Reverse spin hall effect based magnetic sensor half-bridge with reduced thermal drift

Abstract

The present disclosure generally relates to a magnetic sensor half-bridge circuit. The half-bridge circuit includes a bias source connected to a first leg and a second leg. The first branch includes one or more first spin orbit moment (SOT) structures connected in series, each first SOT structure including a first ferromagnetic (FM) layer disposed on the first SOT layer. The first SOT layer has a first end connected to the ground and a second end connected to the first voltage sensor. The second branch includes one or more second SOT structures connected in series, each second SOT structure including a second FM layer disposed on a second SOT layer. The second SOT layer has a first end connected to the second voltage sensor and a second end connected to the ground. The first voltage sensor and the second voltage sensor are disposed adjacent to each other.

Description

Cross Reference to Related Applications

[0001] This application claims the benefit of U.S. Non-Provisional Application No. 18 / 545,847, filed December 19, 2023, entitled “Magnetic Sensor Half-Bridge Based on Inverse Spin Hall Effect with Reduced Thermal Drift,” and the entire contents of which are hereby incorporated by reference for all purposes. BACKGROUND TECHNICAL FIELD

[0002] Embodiments of the present disclosure generally relate to a magnetic sensor half-bridge. Related Art

[0003] A Wheatstone bridge is a circuit used to measure an unknown resistance by balancing two branches of a bridge circuit, one of which includes the unknown component. The Wheatstone circuit provides extremely accurate measurement results compared to a simple voltage divider.

[0004] A Wheatstone bridge includes a plurality of resistors, and in particular, recently these plurality of resistors include magnetic materials, such as magnetic field sensors in which the resistance varies with the magnetic field. The magnetic sensors can include Hall effect magnetic sensors, anisotropic magnetic resistance sensors (AMR), giant magnetoresistance (GMR) sensors, and tunneling magnetoresistance (TMR) sensors.

[0005] A Wheatstone bridge has a linear output signal and is resistant to environmental temperature fluctuations. Any temperature variations in a Wheatstone bridge array are cancelled out. A Wheatstone bridge array has four resistors, one in each branch. Two of these resistors have the same resistance, while the remaining two resistors have the same resistance relative to each other but different from the initial two resistors.

[0006] It is common practice to build a Wheatstone bridge on a single chip, where each branch of the bridge includes one or more sensors to achieve a higher signal output while minimizing thermal drift and achieving zero offset. In operation, the bridge uses opposite sensor field responses for adjacent branches (i.e., one branch resistance increases with field, while the sensor on the adjacent branch produces a decreasing resistance with an externally applied magnetic field). For conventional GMR or TMR based bridge sensors, opposite pinning directions are used between adjacent branches. This can often result in significant variations in design / processing.

[0007] A Wheatstone bridge has four branches as described above. The four branches can occupy a significant amount of space. As devices continue to shrink, the bridge also needs to shrink.

[0008] Accordingly, there is a need in the art for an improved bridge. SUMMARY

[0009] The present disclosure generally relates to a magnetic sensor half-bridge circuit. The half-bridge circuit includes a bias source connected to a first leg and a second leg. The first leg includes one or more first spin orbit torque (SOT) structures connected in series, each first SOT structure including a first ferromagnetic (FM) layer disposed on a first SOT layer. The first SOT layer has a first end connected to a ground and a second end connected to a first voltage sensor. The second leg includes one or more second SOT structures connected in series, each second SOT structure including a second FM layer disposed on a second SOT layer. The second SOT layer has a first end connected to a second voltage sensor and a second end connected to the ground. The first voltage sensor is disposed adjacent to the second voltage sensor.

[0010] In one embodiment, a half-bridge circuit includes a first spin orbit torque (SOT) layer having a first end and a second end opposite the first end; a first ferromagnetic (FM) layer disposed on the first SOT layer; a first ground connected to the first end of the first SOT layer; a first voltage sensor connected to the second end of the first SOT layer; a bias source connected to the first FM layer; a second SOT layer having a first end and a second end opposite the first end; a second FM layer disposed on the second SOT layer, the second FM layer connected to the bias source; a second ground connected to the second end of the second SOT layer; and a second voltage sensor connected to the first end of the second SOT layer.

[0011] In another embodiment, a half bridge circuit includes a bias source, a first leg connected to the bias source, the first leg including one or more first spin orbit torque (SOT) structures, each first SOT structure including: a first SOT layer having a first end and a second end opposite the first end; a first ferromagnetic (FM) layer disposed on the first SOT layer; a first ground connected to the first end of the first SOT layer; and a first voltage sensor connected to the second end of the first SOT layer, and a second leg connected to the bias source, the second leg including one or more second SOT structures, each second SOT structure including: a second SOT layer having a first end and a second end opposite the first end; a second FM layer disposed on the second SOT layer; a second ground connected to the second end of the second SOT layer; and a second voltage sensor connected to the first end of the second SOT layer.

[0012] In yet another embodiment, a half bridge circuit includes a bias source, a first leg connected to the bias source, the first leg including one or more first spin orbit torque (SOT) structures connected in series, each first SOT structure including: a first SOT layer having a first end and a second end opposite the first end; a first ferromagnetic (FM) layer disposed on the first SOT layer; a second FM layer disposed below the first SOT layer; a first ground connected to the first end of the first SOT layer; and a first voltage sensor connected to the second end of the first SOT layer, and a second leg connected to the bias source, the second leg including one or more second SOT structures connected in series, each second SOT structure including: a second SOT layer having a first end and a second end opposite the first end, wherein the first end of the second SOT layer is disposed adjacent to the second end of the first SOT layer; a third FM layer disposed on the second SOT layer; a fourth FM layer disposed below the second SOT layer; a second ground connected to the second end of the second SOT layer; and a second voltage sensor connected to the first end of the second SOT layer. BRIEF DESCRIPTION OF DRAWINGS

[0013] Accordingly, a more complete understanding of the above-mentioned features of the disclosure, and the manner and objects of them, can be obtained by reference to certain implementations thereof, some of which implementations are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical implementations of the disclosure and are therefore not to be considered limiting of its scope, for the disclosure can admit to other equally effective implementations.

[0014] FIG. 1 is a schematic diagram of a Wheatstone bridge array design.

[0015] FIG. 2A and FIG. 2B is a schematic diagram of a half bridge circuit diagram according to one embodiment.

[0016] FIG. 3A and FIG. 3B is a schematic diagram of a half bridge design according to one embodiment. FIG. 2B

[0017] FIG. 4A is a schematic cross-sectional view of a single ferromagnetic (FM) layer bridge according to one embodiment.

[0018] FIG. 4B is a schematic top view of FIG. 4A

[0019] FIG. 4C is a schematic side view of a leg with sensor array according to one embodiment.

[0020] FIG. 5 is a schematic cross-sectional view of a half bridge design according to another embodiment.

[0021] FIG. 6A is a schematic cross-sectional view of a single ferromagnetic (FM) layer bridge according to one embodiment.

[0022] FIG. 6B is a schematic cross-sectional view of a leg with sensor array according to one embodiment.

[0023] To facilitate an understanding of this description, like reference characters are used to identify like elements throughout the description and the drawings. It should be appreciated that elements illustrated in the Figures can have other uses and can be commonly or alternatively labeled. DETAILED DESCRIPTION

[0024] ​​In the following, reference is made to embodiments of the disclosure. However, it should be understood that the disclosure is not limited to the specifically described embodiments. Rather, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice the disclosure. Additionally, although the embodiments of the disclosure can achieve advantages over other possible solutions and / or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the disclosure. Thus, the following aspects, features, embodiments and advantages are merely illustrative and are not considered elements or limitations of the attached claims, unless explicitly recited therein. Likewise, reference to "the disclosure" should not be interpreted as a generalization of any inventive subject matter disclosed herein and should not be considered to be an element or limitation of the attached claims, unless explicitly recited in a claim.

[0025] The present disclosure generally relates to a magnetic sensor half-bridge circuit. The half-bridge circuit includes a bias source connected to a first leg and a second leg. The first leg includes one or more first spin orbit torque (SOT) structures connected in series, each first SOT structure including a first ferromagnetic (FM) layer disposed on a first SOT layer. The first SOT layer has a first end connected to a ground and a second end connected to a first voltage sensor. The second leg includes one or more second SOT structures connected in series, each second SOT structure including a second FM layer disposed on a second SOT layer. The second SOT layer has a first end connected to a second voltage sensor and a second end connected to the ground. The first voltage sensor is disposed adjacent to the second voltage sensor.

[0026] FIG. 1 is a schematic diagram of a Wheatstone bridge array 100 design. The array 100 includes a bias source 102, a first resistor 104, a second resistor 106, a third resistor 108, a fourth resistor 110, a first sense port 112, a second sense port 114, and a ground connection 116. A bias voltage is applied across the array from the bias source 102 to the ground connection 116. The first sense port 112 and the second sense port 114 sense the output of the applied voltage. Any temperature variations from the resistors 104, 106, 108, 110 can be cancelled out.

[0027] As discussed herein, the resistors 104, 106, 108, 110 each include a sensor such as a tunneling magnetoresistance (TMR) sensor. The TMR sensors can each be unique and different such that the resistors 104, 106, 108, 110 have different resistances. The sensors can be the same, but the resistors 104, 106, 108, 110 are different. The resistors 104, 110 can be the same as each other (as are the TMR sensors of the resistors 104, 110), and the resistors 106, 108 are the same as each other (as are the sensors of the resistors 106, 108) but different from the resistors 104, 110. For the TMR sensors in the array 100, the RA of the array 100 is about 100 ohms / square micron.

[0028] A typical magnetic field sensor uses MR (magnetoresistance) devices, such as TMR devices, in a Wheatstone bridge circuit. The sensor requires the MR devices to vary differently in adjacent legs of the bridge. One way to make a magnetic field sensor is to fabricate two different TMR films with opposite pinning directions on the same wafer and anneal the wafer at multiple temperature / field conditions. The reliability and performance of the TMR films determine the magnetoresistance response. In this way, combining different TMR film characteristics, a perfect Wheatstone bridge design for a magnetic field sensor can be made. However, this introduces a lot of wafer / device processing complexity.

[0029] FIG. 2A to FIG. 2B is a schematic diagram of a half-bridge circuit diagram 200 of a magnetic sensor according to one embodiment. The half-bridge circuit 200 can be referred to herein as a magnetic sensor 200.

[0030] The half-bridge circuit 200 includes a first leg 205 including a first three-terminal spin orbit torque (SOT) resistor (Rl) 204 connected to a bias source (Vdd) 202, a first voltage sensor (Vdcl) 220, and a ground 216. The half-bridge circuit 200 also includes a second leg 207 including a second three-terminal SOT resistor (R2) 206 connected to the bias source 202, a second voltage sensor (Vdc2) 222, and the ground 216. The first resistor 204 and the second resistor 206 can be connected to different ground sources 216a, 216b, as FIG. 2BAs shown. In this implementation, the first branch 205 includes a first resistor 204, a ground portion 216a, and a first voltage sensor 220, and the second branch 207 includes a second resistor 206, a ground portion 216b, and a second voltage sensor 222. The first resistor 204 and the second resistor 206 are connected in series with each other. Resistors 204 and 206 may be referred to as an SOT structure. All components and parts of the half-bridge circuit 200 can be deposited and fabricated on the same wafer, thereby avoiding the complexities described in the full Wheatstone bridge based on TMR sensors.

[0031] like FIG. 2B As shown, the first resistor 204 includes an SOT layer 224a and a ferromagnetic (FM) layer 226. A first end 223a of the SOT layer 224a is connected to a ground portion 216a, and a second end 223b of the SOT layer 224a is connected to a first voltage sensor 220. An FM layer 226 is disposed on the SOT layer 224 (possible intermediate layers are not shown, nor are they shown in the following figures) and connected to a bias source 202. The second resistor 206 includes an SOT layer 228 and an FM layer 330. A first end 225a of the SOT layer 228 is connected to a second voltage sensor 222, and a second end 225b of the SOT layer 228 is connected to a ground portion 216b. An FM layer 230 is disposed on the SOT layer 228 (possible intermediate layers are not shown, nor are they shown in the following figures) and connected to a bias source 202. The FM layers 226 and 230 are stabilized such that they are magnetized in the x-direction. More generally, a layer is described as being placed on top of another layer, where the two layers do not need to be in contact, and one or more intermediate layers may exist between the two layers.

[0032] The second end 223a of the SOT layer 224 of the first resistor 204 is disposed adjacent to the first end 225a of the SOT layer 228 of the second resistor 206, such that the first voltage sensor 202 and the second voltage sensor 222 are disposed adjacent to each other. Therefore, ground portions 216a and 216b are disposed on opposite ends of the SOT layers 224 and 228. The SOT layers 224 and 228 are substantially identical, and the FM layers 226 and 230 are substantially identical. This allows the entire stack (FM / SOT) to be deposited in one step and fabricated on the same wafer.

[0033] Each FM layer 226, 230 has a width 232 in the x-direction and a height 233 in the y-direction. The width 232 can be greater than the height 233 to exploit the shape anisotropy of the FM layer 226, 230. The aspect ratio (width divided by height) is typically greater than or equal to 3. For example, the width 232 can be about 300 nm to about 30 pm, and the height 233 can be about 100 nm to about 10 pm. While the FM layers 226, 230 are shown as rectangular, the FM layers 226, 230 can instead be elliptical in shape, as discussed below in FIG. 4B

[0034] The FM layers 226, 230 can each individually comprise NiFe, CoFe, NiFeX, CoFeX, FeX, or NiX, where X = Co, Ni, Cu, Si, Al, Mn, Ge, Ta, Hf, N, and B. The FM layers 226, 230 can include any magnetic layer combination or alloy combination of these elements that can produce low coercivity, negative magnetostriction FM layers 226, 230, or multilayer combinations with other higher polarization materials such as Heusler alloys or high-Ni containing alloy FM layers.

[0035] The SOT layers 224, 228 can each individually comprise doped or undoped bismuth antimony (BiSb) of various thicknesses. In one embodiment, the SOT layers 224, 228 comprise undoped BiSb or doped BiSbX, where X is less than 8 atomic percent, and extracted from elements that do not readily interact with Bi or Sb such as Cu, Ag, Ge, Mg, Ni, Co, Mo, W, Sn, B, N, In, Te, Se, Y, Zr, Pt, Ti, or alloy combinations thereof, or doped as ceramic oxides, carbides, or nitrides of these elements. The SOT layers 224, 228 can each individually comprise YPtBi.

[0036] The bias source 202 provides a vertical current through the FM layers 226, 230, which is spin polarized and injected into the SOT layers 224, 228 of the first and second resistors 202, 204 (along the z-direction). Due to the inverse spin Hall effect (iSHE), a DC voltage is induced longitudinally (along the x-direction) between the ground 216a, 216b and the first and second voltage sensors 220, 222. The magnitude of the DC voltage depends on the magnetization component of the FM layers 226, 230 in the y-direction. If the magnetization of the FM layers 226, 230 is 100% along the y-direction, then both DC voltages (Vdcl and Vdc2) will have a maximum signal. If the magnetization of the FM layers 226, 230 is 100% along the x-direction, then both DC voltages will have a zero induced signal.

[0037] ​When an external magnetic field is applied in the y-direction, the magnetization of FM layers 226 and 230 rotates, causing the first voltage sensor 220 to be greater than 0 at the first resistor 204 and the second voltage sensor 222 to be less than 0 at the second resistor 206 (or vice versa), thereby doubling the signal (Vdc2 - Vdc1). When no external magnetic field is applied or when an external field is applied along the x-direction, the magnetization of FM layers 226 and 230 remains in the x-direction, resulting in no inherent signal output except for some thermal drift, since the first voltage sensor 220 and the second voltage sensor 222 are equal (Vdc1 = Vdc2). Thus, the half-bridge design 200 is only sensitive to magnetic fields along the y-direction and is unaffected by magnetic fields in any other components.

[0038] The half-bridge design 200, which only includes two branch roads 205 and 207, can be implemented in a simpler and more direct way. FIG. 1 The half-bridge circuit 200 functions similarly to the Wheatstone bridge array 100. Because the half-bridge circuit 200 utilizes an SOT structure without employing the TMR effect, it is less likely to break down over time (an inherent reliability issue with TMR sensors). Furthermore, the outputs of the two branches 205 and 207 of the half-bridge design 200 have opposite polarities, thus doubling or amplifying the signal of the half-bridge design 200. Additionally, any environmental / thermal drift will cause identical changes in Vdc1 and Vdc2 (both in magnitude and polarity), resulting in a net cancellation of the signal output.

[0039] FIG. 3A and FIG. 3B It is based on an implementation plan. FIG. 2B A schematic diagram of the branch roads 205 and 207 of the 200-meter half-bridge design. FIG. 3A Example 1: Branch 205, and FIG. 3B The second branch road 207 is shown as an example.

[0040] like FIG. 3A As shown, the first branch 205 may include multiple SOT layers 224a, 224b, 224n (collectively referred to herein as SOT layer 224), on which multiple FM layers 226a, 226b, 226b (collectively referred to herein as FM layer 226) are disposed. The multiple SOT layers 224a, 224b, 224n are connected in series. Each FM layer 226a, 226b, 226n is connected to a bias source 202. An SOT layer 224 and the FM layer 226 disposed on that SOT layer may be referred to herein as an SOT structure. Although three SOT structures are shown, the first branch 205 may include any number of SOT structures.

[0041] The first SOT layer 224a in series has a first end 223a connected to the ground 216a. The last SOT layer 224n in series has a second end 223b connected to the first voltage sensor 220. The bottom surface 223c of the last SOT layer 224n opposite the surface on which the FM layer 226n is disposed is also coupled to the resistor 234b and then to the ground 236b. Similarly, the bottom surface 223c of each intermediate SOT layer 224b opposite the surface on which the FM layer 226b is disposed is coupled to the resistor 234a and then to the ground 236a. Since the first SOT layer 224a is connected to the ground 216a at the first end 223a, the first SOT layer 224a does not require a resistor as do the intermediate SOT layers 224b and the last SOT layer 224n. During operation, the voltage of each of the plurality of SOT layers 224a, 224b, 224n and the FM layers 226a, 226b, 226c is added together, thereby increasing the signal output. Furthermore, all of the SOT layers 224a, 224b, 224n and the FM layers 226a, 226b, 226c can be deposited and fabricated on the same thin wafer, since the SOT layers 224a, 224b, 224n are all the same and the FM layers 226a, 226b, 226c are all the same.

[0042] Similar to the first branch 205, the second branch 207 can include a plurality of SOT layers 228a, 228b, 228n (collectively referred to herein as SOT layers 228) on which is disposed a plurality of FM layers 230a, 230b, 230b (collectively referred to herein as FM layers 230). The plurality of SOT layers 228a, 228b, 228n are connected together in series. Each FM layer 230a, 230b, 230b is connected to the bias source 202. Although three SOT layers 228a, 228b, 228n and three FM layers 226a, 226b, 226b are shown, the second branch 207 can include any number of SOT layers and FM layers. One SOT layer 228 and the FM layer 230 disposed thereon can be referred to herein as a SOT structure.

[0043] The last SOT layer 228n in the series has a second end 225a connected to the ground 216b. The first SOT layer 228a in the series has a first end 225a connected to the second voltage sensor 222. The bottom surface 225c of the first SOT layer 228a opposite the surface on which the FM layer 230a is disposed is also coupled to the resistor 234c and then to the ground 236d. Similarly, the bottom surface 225c of each of the intermediate SOT layers 228b opposite the surface on which the FM layer 228b is disposed is coupled to the resistor 234d and then to the ground 236d. Since the last SOT layer 228n is connected to the ground 216b on the second end 225b, the last SOT layer 228n does not require a resistor as do the first SOT layer 228a and the intermediate SOT layers 228b. During operation, the voltage of each of the plurality of SOT layers 228a, 228b, 228n and the FM layers 230a, 230b, 230b is added together, thereby increasing the signal output.

[0044] Further, all of the SOT layers 228a, 228b, 228n and the FM layers 230a, 230b, 230b can be deposited and fabricated on the same wafer. Further, all of the SOT layers and the FM layers of both the first leg 205 and the second leg 207 can be deposited and fabricated on the same wafer. All of the SOT layers and the FM layers of both the first leg 205 and the second leg 207 can include any of the materials discussed above.

[0045] FIG. 4A is a schematic cross-sectional view of a single ferromagnetic (FM) layer electrical bridge 405 according to one embodiment. FIG. 4B is a schematic top view of the single FM layer electrical bridge 405. The single FM layer electrical bridge 405 can be either the first leg 205 or the second leg 207 of FIG. 4A is a schematic top view of the single FM layer electrical bridge 405. The single FM layer electrical bridge 405 can be either the first leg 205 or the second leg 207 of FIG. 2A to FIG. 3B is a schematic top view of the single FM layer electrical bridge 405. The single FM layer electrical bridge 405 can be either the first leg 205 or the second leg 207 of FIG. 2A to FIG. 3B is discussed above in

[0046] The FM layer bridge 405 includes a SOT layer 224 and an FM layer 226 disposed on the SOT layer (i.e., one SOT structure). The FM layer 226 is sandwiched between a first bias layer 440a and a second bias layer 440b. The first and second bias layers 440a, 440b can include a hard bias layer or a soft bias layer. The first and second bias layers 440a, 440b can each individually include a layer of Co, Pt, Ni, CoPt, CoPtCr, NiFe, CoFe, or combinations thereof. For the case of a soft bias material, there is an additional AFM layer 442 disposed on top of the first and second bias layers 440a, 440b for exchanging the bias of the soft bias layers. For the case of a hard bias layer, the AFM layer 442 can be skipped. The first and second bias layers 440a, 440b enable the FM layer 226 to have a magnetization in the x-direction when no external field is applied. The strength of the first and second bias layers 440a, 440b controls the dynamic range of the entire sensor that includes the FM layer bridge 405. An insulating layer can be disposed between the FM layer 226 and the bias layers 440a, 440b for electrical isolation. As shown in the side view of FIG. 3B (i.e., viewed from the z-direction), the FM layer 226 can be an elliptical shape or an oval shape and can utilize shape anisotropy when the width 232 is greater than the height 233. FIG. 4B As shown in the side view of FIG. 3B (i.e., viewed from the z-direction), the FM layer 226 can be an elliptical shape or an oval shape and can utilize shape anisotropy when the width 232 is greater than the height 233.

[0047] FIG. 4C is a schematic cross-sectional view of a branch 407 having more than one SOT structure according to one embodiment. For clarity, the ground, bias source, and voltage sensor are not shown in the branch 407. However, the branch 407 can be connected as discussed above in FIG. 2A to FIG. 3B FIG. 3A. The branch 407 can be the first branch 205 or the second branch 207 of FIG. 2A to FIG. 3B FIG. 3A.

[0048] The branch 407 is similar to the branch 205, 207 shown in FIG. 3A to FIG. 3B FIG. 3A. The branch 407 further includes a first FM layer 226a disposed above a first SOT layer 224a and a second FM layer 226b disposed above a second SOT layer 224b. The first FM layer 226a is disposed between a first bias layer 440a and a second bias layer 440b. The second FM layer 226b is disposed between the second bias layer 440b and a third bias layer 440c. Thus, the first and second FM layers 226a, 226b can share the second bias layer 440b, enabling the second bias layer 440b to bias both FM layers 226a, 226b. Although two FM layers 226a, 226b and two SOT layers 224a, 224b are shown, the branch 407 can include any number of FM layers, SOT layers, and bias layers.

[0049] FIG. 5 is a schematic diagram of a half-bridge circuit design 500 of a magnetic sensor according to another embodiment. The half-bridge circuit 500 can be referred to herein as a magnetic sensor 500.

[0050] The half-bridge circuit 500 is similar to the half-bridge circuit 200 of FIG. 2A to FIG. 2B such that the half-bridge 500 design includes a first leg 505 and a second leg 507. The first leg 505 is similar to the first leg 205, including a SOT layer 224 and a first FM layer (FM1) 226 disposed on the SOT layer. However, the first leg 505 also includes a second FM layer (FM2) 526 disposed below the SOT layer 224, such that the SOT layer 224 is sandwiched between the first FM layer 226 and the second FM layer 526. The first FM layer 226 is connected to the bias source 202. A first end 223a of the SOT layer 224 is connected to the ground 216a, and a second end 223b of the SOT layer 224 is connected to the first voltage sensor 220.

[0051] Likewise, the second leg 507 is similar to the first leg 207, including a SOT layer 228 and a first FM layer (FM1) 230 disposed on the SOT layer. However, the first leg 507 also includes a second FM layer (FM2) 530 disposed below the SOT layer 228, such that the SOT layer 228 is sandwiched between the first FM layer 230 and the second FM layer 530. The first FM layer 230 is connected to the bias source 202. A first end 225a of the SOT layer 228 is connected to the ground 216b, and a second end 225b of the SOT layer 228 is connected to the second voltage sensor 222.

[0052] The second FM layers 526, 530 can comprise the same material as the first FM layers 226, 230, and have the same or different widths 232 and heights 233. The first leg 505 and the second leg 507 can each individually include one or more SOT structures, as discussed above in FIG. 3A to FIG. 3B and shown in FIG. 6B Additionally, the FM layers 226, 526, 230, 530 can be elliptical in shape. All of the SOT layers 226, 228 and FM layers 226, 526, 230, 530 can be deposited and fabricated on the same thin wafer. Additionally, all of the SOT layers and FM layers of both the first leg 505 and the second leg 507 can be deposited and fabricated on the same thin wafer.

[0053] Bias source 202 provides a vertical current through FM layers 226, 230, 526, 530, resulting in spin-polarized current and injection into SOT layers 224, 228 of first branch 505 and second branch 507 (along the z-direction). Due to the inverse spin Hall effect (iSHE), a DC voltage is induced longitudinally (along the x-direction) between ground sections 216a, 216b and first voltage sensor 220 and second voltage sensor 222. The magnitude of the DC voltage depends on the magnetization of FM layers 226, 230, 526, 530 in the y-direction. In half-bridge design 500, a first signal is induced at the interface between first FM layers 226, 230 and SOT layers 224, 228, and a second signal is induced at the interface between second FM layers 526, 530 and SOT layers 224, 229. The second voltage signal of second FM layers 526, 530 has the same polarity as the first voltage signal of first FM layers 226, 230, and thus the first voltage signal and the second voltage signal can be added together because both the spin current direction and the spin polarization are reversed.

[0054] When an external magnetic field is applied in the y-direction, the magnetization of FM layers 226, 230, 526, 530 will rotate such that at first branch 505, first voltage sensor 220 is greater than 0, and at second branch 507, second voltage sensor 222 is less than 0 (or vice versa), resulting in the voltage difference being doubled again. When no external magnetic field is applied or a field is applied along the x-direction, the magnetization of FM layers 226, 230, 526, 530 remains in the x-direction, resulting in no intrinsic signal output because first voltage sensor 220 and second voltage sensor 222 are equal (Vdcl = Vdc2). As such, half-bridge design 500 is only sensitive to magnetic fields along the y-direction and is not affected by magnetic fields in any other components. Additionally, any environmental / thermal drift will cause the same change (both in magnitude and polarity) in Vdcl and Vdc2, resulting in a net cancellation of the signal output.

[0055] FIG. 6A is a schematic cross-sectional view of a dual ferromagnetic (FM) layer bridge 605 according to one embodiment. Dual FM layer bridge 605 can be a first branch 505 or a second branch 507 of FIG. 5 For clarity, ground sections, bias sources, and voltage sensors are not shown in FM layer bridge 605. However, FM layer bridge 605 can be connected as discussed above in FIG. 2A to FIG. 3B and FIG. 5 .

[0056] The FM layer electrical bridge 605 includes a first FM layer 226, a second FM layer 526, and a SOT layer 224 disposed between the first FM layer and the second FM layer (i.e., a SOT structure). The first FM layer 226 is sandwiched between a first bias layer 440a and a second bias layer 440b. The second FM layer 526 is sandwiched between a third bias layer 640a and a fourth bias layer 640b. The first bias layer 440a, the second bias layer 440b, the third bias layer 640a, and the fourth bias layer 640b can be hard bias layers or soft bias layers. For the case of soft bias materials, there are additional AFM layers 442 disposed on top of the first bias layer 440a and the second bias layer 440b and additional AFM layers 642 disposed below the third bias layer 640a and the fourth bias layer 640b for swapping the bias of the soft bias layers. For the case of hard bias layers, the AFM layers 442, 642 can be skipped. The first bias layer 440a, the second bias layer 440b, the third bias layer 640a, and the fourth bias layer 640b can each individually contain any of the materials disclosed above for the first bias layer 440a and the second bias layer 440b. The first bias layer 440a and the second bias layer 440b enable the first FM layer 226 to have a magnetization in the x-direction when no external field is applied, and the third bias layer 640a and the fourth bias layer 640b enable the second FM layer 526 to have a magnetization in the x-direction when no external field is applied. The strength of the first bias layer 440a, the second bias layer 440b, the third bias layer 640a, and the fourth bias layer 640b controls the dynamic range of the entire sensor that includes the FM layer electrical bridge 605. Insulating layers can be disposed between the first FM layer 226 and the bias layers 440a, 440b and between the second FM layer 526 and the bias layers 640a, 640b.

[0057] FIG. 6B is a schematic cross-sectional or bottom view of a branch 607 having more than one SOT structure according to an embodiment. For clarity, the ground, bias sources, and voltage sensors are not shown in the branch 607. However, the branch 607 can be connected as discussed above in FIG. 2A to FIG. 3B and FIG. 5 . The branch 607 can be the first branch 505 or the second branch 507 of FIG. 5 .

[0058] The branch 607 is similar to the branch 505 of FIG. 5Branches 505 and 507 are shown. Branch 607 includes a first FM layer 226a, a second FM layer 526a, and a first SOT layer 224a disposed between the first FM layer and the second FM layer, and also includes a third FM layer 226b, a fourth FM layer 526b, and a second SOT layer 224b disposed between the third FM layer and the fourth FM layer. The first FM layer 226a is disposed between the first bias layer 440a and the second bias layer 440b. The third FM layer 226b is disposed between the second bias layer 440b and the fifth bias layer 440c. Therefore, the first FM layer 226a and the third FM layer 226b can share the second bias layer 440b, thereby enabling the second bias layer 440b to bias both the first FM layer 226a and the third FM layer 226b.

[0059] Similarly, the second FM layer 526a is disposed between the third bias layer 640a and the fourth bias layer 640b. The fourth FM layer 526b is disposed between the third bias layer 640a and the sixth bias layer 640c. Therefore, the second FM layer 526a and the fourth FM layer 526b can share the fourth bias layer 640b, thereby enabling the fourth bias layer 640b to bias both the second FM layer 526a and the fourth FM layer 526b. Although two SOT structures are shown, branch 607 may include any number of SOT structures.

[0060] Therefore, a magnetic sensor consisting of only two branches can achieve the same function as a Wheatstone bridge array in a simpler and more direct way while being less complex to manufacture. Furthermore, since the half-bridge circuit utilizes an SOT structure without employing the TMR effect, it is less likely to break down over time (an inherent reliability issue with TMR sensors). Additionally, in a half-bridge design, the outputs of the two branches have opposite polarities, thus doubling or amplifying the signal. Moreover, any environmental / thermal drift will cause identical changes in Vdc1 and Vdc2 (both in magnitude and polarity), resulting in a net elimination of drift in the signal output.

[0061] In one embodiment, a half-bridge circuit includes: a first spin-orbit moment (SOT) layer having a first end and a second end opposite to the first end; a first ferromagnetic (FM) layer disposed on the first SOT layer; a first ground portion connected to the first end of the first SOT layer; a first voltage sensor connected to the second end of the first SOT layer; a bias source connected to the first FM layer; a second SOT layer having a first end and a second end opposite to the first end; a second FM layer disposed on the second SOT layer and connected to the bias source; a second ground portion connected to the second end of the second SOT layer; and a second voltage sensor connected to the first end of the second SOT layer.

[0062] A first voltage sensor and a second voltage sensor are disposed adjacent to each other. The ratio of the width to the height of the first FM layer is greater than or equal to 3, and the ratio of the width to the height of the second FM layer is greater than or equal to 3. The half-bridge circuit further includes: a first bias layer disposed adjacent to the first FM layer above a first end of the first SOT layer; a second bias layer disposed adjacent to the first FM layer above a second end of the first SOT layer; a third bias layer disposed adjacent to the second FM layer above a first end of the second SOT layer; and a fourth bias layer disposed adjacent to the second FM layer above a second end of the second SOT layer. The half-bridge circuit further includes a third FM layer disposed below the first SOT layer and a fourth FM layer disposed below the second SOT layer. The first FM layer and the second FM layer are each individually rectangular or elliptical in shape. A magnetic sensor including a half-bridge circuit.

[0063] In another embodiment, a half-bridge circuit includes a bias source, a first branch, and a second branch. The first branch is connected to the bias source and includes one or more first spin-orbit moment (SOT) structures. Each first SOT structure includes: a first SOT layer having a first end and a second end opposite to the first end; a first ferromagnetic (FM) layer disposed on the first SOT layer; a first ground portion connected to the first end of the first SOT layer; and a first voltage sensor connected to the second end of the first SOT layer. The second branch is connected to the bias source and includes one or more second SOT structures. Each second SOT structure includes: a second SOT layer having a first end and a second end opposite to the first end; a second FM layer disposed on the second SOT layer; a second ground portion connected to the second end of the second SOT layer; and a second voltage sensor connected to the first end of the second SOT layer.

[0064] A first branch includes a plurality of first SOT structures connected in series, and a second branch includes a plurality of second SOT structures connected in series. A bias source is connected to a first FM layer and to a second FM layer. The first and second SOT layers each individually contain BiSb or YPtSb. A second end of the first SOT layer is disposed adjacent to a first end of the second SOT layer. A first FM layer is disposed between a first bias layer and a second bias layer, and the second FM layer is disposed between a third bias layer and a fourth bias layer. A magnetic sensor including a half-bridge circuit.

[0065] In another embodiment, a half-bridge circuit includes a bias source, a first branch, and a second branch. The first branch is connected to the bias source and includes one or more first spin-orbit moment (SOT) structures connected in series. Each first SOT structure includes: a first SOT layer having a first end and a second end opposite to the first end; a first ferromagnetic (FM) layer disposed on the first SOT layer; a second FM layer disposed below the first SOT layer; a first ground portion connected to the first end of the first SOT layer; and a first voltage sensor connected to the first SOT layer. The second branch of the T-layer is connected to a bias source. The second branch includes one or more second SOT structures connected in series. Each second SOT structure includes: a second SOT layer having a first end and a second end opposite to the first end, wherein the first end of the second SOT layer is disposed adjacent to the second end of the first SOT layer; a third FM layer disposed on the second SOT layer; a fourth FM layer disposed below the second SOT layer; a second ground portion connected to the second end of the second SOT layer; and a second voltage sensor connected to the first end of the second SOT layer.

[0066] The width-to-height ratio of the first FM layer is greater than or equal to 3; the width-to-height ratio of the second FM layer is greater than or equal to 3; the width-to-height ratio of the third FM layer is greater than or equal to 3; and the width-to-height ratio of the fourth FM layer is greater than or equal to 3. The first FM layer is positioned between the first and second bias layers; the second FM layer is positioned between the third and fourth bias layers; the third FM layer is positioned between the fifth and sixth bias layers; and the fourth FM layer is positioned between the seventh and eighth bias layers. The first, second, third, fourth, fifth, and sixth bias layers are hard bias layers. The first, second, third, fourth, fifth, and sixth bias layers are soft bias layers. The width of the first FM layer is greater than its height; the width of the second FM layer is greater than its height; the width of the third FM layer is greater than its height; and the width of the fourth FM layer is greater than its height. A magnetic sensor including a half-bridge circuit.

[0067] While the foregoing describes embodiments of this disclosure, other and additional embodiments of this disclosure may be contemplated without departing from the essential scope of this disclosure, which is defined by the appended claims.

Claims

1. A half bridge circuit, the half bridge circuit comprising: a first spin orbit torque (SOT) layer having a first end and a second end opposite the first end; a first ferromagnetic (FM) layer disposed on the first SOT layer; a first ground connected to the first end of the first SOT layer; a first voltage sensor connected to the second end of the first SOT layer; a bias source connected to the first FM layer; a second SOT layer having a first end and a second end opposite the first end; a second FM layer disposed on the second SOT layer, the second FM layer connected to the bias source; a second ground connected to the second end of the second SOT layer; and a second voltage sensor connected to the first end of the second SOT layer.

2. The half bridge circuit of claim 1, wherein the first voltage sensor is disposed adjacent the second voltage sensor.

3. The half bridge circuit of claim 1, wherein a ratio of a width of the first FM layer to a height of the first FM layer is greater than or equal to 3, and wherein a ratio of a width of the second FM layer to a height of the second FM layer is greater than or equal to 3.

4. The half bridge circuit of claim 1, further comprising: a first bias layer disposed adjacent the first FM layer over the first end of the first SOT layer; a second bias layer disposed adjacent the first FM layer over the second end of the first SOT layer; a third bias layer disposed adjacent the second FM layer over the first end of the second SOT layer; and a fourth bias layer disposed adjacent the second FM layer over the second end of the second SOT layer.

5. The half bridge circuit of claim 1, further comprising: a third FM layer disposed below the first SOT layer; and a fourth FM layer disposed below the second SOT layer.

6. The half bridge circuit of claim 1, wherein the first FM layer and the second FM layer are each individually rectangular or elliptical in shape.

7. A magnetic sensor comprising the half bridge circuit of claim 1.

8. A half bridge circuit, the half bridge circuit comprising: a bias source; a first leg connected to the bias source, the first leg comprising one or more first spin orbit torque (SOT) structures, each first SOT structure comprising: a first SOT layer having a first end and a second end opposite the first end; a first ferromagnetic (FM) layer disposed on the first SOT layer; a first ground connected to the first end of the first SOT layer; and a first voltage sensor connected to the second end of the first SOT layer. ​ ​ a first voltage sensor connected to the second end of the first SOT layer; and a second branch connected to the bias source, the second branch comprising one or more second SOT structures, each second SOT structure comprising: a second SOT layer having a first end and a second end opposite the first end; a second FM layer disposed on the second SOT layer; a second ground connected to the second end of the second SOT layer; and a second voltage sensor connected to the first end of the second SOT layer.

9. The half bridge circuit of claim 8, wherein the first branch comprises a plurality of first SOT structures connected in series, and the second branch comprises a plurality of second SOT structures connected in series.

10. The half bridge circuit of claim 8, wherein the bias source is connected to the first FM layer and to the second FM layer.

11. The half bridge circuit of claim 8, wherein the first SOT layer and the second SOT layer each individually comprise BiSb or YPtSb.

12. The half bridge circuit of claim 8, wherein the second end of the first SOT layer is disposed adjacent to the first end of the second SOT layer.

13. The half bridge circuit of claim 8, wherein the first FM layer is disposed between a first bias layer and a second bias layer, and wherein the second FM layer is disposed between a third bias layer and a fourth bias layer.

14. A magnetic sensor comprising the half bridge circuit of claim 8.

15. A half bridge circuit, the half bridge circuit comprising: a bias source; a first branch connected to the bias source, the first branch comprising one or more first spin orbit torque (SOT) structures connected in series, each first SOT structure comprising: a first SOT layer having a first end and a second end opposite the first end; a first ferromagnetic (FM) layer disposed on the first SOT layer; a second FM layer disposed below the first SOT layer; a first ground connected to the first end of the first SOT layer; and a first voltage sensor connected to the second end of the first SOT layer; and a second branch connected to the bias source, the second branch comprising one or more second SOT structures connected in series, each second SOT structure comprising: a second SOT layer having a first end and a second end opposite the first end, wherein the first end of the second SOT layer is disposed adjacent to the second end of the first SOT layer; a third FM layer disposed on the second SOT layer; a fourth FM layer disposed below the second SOT layer; a second ground, the second ground connected to the second end of the second SOT layer; and a second voltage sensor, the second voltage sensor connected to the first end of the second SOT layer.

16. The half bridge circuit of claim 15, wherein: a ratio of a width of the first FM layer to a height of the first FM layer is greater than or equal to 3; a ratio of a width of the second FM layer to a height of the second FM layer is greater than or equal to 3; a ratio of a width of the third FM layer to a height of the third FM layer is greater than or equal to 3; and a ratio of a width of the fourth FM layer to a height of the fourth FM layer is greater than or equal to 3.

17. The half bridge circuit of claim 15, wherein: the first FM layer is disposed between a first bias layer and a second bias layer; the second FM layer is disposed between a third bias layer and a fourth bias layer; the third FM layer is disposed between a fifth bias layer and a sixth bias layer; and the fourth FM layer is disposed between a seventh bias layer and an eighth bias layer.

18. The half bridge circuit of claim 17, wherein the first bias layer, the second bias layer, the third bias layer, the fourth bias layer, the fifth bias layer, and the sixth bias layer are hard bias layers.

19. The half bridge circuit of claim 17, wherein the first bias layer, the second bias layer, the third bias layer, the fourth bias layer, the fifth bias layer, and the sixth bias layer are soft bias layers.

20. The half bridge circuit of claim 15, wherein: a width of the first FM layer is greater than a height of the first FM layer; a width of the second FM layer is greater than a height of the second FM layer; a width of the third FM layer is greater than a height of the third FM layer; and a width of the fourth FM layer is greater than a height of the fourth FM layer.

21. A magnetic sensor comprising the half bridge circuit of claim 15.

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