CLAIM OF PRIORITY

[0001] This patent application claims the benefit of priority to U.S.

Application Serial No. 17/018,897, filed September 11, 2020, which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

[0002] Embodiments pertain to monolithic integration of scandium aluminum nitride (ScAIN) with other Group Ill-Nitride circuit elements and filters. Some embodiments pertain to tunable filter banks.

BACKGROUND

[0003] Conventional filter banks suffer from size, functionality, and tunability issues. Typical approaches require the integration of discrete BAW devices and switches or are large and mechanically tuned. Thus, there are general needs for tunable filters and filter banks that overcome the size, functionality, and tunability of conventional filters and filter banks.

SUMMARY

[0004] A single-chip scandium aluminum nitride (ScAIN) tunable filter bank include a plurality of switching elements and a plurality of channel filters integrated on a monolithic platform. The monolithic platform may comprise a single crystal base and each of the switching elements may comprise a scandium aluminum nitride (ScAIN) or other Group Ill-Nitride transistor structure fabricated on the single crystal base. In these embodiments, each channel filter comprises a multi-layered ScAIN structure comprising one or more a single- crystal epitaxial ScAIN layers fabricated on the single crystal base. The ScAIN layers for each channel filter may be based on desired frequency characteristics of an associated one of the RF channels. BRIEF DESCRIPTION OF THE DRAWINGS [0005] FIG. 1 is a monolithic filter bank with multiple channel filters in accordance with some embodiments;

[0006] FIG. 2 is a cross sectional view of a portion of a monolithic device in accordance with some embodiments;

[0007] FIG. 3 illustrates a layered ScAIN structure in accordance with some embodiments;

[0008] FIG. 4A-4B illustrates an example fabrication flow in accordance with some embodiments; [0009] FIGs. 5A through 5D illustrate various steps in the fabrication flow of FIG. 4 in accordance with some embodiments;

[0010] FIG. 6 illustrates a function circuit diagram of a filter in accordance with some embodiments;

[0011] FIG. 7 illustrates function circuit diagrams of filter banks/multiplexers in accordance with some embodiments; and

[0012] FIG. 8 illustrates a function diagram of a front-end module in accordance with some embodiments.

DETAILED DESCRIPTION [0013] The following description and the drawings sufficiently illustrate specific embodiments to enable those skilled in the art to practice 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. Embodiments set forth in the claims encompass all available equivalents of those claims.

[0014] 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 ScAIN and Group Ill-Nitride devices on the same chip. Further, frequency tuning of each BAW filter may be accomplished by the intrinsic giant ferroelectric effect of ScAIN or other device technologies such as varactors, all of which are integrated on the same chip. The ScAIN allows for unprecedented frequency bandwidths. In addition, the growth of this material reduces the loss and allows for integration of other electronic devices onto a single chip. These embodiments are discussed in more detail below. Some embodiments provide tunable and ultra-small filter banks at a chip scale level.

[0015] FIG. 1 is a monolithic filter bank with multiple channel filters in accordance with some embodiments. Single-chip ScAIN tunable filter bank 102 may be configured for selectively filtering multiple RF channels. The single-chip ScAIN tunable filter bank 102 may include a plurality of switching elements 104 and a plurality of channel filters 106. The switching elements 104 and channel filters 106 may be integrated on a monolithic platform 202 (FIG. 2). Each channel filter 106 may be associated with one of the multiple RF channels and configured to provide in an RF signal path between a pair of the switching elements 104.

[0016] FIG. 2 is a cross sectional view of a portion of a monolithic device in accordance with some embodiments. The monolithic platform 202 may comprise a single crystal base and each of the switching elements 104 may comprise a ScAIN or other Group Ill-Nitride transistor structure 204 fabricated on the single crystal base 202. In these embodiments, each channel filter 106 comprises a multi-layered ScAIN structure 206 comprising one or more a singlecrystal epitaxial ScAIN layers 216 (see FIG. 3) fabricated on the single crystal base 202. In some embodiments, the ScAIN layers 216 for each channel filter 106 may be based on desired frequency characteristics (e.g., a center frequency and bandwidth) of an associated one of the RF channels, although the scope of the embodiments is not limited in this respect.

[0017] In some embodiments, the monolithic platform 202 may comprise a single crystal base and at least some of the switching elements 104 may comprise either a scandium aluminum nitride (ScAIN) 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 may comprise a single crystal base and at least some of the switching elements 104 may comprise 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. [0018] In some embodiments, the elements of transistor structure 204, may comprise a heterogenous mix of Group Ill-Nitride devices. In these embodiments, Group Ill-Nitride devices may include, for example, ScAIN, GaN, InGaN, AlGaN, as well as other group Ill-Nitride devices. In some embodiments, the transistors may include HEMTs, MOSFETs, MISFETs, as well as others transistor structures.

[0019] In these embodiments, the number of layers as well as the concentration of Scandium (Sc) in a particular layer may determine the frequency characteristics for each channel filter 106. In some embodiments, a single ScAIN layer may be used to set the highest frequency. Additional etch stop layers allow for thicker ScAIN membrane films for lower resonant frequencies.

[0020] FIG. 3 illustrates a layered ScAIN structure in accordance with some embodiments. In some embodiments, each ScAIN layer 216 comprises a scandium doped aluminum nitride thin film. In some embodiments, the single crystal base 202 may comprise silicon-carbon (SiC), silicon (Si), Gallium Nitride (GaN) or Aluminum Nitride (AIN). In some embodiments, the single crystal base 202 may comprise a heterogenous mix of Group Ill-Nitride materials.

[0021] In some embodiments, the ScAIN layers 216 may comprise a varied concentration of Scandium (Sc). In some embodiments, the ScAIN layers 216 comprise alternating ScAIN layers with higher and lower concentrations of Sc as illustrated in FIG. 3. In some embodiments, the lower concentrations may range from 0-25%Sc and the higher concentrations can range from 25-50%Sc, although the scope of the embodiments is not limited in this respect. In some embodiments, higher %Sc concentration layers may be used as etch stops since its selectivity with increasing %Sc composition increases significantly. In some embodiments, the lower concentrations of Sc range from 0-25% and the higher concentrations of Sc range from 25-50%.

[0022] In some embodiments, after growth of all layers of the multi- layered ScAIN structure 206, some of the ScAIN layers 216 may be selectively etched during fabrication based on the desired frequency characteristics for an associated channel. In these embodiments, lower Sc concentration materials may be selectively etched to control piezo thickness and allowing for frequency and coupling tuning across wafer. In some embodiments, Sc concentrations of greater than 27% may provide ferro-electric properties (i.e., a ferro-electric effect) and may be selected based on the desired frequency characteristics.

[0023] In some embodiments, the layers of the multi-layered ScAIN structure 206 may comprise epitaxial regrowth. In these embodiments, original growth for the HEMT structure may be patterned with Si ₃ N ₄ to open a window for ScAIN regrowth, although the scope of the embodiments is not limited in this respect. This allows for integration of high bandwidth filters and high figure-of- merit (FOM) switches on the same monolithic platform 202, although the scope of the embodiments is not limited in this respect. [0024] In some embodiments, the layers of the multi-layered ScAIN structure 206 may be part of a bulk-acoustic wave (B AW) resonator. In these embodiments, each ScAIN layer 216 may comprise a piezoelectric thin film. In some embodiments, the layers of the multi-layered ScAIN structure 206 may operate as other acoustic devices 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.

[0025] In some embodiments, the desired frequency characteristics of each channel filter may be individually tunable with a DC bias. In these embodiments, a DC bias may be applied to the channel filter 104 for a selected RF channel. An additional DC bias may be applied to change the desired frequency characteristics (e.g., bandwidth and/or center frequency) of the channel filter 106.

[0026] In some embodiments, the monolithic platform 202 may comprise one or more amplifiers instead of or in addition to the switching elements 104. In some embodiments, the one or more amplifiers may comprise a low-noise amplifier (LNA) provided in the RF signal path either prior to or after a channel filter 106, although the scope of the embodiments is not limited in this respect.

[0027] In some embodiments, one or more of the channel filters 106 may include one or more monolithically integrated ScAIN and Group Ill-Nitride based varactors configured for tuning the desired frequency characteristics of the channel filters 106.

[0028] Some embodiments are directed to single-chip structure, comprising an active element 104 and a filter 106. The active element 104 and filter 106 are integrated on the monolithic platform 202 and the monolithic platform 202 comprises a single crystal base. In these embodiments, the active element 104 may comprise either a scandium aluminum nitride (ScAIN), gallium nitride (GaN) or other Group Ill-Nitride transistors such as HEMT structure 204 fabricated on the single crystal base 202. The filter 106 may comprise a multi-layered ScAIN structure 206 comprising single-crystal epitaxial ScAIN layers 216 (FIG. 3) fabricated on the single crystal base 202.

The number of the ScAIN layers 216 may be based on desired frequency characteristics (e.g., a 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.

[0029] FIG. 4 illustrates an example fabrication flow in accordance with some embodiments. The fabrication flow includes epitaxial regrowth. In these embodiments, the original growth for the HEMT structure may be patterned with S13N4 to open window for ScAIN regrowth. This allows for integration of high bandwidth filters and high FOM switches on same device. The fabrication flow also includes a selective etch for varied ScAIN layers. In these embodiments, layers with varied concentration of rare earth materials (e.g., Sc) may be used. This allows for frequency and coupling tuning across wafer and takes advantage of etching selectivity of higher-Sc concentration materials to control piezo thickness.

[0030] FIGs. 5A through 5D illustrate various steps in the fabrication flow of FIG 4 in accordance with some embodiments. FIG 5 A illustrates the re- growth window. FIG. 5B illustrates open contact windows in the dielectric. FIG. 5C illustrates the selective etch of SiC. FIG. 5D illustrate backside metal patterning. [0031] FIG. 6 illustrates a function circuit diagram of a filter in accordance with some embodiments. The function circuit diagram shown in FIG.

6 may be represent a channel filter 106 (FIG. 1). [0032] FIG. 7 illustrates function circuit diagrams of filter banks and multiplexers in accordance with some embodiments. The filter banks and multiplexers may be integrated on a monolithic platform, such as platform 202 (FIG. 2).

[0033] FIG. 8 illustrates a function diagram of a front-end module in accordance with some embodiments. The elements illustrated in FIG. 8 may be integrated on a monolithic platform, such as platform 202 (FIG. 2). In these embodiments, ultra-small, ultra-high-quality factor (Q) BAW filters may be integrated with amplifiers and mixers on a single chip GaN or ScAIN platform that may be tunable and may result in a reduced number of devices with a single local oscillator (LO) input.

[0034] In some embodiments illustrated in FIG. 8, an RF front-end comprises a low-noise amplifier (LNA) configured to receive RF signals, an image reject mixer configured to reject an image signal from the received RF signals, and a mixer configured to mix an output signal from the image reject mixer with an LO signal to generate an IF signal. The LNA and the image reject mixer may comprise a single-chip structure integrated on a monolithic platform. The monolithic platform may comprise a single crystal base. The LNA may comprise either a scandium aluminum nitride (ScAIN), gallium nitride (GaN) or other Group Ill-Nitride based transistor structure fabricated on the single crystal base. The image reject filter may comprise a multi-layered ScAIN structure comprising single-crystal epitaxial ScAIN layers fabricated on the single crystal base. The number of the ScAIN layers and Sc concentration per layer may be based on desired frequency characteristics of the image reject filter.

[0035] The Abstract is provided to allow the reader to ascertain 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. The following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate embodiment.