Gallium nitride surface acoustic wave resonator

Abstract

The invention discloses a gallium nitride surface acoustic wave resonator, and the resonator comprises a substrate which is provided with an epitaxial growth surface; the carbon nano tube layer is arranged on the substrate, the carbon nano tube layer is provided with a plurality of openings, and the epitaxial growth surface of the substrate is exposed through the openings; the gallium nitride layer is arranged on the carbon nano tube layer and the plurality of openings in the carbon nano tube layer; an interdigital transducer, wherein the interdigital transducer is arranged on the gallium nitride layer; and the two reflecting grating units are respectively positioned on the two sides of the interdigital transducer.

Description

Technical Field

[0001] The present invention relates to the technical field of surface acoustic wave devices, and particularly to a gallium nitride surface acoustic wave resonator. Background Art

[0002] Due to characteristics such as high operating frequency, high frequency quality factor, high sensitivity, and high stability, surface acoustic wave (SAW) devices are widely used not only in the field of circuit filters but also in aspects such as mass sensing, temperature sensing, gas sensing, biochemical sensing, humidity sensing, and barometric pressure sensing. The quality factor of a SAW device is its most important technical index. As a filter, the higher the quality factor of a SAW device, the better the roll-off characteristic of the filter and the greater the out-of-band rejection. As a sensor, the higher the quality factor of a SAW device, the higher the sensing sensitivity.

[0003] The material properties of the substrate have a great influence on the quality factor of the surface acoustic wave device. Summary of the Invention

[0004] In view of this, it is indeed necessary to provide a gallium nitride surface acoustic wave resonator with a relatively high quality factor.

[0005] A gallium nitride surface acoustic wave resonator includes: a substrate having an epitaxial growth surface; a carbon nanotube layer disposed on the substrate, the carbon nanotube layer having a plurality of openings through which the epitaxial growth surface of the substrate is exposed; a gallium nitride layer disposed on the carbon nanotube layer and in the plurality of openings of the carbon nanotube layer; an interdigital transducer disposed on the gallium nitride layer; and two reflection grating units respectively located on both sides of the interdigital transducer.

[0006] Compared with the prior art, the gallium nitride surface acoustic wave resonator provided by the present invention uses a patterned carbon nanotube layer as a mask to grow a gallium nitride layer on the epitaxial growth surface of the substrate, thereby reducing the contact area between the grown gallium nitride layer and the substrate, and thus reducing the stress between the gallium nitride layer and the substrate during the growth process. At the same time, the patterned carbon nanotube layer can effectively inhibit the extension of dislocation defects to the epitaxial surface, thereby reducing the defects of the gallium nitride layer and further improving the quality of the gallium nitride layer. Therefore, the quality factor of the gallium nitride surface acoustic wave resonator is greatly improved, thereby improving the performance of the gallium nitride surface acoustic wave resonator. Brief Description of the Drawings

[0007] Figure 1 It is a schematic exploded view of the gallium nitride surface acoustic wave resonator provided by an embodiment of the present invention.

[0008] Figure 2 Schematic cross-sectional structure diagram of the gallium nitride surface acoustic wave resonator provided by an embodiment of the present invention.

[0009] Figure 3 Scanning electron microscope photograph of the carbon nanotube film drawn by an embodiment of the present invention.

[0010] Figure 4 Schematic structure diagram of carbon nanotube fragments in the carbon nanotube film drawn by an embodiment of the present invention.

[0011] Figure 5 Scanning electron microscope photograph of the non-twisted carbon nanotubes provided by an embodiment of the present invention.

[0012] Figure 6 Scanning electron microscope photograph of the twisted carbon nanotubes provided by an embodiment of the present invention.

[0013] Figure 7 Scanning electron microscope photograph of the sapphire substrate with a carbon nanotube layer provided in the gallium nitride surface acoustic wave resonator of an embodiment of the present invention.

[0014] Description of main component symbols

[0015] Gallium nitride surface acoustic wave resonator 10

[0016] Substrate 100

[0017] Epitaxial growth surface 101

[0018] Carbon nanotube layer 102

[0019] Gallium nitride layer 104

[0020] Interdigital transducer 106

[0021] Reflection grating unit 107

[0022] Opening 105

[0023] Hole 103

[0024] Carbon nanotube fragment 143

[0025] Carbon nanotube 145

[0026] First bus bar 108

[0027] Second bus bar 109

[0028] First interdigital electrode 110

[0029] Second interdigital electrode 111

[0030] The following specific embodiments will further illustrate the present invention in conjunction with the above-mentioned drawings. Detailed implementation manners

[0031] The gallium nitride surface acoustic wave resonator provided by the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0032] Please refer to Figure 1 and Figure 2 , a first embodiment of the present invention provides a gallium nitride surface acoustic wave resonator 10. The gallium nitride surface acoustic wave resonator 10 sequentially includes, from bottom to top: a substrate 100, a carbon nanotube layer 102, a gallium nitride layer 104, an interdigital transducer 106, and two reflection grating units 107. The two reflection grating units 1057 are respectively located on both sides of the interdigital transducer 106.

[0033] The substrate 100 has an epitaxial growth surface 101, which is a molecularly smooth surface and impurities such as oxygen or carbon are removed. The material of the substrate 100 can be GaAs, GaN, Si, SOI, AlN, SiC, MgO, ZnO, LiGaO2, LiAlO2, or Al2O3, etc. In this embodiment, the substrate 100 uses a sapphire substrate.

[0034] The carbon nanotube layer 102 is a continuous integral structure including a plurality of carbon nanotubes. The plurality of carbon nanotubes in the carbon nanotube layer 102 extend along a direction substantially parallel to the surface of the carbon nanotube layer 102. When the carbon nanotube layer 102 is disposed on the epitaxial growth surface 101 of the substrate 100, the extending directions of the plurality of carbon nanotubes in the carbon nanotube layer 102 are substantially parallel to the epitaxial growth surface 101 of the substrate 100. The thickness of the carbon nanotube layer is 1 nanometer to 100 micrometers, or 1 nanometer to 1 micrometer, or 1 nanometer to 200 nanometers, and preferably the thickness is 10 nanometers to 100 nanometers.

[0035] The carbon nanotube layer 102 is a patterned structure, that is, the carbon nanotube layer 102 has a plurality of openings 105 which penetrate the carbon nanotube layer 102 in the thickness direction thereof. When the carbon nanotube layer 102 is disposed to cover the epitaxial growth surface 101 of the substrate 100, a portion of the epitaxial growth surface 101 of the substrate 100 corresponding to the opening 105 is exposed to facilitate the growth of the gallium nitride layer 104. The opening 105 may be a micropore or a gap. The size of the opening 105 is 10 nanometers to 500 micrometers, and the size refers to the pore diameter of the micropore or the spacing in the width direction of the gap. The size of the opening 105 is 10 nanometers to 300 micrometers, or 10 nanometers to 120 micrometers, or 10 nanometers to 80 micrometers, or 10 nanometers to 10 micrometers. The smaller the size of the opening 105, the more beneficial it is to reduce the generation of dislocation defects during the growth of the gallium nitride layer, so as to obtain a high-quality gallium nitride layer 104. Preferably, the size of the opening 105 is 10 nanometers to 10 micrometers. Further, the duty cycle of the carbon nanotube layer 102 is 1:100 to 100:1, or 1:10 to 10:1, or 1:2 to 2:1, or 1:4 to 4:1. Preferably, the duty cycle is 1:4 to 4:1. The so-called "duty cycle" refers to the area ratio of the portion of the epitaxial growth surface 101 occupied by the carbon nanotube layer 102 to the portion exposed through the opening 105 after the carbon nanotube layer 102 is disposed on the epitaxial growth surface 101 of the substrate 100.

[0036] The carbon nanotube layer 102 can also be directly grown on the epitaxial growth surface 101 of the substrate 100 by methods such as chemical vapor deposition (CVD), or first grown on the surface of a silicon substrate and then transferred to the epitaxial growth surface 101 of the substrate 100.

[0037] Specifically, the carbon nanotube layer 102 may include a carbon nanotube film or carbon nanotube wires. The carbon nanotube layer 102 may be a single-layer carbon nanotube film or multiple stacked carbon nanotube films. The carbon nanotube layer 102 may also include multiple parallel carbon nanotube wires or multiple cross-set carbon nanotube wires. When the carbon nanotube layer 102 is multiple stacked carbon nanotube films, the number of layers of the carbon nanotube films should not be too many. Preferably, it is 2 to 100 layers. When the carbon nanotube layer 102 is multiple parallel carbon nanotube wires, the distance between two adjacent carbon nanotube wires is 0.1 micrometer to 200 micrometers. Preferably, it is 10 micrometers to 100 micrometers. The space between two adjacent carbon nanotube wires constitutes the opening 105 of the carbon nanotube layer 102. The gap length between two adjacent carbon nanotube wires may be equal to the length of the carbon nanotube wires. The carbon nanotube film or carbon nanotube wires may be directly laid on the epitaxial growth surface 101 of the substrate 100 to form the carbon nanotube layer 102. By controlling the number of layers of the carbon nanotube film or the distance between the carbon nanotube wires, the size of the opening 105 in the carbon nanotube layer 102 can be controlled.

[0038] The carbon nanotube film is a self-supporting structure composed of a number of carbon nanotubes. The number of carbon nanotubes extends preferentially in the same direction. The preferential orientation means that the overall extension directions of most carbon nanotubes in the carbon nanotube film are basically in the same direction. Moreover, the overall extension directions of most carbon nanotubes are basically parallel to the surface of the carbon nanotube film. Further, most carbon nanotubes in the carbon nanotube film are connected end to end by van der Waals forces. Specifically, each carbon nanotube among the most carbon nanotubes that basically extend in the same direction in the carbon nanotube film is connected end to end by van der Waals forces with the adjacent carbon nanotube in the extension direction. Of course, there are a small number of randomly arranged carbon nanotubes in the carbon nanotube film, and these carbon nanotubes will not significantly affect the overall orientation arrangement of most carbon nanotubes in the carbon nanotube film. The self-support means that the carbon nanotube film does not require a large-area carrier support, but can be suspended as a whole and maintain its own film state as long as support forces are provided on relatively two sides. That is, when the carbon nanotube film is placed (or fixed) on two supports set at a specific distance, the carbon nanotube film between the two supports can be suspended and maintain its own film state. The self-support is mainly achieved by the continuous carbon nanotubes connected end to end by van der Waals forces existing in the carbon nanotube film.

[0039] Specifically, most carbon nanotubes that basically extend in the same direction in the carbon nanotube film are not absolutely straight and can be appropriately bent; or they are not completely arranged in the extension direction and can be appropriately deviated from the extension direction. Therefore, it cannot be excluded that there may be partial contact between the juxtaposed carbon nanotubes among most carbon nanotubes that basically extend in the same direction in the carbon nanotube film.

[0040] Please refer to Figure 3 and Figure 4 specifically, the carbon nanotube film includes a plurality of continuously and directionally extending carbon nanotube segments 143. The plurality of carbon nanotube segments 143 are connected end to end by van der Waals forces. Each carbon nanotube segment 143 includes a plurality of mutually parallel carbon nanotubes 145, and the plurality of mutually parallel carbon nanotubes 145 are tightly combined by van der Waals forces. The carbon nanotube segment 143 has arbitrary length, thickness, uniformity and shape. The carbon nanotube film can be obtained by directly pulling after selecting a part of carbon nanotubes from a carbon nanotube array. The thickness of the carbon nanotube film is 1 nanometer to 100 micrometers, the width is related to the size of the carbon nanotube array from which the carbon nanotube film is pulled out, and the length is not limited. There are micropores or gaps between adjacent carbon nanotubes in the carbon nanotube film to form openings 105, and the pore diameter of the micropores or the size of the gaps is less than 10 micrometers. Preferably, the thickness of the carbon nanotube film is 100 nanometers to 10 micrometers. The carbon nanotubes 145 in the carbon nanotube film extend along the same direction with preferred orientation. For the specific carbon nanotube film and its preparation method, please refer to the Chinese Patent Publication No. CN101239712B, titled "Carbon Nanotube Film Structure and Its Preparation Method", filed by the applicant on February 9, 2007 and announced on May 26, 2010. For the sake of brevity, it is only cited here, but all the technical disclosures in the above application should also be regarded as part of the technical disclosures of the present invention application.

[0041] When the carbon nanotube layer includes multiple layers of carbon nanotube films stacked, the extending directions of the carbon nanotubes in adjacent two layers of carbon nanotube films form a crossing angle α, and α is greater than or equal to 0 degree and less than or equal to 90 degrees (0°≤α≤90°).

[0042] The carbon nanotube wire can be a non-twisted carbon nanotube wire or a twisted carbon nanotube wire. Both the non-twisted carbon nanotube wire and the twisted carbon nanotube wire are self-supporting structures. Specifically, please refer to Figure 5, the non-twisted carbon nanotube line includes a plurality of carbon nanotubes extending along the length direction of the non-twisted carbon nanotube line. Specifically, the non-twisted carbon nanotube line includes a plurality of carbon nanotube segments, and the plurality of carbon nanotube segments are connected end to end by van der Waals forces. Each carbon nanotube segment includes a plurality of carbon nanotubes that are parallel to each other and tightly bonded by van der Waals forces. The carbon nanotube segment has an arbitrary length, thickness, uniformity, and shape. The length of the non-twisted carbon nanotube line is not limited, and the diameter is 0.5 nanometers to 100 micrometers. The non-twisted carbon nanotube line is obtained by treating a carbon nanotube film with an organic solvent. Specifically, the entire surface of the carbon nanotube film is infiltrated with the organic solvent, and under the action of the surface tension generated when the volatile organic solvent evaporates, a plurality of carbon nanotubes parallel to each other in the carbon nanotube film are tightly bonded by van der Waals forces, so that the carbon nanotube film shrinks into a non-twisted carbon nanotube line. The organic solvent is a volatile organic solvent, such as ethanol, methanol, acetone, dichloroethane, or chloroform. Ethanol is used in this embodiment. Compared with the carbon nanotube film without being treated with an organic solvent, the non-twisted carbon nanotube line treated with an organic solvent has a reduced specific surface area and reduced viscosity.

[0043] The twisted carbon nanotube line is obtained by twisting the two ends of the carbon nanotube film in opposite directions with a mechanical force. Please refer to Figure 6 , the twisted carbon nanotube line includes a plurality of carbon nanotubes helically extending around the axis of the twisted carbon nanotube line. Specifically, the twisted carbon nanotube line includes a plurality of carbon nanotube segments, and the plurality of carbon nanotube segments are connected end to end by van der Waals forces. Each carbon nanotube segment includes a plurality of carbon nanotubes that are parallel to each other and tightly bonded by van der Waals forces. The carbon nanotube segment has an arbitrary length, thickness, uniformity, and shape. The length of the twisted carbon nanotube line is not limited, and the diameter is 0.5 nanometers to 100 micrometers. Further, a volatile organic solvent can be used to treat the twisted carbon nanotube line. Under the action of the surface tension generated when the volatile organic solvent evaporates, adjacent carbon nanotubes in the treated twisted carbon nanotube line are tightly bonded by van der Waals forces, so that the specific surface area of the twisted carbon nanotube line is reduced, and the density and strength are increased.

[0044] For the carbon nanotube line and its preparation method, please refer to the Chinese Patent Publication No. CN100411979C, titled "A Carbon Nanotube Rope and Its Manufacturing Method", filed on September 16, 2002 and announced on August 20, 2008, with the applicants being Tsinghua University and Hon Hai Precision Industry (Shenzhen) Co., Ltd., and the Chinese Patent Publication No. CN100500556C, titled "Carbon Nanotube Wire and Its Manufacturing Method", filed on December 16, 2005 and announced on June 17, 2009, with the applicants being Tsinghua University and Hon Hai Precision Industry (Shenzhen) Co., Ltd.

[0045] In this embodiment, please also refer to Figure 7 , the carbon nanotube layer is a patterned structure, including 6 layers of carbon nanotube films arranged in a stacked manner. The crossing angle α formed by the extending directions of the carbon nanotubes in adjacent two layers of carbon nanotube films is 90 degrees, that is, the extending directions of the carbon nanotubes in adjacent two layers of carbon nanotube films are perpendicular to each other. The carbon nanotube layer is formed with a plurality of openings, and the part of the epitaxial growth surface of the substrate corresponding to the openings is exposed.

[0046] The gallium nitride layer 104 is disposed on the epitaxial growth surface 101 of the substrate 100, covers the carbon nanotube layer 102, and is disposed such that the plurality of openings 105 of the carbon nanotube layer 102 are in contact with the epitaxial growth surface 101 of the substrate 100, that is, the gallium nitride layer 104 grows in each of the plurality of openings 105 of the carbon nanotube layer 102. The gallium nitride layer 104 and the carbon nanotube layer 102 covered by it are microscopically spaced apart, that is, a plurality of holes 103 are formed on the surface of the gallium nitride layer 104 in contact with the substrate 100, and the carbon nanotube layer 102 is disposed in the holes 103. Specifically, the carbon nanotubes in the carbon nanotube layer 102 are respectively disposed in a plurality of holes 103. The holes 103 are formed on the surface of the gallium nitride layer 104 in contact with the substrate 100, and the holes 103 are blind holes in the thickness direction of the gallium nitride layer 104. In each hole 103, the carbon nanotubes are substantially not in contact with the gallium nitride layer 104.

[0047] The growth method of the gallium nitride layer 104 can be realized by one or more of molecular beam epitaxy (MBE), chemical beam epitaxy (CBE), reduced pressure epitaxy, low temperature epitaxy, selective epitaxy, liquid phase deposition epitaxy (LPE), metal organic vapor phase epitaxy (MOVPE), ultra-high vacuum chemical vapor deposition (UHVCVD), hydride vapor phase epitaxy (HVPE), and metal organic chemical vapor deposition (MOCVD), etc.

[0048] Please refer to Figure 1, the interdigital transducer 106 includes a first bus bar 108 and a second bus bar 109 that are relatively spaced apart; a plurality of first interdigital electrodes 110 and a plurality of second interdigital electrodes 111 are alternately and spaced apart between the first bus bar 108 and the second bus bar 109; the first interdigital electrodes 110 extend from the first bus bar 108 and extend toward the second bus bar 109, and the second interdigital electrodes 111 extend from the second bus bar 109 and extend toward the first bus bar 108. In this embodiment, the first interdigital electrode 110 includes a first long interdigital electrode and a first short interdigital electrode, and the first long interdigital electrode and the first short interdigital electrode are alternately and spaced apart; correspondingly, the second interdigital electrode 111 also includes a second long interdigital electrode and a second short interdigital electrode, and the second long interdigital electrode and the second short interdigital electrode are alternately and spaced apart; the first long interdigital electrode and the second short interdigital electrode are collinear, and the first short interdigital electrode and the second long interdigital electrode are collinear. Two reflection grating units 107 are respectively arranged on both sides of the interdigital transducer 106, and the reflection grating unit 107 can reflect acoustic wave energy to the interdigital transducer 106.

[0049] It can be known through measurement and calculation that the quality of the gallium nitride layer manufactured on the sapphire substrate with a carbon nanotube layer in this embodiment has been significantly improved. The gallium nitride surface acoustic wave resonator manufactured on the sapphire substrate with a carbon nanotube layer in this embodiment has a quality factor increased by 33% compared with the gallium nitride surface acoustic wave resonator manufactured on the sapphire substrate. This shows that the introduction of the carbon nanotube layer improves the quality of the crystalline gallium nitride, thereby improving the performance of the gallium nitride surface acoustic wave resonator. When the gallium nitride surface acoustic wave resonator manufactured on the sapphire substrate with a nanotube layer is applied to various electronic devices, the performance of various electronic devices will be greatly improved.

[0050] The present invention uses a carbon nanotube layer as a mask and arranges it on the epitaxial growth surface of the substrate to grow a gallium nitride layer. Since the carbon nanotube layer is a patterned structure, the patterned carbon nanotube layer has a plurality of openings, so that the epitaxial growth surface of the substrate is partially exposed through the plurality of openings. When the substrate is used to grow the gallium nitride layer, the gallium nitride layer can grow only from the exposed epitaxial growth surface and then laterally epitaxially grow into one body, so that the contact area between the grown gallium nitride layer and the substrate is reduced, thereby reducing the stress between the gallium nitride layer and the substrate during the growth process. At the same time, the patterned carbon nanotube layer can effectively inhibit the extension of dislocation defects to the epitaxial surface, thereby reducing the defects of the gallium nitride layer and further improving the quality of the gallium nitride layer.

[0051] In addition, those skilled in the art can also make other changes within the spirit of the present invention. Of course, these changes made according to the spirit of the present invention should all be included within the scope claimed by the present invention.

Claims

1. A gallium nitride surface acoustic wave resonator, characterized in that, Comprising: A substrate having an epitaxial growth surface; A carbon nanotube layer disposed on the substrate, the carbon nanotube layer having a plurality of openings through which the epitaxial growth surface of the substrate is exposed; A gallium nitride layer disposed on the carbon nanotube layer and in the plurality of openings in the carbon nanotube layer; An interdigital transducer disposed on the gallium nitride layer; Two reflection grating units respectively located on both sides of the interdigital transducer.

2. The gallium nitride surface acoustic wave resonator according to claim 1, characterized in that, The carbon nanotube layer includes a plurality of carbon nanotubes extending along a direction parallel to the surface of the carbon nanotube layer.

3. The gallium nitride surface acoustic wave resonator according to claim 1, wherein The size of the opening is 10 nanometers to 500 micrometers.

4. The gallium nitride surface acoustic wave resonator according to claim 1, wherein The size of the opening is 10 nanometers to 10 micrometers.

5. The gallium nitride surface acoustic wave resonator according to claim 1, wherein The carbon nanotube layer includes at least one carbon nanotube film, the carbon nanotube film includes a plurality of carbon nanotubes, and the axial directions of the plurality of carbon nanotubes extend preferentially in the same direction.

6. The gallium nitride surface acoustic wave resonator according to claim 1, wherein, The carbon nanotube layer includes a plurality of stacked carbon nanotube films, and the extending directions of the carbon nanotubes in adjacent two carbon nanotube films form an intersection angle α, and α is greater than or equal to 0 degree and less than or equal to 90 degrees.

7. The gallium nitride surface acoustic wave resonator according to claim 1, characterized in that The carbon nanotube layer includes a plurality of parallel and spaced carbon nanotube lines.

8. The gallium nitride surface acoustic wave resonator according to claim 1, wherein The carbon nanotube layer includes a plurality of intersecting carbon nanotube lines.

9. The gallium nitride surface acoustic wave resonator according to claim 1, wherein the interdigital transducer includes a first bus bar and a second bus bar which are relatively spaced apart, and a plurality of first interdigital electrodes and a plurality of second interdigital electrodes are alternately spaced between the first bus bar and the second bus bar. The first interdigital electrodes extend from the first bus bar towards the second bus bar, and the second interdigital electrodes extend from the second bus bar towards the first bus bar.

10. The gallium nitride surface acoustic wave resonator according to claim 9, wherein the first interdigital electrodes include first long interdigital electrodes and first short interdigital electrodes which are alternately spaced apart; the second interdigital electrodes include second long interdigital electrodes and second short interdigital electrodes which are alternately spaced apart; the first long interdigital electrodes and the second short interdigital electrodes are collinear, and the first short interdigital electrodes and the second long interdigital electrodes are collinear.

Images