A flexible lateral field excited thin film bulk acoustic wave magnetoelectric antenna

Abstract

The application belongs to the technical field of radio frequency band micro-antenna, and particularly relates to a flexible transverse field excited film bulk acoustic wave magnetoelectric antenna. The flexible transverse field excited film bulk acoustic wave magnetoelectric antenna comprises a flexible support substrate, a piezoelectric single crystal arranged on the flexible support substrate, a coplanar electrode arranged on the piezoelectric single crystal, and a magnetostrictive film arranged between an input electrode and a grounding electrode. The magnetoelectric antenna works in an in-plane vibration mode, has a stronger magnetoelectric coupling coefficient, and can effectively improve the radiation power. Compared with a traditional cavity FBAR magnetoelectric antenna, the flexible transverse field excited film bulk acoustic wave magnetoelectric antenna has a simple preparation process, is compatible with a CMOS process, can work in a flexible application scenario, and has a high quality factor.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of radio frequency band micro antennas, and relates to a chip radio frequency mechanical antenna, in particular to a flexible transverse field excited thin film bulk acoustic magnetoelectric antenna. BACKGROUND

[0002] As one of the core elements in a wireless communication system, an antenna is used for receiving and transmitting electromagnetic waves. With the rapid development of wireless communication systems, especially the advent of the 5G communication era, there is an increasingly high demand for electrically small antennas that are small, efficient and integrated, and it is urgent to find a kind of alternative antenna with a size that can be miniaturized and high radiation efficiency.

[0003] In recent years, researchers have made a lot of efforts in antenna miniaturization, but electrically small antennas still have various problems, such as relatively large physical size. Therefore, antenna designs based on different radiation mechanisms are increasingly valued, and mechanical antennas are a viable solution, among which mechanical resonance and magnetoelectric coupling in magnetoelectric composites are the focus of research.

[0004] Portable radio frequency wireless communication is an important application of mechanical antennas. Based on the FBAR structure, by selecting a suitable resonant cavity thickness, an antenna for GPS (1.2 GHz and 1.5 GHz) and Bluetooth (2.45 GHz) can be designed, and the small physical size makes the antenna applicable to some small electronic devices. By combining resonators of different thicknesses or lengths in an antenna array, a multi-band antenna can be achieved. One application of such a multi-band mechanical antenna is radio frequency identification (RFID).

[0005] In 2015, Yao et al. from UCLA first proposed the theoretical analysis of the magneto-electric composite material generating very high frequency electromagnetic waves under the excitation of electric field, and evaluated the radiation performance of the sound-excited bulk acoustic wave medium multi-ferroelectric antenna. In 2017, Nan et al. from Northeastern University in the United States designed and prepared a practical integrated ME antenna based on the FBAR structure using MEMS technology. The resonant frequency of the FBAR magneto-electric antenna is determined by the thickness of the magneto-electric heterostructure. The magneto-electric composite material in the FBAR magneto-electric antenna mainly includes a piezoelectric layer and a magnetostrictive layer. When the antenna works in the transmitting process, a voltage is applied to the piezoelectric layer, a strain is generated through the inverse piezoelectric effect and is transmitted to the magnetostrictive layer, and a magnetization oscillation is excited through the piezomagnetic effect to radiate electromagnetic waves into space. Such an antenna works in the acoustic wave resonance rather than the electromagnetic wave resonance. Since the wave speed of the acoustic wave is five orders of magnitude smaller than that of the electromagnetic wave, the size of the magneto-electric antenna can be effectively reduced. However, the vibration mode of the piezoelectric layer of the FBAR resonator is the out-of-plane longitudinal wave, and the stress equivalent field acting on the magnetostrictive layer is also in the out-of-plane direction. Due to the influence of the demagnetizing field in the magnetic layer, the magnetic moment is in the in-plane direction, resulting in a weak magnetization oscillation excited by the FBAR resonator, which limits the radiation efficiency of the antenna. In addition, the resonator of the cavity type FBAR structure has a complex preparation process and poor mechanical stability. At the same time, due to the rigid support substrate, it is difficult to apply to wearable medical devices and other application fields. SUMMARY

[0006] The purpose of the present application is to provide a flexible transverse field excited thin film bulk acoustic wave magneto-electric antenna to solve the problems of difficult preparation process, poor mechanical stability and difficulty in application to flexible application scenarios based on the cavity type FBAR device.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0008] A flexible transverse field excited thin film bulk acoustic wave magneto-electric antenna, comprising: a flexible support substrate, a piezoelectric single crystal is arranged on the flexible support substrate, a coplanar electrode is arranged on the piezoelectric single crystal, the coplanar electrode is composed of an input electrode and a ground electrode, and a magnetostrictive film is arranged between the input electrode and the ground electrode.

[0009] Further, the flexible support substrate is a PI substrate, and the thickness is 1mm-5mm.

[0010] Further, the piezoelectric single crystal is lithium niobate or lithium carbonate, and the thickness is 700μm-2000μm.

[0011] Further, the material of the coplanar electrode is aluminum or platinum, and the thickness is 100-300nm.

[0012] Further, the magnetostrictive film is iron cobalt silicon boron, iron silicon boron, iron silicon boron carbon or iron gallium boron.

[0013] Further, the thickness of the magnetostrictive film is 250-750nm.

[0014] Further, the piezoelectric single crystal is bonded with the flexible supporting substrate by using the transfer single crystal method, so that the piezoelectric performance of the piezoelectric layer and the quality factor of the device are effectively improved.

[0015] The flexible transverse field excited film bulk acoustic wave magnetoelectric antenna provided by the application is a kind of magnetoelectric antenna using transverse field excited FBAR resonator (LFE FBAR) to realize the function of magnetoelectric antenna.

[0016] During the transmitting process, alternating voltage signals are applied to the coplanar electrode input electrode and the ground electrode, and resonant elastic standing waves are generated in the piezoelectric single crystal through the inverse piezoelectric effect.

[0017] The flexible transverse field excited film bulk acoustic wave magnetoelectric antenna provided by the application uses PI substrate as flexible substrate, and because the low acoustic impedance of PI, it is an excellent acoustic reflector, which can effectively limit acoustic waves. Based on the PI substrate, the piezoelectric single crystal layer is prepared by using the transfer single crystal method, so that the PI substrate and the piezoelectric single crystal are highly combined. Compared with the traditional piezoelectric film deposited by magnetron sputtering, the piezoelectric single crystal has better piezoelectric performance, and solves the problem of low quality factor of traditional flexible piezoelectric devices.

[0018] Compared with the prior art, the application has the following advantages:

[0019] 1. The flexible transverse field excited film bulk acoustic wave magnetoelectric antenna provided by the application uses acoustic resonance mode, and strain is transmitted from the piezoelectric layer to the magnetostrictive layer.

[0020] 2.The flexible transverse field excited thin film bulk acoustic wave magnetoelectric antenna provided by the application works in a "contour-mode" and belongs to an in-plane acoustic mode.Piezoelectric single crystals and magnetic films are coupled in a plane, and the coupling mode has a larger magnetoelectric coupling coefficient than an out-of-plane mode, so that the device has higher antenna gain and transceiving power.

[0021] 3.The flexible transverse field excited thin film bulk acoustic wave magnetoelectric antenna provided by the application uses flexible PI as a substrate to limit acoustic waves, effectively solving the problem that a traditional rigid substrate and a cavity type structure have a complex preparation process and cannot be applied to a flexible scene. A transfer piezoelectric single crystal instead of a piezoelectric film is used as a piezoelectric layer, which effectively improves the piezoelectric performance of the piezoelectric layer and the quality factor of the device.

[0022] 4.The magnetoelectric antenna provided by the application can be reduced to a millimeter or even sub-millimeter level, and is compatible with a CMOS process, so that an integrated array antenna can be realized while the size of a single antenna is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 A structure schematic diagram of the flexible transverse field excited thin film bulk acoustic wave magnetoelectric antenna provided by the application is shown in the figure.

[0024] Figure 2 A resonance mode simulation result of the FBAR magnetoelectric antenna device is shown in the figure.

[0025] Figure 3 A stress field simulation result of the magnetoelectric antenna device in a resonance state is shown in the figure.

[0026] Figure 4 An S 11 parameter simulation result of the magnetoelectric antenna device is shown in the figure.

[0027] REFERENCE SIGNS:

[0028] 100, flexible support substrate, 110, piezoelectric single crystal, 120, coplanar electrode, 130, magnetostrictive film. DETAILED DESCRIPTION

[0029] The technical solutions of the application will be described in detail below with reference to the accompanying drawings and embodiments.

[0030] EMBODIMENT

[0031] As Figure 1As shown, the flexible transverse field excited thin film bulk acoustic wave magnetoelectric antenna provided in the embodiment comprises a flexible support substrate 100, the flexible support substrate 100 is provided with a piezoelectric single crystal 110, the piezoelectric single crystal 110 is provided with a coplanar electrode 120, the coplanar electrode 120 is composed of an input electrode and a ground electrode, and a magnetostrictive film 130 is arranged between the input electrode and the ground electrode. The flexible support substrate 100 is a PI substrate with a thickness of 20 μm. The piezoelectric single crystal 110 is lithium tantalate with a thickness of 2 μm. The coplanar electrode 120 is made of Al with a thickness of 0.2 μm, and the distance between the input electrode and the ground electrode is 300 μm. The magnetostrictive film 130 is FeCoSiB with a width of 280 μm and a thickness of 750 nm.

[0032] The resonant mode excited in the embodiment belongs to an in-plane vibration mode. The in-plane vibration is generated by exciting the piezoelectric single crystal 110 by voltage, and drives the upper magnetostrictive film 130 to resonate, thereby generating magnetization oscillation. Similarly, the magnetostrictive film 130 generates strain under the excitation of an external magnetic field, and the strain is matched to the coplanar electrode 120 through the piezoelectric single crystal 110 to output voltage. The coplanar electrode 120 and the magnetostrictive film 130 are realized by photolithography and magnetron sputtering process, and the combination of the piezoelectric single crystal 120 and the PI substrate 100 is realized by transfer single crystal method. The magnetostrictive film 130 can be applied with a DC magnetic field in the plane during sputtering to induce uniaxial anisotropy, thereby obtaining a high pressure magnetic coefficient.

[0033] The piezoelectric single crystal 110 is modeled by a piezoelectric constitutive equation, and the magnetostrictive film 130 is modeled by a piezomagnetic constitutive equation by using COMSOL Multiphysics finite element simulation, which can be used to simulate the dynamic bidirectional coupling among electricity, sound and magnetism. The three resonant modes of the FBAR magnetoelectric antenna device obtained by simulation are shown in Figure 2 The mode 1 and the mode 2 are two fundamental modes. The second harmonic of the mode 1 is the mode 3. The mode 1 is a thickness shear mode (TSM) excited by transverse point formation between the coplanar electrodes, and the mode 2 is a thickness extension mode (TEM). The magnetoelectric antenna described in the embodiment mainly utilizes the thickness shear mode of the mode 1, which is an in-plane vibration excited by the piezoelectric single crystal 110, and drives the upper magnetostrictive film 130 to resonate. Figure 3 The stress field simulation results of the magnetoelectric antenna device under the TSM fundamental mode are given. As can be seen from the results, the in-plane vibration strain generated by the piezoelectric single crystal 110 is transmitted to the magnetostrictive layer 130, which drives the magnetostrictive film 130 to vibrate, generates magnetization oscillation, and further generates electromagnetic waves. Figure 4 The S11 simulation results of the structure magnetoelectric antenna device are shown in the following table.

[0034] Compared with the FBAR magnetoelectric antenna working in the out-of-plane mode, the flexible transverse field excited film bulk acoustic wave magnetoelectric antenna works in the in-plane vibration mode, has a stronger magnetoelectric coupling coefficient, and can effectively improve the radiation power; compared with the traditional cavity FBAR magnetoelectric antenna, the flexible transverse field excited film bulk acoustic wave magnetoelectric antenna not only has a simple preparation process and is compatible with the CMOS process, but also can work in a flexible application scene and has a high quality factor.

[0035] It should be noted that the size of the magnetoelectric antenna in the embodiment is 1.5*1.5*2mm, which is far smaller than the size of the traditional electric resonant antenna. It should be noted that the actual device is not limited to the length, width and thickness ratio in the example. These parameters can be adjusted according to specific applications and desired operating frequencies.

Claims

1. A flexible lateral field excited thin film bulk acoustic wave magnetoelectric antenna comprising: A flexible support substrate is characterized in that: The flexible support substrate is a PI substrate, and a piezoelectric single crystal is arranged on the PI substrate; a coplanar electrode is arranged on the piezoelectric single crystal, and the coplanar electrode is composed of an input electrode and a grounding electrode; a magnetostrictive film is arranged between the input electrode and the grounding electrode; the flexible transverse field excited film bulk acoustic wave magneto-electric antenna adopts an acoustic wave resonance mode, strain is transmitted from the piezoelectric layer to the magnetostrictive layer, and mutual conversion of electromagnetic characteristics and acoustic characteristics is realized by using magneto-acoustic-electric coupling; the resonance mode belongs to an in-plane vibration mode; in-plane vibration of the piezoelectric single crystal is generated by voltage excitation, the upper magnetostrictive film is driven to resonate, and magnetization oscillation is generated; strain is generated in the magnetostrictive film under excitation of an external magnetic field, and the strain is matched to the coplanar electrode through the piezoelectric single crystal, and output voltage is generated.

2. A flexible transverse field excited thin film bulk acoustic wave magnetoelectric antenna as in claim 1, wherein: The piezoelectric single crystal is bonded to the flexible support substrate by using a transfer single crystal method.

3. A flexible transverse field excited thin film bulk acoustic wave magnetoelectric antenna as in claim 1, wherein: The thickness of the flexible support substrate is 1 mm to 5 mm.

4. A flexible transverse field excited thin film bulk acoustic wave magnetoelectric antenna as defined in claim 1, wherein: The piezoelectric single crystal is lithium niobate or lithium carbonate, and the thickness is 700 μm to 2000 μm.

5. A flexible transverse field excited thin film bulk acoustic wave magnetoelectric antenna as defined in claim 1, wherein: The material of the coplanar electrode is aluminum or platinum, and the thickness is 100 nm to 300 nm.

6. A flexible transverse field excited thin film bulk acoustic wave magnetoelectric antenna according to any one of claims 1 to 5, characterized in that: The magnetostrictive film is iron cobalt silicon boron, iron silicon boron, iron silicon boron carbon or iron gallium boron, and the thickness is 250 nm to 750 nm.

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