Filter, temperature compensation type BAW device with adjustable effective electromechanical coupling coefficient and preparation method of filter and temperature compensation type BAW device

Abstract

The invention discloses a filter, a temperature compensation type BAW device with an adjustable effective electromechanical coupling coefficient and a preparation method of the temperature compensation type BAW device. The temperature compensation type BAW device comprises a substrate; the piezoelectric oscillation pile comprises a first electrode, a piezoelectric layer, a second electrode and a protective layer which are sequentially stacked on the substrate; the temperature compensation layer is located between the first electrode and the piezoelectric layer or located between the second electrode and the piezoelectric layer; the insulating layer and the cavity are arranged between the substrate and the first electrode, and the insulating layer is located on the cavity; wherein the relationship between the thickness of the temperature compensation layer and the thickness of the piezoelectric layer meets the following formula: the thickness of the temperature compensation layer / the piezoelectric layer is greater than or equal to 0.01 and less than or equal to 0.5. According to the temperature compensation type BAW device, the effective electromechanical coupling coefficient can be adjusted, and the same effect as that of an external cascade passive device is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of MEMS devices, and in particular relates to a filter, a temperature-compensated BAW device with adjustable effective electromechanical coupling coefficient, and a preparation method thereof. Background Art

[0002] With the rapid development of mobile communication and defense electronic equipment system technology, the communication frequency band has been further expanded to higher frequencies, and the high-frequency Film Bulk Acoustic Resonator filter (FBARfilter) is a key component in the system to filter out other frequency bands and malicious interference signals; in the face of increasingly complex use environments, military and civilian communication systems, radars, navigation and other equipment have put forward higher requirements for the temperature stability of FBAR filters. Due to the low temperature stability of conventional FBAR filters (large frequency temperature coefficient), it is necessary to increase the protection bandwidth of the system signal, increase the number of interference signals entering the receiving end, deteriorate the signal-to-noise ratio and sensitivity, increase the bit error rate of the whole machine, shorten the communication and detection distance, and make the communication system and equipment system unable to work normally in harsh environments.

[0003] In addition, the implementation of carrier aggregation (CA) and multiple-input multiple-output (MIMO) technologies further increases data rates by using multiple data communication channels in parallel. This scenario will further increase the number of filters, and in many cases, high isolation filtering is required between adjacent frequency bands to avoid interference between different data communication links operating simultaneously.

[0004] Conventional FBAR filters are large in size, and usually achieve high roll-off by external cascade passive devices, which increases the size of the system again and makes it impossible to further miniaturize it. Therefore, the preparation of filters with high roll-off, high temperature stability and miniaturization is of great significance to the current and future development of mobile communications, complete systems and weapon equipment.

[0005] The invention with publication number CN113746446A provides a bulk acoustic wave resonator with a frequency stabilization function. The temperature frequency coefficient is optimized by forming a temperature compensation layer. The cavity resonance region has only a resonance structure composed of multiple layers of thin films, and the lead-out electrodes and through-holes are far away from the cavity, which can avoid the generation of clutter. When forming the cavity structure, the invention adopts a bonding transfer method, thereby realizing a process without release, but the bonding transfer method is complex; at the same time, the temperature compensation layer disclosed in the patent application is buried in the piezoelectric film, the first electrode or the second electrode, and its function is only temperature compensation. Its location cannot achieve the purpose of replacing the external passive capacitor.

[0006] The invention with publication number CN111327295A provides a method for realizing the mass load of a piezoelectric filter, a piezoelectric filter, a duplexer, a high-frequency front-end circuit, and a communication device. In the method, the piezoelectric filter includes a series branch and a parallel branch, the series branch includes three or more bulk acoustic wave resonators connected in series between the input and output ends of the piezoelectric filter, and a parallel circuit is arranged between the connection point of adjacent resonators and the ground end. In the method, the temperature compensation layer of the resonator is used as the mass load, and: all series resonators are the same resonator, 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. The technical solution of the patent application is adopted, taking into account the left roll-off of the filter and the better choice of the passband insertion loss performance. The temperature compensation layer provided in the patent application as a mass load, although taking into account the left roll-off of the filter, greatly reduces the bandwidth of the filter, and has a high limit for the large bandwidth required by future mobile communication technology. At the same time, the function of temperature compensation is not well implemented, and only unilateral temperature compensation can be achieved. Summary of the invention

[0007] The present invention provides a temperature-compensated BAW device with an adjustable effective electromechanical coupling coefficient. The temperature-compensated BAW device can adjust the effective electromechanical coupling coefficient and achieve the same effect as an external cascade passive device.

[0008] The present invention provides a temperature-compensated BAW device with adjustable effective electromechanical coupling coefficient, comprising: Insulating substrate; A piezoelectric oscillator stack comprises a first electrode, a piezoelectric layer, a second electrode and a passivation protection layer sequentially stacked on the substrate; A temperature compensation layer is located between the first electrode and the piezoelectric layer, or between the second electrode and the piezoelectric layer; A cavity is disposed between the substrate and the first electrode; The relationship between the thickness of the temperature compensation layer and the thickness of the piezoelectric layer satisfies the following formula: 0.01≤thickness of temperature compensation layer / thickness of piezoelectric layer≤0.5.

[0009] When the thickness of the temperature compensation layer / piezoelectric layer satisfies the above relationship, due to the potential difference between the two electrodes, the additional temperature compensation layer will cause the BAW resonator to introduce additional parasitic capacitance, resulting in the resonator being able to achieve the same adjustment function of the effective electromechanical coupling coefficient as when the BAW resonator has an external cascade passive capacitor. If the ratio is too high, it will lead to excessive adjustment of the effective electromechanical coupling coefficient, which is not conducive to practical applications and will greatly increase the insertion loss of the constructed filter. If the ratio is too low, it will be difficult to adjust the effective electromechanical coupling coefficient and compensate for temperature.

[0010] When the temperature compensation layer provided by the present invention is located on or under the piezoelectric layer, the effective electromechanical coupling coefficient can be adjusted accordingly by adjusting the thickness of the temperature compensation layer, thereby replacing external passive components and facilitating the miniaturization of the constructed filter.

[0011] Preferably, the thickness of the first electrode is 10nm-1000nm, the thickness of the second electrode is 10nm-1000nm, the thickness of the piezoelectric layer is 10nm-4000nm, and the thickness of the temperature compensation layer is 10nm-2000nm.

[0012] The present invention can obtain a suitable effective electromechanical coupling coefficient at a relatively low temperature compensation layer thickness by controlling the thickness of the electrode, the piezoelectric layer and the temperature compensation layer.

[0013] Preferably, the insulating substrate comprises an insulating layer and a substrate, the insulating layer is located on the low-resistance substrate, and the material of the low-resistance substrate in the cavity is silicon with a resistivity of less than 10Ω·cm; when the resistivity of the substrate is low, the substrate will conduct electricity, shunt the radio frequency signal from the thin film bulk acoustic wave resonator, and interfere with the electrical operation of the final device, so the present invention sets an insulating layer on the low-resistance substrate; Or the insulating substrate is a high-resistance substrate, and the material of the high-resistance substrate is one of materials such as silicon, ceramics, sapphire, etc. with a resistivity greater than 1000Ω·cm, or any combination thereof.

[0014] Preferably, the temperature compensation layer is located above the cavity.

[0015] Preferably, the material of the temperature compensation layer is silicon dioxide, doped silicon dioxide, chromium or tellurium oxide.

[0016] On the other hand, the present invention also provides a method for preparing the temperature-compensated BAW device with adjustable effective electromechanical coupling coefficient, comprising: S1, a cavity is provided in the insulating substrate; S2, filling the cavity to form a sacrificial layer, wherein the material of the sacrificial layer is ZnO; S3, forming a piezoelectric oscillation stack on the insulating substrate and the sacrificial layer; S4, etching the piezoelectric oscillator stack to form a first window, a second window and a release hole, exposing the first electrode through the first window, and exposing the second electrode through the second window; S5, forming a metal pad layer on the first electrode and the second electrode of the piezoelectric oscillator stack to lead out the first electrode and the second electrode; S6. Corrode the first sacrificial layer with a dilute hydrochloric acid solution through the release hole to form an air gap below the resonant cavity.

[0017] Preferably, the method for preparing the piezoelectric oscillator stack comprises: A first electrode is formed on the insulating substrate and the sacrificial layer, a temperature compensation layer is formed on the first electrode and above the cavity, a piezoelectric layer is formed on the first electrode and the temperature compensation layer, a second electrode is formed on the piezoelectric layer, and a passivation protection layer is formed on the second electrode; Alternatively, a first electrode is formed on the insulating substrate and the sacrificial layer, a piezoelectric layer is formed on the first electrode, a temperature compensation layer is formed on the piezoelectric layer and above the cavity, a second electrode is formed on the piezoelectric layer and the temperature compensation layer, and a passivation protective layer is formed on the second electrode.

[0018] On the other hand, the present invention also provides a filter, including a series branch and a parallel branch, the series branch includes at least two series BAW resonators connected in series between the input and output ends of the filter, a parallel branch is arranged between the connection point of adjacent series BAW resonators and the ground end, the parallel branch includes one parallel BAW resonator or multiple parallel BAW resonators connected in series with each other, and at least one series or parallel BAW resonator is the temperature compensated BAW device with adjustable effective electromechanical coupling coefficient.

[0019] The filter provided by the present invention introduces a temperature-compensated BAW device with an adjustable effective electromechanical coupling coefficient in a series resonator or a parallel resonator, and can achieve a high steep drop under the condition of ensuring a relatively high broadband without introducing an external passive device for adjustment.

[0020] Compared with the prior art, the present invention has the following beneficial effects: In the prior art, the effective electromechanical coupling coefficient of the resonator is adjusted by cascading passive devices outside the resonator. However, the present invention adjusts the effective electromechanical coupling coefficient while achieving temperature compensation inside the resonator by controlling the position and thickness of the temperature compensation layer, thereby being able to construct a miniaturized filter with high roll-off performance.

[0021] The present invention uses ZnO as the material of the sacrificial layer and adopts dilute hydrochloric acid solution as the etching solution. While completely etching ZnO, the dilute hydrochloric acid solution can also be prevented from etching the insulating layer and the temperature compensation layer, thereby obtaining a high-performance BAW device. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1a A cross-sectional view of a temperature-compensated BAW resonator with adjustable effective electromechanical coupling coefficient provided by a specific embodiment of the present invention; Figure 1b A cross-sectional view of another temperature-compensated BAW resonator with adjustable effective electromechanical coupling coefficient provided by a specific embodiment of the present invention; Figure 2aThe impedance curve of the effective electromechanical coupling coefficient of the BAW resonator provided by the specific embodiment of the present invention changing with the thickness of the temperature compensation layer; Figure 2b A comparison diagram of impedance curves of a temperature-compensated BAW resonator with adjustable effective electromechanical coupling coefficient, a BAW resonator with a temperature compensation layer located above a passivation protection layer, and a traditional BAW resonator provided in a specific embodiment of the present invention; Figure 3 A flow chart for preparing a temperature-compensated BAW resonator with adjustable effective electromechanical coupling coefficient provided by a specific embodiment of the present invention; Figure 4a-4l A processing flow chart of a temperature-compensated BAW resonator with adjustable effective electromechanical coupling coefficient provided by a specific embodiment of the present invention; Figure 5a This is the topological structure diagram of the traditional BAW filter; Figure 5b A topological structure diagram after replacing the original structure with a temperature-compensated BAW resonator with adjustable effective electromechanical coupling coefficient provided by a specific embodiment of the present invention; Figure 5c A performance comparison diagram of a temperature-compensated BAW filter with adjustable effective electromechanical coupling coefficient provided by a specific embodiment of the present invention and a traditional BAW filter; Figure 6a A transmission curve diagram of a BAW filter according to a specific embodiment of the present invention that varies with temperature; Figure 6b This is the transmission curve of the traditional BAW filter as the temperature changes. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with the embodiments and drawings. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0024] In order to realize a miniaturized filter, the specific embodiment of the present invention controls the effective electromechanical coupling coefficient by controlling the position of the temperature compensation layer and the thickness relationship between the temperature compensation layer and the piezoelectric layer, thereby achieving the effect of an external passive device, which is equivalent to integrating the external passive device into the filter provided by the specific embodiment of the present invention. The temperature-compensated BAW device with an adjustable effective electromechanical coupling coefficient provided by the specific embodiment of the present invention is as follows. Figure 1a and Figure 1b As shown, the specific description is as follows, including: A low-resistance substrate 100 , an insulating layer 102 , a piezoelectric oscillator stack, and a first cavity 113 . The piezoelectric oscillator stack is located on the substrate 100 , and the first cavity 113 is located between the piezoelectric oscillator stack and the insulating layer 102 .

[0025] The piezoelectric oscillator stack provided in a specific embodiment of the present invention includes a first electrode 104, a temperature compensation layer 105, a piezoelectric layer 106, a second electrode 107 and a passivation protection layer 108; wherein, the first electrode 104 is located on the first cavity 113, the piezoelectric layer 106 is located on the first electrode 104, the second electrode 107 is located on the piezoelectric layer 106, the passivation protection layer 108 is located on the second electrode 107, and the temperature compensation layer 105 can be selectively located between the first electrode 104 and the piezoelectric layer 106, or between the second electrode 107 and the piezoelectric layer 106.

[0026] The BAW device provided in a specific embodiment of the present invention also includes a metal pad layer, which includes a first metal pad layer 111 and a second metal pad layer 111-1; the first metal pad layer 111 is connected to the first electrode 104; the second metal pad layer 111-1 is connected to the second electrode 107, and is used to lead out the first electrode 104 and the second electrode 107.

[0027] The temperature-compensated BAW device with an adjustable effective electromechanical coupling coefficient provided in a specific embodiment of the present invention realizes a BAW device with a low-frequency temperature coefficient by adding a temperature compensation layer 105 between the first electrode 104 and the piezoelectric layer 106, or between the second electrode 107 and the piezoelectric layer 106. Among them, since the temperature compensation layer provided by the present invention is located between the piezoelectric oscillator stacks, when there is a potential difference between the first electrode and the second electrode of the BAW resonator, additional parasitic capacitance will be introduced into the resonator, resulting in a certain reduction in the effective electromechanical coupling coefficient of the resonator. At the same time, the relationship between the thickness of the temperature supplementary layer and the thickness of the piezoelectric layer is controlled to satisfy the following formula: 0.01≤thickness of the temperature compensation layer / thickness of the piezoelectric layer≤0.5, which can achieve the same function as an external passive capacitor, adjust the effective electromechanical coupling coefficient of the BAW resonator, and realize the miniaturization of the device while improving the roll-off of the BAW filter.

[0028] like Figure 2a As shown, when the SiO2 temperature compensation layer 105 is located between the first electrode 104 and the piezoelectric layer 106, the effective electromechanical coupling coefficient of the BAW resonator gradually decreases with the increase of the thickness of the SiO2 temperature compensation layer 105 when the thickness of other layers remains unchanged. This step will cause the BAW resonator frequency to shift to a low frequency, and the shifted resonant frequency can be adjusted to the desired resonant frequency by adjusting the thickness of other layers.

[0029] Table 1 shows the effect of the thickness of the temperature compensation layer 105 on the BAW resonator after the temperature compensation layer 105 is added between the first electrode 104 and the piezoelectric layer 106. When the thickness of each layer described in Table 1 is met and scandium-doped AlN is used as the piezoelectric layer, the relationship between the thickness of the temperature compensation layer and the effective electromechanical coupling coefficient approximately satisfies the following formula: Effective electromechanical coupling coefficient = -0.0078*temperature compensation layer thickness + 13.091.

[0030] Table 1 Influence of the thickness of the temperature compensation layer 105 on the BAW resonator when the SiO2 temperature compensation layer 105 is located between the first electrode 104 and the piezoelectric layer 106

[0031] Table 2 shows the effect of the thickness of the temperature compensation layer on the BAW resonator after adding the temperature compensation layer between the second electrode 107 and the piezoelectric layer 106. When the temperature compensation layer is located between the second electrode and the piezoelectric layer and satisfies the thickness of each layer as described in Table 2 below and a specific scandium-doped AlN is used as the piezoelectric layer, the relationship between the thickness of the temperature compensation layer and the effective electromechanical coupling coefficient approximately satisfies the following formula: Effective electromechanical coupling coefficient = -0.0084*temperature compensation layer thickness + 13.094.

[0032] Table 2 Influence of the thickness of the temperature compensation layer 105 on the BAW resonator when the SiO2 temperature compensation layer 105 is located between the second electrode 107 and the piezoelectric layer 106

[0033] Table 3 shows the effect of the thickness of the temperature compensation layer 105 on the BAW resonator when the SiO2 temperature compensation layer 105 is located above the passivation protection layer. When the thickness of each layer described in Table 1 is met and scandium-doped AlN is used as the piezoelectric layer, the relationship between the thickness of the temperature compensation layer and the effective electromechanical coupling coefficient approximately satisfies the following formula: Effective electromechanical coupling coefficient = temperature compensation layer thickness * temperature compensation layer thickness * 0.000001-0.0007*temperature compensation layer thickness + 13.13.

[0034] Table 3 Effect of the thickness of the temperature compensation layer 105 on the BAW resonator when the SiO2 temperature compensation layer 105 is located above the passivation protection layer

[0035] It can be seen from Tables 1 and 2 that when the thickness of other layers remains unchanged, as the thickness of the temperature compensation layer increases, the BAW resonator gradually becomes smaller, which is consistent with the function that can be achieved by the external passive capacitor; Correspondingly, it can be seen from Table 3 that when the thickness of other layers remains unchanged, the effect of a small change in the thickness of the temperature compensation layer on the effective electromechanical coupling coefficient is almost non-existent. Therefore, when the temperature compensation layer is located between the piezoelectric oscillator stacks, the adjustment effect on the effective electromechanical coupling coefficient of the resonator is the best, while when it is located on the passivation protection layer, the adjustment effect is poor.

[0036] Figure 2b A comparison of impedance curves of three different types of BAW resonators is shown, namely: a temperature compensated BAW resonator with an adjustable effective electromechanical coupling coefficient, a BAW resonator with a temperature compensation layer located above the passivation protection layer, and a traditional BAW resonator. Among them, the temperature compensation layer thickness of the BAW resonator containing the temperature compensation layer is the same. The effective electromechanical coupling coefficients corresponding to the three different BAW resonators are shown in Table 4. It can be seen that the temperature compensation layer located between the piezoelectric oscillator stacks has the greatest influence on the effective electromechanical coupling coefficient of the resonator. Therefore, the temperature compensation layer located between the piezoelectric oscillator stacks used in the present invention can achieve the adjustment of the effective electromechanical coupling coefficient with the smallest thickness.

[0037] Table 4 Effect of temperature compensation layers of the same thickness at different positions on the BAW resonator

[0038] A specific embodiment of the present invention provides a method for preparing a temperature-compensated BAW device with an adjustable effective electromechanical coupling coefficient, comprising: S1, a cavity is provided in the insulating substrate; S2, filling the cavity to form a sacrificial layer, wherein the material of the sacrificial layer is ZnO; S3, forming a piezoelectric oscillation stack on the insulating substrate and the sacrificial layer; S4, etching the piezoelectric oscillator stack to form a first window, a second window and a release hole, exposing the first electrode through the first window, and exposing the second electrode through the second window; S5, forming a metal pad layer on the first electrode and the second electrode of the piezoelectric oscillator stack to lead out the first electrode and the second electrode; S6. Corroding the first sacrificial layer with a dilute hydrochloric acid solution through the release hole to form an air gap below the resonant cavity.

[0039] In a specific embodiment of the present invention, the air gap below the resonant cavity is formed by etching the first sacrificial layer with a dilute hydrochloric acid solution through the release hole. Preferably, the concentration of the dilute hydrochloric acid solution is 0.1%-30%. At this concentration, the release rate will not be too slow due to too low a concentration, nor will the hydrochloric acid partially corrode the SiO2 insulating layer due to too high a concentration.

[0040] The material of the piezoelectric layer provided in the specific embodiment of the present invention is AlN and AlxSc(1-x)N. The present invention uses ZnO as a sacrificial layer. Since it has the same wurtzite structure as AlN, it can be used to induce the grain arrangement of Mo, which is conducive to the preferred orientation growth of the Mo (110) film, thereby further enabling the preferred orientation growth of the piezoelectric layer AlN (002) film, so that it has better piezoelectric properties; therefore, the present invention can omit the preparation of the seed layer and the subsequent removal process, and ZnO can be completely released by the release material dilute hydrochloric acid used in the present invention, thereby improving the operating frequency of the device.

[0041] In a specific embodiment, the method for preparing a piezoelectric oscillating stack provided by the specific embodiment of the present invention includes: A first electrode is formed on the insulating substrate and the sacrificial layer, a temperature compensation layer is formed on the first electrode and above the cavity, a piezoelectric layer is formed on the first electrode and the temperature compensation layer, a second electrode is formed on the piezoelectric layer, and a passivation protection layer is formed on the second electrode; Alternatively, a first electrode is formed on the insulating substrate and the sacrificial layer, a piezoelectric layer is formed on the first electrode, a temperature compensation layer is formed on the piezoelectric layer and above the cavity, a second electrode is formed on the piezoelectric layer and the temperature compensation layer, and a passivation protective layer is formed on the second electrode.

[0042] The temperature compensation layer material TeO provided in the specific embodiment of the present invention x 、Cr、SiO2、doped SiO2、ZrW2O8、ZrV2O7、ZrMo2O8、HfMo2O8、HfW2O8、HfV2O7、Sc(WO4)3、LiAlSiO4、Lu2W3O 12 , and BiFeO3, etc.

[0043] A specific embodiment of the present invention further provides a method for preparing a BAW device with a temperature compensation layer and a BAW device without a temperature compensation layer in the same BAW filter. Figure 3 As shown, including: like Figure 4aAs shown, the silicon substrate 100 is ultrasonically cleaned with an SPM solution, and a first cavity 101 and a second cavity 101-1 are formed on the silicon substrate 100 by a dry etching process. The lateral width of the first cavity 101 and the reserved window 101-1 for placing passive devices can be changed according to actual needs. The etching angle of the cavity sidewall is 100° to 120°, which is convenient for sufficient filling of the sacrificial layer. The etching depth is about 3.5μm, and the cavity depth under BAW only needs to be sufficient to accommodate the displacement generated by the piezoelectric layer. The insulating substrate of the acoustic device has a higher resistivity to prevent the substrate from coupling with the resonator, or a lower resistivity, but an insulating layer needs to be formed on the lower resistivity substrate to prevent the low resistance contrast from coupling with the resonator. In one embodiment, the insulating substrate provided by the following method includes an insulating layer and a low resistivity substrate.

[0044] Preferably, the material of the low-resistivity substrate 100 used in the specific embodiment of the present invention is Si, and its resistivity is less than 10Ω·cm.

[0045] like Figure 4b As shown, a layer of thermal oxide SiO2 is grown on the surface of the substrate to form an insulating layer 102 to prevent Zn in ZnO from diffusing into the substrate. Such diffusion will cause the surface of the silicon substrate 100 to be conductive, thereby shunting the radio frequency signal from the thin film bulk acoustic wave resonator and interfering with the electrical operation of the final device. The thermal oxidation growth method has better film density than methods such as PECVD or LPCVD, so as to protect the substrate when the sacrificial layer is released. Preferably, the thickness of the insulating layer is 100nm to 5000nm.

[0046] For those skilled in the art, other materials are also optional. For example, the material of the insulating layer is formed of at least one of silicon dioxide (SiO2), silicon nitride (Si3N4), aluminum oxide (Al2O3) and aluminum nitride (AlN).

[0047] The insulating substrate constructed in the above manner can better avoid the interference of the substrate on the device performance.

[0048] like Figure 4c As shown, a layer of zinc oxide (ZnO) is deposited on the insulating layer 102 by the PECVD method as a sacrificial layer material, and the wafer surface is flattened by CMP treatment to form a sacrificial layer filling 103, 103-1 with an edge gap less than 30nm.

[0049] In a specific embodiment of the present invention, ZnO is selected as the sacrificial layer material, and the AlN piezoelectric film is a wurtzite structure, a hexagonal crystal form, and the (002) preferred orientation growth requires that the lower electrode film is of the same crystal form, or a face-centered cubic crystal form (111) orientation, or a body-centered cubic (110) orientation. When the lattice arrangement of the electrode material is closer to the lattice arrangement of the (002) plane of the AlN film, it is more conducive to the preferred orientation growth of the AlN film. In the traditional BAW device preparation process, a layer of AlN seed layer is deposited before depositing the bottom electrode to induce the grain arrangement of Mo, which is conducive to the preferred orientation growth of the Mo (110) film, thereby further enabling the piezoelectric layer AlN (002) film to grow in a preferred orientation, so that it has better piezoelectric properties. When ZnO is used as the sacrificial layer material, since ZnO has the same wurtzite structure as AlN, the preparation of the seed layer and the subsequent removal process can be omitted.

[0050] Since the rough surface is not conducive to the columnar growth of piezoelectric materials in the plane perpendicular to the electrode, the smooth surface after CMP treatment in the specific embodiment of the present invention can provide a basis for the deposition of highly textured c-axis piezoelectric materials, so that the subsequent steps can have excellent piezoelectric performance. A higher quality piezoelectric layer can realize a higher quality resonator, thereby realizing a higher quality filter circuit.

[0051] like Figure 4d As shown, after cleaning the surface after the CMP step, a layer of metal molybdenum (Mo) is deposited on the substrate 100 and the sacrificial layers 103 and 103-1 by thermal evaporation or magnetron sputtering, and dry etching is used to form the first electrodes 104 and 104-1 of the BAW device.

[0052] For those skilled in the art, other materials are also optional. For example, the first electrode is Al, W, Au, Pt or Ti.

[0053] In one embodiment, the electrode material for depositing the first electrode in this embodiment is molybdenum. Since the temperature is extremely high when manufacturing the piezoelectric film, the electrode is mostly made of heavy metals such as molybdenum that can withstand high heat. The mass compound effect of the electrode will be particularly prominent and compatible with the etching of AlN. Preferably, the thickness of the first electrode is 10nm to 1000nm.

[0054] like Figure 4e As shown, a layer of SiO2 is deposited on the surface of the first electrode 104 - 1 by a thermal oxidation method as the temperature compensation layer 105 .

[0055] For those skilled in the art, other materials are also optional. For example, the temperature compensation layer can be TeO x、Cr、SiO2、doped SiO2、ZrW2O8、ZrV2O7、ZrMo2O8、HfMo2O8、HfW2O8、HfV2O7、Sc(WO4)3、LiAlSiO4、Lu2W3O 12 , and BiFeO3 and other materials.

[0056] The temperature compensation layer provided in this embodiment has a thickness of 10 nm to 2000 nm.

[0057] In particular, the temperature compensation layer can be located between the piezoelectric layer and the second electrode, or between the piezoelectric layer and the first electrode, and can also play a role in adjusting the effective electromechanical coupling coefficient of the BAW device. For different embodiments, it is necessary to specifically study the different positions of the temperature compensation layer to achieve the optimal effect.

[0058] In a specific embodiment, the material of the temperature compensation layer 105 provided in this embodiment is SiO2.

[0059] like Figure 4f As shown, a layer of scandium-doped aluminum nitride (AlScN) as the piezoelectric layer 106 is deposited on the surface of the substrate 100, the first electrodes 104, 104-1, and the temperature compensation layer 105 by magnetron sputtering or MOCVD.

[0060] The AlxSc(1-x)N piezoelectric layer 106 is typically c-axis oriented and is typically 0.5≤x≤1, and preferably 0.57≤x≤1. These films have a root mean square (RMS) surface roughness of less than 1 nm and a rocking curve value of less than 500 arc seconds.

[0061] The ideal candidates for the piezoelectric layer 106 material provided in the specific embodiment of the present invention are: crystalline BaxSr(1-x)TiO3 (BST), zinc oxide (ZnO), aluminum nitride (AlN), doped aluminum nitride, lead zirconate titanate, quartz and other materials. Doped aluminum nitride may also include rare earth metals, transition metals or alkaline earth metals. Rare earth metals may include at least one of scintillation (Sc), erbium (Er), ytterbium (Y) and ytterbium (La). Transition metals may include at least one of helium (Hf), titanium (Ti), zirconium (Zr), tantalum (Ta) and niobium (Nb). In addition, alkaline earth metals may include magnesium (Mg). Adding gallium or scandium to the AlN lattice can increase the effective electromechanical coupling coefficient for a wider bandwidth resonator.

[0062] In a specific embodiment, the piezoelectric layer provided in this embodiment is made of aluminum nitride piezoelectric single crystal resonant material. Preferably, the thickness of the piezoelectric layer is 10 nm to 4000 nm.

[0063] Figure 4gAs shown, a layer of metal molybdenum (Mo) is deposited on the surface of the piezoelectric layer 106 by magnetron sputtering or MOCVD, and then dry-etched to form the common second electrode 107 of the BAW device.

[0064] Figure 4h As shown, a layer of metal molybdenum (Mo) is deposited on the surface of the second electrode 107 by magnetron sputtering or MOCVD to form a second electrode thickening layer 107 - 1 for BAW devices with different electrode thicknesses.

[0065] The main function of this step is to adjust the resonant frequency of the BAW resonator after adding the temperature compensation layer by adjusting the layer thickness. In particular, the frequency adjustment of the BAW resonator can also be achieved by adjusting the thickness of other layers, such as the first electrode 104, the piezoelectric layer 106 and the passivation protection layer 108.

[0066] For those skilled in the art, other materials are also optional. For example, the electrode can be made of Al, W, Au, Pt or Ti, and the material of the protrusion structure can be different from the electrode material.

[0067] Preferably, the thickness of the second electrode is 10 nm to 1000 nm.

[0068] like Figure 4i As shown, a layer of silicon dioxide (SiO2) is deposited on the surface of the second electrode 107, 107-1 by magnetron sputtering or MOCVD, and a passivation protection layer 108, 108-1 is formed after dry etching to expose the window 109 of the second electrode 108 of the BAW device.

[0069] The passivation protective layer provided in the specific embodiment of the present invention can be, for example but not limited to SiO2, AlN, TiN, silicon, chromium or any other suitable material or combination of materials. The passivation protective layer is a part of the resonator and affects the performance of the resonator. The passivation protective layer is generally made of an inert material that is not easily interacted with the environment, which can prevent the top electrode from being exposed to the air and oxidized. At the same time, adjusting the thickness of the passivation protective layer can adjust the operating frequency of the resonator.

[0070] Preferably, this embodiment uses SiO2, which is the same material as the insulating layer and the temperature compensation layer. Preferably, the thickness of the passivation protection layer is 100 nm to 2000 nm.

[0071] like Figure 4j As shown, the piezoelectric layer 106 is dry-etched to form windows 110, 110-1, and release holes 110-2, 110-3 that expose the first electrode 104 of the BAW device. The lateral width of the windows 110, 110-1 can be changed according to actual needs. The release holes 110-2 and 110-3 are not in the same cross section and are indicated by dotted lines.

[0072] like Figure 4k As shown, a layer of gold is deposited on the piezoelectric layer 106, the passivation protection layer 108 and the windows 109, 110, and 110-1 by thermal evaporation or magnetron sputtering, and a first metal pad layer 111, a second metal pad layer 111-1, and a third metal pad layer 111-2 are formed by dry etching or wet etching. The first metal pad layer 111 and the third metal pad layer 111-2 are not connected to the BAW second electrode 107.

[0073] The metal pad layer may be one of molybdenum, gold, platinum, copper, aluminum, silver, titanium, tungsten, nickel or any group thereof.

[0074] Preferably, gold is used as the material of the metal pad layer in this embodiment. Preferably, the thickness of the metal pad layer is 50 nm to 12000 nm.

[0075] like Figure 4l As shown, a dilute hydrochloric acid (HCl) solution is used to etch the ZnO filler in the ZnO sacrificial layers 103 and 103 - 1 to form a first cavity 113 and a second cavity 113 - 1 .

[0076] A specific embodiment of the present invention further provides a filter circuit with high roll-off based on the BAW resonator of the present invention. Figure 5a The filter shown shows a traditional ladder filter topology, which is realized by arranging BAW resonators in series and in parallel. Part or all of the BAW resonators are replaced with a temperature-compensated BAW resonator with adjustable electromechanical coupling coefficient based on the present invention, so that a temperature-compensated BAW filter with a higher roll-off than a traditional BAW filter can be realized. In a specific embodiment, Figure 5b As shown, the specific embodiment of the present invention replaces two series BAW resonators in the series circuit of the traditional ladder filter topology structure with a temperature compensated BAW device with adjustable effective electromechanical coupling coefficient provided by the specific embodiment of the present invention.

[0077] Figure 5c As shown, based on the filter composed of the temperature-compensated BAW resonator with adjustable electromechanical coupling coefficient of the present invention, curve 1 is Figure 5a The corresponding BAW filter transmission response curve, curve 2 is Figure 5b Corresponding transmission response curve of the BAW filter. Without external passive devices, the BAW filter provided by the specific embodiment of the present invention achieves higher roll-off performance while achieving temperature compensation, further improving the anti-interference ability of adjacent bands, and providing a solution to the anti-interference ability and miniaturization problem of the BAW filter.

[0078] Figure 6a The transmission curve of the filter composed of the BAW resonator according to the present invention changes with temperature. As the temperature changes, there is basically no deviation in the transmission curve, and the transmission curve has high frequency stability.

[0079] Figure 6b The transmission curve of the filter composed of traditional BAW resonators changes with temperature. As the temperature changes, the transmission curve will shift significantly, which has a great impact on the actual application of the filter.

Claims

1. A temperature-compensated BAW device with adjustable effective electromechanical coupling coefficient, characterized in that: include: Insulating substrate; A piezoelectric oscillator stack comprises a first electrode, a piezoelectric layer, a second electrode and a passivation protection layer sequentially stacked on the insulating substrate; A temperature compensation layer is located between the first electrode and the piezoelectric layer, or between the second electrode and the piezoelectric layer; A cavity is disposed between the substrate and the first electrode; The relationship between the thickness of the temperature compensation layer and the thickness of the piezoelectric layer satisfies the following formula: 0.01≤thickness of temperature compensation layer / thickness of piezoelectric layer≤0.

5.

2. The temperature-compensated BAW device with adjustable effective electromechanical coupling coefficient according to claim 1, characterized in that: The thickness of the first electrode is 10nm-1000nm, the thickness of the second electrode is 10nm-1000nm, the thickness of the piezoelectric layer is 10nm-4000nm, and the thickness of the temperature compensation layer is 10nm-2000nm.

3. The temperature-compensated BAW device with adjustable effective electromechanical coupling coefficient according to claim 1, characterized in that: The insulating substrate comprises an insulating layer and a low-resistance substrate, the insulating layer is located on the low-resistance substrate, and the material of the low-resistance substrate is silicon with a resistivity less than 10Ω·cm; Or the insulating substrate is a high-resistance substrate; or the insulating substrate is a high-resistance substrate and an insulating layer, and the insulating layer is located on the high-resistance substrate; The resistivity of the high-resistance substrate is greater than 1000Ω·cm.

4. The temperature-compensated BAW device with adjustable effective electromechanical coupling coefficient according to claim 3, characterized in that: The material of the high-resistance substrate is one of silicon, ceramic, sapphire and the like or any combination thereof.

5. The temperature-compensated BAW device with adjustable effective electromechanical coupling coefficient according to claim 1, characterized in that: The temperature compensation layer is located above the cavity.

6. The temperature-compensated BAW device with adjustable effective electromechanical coupling coefficient according to claim 1, characterized in that: The material of the temperature compensation layer is TeO x 、Cr、SiO2、doped SiO2、ZrW2O8、ZrV2O7、ZrMo2O8、HfMo2O8、HfW2O8、HfV2O7、Sc(WO4)3、LiAlSiO4、Lu2W3O 12 , and BiFeO3.

7. A method for preparing a temperature-compensated BAW device with adjustable effective electromechanical coupling coefficient according to any one of claims 1 to 6, characterized in that: include: S1, a cavity is provided in the insulating substrate; S2, filling the cavity to form a sacrificial layer, wherein the material of the sacrificial layer is ZnO; S3, forming a piezoelectric oscillation stack on the insulating substrate and the sacrificial layer; S4, etching the piezoelectric oscillator stack to form a first window, a second window and a release hole, exposing the first electrode through the first window, and exposing the second electrode through the second window; S5, forming a metal pad layer on the first electrode and the second electrode of the piezoelectric oscillator stack to lead out the first electrode and the second electrode; S6. Corroding the first sacrificial layer with a dilute hydrochloric acid solution through the release hole to form an air gap below the resonant cavity.

8. The method for preparing a temperature-compensated BAW device with an adjustable effective electromechanical coupling coefficient according to claim 7, wherein the method for preparing the piezoelectric oscillator stack comprises: A first electrode is formed on the insulating substrate and the sacrificial layer, a temperature compensation layer is formed on the first electrode and above the cavity, a piezoelectric layer is formed on the first electrode and the temperature compensation layer, a second electrode is formed on the piezoelectric layer, and a passivation protection layer is formed on the second electrode; Alternatively, a first electrode is formed on the insulating substrate and the sacrificial layer, a piezoelectric layer is formed on the first electrode, a temperature compensation layer is formed on the piezoelectric layer and above the cavity, a second electrode is formed on the piezoelectric layer and the temperature compensation layer, and a passivation protective layer is formed on the second electrode.

9. A filter, comprising a series branch and a parallel branch, wherein the series branch or the parallel branch comprises at least two series BAW resonators connected in series between the input and output ends of the filter, a parallel branch is provided between the connection point of adjacent series BAW resonators and the ground end, the parallel branch comprises one parallel BAW resonator or a plurality of parallel BAW resonators connected in series, characterized in that: At least one of the series or parallel BAW resonators is a temperature-compensated BAW device with an adjustable effective electromechanical coupling coefficient as described in any one of claims 1 to 8.

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