Antenna element

Abstract

Provided is an antenna element capable of widening the band of available electromagnetic waves. An antenna element according to an embodiment of the present invention comprises: an inorganic material substrate; a first conductor layer; a support substrate; a cavity; and a ground conductor layer. The first conductor layer is disposed on one side in the thickness direction of the inorganic material substrate, and includes a patch antenna. The support substrate is disposed on the side opposite to the first conductor layer with respect to the inorganic material substrate. The cavity is disposed on the side opposite to the first conductor layer with respect to the inorganic material substrate and on the inorganic material substrate side of the support substrate. The ground conductor layer is disposed in the cavity. The thickness t of the inorganic material substrate satisfies formula (1). When the patch antenna is projected in the thickness direction of the inorganic material substrate, at least a part of the projection surface of the patch antenna overlaps the cavity.

Description

Antenna element

[0001] The present invention relates to an antenna element.

[0002] Electromagnetic wave sensors that detect an object by transmitting electromagnetic waves to the object and receiving the waves reflected by the object have been known. An antenna element capable of transmitting and / or receiving electromagnetic waves is typically used in such electromagnetic wave sensors. One example of an antenna element proposed is a single antenna including a dielectric substrate, a signal converter disposed on the front surface of the dielectric substrate, and a ground plate disposed on the back surface of the dielectric substrate (see Patent Document 1).

[0003] Patent No. 6955590

[0004] In recent years, the applications of electromagnetic wave sensors have expanded, and the use of electromagnetic wave sensors as motion sensors has been considered. However, when the single antenna described in Patent Document 1 is applied to a motion sensor, the resolution required for the motion sensor may not be fully achieved. The resolution of an electromagnetic wave sensor depends on the width of the frequency range (hereinafter referred to as the band) of electromagnetic waves usable by the antenna element. Therefore, a wider band of electromagnetic waves usable by the antenna element is desired. A primary object of the present invention is to provide an antenna element that can realize a wider band of usable electromagnetic waves.

[0005] [1] An antenna element according to an embodiment of the present invention comprises an inorganic material substrate, a first conductor layer, a support substrate, a cavity, and a ground conductor layer. The first conductor layer is disposed on one side of the inorganic material substrate in the thickness direction. The first conductor layer includes a patch antenna. The support substrate is disposed on the opposite side of the inorganic material substrate from the first conductor layer. The cavity is disposed on the opposite side of the inorganic material substrate from the first conductor layer and on the inorganic material substrate side of the support substrate. The ground conductor layer is disposed within the cavity. The ground conductor layer is capable of generating an electric field between itself and the patch antenna. The thickness t of the inorganic material substrate satisfies the following formula (1). When the patch antenna is projected in the thickness direction of the inorganic material substrate, at least a portion of the projection surface of the patch antenna overlaps the cavity. (wherein t represents the thickness of the inorganic material substrate, λ represents the wavelength of the electromagnetic wave transmitted and / or received by the antenna element, ε represents the relative dielectric constant of the inorganic material substrate, and a represents a numerical value of 3 or more.) [2] In the antenna element described in [1] above, when the patch antenna is projected in the thickness direction of the inorganic material substrate, the entire projection surface of the patch antenna may overlap the cavity. [3] In the antenna element described in [1] or [2] above, the first conductor layer may further include a transmission line. The transmission line is connected to the patch antenna. [4] The antenna element described in [3] above may further include a first ground layer. The first ground layer is arranged in a portion between the inorganic material substrate and the support substrate that is different from the cavity. When the transmission line is projected in the thickness direction of the inorganic material substrate, at least a portion of the projection surface of the transmission line overlaps the first ground layer. [5] The antenna element described in [4] above may further include a junction. The bonding portion bonds the inorganic material substrate and the support substrate. [6] In the antenna element described in [5] above, the bonding portion may include a first bonding layer and a second bonding layer. The first bonding layer is provided on a surface of the inorganic material substrate opposite the first conductor layer in the thickness direction of the inorganic material substrate. The second bonding layer is provided on a surface of the first ground layer opposite the support substrate in the thickness direction of the inorganic material substrate. The second bonding layer is bonded to the first bonding layer. [7] In the antenna element described in any of [1] to [6] above, the thickness t of the inorganic material substrate may be 100 μm or less. [8] In the antenna element described in any of [1] to [7] above, the frequency of the electromagnetic waves transmitted and / or received by the antenna element may be 20 GHz to 20 THz. [9] In the antenna element described in any of [1] to [8] above, the inorganic material substrate may be made of quartz glass.

[10] In the antenna element according to any one of [1] to [9] above, the support substrate may be made of silicon.

[0006] According to the embodiment of the present invention, it is possible to realize a wider band of available electromagnetic waves.

[0007] FIG. 1 is a schematic perspective view of an antenna element according to an embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line II-II' of the antenna element of FIG. 1. FIG. 3 is a schematic perspective view of an antenna element according to another embodiment of the present invention. FIG. 4 is a schematic perspective view of an antenna element according to yet another embodiment of the present invention. FIG. 5 is a schematic perspective view of an antenna element according to yet another embodiment of the present invention. FIG. 6 is a schematic perspective view of an antenna element according to yet another embodiment of the present invention. FIG. 7 is a schematic perspective view of a support substrate and a second conductor layer provided in the antenna element of FIG. 1. FIG. 8 is a schematic perspective view showing another embodiment of the second conductor layer of FIG. 7. FIG. 9 is a schematic perspective view showing yet another embodiment of the second conductor layer of FIG. 7. FIG. 10 is a graph showing the S11 parameter of the antenna element of Example 1. FIG. 11 is a graph showing the S11 parameter of the antenna element of Comparative Example 1.

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments. In addition, in order to clarify the description, the drawings may show the width, thickness, shape, etc. of each part more schematically than in the embodiment, but these are merely examples and do not limit the interpretation of the present invention.

[0009] A. Overall Configuration of the Antenna Element FIG. 1 is a schematic perspective view of an antenna element according to one embodiment of the present invention, and FIG. 2 is a cross-sectional view of the antenna element of FIG. 1 taken along line II-II'. The antenna element 100 is typically capable of transmitting and / or receiving electromagnetic waves ranging from millimeter waves to terahertz waves. Millimeter waves are typically electromagnetic waves with frequencies ranging from about 20 GHz to 300 GHz, and terahertz waves are typically electromagnetic waves with frequencies ranging from about 300 GHz to 20 THz. The frequencies of the electromagnetic waves that the antenna element can transmit and / or receive are, for example, 20 GHz to 20 THz, or 20 GHz to 500 GHz, or 20 GHz to 300 GHz, or 100 GHz to 200 GHz.

[0010] The antenna element 100 includes an inorganic material substrate 2, a first conductor layer 1, a support substrate 3, a cavity 5, and a ground conductor layer 41. The first conductor layer 1 is disposed on one side of the inorganic material substrate 2 in the thickness direction. The first conductor layer 1 includes a patch antenna 11. The support substrate 3 is disposed on the opposite side of the inorganic material substrate 2 from the first conductor layer 1. The cavity 5 is disposed on the opposite side of the inorganic material substrate 2 from the first conductor layer 1, and on the inorganic material substrate side of the support substrate 3. The ground conductor layer 41 is disposed within the cavity 5. The patch antenna 11, the ground conductor layer 41, and the inorganic material substrate 2 located therebetween typically constitute a planar antenna. The ground conductor layer 41 can generate an electric field between the patch antenna 11 and the ground conductor layer 41. More specifically, when the patch antenna 11 receives and / or transmits the high-frequency electromagnetic waves described above, an electric field is generated between the patch antenna 11 and the ground conductor layer 41. The thickness t of the inorganic material substrate 2 satisfies the following formula (1): When the patch antenna 11 is projected in the thickness direction of the inorganic material substrate 2 , at least a part of the projection surface of the patch antenna 11 overlaps with the cavity 5 . (In the formula, t represents the thickness of the inorganic material substrate 2, λ represents the wavelength of the electromagnetic wave transmitted and / or received by the antenna element 100, ε represents the relative dielectric constant of the inorganic material substrate 2, and a represents a numerical value of 3 or more.) With this configuration, the thickness of the inorganic material substrate 2 satisfies the above formula (1), so that even when the antenna element 100 transmits and / or receives the above-mentioned high-frequency electromagnetic wave, induction of a slab mode can be suppressed, and resonance of the inorganic material substrate 2 can be suppressed. Furthermore, when the patch antenna 11 is projected in the thickness direction of the inorganic material substrate 2, at least a part of the projection surface of the patch antenna 11 overlaps the cavity 5. This makes it possible to widen the band of frequencies (resonant frequencies) at which resonance can occur between the patch antenna 11 and the ground conductor layer 41, and as a result, the band of frequencies radiated from the antenna element 100 can be broadened. These features make it possible to sufficiently reduce the reflection loss of electromagnetic waves in the antenna element 100. As a result, the antenna element 100 can expand the bandwidth of electromagnetic waves with sufficiently small reflection loss, i.e., the bandwidth of electromagnetic waves for which the S11 parameter, which represents reflection loss, is equal to or less than a predetermined value. In other words, the antenna element 100 can function as a wideband antenna. In one embodiment, the bandwidth of electromagnetic waves for which the S11 parameter (reflection loss) of the antenna element 100 is equal to or less than −10 dB (−10 dB bandwidth) is, for example, 5.0 GHz or more, preferably 8.0 GHz or more, more preferably 10.0 GHz or more, and even more preferably 13.0 GHz or more. Meanwhile, the upper limit of the −10 dB bandwidth of the antenna element 100 is typically 50 GHz. The S11 parameter is measured, for example, using a network analyzer. Furthermore, developments are underway to miniaturize the antenna element 100, and with circuit integration expected in the future, it is expected that the antenna element 100 will also require corresponding miniaturization. In the above antenna element 100, the thickness of the inorganic material substrate 2 satisfies the above formula (1), and the inorganic material substrate 2 is made thinner, so that the antenna element 100 can have a broadband while also meeting the demand for miniaturization.

[0011] The area ratio of the projection surface of patch antenna 11 that overlaps with cavity 5 is, for example, 70% or more, preferably 80% or more, and more preferably 90% or more. When the projection surface of patch antenna 11 overlaps with cavity 5 at the above-mentioned area ratio, the bandwidth of antenna element 100 can be stably broadened.

[0012] In one embodiment, when the patch antenna 11 is projected in the thickness direction of the inorganic material substrate 2, the entire projection surface of the patch antenna 11 overlaps with the cavity 5. In other words, the area ratio of the portion of the projection surface of the patch antenna 11 that overlaps with the cavity 5 is 100%. With this configuration, the bandwidth of the antenna element 100 can be stably widened.

[0013] In one embodiment, when patch antenna 11 and cavity 5 are each projected in the thickness direction of inorganic material substrate 2, the projected area of ​​cavity 5 is equal to or larger than the projected area of ​​patch antenna 11. The projected area of ​​cavity 5 is, for example, 1 to 4 times, and preferably 1 to 3 times, the projected area of ​​patch antenna 11. When the projected area of ​​cavity 5 has such a relationship with the projected area of ​​patch antenna 11, patch antenna 11 can be easily positioned so that patch antenna 11 overlaps cavity 5 when viewed in the thickness direction of inorganic material substrate 2. This improves the degree of freedom in designing patch antenna 11 and makes it possible to more reliably broaden the bandwidth of antenna element 100.

[0014] In the illustrated example, when patch antenna 11 and cavity 5 are projected in the thickness direction of inorganic material substrate 2, the outer edge of the projection surface of cavity 5 is spaced apart from the outer edge of the projection surface of patch antenna 11. As shown in FIG. 2 , in the normal direction to the outer edge of the projection surface of patch antenna 11, the distance L between the outer edge of the projection surface of cavity 5 and the outer edge of the projection surface of patch antenna 11 is, for example, 0 μm to λ / 2ε μm, for example, 0 μm to λ / 4ε μm, where ε represents the relative dielectric constant of inorganic material substrate 2. If the distance L between the outer edges of cavity 5 and patch antenna 11 is within this range, the degree of freedom in designing patch antenna 11 can be further improved, and the bandwidth of antenna element 100 can be more reliably broadened.

[0015] 1 , the patch antenna 11 has any appropriate shape. Examples of the shape of the patch antenna 11 when viewed from the thickness direction of the inorganic material substrate 2 include a triangle, a rectangle, a pentagon, a hexagon or more polygon, a circle, and an ellipse. In the illustrated example, the patch antenna 11 has a substantially rectangular shape when viewed from the thickness direction of the inorganic material substrate 2.

[0016] The cavity 5 has any appropriate shape. An example of the shape of the cavity 5 as viewed in the thickness direction of the inorganic material substrate 2 is a shape similar to that of the patch antenna 11 described above. In one embodiment, the cavity 5 has a shape similar to that of the patch antenna 11 as viewed in the thickness direction of the inorganic material substrate 2. In the illustrated example, the cavity 5 and the patch antenna 11 have shapes similar to each other, and the center of the patch antenna 11 and the center of the cavity 5 are positioned on the same axis along the thickness direction of the inorganic material substrate 2.

[0017] In one embodiment, the first conductor layer 1 further includes a transmission line 12 in addition to the patch antenna 11. The transmission line 12 is connected to the patch antenna 11. The end of the transmission line 12 opposite the patch antenna 11 is typically configured to be connectable to an external device. With this configuration, an electrical signal input from an external device can be supplied to the patch antenna 11 via the transmission line 12. When an electrical signal is supplied to the patch antenna 11, the patch antenna 11 and the ground conductor layer 41 can convert the electrical signal into an electromagnetic wave. Therefore, the patch antenna 11 can radiate the electromagnetic wave converted from the electrical signal. Furthermore, when the patch antenna 11 receives an electromagnetic wave, the patch antenna 11 and the ground conductor layer 41 can convert the electromagnetic wave into an electrical signal. Therefore, the antenna element 100 can transmit the electrical signal converted from the electromagnetic wave to the external device via the transmission line 12.

[0018] The transmission line 12 typically has a flat band shape extending in a predetermined direction. The width of the transmission line 12 is, for example, 2 μm to 800 μm. When the patch antenna 11 has a substantially rectangular shape, the direction in which the transmission line 12 extends is typically substantially parallel to the width direction of the patch antenna 11.

[0019] In one embodiment, the patch antenna 11 and the transmission line 12 are configured to have matching impedances. As shown in FIG. 3 , the patch antenna 11 may have a notch 111. The notch 111 is provided adjacent to a connection portion of the patch antenna 11 with the transmission line 12. The notch 111 may have any appropriate configuration. The notch 111 is recessed inward from the outer edge of the patch antenna 11. As shown in FIG. 4 , the patch antenna 11 may have a slit 112. The slit 112 penetrates the patch antenna 11 in the thickness direction. The slit 112 may have any appropriate configuration. In the illustrated example, the slit 112 has a substantially U-shape when viewed from the thickness direction of the inorganic material substrate 2. The transmission line 12 may have a narrow portion 121 and a wide portion 122. The narrow portion 121 is located at the end of the transmission line 12 on the patch antenna 11 side. The narrow portion 121 is connected to the patch antenna 11. The width of the narrow portion 121 is smaller than the width of the wide portion 122. The width of the narrow portion 121 may be adjusted arbitrarily and appropriately. The wide portion 122 is located on the opposite side of the narrow portion 121 from the patch antenna 11. The range of the width of the wide portion 122 is, for example, the same as the range of the width of the transmission line 12 described above.

[0020] As shown in FIGS. 1 and 2 , in one embodiment, the transmission line 12 forms a waveguide capable of propagating electromagnetic waves. This allows electromagnetic waves to be supplied to the patch antenna 100. In the illustrated example, the transmission line 12, together with the first ground layer 42, forms a microstrip line. The transmission line 12 forming the microstrip line may be referred to as an MS-type signal wiring 12a hereinafter. The antenna element 100 includes the patch antenna 11, a ground conductor layer 41, the MS-type signal wiring 12a, and the first ground layer 42, and forms a microstrip patch antenna. The width of the MS-type signal wiring 12a is, for example, 20 μm to 800 μm, and preferably 50 μm to 500 μm. The first ground layer 42 is typically disposed between the inorganic material substrate 2 and the support substrate 3, in a location different from the cavity 5. When the transmission line 12 (MS type signal wiring 12 a) is projected in the thickness direction of the inorganic material substrate 2, at least a portion of the projection surface of the transmission line 12 overlaps with the first ground layer 42. With this configuration, when a voltage is applied to the MS type signal wiring 12 a and the first ground layer 42, an electric field is generated between the MS type signal wiring 12 a and the first ground layer 42. Therefore, an electromagnetic wave input from an external device is coupled with the electric field generated between the MS type signal wiring 12 a and the first ground layer 42, propagates through the inorganic material substrate 2, and can reach the patch antenna 11. Furthermore, when the patch antenna 11 receives an electromagnetic wave, the electromagnetic wave can propagate through the inorganic material substrate 2 and be transmitted to the external device due to the electric field generated between the MS type signal wiring 12 a and the first ground layer 42.

[0021] 5, in another embodiment, the transmission line 12 and the second ground layer 13 form a coplanar waveguide. In this embodiment, the first conductor layer 1 further includes the second ground layer 13. The transmission line 12 forming the coplanar waveguide may be referred to as a CP type signal wiring 12b hereinafter. The antenna element 100 includes the patch antenna 11, the ground conductor layer 41, the CP type signal wiring 12b, and the second ground layer 13, and forms a coplanar patch antenna. The width of the CP type signal wiring 12b is, for example, 2 μm to 200 μm, and preferably 20 μm to 150 μm. The second ground layer 13 is disposed to sandwich the transmission line 12 in a direction perpendicular to the extension direction of the transmission line 12 (CP type signal wiring 12b). A gap (slit) is formed between the second ground layer 13 and the transmission line 12 (CP type signal wiring 12b) in a direction perpendicular to the extension direction of the transmission line 12. The width of the gap is, for example, 2 μm to 100 μm, preferably 5 μm to 80 μm. With this configuration, when a voltage is applied to the CP type signal wiring 12b, an electric field is generated between the CP type signal wiring 12b and the second ground layer 13. Therefore, an electromagnetic wave input from an external device is coupled with the electric field generated between the CP type signal wiring 12b and the second ground layer 13, propagates through the inorganic material substrate 2, and can reach the patch antenna 11. Furthermore, when the patch antenna 11 receives an electromagnetic wave, the electromagnetic wave can propagate through the inorganic material substrate 2 and be transmitted to the external device due to the electric field generated between the CP type signal wiring 12b and the second ground layer 13.

[0022] 6, the second ground layer 13 may be provided so as to surround the patch antenna 11 in addition to the transmission line 12. In this case, the above-mentioned gap (slit) is formed between the second ground layer 13 and the patch antenna 11. This allows the antenna to be configured with a different design from the configuration in FIG.

[0023] Furthermore, the antenna element 100 including the CP type signal wiring 12b preferably further includes the first ground layer 42 described above. This configuration can prevent the electric field generated between the CP type signal wiring 12b and the second ground layer 13 from leaking to the support substrate 3, sufficiently suppress the occurrence of resonance and / or stray capacitance, and suppress fluctuations in antenna characteristics due to dimensional variations. Although not shown, the first ground layer 42 and the second ground layer 13 may be electrically connected. Conduction between the first ground layer 42 and the second ground layer 13 strengthens the ground and suppresses stray capacitance due to surrounding lines and elements. In one embodiment, the first ground layer 42 and the second ground layer 13 are short-circuited by forming multiple via holes in the inorganic material substrate 2 and providing vias in each of the via holes.

[0024] In this specification, the term "antenna element" encompasses both a wafer (antenna element wafer) on which at least one antenna element is formed and chips obtained by cutting the antenna element wafer.

[0025] B. Details of the Antenna Element Hereinafter, each component of the antenna element 100 will be described in detail with reference to Figures 1 and 2. B-1. Inorganic Material Substrate The inorganic material substrate 2 has an upper surface on which the first conductor layer 1 is provided, and a lower surface located within the antenna element 100. The thickness t of the inorganic material substrate 2 satisfies the above-mentioned formula (1). In the above-mentioned formula (1), a preferably represents a numerical value of 6 or more.

[0026] The thickness of the inorganic material substrate 2 is, for example, 1 μm or more, preferably 2 μm or more, more preferably 10 μm or more, even more preferably 20 μm or more, particularly preferably 30 μm or more, and particularly preferably 40 μm or more. If the thickness of the inorganic material substrate 2 is below this lower limit, the thickness and size of the electrodes constituting the transmission line 12 will be reduced to about several μm, making it difficult to achieve impedance matching with the patch antenna 11. Furthermore, the tolerance of transmission performance due to manufacturing variations may be significantly reduced. On the other hand, the thickness of the inorganic material substrate 2 is, for example, 500 μm or less, preferably 200 μm or less, more preferably 100 μm or less, even more preferably 80 μm or less, and particularly preferably 60 μm or less. If the thickness of the inorganic material substrate 2 is below this upper limit, induction of slab modes and / or resonance of the inorganic material substrate 2 can be stably suppressed. Therefore, reflection loss when the antenna element 100 transmits and / or receives electromagnetic waves can be further reduced. As a result, the bandwidth of the electromagnetic wave for which the reflection characteristic is sufficiently small in the antenna element 100 (typically, a −10 dB bandwidth) can be expanded, and the bandwidth of the antenna element 100 can be further widened.

[0027] The relative permittivity ε of the inorganic material substrate 2 at 300 GHz is, for example, 12.0 or less, preferably 10.0 or less, and more preferably 5.0 or less. The lower limit of the relative permittivity ε of the inorganic material substrate 2 at 300 GHz is typically 3.5. The dielectric loss tangent (dielectric loss) tanδ of the inorganic material substrate 2 at 300 GHz is, for example, 0.0030 or less, preferably 0.0020 or less, and more preferably 0.0015 or less. When the relative permittivity ε and dielectric loss tangent (dielectric loss) tanδ of the inorganic material substrate 2 are within such ranges, the reflection loss in the antenna element 100 can be further reduced. Note that the relative permittivity ε and dielectric loss tangent (dielectric loss) tanδ can be measured, for example, by terahertz time-domain spectroscopy. Furthermore, in this specification, when no measurement frequency is mentioned for the relative permittivity and dielectric loss tangent, the relative permittivity and dielectric loss tangent at 300 GHz are meant.

[0028] The inorganic material substrate 2 is made of an inorganic material. Any appropriate material may be used as the inorganic material as long as the effects of the embodiment of the present invention are obtained. Examples of inorganic materials that can be used to form the inorganic material substrate 2 include single crystal quartz (relative dielectric constant: 4.5, dielectric dissipation factor: 0.0013), amorphous quartz (quartz glass, relative dielectric constant: 3.8, dielectric dissipation factor: 0.0010), spinel (relative dielectric constant: 8.3, dielectric dissipation factor: 0.0020), AlN (relative dielectric constant: 8.5, dielectric dissipation factor: 0.0015), sapphire (relative dielectric constant: 9.4, dielectric dissipation factor: 0.0030), SiC (relative dielectric constant: 9.8, dielectric dissipation factor: 0.0022), magnesium oxide (relative dielectric constant: 10.0, dielectric dissipation factor: 0.0012), and silicon (relative dielectric constant: 11.7, dielectric dissipation factor: 0.0016). Among these inorganic materials, amorphous quartz (quartz glass) is preferred. If the inorganic material substrate 2 is made of quartz glass, the reflection loss in the antenna element 100 can be further stably reduced. Furthermore, since the dielectric constant is larger than that of resin-based substrates, the substrate size can be reduced, and since the dielectric constant is relatively small among inorganic materials, it is advantageous in terms of reducing delay. Furthermore, the first conductor layer 1 (metal layer) can be formed without roughening or surface treatment.

[0029] Although not shown, the inorganic material substrate 2 may be curved so that the portion that overlaps with the cavity 5 sinks into the cavity 5 when viewed in the thickness direction.

[0030] B-2. First Conductive Layer In one embodiment, the first conductor layer 1 is provided on the surface (one surface in the thickness direction) of the inorganic material substrate 2 and is in direct contact with the inorganic material substrate 2. The first conductor layer 1 is typically made of a metal. Examples of metals include chromium (Cr), nickel (Ni), copper (Cu), and gold (Au). The metals may be used alone or in combination. The first conductor layer 1 may be a single layer, or may be formed by laminating two or more layers. The thickness of the first conductor layer 1 is, for example, 1 μm to 20 μm, and preferably 4 μm to 10 μm.

[0031] B-3. ​​Support Substrate The support substrate 3 can provide excellent strength to the antenna element 100. In the illustrated example, the support substrate 3 supports the inorganic material substrate 2 via the first ground layer 42 and the bonding portion 6 (described later). This allows the inorganic material substrate 2 to be thinned as described above. The support substrate 3 can have any appropriate configuration. Examples of materials that can be used to form the support substrate 3 include indium phosphide (InP), silicon (Si), glass, and sialon (Si ３ N ４ -Al ２ O ３ ), mullite (3Al ２ O ３ 2SiO ２ , 2Al ２ O ３ 3SiO ２ ), aluminum nitride (AlN), magnesium oxide (MgO), aluminum oxide (Al ２ O ３ ), spinel (MgAl ２ O ４ ), sapphire, quartz, crystal, gallium nitride (GaN), silicon carbide (SiC), silicon nitride (Si ３ N ４ ), gallium oxide (Ga ２ O ３ ) are listed.

[0032] The thermal conductivity of the material constituting the support substrate 3 is preferably 150 W / Km or more, more preferably 200 W / Km or more. When an external device (e.g., an amplifier) ​​is connected to the antenna element 100, the inorganic material substrate 2 may be heated by the external device, and the heat from the inorganic material substrate 2 may adversely affect the external device. In this regard, if the material constituting the support substrate 3 has the above-mentioned thermal conductivity, the support substrate 3 can function as a heat sink and smoothly dissipate the heat from the inorganic material substrate 2. Among the materials constituting the support substrate 3, silicon (thermal conductivity: approximately 160 W / Km), silicon carbide (thermal conductivity: approximately 270 W / Km), and aluminum nitride (thermal conductivity: approximately 150 W / Km to 250 W / Km) are preferable from the viewpoint of thermal conductivity.

[0033] Furthermore, it is preferable that the linear expansion coefficient of the material constituting the support substrate 3 is as close as possible to the linear expansion coefficient of the material constituting the inorganic material substrate 2. The linear expansion coefficient of the material constituting the support substrate 3 is, for example, within a range of 50% to 150% of the linear expansion coefficient of the material constituting the inorganic material substrate 2. If the linear expansion coefficient of the material constituting the support substrate 3 is within this range, thermal deformation (typically, warpage) of the antenna element 100 can be suppressed.

[0034] Of the materials constituting such a support substrate 3, indium phosphide, silicon, aluminum nitride, gallium nitride, silicon carbide, and silicon nitride are preferred, silicon, aluminum nitride, gallium nitride, silicon carbide, and silicon nitride are more preferred, and silicon is particularly preferred.

[0035] As shown in FIG. 2 , in one embodiment, the support substrate 3 has a recess 31 corresponding to the cavity 5. The recess 31 is typically recessed downward (away from the inorganic material substrate 2) from the upper surface (surface facing the inorganic material substrate 2) of the support substrate 3. When viewed in the thickness direction of the inorganic material substrate 2, the recess 31 has the same shape as the above-described cavity 5. In the illustrated example, the recess 31 has a substantially U-shape that opens toward the inorganic material substrate 2 on a cross section obtained by cutting the support substrate 3 in the thickness direction. The inner surface of the recess 31 includes a side surface and a bottom surface. The side surface of the recess 31 extends in the thickness direction of the inorganic material substrate 2. The extending direction of the side surface of the recess 31 may be completely the same as (i.e., parallel to) the thickness direction of the inorganic material substrate 2, or may be slightly inclined with respect to the thickness direction of the inorganic material substrate 2. The bottom surface of the recess 31 extends in a direction intersecting (typically perpendicular to) the thickness direction of the inorganic material substrate 2.

[0036] B-4. Second Conductor Layer In one embodiment, the antenna element 100 further includes a second conductor layer 4 including a ground conductor layer 41. The second conductor layer 4 is disposed between the inorganic material substrate 2 and the support substrate 3. The second conductor layer 4 is typically provided on the upper surface of the support substrate 3 (the surface on the inorganic material substrate 2 side) and is in direct contact with the support substrate 3.

[0037] In the illustrated example, the ground conductor layer 41 included in the second conductor layer 4 is located in the recess 31 of the support substrate 3. The ground conductor layer 41 is provided on at least the bottom surface of the recess 31. In the illustrated example, the ground conductor layer 41 is provided on the entire inner surface of the recess 31. As a result, at least a portion of the ground conductor layer 41 is disposed opposite the patch antenna 11 in the thickness direction of the inorganic material substrate 2. Therefore, a stable electric field can be generated between the patch antenna 11 and the ground conductor layer 41.

[0038] In one embodiment, the second conductor layer 4 further includes a first ground layer 42. The first ground layer 42 may be provided in any appropriate location as long as it overlaps at least a portion of the projection surface of the transmission line 12 as described above. The first ground layer 42 is provided in a portion of the upper surface of the support substrate 3 (the surface on the inorganic material substrate 2 side) other than the recessed portion 31. The first ground layer 42 may be provided in a portion of the upper surface of the support substrate 3 excluding the recessed portion 31 (see FIG. 7 ), or may be provided over the entire upper surface of the support substrate 3 excluding the recessed portion 31 (see FIG. 8 ).

[0039] 8 , in one embodiment, the first ground layer 42 is provided over the entire top surface of the support substrate 3 except for the recess 31. In the illustrated example, the first ground layer 42 and the ground conductor layer 41 are continuous with each other. When the ground conductor layer 41 and the first ground layer 42 are continuous with each other to form the second conductor layer 4, the ground function is stable across the entire substrate, which may facilitate the design and manufacture of the antenna element 100.

[0040] The second conductor layer 4 is made of, for example, the same metal as the first conductor layer 1. The thickness of the second conductor layer 4 is typically smaller than the thickness of the first conductor layer 1. The thickness of the second conductor layer 4 is, for example, 1 nm to 30 μm, and preferably 10 nm to 10 μm.

[0041] 1 and 2, in one embodiment, the antenna element 100 further includes a joint 6. The joint 6 joins the inorganic material substrate 2 and the support substrate 3. In the illustrated example, the joint 6 joins the inorganic material substrate 2 and the support substrate 3 on which the first ground layer 42 is provided, and is located between the inorganic material substrate 2 and the first ground layer 42. The joint 6 may be made of an organic material (typically an organic adhesive) or an inorganic material.

[0042] In one embodiment, the bonding portion 6 is made of an inorganic material. Examples of the inorganic material that forms the bonding portion 6 include SiO. ２ , amorphous silicon, and tantalum oxide, and amorphous silicon is preferred. The thickness of the bonding portion 6 is, for example, 0.001 μm to 10 μm, and preferably 0.01 μm to 3 μm.

[0043] In one embodiment, the inorganic material substrate 2 and the support substrate 3 on which the first ground layer 42 is formed are directly bonded. This forms a bonded portion 6 between the inorganic material substrate 2 and the first ground layer 42. In this specification, "direct bonding" means that two layers or substrates are bonded without an organic material (typically, an organic adhesive). The form of direct bonding can be appropriately set depending on the configuration of the layers or substrates to be bonded. Furthermore, the interface bonded by direct bonding is typically amorphous. Therefore, it is possible to significantly reduce the thermal resistance of the bonded interface compared to resin bonding. As a result, when an external device is connected to the antenna element 100, even if heat generated by the external device is transferred to the inorganic material substrate 2, such heat can be smoothly dissipated from the inorganic material substrate 2 to the package via the support substrate 3. As a result, heat can be efficiently dissipated from the inorganic material substrate 2, and deterioration of the characteristics of the external device can be suppressed. Furthermore, by integrating them by direct bonding, it is possible to effectively prevent peeling in the antenna element 100, and as a result, it is possible to effectively prevent damage (for example, cracks) to the inorganic material substrate 2 caused by such peeling. Furthermore, by integrating them by direct bonding without using a resin, it is possible to improve heat resistance and chemical resistance in later manufacturing processes, and it is possible to prevent deterioration of the antenna characteristics of the antenna element 100 due to heat or moisture absorption.

[0044] The bonding portion 6 may have a single-layer structure or a laminated structure. As shown in Fig. 2, in one embodiment, the bonding portion 6 has a laminated structure. The bonding portion 6 includes a first bonding layer 61 and a second bonding layer 62.

[0045] The first bonding layer 61 is provided on the surface of the inorganic material substrate 2. More specifically, the first bonding layer 61 is provided on the surface of the inorganic material substrate 2 opposite the first conductor layer 1 in the thickness direction of the inorganic material substrate 2. In the illustrated example, the first bonding layer 61 is provided on the lower surface of the inorganic material substrate 2 (the surface opposite the first conductor layer 1) and is in direct contact with the inorganic material substrate 2. The first bonding layer 61 may be provided partially on the lower surface of the inorganic material substrate 2 or may be provided on the entire lower surface of the inorganic material substrate 2. In the illustrated example, the first bonding layer 61 is provided on the entire lower surface of the inorganic material substrate 2. The thickness of the first bonding layer 61 is, for example, 0.5 nm to 5 μm, preferably 0.01 μm to 1.5 μm, and more preferably 0.01 μm to 0.05 μm.

[0046] The second bonding layer 62 is provided on the surface of the first ground layer 42. More specifically, the second bonding layer 62 is provided on the surface of the first ground layer 42 opposite the support substrate 3 in the thickness direction of the inorganic material substrate 2. In the illustrated example, the second bonding layer 62 is provided on the upper surface of the first ground layer 42 (the surface opposite the support substrate 3) and is in direct contact with the first ground layer 42. The second bonding layer 62 may be provided only on the first ground layer 42, or may be provided on the ground conductor layer 41 in addition to the first ground layer 42. In the illustrated example, the second bonding layer 62 is provided on the entire upper surfaces of the ground conductor layer 41 and the first ground layer 42. In other words, the second bonding layer 62 is laminated over the entire second conductor layer 4. The thickness range of the second bonding layer 62 is, for example, the same as the thickness range of the first bonding layer 61 described above. The second bonding layer 62 is bonded to the first bonding layer 61 and is integrated with the first bonding layer 61. In the illustrated example, the portion of the second bonding layer 62 located on the first ground layer 42 is directly bonded to the first bonding layer 61.

[0047] 9, the second conductor layer 4 may be composed of only the ground conductor layer 41 without including the first ground layer 42. In this case, although not shown, a joint 6 is located between the inorganic material substrate 2 and the portion of the upper surface of the support substrate 3 other than the recess 31, and joins them together.

[0048] B-6. Cavity As shown in FIG. 2 , in one embodiment, the cavity 5 is located inside the region surrounded by the inorganic material substrate 2 and the ground conductor layer 41. The cavity 5 is a groove formed in the support substrate 3. The cavity 5 is defined by a first bonding layer 61 provided on the lower surface of the inorganic material substrate 2 or on the lower surface of the inorganic material substrate 2, and a second bonding layer 62 provided on the upper surface of the ground conductor layer 41 or on the upper surface of the ground conductor layer 41. In the illustrated example, the cavity 5 is defined by the first bonding layer 61 provided on the lower surface of the inorganic material substrate 2 and the second bonding layer 62 provided on the upper surface of the ground conductor layer 41. Air typically exists in the cavity 5. In another embodiment, the cavity 5 is in a vacuum state.

[0049] The dimension d of the cavity 5 in the thickness direction of the inorganic material substrate 2 (hereinafter referred to as the depth d) can be arbitrarily and appropriately changed depending on the configuration of the antenna element 100 and the frequency of the electromagnetic waves transmitted and / or received by the antenna element 100. The depth d of the cavity 5 is, for example, 1 μm to 250 μm. The depth d of the cavity 5 refers to the distance between the bottom surface of the inorganic material substrate 2 (the surface opposite to the first conductor layer 1) and the top surface of the ground conductor layer 41 (the surface opposite to the support substrate 3) in the thickness direction of the inorganic material substrate 2. In one embodiment, when the patch antenna 11 has a rectangular shape and the antenna element 100 transmits and receives electromagnetic waves with a frequency of 100 GHz to 200 GHz, the depth d of the cavity 5 is, for example, 5 μm to 250 μm. In another embodiment, when the patch antenna 11 has a rectangular shape and the antenna element 100 transmits and receives electromagnetic waves with a frequency of 250 GHz to 350 GHz, the depth d of the cavity 5 is, for example, 5 μm to 200 μm.

[0050] C. Method of Manufacturing the Antenna Element One embodiment of a method of manufacturing the antenna element 100 will now be described with reference to FIG.

[0051] In one embodiment, first, a support substrate 3 is prepared having a recess 31. The recess 31 is formed in the support substrate 3 by, for example, reactive ion etching.

[0052] Next, the second conductor layer 4 is formed on the upper surface of the support substrate 3 with the recess 31 formed therein. Any appropriate film formation method can be used as the film formation method. Examples of the film formation method include sputtering, plating, and vapor deposition, and plating is preferred.

[0053] Next, the inorganic material substrate 2 is prepared, and the inorganic material substrate 2 and the support substrate 3 are directly bonded together. More specifically, a first bonding layer 61 is formed on the lower surface of the inorganic material substrate 2. A second bonding layer 62 is formed on the upper surface of the second conductor layer 4. Examples of methods for forming these layers include sputtering, plating, and vapor deposition, with sputtering being preferred. The surfaces of the first bonding layer 61 and the second bonding layer 62 are planarized by polishing as necessary.

[0054] Direct bonding can be achieved, for example, by the following procedure: In a high vacuum chamber (for example, 1×10 －６A neutralization beam is irradiated onto the bonding surfaces of the components (layers or substrates) to be bonded at a pressure of about 1000 kJ / cm² (approximately 1000 kJ / cm²). In one embodiment, when surface activation is performed using the neutralization beam, an inert gas is introduced into a chamber, and a high voltage is applied from a DC power supply to an electrode disposed in the chamber. With this configuration, an electric field generated between the electrode (positive electrode) and the chamber (negative electrode) causes electrons to move, generating a beam of atoms and ions from the inert gas. Of the beams that reach the grid, the ion beam is neutralized by the grid, and a beam of neutral atoms is emitted from the fast atom beam source. The atomic species constituting the beam are preferably inert gas elements (e.g., argon (Ar) or nitrogen (N)). The voltage during activation by beam irradiation is, for example, 0.5 kV to 2.0 kV, and the current is, for example, 50 mA to 200 mA. The irradiation time of the neutralization beam is, for example, 10 to 300 seconds, preferably 30 to 120 seconds. This activates the inorganic material present on each bonding surface, more specifically, on the beam-irradiated surface. Next, the activated bonding surfaces are brought into contact with each other in a vacuum atmosphere at room temperature (23°C). The load during this contact can be, for example, 100 N to 20,000 N. The first bonding layer 61 and the second bonding layer 62 are then bonded to form a bonding portion 6. This results in a laminate having a structure of inorganic material substrate 2 / bonding portion 6 / second conductor layer 4 / support substrate 3. Note that the direct bonding method is not limited to this, and other methods such as surface activation using FAB (Fast Atom Beam) or an ion gun, atomic diffusion, and plasma bonding can also be applied. The laminate is heat-treated as needed. This can improve the bonding strength between the inorganic material substrate and the support substrate. The heating temperature is, for example, 60°C to 140°C, preferably 80°C to 120°C. The heating time is, for example, 10 minutes to 5 hours, preferably 30 minutes to 3 hours.

[0055] Thereafter, if necessary, the inorganic material substrate 2 is polished to reduce its thickness to the above-mentioned thickness. As a polishing method, for example, chemical mechanical polishing (CMP polishing) can be mentioned.

[0056] Next, a first conductor layer 1 is formed on the upper surface of the inorganic material substrate 2. In one embodiment, a resist having an opening corresponding to the first conductor layer is formed on the upper surface of the inorganic material substrate 2, and then the first conductor layer is formed through the resist. Examples of methods for forming the metal film include sputtering, plating, and vapor deposition, and plating is preferred. In this manner, an antenna element 100 having a structure of first conductor layer 1 / inorganic material substrate 2 / joint 6 / second conductor layer 4 / support substrate 3, and including a cavity 5, is manufactured.

[0057] Such an antenna element 100 can be applied to any appropriate optical device (e.g., a waveguide element, an electromagnetic wave sensor). In particular, the antenna element 100 has a wide band of available electromagnetic waves, and therefore can be suitably used in a human presence sensor that requires excellent resolution. When the above-described antenna element 100 is applied to a human presence sensor, it can accurately detect the movements (gestures) of a person. Examples of human presence sensors include an in-vehicle gesture detection sensor and a gesture detection sensor for a human-machine interface (HMI).

[0058] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0059] Example 1: A 0.5 mm thick quartz glass wafer (inorganic material substrate) was prepared. A 0.02 μm thick amorphous silicon film (first bonding layer) was formed on the surface of the inorganic material substrate by sputtering. After film formation, the first bonding layer was polished and planarized. The arithmetic mean roughness of the surface of the first bonding layer over a 10 μm square was measured using an atomic force microscope and found to be 0.2 nm.

[0060] A silicon wafer (support substrate) with a thickness of 250 μm was prepared. Then, a recess was formed on the upper surface of the support substrate by reactive ion etching. The recess had a substantially rectangular shape when viewed from the thickness direction of the support substrate. The long side dimension of the recess was 1100 μm, the short side dimension of the recess was 720 μm, and the depth of the recess was 175 μm.

[0061] Next, a 1 μm-thick gold film (second conductor layer) was formed by sputtering on the upper surface of the support substrate with the recessed portion. The second conductor layer integrally comprised a ground conductor layer located within the recessed portion and a first ground layer located on the upper surface of the support substrate other than the recessed portion. Next, a 0.02 μm-thick amorphous silicon film (second bonding layer) was formed by sputtering on the second conductor layer. After deposition, the second bonding layer was polished and flattened. The arithmetic mean roughness of the surface of the second bonding layer over a 10 μm square was measured using an atomic force microscope and found to be 0.2 nm.

[0062] Next, the inorganic material substrate and the support substrate were directly bonded as follows: First, the inorganic material substrate on which the first bonding layer was formed and the support substrate on which the second bonding layer and the second conductor layer were formed were placed in a vacuum chamber. －６ In a vacuum of the Pa range, both bonding surfaces (the surfaces of the first bonding layer and the second bonding layer) were irradiated with a high-speed Ar neutral atom beam (accelerating voltage 1 kV, Ar flow rate 60 sccm) for 70 seconds. After irradiation, the inorganic material substrate and the support substrate were allowed to cool for 10 minutes, and then the surfaces (beam-irradiated surfaces) of the first bonding layer and the second bonding layer were brought into contact and pressed at 4.90 kN for 2 minutes to bond the inorganic material substrate and the support substrate. That is, the inorganic material substrate and the support substrate were directly bonded via the bonding portion and the second conductor layer. After bonding, the inorganic material substrate was polished until its thickness reached 50 μm.

[0063] Next, a resist was applied to the surface (polished surface) of the inorganic material substrate opposite the bonding portion, and patterned by photolithography to expose the portion where the first conductor layer would be formed. A 5 μm-thick copper film (first conductor layer) was then formed by sputtering on the upper surface of the inorganic material substrate exposed from the resist. The resist was then removed. The first conductor layer included a patch antenna and an MS-type signal wiring. The patch antenna had a substantially rectangular shape when viewed from the thickness direction of the inorganic material substrate. The length of the patch antenna (in a direction perpendicular to the II-II' direction in FIG. 1) was 860 μm, and the width of the patch antenna (in the II-II' direction in FIG. 1) was 590 μm. The MS-type signal wiring consisted of a wide portion and a narrow portion, and the line width of each was set to match the impedance to 50 Ω.

[0064] As a result, the antenna element shown in Figure 1 was obtained, i.e., an antenna element having a configuration of first conductor layer / inorganic material substrate / joint portion / second conductor layer / support substrate. The antenna element had a cavity corresponding to the recess. When the patch antenna was projected in the thickness direction of the inorganic material substrate, the entire projection surface of the patch antenna overlapped with the cavity. The projection surface of the patch antenna was 507,400 μm ２ The projected area of ​​the cavity is 792,000 μm ２ It was.

[0065] Comparative Example 1 An antenna element was obtained in the same manner as in Example 1, except that no recess was formed in the support substrate. This antenna element did not have a cavity.

[0066] <Measurement of S11 Parameter> The S11 parameter, which represents the return loss, was measured for the antenna elements obtained in the examples and comparative examples using a network analyzer with a sampling frequency set to 120 GHz. The results are shown in FIGS. 10 and 11. As is clear from FIG. 10, when the antenna element includes a cavity, the bandwidth of the electromagnetic wave where the S11 parameter of the antenna element is −10 dB or less (−10 dB bandwidth) is 10.2 GHz. On the other hand, as shown in FIG. 11, for an antenna element without a cavity, the −10 dB bandwidth is 4.9 GHz. This shows that including a cavity in an antenna element can broaden the bandwidth of the antenna element.

[0067] The antenna element according to the embodiment of the present invention can be used in a wide range of fields such as next-generation high-speed communications and sensors, and can be particularly suitably used as a human presence sensor.

[0068] REFERENCE SIGNS LIST 1 First conductor layer 11 Patch antenna 12 Transmission line 2 Inorganic material substrate 3 Support substrate 31 Recess 4 Second conductor layer 41 Ground conductor layer 5 Cavity 6 Bonding portion 61 First bonding layer 62 Second bonding layer 100 Antenna element

Claims

1. An antenna element comprising: an inorganic material substrate; a first conductor layer disposed on one side of the inorganic material substrate in a thickness direction, the first conductor layer including a patch antenna; a support substrate disposed on an opposite side of the inorganic material substrate from the first conductor layer; a cavity disposed on an opposite side of the inorganic material substrate from the first conductor layer and on the inorganic material substrate side of the support substrate; and a ground conductor layer disposed within the cavity, the ground conductor layer being capable of generating an electric field between the patch antenna and the inorganic material substrate, wherein a thickness t of the inorganic material substrate satisfies the following formula (1), and when the patch antenna is projected in the thickness direction of the inorganic material substrate, at least a portion of the projection surface of the patch antenna overlaps with the cavity: (In the formula, t represents the thickness of the inorganic material substrate, λ represents the wavelength of the electromagnetic wave transmitted and / or received by the antenna element, ε represents the relative dielectric constant of the inorganic material substrate, and a represents a numerical value of 3 or more.) 2. The antenna element according to claim 1, wherein when the patch antenna is projected in the thickness direction of the inorganic material substrate, the entire projection surface of the patch antenna overlaps with the cavity portion.

3. The antenna element according to claim 1 or 2, wherein the first conductor layer further comprises a transmission line connected to the patch antenna.

4. The antenna element described in claim 3, further comprising a first ground layer disposed between the inorganic material substrate and the support substrate in a portion different from the cavity, wherein when the transmission line is projected in the thickness direction of the inorganic material substrate, at least a portion of the projection surface of the transmission line overlaps with the first ground layer.

5. The antenna element according to claim 4, further comprising a bonding portion for bonding said inorganic material substrate and said supporting substrate.

6. The antenna element described in claim 5, wherein the bonding portion includes: a first bonding layer provided on a surface of the inorganic material substrate opposite the first conductor layer in the thickness direction of the inorganic material substrate; and a second bonding layer provided on a surface of the first ground layer opposite the supporting substrate in the thickness direction of the inorganic material substrate, the second bonding layer being bonded to the first bonding layer.

7. The antenna element according to claim 1 or 2, wherein the thickness t of said inorganic material substrate is 100 μm or less.

8. An antenna element according to claim 1 or 2, wherein the frequency of the electromagnetic waves transmitted and / or received by the antenna element is between 20 GHz and 20 THz.

9. The antenna element according to claim 1 or 2, wherein the inorganic material substrate is made of quartz glass.

10. The antenna element according to claim 1 or 2, wherein the supporting substrate is made of silicon.

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