HIGH Q BULK ACOUSTIC RESONATOR WITH DIELECTRIC FLAPS

Abstract

A high Q acoustic BAW resonator with high coupling and improved spurious mode suppression is given. The BAW resonator comprises an active resonator region (AR) formed by an overlap of the three layers bottom electrode (BE), piezoelectric layer (PL) and top electrode layer (TE). An inner-flap (IF) is formed by a dielectric 3D structure sitting on a marginal region (MR) of the active resonator region (AR) or adjacent thereto, extending inwardly towards the center thereof and having a section that runs in parallel and distant to the top surface of the resonator keeping an inner gap (IG) thereto or an angle .

Claims

1. A BAW resonator, comprising in a sequence from bottom to top a substrate (SU) a bottom electrode (BE) a piezoelectric layer (PL) a top electrode (TE) wherein an active resonator region (AR) is formed by an overlap of the three layers bottom electrode, piezoelectric layer and top electrode layer an inner-flap (IF) formed by a dielectric 3D structure is sitting on a marginal region (MR) of the active resonator region (AR) or adjacent thereto, is extending inwardly towards the center of the active resonator region (AR) and having a section that runs with a distance to the top surface of the resonator.

2. The BAW resonator of claim 1, wherein the top electrode (TE) is electrically terminated at one side edge by a top electrode connection (TC) above the top electrode connection an outer-flap (OF) is sitting on the top electrode connection (TC), extending away from the active resonator region (AR) and having a projecting section that runs in parallel and distant to the top surface of the top electrode connection keeping an outer gap (OG).

3. The BAW resonator of claim 1, wherein the outer-flap (OF) and inner-flap (IF) form a common 3D structure.

4. The BAW resonator of claim 1, wherein the outer-flap extends along the whole perimeter of the active resonator region (AR) keeping an outer extending gap (OG) to the underlying layer at all peripheral positions thereof.

5. The BAW resonator of claim 4, wherein the inner-flap (IF) extends inwardlay keeping an inner gap (IG) of constant height to the underlying layer.

6. The BAW resonator of claim 1, wherein the resonator comprises a marginal region (MR) in which the top electrode (TE) has a lower thickness than in the active resonator region (AR) and forms a step to the central area.

7. The BAW resonator of claim 1, wherein the top electrode (TE) comprises a marginal region (MR) in which the overlying passivation layer (IL) has a lower thickness than in the active resonator region (AR) and the thickness of the top electrode (TE) is the same in the marginal region (MR) and the active resonator region (AR).

8. The BAW resonator of claim 7, wherein the inner-flap (IF) follows the topography of the surface in the margin region keeping an inner gap (IG) of constant height.

9. The BAW resonator of claim 1, wherein a passivation layer (IL) covers the BAW resonator at least in the active resonator region (AR).

10. The BAW resonator of claim 1, wherein the common 3D structure of inner-flap (IF) and outer-flap (OF) is at least partly arranged above the dielectric layer.

11. The BAW resonator of claim 1, wherein the substrate (SU) comprises a recess (RC) below the active resonator region (AR) forming an air-filled cavity.

12. The BAW resonator of claim 1, wherein the substrate (SU) comprises a bragg mirror (BM) arranged below the active resonator region (AR).

Description

[0027] In the following the invention will be explained in more detail with reference to specific embodiments and the accompanying figures. The figures are schematically only and are not drawn to scale. For better understanding some detail may be depicted in enlarged form.

[0028] FIG. 1 shows a cross-sectional view through a BAW resonator according to the art;

[0029] FIG. 2 shows a cross-sectional view through a BAW resonator according an embodiment with inner-flaps and outer-lap, trench, and under-lap formed by patterning of the passivation layer, whereas the left side of the image shows a bottom electrode connection region and the right side of the image shows a top electrode region;

[0030] FIG. 3 shows an embodiment that has the same features of the FIG. 2 embodiment, but is an SMR resonator type rather than an FBAR type;

[0031] FIG. 4 shows an embodiment that has the same features of the FIG. 2 embodiment, but has a TE connection electrode that is thinner than the active region electrode;

[0032] FIG. 5 shows in a cross-sectional view an embodiment that has the same features of the FIG. 2 embodiment, but has the under-lap being formed in the top electrode rather than in the passivation layer;

[0033] FIG. 6 shows in a cross-sectional an embodiment that has the same features of the FIG. 2 embodiment, but also includes optional outer-flaps in each of the following termination types: (i) non-connection, (ii) top-electrode connection, and (iii) bottom-electrode connection regions;

[0034] FIG. 7 shows in a cross-sectional view an embodiment that has the same features of the FIG. 2 embodiment, but has inner-flaps that are not entirely parallel to the device surface, but rather are formed with a particular angle, but are generally pointed inward toward the active area;

[0035] FIG. 8 shows an embodiment that has the same features of the FIG. 2 embodiment, but the bottom electrode (for type I and/or type ii terminations) is terminated before the substrate anchor point.

[0036] A cross-sectional view through BAW resonator according to the art is depicted in FIG. 1. In a substrate SU of silicon for example a recess RC is formed. The active resonator region AR is arranged above the recess RC and comprises a substrate a bottom electrode BE, a piezoelectric layer PL and a top electrode TE. The bottom electrode Bauelement covers the recess RC. Under-lap UL, over-lap OL.sub.E, and outer-flap OF.sub.E structures are patterned out of the top electrode TE for termination regions of type i (none) and iii (bottom). In the under-lap UL.sub.E region the top electrode is thinner than in the active region AR. In the over-lap OL.sub.E region the top electrode TE is thicker than the active region AR. Here, the outer-flap OF.sub.E is made of metal and extends outward from the active region AR. For the type ii termination region (top) an under-lap UL, over-lap OL.sub.E, and an acoustic bridge AB connection are formed. The acoustic bridge forms the tope elecectrode connection TC for connecting the top electrode to another resonator or a terminal of a filter. A passivation layer IL is applied over the top electrode TE, but does not passivate the sides of the electrode or the underside of the top electrode connection connection TC (air bridge).

[0037] FIG. 2 shows a cross-sectional view through a BAW resonator according to a first embodiment. Along the total perimeter of the active resonator region AR a dielectric 3D structure structured from a dielectric layer DL forms inner flaps IF. A top electrode connection TC is structured from an extension of the top electrode layer TE. The top electrode TE has same thickness in the active region AR and the top electrode conection TC. The outer-lap OL is the part of the dielectric layer that directly contacts the piezoelectric layer PL along the perimeter of the active region AR but not at the region of the top electrode connection TC.

[0038] In a section of the passivation layer IS that covers the top electrode TE in the margin region MR the thickness of the passivation layer IL and/or dielectric layer DL is reduced by an under-lap UL.

[0039] The 3D structure/dielectric layer DL has an overlap with the region where the under-lap UL is formed. This overlap is a small margin having a width G and extends along the whole perimeter of the active region with the exception of the section where the top electrode connection TC is formed. In this margin the 3D structure forming the inner-flap IF sits on the passivation layer IL at a region where it overlaps the bottom electrode BE.

[0040] In a trench TR that structures the dielectric layer DL/passivation layer IS the top surface of the piezoelectric layer PL is exposed but not in the top electrod connection TC.

[0041] Between inner-flap IF and dielectric layer an inner gap IG is formed where the dielectric 3D structure is in a constant distance to the dielectric surface. Over the top electrode connection passivation layer IS and dielectric layer DL have the original thickness.

[0042] The 3D structure/dielectric layer DL is formed from e.g. SiN and sits on the passivation layer IL. The inner flap IF that is the inwardly projecting part of the 3D structure follows the topography of the top electrode layer TE in a constant distance keeping the inner gap IG of constant height. Hence, the inner flap follows the step from the under-lap UL to the active region AR.

[0043] The bottom electrode BE may be elongated at on side edge of the active resonator region AR to form a bottom electrode connection BC.

[0044] A thin passivation layer IL of e.g. SiN or SiO.sub.2 covers the total surface of the top electrode TE and the top electrode connection TC. The thickness of the passivation layer IL is smaller than the thickness of the inner flaps and hence smaller than the thickness of the layer the 3D structure is structured from.

[0045] Under the active resonator region AR the substrate has an air-filled recess RC like shown in the prior art resonator of FIG. 1.

[0046] Bottom and top electrode BE, TE are made commonly used materials. The materials may be chosen from tungsten W, molybdenum Mo, and AlCu alloy or the electrodes may be multilayer hybrid electrodes e.g. W/AlCu. The piezoelectric layer PL may comprise AlScN that is aluminium nitride AlN that additionally contains scandium nitride ScN.

[0047] The substrate SU preferably comprises silicon Si but may made from other suitable material too like HTCC and LTTC ceramics for example.

[0048] Passivation layer IL and dielectric 3D structures may comprise the same material e.g. SiN.

[0049] The non-connection region (not shown) is similar to the bottom electrode connection region, but has a bottom electrode that is terminated after the outer-lap termination.

[0050] FIG. 3 shows a second embodiment of a new BAW resonator similar to the first embodiment. As an alternative to the recess RC, a Bragg mirror BM is arranged between substrate SU and bottom electrode BE. The Bragg mirror BM comprises alternating layers of a first material HI of high acoustic impedance and a second material LI of low acoustic impedance. The different layers of the acoustic Bragg mirror BM may form layers with decreasing area that a stepped mesa structure is formed. For clarity reasons the stepped Bragg mirror is not depicted.

[0051] The first material of high acoustic impedance HI may be a metal like thungsten W for example. The second material of low acoustic impedance LI may be a dielectric like SiO.sub.2 for example. Usually, the high impedance layers HI are structured and embedded with the second material that is a dielectric to avoid coupling with neighbored resonators. Bottom electrode BE and the further layers above are embodied the same way as shown and explained with reference to FIG. 2.

[0052] FIG. 4 shows a cross-sectional view through a BAW resonator according a third embodiment. This embodiment complies with the first embodiment with the exception that the thickness D of the top electrode in the top electrode connection TC is thinner than in the active region AR.

[0053] A fourth embodiment of the invention is shown in FIG. 5. This embodiment complies with the first embodiment as shown in FIG. 2 with the exeption that the thickness H of the top electrode TE in the active region AR is reduced by an underlap UL in the margin region. Thickness of passivation layer IS may be the same in the active region AR and in the margin region MR.

[0054] FIG. 6 shows a fifth embodiment. Along the whole perimeter of the active resonator region AR the dielectric layer DL/3D structure forms inner flaps IF as shown in FIG. 2. Along the whole perimeter of the active resonator region AR the dielectric layer forming the 3D structure additionally forms outer flaps OF where the dielectric layer extends the outer-lap OL in a distance to the surface passivation layer IS. Thereby, an outer gap OG is formed. All other features of this embodiment may comply with FIG. 2. However, the passivation layer IL covers the entire surface of the top electrode TE, the top electrode connection TC and may further cover the piezoelectric layer PL where it is not covered by the top electrode TE or top electrode connection TC. Hence, the trench TR that is present in the embodiments of FIGS. 2 to 5 is omitted.

[0055] In this embodiment, the outer flaps are optional feature for each termination type I, ii and iii.

[0056] FIG. 7 shows a BAW resonator according to a sixth embodiment in a cross-sectional view. This embodiment that has the same features like the BAW resonator shown in FIG. 2 according to the first embodiment embodiment, but has inner-flaps IF that are not entirely parallel to the device surface, but rather are formed with a particular angle , but are generally pointed inward toward the active region AR.

[0057] FIG. 8 shows a seventh embodiment that has the same features of the FIG. 2 embodiment with the exception that the bottom electrode BE (for type I and/or type ii terminations) is terminated before the substrate anchor point where the bottom electrode BE contacts the edge of the substrate SU in the recess RC.

[0058] The manufacture of the BAW resonator can be done in accordance with well-known processes. Each layer may be deposited separately and may be structures if requires after deposition. Deposition methods are sputtering, and CVD methods that can be plasma enhanced. The electrodes may be reinforced by galvanic process. Resist masks and photolithography may be used where required. Projecting parts (inner and outer flaps) are formed by means of a sacrificial layers underlying the projecting portion when applied as a layer. After lateral structuring the dielectric layer (precursor of the 3D structure) the sacrificial layer can be removed by etching. A sacrificial layer of SiO.sub.2 can be selectively etched against SiN so that SiN can function as an etch stop. With other words, SiO.sub.2 can be etched without removing the SiN of the dielectric 3D structure.

[0059] In the figures only one resonator is depicted respectively. In reality, on a large area substrate a number of BAW resonators may be manufactured in parallel. Circuiting such resonators to a filter circuit in a ladder type arrangement, electrical connections and circuitry can be manufactured in an integrated process.

[0060] As the invention has been depicted in few concrete embodiments only the scope of the invention may not be restricted to the specified embodiments. Further, embodiments are possible that combine features that are shown in different figures. Any other variation within the scope is possible too.

LIST OF USED REFERENCE SYMBOLS

[0061] AB air bridge [0062] AR active resonator region [0063] BC bottom electrode connection [0064] BE bottom electrode [0065] BM Bragg mirror [0066] D thickness of top electrode in top electrode connection [0067] DL dielectric layer forming 3D structures [0068] G margin where 3D structure overlaps section of under-lap [0069] H height of top electrode in active region [0070] HI first material of high acoustic impedance [0071] IF inner flap [0072] IG inner gap [0073] IL passivation layer [0074] LI second material of low acoustic impedance [0075] MR marginal region [0076] OF outer-flap [0077] OG outer gap [0078] OL outer-lap [0079] PL piezoelectric layer [0080] RC recess in SU [0081] SU substrate [0082] TC top electrode connection [0083] TE top electrode [0084] TR trench [0085] UL under-lap [0086] angle of inner-flaps in embodiment 6