COMPOSITE SURFACE ACOUSTIC WAVE (SAW) DEVICE WITH ABSORBING LAYER FOR SUPPRESSION OF SPURIOUS RESPONSES

Abstract

A surface acoustic wave (SAW) device includes: a base substrate; a piezo-electric material layer; at least one interdigitated electrode pair disposed on the piezo-electric material layer; and an acoustic wave suppression layer disposed between the piezo-electric material layer and the base substrate, the acoustic wave suppression layer being configured to suppress an acoustic wave propagating in a direction from the piezo-electric material layer to the base substrate.

Claims

1. A surface acoustic wave (SAW) device, comprising: a base substrate; a piezo-electric material layer; at least one interdigitated electrode pair disposed on the piezo-electric material layer; and an acoustic wave suppression layer disposed between the piezo-electric material layer and the base substrate, the acoustic wave suppression layer being configured to suppress an acoustic wave propagating in a direction from the piezo-electric material layer to the base substrate.

2. The SAW device of claim 1, wherein the piezo-electric material layer has a first shear velocity, and the base substrate has a second shear velocity, and the acoustic wave suppression layer has a third shear velocity which is less than the first shear velocity and less than the second shear velocity.

3. The SAW device of claim 1, wherein the acoustic wave suppression layer comprises a dielectric layer.

4. The SAW device of claim 1, wherein the acoustic wave suppression layer comprises at least one of a silicon low-k resin and carbon doped silicon oxide.

5. The SAW device of claim 1, wherein the acoustic wave suppression layer comprises a doped piezo-electric material layer, doped with an impurity which causes a viscous loss to the acoustic wave propagating in the direction from the piezo-electric material layer to the base substrate.

6. The SAW device of claim 5, wherein the impurity comprises hydrogen or oxygen.

7. The SAW device of claim 1, wherein the base substrate comprises one of a silicon base substrate or a sapphire base substrate.

8. The SAW device of claim 1, wherein the piezo-electric material layer comprises one of LiNbO3 or LiTaO3.

9. The SAW device of claim 1, further comprising a temperature compensating material layer disposed: between the at least one interdigitated electrode pair and the piezo-electric material layer, or on the at least one interdigitated electrode pair and the piezo-electric material layer.

10. A surface acoustic wave (SAW) device, comprising: a base substrate, comprising silicon or sapphire; an acoustic wave absorbing layer disposed on the base substrate; a piezo-electric material layer disposed on the acoustic wave absorbing layer, the piezo-electric material layer comprising LiNbO3 or LiTaO3; and at least one interdigitated electrode pair disposed on the piezo-electric material layer, the electrode pair comprising an electrically conductive material, wherein the acoustic wave absorbing layer comprises a material having properties to substantially trap within the acoustic wave absorbing layer an acoustic wave propagating in a direction from the piezo-electric material layer to the base substrate.

11. The device of claim 10, wherein the piezo-electric material layer has a first shear velocity, and the base substrate has a second shear velocity, and the acoustic wave absorbing layer has a third shear velocity which is less than the first shear velocity and less than the second shear velocity.

12. The SAW device of claim 10, wherein the acoustic wave absorbing layer comprises a dielectric layer.

13. The SAW device of claim 10, wherein the acoustic wave suppression layer comprises at least one of a silicon low-k resin and carbon doped silicon oxide.

14. The SAW device of claim 10, further comprising an undoped silicon glass (USG) layer disposed: between the at least one interdigitated electrode pair and the piezo-electric material layer, or on the at least one interdigitated electrode pair and the piezo-electric material layer.

15. A method of producing a surface acoustic wave (SAW) device, comprising: providing a base substrate; providing an acoustic wave suppression layer and a piezo-electric material layer on the base substrate, wherein the acoustic wave suppression layer is provided between the piezo-electric material layer and the base substrate; and forming at least one interdigitated electrode pair on the piezo-electric material layer, wherein the acoustic wave suppression layer is configured to suppress an acoustic wave propagating in a direction from the piezo-electric material layer to the base substrate.

16. The method of claim 15, wherein the base substrate comprises one of silicon or sapphire.

17. The method of claim 15, wherein the acoustic wave suppression layer comprises at least one of a silicon low-k resin and carbon doped silicon oxide.

18. The method of claim 15, wherein providing the acoustic wave suppression layer and the piezo-electric material layer on the base substrate comprises: doping the piezo-electric material layer with an impurity which causes a viscous loss to the acoustic wave propagating in the piezo-electric material layer to produce the acoustic wave suppression layer; and bonding the piezo-electric material layer having the acoustic wave suppression layer formed thereon to the base substrate such that the acoustic wave suppression layer is disposed between the piezo-electric material layer and the base substrate.

19. The method of claim 18, wherein doping the piezo-electric material layer to produce the acoustic wave suppression layer comprises implanting hydrogen or oxygen from the backside of the piezo-electric material layer.

20. The method of claim 13, wherein providing the acoustic wave suppression layer and the piezo-electric material layer on the base substrate comprises: depositing the acoustic wave suppression layer on the base substrate; and bonding the piezo-electric material layer to the base substrate having the acoustic wave suppression layer disposed thereon.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The example embodiments are best understood from the following detailed description when read with the accompanying drawing figures. It is emphasized that the various features are not necessarily drawn to scale. In fact, the dimensions may be arbitrarily increased or decreased for clarity of discussion. Wherever applicable and practical, like reference numerals refer to like elements.

[0035] FIG. 1 is a schematic illustration of a SAW device.

[0036] FIG. 2 illustrates a cross-section of a portion of an example of a SAW device.

[0037] FIG. 3 illustrates a cross-section of a portion of an example of a SAW device having a composite substrate.

[0038] FIG. 4 plots an example of the global admittance frequency response for an example SAW device.

[0039] FIG. 5 illustrates a cross-section of a portion of one embodiment of a SAW device having an acoustic wave suppression layer.

[0040] FIG. 6 illustrates a cross-section of a portion of another embodiment of a SAW device having an acoustic wave suppression layer.

[0041] FIGS. 7A, 7B, 7C and 7D are cross-sectional views illustrating one embodiment of a method of making a SAW device having an acoustic wave suppression layer.

[0042] FIGS. 8A, 8B, 8C and 7D are cross-sectional views illustrating another embodiment of a method of making a SAW device having an acoustic wave suppression layer.

[0043] FIGS. 9A, 9B, 9C and 9D are cross-sectional views illustrating yet another embodiment of a method of making a SAW device having an acoustic wave suppression layer.

[0044] FIGS. 10A, 10B, 10C and 10D are cross-sectional views illustrating still another embodiment of a method of making a SAW device having an acoustic wave suppression layer.

[0045] FIG. 11 plots an example of the global admittance frequency response for an example SAW device having an acoustic wave suppression layer.

[0046] FIG. 12 overlaps the plots of FIGS. 4 and 11.

DETAILED DESCRIPTION

[0047] In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth in order to provide a thorough understanding of an embodiment according to the present teachings. However, it will be apparent to one having ordinary skill in the art having had the benefit of the present disclosure that other embodiments according to the present teachings that depart from the specific details disclosed herein remain within the scope of the appended claims. Moreover, descriptions of well-known apparati and methods may be omitted so as to not obscure the description of the example embodiments. Such methods and apparati are clearly within the scope of the present teachings.

[0048] It is to be understood that the terminology used herein is for purposes of describing particular embodiments only, and is not intended to be limiting. The defined terms are in addition to the technical and scientific meanings of the defined terms as commonly understood and accepted in the technical field of the present teachings.

[0049] As used in the specification and appended claims, the terms ‘a’, ‘an’ and ‘the’ include both singular and plural referents, unless the context clearly dictates otherwise. Thus, for example, ‘a device’ includes one device and plural devices.

[0050] As used in the specification and appended claims, and in addition to their ordinary meanings, the terms ‘substantial’ or ‘substantially’ mean to within acceptable limits or degree.

[0051] As used in the specification and the appended claims and in addition to its ordinary meaning, the term ‘approximately’ means to within an acceptable limit or amount to one having ordinary skill in the art. For example, ‘approximately the same’ means that one of ordinary skill in the art would consider the items being compared to be the same. As used in the specification and the appended claims and in addition to its ordinary meaning, the term ‘about’ means to within 10%.

[0052] Generally, it is understood that the drawings and the various elements depicted therein are not drawn to scale. Further, relative terms, such as “above,” “below,” “top,” “bottom,” “upper” and “lower” may be used to describe the various elements' relationships to one another, as illustrated in the accompanying drawings. It is understood that these relative terms are intended to encompass different orientations of the device and/or elements in addition to the orientation depicted in the drawings. For example, if the device were inverted with respect to the view in the drawings, an element described as “above” another element, for example, would now be below that element.

[0053] Without wishing to be bound by any specific theory, the present inventors have theorized that formation of the spurious responses or “rattles” above-Fs as described above with respect to FIG. 4 can be explained in terms of lost surface confinement of energy as frequency increases above a certain cut-off frequency under the periodic voltage driving conditions. Acoustic waves propagating into the piezo-electric material layer experiences constructive/destructive interference with waves reflected from piezo/base substrate interface (e.g., LT/Si interface), forming rattles in the S-chart. Moreover, for a silicon substrate, total internal reflection occurs at the LT/Si interface, preventing the energy from propagating into the Si substrate. Notably, if acoustic energy were allowed to propagate into the Si substrate instead of being reflected from the LT/Si interface, it might have then led to weaker rattles, or dissipated rattles.

[0054] FIG. 5 illustrates a cross-section of a portion of one embodiment of a SAW device 500 having an acoustic wave suppression layer. SAW device 500 includes a composite substrate 502, comprising: a base substrate 510; an acoustic wave suppression layer 520 disposed on base substrate 510; and a piezo-electric material layer 530 disposed on acoustic wave suppression layer 520. SAW device 500 also includes at least one interdigitated electrode pair 542/544 disposed on piezo-electric material layer 530.

[0055] In some embodiments, base substrate 510 may comprise silicon, sapphire (i.e., Al.sub.2O.sub.3), or glass.

[0056] In some embodiments, piezo-electric material layer 530 may comprise lithium tantalite (LiTaO.sub.3—hereinafter simply referred to as LT) or lithium niobate (LiNbO.sub.3—hereinafter simply referred to as LN).

[0057] Electrode pair 542/544 may be two fingers of an interdigitated transducer having dozens or even hundreds of “fingers.” Electrodes 542 and 544 comprise an electrically conductive material, such as gold or aluminum. The distance D between electrode 542 and electrode 544 may be λ/2, where λ is the wavelength of the acoustic wave in SAW device 500.

[0058] Beneficially, acoustic wave suppression layer 520 may comprise a dielectric.

[0059] In SAW device 500, acoustic wave suppression layer 520 is an acoustic wave absorbing layer 525, which comprises a material having properties to substantially trap within acoustic wave absorbing layer 525 an acoustic wave propagating in a direction from piezo-electric material layer 530 to the base substrate 510 thereby reducing spurious responses or “rattles.” For example, in some embodiments acoustic wave absorbing layer 525 may be selected such that when piezo-electric material layer 530 has a first shear velocity, and base substrate 510 has a second shear velocity, then acoustic wave absorbing layer 525 has a third shear velocity which is less than the first shear velocity and less than the second shear velocity. Accordingly, an acoustic wave which propagates in a direction from piezo-electric material layer 530 toward base substrate 510 may be effectively coupled into acoustic wave absorbing layer 525, but may not be effectively coupled out of acoustic wave absorbing layer 525 into either piezo-electric material layer 530 or base substrate 510, thereby becoming trapped within acoustic wave absorbing layer 525.

[0060] In some embodiments, acoustic wave absorbing layer 525 may comprise a silicon low-k resin material, such as SiLK™ semiconductor dielectric resin materials manufactured and marketed by DOW®. In some embodiments, acoustic wave absorbing layer 525 may comprise carbon doped silicon oxide (CDO), for example CDO26 and CDO40. Here, for illustrative purposes CDO26 designates a material layer where a CDO material is deposited onto base substrate 510 (e.g., Si) at a pressure of 2.6 torrs, and CDO40 designates a material layer where a CDO material is deposited onto base substrate 510 at a pressure of 4.0 torrs. Of course other deposition conditions are possible leading to CDO materials with slightly different acoustic characteristics. In other embodiments, other materials may be employed for acoustic wave absorbing layer 525.

[0061] U.S. Pat. No. 8,390,397, issued to Jamneala et al. on Mar. 5, 2013, and U.S. Pat. No. 8,587,391 to Gilbert et al., both of which incorporated herein by reference, describe some details regarding methods of producing devices which include SiLK™ and CDO material layers.

[0062] Table 1 below lists some estimated characteristics for some materials which may be employed in various embodiments of SAW device 500.

TABLE-US-00001 TABLE 1 Material Layer Density VL (m/s) VS (m/s) ZL (MR) ZS (MR) LiTaO.sub.3 Piezo-electric 7.45 6085 3568 45.3 26.6 42 deg LiTaO.sub.3 Piezo-electric 7.45 5885 3393 43.8 25.3 LiNbO.sub.3 Piezo-electric 4.63 6940 3600 32.1 16.7 Si Base Substrate 2.33 8437 5820 19.7 13.6 Sapphire Base Substrate 3.98 10658 5796 42.4 23.1 SiLK Absorbing Layer 1.13 1960 1226 2.2 1.4 CDO40 Absorbing Layer 1.16 2334 1459 2.7 1.7 CDO26 Absorbing Layer 1.43 3737 2336 5.3 3.3

[0063] In Table 1, VL designates a longitudinal velocity of an acoustic wave in the material, VL designates a shear velocity of an acoustic wave in the material, ZL designates a longitudinal impedance of the material, and ZS designates a shear impedance of the material. The values of acoustic impedances ZL and ZS are provided in mega-Rayls (MR). As can be seen in Table 1, the shear velocities of SiLK, CDO26 and CDO 40 are all less than the shear velocities of silicon, sapphire, LiTaO.sub.3, 42 degree LiTaO.sub.3, and LiNbO.sub.3.

[0064] In beneficial embodiments, acoustic wave absorbing layer 525 may have a shear velocity (VS) greater than about 1.7 km/sec. and a shear impedance (ZS) greater than about 1.7 MR.

[0065] In some embodiments, piezo-electric material layer 530 (e.g., LN) may have a thickness of about 10 μm, acoustic wave absorbing layer 525 (e.g., CDO) may have a thickness of about 10 μm, and base substrate 510 (e.g., Si) may have a thickness of about 20 μm or more. Other embodiments may have other thicknesses.

[0066] FIG. 6 illustrates a cross-section of a portion of another embodiment of a SAW device 600 having an acoustic wave suppression layer. SAW device 600 includes a composite substrate 602, comprising: base substrate 510 and a piezo-electric material layer 530 with a bottom portion of it forming an acoustic wave suppression layer 620, disposed on base substrate 510. SAW device 600 also includes at least one interdigitated electrode pair 542/544 disposed on piezo-electric material layer 530.

[0067] Base substrate 510, piezo-electric material layer 530, and electrode pair 542/544 may be the same as shown in FIG. 5 and described above, and so a description thereof will not be repeated.

[0068] In SAW device 600, acoustic wave suppression layer 620 comprises a doped piezo-electric material layer 625, doped with an impurity which causes a viscous loss to an acoustic wave propagating in the direction from piezo-electric material layer 530 to base substrate 510. In particular, doped piezo-electric material layer 625 may comprise a lower portion of piezo-electric material layer 530 (e.g., LiTaO.sub.3) which has been doped with one or more impurities which may significantly increase the viscous loss of the piezo-material without substantially impacting its density or the acoustic velocity on the material such that energy from an acoustic wave propagating in the direction from piezo-electric material layer 530 to base substrate 510 may be absorbed, thereby reducing spurious responses or “rattles.” In some embodiments, the impurity may comprise oxygen or hydrogen.

[0069] FIGS. 7A, 7B, 7C and 7D are cross-sectional views illustrating one embodiment of a method of making a SAW device 700 having an acoustic wave suppression layer. Here, SAW device 700 may be one version or variation of SAW device 500.

[0070] As illustrated in FIG. 7A, a base substrate 710 is provided, and an acoustic wave suppression layer 720 is formed on base substrate 710. Here, base substrate 710 may be the same as base substrate 510 described above, and acoustic wave suppression layer 720 may be the same as acoustic wave suppression layer 520 and acoustic wave absorbing layer 525 described above.

[0071] FIG. 7B illustrates bonding a piezo-electric material layer 730 to the acoustic wave suppression layer 720 and base substrate 710. Here, piezo-electric material layer 730 may be the same as piezo-electric material layer 530 described above.

[0072] FIG. 7C illustrates forming a temperature compensating material layer 702 on piezo-electric material layer 730. Temperature compensating material layer 702 may provide some temperature compensation for piezo-electric material layer 730. In some embodiments, temperature compensating material layer 702 may be an undoped silicon glass (USG) material layer.

[0073] FIG. 7D illustrates forming at least one interdigitated electrode pair 742 and 744 on temperature compensating material layer 702 and piezo-electric material layer 730.

[0074] FIGS. 8A, 8B, 8C and 7D are cross-sectional views illustrating another embodiment of a method of making a SAW device 800 having an acoustic wave suppression layer. Here, SAW device 800 may be one version or variation of SAW device 500.

[0075] Operations illustrated in FIGS. 8A and 8B are the same as the operations illustrated in FIGS. 7A and 7B above and do descriptions thereof will not be repeated.

[0076] FIG. 8C illustrates forming at least one interdigitated electrode pair 842 and 844 on piezo-electric material layer 730.

[0077] FIG. 8D illustrates forming a temperature compensating material layer 802 on interdigitated electrode pair 842 and 844 and piezo-electric material layer 730. Temperature compensating material layer 802 may provide some temperature compensation for piezo-electric material layer 730. In some embodiments, temperature compensating material layer 802 may be an undoped silicon glass (USG) material layer.

[0078] FIGS. 9A, 9B, 9C and 9D are cross-sectional views illustrating yet another embodiment of a method of making a SAW device 900 having an acoustic wave suppression layer. Here, SAW device 900 may be one version or variation of SAW device 600.

[0079] FIG. 9A illustrates a process of forming an acoustic wave suppression layer 920 on a backside of a piezo-electric material layer 930. Here, acoustic wave suppression layer 920 may be the same as acoustic wave suppression layer 620. In particular, FIG. 9A illustrates an operation of implanting an impurity into the backside of the piezo-electric material layer 930 to produce acoustic wave suppression layer 920 as a doped piezo-electric material layer such as doped piezo-electric material layer 625 described above. In some embodiments, the impurity may comprise oxygen or hydrogen.

[0080] As illustrated in FIG. 9B, a base substrate 910 is provided, and a piezo-electric material layer 930 is bonded to base substrate 910. Here, base substrate 910 may be the same as base substrate 510 described above, and, piezo-electric material layer 930 may be the same as piezo-electric material layer 530 described above.

[0081] Methods of bonding a piezo-electric material layer (e.g., piezo-electric material layer 930) to a base substrate (e.g., base substrate) are described in co-pending U.S. patent application Ser. No. 14/866,273, filed on 26 Sep. 2015; Ser. No. 14/866,394, filed on 26 Sep. 2015; and Ser. No. 15/009,801 filed on 28 Jan. 2016, all in the names of Stephen Gilbert et al. The entire disclosures of each of these patent applications are hereby incorporated herein by reference.

[0082] FIG. 9C illustrates forming a temperature compensating material layer 902 on piezo-electric material layer 930. Temperature compensating material layer 902 may provide some temperature compensation for piezo-electric material layer 930. In some embodiments, temperature compensating material layer 902 may be an undoped silicon glass (USG) material layer.

[0083] FIG. 9D illustrates forming at least one interdigitated electrode pair 942 and 944 on temperature compensating material layer 902 and piezo-electric material layer 930.

[0084] FIGS. 10A, 10B, 10C and 10D are cross-sectional views illustrating still another embodiment of a method of making a SAW device 1000 having an acoustic wave suppression layer. Here, SAW device 1000 may be one version or variation of SAW device 600.

[0085] Operations illustrated in FIGS. 10A and 10B are the same as the operations illustrated in FIGS. 9A and 9B above and do descriptions thereof will not be repeated.

[0086] FIG. 10C illustrates forming at least one interdigitated electrode pair 1042 and 1044 on piezo-electric material layer 930.

[0087] FIG. 10D illustrates forming a temperature compensating material layer 1002 on interdigitated electrode pair 1042 and 1044 and piezo-electric material layer 930. Temperature compensating material layer 1002 may provide some temperature compensation for piezo-electric material layer 930. In some embodiments, temperature compensating material layer 1002 may be an undoped silicon glass (USG) material layer.

[0088] FIG. 11 plots an example of the simulated global admittance frequency response 1100 for an example SAW device, such as SAW device 500, having an acoustic wave suppression layer as described above.

[0089] FIG. 12 overlaps the plots of global admittance frequency response 400 of FIG. 4 and global admittance frequency response 1100 of FIG. 11.

[0090] Comparing global admittance frequency response 400 with global admittance frequency response 1100, one can see that the spurious responses or rattles 420 may be completely or substantially eliminated by the addition of an acoustic wave suppression layer between the piezo-electric material layer and the base substrate layer configured to suppress an acoustic wave propagating in a direction from the piezo-electric material layer to the base substrate, as described above. Accordingly, the performance characteristics of an apparatus which includes such a SAW device (e.g., a communication receiver or transceiver in a mobile telephone) may also be enhanced.

[0091] While example embodiments are disclosed herein, one of ordinary skill in the art appreciates that many variations that are in accordance with the present teachings are possible and remain within the scope of the appended claims. The embodiments therefore are not to be restricted except within the scope of the appended claims.