Bulk acoustic wave monolithic hybrid filter of integrated passive device and preparation method therefor

Abstract

Provided in the present application are a preparation method for a bulk acoustic wave monolithic hybrid filter of an integrated passive device, comprising: (1) by means of deposition, preparing a leakage isolation layer on a support substrate; (2) by means of physical vapor deposition, obtaining an inductance layer on the leakage isolation layer prepared in step (1), keeping a TGV inductance stack cross section on a mask to surround a bottom window of a trench, and patterning inductance metal; (3) by means of chemical vapor deposition, obtaining an insulating layer on the inductance metal prepared in step (2) and, by means of lithography, obtaining a lead through hole; (4) alternately repeating step (2) and step (3) to obtain a three-layer stacked TGV inductor; (5) by means of chemical vapor deposition, depositing an insulating layer again above the TGV inductor prepared in step (4); (6) by means of physical vapor deposition, depositing two capacitance layers on the insulating layer deposited in step (5), and depositing an insulating layer between the two capacitance layers to form an MIM capacitor; and (7) preparing a BAW resonator on the MIM capacitor prepared in step (6) and, by means of the lead through hole, connecting the TGV inductor, the MIM capacitor and the BAW resonator.

Description

A bulk acoustic wave monolithic hybrid filter with integrated passive devices and its preparation method Technical Field

[0001] The present application relates to the field of third-generation semiconductor technology and radio frequency front-end devices, and in particular to a bulk acoustic wave monolithic hybrid filter with integrated passive devices and a preparation method thereof. Background Art

[0002] RF front-end chips are extremely important strategic devices in the semiconductor industry chain and are core components of smart communication products such as mobile phones. According to the China Industry Information Network, the use of filters will further increase in the 5G era. Filters have surpassed PAs to become the most important component in the entire RF front-end module market. High-frequency, broadband RF filters also play a strategically important role in military communications, with applications in satellite communications, phased array radar, guided artillery, and other military applications.

[0003] According to the international radio regulations promulgated by the International Telecommunication Union (ITU), most of the frequency resources in the low-frequency band (0.6-2 GHz) are already occupied by 1G-4G technologies. To increase transmission speeds while minimizing overlap with already developed frequency bands, the 5G frequency band has been expanded to include the Sub6G (0.4-6 GHz) and millimeter wave (26.5-300 GHz) bands. Unlike the (1T2R) antenna modulation technology used in the 4G band, 5G technology uses (MIMO) modulation technology, which deploys multiple antennas at the transmitter and receiver to expand communication paths, exponentially increasing the number of communication paths. RF filters have experienced rapid development in the 5G era. For example, in the 4G era, the iPhone 8 supported approximately 20 frequency bands, including 1G / 2G / 3G / 4G, requiring at least two filters in the transceiver system for each band. The iPhone 12 5G version now supports 17 Sub6G bands and 3 millimeter wave bands, increasing the number of filters in a single device to over 40.

[0004] In recent years, bulk acoustic wave (BAW) resonators have become the only integrable RF front-end filter due to their advantages, including high frequency, miniaturization, high performance, low power consumption, and high power handling. Furthermore, BAW filter manufacturing processes are compatible with IC processes and can be integrated, which helps reduce device power consumption and size. Therefore, BAW filters will become a core component for future 5G high-frequency communications. BAW filters, using micromachining technology (MEMS), can operate in frequencies ranging from hundreds of MHz to tens of GHz, fully covering the requirements of the wireless communication frequency band. Traditional dielectric filters are too large, and SAW filters have higher insertion loss than BAW filters, and cannot meet the requirements of high frequencies (>3 GHz). Therefore, BAW filters are the optimal solution for high-frequency bands above 3 GHz.

[0005] Currently, BAW typically uses AlN thin film as the resonator piezoelectric layer material. This is because compared to traditional piezoelectric materials such as ZnO and PZT, AlN thin film materials have excellent physical properties such as high resistivity, high thermal conductivity, high stability, and high acoustic wave transmission rate. However, the small piezoelectric coefficient limits the strain capacity of AlN thin film in the high-frequency band. To solve this bottleneck of AlN thin film materials while retaining other excellent properties, the current method is to enhance its piezoelectric properties by doping it.

[0006] However, doping technology still has key drawbacks that need to be overcome. Sc doping increases lattice scattering within the AlScN crystal, introduces additional lattice stress, and alters the electronic properties of AlN. This leads to increased acoustic wave propagation losses within the AlScN crystal, ultimately reducing the filter's quality factor (Q). This increases the filter's in-band insertion loss, reducing the signal quality of in-band communications.

[0007] While LC filters can achieve a wide bandwidth, they have poor roll-off, limiting their application in today's crowded and scarce spectrum landscape. The current method for improving LC filter roll-off is to increase the order, using more capacitors and inductors to enhance signal filtering. However, this results in an exponential increase in filter size, and the increased number of capacitors and inductors leads to increased signal loss, which reduces the filter's Q factor.

[0008] Summary of the Invention

[0009] This application aims to solve the problems of BAW circuits that are difficult to achieve large bandwidth, poor LC circuit roll-off and signal screening capabilities, and the difficulty in reducing the filter volume due to the need to set multiple capacitors and inductors in high-order LC circuits. It provides a bulk acoustic wave monolithic hybrid filter with integrated passive components and a preparation method thereof to solve the problems existing in the related art. The technical solution is as follows:

[0010] In a first aspect, an embodiment of the present application provides a method for preparing a bulk acoustic wave monolithic hybrid filter with integrated passive components, comprising:

[0011] (1) preparing a leakage isolation layer on a supporting substrate by deposition;

[0012] (2) forming an inductor layer on the leakage isolation layer prepared in step (1) by physical vapor deposition, leaving a window at the bottom of the trench surrounding the cross section of the TGV inductor stack on the mask, and patterning the inductor metal at the same time;

[0013] (3) forming an insulating layer on the inductor metal prepared in step (2) by chemical vapor deposition, and forming lead through holes by photolithography;

[0014] (4) Repeating steps (2) and (3) alternately to obtain a three-layer stacked TGV inductor;

[0015] (5) depositing another insulating layer on the TGV inductor prepared in step (4) by chemical vapor deposition to serve as a partition between the capacitor layer and the TGV inductor;

[0016] (6) depositing two capacitor layers on the insulating layer deposited in step (5) by physical vapor deposition, and depositing an insulating layer between the two capacitor layers to form a MIM capacitor;

[0017] (7) A BAW resonator is prepared on the MIM capacitor prepared in step (6), and the TGV inductor, MIM capacitor and BAW resonator are connected through lead through-holes to obtain a bulk acoustic wave monolithic hybrid filter with integrated passive devices.

[0018] In one embodiment, the BAW resonator connection includes a bottom electrode, a piezoelectric layer, a top electrode, and an anti-oxidation layer arranged in sequence, and an air gap is formed between the bottom electrode and the MIM capacitor.

[0019] In one embodiment, the bottom electrode and the top electrode are made of one or more of aluminum, molybdenum, tungsten, platinum, titanium, and gold.

[0020] In one embodiment, the material of the piezoelectric layer is single-crystalline aluminum nitride, or polycrystalline aluminum nitride, or zinc oxide, or lead zirconate titanate, or BST, or LiNbO 3 .

[0021] In one embodiment, the material of the anti-oxidation layer is aluminum nitride.

[0022] In one embodiment, the support substrate is made of silicon, sapphire, LiGaO2, or metal.

[0023] In one embodiment, the material of the leakage isolation layer is gallium arsenide.

[0024] In one embodiment, the insulating layer is made of silicon dioxide.

[0025] In one embodiment, the material of the lead through hole is gold, copper, or molybdenum.

[0026] In one embodiment, the material of the inductor layer is copper.

[0027] In one embodiment, the capacitor layer is made of copper.

[0028] In a second aspect, an embodiment of the present application provides a bulk acoustic wave monolithic hybrid filter with integrated passive components, comprising:

[0029] a supporting substrate;

[0030] an isolation leakage layer, the isolation leakage layer being provided on the supporting substrate;

[0031] An IPD inductor structure, wherein the IPD inductor structure is provided on the isolation leakage layer;

[0032] An IPD capacitor structure, wherein the IPD capacitor structure is arranged on the IPD inductor structure;

[0033] A BAW resonator, wherein the BAW resonator is arranged on the IPD capacitor structure;

[0034] The IPD capacitor structure and the BAW resonator are connected through lead vias.

[0035] In one embodiment, the IPD inductor structure includes one or more combinations of TGV inductors, meander line inductors, square spiral inductors, circular spiral inductors, and octagonal spiral inductors;

[0036] When the IPD inductor structure is a TGV inductor, the bulk acoustic wave monolithic hybrid filter with integrated passive devices is prepared by any of the above methods for preparing a bulk acoustic wave monolithic hybrid filter with integrated passive devices.

[0037] In one embodiment, the IPD capacitor structure includes one or more combinations of MIM capacitors, interdigital capacitors, and VLC capacitors;

[0038] When the IPD capacitor structure is a MIM capacitor, the bulk acoustic wave monolithic hybrid filter with integrated passive devices is prepared by any of the above methods for preparing a bulk acoustic wave monolithic hybrid filter with integrated passive devices.

[0039] The advantages or beneficial effects of the above technical solution include at least:

[0040] The present application provides a bulk acoustic wave monolithic hybrid filter with integrated passive devices and a preparation method thereof, which utilizes the hybrid integration technology of BAW and IPD inductors and LC circuits. It innovatively uses IPD technology to integrate inductors and capacitors with resonators through integrated etching and molding based on BAW resonators, breaking through the traditional BAW preparation route and realizing the preparation of new BAW devices with large bandwidth, high carrying power and high roll-off. It solves the problems of traditional BAW being difficult to achieve large bandwidth, poor roll-off and signal screening capability of LC circuits, and difficulty in reducing the filter volume due to the need to set multiple capacitors and inductors in high-order LC circuits.

[0041] This application is a monolithic integrated structure, a structure in which the non-substrate IPD and the BAW filter are connected via solder balls, and a lead connection structure between the non-monolithic IPD and the monolithic BAW filter. Compared with the current production method of placing winding inductors on the substrate, this application uses IPD integrated capacitors and inductors to greatly reduce the size of the filter. At the same time, monolithic integration technology avoids processes such as bonding and welding that have a greater impact on yield, greatly simplifying the production process and manufacturing difficulty, thereby improving the stability of the device, effectively reducing the complexity of production and reducing the size of the filter, thereby reducing the cost of filter production, and the entire process is relatively simple and easy to implement.

[0042] The above summary is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments and features described above, further aspects, embodiments and features of the present application will be readily apparent by reference to the accompanying drawings and the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the multiple drawings represent the same or similar components or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings only depict some embodiments disclosed in this application and should not be construed as limiting the scope of this application.

[0044] Figures 1 to 30 are schematic diagrams of the structures of the prepared samples in steps (1) to (7) in Example 1.

[0045] FIG31 is a transmission curve diagram of a filter composed of two BAW resonators extracted from Example 1. ...

[0046] FIG32 is a schematic diagram showing the passband ripple of Example 1 of the present application.

[0047] Figure 33 is a schematic diagram of the parameter curve S21 of Example 1 of the present application.

[0048] Figure 34 is a schematic diagram of the parameter curve S21 of Comparative Example 2. Implementation Method

[0049] Hereinafter, only certain exemplary embodiments are briefly described. As will be appreciated by those skilled in the art, the described embodiments may be modified in various ways without departing from the spirit or scope of the present application. Therefore, the drawings and description are to be regarded as illustrative in nature and not restrictive.

[0050] In a first aspect, an embodiment of the present application provides a method for preparing a monolithic hybrid filter of a bulk acoustic wave (BAW) integrated passive device (IPD), comprising:

[0051] (1) A leakage isolation layer is prepared by deposition on a supporting substrate to improve the Q value of the lumped element IPD capacitor and inductor.

[0052] (2) The inductor layer is formed on the leakage isolation layer prepared in step (1) by physical vapor deposition (PVD), and a window around the bottom of the trench of the TGV inductor stack cross section is left on the mask, and the inductor metal is patterned as required.

[0053] (3) An insulating layer (a two-dimensional plate-like thin film, which needs to be deposited between different inductor layers to ensure that mutual inductance and coupling effects do not occur between inductor elements) is obtained by chemical vapor deposition (CVD) on the inductor metal prepared in step (2), and lead holes are obtained by photolithography.

[0054] (4) Repeat steps (2) and (3) alternately to obtain a three-layer stacked TGV inductor (Through Glass Via, TGV).

[0055] (5) Depositing another insulating layer on the TGV inductor prepared in step (4) by chemical vapor deposition as a partition between the capacitor layer and the TGV inductor to avoid a strong dielectric coupling effect.

[0056] (6) Two capacitor layers (two-dimensional plate-like films) are deposited on the insulating layer deposited in step (5) by physical vapor deposition, and an insulating layer is deposited between the two capacitor layers to form a MIM (Metal Insulator Metal) capacitor.

[0057] (7) A BAW resonator is prepared on the MIM capacitor prepared in step (6), and the TGV inductor, MIM capacitor and BAW resonator are connected through lead through-holes to obtain a bulk acoustic wave monolithic hybrid filter with integrated passive devices.

[0058] In one embodiment, the BAW resonator connection includes a bottom electrode, a piezoelectric layer, a top electrode, and an anti-oxidation layer arranged in sequence, with an air gap formed between the bottom electrode and the MIM capacitor. The bottom electrode, the piezoelectric layer, and the top electrode form a sandwich structure.

[0059] The preparation of the anti-oxidation layer is to protect the top electrode from high-temperature oxidation. Under high-frequency conditions, continuous signal access will cause the entire device to heat up. If oxidation occurs on the electrode surface, it will greatly affect the filter's energy conversion efficiency. When preparing the anti-oxidation layer, the thickness margin can be appropriately increased. In the process preparation of this application, the anti-oxidation layer must also have the function of a frequency modulation layer. The thickness of the deposited piezoelectric film fluctuates within an allowable range. The thickness of the piezoelectric layer is directly related to the center frequency of the filter. The center frequency can be fine-tuned by thinning the thickness of the frequency modulation layer (i.e., the anti-oxidation layer).

[0060] In one embodiment, the material of the bottom electrode and the top electrode is one or more of aluminum (Al), molybdenum (Mo), tungsten (W), platinum (Pt), titanium (Ti), and gold (Au).

[0061] In one embodiment, the material of the piezoelectric layer is single-crystalline aluminum nitride, or polycrystalline aluminum nitride, or zinc oxide, or lead zirconate titanate, or BST, or LiNbO 3 .

[0062] In one embodiment, the material of the anti-oxidation layer is aluminum nitride (AlN).

[0063] In one embodiment, the material of the support substrate is silicon, sapphire, LiGaO2, or metal.

[0064] In one embodiment, the material of the leakage isolation layer is gallium arsenide.

[0065] In one embodiment, the insulating layer is made of silicon dioxide (SiO 2 ).

[0066] In one embodiment, the material of the lead through hole is gold, copper, or molybdenum.

[0067] In one embodiment, the material of the inductive layer is copper.

[0068] In one embodiment, the material of the capacitor layer is copper.

[0069] It should be understood that, in specific implementation, input pins, output pins, and ground pins need to be provided, and the materials used are copper (Cu), gold (Au), or molybdenum (Mo).

[0070] In a second aspect, an embodiment of the present application provides a bulk acoustic wave monolithic hybrid filter with integrated passive components, comprising:

[0071] a supporting substrate;

[0072] An isolation leakage layer, the isolation leakage layer is provided on the supporting substrate;

[0073] IPD inductor structure, the IPD inductor structure is arranged on the isolation leakage layer;

[0074] IPD capacitor structure, the IPD capacitor structure is arranged on the IPD inductor structure;

[0075] BAW resonator, the BAW resonator is set on the IPD capacitor structure;

[0076] The IPD capacitor structure, the IPD capacitor structure and the BAW resonator connection are connected through lead vias.

[0077] In one embodiment, the IPD inductor structure includes one or more combinations of a TGV inductor, a meander line inductor, a square spiral inductor, a circular spiral inductor, and an octagonal spiral inductor.

[0078] IPD can be understood as a means of realizing "matching inductive and capacitive circuits, branch series inductors, branch parallel inductors, branch series capacitors, branch parallel capacitors, low-pass filter circuits, high-pass filters, and band-pass filters." In the process of mixing the two technologies of IPD and BAW: 1. Band-pass filters can be realized through IPD and cascaded with BAW band-pass filters. The two work together to achieve the effects of large bandwidth and high roll-off. In the process of using IPD to realize band-pass filters, that is, the process of building circuits, it is usually not a single circuit, but often a combination of branch series inductors, branch parallel inductors, branch series capacitors, and branch parallel capacitors. 2. The matching inductive and capacitive circuits mentioned here use IPD technology to realize matching circuits, which reduces the reflection caused by the signal entering the device, thereby reducing the distortion of the RF signal.

[0079] When the IPD inductor structure is a TGV inductor, the BAW monolithic hybrid filter with integrated passive devices is prepared using the above-mentioned method for preparing the BAW monolithic hybrid filter with integrated passive devices. In this case, the TGV inductor includes a multi-layer stacked structure formed by shaping the inductor layer and the insulating layer.

[0080] In one embodiment, the IPD capacitor structure includes one or more combinations of MIM capacitors, interdigital capacitors, and VLC capacitors.

[0081] MIM capacitors, interdigital capacitors, and VLC capacitors are different forms of IPD capacitors. The examples use MIM capacitors. However, in epitaxial structure design, if the available design space is too small, interdigital capacitors with smaller capacitance that can be fabricated within a single epitaxial layer may be used. The choice is typically based on capacitance and volume, and combinations are often used.

[0082] When the IPD capacitor structure is a MIM capacitor, the BAW monolithic hybrid filter with integrated passive devices is prepared using the above-mentioned method for preparing the BAW monolithic hybrid filter with integrated passive devices. In this case, the MIM capacitor includes a multilayer sandwich structure formed by a capacitor layer, an insulating layer, and a capacitor layer.

[0083] It should be noted that, in specific implementation, the IPD circuit includes one or more combinations of matching inductor and capacitor circuits, branch series inductors, branch parallel inductors, branch series capacitors, branch parallel capacitors, low-pass filter circuits, high-pass filters, and band-pass filters.

[0084] Since the required inductance is relatively large, this application uses TGV inductors, which can be cascaded to achieve higher inductance. Of course, since the circuit uses inductors of different sizes, and small inductance inductors use planar inductors such as circular spiral inductors or octagonal spiral inductors, which often save more space, any combination mentioned in this application may be used.

[0085] The following is a structure of a bulk acoustic wave monolithic hybrid filter with integrated passive devices when the IPD inductor structure is a TGV inductor and when the IPD capacitor structure is a MIM capacitor, including a supporting substrate 1, a leakage isolation layer 2, an inductor layer 3, an insulating layer 4, an inductor layer 5, an insulating layer 6, an inductor layer 7, an insulating layer 8, a capacitor layer 9, an insulating layer 10, a capacitor layer 11, a sacrificial layer 12, a bottom electrode 13, a piezoelectric layer 14, a top electrode 15, an anti-oxidation layer 16, a metal conductive pad 17, an access pin 18, a ground pin 19, an output pin 20, an IPD TGV inductor 21, an IPD MIM capacitor 22, a lead through hole 23, and an air gap 24. Inductive layer 3, insulating layer 4, inductive layer 5, insulating layer 6, and inductive layer 7 together form a TGV inductor 21; capacitor layer 9, insulating layer 10, and capacitor layer 11 together form an IPD MIM capacitor 22; bottom electrode 13, piezoelectric layer 14, top electrode 15, anti-oxidation layer 16, and air gap 24 together form a BAW resonator. The IPD TGV inductor 21, IPD MIM capacitor 22, and BAW resonator are connected via lead vias 23 to form a monolithic bulk acoustic wave hybrid filter with integrated passive components.

[0086] More specifically, the piezoelectric layer 14 is a single-crystal aluminum nitride layer.

[0087] The material for preparing the supporting substrate 1 is a 4-8 inch high-resistance silicon wafer.

[0088] The bottom electrode 13 and the top electrode 15 are made of molybdenum (Mo).

[0089] The leakage isolation layer 2 is made of gallium arsenide.

[0090] The material of the lead through hole 23 is gold (Au).

[0091] The insulating layer material is silicon dioxide (SiO2).

[0092] The material of the anti-oxidation layer (frequency modulation layer) 16 is aluminum nitride (AlN).

[0093] The input pin 18 , the output pin 20 , and the ground pin 19 are made of gold (Au).

[0094] The material of the inductor layers 3 , 5 , and 7 is copper (Cu).

[0095] The material of the capacitor layers 9 and 11 is copper (Cu). Example 1

[0096] A bulk acoustic wave monolithic hybrid filter with integrated passive components is prepared, and the specific steps are as follows:

[0097] (1) First, clean the high-resistance silicon wafer. As shown in Figure 1, select quartz glass (silicon dioxide) with a size of 4 inches and wash it with acetone and anhydrous ethanol. Then, clean it with H2SO4:H2O2:H2O (3:1:1) and HF:H2O (1:10) to remove the oxide and contaminant particles on the silicon surface. Then, wash it with deionized water for 10 minutes. Finally, spin dry and wash it with HF solution at a concentration of 1.5%. Put it in an oven to dry for use.

[0098] (2) As shown in Figure 2, a high-quality AsGa (gallium arsenide) leakage isolation layer 2 is grown on a high-resistance silicon substrate. During the growth process, the GaAs low-temperature nucleation layer is fed with AsH3 at a flow rate of 4.5×10 -3 mol / min, TMGa flow rate 1.8×10 -5 mol / min, the AsH3 flow rate of GaAs high temperature epitaxial layer and higher temperature GaAs epitaxial layer at 600 ℃ / 650 ℃ was 2.7×10 -3 mol / min, TMGa flow rate 4.1×10 -5 mol / min.

[0099] (3) As shown in FIG3 , SiO2 is deposited on the leakage isolation layer 2 prepared in step 2 by low-temperature CVD to prepare the prototype of the inductor layer 3. The silane low-temperature oxidation deposition temperature is about 400°C. In an oxygen-containing atmosphere, silane (SiH4) is thermally decomposed on the substrate surface and reacts with oxygen to form SiO2.

[0100] (4) As shown in Figure 4-5, a Cu film was deposited on the SiO2 film prepared in step 3 by CVD. A thickener was applied to the surface of the prepared SiO2 film, and a photoresist was spin-coated. The film was pre-baked to remove moisture, and exposed to UV light for 5 seconds. The film was immersed in a developer for 40-60 seconds to obtain a sample with an inductor shape. Then, the wafer was loaded into the PVD carrier chamber with a back pressure of 5×10 -7Torr, Cu was sputter-grown at 4 kW AC power. Before starting sputtering growth, the Cu target was pre-sputter-cleaned for 10 minutes. Subsequently, the Cu film (typically 100 nm thick copper, used as the inductor material) was stripped and patterned. The inductor layer 3 was then patterned by stripping the metal from the photoresist in acetone for 3 minutes.

[0101] (5) As shown in Figure 7, the inductor layer 3 prepared in step 4 is deposited with SiO2 by low-temperature CVD to form the prototype of the isolation layer 4, on which the through-holes will be subsequently etched. The silane low-temperature oxidation deposition temperature is around 400°C. In an oxygen-containing atmosphere, silane (SiH4) thermally decomposes on the substrate surface and reacts with oxygen to form SiO2.

[0102] (6) As shown in Figures 8-9, an Au film was deposited on the SiO2 film prepared in step 5 by CVD. A thickener was applied to the surface of the prepared SiO2 film, and a photoresist was spin-coated. The film was pre-baked to remove moisture, exposed to UV light for 5 seconds, and immersed in a developer for 40-60 seconds to obtain a sample with a through-hole shape. Then, the wafer was loaded into the PVD carrier chamber with a back pressure of 5×10 -7 Torr, Au is sputtered at 5.2 kW AC power. Subsequently, the Au film is stripped and patterned. The through-hole material is typically copper, with a thickness of 150 nm. The film is then immersed in acetone for 5 minutes, and the metal on the photoresist is stripped to obtain a patterned isolation layer 4.

[0103] (7) As shown in FIG9 , by following the same method and process parameters and repeating steps (3) to (6) three times by replacing different masks, a complete IPD TGV inductor 21 and an IPD MIM capacitor 22 can be obtained.

[0104] (8) As shown in FIG10 , a sacrificial layer 12 of PSG (phosphosilane glass) with a thickness of 600 nm is deposited on the capacitor layer 11 prepared in step 7 by low-temperature CVD.

[0105] (9) As shown in FIG11 , the basic shape of the support structure is obtained by etching the sacrificial layer 12 prepared in step 8. The specific process is as follows: a commonly used etching equipment, an inductively coupled plasma (ICP) etcher, is used to perform the dry etching process of the AlN film. The equipment parameters are set as follows: ICP coil power of 1500 W, etching chamber temperature of 10°C, chamber pressure of 5 mTorr, and substrate bias of -400 V. The volume flow rates of Cl2, BCl3, and Ar are 70, 50, and 30 cm3, respectively. 3 The dry etching is performed under the condition of 0.05 mol / min, and the etching depth penetrates the sacrificial layer 12 until the bottom capacitor layer 11 is exposed.

[0106] (10) As shown in FIG12 , a supporting structure SiN is deposited on the SiO2 sacrificial layer 12 etched in step 9, with a deposition thickness of 680 nm.

[0107] (11) As shown in Figures 13-14, the surface of the sacrificial layer 12 deposited in step 10 is coated with a tackifier, and photoresist is spin-coated. The sample is pre-baked to remove moisture, exposed to UV light for 5 seconds, and immersed in a developer for 40-60 seconds to obtain a sample with a through-hole shape. Then, the wafer is loaded into the PVD carrier chamber with a back pressure of 5 × 10 -7 Torr, Au is sputtered at 5.2 kW AC power. Subsequently, the Au film is stripped and patterned. The through-hole material is typically copper, with a thickness of 150 nm. The film is then immersed in acetone for 5 minutes, and the metal on the photoresist is stripped to obtain patterned lead through-holes 23.

[0108] (12) As shown in Figures 15-17, a DC vacuum magnetron sputtering coating machine is used to sputter-deposit a layer of metal molybdenum as the bottom electrode 13 on the surface of the substrate after photolithography based on the sacrificial layer 12 prepared in step 11. The top electrode 15 and the bottom electrode 13 are usually made of molybdenum with a thickness of 100 nm. The top electrode 15 and the bottom electrode 13 are soaked in acetone for 3 minutes, and the metal on the photoresist is stripped to obtain a patterned bottom electrode 13.

[0109] (13) As shown in FIG18 , a high-quality AlN piezoelectric layer 14 is prepared by magnetron sputtering on the basis of the bottom electrode 13 with a piezoelectric stack cross section surrounding the bottom of the groove prepared in step 12. The specific process is as follows: the equipment parameters and target materials are adjusted, and the back pressure in the PVD chamber is 5×10 −7 Torr, AlN was sputtered to a thickness of 200nm under the conditions of AC power 6kW, Ar flow rate 10sccm, and N2 flow rate 45sccm. The sputtering gas was 99.9999% high-purity N 2 and Ar, the purity of the sputtered Al target was 99.999%, and the Al target was also pre-sputter cleaned for 10 minutes before starting sputtering growth.

[0110] (14) As shown in Figures 19-21, a top electrode 15 is prepared on the surface of the piezoelectric layer 14 after the etching step in step 13, and patterned by photolithography. The top electrode 15 is obtained on the piezoelectric layer 14 by photolithography, magnetron sputtering, and stripping. The specific process is as follows: a viscosity enhancer is applied to the surface of the piezoelectric layer 14, photoresist is spin-coated, ultraviolet light is exposed for 5 seconds, and a sample with a top electrode 15 is developed. Then, a DC vacuum magnetron sputtering coating machine is used to sputter-deposit a layer of metal molybdenum as the top electrode 15 on the surface of the substrate after photolithography. The top electrode 15 is usually made of molybdenum with a thickness of 100 nm; the top electrode 15 is soaked in acetone for 3 minutes, and the metal on the photoresist is stripped to obtain a patterned top electrode 15.

[0111] (15) As shown in FIG22, the top electrode 15 prepared in step 14 is deep-hole etched to connect the top and bottom electrodes of the two resonators, making it easier for the two resonators to be cascaded. The specific process is as follows: a commonly used etching equipment, an inductively coupled plasma (ICP) etcher, is used to perform the dry etching process of the AlN film. The equipment parameters are set as follows: ICP coil power of 1500W, etching chamber temperature of 10°C, chamber pressure of 5mTorr, and substrate bias of -400V. The volume flow rates of Cl2, BCl3, and Ar are 70, 50, and 30 cm3, respectively. 3 The dry etching is performed under the condition of 0.0447 W / min, and the etching depth penetrates the AlN piezoelectric layer 14 until the bottom electrode 13 is exposed.

[0112] (16) As shown in FIG23 , a layer of Mo metal is deposited on the surface of the deep hole etched in step 15 to connect the top and bottom electrodes of the two resonators, thereby connecting the two resonators in series.

[0113] (17) As shown in FIG24 , a thin AlN film is deposited by PVD on the top electrode 15 prepared in step 16 as an anti-oxidation layer 16, which is usually 70 nm. Its function is to protect the Mo electrode, i.e., the top electrode 15, from oxidation. The 20 nm thickness is a thickening margin, which is reserved for subsequent frequency modulation.

[0114] (18) As shown in Figure 25, HF is used to react with the PSG (phosphosilica glass) sacrificial layer. This step is usually called releasing the sacrificial layer. When the reaction is complete, the area originally filled with PSG (phosphosilica glass) will become a cavity.

[0115] (19) As shown in FIG26 , the wafer is inverted so that the substrate faces upward, and the conductive vias are subsequently etched.

[0116] (20) As shown in Figures 27-29, ICP etching is performed to penetrate the substrate 1 until the leakage isolation layer 2 is exposed. The shape of the metal conductive pad 17 is obtained on the reverse side of the substrate 1 by photolithographic stripping. Copper with a thickness of 100 nm is deposited by PVD to obtain the access pin 18, the ground pin 19, and the output pin 20.

[0117] (21) As shown in FIG30 , the wafer is flipped to obtain a bulk acoustic wave (BAW) monolithic hybrid filter with integrated IPD.

[0118] Performance Analysis:

[0119] Example 1 is a hybrid filter structure with two BAW resonators, six IPD inductors, and two capacitors. The parameter curve S21 is shown in Figure 33. The bulk acoustic wave (BAW) monolithic hybrid filter with integrated IPD obtained through the above steps exhibits an extremely high roll-off coefficient at frequencies below and above the passband. After the secondary roll-off, it can even reach a roll-off zero point of 120dB. This is due to the excellent roll-off coefficient of the BAW resonator, which is a prominent advantage after the integration of the IPD circuit and the BAW.

[0120] As shown in Figure 32, which shows the passband ripple performance of Example 1 of the present invention, it can be seen that within the passband, the maximum insertion loss is less than 0.9dB (the industry standard is that the designed filter is usable when the insertion loss is less than 3dB, and less than 1.2dB is the industry-leading level). This shows that the insertion loss control of this application is at a very high level. Lower insertion loss ensures higher fidelity of RF signal transmission.

[0121] Comparative Example 1

[0122] Example 1 is a hybrid filter structure with two BAW resonators, six IPD inductors, and two capacitors. Comparative Example 1 will give the performance of the filter when there are only two BAW resonators. As shown in Figure 31, Figure 31 is the transmission curve of the filter composed of two BAW resonators extracted from Example 1. It can be seen from the figure that the RF filter composed of a simple BAW resonator has a very high roll-off coefficient, but there is a significant depression in the passband. If the problem of passband depression is to be solved, the method commonly used in the industry is to perform multi-stage cascade of BAW. When the number reaches about 4 orders (about 7-8 resonators), it can have a passband performance that meets the use requirements. However, BAW filters cannot be integrated vertically in multiple (more than two resonators). They are usually connected by horizontal wires on the same wafer. As the communication frequency increases, if this solution is still used, the volume is bound to become larger and larger, accompanied by serious heat generation and power capacity overload problems, which will violate the original intention of high frequency, integration, and miniaturization of RF devices.

[0123] Comparative Example 2

[0124] Comparative Example 2 shows the signal transmission curve for Example 1, where the IPD circuit (six IPD inductors + two capacitors) is isolated and used as a separate component. As shown in Figure 34, the filter formed by the IPD circuit has excellent passband performance, but it is obvious that the IPD filter's roll-off performance is too slow to meet the increasingly crowded frequency band division in the era of high-frequency communications. This slow roll-off cannot accurately extract the frequency band required by the receiver, resulting in spectral chaos.

[0125] Therefore, this application integrates the IPD filter and the BAW filter into a monolithic chip, which essentially provides a relatively mature solution for the high-frequency and broadbandization of future filters.

[0126] In the description of this specification, the reference terms "one embodiment," "some embodiments," "example," "specific example," or "some examples" mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. Moreover, the specific features, structures, materials, or characteristics described may be combined in any appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification, as well as features of different embodiments or examples, unless they are mutually inconsistent.

[0127] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. Throughout the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0128] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various modifications or substitutions within the technical scope disclosed in this application, and such modifications or substitutions should be included within the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for fabricating a bulk acoustic wave monolithic hybrid filter integrated with passive devices, characterized in that, it includes: (1) Fabricating a leakage isolation layer on a support substrate by deposition; (2) Obtaining an inductor layer by physical vapor deposition on the leakage isolation layer prepared in step (1), leaving a window at the bottom of the trench surrounded by the cross-section of the TGV inductor stack on the mask, and simultaneously patterning the inductor metal; (3) Obtaining an insulating layer by chemical vapor deposition on the inductor metal prepared in step (2), and obtaining via holes for leads by photolithography; (4) Alternately repeating steps (2) and (3) to obtain a three-layer stacked TGV inductor; (5) Depositing another insulating layer by chemical vapor deposition above the TGV inductor prepared in step (4) as a partition between the capacitor layer and the TGV inductor; (6) Depositing two capacitor layers by physical vapor deposition on the insulating layer deposited in step (5), and depositing an insulating layer between the two capacitor layers to form a MIM capacitor; (7) Fabricating a BAW resonator on the MIM capacitor prepared in step (6), and connecting the TGV inductor, MIM capacitor, and BAW resonator through the via holes for leads to obtain a bulk acoustic wave monolithic hybrid filter integrated with passive devices.

2. The method for fabricating a bulk acoustic wave monolithic hybrid filter integrated with passive devices according to claim 1, characterized in that, the connection of the BAW resonator includes a bottom electrode, a piezoelectric layer, a top electrode, and an antioxidant layer arranged in sequence, and an air gap is formed between the bottom electrode and the MIM capacitor.

3. The method for fabricating a bulk acoustic wave monolithic hybrid filter integrated with passive devices according to claim 2, characterized in that, the materials of the bottom electrode and the top electrode are one or more of aluminum, molybdenum, tungsten, platinum, titanium, and gold.

4. The method for fabricating a bulk acoustic wave monolithic hybrid filter integrated with passive devices according to claim 2, characterized in that, The material of the piezoelectric layer is single-crystalline aluminum nitride, or polycrystalline aluminum nitride, or zinc oxide, or lead zirconate titanate, or BST, or LiNbO 3 .

5. The method for fabricating a bulk acoustic wave monolithic hybrid filter integrated with passive devices according to claim 2, characterized in that, the material of the antioxidant layer is aluminum nitride.

6. The method for fabricating a bulk acoustic wave monolithic hybrid filter integrated with passive devices according to any one of claims 1-5, characterized in that, The material of the supporting substrate is silicon, or sapphire, or LiGaO 2 , or metal.

7. The method for fabricating a bulk acoustic wave monolithic hybrid filter integrated with passive devices according to any one of claims 1-5, characterized in that, the material of the isolation leakage layer is gallium arsenide.

8. The method for fabricating a bulk acoustic wave monolithic hybrid filter integrated with passive devices according to any one of claims 1-5, characterized in that, the material of the insulating layer is silicon dioxide.

9. The method for fabricating a bulk acoustic wave monolithic hybrid filter integrated with passive devices according to any one of claims 1-5, characterized in that, the material of the via holes for leads is gold, or copper, or molybdenum.

10. The method for fabricating a bulk acoustic wave monolithic hybrid filter integrated with passive devices according to any one of claims 1-5, characterized in that, the material of the inductor layer is copper.

11. The method for fabricating a bulk acoustic wave monolithic hybrid filter integrated with passive devices according to any one of claims 1-5, characterized in that, The material of the capacitor layer is copper.

12. A bulk acoustic wave monolithic hybrid filter of an integrated passive device, characterized in that, it includes: a support substrate; an isolation and leakage layer, which is disposed on the support substrate; an IPD inductance structure, which is disposed on the isolation and leakage layer; an IPD capacitance structure, which is disposed on the IPD inductance structure; a BAW resonator, which is disposed on the IPD capacitance structure; the IPD capacitance structure, the IPD capacitance structure and the BAW resonator are connected through via holes.

13. The bulk acoustic wave monolithic hybrid filter of an integrated passive device according to claim 12, characterized in that, the IPD inductance structure includes one or more combinations of a TGV inductance, a meander line inductance, a square spiral inductance, a circular spiral inductance, and an octagonal spiral inductance; when the IPD inductance structure is a TGV inductance, the bulk acoustic wave monolithic hybrid filter of the integrated passive device is prepared by the preparation method of the bulk acoustic wave monolithic hybrid filter of the integrated passive device according to any one of claims 1-11.

14. The bulk acoustic wave monolithic hybrid filter of an integrated passive device according to claim 12, characterized in that, the IPD capacitance structure includes one or more combinations of a MIM capacitance, an interdigital capacitance, and a VLC capacitance; when the IPD capacitance structure is a MIM capacitance, the bulk acoustic wave monolithic hybrid filter of the integrated passive device is prepared by the preparation method of the bulk acoustic wave monolithic hybrid filter of the integrated passive device according to any one of claims 1-11.

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