A thin film bulk acoustic wave filter and a method for improving the power capacity of the thin film bulk acoustic wave filter

Abstract

The present invention discloses a method for improving the power capacity of a thin film bulk acoustic wave filter, comprising obtaining the power density of each order resonator of a prototype thin film bulk acoustic wave filter at maximum input power, replacing a first resonator that does not meet the power capacity requirement with a resonator topology structure, so as to reduce the power density of the first resonator to a range that meets the power capacity requirement; the resonator topology structure is equivalent to the impedance curve of the first resonator. While improving the power capacity by using this method, the impedance curve can be made completely unchanged without introducing other components. The present invention also discloses a thin film bulk acoustic wave filter.

Description

Technical Field

[0001] The present invention belongs to the field of MEMS devices, and in particular relates to a thin film bulk acoustic wave filter and a method for improving the power capacity of the thin film bulk acoustic wave filter. Background Art

[0002] BAW filters use the piezoelectric effect of piezoelectric crystals to produce resonance. Since the resonance is generated by mechanical waves rather than electromagnetic waves, the wavelength of mechanical waves is much shorter than that of electromagnetic waves. Therefore, the volume of BAW filters and the resonators they consist of are greatly reduced relative to the size of traditional electromagnetic filters. On the other hand, since the crystal growth of piezoelectric crystals can currently be well controlled, the loss of the resonator is extremely small, the quality factor is high, and it can cope with complex design requirements such as steep transition bands and low insertion loss. Due to the small size, high roll-off, and low insertion loss of BAW filters, filters with this as the core have been widely used in communication systems.

[0003] Bulk acoustic wave (BAW) filters are the main filter devices used in 5G and subsequent communication frequency bands. With the development of existing communication technologies, more and more application scenarios have put forward higher requirements on the power capacity of bulk acoustic wave filters in RF front-ends. Traditional methods for improving the power capacity of bulk acoustic wave filters, such as solid-mounted BAW-SMR (Solidly Mounted Resonator), have put forward additional requirements on the filter process, and will reduce the resonator Q value, while affecting the filter performance.

[0004] The invention patent application with publication number CN110971209 discloses a method and a filter element for improving the power capacity of a bulk acoustic wave filter. The method includes the following steps: Step S1: increasing the area of ​​each resonator in the current filter; making the power density of these resonators reach a preset value, and recording the current value of the filter port impedance value; Step S2: when the current value is less than the specified value, determining an impedance transformation network based on the current value and the specified value, the impedance transformation network is used to be connected in series at the input and output ends of the filter to form a series body, and making the port impedance of the series body reach the specified value.

[0005] The above patent changes a resonator of area S into a series connection of areas 2S and 2S through a series topology structure. However, the impedance curve of the resonator of this order after changing the topology structure by increasing the area is not completely equivalent, that is, the impedance curve of a resonator of area S and two resonators of area 2S in series is not completely equivalent, and an external impedance change network and the input and output ports of the filter are still required to correct the performance loss caused by the above topology replacement.

[0006] The invention patent application with publication number CN115882816A discloses an acoustic wave filter, including at least two series resonators and at least two parallel resonators located between the input end and the output end, the at least two series resonators have at least two different parallel resonant frequencies, the average parallel resonant frequency is fpav, the parallel resonant frequency of the first series resonator close to the input end is Fp, 1.0×fpav≤Fp. The above patent also splits the first series resonator into two resonators of equal area and connected in series with each other to reduce the power density of the first series resonator and increase the power capacity, and also splits the first parallel resonator into two resonators of equal area and connected in series with each other to further reduce the power density of the first series resonator, but the impedance curves of the resonators split by this method are still not completely equivalent. Summary of the invention

[0007] The invention discloses a method for improving the power capacity of a thin film bulk acoustic wave filter. By using this method, the power capacity can be improved while the impedance curve can be kept completely unchanged without introducing other components.

[0008] The present invention provides a method for improving the power capacity of a thin film bulk acoustic wave filter, comprising: Obtaining the power density of each order resonator of the prototype film bulk acoustic wave filter at the maximum input power, using the resonator that does not meet the power capacity requirement as the first resonator among the resonators of each order, and replacing the first resonator with a resonator topology structure to reduce the power density of the first resonator to a range that meets the power capacity requirement; The resonator topology has the same impedance curve as the first resonator.

[0009] Compared with the prior art in which the impedance curve changes due to changing the area of ​​the resonator or splitting the resonator, the present invention replaces the first resonator by introducing a resonator topology network that is first connected in series and then in parallel, so that the power density of the first resonator is significantly reduced while ensuring that the impedance curve is completely equivalent.

[0010] Preferably, the resonator topology is a first n-order series resonator followed by an n-order parallel connection, thereby reducing the power density of the first resonator to 1 / n 2 times, thereby increasing the power capacity to n 2 times, n is a positive integer.

[0011] The present invention can accurately control the degree of power density reduction by adjusting the order of the resonator topology structure. Compared with the prior art, the present invention adopts resonator topologies of the same order in series and parallel, so that the impedance curve of the resonator topology structure is completely equivalent to the impedance curve of the replaced first resonator.

[0012] Preferably, the impedance curve of the resonator topology is equivalent to that of the first resonator. Since the impedance curves after replacement are completely equivalent, the introduction of new impedance adjustment elements is avoided, thereby reducing the complexity of circuit design and avoiding the loss of other performances.

[0013] Preferably, the area of ​​the sub-resonator in the resonator topology is the same as the area of ​​the first resonator.

[0014] Preferably, the sub-resonator in the resonator topology has the same shape and size as the first resonator. The sub-resonator is completely identical to the first resonator. When the sub-resonator is completely identical to the first resonator, the invention can ensure that n 2 The array topology has exactly the same impedance curve as the first resonator, thus improving power handling without compromising other performance characteristics.

[0015] Preferably, the sub-resonators of the resonator topology structure and the resonators of each order of the prototype thin film bulk acoustic wave filter are all bulk acoustic wave resonators.

[0016] Preferably, the order of the resonator topology is determined based on the power density of the first resonator. The order of the resonator topology, i.e., the value of n, is determined by the power density, so that the waste caused by the excessive redundancy of the resonator topology can be avoided, and the power density of the first resonator can be reduced to meet the power capacity requirement.

[0017] Preferably, the prototype thin film bulk acoustic wave filter is designed by adopting a design method of a ladder or lattice filter topology based on performance indicators other than power capacity, and the performance indicators other than power capacity include filter insertion loss, roll-off, and out-of-band suppression. The resonator topology provided by the present invention can replace any first-order resonator of the prototype bulk acoustic wave filter without causing loss to other performances of the bulk acoustic wave filter.

[0018] Preferably, the prototype thin film bulk acoustic wave filter is a ladder or lattice type bulk acoustic wave filter.

[0019] On the other hand, the present invention also provides a thin film bulk acoustic wave filter, obtaining the power density of each order resonator of the prototype thin film bulk acoustic wave filter at the maximum input power, replacing the first resonator that does not meet the power capacity requirement with a resonator topology structure to reduce the power density of the first resonator to a range that meets the power capacity requirement; The resonator topology is equivalent to the impedance curve of the first resonator.

[0020] Preferably, the resonator topology is a first n-order series resonator followed by an n-order parallel connection, thereby reducing the power density of the first resonator to 1 / n2 times, thereby increasing the power capacity to n 2 times, n is a positive integer.

[0021] Compared with the prior art, the present invention has the following beneficial effects: The present invention utilizes a resonator topology structure to replace a first resonator that does not meet the power capacity, and while reducing the power density of the first resonator to meet the power capacity, it can also make the impedance curve completely equivalent without modifying the external impedance network, thereby not causing losses to other performances of the acoustic wave filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A flow chart of a method for improving the power capacity of a thin film bulk acoustic wave filter provided by a specific embodiment of the present invention; Figure 2A A schematic diagram of the topological structure of the resonator of the prototype thin film bulk acoustic wave filter and the resonator to be replaced provided in a specific embodiment of the present invention; Figure 2B Impedance graphs of the resonator and the resonator topology to be replaced for a prototype FBAW filter according to a specific embodiment of the present invention; Figure 2C A power density graph of a prototype FBAW resonator and a resonator topology to be replaced for a specific embodiment of the present invention; Figure 3A A topological structure diagram of a ladder-type bulk acoustic wave filter and a bulk acoustic wave filter after replacing the resonator topology structure provided by a specific embodiment of the present invention; Figure 3B A schematic diagram of an S-parameter curve of a ladder-type bulk acoustic wave filter and a bulk acoustic wave filter after replacing the resonator topology structure provided in a specific embodiment of the present invention; Figure 4A A topological structure diagram of the ladder-type bulk acoustic wave filter provided in comparative example 1 and the replaced bulk acoustic wave filter; Figure 4B A schematic diagram of impedance curves of the ladder-type bulk acoustic wave filter provided in comparative example 1 and the replaced bulk acoustic wave filter; Figure 4C Schematic diagram of S-parameter curves of the ladder-type bulk acoustic wave filter provided in comparative example 1 and the replaced bulk acoustic wave filter. DETAILED DESCRIPTION

[0023] The present invention is described in detail below with reference to specific embodiments and accompanying drawings.

[0024] In the prior art, the power capacity is increased by changing the area of ​​each order of resonators or splitting each order of resonators to reduce the power density, but the above method causes the impedance curve to change, and it is necessary to add impedance elements to adjust the impedance curve, which increases the structural complexity of the filter and also affects other performance indicators except power capacity. The specific embodiment of the present invention replaces the resonator topology structure with a resonator that does not meet the power capacity requirement, and then increases the power capacity requirement without changing the impedance curve.

[0025] A specific embodiment of the present invention provides a method for improving the power capacity of a thin film bulk acoustic wave filter, such as Figure 1 As shown, including: (1) Based on the design requirements, a prototype thin film bulk acoustic wave filter is designed using the design method of the ladder or lattice filter topology to meet other performance indicators besides power capacity. These other performance indicators include filter insertion loss, roll-off, and out-of-band suppression.

[0026] (2) According to the power capacity requirement, the power density of each order resonator of the prototype thin film bulk acoustic wave filter under the maximum input power is calculated. The resonator with a high power density that cannot meet the power capacity requirement is obtained through the power density, and this resonator is used as the first resonator.

[0027] (3) In order to reduce the power density of the first resonator and keep the impedance curve of the first resonator unchanged, a specific embodiment of the present invention constructs a resonator topology structure, and replaces the first resonator that does not meet the power capacity with the resonator topology structure. The resonator topology structure is first connected in series and then in parallel, and the order of the series connection is the same as the order of the parallel connection, both of which are n, and n is a positive integer greater than or equal to 1. The area, size, and resonant frequency of the sub-resonator of the resonator topology structure are the same as those of the first resonator, so that the power density of the first resonator can be reduced to 1 / n. 2 times, thereby increasing the power capacity to n 2 times, n is a positive integer, which can achieve precise control while ensuring that the impedance curve is completely consistent with the first resonator.

[0028] In a specific embodiment, if Figure 2A As shown, Figure 2A (a) shows a schematic diagram of a first resonator in a prototype BAW filter. The resonator area of ​​the first resonator is S, and the first resonator is usually connected to a series branch or a parallel branch of a BAW filter.

[0029] Figure 2A (b) and (c) show that the first resonator is replaced by a resonator topology structure that is first connected in series and then in parallel, and the area of ​​the sub-resonator of the resonator topology structure is the same as that of the first resonator, as shown in FIG. Figure 2AAs shown in (b), the two sub-resonators are first connected in series and then in parallel in two stages, and the transformed four resonators with an area of ​​S are equivalent to Figure 2A (a) of the form; Figure 2A (c) uses the method of first three series connection and then three-order parallel connection to transform the transformed 9 resonators with an area of ​​S into Figure 2A In the form of (a). By analogy, in this topology, a single resonator with an area of ​​S can be equivalently replaced by n^2 resonators of the same area of ​​S, connected in series first and then in parallel in n stages. According to the impedance characteristics of the thin film bulk acoustic wave resonator, a single resonator is equivalent to a flat plate capacitor in the frequency range outside the resonator frequency, and its capacitance is determined by the area of ​​the resonator. When two capacitors with a capacitance of C are connected in series, their equivalent capacitance is 1 / 2*C, and when two capacitors with a capacitance of C are connected in parallel, their equivalent capacitance is 2*C. It can be inferred from this that Figure 2A The three circuits with different topological structures (a), (b), and (c) are actually equivalent circuits to each other. Figure 2A The impedance curves of (a), (b), and (c) are as follows: Figure 2B As shown, they correspond to Zin1, Zin2 and Zin3 respectively. It can be seen that their impedance curves are completely equivalent. Figure 2A When (a), (b) and (c) are respectively placed in a certain order of the BAW filter circuit, they work exactly the same and the constructed filter transmission curves are also exactly the same.

[0030] from Figure 2B The three impedance curves (a), (b) and (c) show that when the three circuits they correspond to Figure 2A When (a), (b) and (c) are connected to the same BAW filter circuit at the same stage, the voltage across them and the current flowing through the entire equivalent circuit are exactly the same, then Figure 2A The power consumed by the three topological circuits (a), (b) and (c) is exactly the same. From the circuit principle, we can know that: Figure 2A When (a), (b) and (c) consume the same power P, Figure 2A The theoretical power density values ​​of a single sub-resonator in (a), (b) and (c) should be P / S, (1 / 4)*(P / S) and (1 / 9)*(P / S) respectively. Figure 2A The power density curves of a single resonator in (a), (b) and (c) are shown in Figure 2C As shown, it is basically consistent with the theoretical value. Figure 2A The proposed topology of first n series connection and then n-order parallel connection can effectively reduce the power density of each order resonator in the BAW filter, reducing the power density to 1 / n^2 of the prototype BAW filter, thereby increasing the power capacity by n^2 times, and the impedance curve is equivalent.

[0031] According to the design steps provided in this embodiment, at the beginning of the design, the performance indicator requirements of power capacity can be ignored, and circuit design and optimization are only performed for other performance indicators other than power capacity. After other design indicators meet the requirements, the power density of each order resonator of the BAW filter under the maximum input power is calculated, and the resonators of each order that do not meet the power capacity requirements are equivalently replaced with the resonator topology structure to obtain a new BAW filter circuit structure. Because the replaced circuit structures are completely equivalent, the new BAW filter only reduces the power density and improves the power capacity, while other filter performance remains unchanged.

[0032] In one embodiment, if Figure 3A As shown, Figure 3A The 4X4 ladder type FBAW filter shown in (a) is replaced by Figure 3A or replace it with Figure 3A (c) shows a thin film bulk acoustic wave filter.

[0033] like Figure 3A As shown in (b) in the figure, the resonators of each order in the 4X4 ladder-type film bulk acoustic wave filter are replaced by a resonator topology structure of first 2 orders in series and then 2 orders in parallel, and the sub-resonator of the resonator topology has the same area as the replaced resonator, so that the power density is reduced to 1 / 4 of the original power density and the power capacity is increased by 4 times, as shown in FIG. Figure 3B As shown, the impedance curve of the resonator topology structure with two-order series connection and two-order parallel connection is Figure 3B The (b) curve is the impedance curve of the 4X4 ladder-type film bulk acoustic wave filter, that is, Figure 3B The (a) curve is completely equivalent.

[0034] like Figure 3A As shown in (c) in the figure, the resonators of each order in the 4X4 ladder-type film bulk acoustic wave filter are replaced by a resonator topology structure in which 3 orders are connected in series and 3 orders are connected in parallel, and the sub-resonator of the resonator topology has the same area as the replaced resonator, so that the power density is reduced to 1 / 9 of the original power density and the power capacity is increased by 9 times, as shown in FIG. Figure 3B As shown, the impedance curve of the resonator topology structure with three-order series connection and three-order parallel connection is Figure 3B The (c) curve is the impedance curve of the 4X4 ladder-type film bulk acoustic wave filter, that is, Figure 3B The (a) curve is completely equivalent.

[0035] Figure 3AThe transmission curves of the three BAW filters shown in (a), (b) and (c) are exactly the same. Except for the power capacity increasing in sequence, other performances are exactly the same, which greatly reduces the design complexity of high power capacity BAW filters.

[0036] The advantage of the method for improving the power capacity of a thin film bulk acoustic wave filter provided by the present invention over the above-mentioned invention is that the present invention replaces the topological structure of a certain order resonator in the bulk acoustic wave filter, and the impedance curve remains completely unchanged compared to before the replacement, without the need to correct the external impedance network, and the topological structure of the present invention can be applied to replace any first-order resonator in the bulk acoustic wave filter without causing any loss to other performance of the bulk acoustic wave filter.

[0037] The present invention also provides a thin film bulk acoustic wave filter, which obtains the power density of each order resonator of the prototype thin film bulk acoustic wave filter at the maximum input power, and replaces the first resonator that does not meet the power capacity requirement with a resonator topology structure to reduce the power density of the first resonator to a range that meets the power capacity requirement; The resonator topology has the same impedance curve as the first resonator.

[0038] In a specific embodiment, the resonator topology provided by the specific embodiment of the present invention is a resonator of n-order series connection followed by n-order parallel connection, thereby reducing the power density of the first resonator to 1 / n 2 times, thereby increasing the power capacity to n 2 times, n is a positive integer.

[0039] The thin film bulk acoustic wave filter designed by the present invention has a manufacturing process that is fully compatible with ordinary thin film bulk acoustic wave filters, and does not increase the design complexity of the filter circuit. It only requires a simple topological adjustment of the bulk acoustic wave resonators of each order on the series-parallel arm of the bulk acoustic wave filter according to the power density requirements, and adopts a topological form of first series connection and then parallel connection, so that the power density of each order resonator of the bulk acoustic wave filter is reduced to 1 / n of that of the prototype filter. 2 , where n depends on the parallel / series order of the resonators, thus increasing the power handling capacity of the BAW filter by n 2 times.

[0040] Comparative Example 1: This comparative example provides a method for improving the power capacity of a thin film bulk acoustic wave filter, comprising: In order to improve the power capacity of the traditional prototype BAW filter, the resonator with an area of ​​S is replaced by two resonators with an area of ​​2S. The power capacity of the resonator is reduced to approximately 1 / 4 of the original. However, since the resonant frequency, capacitance, Q value, etc. of the BAW resonator have an area effect, the impedance curve of the resonator will change significantly as the area increases. Therefore, this traditional way of increasing the power capacity will have a significant impact on the transmission curve of the filter, and it is impossible to achieve complete equivalence before and after the replacement. Figure 4A (a) and (b) show the traditional method of improving the power capacity of BAW filters, where the first order is replaced by two 2S1s in series. The impedance curve is shown in Figure 4B As shown in curves (a) and (b) in FIG. , the transmission curves of the BAW filter formed by them are respectively as follows: Figure 4C As shown in curves (a) and (b) in the figure, it can be seen that the traditional method of improving the power capacity of bulk acoustic wave filters will have a significant impact on other performances of the filter while improving the power capacity performance, and the correction method is relatively complicated.

Claims

1. A method for improving the power capacity of a thin film bulk acoustic wave filter, characterized in that: include: Obtaining the power density of each order resonator of the prototype film bulk acoustic wave filter at the maximum input power, using the resonator that does not meet the power capacity requirement as the first resonator among the resonators of each order, and replacing the first resonator with a resonator topology structure to reduce the power density of the first resonator to a range that meets the power capacity requirement; The resonator topology has the same impedance curve as the first resonator.

2. The method for improving the power capacity of a thin film bulk acoustic wave filter according to claim 1, characterized in that: The resonator topology is a first n-order series resonator followed by an n-order parallel connection, so as to reduce the power density of the first resonator to 1 / n 2 times, thereby increasing the power capacity to n 2 times, n is a positive integer.

3. The method for improving the power capacity of a thin film bulk acoustic wave filter according to claim 1, characterized in that: The area of ​​the sub-resonator in the resonator topology is the same as the area of ​​the first resonator.

4. The method for improving the power capacity of a thin film bulk acoustic wave filter according to claim 1, characterized in that: The sub-resonator in the resonator topology has the same shape and size as the first resonator.

5. The method for improving the power capacity of a thin film bulk acoustic wave filter according to claim 1, characterized in that: The sub-resonators of the resonator topology structure and the resonators of each order of the prototype thin film bulk acoustic wave filter are all bulk acoustic wave resonators.

6. The method for improving the power capacity of a thin film bulk acoustic wave filter according to claim 1, characterized in that: An order of the resonator topology is determined based on the power density of the first resonator.

7. The method for improving the power capacity of a thin film bulk acoustic wave filter according to claim 1, characterized in that: The prototype thin film bulk acoustic wave filter is designed by adopting a design method of a ladder or lattice filter topology structure based on performance indicators other than power capacity, and the performance indicators other than power capacity include filter insertion loss, roll-off or out-of-band suppression.

8. The method for improving the power capacity of a thin film bulk acoustic wave filter according to claim 1, characterized in that: The prototype thin film bulk acoustic wave filter is a ladder or laatice type bulk acoustic wave filter.

9. A thin film bulk acoustic wave filter, characterized in that: Obtaining the power density of each order resonator of the prototype film bulk acoustic wave filter at the maximum input power, replacing the first resonator that does not meet the power capacity requirement with a resonator topology structure to reduce the power density of the first resonator to a range that meets the power capacity requirement; The resonator topology has the same impedance curve as the first resonator.

10. The thin film bulk acoustic wave filter according to claim 9, characterized in that: The resonator topology is a first n-order series resonator followed by an n-order parallel connection, thereby reducing the power density of the first resonator to 1 / n 2 times, thereby increasing the power capacity to n 2 times, n is a positive integer.

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