WO2019170461A1 - Baw resonator with increased quality factor - Google Patents

Baw resonator with increased quality factor Download PDF

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Publication number
WO2019170461A1
WO2019170461A1 PCT/EP2019/054585 EP2019054585W WO2019170461A1 WO 2019170461 A1 WO2019170461 A1 WO 2019170461A1 EP 2019054585 W EP2019054585 W EP 2019054585W WO 2019170461 A1 WO2019170461 A1 WO 2019170461A1
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WIPO (PCT)
Prior art keywords
layer
baw resonator
mirror
foregoing
top electrode
Prior art date
Application number
PCT/EP2019/054585
Other languages
French (fr)
Inventor
Thomas Pollard
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RF360 Europe GmbH
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Publication date
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Publication of WO2019170461A1 publication Critical patent/WO2019170461A1/en

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/125—Driving means, e.g. electrodes, coils
    • H03H9/13—Driving means, e.g. electrodes, coils for networks consisting of piezoelectric or electrostrictive materials
    • H03H9/132—Driving means, e.g. electrodes, coils for networks consisting of piezoelectric or electrostrictive materials characterized by a particular shape
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; 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
    • H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
    • H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
    • H03H3/02—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks
    • H03H2003/025—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks the resonators or networks comprising an acoustic mirror
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02007—Details of bulk acoustic wave devices
    • H03H9/02086—Means for compensation or elimination of undesirable effects
    • H03H9/02118—Means for compensation or elimination of undesirable effects of lateral leakage between adjacent resonators
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/54—Filters comprising resonators of piezo-electric or electrostrictive material
    • H03H9/58—Multiple crystal filters
    • H03H9/582—Multiple crystal filters implemented with thin-film techniques
    • H03H9/586—Means for mounting to a substrate, i.e. means constituting the material interface confining the waves to a volume
    • H03H9/589—Acoustic mirrors

Definitions

  • the present invention refers to BAW resonators, e.g. for RF filters, having improved acoustic and electric properties.
  • BAW resonators can be used to build bandpass or band rejection filters for RF applications, e.g. wireless communication devices. Such devices can use filters comprising such resonators.
  • wireless communication devices e.g. wireless communication devices.
  • Such devices can use filters comprising such resonators.
  • communication devices have an energy source with limited energy resources and power saving circuits are preferred.
  • BAW resonators have an active region comprising a sandwich construction with a piezoelectric material between a bottom electrode and a top electrode. Due to the piezoelectric effect such resonators convert between RF signals and
  • BAW resonators are known from US 9,571,063 B2 and from US 9, 219, 464 B2.
  • An acoustic Bragg mirror is arranged between the sandwich construction of the resonator and the substrate onto which the layer stack is deposited. On top of the sandwich the leap of acoustic impedance from the top resonator layer to environmental air is sufficient for reflecting acoustic waves back into the resonator.
  • Such resonators are classified as SMR type BAW resonators (solidly mounted resonator) .
  • An acoustic Bragg mirror comprises at least one pair of mirror layers with alternating high and low acoustic
  • SiCy (a commonly used low impedance mirror material employed in state of the art BAW resonators) is a material with relatively more intrinsic acoustic losses compared to high impedance (e.g. W) and piezoelectric
  • the SiCy losses in the topmost low impedance layer of the mirror can be considered significant relative to the lower low impedances layers because it hosts and operates with a significant acoustic energy at the BAW resonator' s resonance and anti-resonance frequency as it is closer to the region of maximum energy distribution that is in the piezoelectric and top and bottom electrodes.
  • a material is provided for at least the topmost low impedance layer that produce less acoustic losses than SiCy. In combination with a conventional high impedance mirror layer the quality factor of the mirror and hence of the whole BAW resonator is improved.
  • a BAW resonator of the SMR type comprising a layer of a piezoelectric material sandwiched between a bottom electrode and a top electrode, a substrate and an acoustic Bragg mirror arranged between the sandwich and a substrate.
  • the mirror comprises a stack of mirror layers of alternating low and high acoustic impedance with at least one SiCy layer as a low impedance layer.
  • At least the top mirror layer is a high quality low impedance layer that has an acoustic material quality superior to that of SiCy.
  • the high quality low impedance layer comprises one high quality AIN layer that may or may not be doped with Sc. This material produces lower acoustic losses than conventionally used SiCy.
  • AIN has an acoustic impedance higher than SiCy the impedance leap to the high impedance layer is smaller and the reflection of the top pair of mirror layers is lower which also tends to reduce the electromechanical coupling factor of the resonator. Without further measures this would reduce the quality factor Qmirror and hence the quality factor Qsmr of the whole resonator.
  • a third mirror is added below the high quality mirror to keep Qmirror sufficiently high enough compared to a conventional mirror in a state of the art BAW resonator wherein the acoustic mirror comprises two mirrors.
  • Each conventional mirror comprises Si0 2 as a low impedance layer and W as a high impedance layer.
  • an alternative higher piezoelectrically-active material could be employed as the main piezoelectric layer, such as Sc doped AIN.
  • the top most two mirror layers comprise high quality materials respectively embodied as polycrystalline materials.
  • the high quality low impedance layer comprises polycrystalline high quality AIN or AlScN
  • a high quality high impedance layer comprises polycrystalline high impedance material.
  • the material W may be used like in conventional mirrors of SMR BAW resonators. Again, in order to compensate for a drop in resonator
  • an alternative higher piezoelectrically- active material could be employed as the main piezoelectric layer, such as Sc doped AIN.
  • a further improvement of the mirror quality can be achieved when using a high impedance material having a larger acoustic impedance than W. Possible materials can be chosen from Ir and Ft. Then it may be possible to keep the number of mirrors that is the number of pairs of mirror layers at two like in a conventional mirror.
  • any other material with less acoustic impedance than AIN may be used for the topmost low impedance layer. Accordingly, any other material with higher acoustic impedance than W may be used for the topmost high impedance layer.
  • High impedance layers may be chosen from Mo, and Ru .
  • the BAW resonator comprises a bottom electrode of W and AlCu, a piezoelectric layer of A1 or AlScN and a top electrode of W and AlCu.
  • promoting oriented crystal growth can be added as well -- e.g. thin layers of Ti or AIN below the top or bottom
  • electrode W layers In addition thin layers of TiN can be applied to the top surface of top and/or bottom electrodes to act as a capping layer to act as an etch-stop layers for additional resonator detuning layers, e.g. additional W layer to shift frequency down.
  • a dielectric layer of SiN for example may cover the whole resonator for device passivation purposes .
  • a BAW resonator may comprise
  • central region e.g. a raised frame
  • a frame or other mode suppression/shaping feature can be applied along the top electrode outer perimeter to reduce spurious mode coupling and improve fundamental mode quality factor.
  • the flap structure is provided for counterbalancing
  • the trench, the frame and the flap structure act together to shape the oscillation mode in order to avoid spurious modes.
  • the trench in the top electrode is characterized by a recess in the top electrode. This means that the trench is located at an area where the thickness of the top electrode is smaller than the thickness of the top electrode in the center area .
  • the trench may be formed by reducing the thickness of any layer in the trench region, e.g. by reducing the SiN layer in this region to be less than that in the resonator central area.
  • the frame is characterized by additional material arranged along the top electrode outer perimeter.
  • the material may be chosen from a dielectric like SiCy or from higher impedance materials like W.
  • the total added thickness of the layers above the piezoelectric layer in the frame region is higher than in the center area.
  • Fig. 1 shows a cross-section through a conventional
  • Fig. 2 shows a cross-section through a BAW resonator
  • Fig. 3a to 3e show cross-sections through the top electrode of a BAW resonator with various possible embodiments of flap structures .
  • Figs. 4 to 6 show schematic block diagrams of filter circuits comprising a cross-section through a resonator stack having a Bragg structure in the top electrode connection.
  • Fig. 1 shows a schematic cross-section through a conventional BAW resonator having some additional features.
  • An improved resonator of the invention is based on this conventional structure .
  • the layer stack of the resonator is formed on a substrate SU of e.g. Si. Any other suitable rigid material can be used too.
  • a layer of Si0 2 may be formed for isolation purpose.
  • an acoustic Bragg mirror is formed and structured on the substrate SU comprising two mirrors Ml, M2 that is from two pairs of mirror layers.
  • the Bragg mirror high
  • impedance layer HI and low impedance layers LI are
  • High impedance layer HI may comprise W and low impedance layers LI comprise SiCy.
  • Additional thin adhesion or orientation-promoting layers may be deposited below the mirror pair, e.g. Ti or AIN.
  • the bottom electrode BE is formed using a hybrid highly conductive AlCu layer and a high impedance W layer. Again a thin adhesion or orientation-promoting layer may be employed between the bottom electrode and uppermost mirror, e.g. Ti or AIN. Also a capping and/or etch-stop layer may be applied to the top of the AlCu layer to allow patterning of additional resonator detuning material located between the Tungsten and AlCu layer of the bottom electrode. Atop the bottom
  • a piezoelectric layer PL of e.g. AIN or AlScN is formed.
  • the thickness thereof is set to lower than half the wavelength of the desired resonance frequency due the
  • All the above layers in the stack are continuous layers all extending at least over the later active resonator area.
  • a frame structure FR of e.g. Si0 2 or W is formed that surrounds the center area CA of the resonator.
  • This frame structure FR may be applied just between the tungsten layer of the top electrode TE and the piezoelectric layer PL. A position of the frame structure FR between any other two layers or above the top layer is possible too.
  • top electrode TE In the center area CA and above the frame structure a stack of layers form the top electrode TE and the top dielectric passivation layer. Starting on the surface of the
  • piezoelectric layer PL a thin adhesive Ti layer, a tungsten layer, an AlCu layer, a thin TiN layer and a dielectric layer of e.g. SiN are deposited.
  • the SiN layer provides device passivation as serves as frequency fine-tuning trimming layer .
  • Fig. 2 shows a cross-section through a BAW resonator
  • a third mirror M3 deposited above the second mirror M2 of Fig. 1 and just below the bottom electrode. Thickness of the layers of the third mirror M3 are set as usual in view of a desired reflection band. However, deposition process is controlled to allow growth of polycrystalline mirror layers having improved acoustic impedance and quality.
  • a CVD, a PECVD or a sputter method may be used.
  • the condition are set and controlled to achieve a slow and homogeneous crystal growing.
  • Other process parameters too like temperature, gas flow, pressure or BIAS voltage are carefully controlled to support a regular
  • Fig. 3a to 3e are cross-sections through the top electrode of a BAW resonator to show various possible embodiments of flap structures FL that may be formed at the BAW resonator for improving and forming the desired wave mode and for
  • Fig. 3 does not differentiate or depict different materials that are comprised by the shown structure. Hence the structure is depicted unitary though it may not be formed from a uniform material.
  • the depicted structure comprises all top electrode layers of the top electrode TE, the frame and the top dielectric layer.
  • the structure of Fig. 3 rests on the piezoelectric layer PL that is not shown.
  • the flap structure FL of Fig. 3A is a linear extension of any material that is directed inwardly to the center area.
  • the flap structure FL of Fig. 3B is a linear extension that is directed upwardly.
  • Fig. 3C shows a flap structure FL that is directed outwardly to enclose an angle to the surface of 0 to 90 degrees.
  • the flap structure FL of Fig. 3E extends outwardly but is inclined versus the surface.
  • the flap structures FL are oriented in an angle with respect to the wave vector of a main mode of the resonator.
  • the angle can be selected from 0°, 45°, 90°, and 135°. In this case, when the angle is 45°, the flap structure points towards the top side. When the angle equals 135°, the flap structure points towards the bottom side.
  • the angle can be, e.g., between 0° and 45° or between 45° and 90° or between 90° and 135° or between 135° and 180°.
  • Figs. 4 to 6 show schematic block diagrams of filter circuits comprising resonators that are circuited to form RF filters. BAW resonators as described above may advantageously be used in these filter circuits.
  • Figure 4 shows a ladder-type arrangement comprising series BAW resonators SRs and parallel BAW resonators BRp that may be formed according to the invention with high quality mirror layers.
  • a respective series BAW resonator SRs and an according parallel BAW resonator BRp form a basic section BS LT of the ladder-type arrangement.
  • a ladder-type arrangement comprises a number of basic sections BS LT that can be circuited in series to achieve a desired filter function .
  • Figure 5 shows a block diagram of a hybrid filter that is depicted with a minimum number of elements.
  • a real circuit may comprise a higher number of such structures.
  • a first partial circuit PCI of the hybrid filter comprises a series impedance element I Es and a parallel impedance element I Ep .
  • the series impedance element I Es can be embodied as a capacitor and the parallel impedance elements I Ep can be embodied as a coil.
  • a second partial circuit PC2 comprises at least one series BAW resonator BRs and at least one parallel BAW resonator BRp .
  • first and second partial circuits PCI, PC2, as shown in Figure 4 and 6, can alternate or be arranged in an arbitrary sequence.
  • the exact design of such a hybrid filter can be optimized according to the requirements of the desired hybrid filter. Such an optimization can easily be done by a skilled worker by means of an optimizing computer program.
  • Figure 6 shows a lattice-type arrangement of BAW resonators comprising series and parallel BAW resonators.
  • the parallel BAW resonators BRp are arranged in parallel branches that interconnect two series signal lines with series BAW resonators BRs .
  • the parallel branches are circuited in a crossover arrangement such that the basic section of the lattice-type arrangement BS L C comprises a first and a second series BAW resonator SRs arranged in two different signal lines and two parallel branches circuited to mutually cross over with a respective parallel BAW resonator SRp arranged therein.
  • a lattice-type filter may comprise a higher number of basic sections
  • Two or more of the filter circuits as shown in Figs 4 to 6 may form combined filters like duplexers or multiplexers.
  • the filters may be used in RF circuits as band pass, notch or edge filters.
  • the filter circuits may be combined with other circuit elements not shown or mentioned but generally known from the art.
  • the invention has been explained by a limited number of examples only and is thus not restricted to these examples. The invention is defined by the scope of the claims and may deviate from the provided embodiments.
  • Ml to M3 mirror comprising a LI and a HI mirror layer

Abstract

A BAW resonator of the SMR type is provided comprising a sandwich of a piezoelectric material (PL) between a bottom electrode (BE) and a top electrode (TE), a substrate (SU) and an acoustic Bragg mirror (M1, M2, M3) arranged between sandwich and substrate. The Bragg mirror comprises a stack of mirror layers of alternating low and high acoustic impedance with at least one SiO2layer as a low impedance layer. At least the top mirror layer is a high quality low impedance layer (HQLI), e.g. AIN or AIScN, having an acoustic material quality superior to that of SiO2. Aim is to reduce losses through the mirror and thereby increase the quality factor of the mirror and the resulting resonator.

Description

Description
BAW resonator with increased quality factor
The present invention refers to BAW resonators, e.g. for RF filters, having improved acoustic and electric properties.
BAW resonators (BAW = bulk acoustic wave) can be used to build bandpass or band rejection filters for RF applications, e.g. wireless communication devices. Such devices can use filters comprising such resonators. Usually, wireless
communication devices have an energy source with limited energy resources and power saving circuits are preferred.
BAW resonators have an active region comprising a sandwich construction with a piezoelectric material between a bottom electrode and a top electrode. Due to the piezoelectric effect such resonators convert between RF signals and
acoustic waves if an RF signal is applied to the resonator electrodes .
BAW resonators are known from US 9,571,063 B2 and from US 9, 219, 464 B2.
One way to keep the acoustic energy within the layer stack of the active region is to use acoustic mirrors. An acoustic Bragg mirror is arranged between the sandwich construction of the resonator and the substrate onto which the layer stack is deposited. On top of the sandwich the leap of acoustic impedance from the top resonator layer to environmental air is sufficient for reflecting acoustic waves back into the resonator. Such resonators are classified as SMR type BAW resonators (solidly mounted resonator) . An acoustic Bragg mirror comprises at least one pair of mirror layers with alternating high and low acoustic
impedance. In current BAW resonators mirror layers are chosen to provide an impedance leap as high as possible. Tungsten has been a good choice for a high impedance mirror layer while the availability and relatively low impedance of silicon oxide makes SiCy a preferred low impedance mirror layer .
It has been found out that the Q factor (QSmr) of a BAW SMR resonator can be broken down into the combination of three Q factors :
(i) mirror Q (Qmirror) ;
(ii) lateral Q (Qiateral) ; and
(iii) material Q (Qmat) , where
1/Qsmr — 1/Qmirro^ + 1 / Qiateral + 1 / Qmaterial ·
Calculations using a current sophisticated exemplary design and its material parameters have shown that the BAW SMR design and lateral geometry improvements permit a Qmirror of about 20k and a Qiaterai of about 10k. However, Qmaterial is limited to about 3.2k and hence represents the most limiting factor in improving the quality factor of the whole BAW resonator .
As a consequence the achievable QSmr seems to be limited to around 2.5k for operation at roughly 2-3 GHz.
It is an object of the invention to provide a BAW resonator that has a further increased quality factor Qsmr. This and other objects are met by a BAW resonator according to claim 1. Further improvements and preferred embodiments are provided by dependent claims.
It has been observed that SiCy (a commonly used low impedance mirror material employed in state of the art BAW resonators) is a material with relatively more intrinsic acoustic losses compared to high impedance (e.g. W) and piezoelectric
materials (e.g. AIN) . As a result, the SiCy losses in the topmost low impedance layer of the mirror can be considered significant relative to the lower low impedances layers because it hosts and operates with a significant acoustic energy at the BAW resonator' s resonance and anti-resonance frequency as it is closer to the region of maximum energy distribution that is in the piezoelectric and top and bottom electrodes. Hence, a material is provided for at least the topmost low impedance layer that produce less acoustic losses than SiCy. In combination with a conventional high impedance mirror layer the quality factor of the mirror and hence of the whole BAW resonator is improved.
A BAW resonator of the SMR type is provided comprising a layer of a piezoelectric material sandwiched between a bottom electrode and a top electrode, a substrate and an acoustic Bragg mirror arranged between the sandwich and a substrate. The mirror comprises a stack of mirror layers of alternating low and high acoustic impedance with at least one SiCy layer as a low impedance layer. At least the top mirror layer is a high quality low impedance layer that has an acoustic material quality superior to that of SiCy.
According to a preferred embodiment the high quality low impedance layer comprises one high quality AIN layer that may or may not be doped with Sc. This material produces lower acoustic losses than conventionally used SiCy.
Because AIN has an acoustic impedance higher than SiCy the impedance leap to the high impedance layer is smaller and the reflection of the top pair of mirror layers is lower which also tends to reduce the electromechanical coupling factor of the resonator. Without further measures this would reduce the quality factor Qmirror and hence the quality factor Qsmr of the whole resonator. For compensation of this effect a third mirror is added below the high quality mirror to keep Qmirror sufficiently high enough compared to a conventional mirror in a state of the art BAW resonator wherein the acoustic mirror comprises two mirrors. Each conventional mirror comprises Si02 as a low impedance layer and W as a high impedance layer. In order to compensate for a drop in resonator
electromechanical coupling, if required, an alternative higher piezoelectrically-active material could be employed as the main piezoelectric layer, such as Sc doped AIN.
According to a more preferred embodiment the top most two mirror layers comprise high quality materials respectively embodied as polycrystalline materials. While the high quality low impedance layer comprises polycrystalline high quality AIN or AlScN a high quality high impedance layer comprises polycrystalline high impedance material. The material W may be used like in conventional mirrors of SMR BAW resonators. Again, in order to compensate for a drop in resonator
electromechanical coupling due to lower mirror impedance ratios, if required, an alternative higher piezoelectrically- active material could be employed as the main piezoelectric layer, such as Sc doped AIN. Alternatively a further improvement of the mirror quality can be achieved when using a high impedance material having a larger acoustic impedance than W. Possible materials can be chosen from Ir and Ft. Then it may be possible to keep the number of mirrors that is the number of pairs of mirror layers at two like in a conventional mirror.
But any other material with less acoustic impedance than AIN may be used for the topmost low impedance layer. Accordingly, any other material with higher acoustic impedance than W may be used for the topmost high impedance layer.
Other possible high impedance layers may be chosen from Mo, and Ru .
According to an embodiment the BAW resonator comprises a bottom electrode of W and AlCu, a piezoelectric layer of A1 or AlScN and a top electrode of W and AlCu.
Intervening layers for improvement of adhesion or for
promoting oriented crystal growth can be added as well -- e.g. thin layers of Ti or AIN below the top or bottom
electrode W layers. In addition thin layers of TiN can be applied to the top surface of top and/or bottom electrodes to act as a capping layer to act as an etch-stop layers for additional resonator detuning layers, e.g. additional W layer to shift frequency down. A dielectric layer of SiN for example may cover the whole resonator for device passivation purposes .
As further design features a BAW resonator may comprise
- a center area wherein the three layers of the sandwich and mirror overlap each other - a trench laterally surrounding the center area
- mode suppression/shaping feature (s) surrounding the
central region, e.g. a raised frame
- a flap structure mechanically connected to the top
electrode, surrounding the center area and extending either inwardly to the center area, upwardly or
outwardly .
In the sandwiched center area bulk acoustic waves are
generated. A frame or other mode suppression/shaping feature can be applied along the top electrode outer perimeter to reduce spurious mode coupling and improve fundamental mode quality factor.
The flap structure is provided for counterbalancing
oscillations of the center area.
Further, the trench, the frame and the flap structure act together to shape the oscillation mode in order to avoid spurious modes.
The trench in the top electrode is characterized by a recess in the top electrode. This means that the trench is located at an area where the thickness of the top electrode is smaller than the thickness of the top electrode in the center area .
Alternatively, the trench may be formed by reducing the thickness of any layer in the trench region, e.g. by reducing the SiN layer in this region to be less than that in the resonator central area. As an example the frame is characterized by additional material arranged along the top electrode outer perimeter.
The material may be chosen from a dielectric like SiCy or from higher impedance materials like W. The total added thickness of the layers above the piezoelectric layer in the frame region is higher than in the center area.
As a consequence, a BAW resonator with improved electric and acoustic properties is obtained.
In the following the BAW resonator of the invention will be explained in more detail with reference to embodiments and the accompanied figures. The drawings are schematic only. Details may be depicted in enlarged form that neither a dimension nor a relation of dimensions can be taken from the figures .
Fig. 1 shows a cross-section through a conventional
resonator .
Fig. 2 shows a cross-section through a BAW resonator
comprising a high quality low impedance layer.
Fig. 3a to 3e show cross-sections through the top electrode of a BAW resonator with various possible embodiments of flap structures .
Figs. 4 to 6 show schematic block diagrams of filter circuits comprising a cross-section through a resonator stack having a Bragg structure in the top electrode connection.
Fig. 1 shows a schematic cross-section through a conventional BAW resonator having some additional features. An improved resonator of the invention is based on this conventional structure .
The layer stack of the resonator is formed on a substrate SU of e.g. Si. Any other suitable rigid material can be used too. On top of the Si body a layer of Si02 may be formed for isolation purpose.
Next, an acoustic Bragg mirror is formed and structured on the substrate SU comprising two mirrors Ml, M2 that is from two pairs of mirror layers. In the Bragg mirror, high
impedance layer HI and low impedance layers LI are
alternating. The mirror layers may slightly vary in thickness to set a desired reflection band. High impedance layer HI may comprise W and low impedance layers LI comprise SiCy.
Additional thin adhesion or orientation-promoting layers may be deposited below the mirror pair, e.g. Ti or AIN.
Next the bottom electrode BE is formed using a hybrid highly conductive AlCu layer and a high impedance W layer. Again a thin adhesion or orientation-promoting layer may be employed between the bottom electrode and uppermost mirror, e.g. Ti or AIN. Also a capping and/or etch-stop layer may be applied to the top of the AlCu layer to allow patterning of additional resonator detuning material located between the Tungsten and AlCu layer of the bottom electrode. Atop the bottom
electrode W a piezoelectric layer PL of e.g. AIN or AlScN is formed. The thickness thereof is set to lower than half the wavelength of the desired resonance frequency due the
additional mass loading effect from being attached to the top/bottom electrodes and mirror. All the above layers in the stack are continuous layers all extending at least over the later active resonator area.
On top of the piezoelectric layer PL a frame structure FR of e.g. Si02 or W is formed that surrounds the center area CA of the resonator. This frame structure FR may be applied just between the tungsten layer of the top electrode TE and the piezoelectric layer PL. A position of the frame structure FR between any other two layers or above the top layer is possible too.
In the center area CA and above the frame structure a stack of layers form the top electrode TE and the top dielectric passivation layer. Starting on the surface of the
piezoelectric layer PL a thin adhesive Ti layer, a tungsten layer, an AlCu layer, a thin TiN layer and a dielectric layer of e.g. SiN are deposited. The SiN layer provides device passivation as serves as frequency fine-tuning trimming layer .
Fig. 2 shows a cross-section through a BAW resonator
comprising a high quality low impedance layer HQLI and optionally a high impedance layer HQHI . These two layers form a third mirror M3 deposited above the second mirror M2 of Fig. 1 and just below the bottom electrode. Thickness of the layers of the third mirror M3 are set as usual in view of a desired reflection band. However, deposition process is controlled to allow growth of polycrystalline mirror layers having improved acoustic impedance and quality.
For the deposition, a CVD, a PECVD or a sputter method may be used. Preferably the condition are set and controlled to achieve a slow and homogeneous crystal growing. Other process parameters too like temperature, gas flow, pressure or BIAS voltage are carefully controlled to support a regular
orientation and the formation of large grains within the polycrystalline layers.
Fig. 3a to 3e are cross-sections through the top electrode of a BAW resonator to show various possible embodiments of flap structures FL that may be formed at the BAW resonator for improving and forming the desired wave mode and for
counterbalancing oscillations that mainly are generated in the center area CA.
For simplification only Fig. 3 does not differentiate or depict different materials that are comprised by the shown structure. Hence the structure is depicted unitary though it may not be formed from a uniform material. The depicted structure comprises all top electrode layers of the top electrode TE, the frame and the top dielectric layer. The structure of Fig. 3 rests on the piezoelectric layer PL that is not shown.
The flap structure FL of Fig. 3A is a linear extension of any material that is directed inwardly to the center area.
The flap structure FL of Fig. 3B is a linear extension that is directed upwardly.
Fig. 3C shows a flap structure FL that is directed outwardly to enclose an angle to the surface of 0 to 90 degrees.
According to Fig. 3E the flap structure FL extends
horizontally outwardly from the frame structure FR. The flap structure FL of Fig. 3E extends outwardly but is inclined versus the surface.
It is possible that the flap structures FL are oriented in an angle with respect to the wave vector of a main mode of the resonator. The angle can be selected from 0°, 45°, 90°, and 135°. In this case, when the angle is 45°, the flap structure points towards the top side. When the angle equals 135°, the flap structure points towards the bottom side. However, other angles are also possible. The angle can be, e.g., between 0° and 45° or between 45° and 90° or between 90° and 135° or between 135° and 180°.
Figs. 4 to 6 show schematic block diagrams of filter circuits comprising resonators that are circuited to form RF filters. BAW resonators as described above may advantageously be used in these filter circuits.
Figure 4 shows a ladder-type arrangement comprising series BAW resonators SRs and parallel BAW resonators BRp that may be formed according to the invention with high quality mirror layers. In this embodiment a respective series BAW resonator SRs and an according parallel BAW resonator BRp form a basic section BSLT of the ladder-type arrangement. A ladder-type arrangement comprises a number of basic sections BSLT that can be circuited in series to achieve a desired filter function .
Figure 5 shows a block diagram of a hybrid filter that is depicted with a minimum number of elements. A real circuit may comprise a higher number of such structures. In Figure 5 a first partial circuit PCI of the hybrid filter comprises a series impedance element I Es and a parallel impedance element I Ep . The series impedance element I Es can be embodied as a capacitor and the parallel impedance elements I Ep can be embodied as a coil. A second partial circuit PC2 comprises at least one series BAW resonator BRs and at least one parallel BAW resonator BRp . Within the combined filter circuit first and second partial circuits PCI, PC2, as shown in Figure 4 and 6, can alternate or be arranged in an arbitrary sequence. The exact design of such a hybrid filter can be optimized according to the requirements of the desired hybrid filter. Such an optimization can easily be done by a skilled worker by means of an optimizing computer program.
Figure 6 shows a lattice-type arrangement of BAW resonators comprising series and parallel BAW resonators. In contrast to the ladder-type arrangement, the parallel BAW resonators BRp are arranged in parallel branches that interconnect two series signal lines with series BAW resonators BRs . The parallel branches are circuited in a crossover arrangement such that the basic section of the lattice-type arrangement BSLC comprises a first and a second series BAW resonator SRs arranged in two different signal lines and two parallel branches circuited to mutually cross over with a respective parallel BAW resonator SRp arranged therein. A lattice-type filter may comprise a higher number of basic sections
according to the filter requirements.
Two or more of the filter circuits as shown in Figs 4 to 6 may form combined filters like duplexers or multiplexers. The filters may be used in RF circuits as band pass, notch or edge filters. The filter circuits may be combined with other circuit elements not shown or mentioned but generally known from the art. The invention has been explained by a limited number of examples only and is thus not restricted to these examples. The invention is defined by the scope of the claims and may deviate from the provided embodiments.
List of reference symbols
BE bottom electrode
BRP parallel BAW resonator
BRS series BAW resonator
BSLC basic section of a lattice filter arrangement
BSLT basic section of a ladder type arrangement
FL flap structure
FR frame structure
HI high acoustic impedance layer
HQHI high quality high impedance layer
HQLI high quality low impedance layer
IEP parallel impedance element
IES series impedance element
LI low acoustic impedance layer and
Ml to M3 mirror comprising a LI and a HI mirror layer
PL piezoelectric layer between
SiN dielectric layer
SU substrate
TE top electrode

Claims

Claims (We claim)
1. A BAW resonator of the SMR type comprising
a sandwich of a piezoelectric material between a bottom electrode and a top electrode
a substrate and
an acoustic Bragg mirror arranged between sandwich and substrate, comprising
a stack of mirror layers of alternating low and high acoustic impedance with at least one SiCy layer as a low impedance layer
at least the top mirror layer being a high quality low impedance layer having an acoustic material quality superior to that of SiCy.
2. The BAW resonator of the foregoing claim,
wherein the high quality low impedance layer comprises AIN or AIN doped with Sc.
3. The BAW resonator of one of the foregoing claims,
wherein at least the topmost pair at mirror layers comprises a high quality polycrystalline material respectively.
4. The BAW resonator of one of the foregoing claims,
wherein at least the topmost pair of mirror layers comprises a high quality high impedance layer chosen from the group of W, Mo, Ru, Ir and Pt .
5. The BAW resonator of one of the foregoing claims,
comprising three pairs of mirror layers.
6. The BAW resonator of one of the foregoing claims,
comprising a bottom electrode of W, a piezoelectric layer of A1 or AlScN and a top electrode of AlCu.
7. The BAW resonator of one of the foregoing claims,
comprising a dielectric layer covering at least the top electrode and possibly surrounding top surfaces of the piezoelectric layer.
8. The BAW resonator of one of the foregoing claims,
comprising
- a center area wherein the three layers of the sandwich overlap each other
- a trench surrounding the center area
- a frame, surrounding the trench
- a flap structure mechanically connected to the top
electrode, surrounding the center area and extending either inwardly to the center area, upwardly or
outwardly .
9. The BAW resonator of the foregoing claim,
wherein the flap structure is a 3-D structure formed from a dielectric or from the top electrode material.
10. The BAW resonator of one of the foregoing claims, wherein in the trench the thickness of the layers above the piezoelectric layer is reduced in view of the center area, wherein the trench is formed by reducing the thickness of the top electrode or by reducing the thickness of the dielectric layer above the top electrode.
PCT/EP2019/054585 2018-03-05 2019-02-25 Baw resonator with increased quality factor WO2019170461A1 (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113293355A (en) * 2021-06-11 2021-08-24 武汉大学 Temperature-resistant and wear-resistant AlCrN/AlScN nano composite piezoelectric coating for intelligent bolt and preparation method thereof
CN117294278A (en) * 2023-11-24 2023-12-26 广州市艾佛光通科技有限公司 Composite resonator and preparation method thereof

Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050029629A1 (en) * 2003-08-07 2005-02-10 Tdk Corporation Substrate for electronic device, electronic device and methods of manufacturing same
US20080169728A1 (en) * 2007-01-15 2008-07-17 Kengo Asai Piezoelectric thin film resonator, piezoelectric thin film resonator filter and manufacturing method thereof
DE102010032365A1 (en) * 2010-07-27 2012-02-02 Epcos Ag Resonator is operated by acoustic bulk wave and has trim section with silicon dioxide, silicon nitride and titanium, where lower electrode is arranged with layer of aluminum copper
US20120096697A1 (en) * 2010-10-26 2012-04-26 Avago Technologies Wireless Ip (Singapore) Pte. Ltd. Method of forming acoustic resonator using intervening seed layer
US20150280687A1 (en) * 2014-03-31 2015-10-01 Avago Technologies General Ip (Singapore) Pte.Ltd. Acoustic resonator comprising acoustic redistribution layers and lateral features
US20150318837A1 (en) * 2014-04-30 2015-11-05 Avago Technologies General Ip (Singapore) Pte. Ltd. Acoustic resonator device with air-ring and temperature compensating layer
US9219464B2 (en) 2009-11-25 2015-12-22 Avago Technologies General Ip (Singapore) Pte. Ltd. Bulk acoustic wave (BAW) resonator structure having an electrode with a cantilevered portion and a piezoelectric layer with multiple dopants
US20160126930A1 (en) * 2011-02-28 2016-05-05 Avago Technologies General Ip (Singapore) Pte. Ltd. Bulk acoustic wave resonator comprising a ring
US9571063B2 (en) 2014-10-28 2017-02-14 Avago Technologies General Ip (Singapore) Pte. Ltd. Acoustic resonator device with structures having different apodized shapes

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050029629A1 (en) * 2003-08-07 2005-02-10 Tdk Corporation Substrate for electronic device, electronic device and methods of manufacturing same
US20080169728A1 (en) * 2007-01-15 2008-07-17 Kengo Asai Piezoelectric thin film resonator, piezoelectric thin film resonator filter and manufacturing method thereof
US9219464B2 (en) 2009-11-25 2015-12-22 Avago Technologies General Ip (Singapore) Pte. Ltd. Bulk acoustic wave (BAW) resonator structure having an electrode with a cantilevered portion and a piezoelectric layer with multiple dopants
DE102010032365A1 (en) * 2010-07-27 2012-02-02 Epcos Ag Resonator is operated by acoustic bulk wave and has trim section with silicon dioxide, silicon nitride and titanium, where lower electrode is arranged with layer of aluminum copper
US20120096697A1 (en) * 2010-10-26 2012-04-26 Avago Technologies Wireless Ip (Singapore) Pte. Ltd. Method of forming acoustic resonator using intervening seed layer
US20160126930A1 (en) * 2011-02-28 2016-05-05 Avago Technologies General Ip (Singapore) Pte. Ltd. Bulk acoustic wave resonator comprising a ring
US20150280687A1 (en) * 2014-03-31 2015-10-01 Avago Technologies General Ip (Singapore) Pte.Ltd. Acoustic resonator comprising acoustic redistribution layers and lateral features
US20150318837A1 (en) * 2014-04-30 2015-11-05 Avago Technologies General Ip (Singapore) Pte. Ltd. Acoustic resonator device with air-ring and temperature compensating layer
US9571063B2 (en) 2014-10-28 2017-02-14 Avago Technologies General Ip (Singapore) Pte. Ltd. Acoustic resonator device with structures having different apodized shapes

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
GARCIA-PASTOR D ET AL: "Nonlinear effects of electrode and Bragg reflector materials in BAW resonators", 2017 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM, 6 September 2017 (2017-09-06), pages 1 - 4, XP033244916 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113293355A (en) * 2021-06-11 2021-08-24 武汉大学 Temperature-resistant and wear-resistant AlCrN/AlScN nano composite piezoelectric coating for intelligent bolt and preparation method thereof
CN117294278A (en) * 2023-11-24 2023-12-26 广州市艾佛光通科技有限公司 Composite resonator and preparation method thereof

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