CN110220608B - A method for measuring temperature using the coercive field of a magnetic tunnel junction reference layer - Google Patents

Abstract

The invention discloses a method for measuring temperature by using the coercive field of a reference layer of a magnetic tunnel junction, comprising the following steps: using a resistance heating platform to measure the change curve of the coercive field of the reference layer of the magnetic tunnel junction with temperature, and calculate the temperature coercion Field coefficient; by measuring the magnetic tunnel junction coercive field and using the obtained temperature coercive field coefficient, the coercive field signal is converted into a temperature signal; the present invention can be used for monitoring the ambient temperature, and is also suitable for other heating conditions, such as laser heating. The invention uses the nano-scale magnetic tunnel junction as a temperature measuring component, and utilizes the variation relationship of the coercive field of the reference layer with the temperature, so that the temperature measurement range is wide, the anti-interference performance is good, the operation is simple, and the magnetic tunnel junction is very small. Magnetic tunnel junctions are fabricated into temperature sensors with high spatial resolution, which have broad application prospects.

Description

A method for measuring temperature using the coercive field of a magnetic tunnel junction reference layer

technical field

The invention relates to a method for accurately measuring temperature by utilizing a magnetic tunnel junction, and belongs to the technical field of temperature sensing.

Background technique

In recent years, temperature sensors have developed rapidly and the market has risen rapidly, accounting for almost 40% of the total demand for sensors. According to the company's analysis and forecast, the temperature sensor market will increase at a CAGR of 5.11% between 2014 and 2020, and its total volume will reach $6.05 billion in 2020. At present, only medium and low-grade products of temperature sensors in my country basically meet the market demand, and the satisfaction rate of product varieties is about 60%-70%. However, from the perspective of the product structure of the industry, the proportion of old products accounts for more than 60%, the new products are obviously insufficient, and there are fewer high-tech products; at the same time, digital, intelligent and miniaturized products are seriously lacking.

With the rapid miniaturization of electronic devices, heat dissipation and heat conduction have become more and more important, and are becoming the limiting factor for further miniaturization of electronic devices and a key factor in the field of basic research. The temperature and ambient temperature need to be accurately grasped, and the required measurement method is more accurate, fast, and has a higher spatial resolution. The research shows that the coercive field of the reference layer of the magnetic tunnel junction is related to the RKKY coupling, and the coercive field of the reference layer is close to a linear relationship with the temperature around room temperature. This variation law provides the basis for the direct measurement of temperature using the coercive field. The invention has a helpful effect on the development of high-end sensors in China, and at the same time, can promote the development of basic research such as spin thermoelectronics.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method for measuring temperature using a magnetic tunnel junction coercive field.

The measuring device and schematic diagram of the present invention are shown in Figure 1:

The measurement steps are as follows:

1. A method for measuring temperature by using the coercive field of a magnetic tunnel junction reference layer, the structure of the magnetic tunnel junction (MTJ) mainly includes: using magnesium oxide or aluminum oxide as an insulating layer, CoFeB as a magnetic free layer and a reference layer, and a protective layer. layer and connection layer, one or more layers of Ru, Ta, Cu are used as protective layers, and one or more layers of Cu, Ta and CuN are used as connection layers, and the shape of the magnetic tunnel junction is oval or square, It is characterized in that the size below 50 nm has very good in-plane uniaxial anisotropy, and requires very good monolithic characteristics, the smaller the magnetic tunnel junction, the better;

2. The calibration method of the magnetic tunnel junction temperature coercive field coefficient is: the resistance heating platform used is heated by nickel-chromium resistance wire or tungsten wire, and the resistance temperature temperature measuring device used is Pt100; the temperature that the resistance heating platform can reach is 100 ^o C, use Keithley 2400 to measure the magnetoresistance curve to obtain the coercive field H _C =(H _AP-P +H _P-AP )/2 of the easy axis of the reference layer, H _AP-P means high resistance state to low resistance Coercive field of state transition, HP _-AP represents the coercive field of transition from low resistance state to high resistance state;

3. The calculation method of the temperature coercive field coefficient is as follows: the relationship between the reference layer coercive field and temperature is used, and the resistance temperature coefficient: β=ΔH _C /ΔT; ΔH _C is the change of the magnetic tunnel junction coercive field; ΔT is The change of the resistance heating platform temperature (TT ₀ ), the coercive field at room temperature 23 ^o C (T ₀ ) is used as the reference coercive field;

4. In the process of measuring the MTJ magnetoresistance curve (MR), use Keithley 2400 to apply a DC current in the MTJ, the current size is 10 µA to 1mA; use the 2-wire or 4-wire method to measure the MTJ's MR curve;

5. Temperature measurement: a) To measure the change of the ambient temperature, first measure the change of the coercive field of the reference layer of the magnetic tunnel junction with the ambient temperature. The calculation method is: T=ΔH _C /β +T _0. b); b) The temperature change under laser heating, the laser used is a femtosecond laser pulse or other laser, and the lens is focused on the surface of the magnetic tunnel junction, and the measurement is carried out in the laser. The change of the coercive field of the reference layer under the pulse, and the temperature change of the magnetic tunnel junction under the laser heating is calculated.

Compared with the prior art, the beneficial effects of the present invention are as follows:

(1) The method of measuring temperature using the coercive field of the reference layer of the magnetic tunnel junction has high measurement accuracy and an error of ±1 K;

(2) Since the magnetic tunnel junction is very small, it is beneficial to be fabricated into a nano-scale temperature sensor;

(3) The operation of the present invention is simple, environmentally friendly, and easy to industrialize.

Description of drawings

Figure 1. Schematic diagram of the measurement method. 1 is a heating resistance wire, 2 is a heat conduction platform, the material is Cu or Al, 3 is a magnetic tunnel junction, 4 is a DC current, and 5 is a Pt100 temperature sensor.

Figure 2, the measured magnetoresistance curve.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments and comparative examples.

Example 1, taking a 20 nm×30 nm magnetic tunnel junction as a temperature sensor as an example, first place the magnetic tunnel junction on a resistance heating platform, use a tungsten wire resistance wire to gradually heat the platform to 100 ^o C, and measure the temperature of the platform and the coercive field of the reference layer of the magnetic tunnel junction, which is obtained by measuring the magnetoresistance curve, as shown in Figure 2. The temperature coercive field coefficient is calculated to be 301 mOe/K. The magnetic tunnel junction is placed in the air-conditioned room and outside the room, and the coercive fields in the two environments are measured. The calculated temperature in the air-conditioned room is 22.1 ^o C, the room The outside temperature is 33.1 ^o C.

The calculated temperature inside the air-conditioned room is 23.1 ^o C, and the temperature outside the room is 33.5 ^o C.

Example 2, taking a magnetic tunnel junction of 30 nm × 50 nm as a temperature sensor as an example, the magnetic tunnel junction was placed on a resistance heating platform, using a tungsten wire resistance wire, the platform was gradually heated to 100 ^o C, and the temperature of the platform was measured. and the coercive field of the magnetic tunnel junction reference layer. The coercive field is obtained by measuring the magnetoresistance curve, and the temperature resistivity is calculated to be 342 mΩ/K. The surface of the sample is heated by a femtosecond laser, and the magnetoresistance is measured. After laser heating, the temperature of the magnetic tunnel junction is calculated to be 161 ^o C .

Claims (3)

1. A method for measuring temperature by using a coercive field of a reference layer of a Magnetic Tunnel Junction (MTJ) is characterized in that the structure of the MTJ mainly comprises: the magnetic tunnel junction is characterized in that magnesium oxide or aluminum oxide is used as an insulating layer, CoFeB is used as a magnetic free layer and a reference layer, a protective layer and a connecting layer, one or more layers of Ru, Ta and Cu are used as the protective layer, one or more layers of Cu, Ta and CuN are used as the connecting layer, the shape of the magnetic tunnel junction is oval, the size of the magnetic tunnel junction is below 50 nanometers, and the magnetic tunnel junction has very good in-plane uniaxial anisotropy; the method for obtaining the corresponding relation of the standard curve of the temperature coercive field coefficient of the magnetic tunnel junction comprises the following steps: a resistance heating platform is used, a resistance heating wire is a nickel-chromium resistance wire or a tungsten wire, the diameter is 2 mm, a used resistance temperature measuring device is Pt100, and the temperature which can be reached by the resistance heating platform is 100^oC, measuring a magneto-resistance curve (MR) by utilizing Keithley 2400 to obtain a coercive field of the easy magnetization axis of the reference layerH _C=(H _AP-P+H _P-AP)/2，H _AP-PA coercive field indicating the transition of a high resistance state to a low resistance state,H _P-APindicating the transition of the low resistance state to the high resistance state;the method for calculating the temperature coercive field coefficient comprises the following steps: temperature coefficient of resistance: β = ΔH _C/ΔT，ΔH _CChange of coercive field of magnetic tunnel junction, DeltaTFor heating the platform temperature by resistance (T-T ₀) At room temperature 23^oC（T ₀) Taking the coercive field of the reference layer as a reference coercive field; taking a magnetic tunnel junction as a temperature measurement component, a) measuring the change of ambient temperature, firstly measuring the change of coercive field of a reference layer of the magnetic tunnel junction along with the ambient temperature, and adopting a measuring instrument Keithley 2400; and then calculating to obtain a change curve of the environmental temperature, wherein the adopted calculation method comprises the following steps: t = ΔH _C/β +T _0.b) And (3) temperature change under laser heating, namely adopting laser as a heat source, focusing the laser on the surface of the magnetic tunnel junction by using a lens, measuring the change of the coercive field of the reference layer under laser pulse, and calculating to obtain the temperature change of the magnetic tunnel under laser heating.

2. The method according to claim 1, wherein during the measurement of the MTJ magnetoresistive curve (MR), a direct current is applied in the MTJ using Keithley 2400, the magnitude of the current being 10 μ A to 1 mA; the magnetoresistive curves of the MTJs were measured using either a 2-wire or a 4-wire method.

3. The method of claim 1, wherein the laser is a titanium ruby laser and/or other laser.

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