A wireless energy harvesting system, a spin diode and a method for preparing the same

Abstract

A wireless energy harvesting system, a spin diode and a preparation method thereof, comprising a microwave antenna, an impedance matching circuit, a microwave rectifier and an energy storage unit connected in sequence; the microwave rectifier adopts a spin diode based on a nano-magnetic tunnel junction. The system of the present invention adopts a spin diode, has the characteristics of high working bandwidth and wide dynamic range, and has high conversion efficiency at low input power.

Description

Technical Field

[0001] The present invention relates to the field of wireless energy harvesting, and in particular to a wireless energy harvesting system, a spin diode and a preparation method thereof. Background Art

[0002] Wireless energy harvesting systems can convert microwave radiation in the environment into DC current, and are ideal power sources for wireless sensor networks and IoT nodes. Wireless energy harvesting systems are usually composed of RF antennas, microwave rectifiers, impedance matching circuits, and energy storage systems, and the energy conversion efficiency of microwave rectifiers is a key component that determines the performance of wireless energy harvesting systems. Since the power of microwave signals in the environment is very low (0.1-1μW), microwave rectifiers are required to have high energy conversion efficiency at low power.

[0003] However, due to the working principle, the thermodynamic limit of the response rate of the commonly used microwave rectifiers, such as Schottky diodes, to microwave current is only 19.4A / W, corresponding to an energy conversion efficiency of only 5% at a power of 1μW. Therefore, there is an urgent need to develop a microwave rectifier element with a higher response rate at low power and apply it to wireless energy harvesting systems. Summary of the invention

[0004] The main purpose of the present invention is to overcome the defect of low response rate of microwave rectifiers in the prior art at low power, and to propose a wireless energy harvesting system, a spin diode and a preparation method thereof.

[0005] The present invention adopts the following technical solution:

[0006] A wireless energy harvesting system comprises a microwave antenna, an impedance matching circuit, a microwave rectifier and an energy storage unit which are connected in sequence; the characteristic is that the microwave rectifier adopts a spin diode based on a nano-magnetic tunnel junction.

[0007] A spin diode based on a nanomagnetic tunnel junction, characterized in that it includes a substrate, a bottom electrode pattern, an insulating layer and a planar waveguide electrode; the bottom electrode pattern is located on the surface of the substrate and is in an I-shape, and a nanocolumn is provided in the middle of the bottom electrode pattern; the insulating layer covers the substrate surface, the bottom electrode pattern and the nanocolumn and has three channels, the first channel is connected to the top layer of the nanocolumn, and two second channels are located on both sides of the nanocolumn and connected to the bottom reference layer; the planar waveguide electrode includes a source electrode and two ground electrodes, the source electrode is deposited at the first channel on the surface of the insulating layer and is electrically connected to the free layer, and the two ground electrodes are respectively deposited at the two second channels on the surface of the insulating layer and are electrically connected to the reference layer.

[0008] A method for preparing a spin diode based on a nanomagnetic tunnel junction, characterized in that it comprises the following steps:

[0009] 1) Fabricating a multilayer thin film on the substrate surface, including a reference layer, a tunneling layer and a free layer from bottom to top;

[0010] 2) forming a bottom electrode pattern of an I-shape by forming the multilayer film;

[0011] 3) etching the free layer and the tunneling layer to form a nanocolumn in the middle of the bottom electrode pattern;

[0012] 4) depositing an insulating layer on the substrate and covering the bottom electrode pattern and the nanorods;

[0013] 5) making three channels on the insulating layer, the first channel connected to the free layer of the nanocolumn, and two second channels located on both sides of the nanocolumn and connected to the reference layer;

[0014] 6) Metals are deposited at three channel positions on the surface of the insulating layer to form a source electrode and two ground electrodes, thereby constituting a planar waveguide electrode.

[0015] Preferably, in step 1), the multilayer film further comprises a buffer layer, and the buffer layer is located between the reference layer and the substrate.

[0016] Preferably, the buffer layer is made of Pd, Ta or Ru.

[0017] Preferably, the tunneling layer has a thickness of 0.6 nm-2 nm and is made of MgO, Al2O3 or MgAl2O4.

[0018] Preferably, the free layer is made of soft magnetic material, such as Fe, FeB, CoFeB or NiFe.

[0019] Preferably, the insulating layer has a thickness greater than 100 nm and is a combination of one or more dielectric materials selected from SiO2, Al2O3, TiO2, Si3N4 and HfO2.

[0020] Preferably, the reference layer is made of exchange-coupled ferromagnetic / antiferromagnetic material or ferromagnetic / non-magnetic / ferromagnetic / antiferromagnetic material.

[0021] Preferably, in step 1), the multilayer film is produced by molecular beam epitaxy, magnetron sputtering, atomic layer deposition or electron beam evaporation; in step 2), the bottom electrode pattern is produced by photolithography and ion beam etching, and the nanocolumns are produced by electron beam exposure and ion beam etching.

[0022] It can be seen from the above description of the present invention that, compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The system of the present invention integrates the spin diode as a microwave rectifier in the wireless energy harvesting system, and can obtain a wireless energy harvesting system with high conversion efficiency, high working bandwidth and wide dynamic range.

[0024] 2. The system of the present invention can be used in low-power conditions such as ambient wireless energy harvesting, solving the energy problem of distributed wireless sensor networks.

[0025] 3. The method of the present invention uses the magnetic multilayer film as the basic structure and makes it into an I-shaped bottom electrode pattern, which can reduce the overlapping area of ​​the top electrode and the bottom electrode pattern, reduce the leakage current, and make nanocolumns thereon as the core structure of the spin diode with a higher current density.

[0026] 4. The diode made by the method of the present invention is a new type of microwave rectifier based on the spin torque effect of current in a nanomagnetic tunnel junction. The operating frequency can be adjusted in the range of 0.1-100 GHz by an external magnetic field. It has the characteristics of high operating bandwidth and wide dynamic range, and has high conversion efficiency at low input power. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a structural diagram of the diode of the present invention;

[0028] Figure 2 Schematic diagram for making multilayer films;

[0029] Figure 3 A schematic diagram for making a bottom electrode pattern;

[0030] Figure 4 Schematic diagram of covering electron beam photoresist;

[0031] Figure 5 Schematic diagram of ion beam etching;

[0032] Figure 6 Schematic diagram of the fabricated nanopillars;

[0033] Figure 7 Schematic diagram for making an insulating layer;

[0034] Figure 8 Schematic diagram of covering photoresist;

[0035] Fig. 9 To make a schematic diagram of the channel in the insulating layer;

[0036] Fig.10 Schematic diagram of covering photoresist;

[0037] Fig.11 It is a schematic diagram of the diode rectification characteristics of the present invention;

[0038] Fig.12 It is a schematic diagram of current, resistance and voltage of the diode of the present invention under the action of microwave current;

[0039] Fig.13 is the frequency response of the diode rectifier voltage of the present invention;

[0040] Fig.14 This is a schematic diagram showing that the peak frequency of the diode of the present invention can be adjusted with an external magnetic field;

[0041] Fig.15 is a circuit diagram of the system of the present invention;

[0042] in:

[0043] 10. substrate, 20. reference layer, 30. tunneling layer, 40. free layer, 50. buffer layer, 60. bottom electrode pattern, 61. nanopillars, 70. insulating layer, 71. first channel, 72. second channel, 81. source electrode, 82. ground electrode, 90. photoresist, 100. metal.

[0044] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. DETAILED DESCRIPTION

[0045] The present invention is further described below through specific implementation modes.

[0046] In the present invention, the terms "first", "second", "third", etc. are only used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence, nor can they be understood as indicating or implying relative importance. In the description, the directions or positional relationships indicated by "upper", "lower", "left", "right", "front", and "back" are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention, and are not intended to indicate or imply that the device referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the scope of protection of the present invention. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0047] In addition, in the description of this application, unless otherwise specified, "plurality" means two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0048] The present invention also proposes a wireless energy harvesting system, see Fig.15, including a microwave antenna, a matching circuit, a microwave rectifier and an energy storage unit connected in sequence; wherein the microwave rectifier adopts a spin diode based on a nanomagnetic tunnel junction.

[0049] The system of the present invention can select a microwave antenna with an operating frequency in the wireless communication frequency band, receive electromagnetic radiation in the environment and convert it into radio frequency current, match the resistance of the spin diode of the nano magnetic tunnel junction to 50Ω through a matching circuit, and after microwave rectification by the spin diode, convert it into direct current and store it in the energy storage element for use by the load. In order to increase the voltage output, a microwave antenna array with higher gain can be introduced, and the received microwave power can be increased by optimizing the orientation of the antenna array.

[0050] A spin diode based on a nanomagnetic tunnel junction of the present invention comprises a substrate 10, a bottom electrode pattern 60, an insulating layer 70 and a planar waveguide electrode; the bottom electrode pattern 60 is located on the surface of the substrate 10 and is in an I-shape, and a nanocolumn 61 is provided in the middle of the bottom electrode pattern 60; the insulating layer 70 covers the surface of the substrate 10, the bottom electrode pattern 60 and the nanocolumn 61 and has three channels, the first channel 71 is connected to the top layer of the nanocolumn 61, and two second channels 72 are located on both sides of the nanocolumn 61 and are connected to the reference layer 20 at the bottom; the planar waveguide electrode comprises a source electrode 81 and two ground electrodes 82, the source electrode 81 is deposited at the position of the first channel 71 on the surface of the insulating layer 70 and is electrically connected to the free layer 40, and the two ground electrodes 82 are respectively deposited on the two second channels 72 on the surface of the insulating layer 70 and are electrically connected to the reference layer 20.

[0051] In the spin diode of the present invention, when microwave current passes through the reference layer 20, the spin direction of the electrons will be polarized, thereby transmitting a periodically changing spin torque to the magnetic moment of the free layer 40. The oscillation of the magnetic moment direction of the free layer 40 under the action of the spin torque causes a periodic change in the device resistance (see Fig.11 The changing resistance and alternating current mix to produce a DC voltage (V mix )(See Fig.12 The magnitude of the DC voltage is related to the microwave frequency, and when the microwave frequency is equal to the ferromagnetic resonance frequency (f P ) reaches its maximum value (see Fig.13 The resonant frequency can be adjusted by an external magnetic field, so the spin diode has a large operating bandwidth (see Fig.13 ).

[0052] The present invention also proposes a method for preparing a spin diode based on a nanomagnetic tunnel junction, comprising the following steps:

[0053] 1) A multilayer thin film is fabricated on the surface of the substrate 10, which includes at least a reference layer 20, a tunneling layer 30 and a free layer 40 from bottom to top, see Figure 2 The magnetic multilayer film is the basic structure of the spin diode. In this step, the multilayer film can be made by molecular beam epitaxy, magnetron sputtering, atomic layer deposition or electron beam evaporation.

[0054] Wherein, the substrate 10 is a silicon oxide / silicon substrate. The reference layer 20 uses exchange-coupled ferromagnetic / antiferromagnetic materials including but not limited to CoFeB / IrMn, CoFe / PtMn or ferromagnetic / non-magnetic / ferromagnetic / antiferromagnetic materials, including but not limited to CoFeB / Ru / CoFeB / PtMn, etc. The tunneling layer 30 uses an extremely thin insulating medium, including but not limited to MgO, Al2O3, MgAl2O4, etc., and its thickness can be 0.6nm-2nm. The free layer 40 is usually made of soft magnetic metals, such as Fe, FeB, CoFeB or NiFe, etc.

[0055] In this step, the multilayer film may further include a buffer layer 50, which is located between the reference layer 20 and the substrate 10. The buffer layer 50 is used to enhance the adhesion between the metal film and the substrate 10, and is generally made of Pd, Ta, Ru, etc.

[0056] Furthermore, a capping layer may be added on the surface of the free layer 40 to prevent oxidation of the underlying metal, and Au, Ru, Ta, etc. may be used.

[0057] 2) The multilayer film is made into an I-shaped bottom electrode pattern 60. In this step, the basic shape of the bottom electrode pattern 60 can be made by photolithography and ion beam etching, see Figure 3 The bottom electrode pattern 60 includes a transverse portion and two longitudinal portions, wherein the transverse portion can be vertically connected between the two longitudinal portions, wherein the width of the transverse portion is smaller than the length of the longitudinal portion. The larger portions at both ends of the bottom electrode pattern 60, namely the transverse portions, will serve as the bottom electrodes connected to the bottom of the magnetic tunnel junction, while the thinner portion in the middle, namely the longitudinal portions, can reduce the overlapping area of ​​the top electrode (such as the source electrode) and the bottom electrode, thereby reducing the leakage current.

[0058] 3) Etching the free layer 40 and the tunneling layer 30 to form a nanorod 61 in the middle of the bottom electrode pattern 60 .

[0059] In this step, electron beam exposure and ion beam etching techniques are used to etch a nanorod 61 in the bottom electrode pattern 60 as the core structure of the spin diode, and the etching depth reaches the reference layer 20. The cross section of the nanorod 61 can be circular or elliptical, and the size is usually between a few nanometers and hundreds of nanometers.

[0060] See also Figure 4 , Figure 5, the surface of the substrate 10 is covered with an electron beam photoresist 90, and after an electron beam exposure process, an image of the nanorod 61 is produced, and then the free layer 40 and the tunneling layer 30 are etched by ion beam etching technology to obtain the nanorod 61, see Figure 6 , wherein the top of the nanorod 61 also has a photoresist 90 .

[0061] 4) Depositing an insulating layer 70 on the substrate 10 and covering the bottom electrode pattern 60 and the nanorods 61. Meanwhile, the photoresist 90 on the top of the nanorods 61 is not completely covered by the insulating layer 70 because its thickness is greater than that of the insulating layer 70.

[0062] In this step, the deposited insulating layer 70 is relatively thick, with a thickness greater than 100 nm, and the material may be one or more combinations of dielectric materials such as SiO2, Al2O3, TiO2, Si3N4 and HfO2, see Figure 7 .

[0063] 5) Three channels are made on the insulating layer 70 , the first channel 71 is connected to the free layer 40 of the nano-pillar 61 , and the two second channels 72 are located on both sides of the nano-pillar 61 and connected to the reference layer 20 .

[0064] In this step, a second photolithography and ion beam etching are performed to open a path in the insulating layer 70 that is connected to the bottom electrode pattern 60 of the nanorod 61 reference layer 20. For details, see Figure 8 , the surface of the insulating layer 70 is covered with a photoresist 90 and a pattern of two second channels 72 is obtained by photolithography, and then the insulating layer 70 is etched by ion beam etching technology to remove all the photoresist 90 (including the photoresist on the surface of the insulating layer 70 and the photoresist on the top of the nanorod 61) to obtain a first channel 71 and two second channels 72, see Fig. 9 The diameter or width of the first channel 71 is the same as the diameter or width of the nanorod 61 , and the length and width of the two second channels 72 are the same as the length and width of the longitudinal portion of the bottom electrode pattern 60 .

[0065] 6) Metal 100 is deposited on three channel positions on the surface of the insulating layer 70 to form a source electrode 81 and two ground electrodes 82 to form a planar waveguide electrode. The planar waveguide electrode is located on the surface of the insulating layer 70, and the source electrode 81 is filled into the first channel 71 and electrically connected to the nanorod 61, and the ground electrode 82 is filled into the second channel 72 and connected to the reference layer 20 electrode.

[0066] In this step, a planar waveguide electrode is fabricated by a third photolithography and metal (Au) deposition for connecting a microwave source, wherein the source electrode 81 and the two ground electrodes 82 are parallel to each other, and the length of the source electrode 81 is greater than the length of the ground electrode 82 .

[0067] The above is only a specific implementation of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial changes to the present invention using this concept shall be deemed as an infringement of the protection scope of the present invention.

Claims

1. A method for preparing a spin diode based on a nanomagnetic tunnel junction, characterized in that: The steps include: 1) Fabricate a multilayer film on the substrate surface, including a reference layer, a tunneling layer, and a free layer from bottom to top; 2) The multilayer film is made into an I-shaped bottom electrode pattern; 3) Etching the free layer and the tunneling layer to form a nanocolumn in the middle of the bottom electrode pattern; covering the substrate surface with a first photoresist of an electron beam, making a nanocolumn image after an electron beam exposure process, and then etching the free layer and the tunneling layer with an ion beam etching technique to obtain a nanocolumn, the etching depth reaches the reference layer, and the top of the nanocolumn is also covered with the first photoresist; 4) depositing an insulating layer on the substrate and covering the substrate surface, the bottom electrode pattern and the nanocolumns, wherein the thickness of the first photoresist on the top of the nanocolumns is greater than the thickness of the insulating layer and is not completely covered by the insulating layer; 5) Three channels are made on the insulating layer, the first channel is connected to the free layer of the nanocolumn, and the two second channels are located on both sides of the nanocolumn and connected to the reference layer; A second photoresist is covered on the surface of the insulating layer and two second channel patterns are obtained by photolithography, and then the insulating layer is etched by ion beam etching technology to remove the second photoresist on the surface of the insulating layer and the first photoresist on the top of the nano-pillar to obtain a first channel and two second channels, wherein the diameter or width of the first channel is the same as the diameter or width of the nano-pillar, and the length and width of the two second channels are the same as the length and width of the longitudinal portion of the bottom electrode pattern; 6) Metal is deposited at the three channel positions on the surface of the insulating layer to form a source electrode and two ground electrodes to constitute a planar waveguide electrode. The source electrode is deposited at the first channel on the surface of the insulating layer and is electrically connected to the free layer. The two ground electrodes are deposited at the two second channels on the surface of the insulating layer and are electrically connected to the reference layer.

2. The method for preparing a spin diode based on a nano-magnetic tunnel junction according to claim 1, characterized in that: In step 1), the multilayer film further includes a buffer layer, and the buffer layer is located between the reference layer and the substrate.

3. The method for preparing a spin diode based on a nano-magnetic tunnel junction according to claim 2, characterized in that: The buffer layer is made of Pd, Ta or Ru.

4. The method for preparing a spin diode based on a nano-magnetic tunnel junction according to claim 1, characterized in that: The tunneling layer has a thickness of 0.6 nm to 2 nm and is made of MgO, Al2O3 or MgAl2O4.

5. The method for preparing a spin diode based on a nano-magnetic tunnel junction according to claim 1, characterized in that: The free layer is made of soft magnetic material, such as Fe, FeB, CoFeB or NiFe.

6. The method for preparing a spin diode based on a nano-magnetic tunnel junction according to claim 1, characterized in that: The thickness of the insulating layer is greater than 100 nm, and the insulating layer is one or more combinations of dielectric materials SiO2, Al2O3, TiO2, Si3N4 and HfO2.

7. The method for preparing a spin diode based on a nano-magnetic tunnel junction according to claim 1, characterized in that: The reference layer is made of exchange-coupled ferromagnetic / antiferromagnetic material or ferromagnetic / non-magnetic / ferromagnetic / antiferromagnetic material.

8. The method for preparing a spin diode based on a nano-magnetic tunnel junction according to claim 1, characterized in that: In step 1), the multilayer film is produced by molecular beam epitaxy, magnetron sputtering, atomic layer deposition or electron beam evaporation; in step 2), the bottom electrode pattern is produced by photolithography and ion beam etching, and the nanocolumns are produced by electron beam exposure and ion beam etching.

9. A wireless energy harvesting system, comprising a microwave antenna, an impedance matching circuit, a microwave rectifier and an energy storage unit connected in sequence; characterized in that: The microwave rectifier is a spin diode based on a nano-magnetic tunnel junction manufactured by the method for preparing a spin diode based on a nano-magnetic tunnel junction according to any one of claims 1 to 8.

Images