Transversely excited film bulk acoustic resonator with tethered diaphragm

Abstract

An acoustic resonator device includes a substrate and a piezoelectric plate. A first portion of the piezoelectric plate is attached to the substrate. A second portion of the piezoelectric forms a diaphragm suspended over a cavity in the substrate. An interdigital transducer (IDT) is formed on a surface of the piezoelectric plate, the IDT including first and second bus bars disposed on the first portion and interleaved IDT fingers disposed on the diaphragm. A plurality of tethers support the diaphragm over the cavity, each tether providing an electrical connection between a corresponding one of the interleaved IDT fingers and one of the first and second bus bars.

Description

Technical Field

[0001] This disclosure relates to radio frequency filters using acoustic resonators, and more particularly to filters used in communication devices. Background Technology

[0002] Radio frequency (RF) filters are two-ended devices configured to allow some frequencies to pass while blocking others. "Passing" means transmitting with relatively low signal loss, while "blocking" means blocking or essentially attenuating the signal. The range of frequencies a filter can pass through is called its "passband." The range of frequencies blocked by such a filter is called its "stopband." A typical RF filter has at least one passband and at least one stopband. The specific requirements for the passband or stopband depend on the application. For example, a "passband" can be defined as a frequency range where the filter's insertion loss is better than defined values ​​such as 1 dB, 2 dB, or 3 dB. A "stopband" can be defined as a frequency range where the filter's rejection is greater than defined values, such as 20 dB, 30 dB, 40 dB, or greater, depending on the application.

[0003] RF filters are used in communication systems that transmit information over wireless links. For example, RF filters can be found in cellular base stations, mobile phones and computing devices, satellite transceivers and ground stations, Internet of Things (IoT) devices, laptops and tablets, fixed-point radio links, and the RF front end of other communication systems. RF filters are also used in radar and electronic and information warfare systems.

[0004] RF filters typically require numerous design trade-offs to achieve the optimal balance between performance parameters such as insertion loss, rejection, isolation, power handling, linearity, size, and cost for each specific application. Specific design and manufacturing approaches and enhancements can simultaneously benefit one or more of these requirements.

[0005] Enhancements to the performance of RF filters in wireless systems can have a wide-ranging impact on system performance. Improvements to RF filters can lead to improvements such as larger cell size, longer battery life, higher data rates, greater network capacity, lower cost, enhanced security, and higher reliability. These improvements can be implemented individually or in combination at various levels of the wireless system, such as at the RF module, RF transceiver, mobile or fixed subsystem, or network level.

[0006] High-performance RF filters used in current communication systems typically incorporate acoustic resonators, including surface acoustic wave (SAW) resonators, bulk acoustic wave (BAW) resonators, thin-film bulk acoustic wave (FBAR) resonators, and other types of acoustic resonators. However, these existing technologies are not suitable for use at higher frequencies and bandwidths, which future communication networks require.

[0007] To obtain wider communication channel bandwidth, higher frequency communication bands are necessary. 3GPP (3rd Generation Partnership Project) has standardized radio access technologies for mobile phone networks. The 5G NR (New Radio) standard defines radio access technologies for fifth-generation mobile networks. The 5G NR standard defines several new communication bands. Among these new bands are n77 and n79, where n77 uses a frequency range of 3300 MHz to 4200 MHz, and n79 uses a frequency range of 4400 MHz to 5000 MHz. Both bands n77 and n79 use Time Division Duplex (TDD), therefore, communication devices operating in bands n77 and / or n79 will use the same frequencies for uplink and downlink transmissions. Bandpass filters in bands n77 and n79 must be able to handle the transmit power of the communication devices. High frequencies and wireless bandwidth are also required in the 5GHz and 6GHz 5G bands. The 5G NR standard also defines millimeter wave communication bands between 24.25 GHz and 40 GHz.

[0008] The transversely excited film bulk acoustic resonator (XBAR) is an acoustic resonator structure used in microwave filters. Such an XBAR is described in U.S. Patent 10,491,291, entitled "TRANSVERSELY EXCITED FILM BULK ACOUSTIC RESONATOR". The XBAR resonator includes an interdigital transducer (IDT) formed on a thin floating layer or diaphragm of a single-crystal piezoelectric material. The IDT includes a first set of parallel fingers extending from a first busbar and a second set of parallel fingers extending from a second busbar. The first and second sets of parallel fingers are interleaved. A microwave signal applied to the IDT excites a sheared master acoustic wave in the piezoelectric diaphragm. The XBAR resonator provides high electromechanical coupling and high-frequency capability. XBAR resonators can be used in a variety of RF filters, including band-stop filters, band-pass filters, duplexers, and multiplexers. XBARs are particularly well-suited for use in filters in communication bands above 3 GHz. Summary of the Invention

[0009] This invention discloses an acoustic resonator device, characterized in that it comprises: a substrate; a piezoelectric plate, a first portion of which is attached to the substrate, and a second portion of which forms a diaphragm suspended above a cavity in the substrate; an interdigital transducer (IDT) formed on the surface of the piezoelectric plate, the IDT including first and second busbars disposed on the first portion and interlaced IDT fingers disposed on the diaphragm; and a plurality of tethers supporting the diaphragm above the cavity, each tether providing an electrical connection between a corresponding finger of the interlaced IDT fingers and one of the first and second busbars.

[0010] The first busbar and the second busbar are located on opposite sides of the cavity.

[0011] The interlaced IDT fingers are alternately connected to the first busbar and the second busbar.

[0012] The interlaced IDT fingers include a first conductor layer, and each tether includes the first conductor layer and a corresponding portion of the piezoelectric plate connecting the first portion and the second portion.

[0013] Each of the first and second busbars includes the first conductor layer and the second conductor layer.

[0014] In this arrangement, a portion of each tether forms an oblique angle with the longitudinal direction of the corresponding interlaced IDT fingers.

[0015] The oblique angle is greater than or equal to 30 degrees and less than or equal to 60 degrees.

[0016] At least a portion of each rope is bent.

[0017] Each of the ropes is continuously bent.

[0018] Each tether includes: a first segment extending from the first or second busbar; a third segment extending from a diaphragm collinear with the corresponding IDT finger; and a second segment connecting the first and third segments, wherein the second segment forms an oblique angle with the longitudinal direction of the corresponding IDT finger.

[0019] Each tether is wider than the corresponding IDT finger.

[0020] The width of each tether is half the distance between the IDT fingers.

[0021] The present invention also discloses an acoustic resonator device, characterized in that it comprises: a piezoelectric plate attached to the substrate, a portion of the piezoelectric plate forming a diaphragm suspended above a cavity in the substrate; an interdigital transducer (IDT) located on the piezoelectric plate, the IDT including staggered IDT fingers arranged on the diaphragm and a first busbar and a second busbar not arranged on the diaphragm; and a plurality of tethers supporting the diaphragm above the cavity, each tether electrically connecting a corresponding IDT finger among the staggered IDT fingers to one of the first and second busbars through an open space spanning the diaphragm and the piezoelectric plate.

[0022] The first busbar and the second busbar are located on opposite sides of the cavity.

[0023] The interlaced IDT fingers are alternately connected to the first busbar or the second busbar.

[0024] The interlaced IDT fingers include a first conductor layer, and each tether includes a corresponding portion of the first conductor layer and the piezoelectric plate.

[0025] Each of the first busbar and the second busbar includes a first conductor layer and a second conductor layer.

[0026] In this arrangement, a segment of each tether forms an oblique angle with the longitudinal direction of the corresponding intersecting IDT fingers.

[0027] The oblique angle is greater than or equal to 30 degrees and less than or equal to 60 degrees.

[0028] Each tether includes: a first end extending from the first or second busbar; a third segment extending from the diaphragm collinear with the corresponding IDT finger; and a second segment connecting the first and third segments, the second segment forming an angle with the longitudinal direction of the corresponding interlaced IDT finger.

[0029] At least a portion of each rope is bent.

[0030] Each of the ropes is continuously bent.

[0031] In this case, the width of each tether is greater than the width of the corresponding interlaced IDT fingers.

[0032] The width of each tether is half the spacing between the interlaced IDT fingers. Attached Figure Description

[0033] Figure 1 Includes a schematic plan view and two schematic cross-sectional views of a transversely excited thin-film bulk acoustic resonator (XBAR).

[0034] Figure 2 This is a plan view of an XBAR with a diaphragm supported by tethers.

[0035] Figure 3A Is Figure 2 A schematic cross-sectional view of an XBAR with a diaphragm supported by ropes at section CC as defined in the diagram.

[0036] Figure 3B Is Figure 2 A schematic cross-sectional view of an XBAR with a diaphragm supported by ropes at section DD as defined in the figure.

[0037] Figure 4A Is Figure 2 A schematic cross-sectional view of an XBAR with a diaphragm supported by ropes at section EE as defined in the diagram.

[0038] Figure 4B Is Figure 2 An alternative schematic cross-sectional view of the XBAR with a diaphragm supported by ropes at section EE as defined in the diagram.

[0039] Figure 5 It is a schematic plan view showing the bending state of a single tether.

[0040] Figure 6 This is a diagram showing the displacement of the diaphragm and the tethered diaphragm of a conventional XBAR due to a 20-degree temperature change.

[0041] Figure 7 This is a flowchart of a method for manufacturing an XBAR with a diaphragm supported by tethers.

[0042] Throughout the specification, elements appearing in the accompanying drawings are assigned three- or four-digit reference numerals, where the two least significant digits are unique to that element, and one or two most significant digits are the drawing number in which the element is first shown. Elements not described in conjunction with the accompanying drawings may be assumed to have the same characteristics and functions as previously described elements with the same reference numerals. Detailed Implementation

[0043] Component Description

[0044] Figure 1 A simplified schematic top view and orthogonal cross-sectional view of the XBAR100 are shown. XBAR resonators, such as the resonator 100, can be used in a variety of RF filters, including band-stop filters, band-pass filters, duplexers, and multiplexers.

[0045] XBAR 100 consists of a thin-film conductor pattern formed on the surface of a piezoelectric plate 110, which has substantially parallel front and back faces 112 and 114. The piezoelectric plate is a thin single-crystal layer made of a piezoelectric material, such as lithium niobate, lithium tantalate, lanthanum gallium silicate, gallium nitride, or aluminum nitride. The piezoelectric plate is cut so that the X, Y, and Z crystal axes are known and aligned with respect to the front and back faces. The piezoelectric plate can be Z-cut, meaning the Z-axis is perpendicular to the front and back faces 112 and 114. The piezoelectric plate can be a rotated Z-cut or a rotated YX-cut. XBARs can be fabricated on piezoelectric plates with other crystal orientations.

[0046] The back surface 114 of the piezoelectric plate 110 is attached to the surface of the substrate 120, except for a portion of the piezoelectric plate 110 that is not attached to the surface of the substrate 120. This portion of the piezoelectric plate 110 forms a diaphragm 115, which spans a cavity 140 formed in the substrate. The portion of the piezoelectric plate 110 that spans the cavity is referred to herein as the "diaphragm" 115 because this portion is physically similar to the diaphragm of a microphone. Figure 1 As shown, the diaphragm 115 is adjacent to the remainder of the piezoelectric plate 110 around the entire periphery 145 of the cavity 140. In this case, "adjacent" means "continuous connection without any other items in between". In other configurations, the diaphragm 115 may be adjacent to the piezoelectric plate for at least 50% of the periphery 145 of the cavity 140.

[0047] Substrate 120 provides mechanical support for piezoelectric plate 110. Substrate 120 can be, for example, silicon, sapphire, quartz, or some other material, or a combination of these materials. The back side 114 of piezoelectric plate 110 can be bonded to substrate 120 using wafer bonding processes. Alternatively, piezoelectric plate 110 can be grown on substrate 120, or attached to substrate in some other way. Piezoelectric plate 110 can be directly attached to substrate, or it can be attached via one or more intermediate material layers (…). Figure 1 (Not shown) is attached to substrate 120.

[0048] The conventional meaning of "cavity" is "an empty space within a solid". Cavity 140 can be a hole that completely passes through substrate 120 (as shown in cross-sections AA and BB), or it can be a groove in substrate 120 below diaphragm 115 (as shown in cross-sections AA and BB). Figure 4B (As shown). For example, the cavity 140 can be formed by selectively etching the substrate 120 before or after attaching the piezoelectric plate 110 to the substrate 120.

[0049] The conductor pattern of the XBAR100 includes an interdigital transducer (IDT) 130. The IDT 130 includes a first plurality of parallel fingers, such as fingers 136, extending from a first busbar 132. The IDT 130 also includes a second plurality of fingers extending from a second busbar 134. The term "busbar" refers to a conductor from which the fingers of the IDT extend. The first and second plurality of parallel fingers are staggered. The staggered fingers overlap by a distance AP, which is commonly referred to as the "aperture" of the IDT. The center-to-center distance L between the outermost fingers of the IDT 130 is the "length" of the IDT.

[0050] The first and second buses 132 and 134 serve as terminals of the XBAR 100. An radio frequency or microwave signal applied between the two buses 132 and 134 of the IDT 130 excites the primary acoustic mode within the piezoelectric plate 110. The primary acoustic mode is a bulk shear mode, in which acoustic energy propagates in a direction substantially perpendicular to the surface of the piezoelectric plate 110, which is also perpendicular or transverse to the direction of the electric field generated by the IDT fingers. Therefore, the XBAR is considered a transversely excited thin-film bulk resonator.

[0051] IDT 130 is placed on piezoelectric plate 110 such that at least the fingers of IDT 130 are positioned on diaphragm 115, which spans or hangs over cavity 140. Figure 1 As shown, the cavity 140 is rectangular, and the size of the rectangle is greater than the aperture AP and the length L of IDT 130. The cavity of the XBAR can have different shapes, such as regular or irregular polygons. The cavity of the XBAR can have more or fewer four sides, which can be straight or curved.

[0052] To facilitate Figure 1 As shown, the geometric spacing and width of the IDT fingers are significantly enlarged relative to the length (dimension L) and aperture (dimension AP) of the XBAR. A typical XBAR in an IDT 130 has more than ten parallel fingers. A single XBAR in an IDT 130 may have hundreds, possibly thousands, of parallel fingers. Similarly, the thickness of the IDT fingers and piezoelectric plate is significantly enlarged in the cross-sectional view.

[0053] Referring now to a detailed schematic cross-sectional view, a front dielectric layer 150 may optionally be formed on the front side of the piezoelectric plate 110. By definition, the “front side” of an XBAR refers to the side facing away from the substrate. The front dielectric layer 150 may be formed only between the IDT fingers (e.g., IDT fingers 138b), or it may be deposited as a capping layer such that the dielectric layer is formed between and on the IDT fingers (e.g., IDT fingers 138a). The front dielectric layer 150 may be a non-piezoelectric dielectric material, such as silicon dioxide, aluminum oxide, or silicon nitride. The thickness of the front dielectric layer 150 is typically less than about one-third the thickness of the piezoelectric plate 110. The front dielectric layer 150 may be formed from multiple layers of two or more materials. In some applications, a back dielectric layer (not shown) may be formed on the back side of the piezoelectric plate 110.

[0054] IDT fingers 138a and 138b may be one or more layers of aluminum, aluminum alloy, copper, copper alloy, beryllium, gold, tungsten, molybdenum, chromium, titanium, or certain other conductive materials. If the IDT fingers are made of aluminum or an alloy containing at least 50% aluminum, the IDT fingers are considered "substantially aluminum." If the IDT fingers are made of copper or an alloy containing at least 50% copper, the IDT fingers are considered "substantially copper." A thin layer (relative to the total thickness of the conductor) of other metals (e.g., chromium or titanium) or other metal layers may be formed below and / or above the fingers as layers within the fingers to improve adhesion between the fingers and the piezoelectric plate 110 and / or passivate or encapsulate the fingers and / or improve power handling. The busbar of the IDT ( Figure 1 132 and 134 in the text can be made of the same or different material as the finger.

[0055] Dimension p is the center-to-center spacing or "pitch" of the IDT fingers, which can be referred to as the IDT pitch and / or XBAR pitch. Dimension w is the width or "mark" of the IDT fingers. The geometry of the IDT in an XBAR is significantly different from that used in a surface acoustic wave (SAW) resonator. In a SAW resonator, the IDT pitch is half the wavelength of the sound wave at the resonant frequency. Furthermore, the mark pitch ratio of an SAW resonator IDT is typically close to 0.5 (i.e., the width of the mark or finger is approximately one-quarter of the wavelength of the sound wave at resonance).

[0056] In XBAR, the spacing p of the IDT is typically 2 to 20 times the finger width w. Additionally, the spacing p of the IDT is typically 2 to 20 times the thickness of the piezoelectric plate 210. The width of the IDT fingers in XBAR is not limited to almost a quarter of the wavelength of the acoustic wave at resonance. For example, the width of the XBAR IDT fingers can be 500 nm or greater, thus allowing for easy fabrication of the IDT using photolithography. The thickness of the IDT fingers can range from 100 nm to approximately equal to the width w. The thickness of the IDT's busbars (132, 134) can be equal to or greater than the thickness tm of the IDT fingers.

[0057] Figure 2 This is a plan view of the XBAR 200 with a diaphragm supported by tethers. Like... Figure 1 Like the XBAR 100, the XBAR 200 has a piezoelectric plate 210. A cavity 240 with a periphery 245 is formed in a substrate (not visible) below the piezoelectric plate 210. A first portion of the piezoelectric plate 210 (i.e., the portion outside the cavity periphery 245) is attached to the substrate. Another portion of the piezoelectric plate 210 forms a diaphragm 215 suspended above the cavity 240. Similar to... Figure 1 Unlike diaphragm 115, diaphragm 215 is not adjacent to the rest of piezoelectric plate 210. Instead, diaphragm 215 is separated from piezoelectric plate by a space opening into cavity 240. This open space is bridged only by a plurality of tethers, in which Figure 2 The winning bidders selected ropes 250 and 252.

[0058] The tethers, such as tethers 250 and 252, serve three functions. First, the tethers provide mechanical support to suspend the diaphragm 215 over the cavity 240. Second, by bending, the tethers provide a way to absorb stresses applied to the diaphragm due to device temperature variations. Third, the tethers provide electrical and thermal connections from the first and second IDT buses 232 and 234 to the staggered IDT fingers (where only IDT fingers 236 and 238 are identified in FIG. 2) arranged on the diaphragm 215. The first and second buses 232 and 234 are disposed on a first portion of the piezoelectric plate 210 (the portion attached to the substrate), which is located on opposite sides of the cavity 240. Since each IDT finger must be connected to one of the buses 232 and 234, there is a one-to-one relationship between the IDT fingers and the tethers. Alternate IDT fingers are connected to either bus 232 or bus 234 via their respective tethers.

[0059] Figure 3A and Figure 3B These are cross-sectional views of the XBAR 200 at sections CC and DD, respectively. Figure 2As shown, sections CC and DD are not planar. Section CC follows the path along the center of tether 250 and IDT finger 236. Section DD follows the path along the center of tether 252 and IDT finger 238.

[0060] Back Figure 3A and 3B A piezoelectric plate 210 is attached to a substrate 320. The piezoelectric plate 210 can be a single-crystal lithium niobate, lithium tantalate, or some other piezoelectric material. The orientation of the axis of the piezoelectric plate 210 is known and consistent. The piezoelectric plate 210 can be Z-cut, rotated Z-cut, rotated YX-cut, or some other orientation. The substrate 320 can be silicon, or some other material anisotropically etched to form the cavity 240.

[0061] The diaphragm 215 is part of the piezoelectric plate 210. IDT fingers 236 / 238 are formed of a first conductor layer 362. The first conductor layer 362 can be one or more layers of metal as previously described. The diaphragm 215 is suspended from the cavity 240 and supported by tethers 250, 252. Tethers 250, 252 are formed of a portion of the piezoelectric plate 210 and the first conductor layer 362. A second conductor layer 364 can be formed on all or part of the busbars 232, 234 to improve thermal and electrical conductivity.

[0062] Figure 4A and Figure 4B yes Figure 2 Alternate sectional views of XBAR 200 at section EE as defined in the diagram. These views of XBAR 200 are consistent with... Figure 1 The cross-sectional view AA of the XBAR 100 shown is equivalent.

[0063] A portion of the piezoelectric plate 210 is attached to and supported by the substrate 320. A portion of the piezoelectric plate 210 forms a diaphragm 215, which is suspended above cavities 240, 240' formed in the substrate 320. Figure 1 Unlike XBAR100, the diaphragm 215 of XBAR 200 is not adjacent to the supported portion of piezoelectric plate 210, but is separated from the supported portion of piezoelectric plate 210 by spaces 410, 415. Interlaced IDT fingers, such as fingers 236, 238, are disposed on the diaphragm 215. The IDT fingers are formed from a first conductor layer 362.

[0064] exist Figure 4A In the middle, cavity 240 completely penetrates substrate 320. Figure 4B In this context, cavity 240' is a recess in substrate 320. In this case, cavity 240' can be formed by etching the substrate using an etchant introduced through the space around diaphragm 215 and the space between the tether (in... Figure 4A and 4B (Not visible in the middle).

[0065] Although Figure 3A , Figure 3B , Figure 4A and Figure 4B Although not shown, XBAR 200 may include one or more dielectric layers. For example, XBAR 200 may include a bonding layer disposed between substrate 320 and piezoelectric plate 210. When the substrate is silicon, the bonding layer may be, for example, silicon dioxide. When a bonding layer exists between substrate 320 and piezoelectric plate 210, the bonding layer may be retained on the back side of diaphragm 215 (i.e., the side facing cavity 240) or removed from the back side of diaphragm 215.

[0066] When multiple XBARs are connected in a ladder filter circuit, a dielectric frequency setting layer can be formed on the diaphragm and IDT fingers of the parallel resonators to reduce the resonant frequency of the parallel resonators relative to the resonant frequency of the series resonators. Furthermore, a thin passivation dielectric layer can be applied to most or all of the XBAR 200s to passivate and seal the surfaces.

[0067] Figure 5 This is an enlarged plan view of a single tether 550. Line 515 is the edge of the diaphragm, while line 532 is the edge of the IDT busbar and the cavity. The area between the edge of the diaphragm and the edge of the busbar is a space that opens into the cavity 540 below the diaphragm. Multiple tethers, including tether 550, span this space to hold the diaphragm above the cavity 540. Tether 550 provides electrical and thermal connections between the busbar and the IDT fingers 536 arranged on the surface of the diaphragm.

[0068] The tether 550 includes a first segment 552 extending from the busbar, a third segment 556 extending from the diaphragm, and a second segment 554 connecting the first and third segments 552 and 556. The second segment 554 is configured to bend within the plane of the diaphragm. For this purpose, the second segment 554 forms an angle of inclination relative to the side of the busbar and the longitudinal direction of the IDT fingers 536; that is, the second segment 554 is neither parallel nor perpendicular to either side of the busbar or the longitudinal direction of the IDT fingers 536. For example, the angle θ between the side of the second segment 554 and the longitudinal direction of the IDT fingers 536 can be 30 to 60 degrees.

[0069] exist Figure 5 In the example, the first segment 552 extends perpendicularly from the edge of the busbar. The first segment 552 may extend from the side of the busbar at some other angle. The first segment 552 may not exist; in this case, the second segment 554 will extend from the side of the busbar at an inclined angle.

[0070] exist Figure 5In this example, the third segment 556 extends perpendicularly from the edge of the diaphragm and is collinear with the corresponding IDT finger 536. The third segment 556 may extend from the side of the diaphragm at some other angle. The third segment 556 may not exist, in which case the second segment 554 will extend from the side of the diaphragm at an inclined angle.

[0071] At nominal temperature, the distance between the side of the busbar and the side of the diaphragm is dimension d4, where d4 is the total distance spanned by the tether 550. The second segment 554 of the tether 550 spans a distance d2, which is greater than or equal to 50% of d4. In other words, d2 ≥ d1 + d3, where d1 and d3 are the distances spanned by the first and third tether segments 552 and 556, respectively. One or both of d1 and d3 can be zero. All d1, d2, d3, and d4 are measured perpendicular to the side of the busbar.

[0072] The tether 550 may have some shape other than the three straight segments. For example, one or all of the angles at which segments 552, 554, and 556 intersect may be rounded. The tether 550 may be continuously curved, in which case at least a portion of the curved tether forms an angle of inclination relative to the side of the generatrix and the longitudinal direction of the IDT finger 536.

[0073] When XBARs are used in filters, some power is dissipated on the diaphragm due to resistive losses in the IDT fingers and acoustic or adhesive losses in the IDT fingers and the diaphragm itself. The primary path for removing heat from the diaphragm is conduction along the IDT fingers to the busbar and then to the device substrate. Compared to conventional XBARs, the presence of tethers increases the length of the heat flow path from the diaphragm to the substrate. To reduce the impact of the longer heat flow path, the width of the tethers ( Figure 5 The dimension (wt) in the middle can be greater than the width of the IDT finger ( Figure 5 The dimension w in the diagram. The width of the tether can be, for example, p / 2, where p is the spacing of the IDT.

[0074] All components of an XBAR have their own coefficient of thermal expansion (TCE). The preferred substrate for XBAR devices is silicon wafers, which are inexpensive and have a well-established cavity formation process. However, the TCE of silicon is significantly lower than that of lithium niobate or lithium tantalate, the preferred materials for piezoelectric plates. The expansion or contraction of the XBAR diaphragm in response to temperature changes will be greater than that of the surrounding area (determined by the low TCE of the silicon substrate). This difference in expansion or contraction can cause the diaphragm to bend or become corrugated.

[0075] exist Figure 5In the diagram, the dashed line 515' represents the position of the diaphragm edge (relative to the edge of the busbar) after a 25-degree Celsius temperature increase. Dimension d4' is the new distance from the edge of the busbar to the edge of the diaphragm, which is smaller than the original distance d4. The new position and shape of the tether 550' are shown as dashed lines. The tether 550' has been bent to absorb the change in distance from the edge of the busbar to the edge of the diaphragm.

[0076] Figure 6 This graph shows the displacement of the diaphragm in a conventional X-BAR and the diaphragm supported by tethers due to a 20-degree temperature change. Specifically, the solid line 610 represents the displacement of the diaphragm relative to a plane perpendicular to the diaphragm plane. Figure 1 The remaining portion of the piezoelectric plate shown is adjacent. A temperature change of 20 degrees Celsius causes the diaphragm to ripple with a peak-to-peak amplitude of 850 nm. The displacement along the center of the diaphragm is determined using a simulation performed using the finite element method. In this example, the aperture and length of the IDT are 50 μm and 325 μm, respectively.

[0077] The dotted line 620 is as follows Figure 2 The diagram shows the displacement of the tethered diaphragm perpendicular to its plane. A temperature change of 20 degrees Celsius causes the diaphragm at the IDT end to curl by approximately 40 nm. The difference between the solid line 610 and the dashed line 620 demonstrates the effectiveness of the tether in absorbing the TCE difference between the diaphragm and the substrate, and thus reducing stress in the diaphragm.

[0078] Method Description

[0079] Figure 7 This is a simplified flowchart of method 700 for manufacturing an XBAR with tethered support or a filter containing such an XBAR. Method 700 begins at 705 with a substrate and a piezoelectric material plate, and ends at 795, where the XBAR or filter is completed. Figure 7 The flowchart only includes the main processing steps. (It can be found in...) Figure 7 Various routine process steps (e.g., surface preparation, cleaning, inspection, baking, annealing, monitoring, testing, etc.) are performed before, during, and after the steps shown.

[0080] The piezoelectric plate can be, for example, lithium niobate or lithium tantalate. The piezoelectric plate can be Z-cut, rotary Z-cut, or rotary YX-cut. The piezoelectric plate can be some other material and / or some other cut. The substrate can be a silicon wafer or a silicon-on-insulator wafer. The substrate can be a wafer of some other material that allows deep cavities to be formed through etching or other processes.

[0081] At 720, the substrate and piezoelectric plate are bonded together. Optional steps can be taken to prepare the substrate prior to bonding. For example, at 710A, lateral and / or vertical etch stop layers can be formed in the substrate. A lateral etch stop layer is a structure that limits the lateral extension of a cavity for subsequent etching. A vertical etch stop layer is a structure that limits the depth of a cavity for subsequent etching. Lateral and vertical etch stop layers can be formed in the substrate, as described in pending patent application 16 / 913,417 entitled “TRANSVERSELY-EXCITED FILM BULK ACOUSTIC RESONATOR WITH LATERALETCH STOP,” which is incorporated herein by reference. Alternatively, at 710B, a cavity can be formed in the substrate and then filled with a sacrificial material that will subsequently be removed.

[0082] At 720°, the piezoelectric plate is bonded to the substrate. The piezoelectric plate and substrate can be bonded using a wafer bonding process. Typically, the mating surfaces of the substrate and piezoelectric plate are highly polished. One or more layers of intermediate material, such as oxide or metal, can be formed or deposited on the mating surface of one or both of the piezoelectric plate and substrate. One or both mating surfaces can be activated using, for example, a plasma process. The mating surfaces can then be pressed together with considerable force to establish molecular bonds between the piezoelectric plate and substrate or the intermediate material layer.

[0083] The conductor pattern of the IDT, including each XBAR, is formed at 730 by depositing and patterning one or more conductor layers on the front side of the piezoelectric plate. The conductor layers can be, for example, aluminum, aluminum alloy, copper, copper alloy, titanium, chromium, tungsten, molybdenum, or some other conductive metal. Optionally, one or more layers of other materials can be disposed below the conductor layers (i.e., between the conductor layers and the piezoelectric plate) and / or above the conductor layers. For example, a thin film of titanium, chromium, or other metals can be used to improve adhesion between the conductor layers and the piezoelectric plate. The conductor pattern formed at 730 includes a first conductor layer 362 comprising IDT fingers, tethers, and busbars. The conductor pattern formed at 730 may also include a second conductor layer 364 to improve the electrical and thermal conductivity of portions of the conductor pattern, such as IDT busbars and interconnections between IDTs.

[0084] At 730, a conductor pattern is formed by sequentially depositing a conductor layer and optionally one or more other metal layers on the surface of the piezoelectric plate. Excess metal can then be removed by etching using a patterned photoresist. The conductor layer can be etched, for example, by plasma etching, reactive ion etching, wet chemical etching, and other etching techniques.

[0085] Alternatively, a stripping process can be used at 730° to form the conductor pattern. A photoresist can be deposited on the piezoelectric plate and patterned to define the conductor pattern. A conductor layer, along with one or more optional additional layers, can be sequentially deposited on the surface of the piezoelectric plate. The photoresist can then be removed, removing excess material and leaving the conductor pattern.

[0086] Two conductor layers 362, 364 ( Figure 3A and 3B The layers (shown) and / or any of the metal layers can be deposited and patterned using different processes.

[0087] At 740, a front dielectric layer can be formed by depositing one or more layers of dielectric material on the front side of the piezoelectric plate. Conventional deposition techniques such as sputtering, evaporation, or chemical vapor deposition can be used to deposit one or more dielectric layers. One or more dielectric layers can be deposited over the entire surface of the piezoelectric plate, including on top of the conductor pattern. Alternatively, one or more photolithography processes (using photomasks) can be used to confine the deposition of dielectric layers to selected areas of the piezoelectric plate, for example, confining it only between the interlaced fingers of the IDT. Masks can also be used to allow the deposition of dielectric material of different thicknesses on different portions of the piezoelectric plate.

[0088] After forming the conductor pattern and dielectric layer, the tethers can be defined at 745 by etching piezoelectric plates between the tethers and around the periphery of the diaphragm.

[0089] Then, one or more cavities are formed in the substrate at 750. A separate cavity can be formed for each resonator in the filter device. For example, one or more cavities can be formed by etching the substrate using an etchant introduced through an opening in the piezoelectric plate formed at 745. A separate cavity can be formed for each resonator in the filter device. The extent of the cavity can be defined by a lateral and / or vertical etch stop layer previously formed in the substrate at 710A. Alternatively, the cavity can be formed at 750 by etching or otherwise removing the sacrificial material that filled the cavity previously formed at 710B.

[0090] In all variations of process 700, the filter device is completed at 760. Actions that may occur at 760 include: depositing a packaging / passivation layer such as SiO2 or Si3O4 on the entire or partial device; forming pads or solder bumps or other means for establishing connections between the device and external circuitry; dicing individual devices from a wafer containing multiple devices; other packaging steps; and testing. Another action that may occur at 760 is tuning the resonant frequency of the resonator within the device by adding or removing metal or dielectric material on the front side of the device. After the filter device is completed, the process ends at 795.

[0091] Conclusion

[0092] Throughout this specification, the embodiments and examples shown should be considered as examples and not as limitations on the disclosed or claimed devices and processes. While many of the examples provided herein relate to specific combinations of method actions or system elements, it should be understood that those actions and elements can be combined in other ways to achieve the same objective. Regarding the flowcharts, additional and fewer steps may be taken, and the steps shown may be combined or further refined to implement the methods described herein. Actions, elements, and features discussed in connection with only one embodiment are not intended to exclude their similarity in other embodiments.

[0093] As used herein, “multiple” means two or more. As used herein, a “group” of items may include one or more such items. As used herein, whether in the written description or in the claims, the terms “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” etc., shall be understood as open-ended, i.e., referring to including but not limited to. Only the transitional phrases “consisting of…” and “substantially consisting of…” are closed or semi-closed transitional phrases relative to the claims. Ordinal numbers used in the claims, such as “first,” “second,” “third,” etc., are used to modify claim elements. This does not in itself indicate the priority, order, or sequence of action of one claim element over another, but is merely used to distinguish one claim element with the same name from another element with the same name (but with ordinal numbers), thereby differentiating claim elements. As used herein, “and / or” means that the listed items are alternatives, but alternatives also include any combination of the listed items.

Claims

1. An acoustic resonator device, characterized in that, include: One substrate; A piezoelectric plate, a first portion of which is attached to the substrate, and a second portion of which forms a diaphragm suspended above a cavity in the substrate; An interdigitated transducer (IDT) is formed on the surface of the piezoelectric plate. The IDT includes a first busbar and a second busbar disposed on a first portion and interlaced IDT fingers disposed on the diaphragm. and Multiple tethers support the diaphragm above the cavity, each tether providing an electrical connection between a corresponding finger of the interlaced IDT fingers and one of the first and second busbars, wherein each tether includes a first conductor layer and a corresponding portion of the piezoelectric plate connecting the first and second portions.

2. The device according to claim 1, characterized in that, The first busbar and the second busbar are disposed on opposite sides of the cavity.

3. The device according to claim 2, characterized in that, Interlaced IDT fingers are alternately connected to the first busbar and the second busbar.

4. The device according to claim 1, characterized in that, The interlaced IDT fingers include the first conductor layer.

5. The device according to claim 4, characterized in that, Each of the first busbar and the second busbar includes the first conductor layer and the second conductor layer.

6. The device according to claim 1, characterized in that, A portion of each tether forms an angle with the longitudinal direction of the corresponding interlaced IDT fingers.

7. The device according to claim 6, characterized in that, The angle of inclination is greater than or equal to 30 degrees and less than or equal to 60 degrees.

8. The device according to claim 1, characterized in that, At least a portion of each rope is bent.

9. The device according to claim 1, characterized in that, Each rope is continuously bent.

10. The device according to claim 1, characterized in that, Each tether includes: The first segment extends from either the first busbar or the second busbar; The third segment extends from the septum collinear with the corresponding IDT fingers; and The second segment connects the first segment and the third segment, and the second segment forms an oblique angle with the longitudinal direction of the corresponding IDT finger.

11. The device according to claim 1, characterized in that, The width of each tether is greater than the width of the corresponding IDT finger.

12. The device according to claim 11, characterized in that, The width of each tether is half the distance between the IDT fingers.

13. An acoustic resonator device, characterized in that, include: A piezoelectric plate is attached to a substrate, and a portion of the piezoelectric plate forms a diaphragm suspended above a cavity in the substrate; An interdigital transducer (IDT) is located on the piezoelectric plate. The IDT includes interlaced IDT fingers arranged on the diaphragm and a first busbar and a second busbar not arranged on the diaphragm. and Multiple tethers support the diaphragm above the cavity. Each tether electrically connects a corresponding IDT finger of the interlaced IDT fingers to one of the first and second busbars through an open space between the diaphragm and the piezoelectric plate. Each tether includes a first conductor layer and a corresponding portion of the piezoelectric plate.

14. The device according to claim 13, characterized in that, The first busbar and the second busbar are disposed on opposite sides of the cavity.

15. The device according to claim 14, characterized in that, The interlaced IDT fingers are alternately connected to the first busbar or the second busbar.

16. The device according to claim 13, characterized in that, The interlaced IDT fingers include the first conductor layer.

17. The device according to claim 16, characterized in that, Each of the first busbar and the second busbar includes the first conductor layer and the second conductor layer.

18. The device according to claim 13, characterized in that, Each section of the tether forms an angle with the longitudinal direction of the corresponding intersecting IDT fingers.

19. The device according to claim 18, characterized in that, The angle of inclination is greater than or equal to 30 degrees and less than or equal to 60 degrees.

20. The device according to claim 18, characterized in that, Each tether includes: The first segment extends from either the first busbar or the second busbar; The third segment extends from the diaphragm collinear with the corresponding IDT fingers; and The second segment connects the first segment and the third segment, and the second segment forms an oblique angle with the longitudinal direction of the corresponding interlaced IDT fingers.

21. The device according to claim 13, characterized in that, At least a portion of each rope is bent.

22. The device according to claim 13, characterized in that, Each rope is continuously bent.

23. The device according to claim 13, characterized in that, The width of each tether is greater than the width of the corresponding interlaced IDT fingers.

24. The device according to claim 23, characterized in that, The width of each tether is half the spacing between the interlaced IDT fingers.

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