19. Fig. 19 is a block diagram showing a configuration example of the storage unit 700. As shown in Fig. 19, the storage unit 700 includes a data buffer 710, a memory cell array 146, a driver 730, an address decoder 740, a bus 750, a control interface 760, and a memory control unit 770.

[0169] The data buffer 710 holds write data and read data in units of access under the control of the memory control unit 770. The memory cell array 146 has a plurality of memory elements 300 arranged in a matrix.

[0170] The driver 730 writes data to or reads data from the memory device 300 selected by the address decoder 740. The address decoder 740 analyzes an address specified by a command and selects the memory device 300 corresponding to that address.

[0171] The bus 750 is a common path for the data buffer 710, the memory cell array 146, the address decoder 740, the memory control unit 770, and the control interface 760 to exchange data with one another.

[0172] The control interface 760 is an interface through which the memory controller 510 and the storage unit 700 exchange data and commands with each other.

[0173] The memory control unit 770 controls the driver 730 and the address decoder 740 to write or read data.

[0174] Next, the operation of the memory system 1 will be described with reference to Fig. 20. Fig. 20 is a flowchart showing an example of the operation of the memory system 1. This operation is started, for example, when the power is turned on to the storage device 500. Note that this operation may also be started when a predetermined period has elapsed since the previous determination, or when the number of accesses since the previous determination has exceeded a predetermined number.

[0175] The storage device 500 acquires a bit error rate (BER) from the measuring device 140 (step S11). Here, the BER is determined based on the inversion rate F described above. Then, the storage device 500 determines whether it is time to perform a refresh based on whether the BER is equal to or greater than a predetermined threshold value Th1 (step S12).

[0176] If it is determined that it is time to perform a refresh because the BER is equal to or higher than Th1 (step S12; Yes), the storage device 500 refreshes the storage unit 700 (step S13) and initializes the measuring device 140 (step S14). On the other hand, if it is determined that it is not time to perform a refresh because the BER is lower than Th1 (step S12; No), the process returns to the above-mentioned step S11 after a predetermined time has elapsed.

[0177] The memory device 500 can detect the optimal timing to refresh the memory unit 700 using the measurement device 140 of the present disclosure, thereby improving the data retention characteristics of the memory unit 700 while reducing power consumption.

[0178] <<11. Supplementary Information>> Although preferred embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings, the technical scope of the present disclosure is not limited to such examples. It is clear that a person skilled in the art of the present disclosure can conceive of various modified or altered examples within the scope of the technical idea described in the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure.

[0179] Furthermore, the components of each device shown in the figures are functional concepts and are not limited to being physically configured as shown in the figures. In other words, the specific form of distribution and integration of each device is not limited to that shown in the figures, and all or part of the devices may be functionally or physically distributed and integrated in any unit.

[0180] Furthermore, the effects described herein are merely descriptive or exemplary and are not limiting. In other words, the technology according to the present disclosure may achieve other effects that will be apparent to those skilled in the art from the description of this specification, in addition to or in place of the above-described effects.

[0181] The present technology can also be configured as follows. (1) A sensor device including: a plurality of sensor elements that change from a first state to a second state depending on temperature and a time period exposed to the temperature; and a magnetic field application unit that applies a magnetic field in a predetermined direction to the plurality of sensor elements, wherein each of the sensor elements is a magnetic tunnel junction element having an energy barrier between the first state and the second state, and the magnetic field application unit applies the magnetic field to each of the sensor elements to increase asymmetry between the potential in the first state and the potential in the second state of each of the sensor elements across the energy barrier. (2) The sensor device according to (1), wherein the magnetic field application unit is made of a plurality of magnetic field application elements formed from magnetic tunnel junction elements and provided adjacent to each of the plurality of sensor elements. (3) The sensor device according to (2), wherein the diameter of the magnetic field application elements is larger than that of the sensor elements. (4) The sensor device according to (1), wherein the magnetic field application unit is made of a magnet layer provided near the plurality of sensor elements. (5) The sensor device according to (1), further comprising a memory unit that stores states of the plurality of sensor elements or performs predetermined control in accordance with states of the plurality of sensor elements, the memory unit having a plurality of memory elements made of magnetic tunnel junction elements. (6) The sensor device according to (5), wherein the diameter of the sensor elements is smaller than that of the memory elements. (7) The sensor device according to (5) or (6), wherein each of the sensor elements has: a first fixed layer whose magnetization direction is fixed; a first non-magnetic layer disposed on the first fixed layer; and a first free layer disposed on the first non-magnetic layer and whose magnetization direction reverses in accordance with the temperature and the time exposed to the temperature. (8) The sensor device according to (7), wherein the magnetic field application unit has a tapered structure in the sensor element whose diameter increases from the first free layer toward the first fixed layer. (9) The sensor device according to (7), wherein each of the memory elements has: a second fixed layer whose magnetization direction is fixed; a second non-magnetic layer disposed on the second fixed layer; and a second free layer disposed on the second non-magnetic layer and whose magnetization direction is reversible.(10) The sensor device according to (9) above, wherein the magnetic field application unit has a laminated structure of the sensor elements in which the film thickness of each layer is adjusted. (11) The sensor device according to (10) above, wherein the film thickness of the first fixed layer is thicker than that of the second fixed layer. (12) The sensor device according to (2) or (3) above, wherein each of the magnetic field application elements has: a third fixed layer whose magnetization direction is fixed; a third non-magnetic layer disposed on the third fixed layer; and a third free layer disposed on the third non-magnetic layer and whose magnetization direction is reversible. (13) The sensor device according to any one of (1) to (12) above, further comprising a sensor circuit unit that detects the states of the plurality of sensor elements. (14) The sensor device according to (13) above, wherein the sensor circuit unit is formed of a non-volatile flip-flop circuit including the plurality of sensor elements. (15) The sensor device according to (13) or (14), wherein the sensor circuit unit further includes an initialization circuit that sets the plurality of sensor elements to the first state. (16) The sensor device according to (15), wherein the initialization circuit controls a plurality of wirings electrically connected to the plurality of sensor elements, and applies a current or a voltage to each of the plurality of sensor elements via the wirings, thereby setting the plurality of sensor elements to the first state. (17) The sensor device according to (15), wherein the initialization circuit has an external magnetic field application unit that applies an external magnetic field to the plurality of sensor elements, and sets the plurality of sensor elements to the first state by applying the external magnetic field to the plurality of sensor elements using the external magnetic field application unit.

[0182] 1 Memory system 10 Sensor circuit 15 Initialization circuit 16, 17, 18, 19, 25, 64, 81, 82, 101, 102 Transistor 22, 41, 46, 51, 52, 61, 62 Inverter 23 Control driver 24 OR circuit 42, 44, 53, 63 Transmission gate 43 Master latch 45 Slave latch 90 Read circuit 140, 140a, 140c, 140d Measurement device 141 Sensor 142 Acquisition unit 143 Determination unit 144 Storage 145 Initialization unit 146 Memory cell array 147 Sensor control unit 148 MRAM control unit 150 Sensor cell array 152 Magnet layer 100 Host computer 200, 200a, 200b, 200c, 200d Sensor element 201 fixed layer 202 coupling layer 203 reference layer 204 tunnel barrier layer 205 free layer 300 memory element 400 magnetic field application element 500 storage device 510 memory controller 511 read / write processing section 512 refresh processing section 700 storage section 710 data buffer 730 driver 740 address decoder 750 bus 760 control interface 770 memory control section

Claims

1. A sensor device comprising: a plurality of sensor elements that change from a first state to a second state depending on the temperature and the time they are exposed to said temperature; and a magnetic field application unit that applies a magnetic field in a predetermined direction to said plurality of sensor elements, wherein each of said sensor elements is a magnetic tunnel junction element having an energy barrier between said first state and said second state, and said magnetic field application unit applies said magnetic field to each of said sensor elements, thereby increasing the asymmetry between the potential in said first state and the potential in said second state of each of said sensor elements across said energy barrier.

2. The sensor device according to claim 1, wherein the magnetic field applying section comprises a plurality of magnetic field applying elements formed from magnetic tunnel junction elements, which are provided adjacent to each of the plurality of sensor elements.

3. The sensor device according to claim 2, wherein the diameter of the magnetic field applying element is larger than that of the sensor element.

4. The sensor device according to claim 1, wherein the magnetic field applying section comprises a magnet layer provided in the vicinity of the plurality of sensor elements.

5. The sensor device according to claim 1, further comprising a memory unit that stores the states of the plurality of sensor elements or that performs predetermined control in accordance with the states of the plurality of sensor elements, the memory unit having a plurality of memory elements made of magnetic tunnel junction elements.

6. The sensor device according to claim 5, wherein the diameter of the sensor element is smaller than that of the memory element.

7. The sensor device according to claim 5, wherein each of the sensor elements comprises: a first fixed layer whose magnetization direction is fixed; a first non-magnetic layer disposed on the first fixed layer; and a first free layer disposed on the first non-magnetic layer, whose magnetization direction reverses depending on the temperature and the time exposed to the temperature.

8. The sensor device according to claim 7, wherein the magnetic field application section has a tapered structure in which the diameter of the sensor element increases from the first free layer toward the first fixed layer.

9. The sensor device of claim 7, wherein each of the memory elements has: a second fixed layer whose magnetization direction is fixed; a second non-magnetic layer disposed on the second fixed layer; and a second free layer disposed on the second non-magnetic layer and whose magnetization direction can be reversed.

10. The sensor device according to claim 9, wherein the magnetic field applying section has a laminated structure of the sensor element in which the film thickness of each layer is adjusted.

11. The sensor device according to claim 10, wherein the first pinning layer has a thickness greater than that of the second pinning layer.

12. The sensor device of claim 2, wherein each of the magnetic field application elements has: a third fixed layer whose magnetization direction is fixed; a third non-magnetic layer disposed on the third fixed layer; and a third free layer disposed on the third non-magnetic layer and whose magnetization direction can be reversed.

13. The sensor device according to claim 1, further comprising a sensor circuit section that detects the state of the plurality of sensor elements.

14. The sensor device according to claim 13, wherein the sensor circuit section comprises a nonvolatile flip-flop circuit including the plurality of sensor elements.

15. The sensor device according to claim 13, wherein the sensor circuit section further includes an initialization circuit that sets the plurality of sensor elements to the first state.

16. The sensor device according to claim 15, wherein the initialization circuit controls a plurality of wirings electrically connected to each of the plurality of sensor elements, and applies a current or a voltage to each of the plurality of sensor elements via the wirings, thereby putting the plurality of sensor elements into the first state.

17. The sensor device according to claim 15, wherein the initialization circuit has an external magnetic field application unit that applies an external magnetic field to the plurality of sensor elements, and the external magnetic field application unit applies the external magnetic field to the plurality of sensor elements, thereby putting the plurality of sensor elements into the first state.

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