A method of increasing the electromechanical coupling coefficient of an xbar device

Abstract

The application provides a method for increasing the electromechanical coupling coefficient of an XBAR device, the XBAR device comprising a piezoelectric substrate layer and an IDT layer disposed on the piezoelectric substrate layer; wherein the IDT layer is composed of a first electrode and a second electrode. The XBAR device has the large bandwidth of a SAW device and the high frequency characteristics of a BAW device, but for some devices that require ultra-large bandwidth at a specific frequency, the maximum electromechanical coupling coefficient of the XBAR device cannot be obtained by using the settings of the SAW device, so the requirement for ultra-large bandwidth at a specific frequency cannot be met. Therefore, the width of the first electrode and the second electrode is changed, the admittance frequency response and the stray response at different metallization rates are analyzed, and a suitable metallization rate is selected to increase the electromechanical coupling coefficient of the XBAR device, so as to meet the requirement for ultra-large bandwidth of the device at a specific frequency. Furthermore, the method is relatively simple to implement, and does not increase the difficulty and cost of manufacturing the XBAR device.

Description

Technical Field

[0001] This invention relates to the field of bulk acoustic wave device technology, and more specifically, to a method for increasing the electromechanical coupling coefficient of an XBAR device. Background Technology

[0002] With the continuous popularization and development of 5G and Sub-6G technologies, higher and more numerous requirements have been placed on filters in the RF front-end market, such as high bandwidth and high frequency. This has also brought new challenges to traditional surface acoustic wave (SAW) devices and bulk acoustic wave (BAW) devices. The reason is that although traditional SAW devices have a high electromechanical coupling coefficient, they are limited to high frequencies. To obtain high-frequency SAW devices, it is necessary to reduce the period length of the SAW device, which not only limits the accuracy of the manufacturing instruments but also increases the manufacturing difficulty and cost. As for traditional BAW devices, thanks to the advancement of process technology, BAW devices can obtain high-frequency devices by compressing the thickness of the piezoelectric substrate. However, due to the limitations of the piezoelectric substrate material itself, the manufactured BAW devices often cannot meet the requirements for high bandwidth.

[0003] Thus, XBAR devices emerged. Their structure is similar to SAW devices, and their working principle is similar to BAW devices, combining the advantages of both traditional BAW and SAW devices. However, XBAR devices are more difficult and costly to manufacture. Continuing to use some of the conventions of SAW devices would lead to a waste of resources. For example, the metallization rate of the interdigital transducer (IDT) in SAW devices is usually set to 50% to achieve a higher electromechanical coupling coefficient and lower cost. However, this is not the case for XBAR devices, especially for devices requiring ultra-high bandwidth at specific frequencies. Often, the settings for SAW devices cannot achieve the maximum electromechanical coupling coefficient of XBAR devices, thus failing to meet the ultra-high bandwidth requirements of some devices at specific frequencies. Summary of the Invention

[0004] The present invention aims to solve the above-mentioned existing technical problems and proposes a method to increase the electromechanical coupling coefficient of an XBAR device: by changing the width of the first electrode and the second electrode, the metallization rate of the total electrode length as a percentage of the entire cycle of the XBAR device is changed, the admittance frequency response under different metallization rates is analyzed, and the influence of changing the metallization rate on the spurious response is comprehensively considered, and a suitable metallization rate is selected to increase the electromechanical coupling coefficient of the XBAR device.

[0005] To achieve the above objectives, the specific solution of the present invention is as follows:

[0006] Design an XBAR device comprising a piezoelectric substrate and an IDT layer, wherein the IDT layer is placed on the piezoelectric substrate and the IDT layer is composed of a first electrode and a second electrode.

[0007] Furthermore, the material of the piezoelectric substrate layer includes 128°YX-cut lithium niobate, optionally with a thickness of 0.4 μm.

[0008] Furthermore, the material of the IDT layer includes Al, and optionally, its thickness is 0.1 μm.

[0009] Furthermore, the first electrode and the second electrode are placed periodically, and the period size is equal to the period size of the XBAR device.

[0010] Furthermore, the distance between the first electrode and the left periodic boundary of the XBAR device is the same as the distance between the second electrode and the right periodic boundary of the XBAR device.

[0011] Furthermore, the first electrode is configured as a terminal 1V and the second electrode is configured as a ground terminal.

[0012] Furthermore, the first electrode and the second electrode have the same shape and size, and the width of the first electrode is a, where the value of a ranges from 0.1*λ / 2≤a≤0.7*λ / 2, and λ is the period length of the XBAR device.

[0013] Furthermore, the distance between the first electrode and the left periodic boundary of the XBAR device is b, where b = λ / 4 - a / 2.

[0014] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0015] XBAR devices possess a structure similar to SAW devices and an operating principle similar to BAW devices, simultaneously combining the high bandwidth of SAW devices with the high-frequency characteristics of BAW devices. This effectively meets the high-frequency and high-bandwidth requirements of the 5G and Sub-6G era. However, continuing to use some of the conventions of SAW devices would lead to a waste of resources. For example, the metallization rate of interdigital transducers (IDTs) in SAW devices is typically set to 50% to achieve a high electromechanical coupling coefficient and reduce costs. However, this is not the case for XBAR devices, especially for some devices requiring ultra-high bandwidth at specific frequencies. Often, the settings for SAW devices cannot achieve the maximum electromechanical coupling coefficient of XBAR devices, thus failing to meet the ultra-high bandwidth requirements of some devices at specific frequencies. Therefore, this invention provides a method for increasing the electromechanical coupling coefficient of an XBAR device: by changing the width of the first electrode and the second electrode, thereby changing the metallization rate of the total electrode length relative to the entire cycle of the XBAR device, analyzing the admittance frequency response under different metallization rates and comprehensively considering the influence of metallization rate changes on spurious response, a suitable metallization rate is selected to increase the electromechanical coupling coefficient of the XBAR device, thereby meeting the device's requirement for ultra-large bandwidth at a specific frequency. Moreover, this method is relatively simple to implement and does not increase the difficulty and cost of manufacturing XBAR devices. Attached Figure Description

[0016] Figure 1 This is a two-dimensional equivalent model diagram of an XBAR device under a periodic structure.

[0017] Figure 2 This is the admittance frequency response diagram for XBAR devices with a period of 4µm and metallization of 0.1, 0.15, 0.2 and 0.25.

[0018] Figure 3 This is the admittance frequency response diagram for XBAR devices with a period of 4µm and metallization of 0.3, 0.35, 0.4 and 0.45.

[0019] Figure 4 This is the admittance frequency response diagram for XBAR devices with a period of 4µm and metallization of 0.5, 0.55, 0.6, 0.65 and 0.7.

[0020] Figure 5 This is a graph showing the change in wave velocity at the resonant and anti-resonant points of an XBAR device with a period of 4µm as a function of metallization.

[0021] Figure 6 This is a graph showing the change in electro-optical coupling coefficient with metallization rate when the XBAR device has a period of 4µm.

[0022] Figure 7 This is the admittance frequency response diagram for XBAR devices with a period of 6µm and metallization of 0.1, 0.15, 0.2 and 0.25.

[0023] Figure 8 This is the admittance frequency response diagram for XBAR devices with a period of 6µm and metallization of 0.3, 0.35, 0.4 and 0.45.

[0024] Figure 9 This is the admittance frequency response diagram for XBAR devices with a period of 6µm and metallization of 0.5, 0.55, 0.6, 0.65 and 0.7.

[0025] Figure 10 This is a graph showing the change in wave velocity at the resonant and anti-resonant points of an XBAR device with a period of 6µm as a function of metallization.

[0026] Figure 11 This is a graph showing the change in electro-optical coupling coefficient with metallization rate when the XBAR device has a period of 6µm.

[0027] Icon labels:

[0028] 1. Piezoelectric substrate; 2. First electrode; 3. Second electrode; 4. IDT layer; a. Width of the first electrode; b. Distance between the first electrode and the left periodic boundary of the XBAR device; λ. Period length of the XBAR device. Detailed Implementation

[0029] The embodiments of the present invention will be described in further detail and clearly below with reference to the accompanying drawings and specific implementations. The described embodiments are merely some of the embodiments included in the present invention.

[0030] The specific implementation scheme of the present invention to solve the above-mentioned technical problems is as follows:

[0031] A method to increase the electromechanical coupling coefficient of XBAR devices, such as Figure 1 As shown, an XBAR device is designed, which includes a piezoelectric substrate layer 1 and an IDT layer 4, wherein the IDT layer 4 is placed on the piezoelectric substrate layer 1; the IDT layer 4 is composed of a first electrode 2 and a second electrode 3.

[0032] Furthermore, the material of the piezoelectric substrate 1 includes 128°YX-cut lithium niobate, and optionally, its thickness is 0.4 μm.

[0033] Furthermore, the material of the IDT layer 4 includes Al, and optionally, its thickness is 0.1 μm.

[0034] Furthermore, the first electrode 2 and the second electrode 3 are placed periodically, and the period size is equal to the period size of the XBAR device.

[0035] Furthermore, the distance between the first electrode 2 and the left periodic boundary of the XBAR device is the same as the distance between the second electrode 3 and the right periodic boundary of the XBAR device.

[0036] Furthermore, the first electrode 2 is configured as a terminal 1V and the second electrode 3 is configured as a ground terminal.

[0037] Furthermore, the first electrode 2 and the second electrode 3 have the same shape and size, and the width of the first electrode 2 is 'a', where the value of 'a' ranges from 0.1*λ / 2 ≤ a ≤ 0.7*λ / 2, and λ is the period length of the XBAR device. The reasons for not expanding the search range for 'a' are as follows: First, the range of 'a' is limited by the period of the XBAR device, and the search range cannot be increased indefinitely; the value of 'a' must be < 0.5*λ. Second, when 'a' > 0.7*λ / 2, not only does its electromechanical coupling coefficient become very small, but its stray response also increases. Third, if the value of 'a' is too large or too small, it easily leads to increased losses in the XBAR device, increased electrode heating, and decreased power handling capability; moreover, when the electrode is too narrow, it also increases unnecessary costs.

[0038] Furthermore, the distance between the first electrode 2 and the left periodic boundary of the XBAR device is b, where b = λ / 4 - a / 2.

[0039] Furthermore, the metallization rate is the ratio of the sum of the widths of the first electrode 2 and the second electrode 3 to the period length of the XBAR device, and its expression is: a*2 / λ.

[0040] Example 1:

[0041] Figures 2-6 The graph shows the changes in admittance frequency response, wave velocity at the resonant and anti-resonant points, and electromechanical coupling coefficient of the XBAR device with a period of 4µm as a function of metallization.

[0042] Furthermore, such as Figures 2-4 As shown: the resonant frequency and anti-resonant frequency decrease with increasing metallization, and the rate of decrease of the resonant frequency remains basically constant with the change in metallization. The anti-resonant frequency, however, remains essentially constant initially, and then its rate of decrease gradually increases with increasing metallization. This is evident in… Figure 5 The admittance curve is more intuitively reflected in the metallization rate; while the stray response increases first and then decreases with the increase of the metallization rate. Especially when the metallization rate is 0.3, its admittance curve is smooth and flat, and the stray response basically disappears.

[0043] Furthermore, such as Figure 5As shown, with increasing metallization, the wave velocity at the resonant frequency gradually decreases, and the rate of decrease is relatively uniform. However, the wave velocity at the anti-resonant frequency remains essentially constant when the metallization is between 0.1 and 0.35, and its rate of decrease is much smaller than that of the resonant frequency. The difference in wave velocity between the two increases with increasing metallization. When the metallization is between 0.4 and 0.7, the rate of decrease in wave velocity at the anti-resonant frequency exceeds that at the resonant frequency, and the difference between the two decreases with increasing metallization. In this embodiment, the electromechanical coupling coefficient of the XBAR device is positively correlated with the difference in wave velocity between the anti-resonant frequency and the resonant frequency. The larger the wave velocity difference, the larger the electromechanical coupling coefficient of the XBAR device. Figure 6 This is better reflected in the text.

[0044] Furthermore, such as Figure 6 As shown, the electromechanical coupling coefficient of the XBAR device first increases and then decreases with the increase of the metallization rate. Specifically, when the metallization rate is 0.1-0.35, the electromechanical coupling coefficient increases with the increase of the metallization rate, and when the metallization rate is 0.4-0.7, the electromechanical coupling coefficient decreases with the increase of the metallization rate.

[0045] Furthermore, when the metallization rate is 0.35, the electromechanical coupling coefficient of the XBAR device increases to its peak value. However, considering the stray response of the XBAR device, the stray response is smaller when the metallization rate is 0.3, and its electromechanical coupling coefficient is also close to the peak value. Moreover, when the metallization rate is 0.3, the total width of the first electrode 2 and the second electrode 3 is moderate, thus avoiding increased XBAR device losses, increased electrode heating, and increased cost. Therefore, in this embodiment, an XBAR device with a metallization rate of 0.3 is selected for construction to increase the electromechanical coupling coefficient of the XBAR device.

[0046] Example 2:

[0047] Furthermore, the period length of the XBAR device was changed to 6µm. Figures 7-11 The admittance frequency response, wave velocity at the resonant and anti-resonant points, and electromechanical coupling coefficient of the XBAR device with a period of 6µm are shown as changes with metallization rate.

[0048] Furthermore, by Figures 7-9As shown, with the increase of metallization, the variation patterns of the resonant frequency and anti-resonant frequency are completely consistent with those in Example 1. The rate of decrease of the resonant frequency remains essentially constant, while the rate of decrease of the anti-resonant frequency is initially slow, but gradually increases with the increase of metallization. Furthermore, regarding the spurious response of the admittance frequency response, with the increase of the period length, the spurious response in Example 2 is more severe than in Example 1, and it does not change significantly with the change of metallization. In Example 2, the magnitude of the spurious response varies relatively evenly with the change of metallization.

[0049] Furthermore, such as Figure 10 As shown, in Example 2, the electromechanical coupling coefficient of the XBAR device is still positively correlated with the difference in wave velocity at the anti-resonant frequency and the resonant frequency. The larger the wave velocity difference, the larger the electromechanical coupling coefficient of the XBAR device. Regarding the decreasing trend of wave velocity at the resonant and anti-resonant frequencies, Example 2 is basically the same as Example 1: the wave velocity at the resonant frequency decreases at a relatively constant rate as the metallization rate increases, while the wave velocity at the anti-resonant frequency remains essentially unchanged when the metallization rate is 0.1-0.25. Its rate of decrease is much smaller than that of the resonant frequency, and the difference in wave velocity between the two increases continuously with the increase of the metallization rate. When the metallization rate is 0.3-0.7, the rate of decrease of the wave velocity at the anti-resonant frequency exceeds that at the resonant frequency, and the difference between the two decreases continuously with the increase of the metallization rate.

[0050] Furthermore, such as Figure 11 As shown, the electromechanical coupling coefficient in Example 2 changes with the metallization rate in a manner that is basically consistent with that in Example 1, both of which increase first and then decrease. However, compared with Example 1, due to the increase in the XBAR device period, the electromechanical coupling coefficient in Example 2 decreases earlier with the change in metallization rate. More specifically, when the metallization rate is 0.1-0.25, the electromechanical coupling coefficient increases with the increase in metallization rate, and when the metallization rate is 0.3-0.7, the electromechanical coupling coefficient decreases with the increase in metallization rate. Especially when the metallization rate is 0.45-0.5, the electromechanical coupling coefficient drops sharply.

[0051] Furthermore, when the metallization rate is 0.25, the electromechanical coupling coefficient of the XBAR device increases to its peak value. Considering the stray response of the XBAR device, the metallization rate has little impact on the stray response in Embodiment 2. Also, when the metallization rate is 0.25, the total width of the first electrode 2 and the second electrode 3 is moderate, thus avoiding increased XBAR device losses, increased electrode heating, and increased cost. Therefore, in this embodiment, an XBAR device with a metallization rate of 0.25 is selected for construction to increase the electromechanical coupling coefficient of the XBAR device.

[0052] Furthermore, considering the two embodiments above, the method of increasing the electromechanical coupling coefficient of an XBAR device by changing its metallization ratio is simple and easy to implement, and compared with a conventional XBAR, the manufacturing difficulty and cost remain essentially unchanged. However, when increasing the electromechanical coupling coefficient of an XBAR device by changing its metallization ratio, it is also important to observe whether the stray response of the XBAR device deteriorates, and whether the ultimately selected metallization ratio is too high or too low, to avoid increasing the XBAR device's losses and manufacturing costs.

[0053] The embodiments described above should be understood only as specific illustrations of this invention and are not intended to limit the specific scope of protection of this invention. After reading the description of this invention, those skilled in the art will understand that this invention can have various changes and modifications. Any changes, modifications, substitutions, combinations, simplifications, improvements, etc., made within the spirit and principles of this application should be considered equivalent substitutions and are included within the scope of protection of this invention.

Claims

1. A method of increasing the electromechanical coupling coefficient of an XBAR device, characterized by, The XBAR device is designed, which comprises a piezoelectric substrate layer, an IDT layer placed on the piezoelectric substrate layer; the IDT layer is composed of a first electrode and a second electrode, and the first electrode and the second electrode are periodically placed, and the period size is equal to that of the XBAR device; the distance of the first electrode relative to the left periodic boundary of the XBAR device is the same as that of the second electrode relative to the right periodic boundary of the XBAR device; the shape size of the first electrode is the same as that of the second electrode, and the width of the first electrode is a, and the value range of a is 0.1*lambda / 2<=a<=0.7*lambda / 2, the distance of the first electrode relative to the left periodic boundary of the XBAR device is b, and b=lambda / 4-a / 2, wherein lambda is the period length of the XBAR device; by changing the width of the first electrode and the second electrode, and then changing the metallization rate of the total length of the electrode to the whole period of the XBAR device, the admittance frequency response under different metallization rates is analyzed, and the influence of the metallization rate change on the stray response is comprehensively considered, and a suitable metallization rate is screened out to increase the electromechanical coupling coefficient of the XBAR device.

2. The method of claim 1, wherein, The material of the piezoelectric substrate layer comprises 128° Y-X cut lithium niobate.

3. The method of increasing electromechanical coupling coefficient of an XBAR device of claim 1, wherein, The material of the IDT layer comprises Al.

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