Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
  • H03H9/15—Constructional features of resonators consisting of piezoelectric or electrostrictive material
  • H03H9/17—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator
  • H03H9/171—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator implemented with thin-film techniques, i.e. of the film bulk acoustic resonator [FBAR] type
  • H03H9/172—Means for mounting on a substrate, i.e. means constituting the material interface confining the waves to a volume
  • H03H9/175—Acoustic mirrors
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
  • H03H9/02—Details
  • H03H9/02007—Details of bulk acoustic wave devices
  • H03H9/02086—Means for compensation or elimination of undesirable effects
  • H03H9/02102—Means for compensation or elimination of undesirable effects of temperature influence
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
  • H03H9/70—Multiple-port networks for connecting several sources or loads, working on different frequencies or frequency bands, to a common load or source
  • H03H9/703—Networks using bulk acoustic wave devices
  • H03H9/706—Duplexers
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/01—Manufacture or treatment
  • H10N30/05—Manufacture of multilayered piezoelectric or electrostrictive devices, or parts thereof, e.g. by stacking piezoelectric bodies and electrodes

Definitions

• the invention relates to BAW resonators whose electroacoustic properties are improved by a reduced self-heating during operation.
• the invention further relates to RF filters or duplexers with appropriately ausgestalte ⁇ th resonators and methods for producing such a resonator.
• the thickness of the piezoelectric sheet ent ⁇ speaks substantially to half the wavelength ⁇ / 2 of the corresponding to the RF signal frequency.
• Such resonators are used in particular in HF filters and duplexers of mobile communication devices.
• HF filters and duplexers of mobile communication devices By a change in heat of a BAW resonator change its acoustic and thus its electrical properties.
• Correspondingly constructed filters therefore respond to a change in temperature due to changes in the center frequencies and bandwidths. Since the filters are subject to strict specifications, a temperature change is undesirable. Although there are ways to compensate for changes in electrical properties despite temperature change. However, a BAW resonator with reduced self-heating is still desirable in any case.
• One way to reduce the self-heating of a BAW resonator is to magnification ßern the resonator ⁇ .
• the BAW resonator with reduced self-heating differs from conventional resonators by a thermal bridge, the heat generated by dissipative losses in the electroacoustic Be ⁇ rich heat to a heat sink, eg. As a Trä ⁇ gersubstrat dissipates.
• a corresponding resonator for this purpose comprises an electroacoustic active region with two electrodes and a piezoelectric layer arranged therebetween.
• the resonator further comprises a carrier substrate as a heat sink and an acoustic mirror arranged between the active region and the carrier substrate.
• the acoustic mirror comprises at least one ply ⁇ low thermal conductivity and a layer of high thermal conductivity.
• the resonator comprises a thermal bridge.
• the location of low thermal conductivity is suitable for egg ⁇ NEN heat flow from the active Due to the relatively low thermal conductivity of the corresponding layer, the heat transfer from the active region to the carrier substrate is reduced, but omitting the layer of low thermal conductivity would bring about a good thermal connection the electro-acoustic range to the carrier substrate, the acoustic mirror would then no longer function properly and the resonator would be useless.
• the thermal bridge is intended to increase the heat flow from the active region to the carrier substrate.
• heat generated in the electroacoustically active region is offered as an additional path of low resistance to the carrier substrate. Based on a heat flow from the electro-acoustically active region to the carrier substrate, a short circuit of least resistance is produced.
• the thermal bridge itself is essentially electroacoustically or electrically active in terms of heat conduction.
• the BAW resonator is therefore at most negligibly degraded in its electrical and acoustic properties. This is in contrast to the attempt to position the low thermal conductivity mirror through higher layers To replace thermal conductivity. For the mirror in from ⁇ alternating sequence layers of high and low acoustic impedance are needed.
• Known materials essentially have either high acoustic impedance and high thermal conductivity or low acoustic impedance and low thermal conductivity.
• the acoustic mirror has one or more further layers of low thermal conductivity in addition to the low thermal conductivity layer.
• the number of layers is determined essentially in terms of its acoustic requirements. The higher the number of layers, the worse in principle the thermal coupling of the electroacoustically active region to the carrier substrate, ie the more layers the mirror has, the greater the influence of the thermal bridge on the reduction of self-heating.
• the layers of low thermal conductivity ⁇ have a low acoustic impedance and the layers of high thermal conductivity a high acoustic impedance on ⁇ .
• the layers of low thermal conductivity may in particular comprise a dielectric material, while the layers of high thermal conductivity comprise or consist of a metal Metal or an alloy exist.
• the usual materials such as silicon dioxide can be used for layers of low acoustic impedance and low thermal conductivity or heavy metals such as tungsten for the layers of high acoustic impedance and high thermal conductivity.
• the thermal bridge has a higher thermal conductivity than the layer of low thermal conductivity.
• the thermal conductivity of the thermal bridge may be smaller, equal to or greater than the thermal conductivity of the layers of high thermal conductivity.
• the thermal bridge is substantially non-acoustic active in choosing the material of the thermal bridge can be exclusively borrowed the ability to conduct heat into consideration while choosing the material capable of high thermal conductivity ⁇ ability in the mirror and whose acoustic properties be ⁇ be taken into have to. It is possible that the distance between the thermal bridge and the active region is smaller than the distance between the active region and the carrier substrate. Further, it is mög ⁇ Lich that the distance between the heat bridge and the Trä ⁇ gersubstrat smaller than the distance between the active loading is rich and the carrier substrate.
• the distance between two elements is the route length of the shortest connection between these two elements.
• thermal bridges Having the thermal bridges a short distance from the active region or support substrate allows it to conduct heat well away from the active region and / or to the support substrate to lead.
• the thermal conductivity of the thermal bridge itself is relatively high. Due to the small distance between the thermal bridge and the corresponding area, sufficient heat flow is possible, even if the material between the bridge and the corresponding area is separated by a material of lower thermal conductivity.
• the thermal bridge connects both directly to the active region and to the carrier substrate and short-circuits the active region and the carrier substrate with respect to a heat flow.
• the thermal bridge has a region enclosing the active region in the lateral direction.
• the electroacoustically active area is within the range of the thermal bridge.
• the thermal bridge can maintain a sufficient distance in the lateral direction so as not to disturb the acoustics of the resonator. In the vertical direction, the thermal bridge can extend from the layers of the active area down to the substrate.
• the resonator is arranged alone or together with other low self-heating resonators on a carrier substrate, e.g. B. in a ladder type structure, so it is particularly possible that the different stack of positions of the different resonators are arranged side by side.
• the surface of the carrier substrate is generally slightly larger than the sum of the areas of the electro-acoustic regions of the various resonators. Therefore exist around the electroacoustic areas, in which material of the thermal bridge, the heat from various electroacoustic Regions of the resonators can dissipate to the carrier substrate, can be arranged.
• the carrier substrate does not need to be larger than in the case of conventional resonators or filters. Without further negative properties, the self-heating of the resonators or the filter is improved.
• the heat bridge it is alternatively or additionally possible for the heat bridge to have a region which is arranged in at least one layer of low thermal conductivity. This region connects at least one layer of high thermal conductivity to the active region or to the carrier substrate. It is alternatively or additionally possible for the thermal bridge to have a region which is arranged in at least one layer of low thermal conductivity and connects two layers of high thermal conductivity to one another. Without disturbing the acoustics of the layer stack, z. B. by the corresponding area of a layer is chosen sufficiently small, the layers of low thermal conductivity z. B. columnar or cylindrical sections that short in relation to a heat flow layers of high thermal conductivity of the stack.
• Corresponding areas within the layers of low heat ⁇ conductivity can include segments that z. B. act as a phononic grating and improve the acoustics in the mirror. So z. B. possible to limit lateral oscillations in the mirror to a few or even a single mode.
• the material of the thermal bridge, z. B. be ⁇ ner acoustic impedance, be selected accordingly.
• Such a filter or individual resonators with reduced self-heating can be used in a duplexer, e.g. B. in one
• Frontend circuit of a mobile communication device to be interconnected.
• Segments of different areas of the thermal bridge can in particular a two- or three-dimensional periodic grating, z. B. the o.g. phononic grid, form.
• the segments of the grating may be configured in size, shape and location to satisfy the Bragg condition with respect to an undesired mode frequency to limit the otherwise free propagation of this mode.
• the segments can z. B. have a width of ⁇ / 4 based on the unwanted mode.
• the spacing of the segments in the horizontal direction may also be ⁇ / 4.
• the quarter wavelength be preferred.
• the width of the segments and the horizontal distance may be identical or different.
• the width n can be ⁇ / 4 and the distance m ⁇ / 4 and m> n. It is particularly possible that m is much larger, z. B. 2, 5, 10, 20 or 100 times greater than n.
• the larger m is compared to n, the smaller the influence on the (longitudinal) main mode propagating in the vertical direction.
• the widths and the states of the segments in different electro-acoustically active regions can be chosen differently and on the
• the thermal bridge may comprise various materials.
• various modifications of carbon such as diamond, carbon nanotube or graphite, sapphire, ruby or another modification of an aluminum oxide, silicon (Si) or
• Germanium (Ge) Germanium (Ge). But also other materials such as oxides of the metals silver (Ag), copper (Cu), gold (Au), potassium (K), molybdenum (Mo), brass, zinc (Zn), magnesium (Mg), tungsten (W), Sodium (Na), nickel (Ni), iron (Fe), platinum (Pt), tin (Sn), tantalum (Ta), lead (Pb) or titanium (Ti) or oxide ceramics with one or more of these metals
• said metals or alloys with these metals may be contained in the thermal bridge.
• the uppermost layer of the thermal bridge may contain metal. However, to avoid the electrical properties of the resonator, a dielectric material in the uppermost layer is preferred.
• a method for producing a BAW resonator with reduced self-heating comprises the steps:
• the method comprises steps for structuring a thermal bridge, which is provided and suitable for transferring heat from the active region to the carrier substrate.
• the steps for forming the thermal bridge are the customary to We ⁇ sentlichen steps for the layer deposition and / or patterning, z.
• lithography processes with resist layers and exposure processes include.
• the process is carried out so that the thermal bridge comprises a region having a material height ⁇ rer thermal conductivity than the layers lower réelleleitfä ⁇ ability.
• the thermal bridge is structured in such a way that at least one of its regions encloses the active region laterally.
• the area of the thermal bridge can form a frame structure around the electro-acoustically active area and heat can lead laterally past the mirror from the active area to the carrier substrate.
• the method comprises steps during which a region of the thermal bridge is structured that has a material of higher thermal conductivity than the layers of low thermal conductivity and is structured within the layers of low thermal conductivity.
• This region within the layers of low thermal conductivity can have an array of periodically arranged fields which are suitable for selecting desired modes and thereby improving the coupling of the resonator.
• Fig. 1 the operation of the thermal bridge as a short circuit with respect to the heat conduction from a heat source to a heat sink, the arrangement of different BAW resonators on a carrier substrate, a cross section through a possible stack of layers of a resonator, a cross section through a stack of sheets, in which the thermal bridge by a frame-shaped structure is formed, a cross-section through a stack of sheets, wherein the thermal bridge a region with segments high Has thermal conductivity between mirror layers of high thermal conductivity, a horizontal cross section through a layer of low thermal conductivity, are arranged in the segments of the thermal bridge,
• Fig. 7 a Que Riehtung du
• FIG. 8 shows a cross section in the horizontal direction through a layer of low thermal conductivity, wherein the thermal bridge comprises on the one hand a region with segments within the layer of low thermal conductivity and on the other hand a frame which encloses the layer of low thermal conductivity.
• FIG. 1 illustrates the function of the thermal bridge.
• Heat source WQ, z. B an electroacoustically active area during the operation of a BAW resonator example, heat is generated by dissipative ⁇ losses.
• heat ⁇ valley WS the carrier substrate of a BAW serves for example resonator.
• the acoustic mirror is arranged, which is constructed in alternating order layers with high thermal conductivity WL and substantially heat insulating layers WI.
• the thermal conductivity between the heat source WQ and the heat sink WS is particularly insulating by the heat
• FIG. 2 shows the top view of an RF filter F, which comprises a plurality of BAW resonators BAWR, which are arranged on a carrier substrate TS.
• the electroacoustically akti ⁇ ven areas and the areas of electrical contact are marked black. The remaining areas (marked hatched) can serve to accommodate one or more thermal bridges WB without disturbing the acoustics of the resonators.
• FIG. 3 shows a horizontal cross section through a stack of layers of a BAW resonator BAWR.
• the layer stack is arranged on a carrier substrate TS, which serves as a heat sink WS.
• the carrier substrate may, for example, silicon, z.
• crystalline silicon which provides a sufficiently high thermal conductivity to absorb the heat from the electroacoustic region EAB and dissipate it to the environment.
• the electroacoustic active region EAB comprises a lower electrode EL and an upper electrode EL and a piezoelectric material therebetween. Below the lower electrode EL, a layer stack of alternately arranged layers of low thermal conductivity WI and high thermal conductivity WL is arranged. The materials of the mirror are first Line selected with respect to the acoustics of the layer stack.
• the piezoelectric material between the electrodes EL has a higher thermal conductivity than the material of the layers niedri ⁇ ger thermal conductivity WI.
• the material of the piezo-electric layer can simultaneously serve as the material of réellebrü ⁇ blocks WB and dissipate on a direct path from the heat elec- roakustician range EAB to the carrier substrate TS. In this case, the piezoelectric layer is widened in such a way that it completely covers the stack of mirror layers and connects the electroacoustic region directly to the carrier substrate TS, without disturbing the acoustics of the resonator BAWR
• Figure 4 shows an embodiment in which - analogous to the embodiment of Figure 3 - two upper electrode layers and a piezoelectric layer arranged therebetween form the elektroakus ⁇ tables area EAB. Including mirror layers with alternating thermal conductivity and accordingly alternating ⁇ the acoustic impedance are arranged.
• the layer stack of the BAW resonator BAWR is in turn arranged on a carrier substrate as a heat sink WS.
• a frame structure of layers of relatively high thermal conductivity is formed flan ⁇ kierend the layer stack of the mirror. These layers form the heat bridges, the heat from the electroacoustic area EAB
• Material of the piezoelectric layer leads to the heat sink WS ⁇ leads.
• the thermal bridge WB is better acoustically decoupled here.
• FIG. 5 shows an embodiment in which the thermal bridge WB covers an area in the layers of low thermal conductivity having.
• the area comprises a plurality of individual segments in the different layers, which can deliver heat as heat transfer between the individual layers of high thermal conductivity from the electroacoustic area to the heat sink.
• the segments of the region of the thermal bridge WB are in principle angeord ⁇ net in areas of the resonator, in the acoustic waves propagate - albeit downwards with decreasing intensity. However, even an improvement in acoustics and / or in particular coupling can be obtained if the segments are dimensioned accordingly and selected for their acoustic impedance.
• the segments of the thermal bridge WB can thus form a phononic grid and reduce or avoid the formation of undesirable vibration modes. Unavoidable unwanted modes of reduced intensity can be trapped and their effects reduced.
• FIG. 6 shows a cross section in the horizontal direction through a layer of low thermal conductivity WI, in which segments of the thermal bridge WB are arranged in a lattice structure and form a phononic lattice.
• the cross section of the individual segments may be square, rectangular, elliptical, circular or a more complex structure, for. B. different polygon shapes have.
• the shape of the cross section and the area of the cross-section ⁇ in the vertical direction are constant, which enables a simplified manufacturing process.
• Figure 7 shows a further possibility, the segments of the heat bridge WB in the layers of low thermal conductivity to arrange WI ⁇ . Accordingly, the segments are arranged as crossing stripes. Heat can thus be easily transferred not only in verti ⁇ ler, but also in the horizontal direction which facilitates heat dissipation, should the heat generation in the electroacoustic area be inhomogeneous.
• FIG. 8 shows a cross section through a layer of low thermal conductivity, in which the thermal bridge comprises both a first region WB1, which is arranged in the form of a frame around the resonator stack.
• Another region WB2 includes segments within the low conductivity layer.
• thermal bridge is not limited to individual Be ⁇ rich.
• the individual described areas of a thermal bridge can be combined and thereby be a thermal bridge with even greater conductivity.
• WI Location low thermal conductivity, heat isolie ⁇ -saving position

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• Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)

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• 2014
  • 2014-11-25 DE DE102014117238.8A patent/DE102014117238B4/de not_active Expired - Fee Related
• 2015
  • 2015-11-10 JP JP2017527692A patent/JP6668347B2/ja active Active
  • 2015-11-10 US US15/528,713 patent/US10298202B2/en active Active
  • 2015-11-10 EP EP15791317.9A patent/EP3224946A1/de not_active Withdrawn
  • 2015-11-10 CN CN201580061603.5A patent/CN107005220B/zh not_active Expired - Fee Related
  • 2015-11-10 WO PCT/EP2015/076197 patent/WO2016083121A1/de active Application Filing

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