Elliptical structure for bulk acoustic wave resonator

An elliptical-shaped resonator device. The device includes a bottom metal plate, a piezoelectric layer overlying the bottom metal plate, and a top metal plate overlying the piezoelectric layer. The top metal plate, the piezoelectric layer, and the bottom metal plate are characterized by an elliptical shape having a horizontal diameter (dx) and a vertical diameter (dy), which can be represented as ellipse ratio R=dx/dy. Using the elliptical structure, the resulting bulk acoustic wave resonator (BAWR) can exhibit equivalent or improved insertion loss, higher coupling coefficient, and higher quality factor compared to conventional polygon-shaped resonators.

BACKGROUND OF THE INVENTION

The present invention relates generally to electronic devices and more particularly to resonators based on piezoelectric epitaxial films and essentially single crystal films.

Mobile telecommunication devices have been successfully deployed world-wide. Over a billion mobile devices, including cell phones and smartphones, were manufactured in a single year and unit volume continues to increase year-over-year. With ramp of 4G/LTE in about 2012, and explosion of mobile data traffic, data rich content is driving the growth of the smartphone segment—which is expected to reach 2B per annum within the next few years. Coexistence of new and legacy standards and thirst for higher data rate requirements is driving RF complexity in smartphones. Unfortunately, limitations exist with conventional RF technology that is problematic, and may lead to drawbacks in the future.

From the above, it is seen that techniques for improving electronic devices are highly desirable.

BRIEF SUMMARY OF THE INVENTION

The present invention relates generally to electronic devices and more particularly to resonators based on piezoelectric epitaxial films and essentially single crystal films.

In an example, the present invention provides an elliptical-shaped resonator device. The device includes a bottom metal plate, a piezoelectric layer overlying the bottom metal plate, and a top metal plate overlying the piezoelectric layer. The top metal plate, the piezoelectric layer, and the bottom metal plate are characterized by an elliptical shape having a horizontal diameter (dx) and a vertical diameter (dy), which can be represented as ellipse ratio R=dx/dy. In a specific example, the ellipse ratio R ranges from about 1.20 to about 2.00.

A plurality of these elliptical-shaped resonator devices can be configured within an RF filter circuit device. A plurality of micro-vias can be configured to coupled certain resonators to each other or couple a resonator to an interconnect metal or bond pad. In a specific example, the present invention provides an RF filter configuration using 11 elliptical-shaped resonator devices, with seven such resonators coupled in series and four such resonators coupled between junctions of the resonator series chain and ground. Those of ordinary skill in the art will recognize other variations, modifications, and alternatives.

One or more benefits are achieved over pre-existing techniques using the invention. In particular, the present device can be manufactured in a relatively simple and cost effective manner while using conventional materials and/or methods according to one of ordinary skill in the art. Using the present method, one can create an improved bulk acoustic wave resonator (BAWR) having equivalent or improved insertion loss compared to conventional polygon-shaped resonators. Such filters or resonators can be implemented in an RF filter device, an RF filter system, or the like. Depending upon the embodiment, one or more of these benefits may be achieved. Of course, there can be other variations, modifications, and alternatives.

A greater understanding of the nature and advantages of the invention may be realized by reference to the latter portions of the specification and attached drawings.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates generally to electronic devices and more particularly to resonators based on piezoelectric epitaxial films and essentially single crystal films.

Generally, a Bulk Acoustic Wave Resonator (BAWR) is a parallel plate capacitor which can be characterized by the geometrical shape of its metal plates and the thickness and composition of the piezoelectric material between the two electrodes of the capacitor. A configuration of such resonators can be used to create an RF filter creating a signal passband that is characterized by the insertion loss (known as “S21”), which describes the impact of placing the filter in an RF circuit.

Conventional resonators are typically constructed using polygons with N-number of sides (where N≥3). Circular-shaped resonators are possible, but typically offer undesirable symmetry, which leads to undesirable modes in the resonator. However, elliptical-shaped resonators can be constructed with a ratio, defined as R, of the horizontal diameter (dx) to vertical diameter (dy) of the resonator, where R=dx/dy. Once defined with R, the resonator can be placed in an RF circuit at an arbitrary angle theta (θ).

According to examples of the present invention, single-crystal piezoelectric-based RF filters using ellipse-shaped resonators with the unique ratio of R between about 1.60 and about 1.61 have been fabricated and tested to provide equivalent or improved insertion loss performance when compared to conventional polygon-shaped resonators. Such filters are characterized by a center frequency ranging from about 0.4 GHz to about 20 GHz and use one or more areas to adjust the electrical impedance of the filter circuit.

FIG. 1Ais a simplified diagram illustrating a side “sandwich” view of an elliptical-shaped resonator according to an example of the present invention. As shown, device101includes a top metal plate110and bottom metal plate120that sandwich a piezoelectric layer130.FIG. 1Bis a simplified diagram illustrating a top view of the same elliptical-shaped resonator according an example of the present invention. Here, device102only shows the top metal plate110, but the previously discussed measurements of the horizontal diameter (dx), vertical diameter (dy), and angle theta (θ) are shown in reference to the top metal plate110.

FIG. 2is a simplified diagram illustrating an RF filter circuit device using several elliptical-shaped resonators according to various examples of the present invention. As shown, device200includes several elliptical-shaped resonators220configured on a circuit die210. In a specific example, the circuit die (or substrate) is selected from a silicon substrate, a sapphire substrate, silicon carbide substrate, a GaN bulk substrate, a GaN template, an AlN bulk, an AlN template, AlxGa1-xN templates, engineered substrates such as silicon on insulator (SOI), and polycrystalline AlN templates. These resonators220can be connected by metal interconnects230with or without micro-vias240to each other or to connections off-chip. In this example, a dielectric passivation layer211-is formed overlying the circuit die210, which can be silicon dioxide (SiO2), silicon nitride (SiN), aluminum nitride (AlN), or aluminum oxide (AlO), or the like. The use of SiO2can improve temperature drift in the RF filter circuit. Those of ordinary skill in the art will recognize other variations, modifications, and alternatives.

FIG. 3Ais a simplified diagram illustrating a cross-sectional view of the RF filter circuit ofFIG. 2along the A-B reference line according to an example of the present invention. As shown, device301includes an elliptical-shaped resonator device320overlying a substrate310, which can include a silicon carbide (SiC) material or the like, and a dielectric passivation layer311, which can include SiO2or the like. The resonator device320includes a top metal plate (top electrode)321and a bottom metal plate (bottom electrode)322sandwiching a piezoelectric layer323, which can include an aluminum nitride (AlN) material or the like. Region324of the piezoelectric layer323shows the portion that is sandwiched between the top and bottom electrodes321,322. In a specific example, the piezoelectric layer includes materials or alloys having at least one of the following: AlN, AlGaN, GaN, InN, InGaN, AlInN, AlInGaN, ScAlN, ScGaN, AlScYN, and BN. A micro-via340is configured adjacent to this resonator320, with a backside metal interconnect331, which can include a molybdenum material or the like, coupling the micro-via340to the bottom metal plate322. Metal interconnects330can be coupled to the top electrode321or to the bottom electrode322through the micro-via340and the backside metal interconnect331.

In a specific example, the resonator320also includes two types of energy confinement features (ECFs), ECF-1341and ECF-2342. The ECF-1341include one or more pillar structures on the top metal plate surface, while the ECF-2342include one or more cavity regions within the top metal electrode surface. These ECF structures can also be formed on the bottom metal plate as well. In a specific example, the bottom metal plate, top metal plate, and the ECF structures can include molybdenum (Mo), ruthenium (Ru), Aluminum Copper (AlCu), or tungsten (W), or the like. Of course, there can be other variations, modifications, and alternatives.

FIG. 3Bis a simplified diagram illustrating a cross-sectional view of the RF filter circuit ofFIG. 2along the A-B reference line according to an example of the present invention. As shown, device302is similar to device301except that only ECF-1 structures are present without any ECF-2 structures. The remaining elements follow the same reference number scheme as those inFIG. 3A.

FIG. 4is a computer-aided design (CAD) layout of an RF filter circuit device using elliptical-shaped resonators according to an example of the present invention. Image400shows a layout similar to that ofFIG. 2.FIG. 5is an image of a physical implementation of an RF filter circuit using elliptical-shaped resonators according to an example of the present invention. Image500is configured in the same orientation asFIG. 4for comparison purposes.

FIG. 6is a simplified circuit diagram illustrating an elliptical-shaped resonator configured RF filter circuit device according to an example of the present invention. As shown, device600includes an RF filter input601and an RF filter output602with elliptical-shaped resonators620configured in between. In a specific example, the RF filter includes 11 such resonators, with seven resonators in series between the input and output and four resonators connected to intersections of the series configurations and ground. Of course, there can be other variations, modifications, and alternatives.

FIG. 7Ais a graph701comparing the insertion loss of a filter passband for a conventional polygon-shaped resonator to one for an elliptical-shaped resonator (R=1.61) according to an example of the present invention. The results for the conventional polygon-shaped resonator are shown by plot710, while the results for the elliptical-shaped resonator are shown by plot720.

FIG. 7Bis a graph702comparing the insertion loss of a filter narrow band spectrum for a conventional polygon-shaped resonator to one for an elliptical-shaped resonator (R=1.61) according to an example of the present invention. The results for the conventional polygon-shaped resonator are shown by plot710, while the results for the elliptical-shaped resonator are shown by plot720.

FIG. 7Cis a graph703comparing the insertion loss of a filter wide band spectrum for a conventional polygon-shaped resonator to one for an elliptical-shaped resonator (R=1.61) according to an example of the present invention. The results for the conventional polygon-shaped resonator are shown by plot710, while the results for the elliptical-shaped resonator are shown by plot720.

FIG. 8A-8Dis are simplified diagrams illustrating elliptical-shaped resonators configured with various ratios of R.FIG. 8Aillustrates a device801having an ellipse ratio of R=1.2.FIG. 8Billustrates a device802having an ellipse ratio of R=1.6.FIGS. 8C and 8Dillustrate devices803and804, which have ellipse ratios of R=1.8 and R=2.0, respectively.

Examples of the present invention take advantage of the fact that the shape of the BAW resonator determines the overall performance. Lateral mode noise reduces as the overall symmetry of the shape decreases, i.e., an elliptical shape shows weaker lateral mode noise than circular shapes. Weak vertical amplitude of acoustic wave in corners of quadrilateral or pentagon shapes reduces the coupling coefficient of the resonator; thus, an elliptical-shaped resonator eliminates the corners to allow a higher coupling coefficient. Further, the ratio of area-to-edge affects the quality factor of the resonator as the acoustic wave radiates outside of the resonator along the edge. Since an ellipse has a shorter edge for a given area compared to a quadrilateral, or other polygonal shape, an elliptical-shaped resonator can exhibit a higher quality factor as well.

In a specific example, an elliptical-shaped resonator with a specific aspect ratio of R=1.6 exhibits a better quality factor near the anti-resonance frequency (Qp). The date from BAW resonators with the resonance frequency around 5 GHz shows a higher Qpwhen the aspect ratio of the ellipse is 1.6. The coupling coefficient for an elliptical-shaped resonator with a ratio of 1.6 is slightly less than an that of an elliptical-shaped resonator with the ratio of 1.2, but the overall figure of merit is higher with R=1.6. The graphs and table ofFIGS. 9A-9Csummarize these results.

FIG. 9Ais a graph901comparing the coupling coefficient variation for the elliptical-shaped resonators shown inFIG. 8. As shown in graph901, the resonator with a ratio of 1.2 starts at the highest coupling coefficient. The value of this coefficient then falls as the ratio reaches 1.8, but rises again at a ratio of 2.0.FIG. 9Bis a graph902comparing the quality factor for the elliptical-shaped resonators shown inFIG. 8. As shown in graph902, the quality factor increases with the ratio as the ratio increases from 1.2 to 1.6, but then falls as the ratio descends to 1.8 and 2.0.FIG. 9Cis a table903summarizing the results of the graphs901,902fromFIGS. 9A and 9B. Although the coupling coefficient variation was higher with an ellipse ratio of 1.2, the overall figure of merit was the highest at R=1.6 (about 1.60 to about 1.61).

One or more benefits are achieved over pre-existing techniques using the invention. In particular, the present device can be manufactured in a relatively simple and cost effective manner while using conventional materials and/or methods according to one of ordinary skill in the art. Using the present method, one can create an improved bulk acoustic wave resonator (BAWR) having equivalent or improved insertion loss compared to conventional polygon-shaped resonators. Such filters or resonators can be implemented in an RF filter device, an RF filter system, or the like. Depending upon the embodiment, one or more of these benefits may be achieved. Of course, there can be other variations, modifications, and alternatives.

While the above is a full description of the specific embodiments, various modifications, alternative constructions and equivalents may be used. As an example, the packaged device can include any combination of elements described above, as well as outside of the present specification. Therefore, the above description and illustrations should not be taken as limiting the scope of the present invention which is defined by the appended claims.