CN103323796B - A kind of MTJ magnetic field sensor using Graphene as barrier layer - Google Patents

Abstract

The invention discloses a kind of MTJ magnetic field sensor using Graphene as barrier layer, comprise two magnetic line of force collectors, be used for forming four MTJ magnet-sensitive elements of Hui Sitong measuring bridge, four electrodes and substrate, two magnetic line of force collectors symmetrically shape layout, the gap location of two described MTJ magnet-sensitive elements between two magnetic line of force collectors, described in two other, MTJ magnet-sensitive element lays respectively at the bottom of two magnetic line of force collectors, each described MTJ magnet-sensitive element includes the substrate stacking gradually arrangement from the bottom to top, bottom electrode layer, first cushion, free ferromagnetic, Graphene barrier layer, pinned ferromagnetic layer, pinning layer, second cushion and top electrode layer.The present invention have simple and compact for structure, volume is little, with low cost, easy to make, there is the advantages such as high resolution.

Description

An MTJ magnetic field sensor using graphene as a barrier layer

technical field

The invention mainly relates to the technical field of weak signal sensing, in particular to an MTJ magnetic field sensor using graphene as a potential barrier layer.

Background technique

Weak magnetic field measurement is widely used in military and national economic fields such as target detection, geomagnetic navigation, magnetic storage, geological exploration, and biomedicine. In the prior art, there are many types of sensors used for weak magnetic field measurement, mainly including fluxgate sensors, optical pump magnetic sensors, proton magnetic sensors, optical fiber magnetic sensors, giant magnetoresistive magnetic sensors, AMR (Anisotropic Magnetoresistive, anisotropic Anisotropic magnetoresistive) magnetic sensor, GMR (Giant Magnetoresistive, giant magnetoresistance) magnetic sensor, MTJ (Magnetic Tunnel Junction, magnetic tunnel junction) magnetic sensor, etc. Compared with other types of magnetic sensors, AMR, GMR and MTJ magnetic sensors have the characteristics of small size, low power consumption, and easy mass production. However, when a magnetic sensor with AMR as a sensitive element is used, it is necessary to set a set/reset coil to perform a preset-reset operation, resulting in a complicated manufacturing process. The setting of the coil structure increases the size and power consumption. The response curve of the magnetic sensor with multilayer film GMR as the sensitive element is evenly symmetrical, which can only measure the magnitude of the magnetic field, but cannot reflect the direction of the magnetic field. The MTJ element uses the tunnel magnetoresistance effect (Tunnel Magnetoresistance, TMR) of the magnetic multilayer film material to sense the magnetic field, and has a greater resistance change rate, higher sensitivity and more Good temperature stability.

In 1975, Julliere observed in the Fe/Ge/Co tunnel junction that when the magnetization directions of the two ferromagnetic layers are parallel or antiparallel, the tunnel junction will have different resistance values (Julliere M. Tunneling Between Ferromagnetic Films. Phys Lett A, 1975, 54(3):225-226). This phenomenon that the external magnetic field changes the magnetization state of the ferromagnetic layer of the tunnel junction and causes its resistance to change is called the magnetic tunnel junction effect. The magnetoresistance change rate of Fe/Ge/Co tunnel junction is as high as 14% at low temperature, but it is very small at room temperature. In the following 30 years, people conducted a series of in-depth studies on MTJ. In 1995, the Miyazaki group achieved a breakthrough in the study of magnetic tunnel junctions (Miyazki T, Tezuka N. Giant magnetic tunneling effect in Fe/Al ₂ O ₃ /Fe junction. J. Magn. Magn. Mater., 1995, 139:L231 ), it was first found in the Fe/Al ₂ O ₃ /Fe tunnel junction that the magnetoresistance change rate is as high as 15.6% at room temperature and a few millitet magnetic field, and is higher at low temperature, about 23%. In 2008, the magnetoresistance change rate of MgO-based MTJ prepared by S. Ikeda et al. reached 604% at room temperature, and 1144% at 5K low temperature (S. Ikeda, J. Hayakawa, Y. Ashizawa, Y. M. Lee, K. Miura, H. Hasegawa, M. Tsunoda, F. Matsukura, and H. Ohno, Appl. Phys. Lett.2008, 93: 082508), this record experimental result is close to the theoretical prediction value of MgO-based MTJ.

In 2004, the Institute of Physics of the Chinese Academy of Sciences applied for a national invention patent for a magnetic tunnel junction element with a composite ferromagnetic layer as a ferromagnetic electrode (application number: 200410030893.0). By adjusting the thickness of the thin ferromagnetic layer in the composite ferromagnetic layer, it can The spin polarizability of the composite ferromagnetic layer can be adjusted continuously, so that the tunnel magnetoresistance value of the element can be regulated; the correction of the free layer can be continuously adjusted by adjusting the thickness of the thin ferromagnetic layer in the composite ferromagnetic layer as the free layer. Coercive force, so that the size of the fast-off field of the element can be adjusted. The MTJ element can be applied to magnetic random access memory, but it is not suitable for accurate measurement of weak magnetic fields.

Xia Li et al. applied for a MTJ structure patent in 2009 (patent number: US20110044096A1). The MTJ consists of a bottom electrode, a fixed layer, a tunnel barrier layer, a free layer and a top electrode. Jason Reid et al. applied for a patent for an MTJ structure including a thermal barrier layer in 2009 (patent number: US20110108937A1), which has faster switching speeds than traditional MTJ structures and better compatibility with standard semiconductor manufacturing processes. Xiaohua Lou et al. applied for a staggered MTJ patent in 2010 (patent number: US20110026320A1, US008203874B2). However, in these existing technical solutions, the MTJ sensitive element is used for weak magnetic field measurement, and the measurement resolution and accuracy need to be further improved.

Throughout the decades of development of MTJ, the intermediate barrier layer plays an extremely important role in promoting the development of the magnetic tunnel junction. The barrier layer ranges from early Ge to Al ₂ O ₃ , and then to MgO. Under the same condition, the magnetoresistance change rate of the magnetic tunnel junction increases approximately exponentially. This development law has inspired people's attention and research on the barrier layer. In addition, when analyzing the noise characteristics of the magnetic tunnel junction, the researchers found that the inconsistency and pinhole defects in the barrier layer during the preparation process will generate 1/f noise, which limits the low-frequency magnetic field measurement capability of the MTJ magnetic sensor.

Contents of the invention

The technical problem to be solved by the present invention is: aiming at the technical problems existing in the prior art, the present invention provides a simple and compact structure, small volume, low cost, convenient manufacture, and high resolution using graphene as a barrier layer The MTJ magnetic field sensor.

In order to solve the problems of the technologies described above, the present invention adopts the following technical solutions:

An MTJ magnetic field sensor using graphene as a potential barrier layer, including two magnetic field line concentrators, four MTJ magnetic sensitive elements used to form a Wheatstone measurement bridge, four electrodes and a substrate, the two magnetic field line concentrators are Symmetrically arranged, the two MTJ magnetic sensitive elements are located in the gap between the two magnetic force line concentrators, and the other two MTJ magnetic sensitive elements are respectively located at the bottom of the two magnetic force line concentrators, each of the MTJ magnetic sensitive Each element includes a substrate, a bottom electrode layer, a first buffer layer, a free ferromagnetic layer, a graphene barrier layer, a pinned ferromagnetic layer, a pinned layer, a second buffer layer, and a top electrode stacked in sequence from bottom to top. layer.

As a further improvement of the present invention:

The graphene barrier layer is single-layer graphene or multi-layer graphene.

The number of layers of the graphene barrier layer is an odd number greater than 1.

The graphene is directly prepared by a chemical vapor deposition method to form a graphene barrier layer on the free ferromagnetic layer.

The graphene is prepared by oxidation-reduction method or organic synthesis method and then transferred to the free ferromagnetic layer.

Compared with prior art, the advantage of the present invention is: the present invention uses graphene as the potential barrier layer of MTJ to manufacture magnetic field sensor, because graphene has excellent spin transport ability, makes graphene-based MTJ have higher The magnetoresistance change rate is high, thereby improving the sensitivity of magnetic field measurement. In addition, it also has the advantages of low low-frequency noise, small size, and low power consumption. The overall structure of the sensor is simple and easy to manufacture, which can effectively reduce the production cost of the magnetic sensor.

Description of drawings

Fig. 1 is a cross-sectional schematic diagram of an MTJ magnetic sensitive element using graphene as a barrier layer in the present invention.

Fig. 2 is the structure of the MTJ magnetic field sensor using graphene as the barrier layer in the present invention.

Fig. 3 is a schematic diagram of the measurement principle of the MTJ magnetic field sensor using graphene as a barrier layer in the present invention.

illustration:

1. Substrate; 2. Bottom electrode layer; 3. First buffer layer; 4. Free ferromagnetic layer; 5. Graphene barrier layer; 6. Pinned ferromagnetic layer; 7. Pinning layer; 8. The third 2 buffer layer; 9, top electrode layer; 1201, first magnetic force line concentrator; 1202, second magnetic force line concentrator; 1301, first MTJ magnetic sensitive element; 1302, second MTJ magnetic sensitive element; 1303, third MTJ magnetic Sensitive element; 1304, fourth MTJ magnetic sensitive element; 1401, first electrode; 1402, second electrode; 1403, third electrode; 1404, fourth electrode.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

As shown in Figure 1, the MTJ magnetic field sensor using graphene as a barrier layer of the present invention includes a substrate 1, a bottom electrode layer 2, a first buffer layer 3, a free ferromagnetic layer 4, and a graphite layer stacked in sequence from bottom to top. An ene barrier layer 5 , a pinned ferromagnetic layer 6 , a pinning layer 7 , a second buffer layer 8 , and a top electrode layer 9 . In this structure, the free ferromagnetic layer 4 is a magnetic free layer, and its magnetic moment direction A changes with the change of the external magnetic field; the pinned ferromagnetic layer 6 is a fixed magnetic layer, because its magnetic moment direction B is pinned The tie layer 7 is fixed in one direction, which cannot be changed under normal conditions. The resistance value of the MTJ magnetic sensitive element is the resistance value between the bottom electrode layer 2 and the top electrode layer 9, when the magnetic moment direction A of the free ferromagnetic layer 4 is parallel to the magnetic moment direction B of the pinned ferromagnetic layer 6 , the MTJ magnetic sensitive element is in a low resistance state; when the magnetic moment direction A of the free ferromagnetic layer 4 is antiparallel to the magnetic moment direction B of the pinned ferromagnetic layer 6, the MTJ magnetic sensitive element is in a high resistance state, and The resistance of the MTJ magnetic sensitive element changes linearly between the high resistance state and the low resistance state with the measuring magnetic field.

In a specific embodiment, the substrate 1 is usually made of silicon, quartz, glass or any other material capable of wafer integration. Silicon processing technology is mature and easy to process, so it is the best choice for integrated circuits. The bottom electrode layer 2 and the top electrode layer 9 are usually made of non-magnetic conductive materials, such as copper, aluminum, gold, silver, etc., and can be prepared on the substrate 1 by evaporation, magnetron sputtering, and other processes. Materials for the first buffer layer 3 and the second buffer layer 8 can generally be selected from tantalum, and can be prepared by magnetron sputtering. Both the free ferromagnetic layer 4 and the pinned ferromagnetic layer 6 are made of ferromagnetic materials, such as iron, nickel, cobalt or their alloy materials, and can also be prepared by magnetron sputtering. The graphene barrier layer 5 is single-layer graphene or multi-layer (generally 3, 5, 7 and other odd-numbered layers) graphene, and graphene can be directly prepared on the free ferromagnetic layer 4 by chemical vapor deposition, or by other Methods The redox method and the organic synthesis method are prepared and then transferred to the free ferromagnetic layer 4 . The pinning layer 7 is made of hard magnetic materials.

As shown in Figure 2, it is the MTJ magnetic field sensor with graphene as the potential barrier layer of the present invention, including the magnetic field line concentrator, four MTJ magnetic sensitive elements (i.e. the first MTJ magnetic sensitive element) that are used to form the Wheatstone measurement bridge 1301, second MTJ magnetic sensitive element 1302, third MTJ magnetic sensitive element 1303, fourth MTJ magnetic sensitive element 1304), four electrodes (namely first electrode 1401, second electrode 1402, third electrode 1403, fourth electrode 1404) and base 1. The magnetic force line concentrator is used to amplify the external measured magnetic field. The magnetic force line concentrator includes a first magnetic force line concentrator 1201 and a second magnetic force line concentrator 1202. The first magnetic force line concentrator 1201 and the second magnetic force line concentrator 1202 are symmetrically arranged, and its shape is not limited to The length direction of the rectangle in the figure is consistent with the magnetic field sensitive direction C of the sensor; there is a gap between the first magnetic force line concentrator 1201 and the second magnetic force line concentrator 1202 . The magnetic force line concentrator can be made of soft magnetic materials according to actual needs. Four MTJ magnetic sensitive elements constitute a Wheatstone measurement bridge, wherein the first MTJ magnetic sensitive element 1301 and the second MTJ magnetic sensitive element 1302 are located in the gap between the first magnetic flux concentrator 1201 and the second magnetic flux concentrator 1202 It is used to induce the amplified magnetic field, and its resistance value changes with the measured magnetic field, which is a sensitive measurement resistance. The third MTJ magnetic sensitive element 1303 and the fourth MTJ magnetic sensitive element 1304 are located at the bottom of the first magnetic force line concentrator 1201 and the second magnetic force line concentrator 1202 respectively, and their resistance values are not affected by the measured magnetic field and are reference resistances. The four electrodes are used to connect four graphene-based MTJ magnetic sensitive elements. The shape and position of the electrodes are not limited to those shown in the figure, as long as the electrodes are located on the edge of the substrate 1 . The four electrodes of the magnetic field sensor can be connected to the package pins of the package case lead frame or ASIC (Application Specific Integrated Circuit, application specific integrated circuit) through leads.

As shown in FIG. 3 , it is a schematic diagram of the measurement principle of the present invention in a specific application example. Four MTJ magnetic sensitive elements (ie, the first MTJ magnetic sensitive element 1301, the second MTJ magnetic sensitive element 1302, the third MTJ magnetic sensitive element 1303, and the fourth MTJ magnetic sensitive element 1304) constitute a Wheatstone full bridge, wherein The first MTJ magnetic sensitive element 1301 and the second MTJ magnetic sensitive element 1302 have the same sensitive direction, and their resistance value changes with the measured magnetic field. The third MTJ magnetic sensitive element 1303 and the fourth MTJ magnetic sensitive element 1304 are reference resistors. Ideally, when the external magnetic field is zero, the resistance values of these four sensitive elements are equal, and the output voltage of the bridge is zero at this time. The voltage difference ( V out1 - V out2 ) between the third electrode 1403 and the first electrode 1401 is the output voltage V out, which has a linear relationship with the external measurement magnetic field.

The bridge-type magnetic sensor mentioned above can be prepared on the same substrate 1 by the same process, and used as a single-chip magnetic sensor, and its electrodes can be connected to the packaging pins of the ASIC or the packaging package lead frame.

The above are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions under the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those skilled in the art, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims (5)

1. the MTJ magnetic field sensor using Graphene as barrier layer, it is characterized in that, comprise two magnetic line of force collectors, be used for forming four MTJ magnet-sensitive elements of Hui Sitong measuring bridge, four electrodes and substrate, two magnetic line of force collectors symmetrically shape layout, the gap location of two described MTJ magnet-sensitive elements between two magnetic line of force collectors, described in two other, MTJ magnet-sensitive element lays respectively at the bottom of two magnetic line of force collectors, each described MTJ magnet-sensitive element includes the substrate stacking gradually arrangement from the bottom to top, bottom electrode layer, first cushion, free ferromagnetic, Graphene barrier layer, pinned ferromagnetic layer, pinning layer, second cushion and top electrode layer.

2. the MTJ magnetic field sensor using Graphene as barrier layer according to claim 1, is characterized in that, described Graphene barrier layer is single-layer graphene or multi-layer graphene.

3. the MTJ magnetic field sensor using Graphene as barrier layer according to claim 2, is characterized in that, when described Graphene barrier layer is multi-layer graphene, the number of plies of described Graphene barrier layer be greater than 1 odd number.

4. the MTJ magnetic field sensor using Graphene as barrier layer according to claim 2, is characterized in that, described Graphene is directly prepared on free ferromagnetic by chemical vapour deposition technique and forms Graphene barrier layer.

5. the MTJ magnetic field sensor using Graphene as barrier layer according to claim 2, is characterized in that, described Graphene is transferred on free ferromagnetic after being prepared by oxidation-reduction method or organic synthesis method.