This application is a National Stage Application of PCT/CN2018/097237, filed 26 Jul. 2018, and which application is incorporated herein by reference. A claim of priority is made to the above-disclosed application.

TECHNICAL FIELD

The present disclosure relates to the field of radio frequency device technologies, and in particular, to a bulk acoustic wave resonator, a manufacturing method of the same, and a filter.

BACKGROUND

Surface Acoustic Wave Filter (SAW) and Film Bulk Acoustic Wave Filter (BAW) are currently two important technologies employed in a radio frequency (RF) filter of a smartphone.

With popularization of the 4th Generation mobile communication technology (4G)/Long Term Evolution (LTE) multi-band smartphone and trial operation of the 5th Generation mobile communication technology (5G), the frequency of mobile communication is getting higher, the bandwidth thereof is getting wider, and the performance requirements of the RF filter becomes stricter.

Bulk acoustic wave filters have been widely used in 4G communication due to their lower insertion loss, better roll-off characteristics, lower temperature coefficient, and greater power handling. However, with the trial operation of 5G, data transmission rate of mobile communication is getting greater, and spectrum resources are becoming more crowded. This, on one hand, requires the filter to have a wider bandwidth and, on the other hand, requires the filter to have better roll-off characteristics and lower insertion loss. Since the operating frequency of the bulk acoustic wave filter is inversely proportional to the thickness of film, electrodes of the bulk acoustic wave filter will become thinner at higher frequencies, which will in turn cause connection resistance to become larger, thereby affecting the insertion loss of the bulk acoustic wave filter. Therefore, it is of great importance to reduce the connection resistance of the bulk acoustic wave filter.

The bulk acoustic wave resonator is an element for constituting a bulk acoustic wave filter, and its basic structure includes a layer of piezoelectric film, a bottom electrode and a top electrode sandwiched between both sides of the piezoelectric film, and an acoustic reflection unit located under the bottom electrode. The overlapping region of the acoustic reflection unit, the bottom electrode, the top electrode, and the piezoelectric film forms an active region for the bulk acoustic wave resonator to operate. When a RF signal is applied between the electrodes, the piezoelectric film vibrates due to the inverse piezoelectric effect and generates sound waves that propagate in a direction perpendicular to the electrode surface and are reflected at the upper and lower interfaces. When the frequency of the applied RF signal is the same as the resonator frequency of the piezoelectric film, the RF signal can pass, thereby achieving the filtering effect.

Chinese Patent No. 103166596A (CN103166596A) discloses a resonator and a filter, wherein a thin film piezoelectric resonator includes a substrate E, an acoustic reflection structure D, a lower electrode B, a piezoelectric layer P, an upper electrode T and a connection structure C. The overlapping portion of the upper electrode T, the piezoelectric layer P, the lower electrode B, and the acoustic reflection structure D is defined as active region A of the thin film piezoelectric resonator. The upper electrode T includes a portion T1 in the active region and a leadout portion T2 as illustrated inFIG. 1. The connection structure C added to the resonator is outside the active region where the resonator operates (d is greater than or equal to 0.1 um), but the resistance of the signal passing through the electrode edge is not reduced, thus, the connection resistance of the resonator cannot be effectively reduced.

US Patent No. 20170346462 A1 (US20170346462A1) discloses a method of manufacturing a bulk acoustic wave resonator 70 including a substrate 71, a bottom electrode 72, a bottom electrode thickness increasing layer 73, an additional metal member 74, a PZ material layer 75, a first top electrode 76 and a second top electrode 77 as illustrated inFIG. 2. The bulk acoustic wave resonator manufacturing method can avoid the bottom electrode being etched too thin to affect the electrical connection when the contact hole of the piezoelectric film is etched. However, the additional metal is distributed outside the active region of the resonator, and therefore, the bottom electrode resistance between the additional metal and the active region cannot be reduced. Further, since the bottom electrode and the top electrode of the bulk acoustic wave resonator have thicknesses close to each other in general design of the bulk acoustic wave filter, the top electrode still has a relatively large electric resistance.

In summary, the existing bulk acoustic wave resonator has the following technical defects: although the connection resistance is reduced to some extent, the connection resistance is still large which would affect the performance, such as insertion loss etc., of the bulk acoustic wave filter; and with an increase in operating frequency, the thickness of the electrode of the bulk acoustic wave resonator will become thinner, and the resistance will become larger. The above effects are even more obvious in the high frequency bulk acoustic resonator and filter.

SUMMARY

(1) Technical Problem to be Solved

The present disclosure provides a bulk acoustic wave resonator, a manufacturing method thereof, and a filter which can at least partially address the above-mentioned technical problems.

(2) Technical Solutions

According to an aspect of the present disclosure, there is provided a bulk acoustic wave resonator comprising: a substrate; an acoustic reflection unit on the substrate; a piezoelectric stack structure on the acoustic reflection unit; and a pad on the piezoelectric stack structure; wherein the pad has an overlapping region with the acoustic reflection unit.

In some embodiments, the piezoelectric stack structure includes: a bottom electrode; a piezoelectric film on the bottom electrode; and a top electrode on the piezoelectric film.

In some embodiments, the piezoelectric stack structure further includes a conductive thin film disposed above or under the bottom electrode, and the conductive thin film has an overlapping region with the acoustic reflection unit.

In some embodiments, the top electrode has an overlapping region of a width d5with the conductive thin film; the overlapping region of the conductive thin film and the acoustic reflection unit has a width of d3; the distance between a non-connect edge of the top electrode and the acoustic reflection unit is d4; d3=d4+d5, d4≥0, d5=k1λ/4, where λ is an equivalent wavelength of the bulk acoustic wave resonator, and k1is an odd number.

In some embodiments, the pad is in contact with the top electrode at a connect edge of the top electrode, and the overlapping region of the pad and the acoustic reflection unit has a width of d6, d6=k2λ/4, where λ is an equivalent wavelength of the bulk acoustic wave resonator, k2is an odd number, and k1≥k2;

a contact hole is formed in the piezoelectric film and above the conductive thin film, and the bulk acoustic wave resonator further includes another pad formed at the contact hole to be in contact with the conductive thin film or the bottom electrode.

According to another aspect of the present disclosure, there is provided a filter including a plurality of bulk acoustic wave resonators which are cascaded.

According to another aspect of the present disclosure, there is provided a method of manufacturing a bulk acoustic wave resonator, comprising: forming an acoustic reflection unit on a substrate; forming a piezoelectric stack structure on the acoustic reflection unit; and forming a pad on the piezoelectric stack structure; wherein the pad has an overlapping region with the acoustic reflection unit.

In some embodiments, forming a piezoelectric stack structure on the acoustic reflection unit includes: forming a bottom electrode on the acoustic reflection unit; forming a piezoelectric film on the bottom electrode; and forming a top electrode on the piezoelectric film.

In some embodiments, before or after forming the bottom electrode, the method further includes forming a conductive thin film, the conductive thin film having an overlapping region with the acoustic reflection unit.

In some embodiments, the top electrode has an overlapping region of a width d5with the conductive thin film; the overlapping region of the conductive thin film and the acoustic reflection unit has a width of d3; the distance between a non-connect edge of the top electrode and the acoustic reflection unit is d4; d3=d4+d5, d4≥0, d5=k1λ/4, where λ is an equivalent wavelength of the bulk acoustic wave resonator, and k1is an odd number;

the overlapping region of the pad and the acoustic reflection unit has a width of d6, d6=k2λ/4, where λ is the equivalent wavelength of the bulk acoustic wave resonator, k2is an odd number, and k1≥k2.

(3) Advantages

As can be seen from the above technical solutions that, the acoustic wave resonator, the manufacturing method thereof and the filter of the present disclosure have at least one of the following advantages.

(1) In the present disclosure, by introducing a conductive thin film and causing the pad to have an overlapping region with the acoustic reflection unit, the pad is extended into the active region of the bulk acoustic wave resonator, the electrode thickness of a circuit connecting the bottom electrode and the top electrode of the bulk acoustic wave resonator is increased, and the connection resistance of the bulk acoustic wave resonator is effectively reduced, thereby enabling reducing insertion loss of filters and duplexers formed by cascading of such resonators.

(2) In the present disclosure, by setting widths of respective overlapping regions and a distance between the non-connect edge of the top electrode and the acoustic reflection unit, a region with a discontinuous acoustic impedance is formed at the edge of the active region of the acoustic wave resonator, thereby reflecting acoustic wave energy that is leaked from the edge, and improving quality factor of the bulk acoustic wave resonator.

