CN111327295B - Piezoelectric filter and its mass load realization method and device containing piezoelectric filter - Google Patents

Abstract

The invention provides a method for realizing mass load of a piezoelectric filter, a piezoelectric filter, a duplexer, a high-frequency front-end circuit and a communication device. In this method, the piezoelectric filter includes a series branch and a parallel branch, and the series branch includes three or more bulk acoustic wave resonators connected in series between the input and output ends of the piezoelectric filter, adjacent to each other. A parallel circuit is arranged between the connection point of the resonator and the ground terminal. In this method, the temperature compensation layer of the resonator is used as a mass load, and: all series resonators are the same resonator, and each series resonator has or No temperature compensation layer; all parallel resonators have temperature compensation layers and are thicker than the temperature compensation layers of the series resonators. By adopting the technical scheme of the present invention, the left roll-off of the filter and the optimal selection of the passband insertion loss performance are taken into consideration.

Description

Piezoelectric filter and its mass load realization method and device containing piezoelectric filter

technical field

The invention relates to the technical field of microelectronics, to a piezoelectric filter, a method for realizing mass load thereof, and a device containing a piezoelectric filter, in particular to a method for realizing mass load of a piezoelectric filter, a piezoelectric filter, and a duplexer , high-frequency front-end circuits and communication devices.

Background technique

At present, the small-sized filter devices that can meet the use of communication terminals are mainly piezoelectric acoustic wave filters. The resonators that constitute such acoustic wave filters mainly include: FBAR (Film Bulk Acoustic Resonator, thin-film bulk acoustic resonator), SMR (Solidly Mounted Resonator, solid-state mounted resonator) and SAW (Surface AcousticWave, surface acoustic wave resonator). Among them, filters based on bulk acoustic wave principle FBAR and SMR (collectively referred to as BAW, bulk acoustic wave resonator) have lower insertion loss and faster roll-off characteristics than filters based on surface acoustic wave principle SAW .

Because the piezoelectric materials and metal materials that constitute the acoustic wave resonator have the characteristics of negative temperature coefficient, that is, when the temperature increases, the resonant frequency of the resonator will move to the low frequency direction in a certain proportion (temperature drift). In general, the temperature coefficient of SAW is -35ppm/℃～-50ppm/℃, and the temperature coefficient of BAW is -25ppm/℃～-30ppm/℃. Although BAW has obvious performance advantages in terms of temperature drift compared to SAW, in some special application scenarios, such a temperature coefficient will still have an adverse effect on the performance of the RF transceiver system with the filter applied, such as a filter The variable frequency range from the passband edge to the out-of-band suppression is defined, and the existence of the temperature coefficient makes this variable range smaller after considering the temperature drift frequency, which greatly increases the difficulty of filter design.

To address the common problem of temperature drift in filters, a common solution is to include materials in the resonator that can compensate for temperature. For acoustic resonators, this temperature compensation material is often chosen to be silicon dioxide, mainly because silicon dioxide has a positive temperature coefficient opposite to that of most materials, and can be fabricated by common processes, while also having low cost The price is suitable for the application of mass production of the product. This type of resonator with temperature-compensated material, also known as TCF resonator, is the building block of a temperature-compensated filter.

However, the introduction of a temperature compensation layer in the resonator is not without cost, it deteriorates the characteristics of the resonator, which is mainly reflected in the increase in the loss of the resonator and the decrease in the electromechanical coupling coefficient. As the loss of the resonator increases, the insertion loss of the filter will increase accordingly, thereby increasing the loss in the RF link and deteriorating the transceiver performance of the RF front-end. The electromechanical coupling coefficient becomes smaller, the distance between the series resonant frequency and the parallel resonant frequency of the resonator decreases, and the roll-off characteristic of the filter may be improved, but at the same time, the bandwidth of the filter will also be narrowed. In most communication systems, The bandwidth of the filter is proposed according to the system requirements, and the bandwidth cannot be narrowed indefinitely.

Therefore, how to achieve high roll-off requirements and temperature characteristics of BAW filter components under the condition of certain bandwidth requirements has become an urgent problem for filter design engineers.

SUMMARY OF THE INVENTION

In view of this, the present invention provides a method for realizing mass load of a piezoelectric filter, a piezoelectric filter, a duplexer, a high-frequency front-end circuit, and a communication device, so as to solve the technical problems in the prior art.

In order to achieve the above object, according to an aspect of the present invention, a method for realizing mass loading of a piezoelectric filter is provided.

In the method for realizing the mass load of the piezoelectric filter of the present invention, the piezoelectric filter includes a series branch and a parallel branch, and the series branch includes three or more input and output outputs of the piezoelectric filter connected in series For the bulk acoustic wave resonator between the terminals, a parallel circuit is set between the connection point of the adjacent resonator and the ground terminal. In this method, the temperature compensation layer of the resonator is used as a mass load, and: all series resonators are Identical resonators, each series resonator with or without a temperature compensation layer; all parallel resonators have a temperature compensation layer and are thicker than the temperature compensation layer of the series resonator.

In the present invention, if only the temperature compensation layer is added to the parallel resonator filter, compared with the ordinary piezoelectric filter without the temperature compensation layer, it has the following advantages: the parallel resonator adopts the temperature compensation of zero temperature drift and small Kt ² resonator, which can effectively improve the roll-off characteristics of the left side of the filter. At the same time, it has the following advantages compared with the temperature-compensated filter made of the temperature-compensated resonator for the series and parallel resonators: 1) The temperature-compensated layer is used as the mass load, eliminating the need for another process step of making the mass load; 2) The series connection The resonator adopts an ordinary resonator instead of a temperature-compensated resonator, and the loss of the resonator is relatively good, thus improving the insertion loss characteristics of the filter; 3) The series resonator adopts an ordinary resonator instead of a temperature-compensated resonator, which appropriately reduces the temperature. The reduction of the complementary resonator Kt ² reduces the bandwidth of the filter.

Optionally, the thickness of the temperature compensation layer of the parallel resonator satisfies the following conditions: the positive temperature drift effect generated by the temperature compensation layer cancels the negative temperature drift effect of other layers of the parallel resonator, so that the The temperature coefficient of the parallel resonator is in the neighborhood of the specified range of 0 ppm/°C.

Optionally, the thickness of the temperature compensation layer of the parallel resonator further satisfies the following conditions: the mass loading effect generated by the thickness of the temperature compensation layer of the parallel resonator makes the series resonant frequency of the series resonator and the temperature compensation layer added. The difference between the parallel resonance frequencies of the subsequent parallel resonators is within a preset range.

Optionally, it also includes: adjusting the thickness of one or more of the upper electrode, the lower electrode, the piezoelectric layer, and the temperature compensation layer of the parallel resonator, so that the temperature coefficient of the parallel resonator is 0ppm/°C within the neighborhood of the preset range, and adjust the thickness of one or more of the upper electrode, the lower electrode, the piezoelectric layer, and the temperature compensation layer of the series resonator, so that the temperature coefficient of the series resonator is within a A specified value of less than 0 ppm/°C is in the neighborhood of a preset range to adjust the roll-off performance of the filter.

According to another aspect of the present invention, a piezoelectric filter is provided.

The piezoelectric filter of the present invention includes a series branch and a parallel branch, and the series branch includes three or more bulk acoustic wave resonators connected in series between the input and output ends of the piezoelectric filter. A parallel circuit is arranged between the connection point and the ground terminal, all series resonators are the same resonator, and each series resonator has or does not have a temperature compensation layer; all parallel resonators have a temperature compensation layer and are thicker than the series Temperature compensation layer of the resonator.

Optionally, the thickness of the temperature compensation layer of the parallel resonator satisfies the following conditions: the positive temperature drift effect generated by the temperature compensation layer cancels the negative temperature drift effect of other layers of the parallel resonator, so that the The temperature coefficient of the parallel resonator is in the neighborhood of the specified range of 0 ppm/°C.

Optionally, the thickness of the temperature compensation layer of the parallel resonator further satisfies the following conditions: the mass loading effect generated by the thickness of the temperature compensation layer of the parallel resonator makes the series resonant frequency of the series resonator and the temperature compensation layer added. The difference between the parallel resonance frequencies of the subsequent parallel resonators is within a preset range.

According to yet another aspect of the present invention, there is provided a duplexer including the piezoelectric filter of the present invention.

According to yet another aspect of the present invention, a high-frequency front-end circuit includes the piezoelectric filter of the present invention.

According to yet another aspect of the present invention, a communication device is provided, including the piezoelectric filter of the present invention.

Description of drawings

The accompanying drawings are used for better understanding of the present invention and do not constitute an improper limitation of the present invention. in:

FIG. 1A is an electrical symbol of BAW, and FIG. 1B is an equivalent electrical model diagram of BAW;

Figure 2 is a schematic diagram of the relationship between resonator impedance and fs, fp;

Fig. 3 is the schematic diagram of traditional common resonator;

4 is a schematic diagram of a temperature compensated resonator;

Fig. 5 is the performance comparison schematic diagram of the resonator before adding the temperature compensation layer and after adding the temperature compensation layer;

FIG. 6 is a circuit diagram of a piezoelectric filter 100 according to an embodiment of the present invention;

FIG. 7 is a circuit diagram of a piezoelectric filter 001 of a first comparative example;

8A is a schematic diagram of the series-parallel resonator impedance-frequency relationship of the piezoelectric filter 001, and FIG. 8B is a schematic diagram of the series-parallel resonator impedance-frequency relationship of the piezoelectric filter 100;

FIG. 9A is a schematic diagram showing the comparison of the amplitude-frequency curves of the piezoelectric filter 100 and the piezoelectric filter 001, and FIG. 9B is a partial enlarged view of FIG. 9A;

FIG. 10A is a schematic diagram of a three-temperature curve of the piezoelectric filter 001 at low temperature, normal temperature, and high temperature, and FIG. 10B is a partial enlarged view of FIG. 10A ;

11A is a schematic diagram of a three-temperature curve of the piezoelectric filter 100 at low temperature, normal temperature, and high temperature, and FIG. 11B is a partial enlarged view of FIG. 11A ;

12 is a circuit diagram of a second comparative piezoelectric filter 002;

13A is a schematic diagram of the series-parallel resonator impedance-frequency relationship of the piezoelectric filter 002, and FIG. 13B is a schematic diagram of the series-parallel resonator impedance-frequency relationship of the piezoelectric filter 100;

14A is a schematic diagram showing the comparison of the amplitude-frequency curves of the piezoelectric filter 100 and the piezoelectric filter 002, and FIG. 14B is a partial enlarged view of FIG. 14A;

15 is a schematic diagram of the structure of a filter according to an embodiment of the present invention, wherein both the series filter and the parallel filter have temperature compensation layers.

Detailed ways

The following describes in detail the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary, and are intended to explain the present invention and should not be construed as limiting the present invention.

In order for those skilled in the art to better understand the content of the present invention, the inventor first briefly introduces the basic structure and performance of the temperature compensated resonator.

Figure 1A is the electrical symbol of the piezoelectric acoustic wave resonator, and Figure 1B is its equivalent electrical model diagram. Without considering the loss term, the electrical model is simplified to a resonant circuit composed of L _m , C _m and C ₀ . According to the resonance conditions, there are two resonance frequency points in the resonance circuit: one is f _s when the impedance value of the resonance circuit reaches the minimum value, and f _s is defined as the series resonance frequency point of the resonator; the other is when the impedance of the resonance circuit reaches the minimum value. f _p when the value reaches the maximum value, and f _p is defined as the parallel resonance frequency of the resonator. in,

Also, f _s is smaller than f _p . At the same time, the electromechanical coupling coefficient Kt ² _eff of the resonator (hereinafter abbreviated as Kt ² ) is defined, which can be expressed by f _s and f _p :

Figure 2 shows the relationship between the resonator impedance and _fs and _fp . At a certain frequency, the greater the effective electromechanical coupling coefficient, the greater the frequency difference between f _s and f _p , that is, the farther the two resonant frequency points are. At the same time, the impedance amplitude of the resonator at f _s is defined as R _s , which is the minimum value in the impedance curve of the resonator; the impedance amplitude of the resonator at f _p is defined as R _p , which is the resonator impedance Maximum value in the impedance curve. R _s and R _p are important parameters to describe the resonance loss characteristics. When R _s is smaller and R _p is larger, the loss of the resonator is smaller and the Q value is higher. At this time, the insertion loss characteristics of the filter are also better.

FIG. 3 is a schematic diagram of a conventional common resonator. As shown in FIG. 3, the resonator is fabricated on the substrate 104, the bottom electrode 102 and the top electrode 101 are metal electrodes, and the thickness is usually several hundred nanometers. The piezoelectric material film 103 is usually made of zinc oxide or aluminum nitride, and the thickness is several hundreds of nanometers to several micrometers. In order to make the sound waves generated therein resonate, it is necessary to make the sound waves reflect on the surface of the top and bottom electrodes. Above the top electrode 101 is air capable of forming sound wave reflection. In order to make the sound wave also reflect on the lower surface of the bottom electrode, an air cavity 100 is formed under the bottom electrode 102 . When an alternating voltage is applied to the top electrode 101 and the bottom electrode 102, the piezoelectric material film 103 is excited to generate a piezoelectric effect to generate mechanical acoustic waves. The acoustic wave propagates and reflects between the top and bottom electrodes, forming a standing wave resonance, which in turn forms a resonance in the electrical response. Due to the use of cavities to form reflections, such resonators are called cavity reflective BAW resonators.

Figure 4 is a schematic diagram of a temperature compensated resonator. The temperature-compensated resonator may include: a top electrode 201, a bottom electrode 202, a piezoelectric layer 203, a substrate 204, a temperature compensation layer 205 inside the bottom electrode 202, and an air cavity 200, which can be considered to be based on FIG. 3 FBAR resonator with temperature compensation layer added. The material of the temperature compensation layer 205 is generally silicon dioxide, and its pattern is smaller than or equal to the pattern of the bottom electrode, that is to say, the compensation layer and the bottom electrode look like sandwich biscuits or sandwiches. Preferably, the temperature compensation layer 205 is completely encapsulated in the bottom electrode material, and the advantage of this fabrication is that it can be effectively protected from being damaged by other fabrication processes. In addition, since the electrode materials above and below the temperature compensation layer are connected together at the edges, the formation of parasitic capacitances consisting of the ^three is avoided, thereby greatly deteriorating the Kt and loss characteristics of the resonator. Optionally, the ratio of the layout area of the temperature compensation layer to the layout area of the top layer of the bottom electrode or the bottom layer of the bottom electrode is 0.5˜1.

Figure 5 is a comparison of the resonator impedance curves before and after adding a temperature compensation layer to the resonator. After adding the temperature compensation layer, the Kt ² of the resonator is reduced from the original 6.5% to 3.4%, the R _s is increased from the original 0.66 ohms to 1.37 ohms, and the Rp is reduced from the original 2592 ohms to 1314 ohms. The temperature coefficient of the resonator changes from -25ppm/°C to -30ppm/°C to about 0ppm/°C. It can be seen that with the addition of the temperature compensation layer, Kt ² will become about half of the original, R _s will increase to about 2 times the original, and R _p will be reduced to about half of the original, the loss of the resonator will also increase To a certain extent, it leads to a decrease in the Q value.

A first aspect of the present invention provides a method for realizing mass load of a piezoelectric filter. The piezoelectric filter includes a series branch and a parallel branch, and the series branch includes three or more connected in series between the output and output ends of the piezoelectric filter. In this method, the temperature compensation layer of the resonator is used as the mass load, and: all series resonators are the same Resonators, each series resonator with or without a temperature compensation layer; all parallel resonators have a temperature compensation layer and are thicker than the temperature compensation layer of the series resonators.

It should be noted that the case where the series resonators are the same common resonators has the advantages of simple structure and easy processing. In this embodiment, the thickness of the temperature compensation layer in the series resonator is zero, so the thickness difference of the temperature compensation layer in the series-parallel resonator is equal to the thickness of the temperature compensation layer in the parallel resonator. It should also be noted that when the series resonators are the same temperature compensation resonator, and the thickness of the temperature compensation layer of the series resonator is smaller than that of the parallel resonator, the temperature compensation layer thickness of the series resonator is different to ensure To realize the series-parallel frequency difference, that is, to realize the load effect.

Further, the temperature coefficient of the series resonator is zero. This means that the positive temperature drift effect produced by the temperature compensation layer can just cancel the negative temperature drift effect of all other layers, making the parallel resonator a temperature compensated resonator with a temperature coefficient equal to 0ppm/°C. In this embodiment, the zero temperature coefficient means that the temperature drift effect of the temperature compensation layer exactly cancels the temperature drift effect of other layers, so that the piezoelectric filter has stable electrical performance under different ambient temperatures.

Further, the thickness of the temperature compensation layer of the parallel resonator is equal to the mass loading effect, so that the parallel resonance frequency of the parallel resonator after adding the temperature compensation layer is equal to the series resonance frequency of the series resonator. It means that the thickness of the temperature compensation layer is exactly equal to the mass loading effect, so that the parallel resonance frequency of the parallel resonator after adding the temperature compensation layer is almost equal to the series resonance frequency of the series resonator without adding the temperature compensation layer, thus forming a filter characteristic curve.

In the method for realizing the mass load of the piezoelectric filter according to the embodiment of the present invention, whether compared with the case where the series-parallel resonators are all set with ordinary FBAR resonators, or compared with the case where the series-parallel resonators are all set as temperature-compensated resonators, Both have obvious advantages in performance, taking into account the left roll-off and the better choice of passband insertion loss performance.

A second aspect of the present invention provides a piezoelectric filter, which includes a series branch and a parallel branch, wherein the series branch includes three or more bulk acoustic wave resonators connected in series between the output ends of the piezoelectric filter, and adjacent resonators A parallel circuit is set between the connection point and the ground terminal, and it is characterized in that all series resonators are the same resonator, and each series resonator has or does not have a temperature compensation layer; all parallel resonators have a temperature compensation layer and The thickness is greater than the temperature compensation layer of the series resonator.

Further, the temperature coefficient of the series resonator is zero.

Further, the thickness of the temperature compensation layer of the parallel resonator is equal to the mass loading effect, so that the parallel resonance frequency of the parallel resonator after adding the temperature compensation layer is equal to the series resonance frequency of the series resonator.

The piezoelectric filter of the embodiment of the present invention has obvious advantages in performance, regardless of whether it is a filter that is all common FBAR resonators or a filter that is all temperature-compensated resonators, and takes into account the left roll-off, And the best choice for passband insertion loss performance.

The piezoelectric filter of the embodiment of the present invention is listed below for comparison with two other piezoelectric filters.

The piezoelectric filter 100 according to the embodiment of the present invention, as shown in FIG. 6 , includes five series resonators and four parallel resonators. All the parallel resonators are temperature compensated resonators as shown in Fig. 4, and all series resonators are common FBAR resonators as shown in Fig. 3. The passband frequency range of this filter is 2565MHz～2595MHz, the passband bandwidth is 30MHz, and it is required to have out-of-band rejection greater than 45dB at 2540MHz.

A first comparative example—piezoelectric filter 001 is provided, the circuit diagram of which is shown in FIG. 7 , including 5 ordinary resonators in series and 4 ordinary resonators in parallel. The piezoelectric filter 001 is composed of a series resonator and a parallel resonator to form a cascade structure similar to a ladder, and a mass load layer is added on the parallel resonator. The material is the same as the electrode material for making the BAW device, so that it resonates in parallel The frequency is substantially the same as the resonant frequency of the series resonator, resulting in the filter's curvilinear characteristic.

FIG. 8A is a schematic diagram of the series-parallel resonator impedance-frequency relationship of the piezoelectric filter 001 , and FIG. 8B is a schematic diagram of the series-parallel resonator impedance-frequency relationship of the piezoelectric filter 100 . It can be seen from the comparison of the two figures that the filter requires an out-of-band suppression greater than 45dB at 2540MHz. The series resonance frequency of the parallel resonators in the piezoelectric filter 100 of the embodiment and the piezoelectric filter 001 of the first comparative example are both set at 2530MHz. However, since the parallel resonator in the embodiment is a temperature compensated resonator with relatively small Kt2, the distance between fs and fp is smaller, so the series resonant frequency of the series resonator in the embodiment is compared with the first comparison. The regular meeting is obviously low, this is to ensure the impedance matching characteristics of the filter in the passband range.

FIG. 9A is a schematic diagram showing the comparison of the amplitude-frequency curves of the piezoelectric filter 100 (solid line) and the piezoelectric filter 001 (dotted line), and FIG. 9B is a partial enlarged view of FIG. 9A . Since the piezoelectric filter 001 adopts the common FBAR resonator, its Kt2 is about 6.5%, and the bandwidth of the filter is wider. In order to ensure the out-of-band rejection at 2540MHz, the insertion loss of the filter at 2565MHz is about 3.2dB. At the same time, because the passband is wide, the insertion loss on the right side of the passband can reach nearly 1.0dB, and the fluctuation value in the 30MHz passband range is relatively high. big. However, the parallel resonator of the embodiment adopts a temperature-compensated resonator, and its Kt2 is about 3.4%, and the frequency range of transition from the minimum impedance value to the maximum impedance value is smaller, so a better left roll-off characteristic can be achieved. At the same time, the zero temperature drift characteristic of the parallel resonator also makes the left roll-off edge of the filter change little with the temperature change, which further increases the roll-off margin of the filter.

FIG. 10A is a schematic diagram of a three-temperature curve of the piezoelectric filter 001 at low temperature, normal temperature, and high temperature, and FIG. 10B is a partial enlarged view of FIG. 10A . The black solid line is the curve at room temperature, because all the resonators used have a temperature coefficient of -25ppm/℃～-30ppm/℃, so compared with the curve at room temperature, the amplitude-frequency curve of the filter at low temperature is in the direction of high frequency At the same time, the insertion loss becomes better, while the amplitude-frequency curve moves to the low frequency direction at high temperature, and the insertion loss becomes worse at the same time.

FIG. 11A is a schematic diagram of a three-temperature curve of the piezoelectric filter 100 at low temperature, normal temperature, and high temperature, and FIG. 11B is a partial enlarged view of FIG. 11A . The black solid line is the curve at room temperature, because the series resonator is an ordinary resonator with a temperature coefficient of -25ppm/℃～-30ppm/℃, while the parallel resonator is a temperature compensated resonator with a temperature coefficient of 0ppm/℃ , so compared with the normal temperature curve, the right edge of the amplitude-frequency curve of the filter moves to the high frequency direction at low temperature, and the insertion loss becomes better, while the right edge of the amplitude-frequency curve moves to the low frequency direction at high temperature, and the insertion loss becomes worse at the same time . The right edge of the filter is anchored by the zero temperature drift characteristic of the temperature compensated resonator, and the position of the frequency from the surface changes very little, thereby improving the roll-off characteristic of the corresponding position of the full eye wave resonator.

From the comparison between the piezoelectric filter 100 and the piezoelectric filter 001 above, it can be seen that a filter with only a temperature compensation layer added to the parallel resonator has the following advantages compared to a common piezoelectric filter without a temperature compensation layer: The parallel resonator adopts a temperature compensated resonator with zero temperature drift and small Kt ² , which can effectively improve the roll-off characteristic of the left side of the filter.

A second comparative example—piezoelectric filter 002 is provided, the circuit diagram of which is shown in FIG. 12 , including 5 series temperature compensated resonators and 4 parallel temperature compensated resonators.

13A is a schematic diagram of the series-parallel resonator impedance-frequency relationship of the piezoelectric filter 002, and FIG. 13B is a schematic diagram of the series-parallel resonator impedance-frequency relationship of the piezoelectric filter 100. It can be seen that the piezoelectric filter 002 has a small Kt ² , the loss is large, the characteristics of zero temperature drift.

FIG. 14A is a comparison of the amplitude-frequency curves of the piezoelectric filter 100 (solid line) and the piezoelectric filter 002 (dotted line), and FIG. 14B is a partial enlarged view of FIG. 14A . Since the piezoelectric filter 002 uses temperature compensated resonators, its Kt ² is about 3.4%, and the loss is relatively large, so the bandwidth of the filter is narrow, the insertion loss at 2565MHz is about 3.6dB, and the insertion loss at 2595MHz is about 3.6dB. The loss is about 2.6dB, and the overall in-band insertion loss in the passband is about 0.35dB worse than the embodiment. Although the piezoelectric filter 002 adopts temperature-compensated resonators, the temperature drift characteristics of the left and right roll-off edges are good, but its loss in bandwidth and insertion loss is relatively large, which cannot meet the application requirements of the filter.

From the comparison between the piezoelectric filter 100 and the piezoelectric filter 002 above, it can be seen that, compared with the piezoelectric filter in which the series and parallel resonators are all made of temperature-compensated resonators, the piezoelectric filter according to the embodiment of the present invention has the following characteristics: Advantages: (1) The temperature compensation layer is used as the mass load, eliminating the need for another process step of making the mass load; (2) The series resonator uses an ordinary resonator instead of a temperature compensated resonator, and the resonator loss is relatively good, thereby improving the The insertion loss characteristics of the filter are improved; (3) the series resonator adopts an ordinary resonator instead of a temperature-compensated resonator, which appropriately reduces the reduction of the filter bandwidth due to the decrease of the temperature-compensated resonator Kt ² .

FIG. 15 is a schematic diagram of the structure of a filter according to an embodiment of the present invention. The circuit diagram of the FBAR filter 300 shown in FIG. 15 is the same as that of FIG. 11 , and both the series and parallel are temperature compensated resonators. The figure shows the cavity made on the substrate, the lower electrode, the piezoelectric layer, the upper electrode, and the temperature compensation layer wrapped in the lower electrode and located in the resonance region. It should be noted that in order to protect the resonator from being oxidized by the environment, a passivation layer is usually formed above the upper electrode, and its material can be a non-metallic material with relatively stable performance, such as silicon dioxide, It is even possible to use the same material as the piezoelectric layer, such as aluminum nitride. The resonator on the left in FIG. 15 is a series resonator, the resonator on the right is a parallel resonator, and the resonators in the other filters are not shown. The thickness of the temperature compensation layer of the series resonator is t1, and the thickness of the temperature compensation layer of the parallel resonator is t2. , the mass loading effect required for filter design. The thickness of the other layers of the series resonator and the parallel resonator are the same. In order to better show the relationship between the thickness of each layer, this figure shows in more detail the thickness of each layer because of the different thickness of the temperature compensation layer. Boundary bevel formed during deposition fabrication. In this embodiment, since the thicknesses of the temperature compensation layers are different for the series and parallel resonators, while the other layers are the same, the temperature coefficients of the two resonators must be different. During the design process, an appropriate stack can be selected according to the characteristics of the electrical performance of the filter, so that the temperature coefficient of the corresponding position is closer to 0ppm/°C. For example, if there is a roll-off requirement on the left side of the passband of the filter, the thickness of each layer can be designed so that the temperature coefficient of the parallel resonator is about 0ppm/℃, while the temperature coefficient of the series resonator can be far from 0ppm/℃ , such as -10ppm. The filter formed in this way can obtain a better left roll-off, and at the same time, the right roll-off will be improved to a certain extent compared with the filter without the TCR.

To sum up, the piezoelectric filter according to the embodiment of the present invention has obvious advantages in performance, regardless of whether it is a filter that is all an ordinary FBAR resonator or a filter that is a temperature-compensated resonator. roll-off, and the best choice for passband insertion loss performance.

The above-mentioned specific embodiments do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions may occur depending on design requirements and other factors. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (8)

1. A method for realizing the mass load of a piezoelectric filter, the piezoelectric filter comprises a series branch and a parallel branch, and the series branch comprises three or more input and outputs connected in series to the piezoelectric filter In the bulk acoustic wave resonator between the terminals, a parallel circuit is arranged between the connection point of the adjacent resonator and the ground terminal, and it is characterized in that, in the method, the temperature compensation layer of the resonator is used as a mass load, and: All series resonators are identical resonators, each with or without a temperature compensation layer; all parallel resonators have temperature compensation layers and are thicker than the temperature compensation layers of the series resonators; The thickness of the temperature compensation layer of the parallel resonator further satisfies the following conditions: the mass loading effect generated by the thickness of the temperature compensation layer of the parallel resonator makes the series resonance frequency of the series resonator and the parallel resonance after adding the temperature compensation layer The difference between the parallel resonant frequencies of the generators is within a preset range. 2 . The method according to claim 1 , wherein the thickness of the temperature compensation layer of the parallel resonator satisfies the following condition: the positive temperature drift effect generated by the temperature compensation layer has on the other layers of the parallel resonator. 3 . The cancellation of the negative temperature drift effect keeps the temperature coefficient of the parallel resonator in the neighborhood of the specified range of 0 ppm/°C. 3. The method of claim 1, further comprising: Adjusting the thickness of one or more of the upper electrode, the lower electrode, the piezoelectric layer, and the temperature compensation layer of the parallel resonator so that the temperature coefficient of the parallel resonator is in the neighborhood of a preset range of 0 ppm/°C , and adjust the thickness of one or more of the upper electrode, lower electrode, piezoelectric layer, and temperature compensation layer of the series resonator, so that the temperature coefficient of the series resonator is at a specified value less than 0ppm/°C within the neighborhood of a preset range to adjust the roll-off performance of the filter. 4. A piezoelectric filter comprising a series branch and a parallel branch, the series branch comprising three or more bulk acoustic wave resonators connected in series between the input and output ends of the piezoelectric filter, adjacent resonances A parallel circuit is set between the connection point of the device and the ground terminal, which is characterized in that: All series resonators are identical resonators, each with or without a temperature compensation layer; all parallel resonators have temperature compensation layers and are thicker than the temperature compensation layers of the series resonators; The thickness of the temperature compensation layer of the parallel resonator further satisfies the following conditions: the mass loading effect generated by the thickness of the temperature compensation layer of the parallel resonator makes the series resonance frequency of the series resonator and the parallel resonance after adding the temperature compensation layer The difference between the parallel resonant frequencies of the generators is within a preset range. 5 . The piezoelectric filter according to claim 4 , wherein the thickness of the temperature compensation layer of the parallel resonator satisfies the following condition: the positive temperature drift effect generated by the temperature compensation layer has an effect on the parallel resonator. 6 . The cancellation of the negative temperature drift effect of the other layers keeps the temperature coefficient of the parallel resonator in the neighborhood of the specified range of 0 ppm/°C. 6. A duplexer, comprising the piezoelectric filter according to claim 4 or 5. 7. A high-frequency front-end circuit, characterized by comprising the piezoelectric filter according to claim 4 or 5. 8. A communication device comprising the piezoelectric filter according to claim 4 or 5.

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