Bulk acoustic wave device and filtering device
By introducing structural layers and void structures into bulk acoustic wave devices and changing the acoustic impedance relationship at the edges of the device, the problems of decreasing Q value and deteriorating S11 curve of conventional bulk acoustic wave devices are solved, and a higher Q value and a smoother S11 curve are achieved.
Patent Information
- Application Number
- CN202311414182.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-10-30
- Publication Date
- 2025-05-02
AI Technical Summary
Due to poor boundary conditions and poor film flatness of conventional bulk acoustic devices, the sound wave lateral vibration, energy leakage, the Q value is reduced, and the lateral parasitic mode is introduced, deteriorating the S11 curve.
By introducing structural layer and void structure into bulk acoustic wave devices, the acoustic impedance relationship at the edges of the device is changed, parasitic mode is suppressed, and the gap width is controlled through the structural layer to ensure the consistency of performance of different bulk acoustic wave devices.
The Q value of the bulk acoustic wave device is improved, the smoothness of the S11 curve is suppressed, the parasitic mode and subresonance are prevented, and the impact of the gap structure width on performance is avoided.
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Figure CN119921709A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of filter devices, and in particular to a bulk acoustic wave device and a filter device. Background Art
[0002] With the development of miniaturization, high frequency and broadband, higher requirements are placed on the insertion loss of Bulk Acoustic Wave (BAW) devices, which requires the BAW devices themselves to have a higher Q value. The sound waves of BAW devices mainly propagate longitudinally along the stacking direction. However, due to unsatisfactory boundary conditions and poor film flatness caused by the process, conventional BAW devices produce vibrations in the lateral direction, and there is a problem of energy leakage in the lateral direction, which reduces the Q value of the device and introduces lateral parasitic modes, thereby deteriorating the S11 curve. In the corresponding filter, the insertion loss decreases and large ripples appear in the passband. The commonly used solution is the apodization method. Although this method can weaken the parasitic mode, it will reduce the overall Q value. Therefore, how to improve the Q value of bulk acoustic wave devices and improve the smoothness of the S11 curve is a technical problem that technicians in this field currently need to solve. Summary of the invention
[0003] The purpose of the present application is to provide a bulk acoustic wave device and a filtering device, so as to enhance the Q value of the bulk acoustic wave device and improve the smoothness of the S11 curve.
[0004] To achieve the above-mentioned object, the present application provides a bulk acoustic wave device, comprising: a substrate; an acoustic reflector, a bottom electrode, a piezoelectric layer, a top electrode, a structural layer and a passivation layer are sequentially arranged on the surface of the substrate along the thickness direction; the overlapping area of the acoustic reflector, the bottom electrode, the piezoelectric layer and the top electrode forms an effective resonance area;
[0005] The non-connected edge of the structural layer extends beyond the non-connected edge of the top electrode, so that the portion of the structural layer exceeding the non-connected edge of the top electrode covers the surface of the piezoelectric layer;
[0006] The non-connected edge of the passivation layer exceeds the non-connected edge of the structural layer, so that a gap is formed between the portion of the passivation layer exceeding the non-connected edge of the structural layer and the piezoelectric layer.
[0007] Optionally, the structural layer is a high acoustic impedance layer.
[0008] Optionally, a protrusion structure is provided on the surface edge of the top electrode.
[0009] Optionally, the protruding structure is provided on a surface edge of the top electrode facing away from the substrate.
[0010] Optionally, a mass loading layer is further provided on the surface of the top electrode facing away from the substrate.
[0011] Optionally, the mass loading layer is a metal or a metal alloy.
[0012] Optionally, the passivation layer includes at least one of aluminum oxide, aluminum nitride, silicon dioxide or silicon nitride; or aluminum oxide, aluminum nitride, silicon dioxide or silicon nitride doped with other elements.
[0013] Optionally, the top electrode is a metal or a metal alloy; the bottom electrode is a metal or a metal alloy.
[0014] Optionally, the structural layer is arranged in a non-connecting side region of the top electrode; the non-connecting side region is close to an edge of the non-connecting side of the top electrode.
[0015] To achieve the above objectives, the present application also provides a filtering device, comprising: at least one BAW device as described in any one of the above items.
[0016] A bulk acoustic wave device provided by the present application comprises: a substrate; an acoustic reflector, a bottom electrode, a piezoelectric layer, a top electrode, a structural layer and a passivation layer are sequentially arranged on the surface of the substrate along the thickness direction; the overlapping area of the acoustic reflector, the bottom electrode, the piezoelectric layer and the top electrode forms an effective resonance area; a protruding structure is arranged on the surface edge of the top electrode; the non-connected side edge of the structural layer extends beyond the non-connected side edge of the top electrode, so that the part of the structural layer exceeding the non-connected side edge of the top electrode covers the surface of the piezoelectric layer; the non-connected side edge of the passivation layer exceeds the non-connected side edge of the structural layer, so that a gap is formed between the part of the passivation layer exceeding the non-connected side edge of the structural layer and the piezoelectric layer.
[0017] Obviously, the gap formed between the part of the passivation layer of the present application that exceeds the non-connected edge of the structural layer and the piezoelectric layer changes the boundary conditions of the device by changing the acoustic impedance relationship of the device edge structure. On the one hand, it can improve the Q value; on the other hand, it can suppress the parasitic mode, thereby improving the smoothness of the S11 curve; at the same time, due to the introduction of the structural layer, the gap structure is introduced outside the edge position of the top electrode, so that the width of the gap is determined by the structural layer. By controlling the parameters of the structural layer, the consistency of the parasitic mode suppression effect of different bulk acoustic wave devices can be guaranteed, thereby avoiding the large performance difference caused by the change of the width of the gap structure due to the different top electrode thicknesses in the effective resonance area. The thickness of the extended area formed by the structural layer is less than the thickness of the effective resonance area, and a similar concave structure is formed in this area, which can reduce the electromechanical coupling coefficient of the high-order parasitic mode, strengthen the main resonance, and form a piston-like vibration. It can also effectively suppress the parasitic mode, thereby improving the smoothness of the S11 curve. The present application also provides a filtering device with the above-mentioned beneficial effects. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.
[0019] Figure 1 is a cross-sectional schematic diagram of a conventional bulk acoustic wave device;
[0020] Figure 2 A schematic cross-sectional view of a bulk acoustic wave device provided in an embodiment of the present application;
[0021] Figure 3 A schematic cross-sectional view of another bulk acoustic wave device provided in an embodiment of the present application;
[0022] Figure 4 is a schematic cross-sectional view of a bulk acoustic wave device with a protruding structure;
[0023] Figure 5 is a reflection coefficient curve diagram of a BAW device with a protruding structure and a conventional BAW device;
[0024] Figure 6 Q curve diagram of a BAW device with a protruding structure and a conventional BAW device;
[0025] Figure 7 is a schematic cross-sectional view of a bulk acoustic wave device with a void structure;
[0026] Figure 8 is a reflection coefficient curve diagram of a BAW device with a void structure and a BAW device with a protrusion structure;
[0027] Fig. 9 Q value curves of a BAW device with a void structure and a BAW device with a protrusion structure;
[0028] Fig.10 is a schematic cross-sectional view of a bulk acoustic wave device with a mass loading layer;
[0029] Fig.11 A reflection coefficient curve diagram of the bulk acoustic wave device of the present application and the bulk acoustic wave device with a protruding structure;
[0030] Fig.12 It is a Q value curve diagram of the bulk acoustic wave device of the present application and the bulk acoustic wave device with a protruding structure.
[0031] The following are the descriptions of the reference numerals:
[0032] 1-top electrode; 2-piezoelectric layer; 3-bottom electrode; 4-substrate; 5-acoustic reflector; 6-passivation layer; 7-convex structure; 8-mass load layer; 9-structural layer. DETAILED DESCRIPTION
[0033] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.
[0034] Acoustic wave filters can be used in radio frequency and microwave circuits, for example, as bandpass filters. Acoustic wave filters are composed of several acoustic wave resonators. Acoustic wave resonators are generally divided into surface acoustic wave (SAW) devices, BAW devices and radial mode resonator (CMR) devices according to the vibration mode. BAW devices generally consist of a sandwich structure consisting of a top electrode layer, a piezoelectric layer and a bottom electrode layer to produce resonance. SAW devices use interdigital transducers (IDTs) to convert electrical energy into acoustic energy, or vice versa. IDT uses a piezoelectric substrate and two relative busbars at two different potentials and two sets of electrodes connected to the two busbars. CMR devices are based on Lamb wave vibrations. Due to the relatively low equivalent coupling coefficient k2eff of the device and poor device reliability, they are rarely used in acoustic filters.
[0035] In recent years, filters and duplexers based on acoustic wave resonators have been increasingly developed towards miniaturization, high frequency and broadband. High-performance devices have increasingly higher insertion loss requirements, which requires the resonator itself to have a high Q value. Conventional BAW devices such as Figure 1 As shown, the acoustic reflector, the top electrode, the piezoelectric layer and the bottom electrode overlap above the substrate, and the overlapping area forms an effective resonance zone. The sound waves mainly propagate longitudinally along the stacking direction. However, due to unsatisfactory boundary conditions and poor film flatness caused by the process, the sound waves vibrate in the lateral direction, and there is a problem of energy leakage in the lateral direction, which reduces the Q value of the device and introduces lateral parasitic modes, thereby deteriorating the S11 curve. In the corresponding filter, the insertion loss decreases and large ripples appear in the passband. The commonly used solution at present is the apodization method: if the resonant device is set to an irregular polygon, the parasitic mode can be weakened, but the overall Q value will be reduced. Therefore, the present application provides a bulk acoustic wave device, which improves the Q value of the bulk acoustic wave device and improves the smoothness of the S11 curve by adding structural layers and gap structures.
[0036] Please refer to Figure 2 , Figure 2 A schematic cross-sectional view of a bulk acoustic wave device provided in an embodiment of the present application, the bulk acoustic wave device may include: a substrate 4; an acoustic reflector 5, a bottom electrode 3, a piezoelectric layer 2, a top electrode 1, a structural layer 9 and a passivation layer 6 are sequentially arranged on the surface of the substrate 4 along the thickness direction; an overlapping area of the acoustic reflector 5, the bottom electrode 3, the piezoelectric layer 2 and the top electrode 1 forms an effective resonance area;
[0037] The non-connected edge of the structure layer 9 extends beyond the non-connected edge of the top electrode 1, so that the portion of the structure layer 9 that exceeds the non-connected edge of the top electrode 1 covers the surface of the piezoelectric layer 2;
[0038] The non-connected edge of the passivation layer 6 exceeds the non-connected edge of the structural layer 9 , so that a gap is formed between the portion of the passivation layer 6 that exceeds the non-connected edge of the structural layer 9 and the piezoelectric layer 2 .
[0039] This embodiment does not limit the specific type of the substrate 4 . For example, the substrate 4 may be silicon, quartz, or aluminum oxide.
[0040] This embodiment does not limit the specific type of the acoustic reflector 5. For example, the acoustic reflector 5 may be a cavity structure; the acoustic reflector 5 may also be a Bragg reflection structure composed of multiple layers of materials alternating. It should be noted that the substrate 4 is usually partially etched and filled with a sacrificial layer, and finally etched and released to form an acoustic reflector 5 with a cavity structure. The bulk acoustic wave device of this structure is a film bulk acoustic wave resonator (FBAR); or the acoustic reflector 5 is formed by a Bragg reflection structure composed of multiple layers of materials alternating at the etching position. The bulk acoustic wave device of this structure is a solid mounted resonator (SMR). The sacrificial layer may be silicon dioxide or phospho-silicate glass; other materials may also be used as sacrificial layers, such as porous silicon, photoresist, etc.
[0041] This embodiment does not limit the specific types of the top electrode 1 and the bottom electrode 3, as long as the top electrode 1 and the bottom electrode can conduct electricity, for example, the top electrode 1 can be a metal or a metal alloy; the bottom electrode 3 can be a metal or a metal alloy. Metals or metal alloys have good electrical conductivity. Furthermore, the top electrode 1 and the bottom electrode 3 can include at least one of aluminum, molybdenum, copper, gold, platinum, silver, nickel, chromium, tungsten, titanium or tin.
[0042] Furthermore, in this embodiment, the surface edge of the top electrode 1 may be provided with a protruding structure 7. It should be noted that by introducing the protruding structure 7, the lateral propagation energy can be limited to the effective vibration area, energy leakage can be avoided, and the Q value can be further improved. In addition, the introduction of the protruding structure 7 may also introduce sub-resonance, and a gap is formed between the portion of the passivation layer 6 that exceeds the non-connected edge of the structural layer 9 and the piezoelectric layer 2, which can not only suppress the parasitic mode, but also suppress the sub-resonance introduced by the protruding structure 7, thereby avoiding the sub-resonance from deteriorating the S11 curve, thereby improving the smoothness of the S11 curve.
[0043] This embodiment does not limit the specific position of the protruding structure 7. For example, the protruding structure 7 may be provided at the edge of the surface of the top electrode 1 away from the substrate 4; or the protruding structure 7 may be provided at the edge of the surface of the top electrode 1 close to the substrate 4. It should be noted that when the protruding structure 7 is located at the edge of the surface of the top electrode 1 away from the substrate 4, the structural layer 9 is located at the surface of the protruding structure 7 away from the substrate 4.
[0044] Furthermore, in this embodiment, a mass load layer 8 may be provided on the surface of the top electrode 1 facing away from the substrate 4. It should be noted that the mass load layer 8 is introduced in this embodiment to adjust the resonant frequency of the bulk acoustic wave device. Among them, the resonator with the mass load layer 8 is generally used as a parallel resonator; the resonator without the mass load layer 8 is generally used as a series resonator, which has a higher resonant frequency. In addition, the mass load layer 8 can be a single layer or a multi-layer; the number of mass load layers 8 of each resonator can be the same or different.
[0045] This embodiment does not limit the specific type of the mass load layer 8, for example, the mass load layer 8 can be a metal or a metal alloy. It should be noted that the mass load layer 8 can be the same material as the top electrode 1, or other metal materials, and it can be understood that the mass load layer 8 and the top electrode 1 layer together constitute the final top electrode 1. In the present application, since the width of the gap is determined by the structural layer 9, by controlling the parameters of the structural layer 9, the consistency of the sub-resonance suppression effect of different bulk acoustic wave devices can be guaranteed, thereby avoiding the performance of the gap structure being greatly different due to the different top electrode 1 thicknesses in the effective resonance area. This structure is not only applicable to structures with a single-layer top electrode 1, but also to multi-layer top electrode 1 structures composed of the mass load layer 8 and the top electrode 1 layer.
[0046] This embodiment does not limit the specific type of the piezoelectric layer 2. For example, the piezoelectric layer 2 may be a piezoelectric layer 2 formed by at least one of aluminum nitride, zinc oxide, lithium niobate or lithium tantalate; the piezoelectric layer 2 may also be aluminum nitride, zinc oxide, lithium niobate or lithium tantalate doped with other elements.
[0047] It should be noted that the gap between the portion of the passivation layer 6 that exceeds the non-connected edge of the structural layer 9 and the piezoelectric layer 2 is formed by internally etching the structural layer 9 at a certain width at the edge of the non-connected edge to form a similar incision-type structure.
[0048] This embodiment does not limit the specific type of the structural layer 9, as long as it is ensured that the structure can form a gap between the passivation layer 6 that exceeds the non-connected edge of the structural layer 9 and the piezoelectric layer 2. For example, the structural layer 9 can be a high acoustic impedance layer. Furthermore, in this embodiment, the structural layer 9 can be made of the same material as the top electrode 1. It should be noted that when the structural layer 9 is made of the same material as the top electrode 1, the top electrode 1 is grown twice, and the first growth and etching are the same as the conventional structure; after the top electrode 1 (or mass load layer 8) is grown and etched, the remaining top electrode 1 portion (i.e., the structural layer 9) and the passivation layer 6 are grown, and the top electrode 1 pattern is etched.
[0049] This embodiment does not limit the specific position of the structural layer 9. It only needs to ensure that the structure can form a gap between the passivation layer 6 and the piezoelectric layer 2 beyond the non-connecting edge of the structural layer 9. For example, the connecting edge of the structural layer 9 can be aligned with the connecting edge of the top electrode 1, so that the structural layer 9 covers the surface of the top electrode 1 away from the piezoelectric layer 2; or the structural layer 9 is arranged in the non-connecting edge area of the top electrode 1; the non-connecting edge area is close to the non-connecting edge of the top electrode 1. It should be noted that because the main functional area of the structural layer 9 is at the edge of the non-connecting edge, the structural layer 9 can be etched, and after retaining the structural layer 9 in the non-connecting edge area, the passivation layer 6 is grown and etched, which can also achieve the purpose of this application. In this way, the top electrode 1 does not need to be grown twice. And when the surface edge of the top electrode 1 is provided with a protruding structure 7, since the structural layer 9 covers the protruding structure 7, the layer thickness and layer material properties of the protruding structure 7 area can be further adjusted by using the layer, and the increased degree of freedom helps to further improve the performance of the device.
[0050] It should be noted that the passivation layer 6 is generated on the surface of the top electrode 1 to protect the electrode structure. The passivation layer 6 can be grown on the surface of the entire device, and only the top and bottom electrodes 3 need to be led out to expose the electrodes. It can also be etched together with the top electrode 1, and the edge is aligned with the top electrode 1. This embodiment does not limit the specific type of the passivation layer 6, which is generally a dielectric material. For example, the passivation layer 6 may include at least one of aluminum oxide, aluminum nitride, silicon dioxide or silicon nitride; or aluminum oxide, aluminum nitride, silicon dioxide or silicon nitride doped with other elements.
[0051] Based on the above embodiments, the gap formed between the part of the passivation layer of the present application that exceeds the non-connected edge of the structural layer and the piezoelectric layer changes the device boundary conditions by changing the acoustic impedance relationship of the device edge structure, which can improve the Q value on the one hand; on the other hand, it can suppress the parasitic mode, thereby improving the smoothness of the S11 curve; at the same time, due to the introduction of the structural layer, the gap structure is introduced outside the edge position of the top electrode, so that the width of the gap is determined by the structural layer. By controlling the parameters of the structural layer, the consistency of the parasitic mode suppression effect of different bulk acoustic wave devices can be guaranteed, thereby avoiding the large performance difference caused by the change in the width of the gap structure due to the different top electrode thicknesses in the effective resonance area. The thickness of the extended area formed by the structural layer is less than the thickness of the effective resonance area, and a similar concave structure is formed in this area, which can reduce the electromechanical coupling coefficient of the high-order parasitic mode, strengthen the main resonance, form a piston-like vibration, and effectively suppress the parasitic mode, thereby improving the smoothness of the S11 curve.
[0052] Please refer to Figure 3 , Figure 3 A schematic cross-sectional view of another bulk acoustic wave device provided in an embodiment of the present application, the bulk acoustic wave device may include: a substrate 4; an acoustic reflector 5, a bottom electrode 3, a piezoelectric layer 2, a top electrode 1, a structural layer 9 and a passivation layer 6 are sequentially arranged on the surface of the substrate 4 along the thickness direction; an overlapping area of the acoustic reflector 5, the bottom electrode 3, the piezoelectric layer 2 and the top electrode 1 forms an effective resonance area;
[0053] A protruding structure 7 is provided on the surface edge of the top electrode 1;
[0054] The structural layer 9 is arranged in the non-connected edge region of the top electrode 1; the non-connected edge region is close to the non-connected edge of the top electrode 1; the non-connected edge of the structural layer 9 extends beyond the non-connected edge of the top electrode 1, so that the portion of the structural layer 9 exceeding the non-connected edge of the top electrode 1 covers the surface of the piezoelectric layer 2;
[0055] The non-connected edge of the passivation layer 6 exceeds the non-connected edge of the structural layer 9 , so that a gap is formed between the portion of the passivation layer 6 that exceeds the non-connected edge of the structural layer 9 and the piezoelectric layer 2 .
[0056] Based on the above embodiments, the present application limits the lateral propagation energy within the effective vibration zone through the raised structure, which can avoid energy leakage and thus improve the Q value. The gap formed between the portion of the passivation layer that exceeds the non-connected edge of the structural layer and the piezoelectric layer changes the device boundary conditions by changing the acoustic impedance relationship of the device edge structure, which can improve the Q value on the one hand; on the other hand, it can suppress the parasitic mode and the sub-resonance introduced by the raised structure, thereby improving the smoothness of the S11 curve; at the same time, due to the introduction of the structural layer, the gap structure is introduced outside the edge position of the top electrode, so that the width of the gap is determined by the structural layer. By controlling the parameters of the structural layer, the consistency of the suppression of parasitic modes and sub-resonances of different bulk acoustic wave devices can be ensured, thereby avoiding the large difference in performance caused by the width of the gap structure being affected by the thickness of different top electrodes in the effective resonance area. The thickness of the extended area formed by the structural layer is less than that of the effective resonance area, and a concave structure is formed in this area, which can reduce the electromechanical coupling coefficient of the high-order parasitic mode, strengthen the main resonance, form a piston-like vibration, and effectively suppress the parasitic mode, thereby improving the smoothness of the S11 curve. In addition, the structural layer is only set in the non-connected edge area, and the layer thickness and layer material properties of the raised structure area can be adjusted by using this layer. The increased degree of freedom helps to further improve the performance of the device.
[0057] An embodiment of the present application further provides a filtering device, which may include: at least one bulk acoustic wave device as described above.
[0058] Based on the above embodiments, the filtering device provided in the present application can also improve the Q value of the bulk acoustic wave device and improve the smoothness of the S11 curve by adopting the bulk acoustic wave device described above, and can avoid the performance difference caused by the width of the gap structure being affected by the different top electrode thicknesses in the effective resonance area.
[0059] The working principle of the above-mentioned bulk acoustic wave device is explained below with reference to specific examples.
[0060] Please refer to Figure 5 and Figure 6 , Figure 5 is a reflection coefficient curve diagram of a BAW device with a protruding structure and a conventional BAW device; Figure 6 Q curve diagram of a BAW device with a protruding structure and a conventional BAW device. Figure 5 and Figure 6 The dashed line corresponds to Figure 1 The conventional structure shown, the solid line corresponds to Figure 4 As shown in Figure 1 The device with a protruding structure 7 added to the structure shown in the figure. The two vertical dotted lines correspond to the positions near the resonance frequency (resonance frequency, fs) and the anti-resonance frequency (anti-resonance frequency, fp). Figure 6 It can be seen that after adding the convex structure 7, the overall Q value of the fs to fp frequency band is improved; Figure 5 There is a strong attenuation near 1.7GHz below the fs frequency (ideally, the closer |S11| (reflection coefficient) is to 0dB, the better), which deteriorates the S11 curve. The reason for this performance degradation is that a sub-resonance is formed at the position of the protruding structure 7, and this sub-resonance also deteriorates the overall Q curve from 1.7GHz to fs frequency, so it is necessary to make a trade-off between the changes in Q values in different frequency bands. Figure 4 The gap structure is added on the basis of the structure shown. Figure 7 As shown, at the edge of the non-connected side of the top electrode 1, when etching the passivation layer 6 and the top electrode 1 layer, the top electrode 1 is internally etched with a certain width to form a gap structure similar to a cutout type, and the width of the gap structure is d1.
[0061] Please refer to Figure 8 and Fig. 9 , Figure 8 is a reflection coefficient curve diagram of a BAW device with a void structure and a BAW device with a protrusion structure; Fig. 9 It is a Q value curve diagram of a bulk acoustic wave device with a gap structure and a bulk acoustic wave device with a protrusion structure. Figure 8 and Fig. 9 The solid line corresponds to Figure 4 The device with the protruding structure 7 shown, the dotted line corresponds to Figure 7 As shown in Figure 4 The device with a gap structure added to the structure shown. The two vertical dotted lines correspond to the positions near the fs frequency and the fp frequency respectively. Figure 8 It can be seen from the figure that after adding the gap structure, |S11| is closer to 0dB below the fs frequency (i.e., the attenuation is reduced), and the S11 curve is also smoother. The gap structure can effectively suppress the sub-resonance caused by the protruding structure 7. Fig. 9 It can be seen from the figure that after adding the gap structure, the smoothness of the Q value curve below the fs frequency is also significantly improved while ensuring that the Q value near fs and fp remains basically unchanged. The gap structure can effectively suppress the sub-resonance caused by the protruding structure 7. However, this structure has a major problem. Fig.10 Another bulk acoustic wave device shown in FIG. Figure 6 The difference between the devices shown is that a mass loading layer 8 is introduced, which is used to Figure 7 The components shown form different resonant frequencies and together build a ladder filter structure. Fig.10 The structure shown and Figure 7 The structures shown have different top electrode 1 thicknesses. Fig.10After the mass load layer 8 is introduced into the structure shown, the top electrode 1 becomes thicker. Therefore, when the top electrode 1 layer is subjected to an inner etching process, it is very easy to Figure 7 The structure shown forms different gap structure widths d2. The experimental results show that the width of this area has a huge and sensitive impact on suppressing the 7th resonance of the protruding structure. Therefore, under the same process, the effects on different resonators in the filter will be quite different. To solve this problem, Figure 7 or Fig.10 Then introduce a structural layer 9 on the basis of Figure 2 As shown, due to the introduction of structural layer 9, the gap structure is led to the outside of the edge position of the top electrode 1, so that the width of the gap is determined by the structural layer 9. By controlling the parameters of the structural layer 9, the consistency of suppressing parasitic modes and sub-resonance effects of different bulk acoustic wave devices can be ensured, thereby avoiding the performance differences caused by the width of the gap structure being affected by the different thicknesses of the top electrode 1 in the effective resonance area.
[0062] Please refer to Fig.11 and Fig.12 , Fig.11 A reflection coefficient curve diagram of the bulk acoustic wave device of the present application and the bulk acoustic wave device with a protruding structure; Fig.12 It is a Q value curve diagram of the bulk acoustic wave device of the present application and the bulk acoustic wave device with a protruding structure. Fig.11 and Fig.12 The dashed line corresponds to Figure 4 The device with the protruding structure 7 shown, the solid line corresponds to Figure 2 As shown in Figure 7 The device with structure layer 9 added to the structure shown in the figure. The two vertical dotted lines correspond to the positions near the fs frequency and the fp frequency respectively. Fig.11 It can be seen from the figure that after adding the structural layer 9, |S11| is closer to 0dB (i.e., the attenuation is reduced), and the S11 curve is smoother, and the parasitic mode is effectively suppressed. Fig.12 It can be seen that after adding the structural layer 9, the Q value curve becomes smoother in the frequency band below fs. Not only that, the Q value curve between fs and fp also becomes smoother, and the parasitic mode is effectively suppressed. This is because the thickness of the extended area formed by the structural layer 9 is thinner than the effective resonance area, and the area forms a concave structure, and the high-order resonance is suppressed, forming a piston vibration mode.
[0063] Specific examples are used herein to illustrate the principles and implementation methods of the present application, and the embodiments are in a progressive relationship, each embodiment focuses on the differences from other embodiments, and the same and similar parts between the embodiments can be referred to each other. The description of the above embodiments is only used to help understand the method and core ideas of the present application. For ordinary technicians in this technical field, without departing from the principles of the present application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the scope of protection of the claims of the present application.
[0064] It should also be noted that, in this specification, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or equipment including the elements.
Claims
1. A bulk acoustic wave device, characterized in that: include: Substrate; the surface of the substrate is provided with an acoustic reflector, a bottom electrode, a piezoelectric layer, a top electrode, a structural layer and a passivation layer in sequence along the thickness direction; The overlapping area of the acoustic reflector, the bottom electrode, the piezoelectric layer and the top electrode forms an effective resonance area; The non-connected edge of the structural layer extends beyond the non-connected edge of the top electrode, so that the portion of the structural layer exceeding the non-connected edge of the top electrode covers the surface of the piezoelectric layer; The non-connected edge of the passivation layer exceeds the non-connected edge of the structural layer, so that a gap is formed between the portion of the passivation layer exceeding the non-connected edge of the structural layer and the piezoelectric layer.
2. The bulk acoustic wave device according to claim 1, characterized in that: The structural layer is a high acoustic impedance layer.
3. The bulk acoustic wave device according to claim 1, characterized in that: A protrusion structure is arranged on the surface edge of the top electrode.
4. The bulk acoustic wave device according to claim 3, characterized in that: The protruding structure is disposed on the edge of the surface of the top electrode facing away from the substrate.
5. The bulk acoustic wave device according to claim 1, characterized in that: A mass loading layer is also disposed on the surface of the top electrode facing away from the substrate.
6. The bulk acoustic wave device according to claim 5, characterized in that The mass-carrying layer is a metal or a metal alloy.
7. The bulk acoustic wave device according to claim 1, characterized in that: The passivation layer includes at least one of aluminum oxide, aluminum nitride, silicon dioxide or silicon nitride; or aluminum oxide, aluminum nitride, silicon dioxide or silicon nitride doped with other elements.
8. The bulk acoustic wave device according to claim 1, characterized in that: The top electrode is a metal or a metal alloy; the bottom electrode is a metal or a metal alloy.
9. The bulk acoustic wave device according to any one of claims 1 to 8, characterized in that: The structural layer is arranged in the non-connecting side region of the top electrode; the non-connecting side region is close to the non-connecting side edge of the top electrode.
10. A filtering device, characterized in that: include: At least one BAW device as claimed in any one of claims 1 to 9.