Tunable Monolithic III-Nitride Filter Banks

Abstract

Embodiments of a single-chip ScAlN tunable filter bank include multiple switching elements and multiple channel filters integrated on a monolithic platform. The monolithic platform may have a single crystal base, and each of the switching elements may include at least one scandium aluminum nitride (ScAlN) or other III-nitride transistor structure fabricated on the single crystal base. In these embodiments, each channel filter has a multilayer ScAlN structure including one or more single crystal epitaxial ScAlN layers fabricated on the single crystal base. The ScAlN layers of each channel filter may be based on the desired frequency characteristics of an associated one of the RF channels.

Description

[Technical field]

[0001] This patent application claims the benefit of priority to U.S. Patent Application No. 17 / 018,897, filed September 11, 2020, which is incorporated herein by reference in its entirety.

[0002] The present embodiments relate to the monolithic integration of scandium aluminum nitride (ScAlN) with other III-nitride circuit elements and filters. Some embodiments relate to tunable filter banks. [Background technology]

[0003] Conventional filter banks suffer from problems of size, functionality, and tunability. Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional approaches require the integration of discrete BAW devices and switches or require extensive mechanical tuning. Thus, there is a need for tunable filters and filter banks that overcome the size, functionality, and tunability of conventional filters and filter banks in general. [Means for solving the problem]

[0005] A single-chip scandium aluminum nitride (ScAlN) tunable filter bank includes a plurality of switching elements and a plurality of channel filters integrated on a monolithic platform. The monolithic platform has a single crystal base, and each of the switching elements is fabricated on the single crystal base and may have a scandium aluminum nitride (ScAlN) or other III-nitride transistor structure. In these embodiments, each channel filter has a multi-layer ScAlN structure including one or more single crystal epitaxial ScAlN layers fabricated on the single crystal base. The ScAlN layers of each channel filter may be based on the desired frequency characteristics of an associated one of the RF channels. [Brief description of the drawings]

[0006] [Figure 1] 1 is a monolithic filter bank having multiple channel filters according to an embodiment. [Diagram 2] 1 is a cross-sectional view of a portion of a monolithic device according to an embodiment. [Diagram 3] FIG. 2 illustrates a layered ScAlN structure according to an embodiment. [Figure 4A] FIG. 1 illustrates an example manufacturing flow according to an embodiment. [Figure 4B] FIG. 1 illustrates an example manufacturing flow according to an embodiment. [Figure 5A] 5 illustrates various steps in the manufacturing flow of FIG. 4 according to one embodiment. [Figure 5B] 5 illustrates various steps in the manufacturing flow of FIG. 4 according to one embodiment. [Figure 5C] 5 illustrates various steps in the manufacturing flow of FIG. 4 according to one embodiment. [Figure 5D] 5 illustrates various steps in the manufacturing flow of FIG. 4 according to one embodiment. [Figure 6] FIG. 2 illustrates a functional circuit diagram of a filter according to an embodiment. [Figure 7]FIG. 2 illustrates a functional circuit diagram of a filter bank / multiplexer according to an embodiment. [Figure 8] FIG. 2 illustrates a functional diagram of a front-end module according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] The following description and drawings sufficiently describe certain embodiments to enable those skilled in the art to implement them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Portions and features of some embodiments may be included in or substituted for those of other embodiments. The embodiments set forth in the claims encompass all available equivalents of those claims.

[0008] Some embodiments disclosed herein may overcome the size, functionality, and tunability issues of conventional filter banks by integrating multiple bulk acoustic wave (BAW) filters at different or the same frequencies with switches, amplifiers, mixers, or other ScAlN and III-nitride devices on the same chip. Furthermore, frequency tuning of each BAW filter may be achieved by the inherent giant ferroelectric effect of ScAlN, or other device technologies such as varactors, all integrated on the same chip. Unprecedented frequency bandwidths are possible with ScAlN. Growth of this material also reduces losses and allows integration of other electronic devices on a single chip. These embodiments are described in more detail below. Some embodiments provide tunable and ultra-compact filter banks at chip-scale levels.

[0009] 1 is a monolithic filter bank having multiple channel filters, according to an embodiment. A single-chip ScAlN tunable filter bank 102 may be configured to selectively filter multiple RF channels. The single-chip ScAlN tunable filter bank 102 may include multiple switching elements 104 and multiple channel filters 106. The switching elements 104 and the channel filters 106 may be integrated on a monolithic platform 202 (FIG. 2). Each channel filter 106 may be associated with one of multiple RF channels and configured to provide an RF signal path between a set of switching elements 104.

[0010] 2 is a cross-sectional view of a portion of a monolithic device according to some embodiments. The monolithic platform 202 has a single crystal base, and each of the switching elements 104 may have a ScAlN or other III-nitride transistor structure 204 fabricated on the single crystal base 202. In these embodiments, each channel filter 106 has a multi-layered ScAlN structure 206 that includes one or more single crystal epitaxial ScAlN layers 216 (see FIG. 3) fabricated on the single crystal base 202. In some embodiments, the ScAlN layer 216 of each channel filter 106 is based on the desired frequency characteristics (e.g., center frequency and bandwidth) of an associated one of the RF channels, although the scope of the embodiments is not limited in this respect.

[0011] In some embodiments, the monolithic platform 202 has a single crystal base and at least a portion of the switching elements 104 may have either a scandium aluminum nitride (ScAlN) high electron mobility transistor (HEMT) structure 204 fabricated on the single crystal base 202, although the scope of the embodiments is not limited in this respect. In some embodiments, the monolithic platform 202 has a single crystal base and at least a portion of the switching elements 104 may have either a gallium nitride (GaN) high electron mobility transistor (HEMT) structure 204 fabricated on the single crystal base 202, although the scope of the embodiments is not limited in this respect.

[0012] In some embodiments, the elements of transistor structure 204 may include a heterogeneous mixture of III-nitride devices. In these embodiments, the III-nitride devices may include, for example, ScAlN, GaN, InGaN, AlGaN, and other III-nitride devices. In some embodiments, the transistors may include HEMTs, MOSFETs, MISFETs, and other transistor structures.

[0013] In these embodiments, the number of layers and the concentration of scandium (Sc) in a particular layer may determine the frequency characteristics of each channel filter 106. In some embodiments, a single ScAlN layer may be used to set the maximum frequency. Additional etch stop layers allow for thicker ScAlN films for lower resonant frequencies.

[0014] 3 illustrates a layered ScAlN structure according to an embodiment. In some implementations, each ScAlN layer 216 comprises a scandium-doped aluminum nitride thin film. In some implementations, the single crystal base 202 may include silicon-carbon (SiC), silicon (Si), gallium nitride (GaN), or aluminum nitride (AlN). In some embodiments, the single crystal base 202 may include a heterogeneous mixture of III-nitride materials.

[0015] In some embodiments, the ScAlN layer 216 may include various concentrations of scandium (Sc). In some embodiments, as shown in FIG. 3, the ScAlN layer 216 has alternating ScAlN layers with higher and lower concentrations of Sc. In some embodiments, the lower concentration may be in the range of 0-25% Sc and the higher concentration may be in the range of 25-50% Sc, although the scope of the embodiments is not limited in this respect. In some examples, the higher % Sc concentration layer may be used as an etch stop, as its selectivity increases significantly with increasing % Sc composition. In some embodiments, the lower Sc concentration is in the range of 0-25% and the higher Sc concentration is in the range of 25-50%.

[0016] In some embodiments, after growth of all layers of the multilayer ScAlN structure 206, portions of the ScAlN layer 216 may be selectively etched during fabrication based on the desired frequency characteristics of the associated channel. In these embodiments, the material with low Sc concentration is selectively etched to control the thickness of the piezo and allow frequency and coupling tuning across the wafer. In some embodiments, a Sc concentration of greater than 27% provides ferroelectric properties (i.e., ferroelectric effect). This concentration may be selected based on the desired frequency characteristics.

[0017] In some embodiments, the layers of the multilayer ScAlN structure 206 may include epitaxial regrowth. In these embodiments, the original growth of the HEMT structure may be patterned with Si3N4 to open windows for ScAlN regrowth, although the scope of the embodiments is not limited in this respect. This allows for the integration of high bandwidth filters and figure of merit (FOM) switches on the same monolithic platform 202, although the scope of the embodiments is not limited in this respect.

[0018] In some embodiments, the layers of the multi-layer ScAlN structure 206 may be part of a bulk acoustic wave (BAW) resonator. In these embodiments, each ScAlN layer 216 may include a piezoelectric thin film. In some embodiments, the layers of the multi-layer ScAlN structure 206 may be operated as other acoustic device types, including, for example, surface acoustic wave (SAW) resonators, Lamb wave resonators, and contour mode resonators, although the scope of the embodiments is not limited in this respect.

[0019] In some embodiments, the desired frequency characteristics of each channel filter may be individually adjustable with a DC bias. In these embodiments, a DC bias may be applied to the channel filter 104 of a selected RF channel. An additional DC bias may be applied to vary the desired frequency characteristics (e.g., bandwidth and / or center frequency) of the channel filter 106.

[0020] In some embodiments, the monolithic platform 202 may include one or more amplifiers instead of or in addition to the switching element 104. In some embodiments, the one or more amplifiers may include a low noise amplifier (LNA) in the RF signal path either before or after the channel filter 106, although the scope of the embodiments is not limited in this respect.

[0021] In some embodiments, the one or more channel filters 106 may include one or more monolithically integrated ScAlN and III-nitride based varactors configured to tune the desired frequency characteristics of the channel filter 106.

[0022] Some embodiments relate to a single chip structure having an active element 104 and a filter 106. The active element 104 and the filter 106 are integrated on a monolithic platform 202, which has a single crystal base. In these embodiments, the active element 104 may have any of scandium aluminum nitride (ScAlN), gallium nitride (GaN), or other III-nitride transistors, such as a HEMT structure 204, fabricated on the single crystal base 202. The filter 106 has a multi-layer ScAlN structure 206, which may include single crystal epitaxial ScAlN layers 216 (FIG. 3) fabricated on the single crystal base 202. The number of ScAlN layers 216 may be based on the desired frequency characteristics (e.g., center frequency and bandwidth) of the filter 106. In some embodiments, the active element comprises a low noise amplifier (LNA). In some other embodiments, the active element comprises a switching element.

[0023] FIG. 4 shows an example fabrication flow according to an embodiment. The fabrication flow includes epitaxial regrowth. In these embodiments, the original growth of the HEMT structure may be patterned with Si3N4 to open windows for ScAlN regrowth. This allows for integration of high bandwidth filters and high FOM switches on the same device. The fabrication flow also includes selective etching of various ScAlN layers. In these embodiments, layers with varying concentrations of rare earth material (e.g., Sc) may be used. This allows for tuning of frequency and coupling across the wafer, and the etch selectivity of the higher Sc concentration material can be used to control the piezo thickness.

[0024] Figures 5A-5D show various steps in the manufacturing flow of Figure 4 according to one embodiment. Figure 5A shows the regrowth window. Figure 5B shows the open contact window in the dielectric. Figure 5C shows the selective etching of SiC. Figure 5D shows the backside metal patterning.

[0025] A functional circuit diagram of a filter according to one embodiment is shown in Figure 6. The functional circuit diagram shown in Figure 6 may represent the channel filter 106 (Figure 1).

[0026] A functional circuit diagram of a filter bank and a multiplexer according to one embodiment is shown in Figure 7. The filter bank and the multiplexer may be integrated on a monolithic platform, such as platform 202 (Figure 2).

[0027] A functional diagram of a front-end module according to an embodiment is shown in Figure 8. The elements shown in Figure 8 may be integrated on a monolithic platform such as platform 202 (Figure 2). In these embodiments, ultra-compact, very high quality factor (Q) BAW filters may be integrated along with amplifiers and mixers on a tunable single-chip GaN or ScAlN platform, reducing the number of devices with a single local oscillator (LO) input.

[0028] In some embodiments shown in FIG. 8, the RF front end includes a low noise amplifier (LNA) configured to receive an RF signal, an image reject mixer configured to reject an image signal from the received RF signal, and a mixer configured to mix an output signal from the image reject mixer with the LO signal to generate an IF signal. The LNA and the image reject mixer may have a single chip structure integrated on a monolithic platform. The monolithic platform may have a single crystal base. The LNA may include any of scandium aluminum nitride (ScAlN), gallium nitride (GaN), or other III-nitride based transistor structures fabricated on the single crystal base. The image reject filter may have a multi-layer ScAlN structure including single crystal epitaxial ScAlN layers fabricated on the single crystal base. The number of ScAlN layers and the Sc concentration per layer may be based on the desired frequency characteristics of the image reject filter.

[0029] This Summary is provided to enable the reader to grasp the nature and gist of the technical disclosure. It is submitted with the understanding that it will not be used to limit or interpret the scope or meaning of the claims. Accordingly, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment.

Claims

1. A single-chip ScAlN frequency tunable filter bank comprising: A plurality of switching elements; a plurality of channel filters, the switching elements and the channel filters being integrated on a monolithic platform, the filter bank being configured to selectively filter a plurality of RF channels; having Each channel filter is associated with one of the plurality of RF channels and configured to provide an RF signal path between a set of the switching elements; the monolithic platform having a single crystal base; each of the switching elements comprises at least one scandium aluminum nitride (ScAlN) or other III-nitride transistor structure fabricated on the single crystal base; A filter bank, wherein each channel filter has a multi-layer ScAlN structure including two or more single crystal epitaxial ScAlN layers fabricated on the single crystal base.

2. Each ScAlN layer comprises a scandium-doped aluminum nitride thin film; 10. The filter bank of claim 1, wherein the monocrystalline base comprises one of silicon-carbon (SiC), silicon (Si), gallium nitride (GaN), and aluminum nitride (AlN).

3. The filter bank of claim 2 , wherein in the multi-layer ScAlN structure, adjacent ScAlN layers have different concentrations of scandium (Sc).

4. The filter bank of claim 3 , wherein the multi-layer ScAlN structure has alternating ScAlN layers with high and low concentrations of Sc.

5. The filter bank of claim 4, wherein the low concentration Sc is in the range of more than 0 and not more than 25%, and the high concentration Sc is in the range of 25 to 50%.

6. the layer of the multi-layer ScAlN structure is part of a bulk acoustic wave (BAW) resonator; Each ScAlN layer has a piezoelectric thin film; 2. The filter bank of claim 1, wherein each channel filter is individually frequency tunable by DC bias using the ferroelectric effect of the piezoelectric thin film.

7. 7. The filter bank of claim 6, wherein one or more of the channel filters comprises one or more monolithically integrated ScAlN or III-nitride based varactors.

8. the monolithic platform comprises a single monolithic platform; The filter bank of claim 7 , wherein the switching elements and the channel filters are integrated onto the single monolithic platform.

9. A single chip structure, An active element; a filter, the active element and the filter being integrated on a monolithic platform, the monolithic platform having a single crystal base; having the active element comprises a scandium aluminum nitride (ScAlN) transistor structure fabricated on the monocrystalline base, the filter has a multi-layer ScAlN structure including a plurality of single crystal epitaxial ScAlN layers fabricated on the single crystal base; the multilayer ScAlN structure has alternating ScAlN layers with high and low concentrations of Sc; The low concentration of Sc is in the range of more than 0 to 25% or less, and the high concentration of Sc is in the range of 25 to 50%.

10. The single chip structure of claim 9, wherein the active element comprises a low noise amplifier (LNA).

11. 10. The single chip structure of claim 9, wherein the active element comprises a switching element.

12. 10. The single chip structure of claim 9, wherein the single crystal base comprises one of silicon-carbon (SiC), silicon (Si), gallium nitride (GaN), and aluminum nitride (AlN).

13. 10. The single chip structure of claim 9, wherein the filter is one of a plurality of filters integrated onto the monolithic platform.

14. An RF front-end device, comprising: a low noise amplifier (LNA) configured to receive RF signals from a plurality of channels; an image reject mixer configured to reject an image signal from the received RF signal; a mixer configured to mix an output signal from the image reject mixer with an LO signal to generate an IF signal; having the LNA and the image reject mixer have a single chip structure integrated on a monolithic platform; the monolithic platform having a single crystal base; the LNA having a scandium aluminum nitride (ScAlN) transistor structure fabricated on the monocrystalline base; the image rejection mixer having a multi-layer ScAlN structure including a single crystal epitaxial ScAlN layer fabricated on the single crystal base; the multilayer ScAlN structure has alternating ScAlN layers with high and low concentrations of Sc; The low concentration of Sc is in the range of more than 0 to 25% or less, and the high concentration of Sc is in the range of 25 to 50%.

15. 15. The apparatus of claim 14, wherein the monocrystalline base comprises one of silicon-carbon (SiC), silicon (Si), gallium nitride (GaN), and aluminum nitride (AlN).

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