Composite piezoelectric substrate structure

Abstract

The utility model relates to the field of semiconductor materials, in particular to a composite piezoelectric substrate structure which comprises a supporting substrate, a silicon dioxide layer stacked on the supporting substrate and a piezoelectric layer stacked on the silicon dioxide layer. The piezoelectric layer is made of lithium tantalate or lithium niobate; and the crystal orientation of the lithium tantalate is 42-degree Y-cut. According to the polycrystalline spinel-based composite piezoelectric substrate provided by the invention, polycrystalline spinel has a relatively large Young modulus and a relatively small thermal diffusion coefficient, so that a lithium tantalate film substrate with excellent mechanical properties and good thermal stability can be obtained. And meanwhile, the preparation of the polycrystalline spinel is relatively simple, and the cost can be further reduced. The frequency temperature coefficient compensation layer, the waveguide layer and the amorphous layer are arranged in the composite substrate, the composite substrate can be widely applied to the fields of surface acoustic wave devices, optical waveguides, nonlinear optical devices and the like, the Q value of the devices can be effectively improved, and the frequency temperature coefficient is reduced.

Description

Technical Field

[0001] The present application relates to the field of semiconductor materials, and in particular to a composite piezoelectric substrate structure. Background Art

[0002] Piezoelectric materials such as lithium tantalate (LiTaO3) are widely used in surface acoustic wave devices, optical waveguides, and nonlinear optical devices due to their excellent ferroelectric, piezoelectric, and photoelectric properties. However, piezoelectric materials such as lithium carbonate and lithium niobate are inherently brittle and have poor thermal stability, making the direct use of lithium tantalate substrates in microelectronic devices difficult. Utility Model Content

[0003] The purpose of the utility model is to provide a composite piezoelectric substrate structure for improving the problems of poor rigidity and poor thermal stability faced by piezoelectric materials when used in microelectronic devices.

[0004] To achieve this purpose, the present invention adopts the following technical solutions:

[0005] A composite piezoelectric substrate structure comprises: a supporting substrate, a silicon dioxide layer stacked on the supporting substrate, and a piezoelectric layer stacked on the silicon dioxide layer;

[0006] The material of the piezoelectric layer is lithium tantalate or lithium niobate;

[0007] The crystal orientation of the lithium tantalate is 42° Y-cut, and the crystal orientation of the lithium niobate is 128° Y-cut.

[0008] Preferably, the support substrate is made of polycrystalline spinel.

[0009] Preferably, the polycrystalline spinel has a thickness of 500-1000 μm.

[0010] Polycrystalline spinel-based composite piezoelectric substrates offer numerous advantages. In terms of lattice structure, polycrystalline spinel lattices well match those of some semiconductor materials, and its cubic crystal structure ensures uniform properties in grown thin films. Physically, it offers high thermal stability, moderate hardness, ease of processing, and a good match in expansion coefficient with common semiconductor materials. Optically, it exhibits excellent transmittance across multiple optical bands, making it suitable for use in optical and optoelectronic devices. Chemically, it resists chemical attack, making it suitable for electronic devices operating in harsh chemical environments.

[0011] Preferably, the grain size is 1-10 μm. When the grains are too small, on the one hand, the increased number of grains per unit volume leads to an increase in grain boundaries. The atomic arrangement at the grain boundaries is disordered, and there is lattice distortion. When subjected to external forces, they easily become stress concentration points. Stress concentration may cause microcracks and gradually expand, ultimately reducing device reliability. On the other hand, sound waves are frequently scattered at the grain boundaries, just like light is scattered when propagating in a medium containing tiny particles. This disperses the sound wave energy, resulting in increased sound wave loss, which affects the sensitivity and efficiency of devices such as acoustic sensors. However, when the grains are too large, firstly, although the atomic arrangement inside the large grains is relatively regular, the ability of adjacent grains to synergistically deform becomes poor, and cracks are easily generated at the grain boundaries when subjected to external forces, resulting in reduced mechanical strength; secondly, due to the difference in physical properties between the interior of the grains and the grain boundaries, the propagation speed of sound waves in large-grain crystals is uneven, and the propagation direction is difficult to control due to the influence of the crystal orientation inside the grains, which has an adverse effect on the performance of acoustic devices such as ultrasonic imaging equipment; finally, in the bonding process of materials such as lithium tantalate, large grains are difficult to contact uniformly with the bonded materials, similar to the gaps between different-sized building blocks, which will lead to local stress concentration at the bonding interface, reduce the bonding strength, and affect the overall performance and stability of the material.

[0012] The silicon dioxide layer has a frequency temperature coefficient compensation function, which offsets the influence of temperature on frequency and ensures that the device prepared by the composite substrate maintains a stable operating frequency at different temperatures.

[0013] Preferably, the resistivity of the support substrate is 10 6 -10 8 Ω·cm.

[0014] The resistivity selection of this application has many advantages. In terms of reducing substrate leakage current, leakage current will be generated due to the conductivity of the semiconductor substrate, and high resistivity can limit the movement of carriers, reducing leakage current. For surface acoustic wave devices, it can reduce the energy loss during the propagation process. Taking insertion loss as an example, it can improve device performance and make the signal more efficient. In reducing the influence of stray capacitance and inductance, the conductive substrate will form stray capacitance and inductance, which will affect the phase delay and frequency response of signal transmission. High resistivity can weaken the conductive ability of the substrate and reduce its formation, thereby improving the frequency stability of the surface acoustic wave device. In applications with high frequency accuracy requirements such as clock generators, frequency accuracy can be ensured. In terms of reducing noise interference, when the substrate is conductive, the movement of carriers will generate noise interference signals. High resistivity can suppress noise generation and improve the signal-to-noise ratio. In applications such as sensors and communication systems, it can improve detection accuracy and signal transmission reliability respectively.

[0015] Preferably, at least one waveguide layer is further included between the silicon dioxide layer and the piezoelectric layer;

[0016] The waveguide layer includes a first waveguide layer and a second waveguide layer;

[0017] The propagation speed of sound in the first waveguide layer is 2-4 times that of the second waveguide layer, forming an effective waveguide structure. The different sound wave velocities are designed to achieve effective sound wave guidance and reduce energy leakage. This difference in sound velocity effectively allows sound waves to propagate within the waveguide structure, rather than leaking into the surrounding medium. The difference in sound velocity also enables acoustic impedance matching between the different waveguide layers, reducing energy loss and transmission discontinuity.

[0018] Preferably, the material of the first waveguide layer is AlN or Al2O3;

[0019] The second waveguide layer is made of SiO2 or Si3N4.

[0020] Preferably, the thickness of the waveguide layer is 20-500 nm.

[0021] Preferably, an amorphous layer is further included between the waveguide layer and the piezoelectric layer.

[0022] Preferably, the thickness of the amorphous layer is 5-200 nm;

[0023] The material of the amorphous layer is amorphous lithium tantalate or amorphous lithium niobate.

[0024] A very thin amorphous layer is introduced to make it lose its piezoelectric properties. The amorphous layer can further reduce the frequency temperature coefficient, thereby reducing the thickness of the silicon dioxide layer and realizing the miniaturization of subsequent device preparation.

[0025] Beneficial effects of the utility model:

[0026] This application proposes a polycrystalline spinel-based composite piezoelectric substrate. The polycrystalline spinel has a large Young's modulus and a small thermal diffusion coefficient, thereby obtaining a lithium tantalate thin film substrate with excellent mechanical properties and good thermal stability. At the same time, the preparation of polycrystalline spinel is relatively simple, which can further reduce costs. This composite substrate is provided with a frequency temperature coefficient compensation layer, a waveguide layer, and an amorphous layer. It can be widely used in fields such as surface acoustic wave devices, optical waveguides, and nonlinear optical devices, and can effectively improve the Q value of the device and reduce the frequency temperature coefficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the structure of the composite piezoelectric substrate of the utility model;

[0028] In the figure: 1-support substrate, 2-silicon dioxide layer, 31-first waveguide layer, 32-second waveguide layer, 4-amorphous layer, 5-piezoelectric layer. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. It should also be noted that, for ease of description, the accompanying drawings only illustrate portions relevant to the present invention, not all of its components.

[0030] In the description of this utility model, unless otherwise specified or limited, the terms "connected," "connect," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in this utility model based on the specific circumstances.

[0031] In the present invention, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Moreover, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly below or obliquely below the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0032] In the description of this embodiment, the terms "upper," "lower," "right," and other orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely for ease of description and simplified operation. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used solely for descriptive purposes and have no special meaning.

[0033] Example 1

[0034] See also Figure 1 This embodiment provides a composite piezoelectric substrate structure, including: a supporting substrate 1, a silicon dioxide layer 2 stacked on the supporting substrate 1, two groups of waveguide layers stacked on the silicon dioxide layer 2, an amorphous layer 4 stacked on the waveguide layer, and a piezoelectric layer 5 stacked on the amorphous layer 4.

[0035] In this embodiment, the support substrate 1 has a thickness of 800 μm, a grain size distribution between 1 and 10 μm, and a resistivity of 10 7Ω·cm polycrystalline spinel. The support substrate 1 is surface treated to achieve a surface roughness of less than 0.5nm. The polycrystalline spinel support substrate has excellent thermal stability and can maintain unchanged material properties in high-temperature environments. This is crucial for devices that need to operate under high-temperature conditions and can avoid performance fluctuations when the temperature changes. The thermal expansion coefficient is low and can be adjusted to better match the thermal expansion coefficient of lithium tantalate or lithium niobate films through formulation adjustment, reducing thermal stress between the film and the substrate and preventing film cracking or warping. The mechanical strength is much higher than that of conventional single crystal materials or glass substrates, and it can withstand greater stress and mechanical shock, making it less susceptible to damage during subsequent device manufacturing, packaging, and use, thereby increasing reliability and lifespan. The manufacturing process is relatively mature and can mass-produce high-quality substrates at a controllable cost, ensuring material consistency and repeatability, making it suitable for industrial applications. It also has excellent electrical insulation properties, which are critical for subsequent device electrode design and signal transmission, and can reduce parasitic capacitance effects, improve signal quality and work efficiency.

[0036] After surface treatment of the support substrate 1, an 80nm thick silicon dioxide layer is deposited on its surface via PVD or CVD. This layer serves as a frequency temperature coefficient compensation layer, offsetting the effects of temperature on frequency and ensuring that devices fabricated from this composite substrate maintain a stable operating frequency at varying temperatures. Two sets of waveguide layers are then deposited on the silicon dioxide layer via physical vapor deposition. Each set of waveguide layers comprises a first waveguide layer 31 and a second waveguide layer 32. The speed of sound propagation in the first waveguide layer 31 is 2-4 times that of the second waveguide layer 32, forming an effective waveguide structure. In this embodiment, the first waveguide layer 31 is made of aluminum nitride, and the second waveguide layer 32 is made of silicon dioxide.

[0037] A lithium tantalate substrate with a 42° Y-cut orientation was prepared, and the surface of the lithium tantalate substrate was treated. A damage layer was formed in the lithium tantalate substrate by ion implantation. The implanted ion species was hydrogen ions, and the implantation dose was 5×10 16 ions / cm 2 , the injection energy is 100keV, the injection depth is 200nm. Ion implantation is performed again, the ion species injected is helium ion, and the injection dose is 10×10 13 ions / cm 2 , the injection energy is 30keV, so that a 10nm amorphous lithium tantalate layer is formed on the surface of the lithium tantalate substrate.

[0038] The waveguide layer and the amorphous lithium tantalate layer were activated to remove impurities and surface activation, and then the waveguide layer and the amorphous lithium tantalate layer were placed face to face and pressure-bonded to form a bonded structure. The pressure was 10,000 N and maintained for 30 minutes.

[0039] The bonded body was annealed in a nitrogen atmosphere at 500°C for one hour. During the annealing process, the damaged layer in the bonded body cracked, separating the lithium tantalate, leaving a thin lithium tantalate film on top of the bonded body. This resulted in a composite piezoelectric substrate consisting, from bottom to top, of a polycrystalline spinel layer, a silicon dioxide layer, a waveguide layer, an amorphous layer, and a lithium tantalate film.

[0040] The polycrystalline spinel-based composite piezoelectric substrate proposed in this embodiment has a large Young's modulus and a small thermal diffusion coefficient, thereby obtaining a lithium tantalate thin film substrate with excellent mechanical properties and good thermal stability. Furthermore, the preparation of the polycrystalline spinel is relatively simple, which can further reduce costs. The composite substrate is provided with a frequency temperature coefficient compensation layer, a waveguide layer, and an amorphous layer, and can be widely used in fields such as surface acoustic wave devices, optical waveguides, and nonlinear optical devices, effectively improving the Q value of the device and reducing the frequency temperature coefficient.

[0041] Obviously, the above-described embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention and are not intended to limit the manner in which the present invention is to be implemented. A person skilled in the art would be able to make various obvious changes, readjustments, and substitutions without departing from the scope of protection of the present invention. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A composite piezoelectric substrate structure, characterized in that: include: A supporting substrate, a silicon dioxide layer stacked on the supporting substrate, and a piezoelectric layer stacked on the silicon dioxide layer; The material of the piezoelectric layer is lithium tantalate or lithium niobate; The crystal orientation of the lithium tantalate is 42° Y-cut, and the crystal orientation of the lithium niobate is 128° Y-cut.

2. The composite piezoelectric substrate structure according to claim 1, wherein: The support substrate is made of polycrystalline spinel.

3. The composite piezoelectric substrate structure according to claim 2, wherein: The polycrystalline spinel has a thickness of 500-1000 μm.

4. The composite piezoelectric substrate structure according to claim 2, wherein: The polycrystalline spinel has a grain size of 1-10 μm.

5. The composite piezoelectric substrate structure according to claim 1, wherein: The resistivity of the support substrate is 10 6 -10 8 Ω·cm.

6. The composite piezoelectric substrate structure according to claim 1, wherein: At least one waveguide layer is further included between the silicon dioxide layer and the piezoelectric layer; Each set of said waveguide layers comprises a first waveguide layer and a second waveguide layer; The propagation speed of sound in the first waveguide layer is 2-4 times that of the second waveguide layer.

7. The composite piezoelectric substrate structure according to claim 6, wherein: The material of the first waveguide layer is AlN or Al2O3; The second waveguide layer is made of SiO2 or Si3N4.

8. The composite piezoelectric substrate structure according to claim 6, wherein: The thickness of the waveguide layer is 20-500 nm.

9. The composite piezoelectric substrate structure according to claim 6, wherein: An amorphous layer is further included between the waveguide layer and the piezoelectric layer.

10. The composite piezoelectric substrate structure according to claim 9, wherein: The thickness of the amorphous layer is 5-200 nm; The material of the amorphous layer is amorphous lithium tantalate or amorphous lithium niobate.

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