Patent Grant
9899725
This invention relates to Mircroelectromecanical systems (MEMS) antennas and more particularly relates to an apparatus system and method for circuitry-isolated MEMS antennas.
The frequency scaling law states that as frequency increases the size of the antenna and distributed microwave circuit decreases. Due to the recent advances in technology that allows for fabricating small devices, the realization of miniaturized wireless equipment operating at high frequencies becomes feasible. This explains the recent interests in the millimeter-wave (mm-wave) range that starts from 30 GHz up to 300 GHz. Several frequencies within this band are already allocated for a number of applications, as listed in Table I.
As frequency of operation increases, the antenna's dielectric losses increase significantly due to the excitation of surface waves inside the substrate carrying the antenna. This serious drawback deteriorates the performance of the conventional planar antennas, such as patches, in the mm-wave range of frequencies. An attractive solution to this problem is the use of the micromachining technology. Typically, the main idea behind the use of this technology for antennas is to etch away as much as possible dielectric volume around the radiating elements. This reduces surface wave losses significantly and allows for high radiation efficiency and gain even at high resonance frequencies. The reduction of substrate losses leads to enhancing battery life time of mobile and hand-held equipment. Moreover, MEMS antennas are still compatible with the driving circuit technology and can be monolithically integrated with the entire millimeter-wave system. Such compatibility leads to miniaturized wireless systems which obey the evolution towards compactness.
MEMS antennas can be classified into two main categories. The first category features one silicon wafer 102 machined such that to create a cavity 104 underneath the antenna 106, as shown in
Embodiments of MEMS antennas are presented. In one embodiment, only one silicon wafer is required while ground plane isolation between the MEMS antenna and circuit exists. Additional embodiments of the MEMS antenna may have diversity in polarization and radiation characteristics. In one embodiment, the frequency of operation of the MEMS antennas is 60 GHz. One of ordinary skill in the art will recognize, however, that these antennas may be tuned for operation at any other frequency within the mm-wave range. While maintaining the same geometry, increasing antenna dimensions results in reducing the frequency of operation, and vice verse. Methods of manufacturing the MEMS antenna may remain substantially the same for the entire range of dimensions along the mm-wave range. In further embodiments, the MEMS antenna may be manufactured on either high-resistivity (2,000 Ω·cm) or low-resistivity (45 Ω·cm) silicon wafers. In a particular embodiment, the wafers may have a thickness of 675 μm and dielectric constant of 11.9.
In one embodiment, the MEMS antenna includes a substrate, a metallic layer disposed over the substrate, the metallic layer forming a ground plane, the ground plane having a region defining a gap disposed therein, a protrusion disposed over the substrate within the region defining the gap, the protrusion extending outwardly from the ground plane, the protrusion having a length and a width, the length being greater than the width, and a first electromagnetic radiator element disposed over the protrusion, the first electromagnetic element having a length and a width, the length being greater than the width.
The MEMS antenna may also include a Through-Silicon Via (TSV) extending through the substrate from a first surface of the substrate to a second surface of the substrate. The TSV may have a length which extends perpendicularly to the length of the first electromagnetic radiator element. In a further embodiment, the TSV has a first end and a second end. Additionally, the first electromagnetic radiator element may include a first end and a second end, In such an embodiment, the first end of the TSV may be disposed adjacent to the first end of the first electromagnetic radiator element. In one embodiment, the first end of the TSV may be separated from the first end of the first electromagnetic radiator element by a gap.
In one embodiment, the length of the first electromagnetic radiator element is equal to one-half a wavelength of a standing electromagnetic wave to be radiated by the first electromagnetic radiator element.
In a further embodiment, the MEMS antenna may include a second protrusion disposed over the substrate within the region defining the gap, the second protrusion extending outwardly from the ground plane, the second protrusion having a length and a width, the length being greater than the width, and a second electromagnetic radiator element disposed over the second protrusion, the second electromagnetic element having a length and a width, the length being greater than the width.
In one embodiment, the length of the second electromagnetic radiator element may also be equal to one-half a wavelength of a standing electromagnetic wave to be radiated by the second electromagnetic radiator element. In an additional embodiment, the first electromagnetic radiator element and the second electromagnetic radiator element are arranged in a linearly polarized configuration. In certain embodiments, the first electromagnetic radiator element and the second electromagnetic radiator element each comprise a half-wavelength dipole. In one embodiment, the length of the first electromagnetic radiator element and the length of the second electromagnetic radiator element are disposed within a common plane.
In an embodiment, the MEMS antenna may include a second TSV extending through the substrate from a first surface of the substrate to a second surface of the substrate, wherein the second TSV comprises a first end and a second end, and the second electromagnetic radiator element comprises a first end and a second end, and wherein the first end of the second TSV is disposed adjacent to the first end of the second electromagnetic radiator element.
In one embodiment, the wherein the length of the first electromagnetic radiator element and the length of the second electromagnetic radiator element are disposed within separate parallel planes. In such an embodiment, the second electromagnetic radiator element may be a parasitic half-wavelength dipole.
In one embodiment, the MEMS antenna also includes a third protrusion disposed over the substrate within the region defining the gap, the third protrusion extending outwardly from the ground plane, the third protrusion having a length and a width, the length being greater than the width, a third electromagnetic radiator element disposed over the third protrusion, the third electromagnetic element having a length and a width, the length being greater than the width, a fourth protrusion disposed over the substrate within the region defining the gap, the fourth protrusion extending outwardly from the ground plane, the fourth protrusion having a length and a width, the length being greater than the width, and a fourth electromagnetic radiator element disposed over the fourth protrusion, the fourth electromagnetic element having a length and a width, the length being greater than the width.
In an embodiment, the first and second electromagnetic radiator elements are active half-wavelength dipoles, and the third and fourth electromagnetic radiator elements are parasitic halve-wavelength dipoles. The first electromagnetic radiator element may be disposed at an angle that is perpendicular to an angle of the second electromagnetic radiator element, and the third electromagnetic radiator element may be disposed at an angle that is perpendicular to an angle of the fourth electromagnetic radiator element. In a further embodiment, the first electromagnetic radiator element is disposed within a first plane, and the third electromagnetic radiator element is disposed within a second plane, and the first plane is parallel to the second plane. In particular, the first electromagnetic radiator element, the second electromagnetic radiator element, the third electromagnetic radiator element, and the fourth electromagnetic radiator element may be arranged in a circularly polarized configuration.
In one embodiment, the first electromagnetic radiator element and the second electromagnetic radiator element are coupled together by a ring coupler. The ring coupler may include a microstrip line disposed on a surface of the substrate that is opposite a surface of the substrate over which the first electromagnetic radiator element and the second electromagnetic radiator element are disposed. In a further embodiment, the ring coupler has a first port and a second port. In such an embodiment, power delivered through the first port is delivered equally to the first electromagnetic radiator element and the second electromagnetic radiator element, but with a one hundred and eighty degree phase shift. Power delivered through the second port may be delivered equally to the first electromagnetic radiator element and the second electromagnetic radiator element with a zero degree phase shift. In such an embodiment, the first electromagnetic radiator element and the second electromagnetic radiator element may be configured to operate as a dipole antenna when power is applied to the first port and configured to operate as a monopole antenna when power is applied to the second port.
In a further embodiment, the MEMS antenna may include a plurality of additional protrusions disposed over the substrate within the region defining the gap, the plurality of additional protrusions extending outwardly from the ground plane, the plurality of additional protrusions each having a length and a width, the length being greater than the width. The MEMS antenna may also include a plurality of additional electromagnetic radiator elements, each disposed over one of the plurality of additional protrusions, the plurality additional electromagnetic elements each having a length and a width, the length being greater than the width. In such an embodiment, the first electromagnetic radiator element and the plurality of additional electromagnetic radiator elements are arranged in a wire-grid array configuration.
A system is also presented. In one embodiment, the system includes a substrate having a first surface and a second surface, the first surface being disposed opposite the second surface. The system may also include a MEMS antenna disposed over the first surface, the MEMS antenna. The MEMS antenna may include a metallic layer disposed over the first surface of the substrate, the metallic layer forming a ground plane, the ground plane having a region defining a gap disposed therein, a protrusion disposed over the substrate within the region defining the gap, the protrusion extending outwardly from the ground plane, the protrusion having a length and a width, the length being greater than the width, and a first electromagnetic radiator element disposed over the protrusion, the first electromagnetic element having a length and a width, the length being greater than the width. Additionally, the system may include an antenna driver circuit coupled to the second surface, the antenna driver circuit being coupled to the MEMS antenna by one or more vias extending from the first surface through the substrate to the second surface.
The system may additionally include the various other embodiments of the MEMS antenna described above.
A method for manufacturing a MEMS antenna is also presented. In one embodiment, the method includes providing a substrate having a first surface and a second surface, the first surface being disposed opposite the second surface. The method may also include forming an oxide layer on at least one of the first surface and the second surface. Additionally, the method may include patterning the oxide layer in regions sufficient to form a protrusion disposed over the first surface of the substrate. An embodiment of the method may also include etching away at least a portion of the first surface of the substrate to form the protrusion disposed over the first surface of the substrate. Further, the method may include depositing a metal layer over a portion of the first surface of the substrate to form a ground plane, the ground plane having a region defining a gap disposed therein, the protrusion being disposed within the region defining a gap. Additionally, the method may include depositing a metal layer over the protrusion to form an electromagnetic radiator element.
A further embodiment of the method may include etching a hole through the substrate from the first surface to the second surface, and depositing a metal layer in the hole to form a via electrically coupling at least a portion of the first surface to at least a portion of the second surface.
The term “coupled” is defined as connected, although not necessarily directly, and not necessarily mechanically.
The terms “a” and “an” are defined as one or more unless this disclosure explicitly requires otherwise.
The term “substantially” and its variations are defined as being largely but not necessarily wholly what is specified as understood by one of ordinary skill in the art, and in one non-limiting embodiment “substantially” refers to ranges within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5% of what is specified.
The terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”) and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a method or device that “comprises,” “has,” “includes” or “contains” one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more elements. Likewise, a step of a method or an element of a device that “comprises,” “has,” “includes” or “contains” one or more features possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed.
Other features and associated advantages will become apparent with reference to the following detailed description of specific embodiments in connection with the accompanying drawings.
The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein.
Various features and advantageous details are explained more fully with reference to the nonlimiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well known starting materials, processing techniques, components, and equipment are omitted so as not to unnecessarily obscure the invention in detail. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the invention, are given by way of illustration only, and not by way of limitation. Various substitutions, modifications, additions, and/or rearrangements within the spirit and/or scope of the underlying inventive concept will become apparent to those skilled in the art from this disclosure.
One embodiment of a MEMS antennas 200 includes one or more narrow vertical silicon walls 202. These walls 202 may carry wire-radiators 204 on top of them, as shown in
The process 300 flow for fabricating the new category of MEMS antennas 200 may require as few as three processing steps. Embodiments of steps of the process 300 are illustrated in
In addition, as illustrated in
An embodiment of a linearly polarized MEMS antenna 400 is shown in
In one embodiment, the antenna may be excited with a differential mode of the feeding line, which may force the currents on the vertical arms to be opposite and hence cancel out. On the other hand, the currents on the horizontal arms may be in the same direction and they may add constructively to each other. A simulation of an embodiment of a linearly polarized MEMS antenna 400 may be performed using Ansoft/HFSS.
The bandwidth of an embodiment of a linearly polarized MEMS antenna 900 may be greatly enhanced by adding parasitic radiators 904, 906 beside the driven ones 402, 902, as shown in
In one embodiment, a gap may be placed between the horizontal and vertical arms of each antenna. The gap may be represented as a capacitor, whose capacitance can be controlled by the gap size. Therefore, having different gap sizes may result in different capacitances for the two antennas. For the same applied voltage difference on both antennas, the difference in capacitances may lead to phase shifts between the currents on the two antennas. By optimizing the gap sizes the required 90° phase shift may be been obtained. Table VI lists the dimensions of an embodiment of a circularly polarized antenna as fabricated on both high- and low-resistivity silicon according to the present embodiments.
The current distribution at 60 GHz on the radiating arms of an embodiment of a circularly polarized antenna 1400 is plotted in
An embodiment of a reconfigurable MEMS antenna 1900 is shown in
The top surface of the substrate may be covered with slotted ground plane 210, through which the silicon walls 202 are penetrating up. This plane 210 may isolates between the antenna 1900 and the bulk silicon substrate 102, which may reduce surface wave losses and increases radiation efficiency. Moreover, this ground plane 210 may reduce significantly the interference between the antenna 1900 and the driving circuit 108 that may be located below the substrate 102. In one embodiment, metallic parts of this structure are made of copper with thickness of 3 μm. One of ordinary skill in the art will recognize other thicknesses and materials suitable for use with the present embodiments. From the bottom side of the substrate 102, the TSVs 206 may be connected to the two output ports 1910, 1912 of a ring coupler 1906 made of microstrip lines. Two feeding microstrip lines 1908 may be connected to the input ports of the ring coupler 1906. The width of each line may be adjusted to have characteristic impedance of 50Ω at 60 GHz. In one embodiment, the ring may be made of a microstrip line whose width corresponds to a characteristic impedance of 70.7Ω. The radius of the ring 1906 may be adjusted such that its electric length equals 1.5λg at the frequency of operation. Geometrical parameters of one embodiment of this antenna 1900 are listed in Table VIII. The photographs of the fabricated prototype are presented in
If an excitation signal is applied to the first port 1910 of the ring coupler 1906, see
S-parameters of an embodiment of the antenna 1900 are plotted versus frequency in
The excitation of the monopole mode is via the second port 1912. In this case, the ring coupler 1906 delivers half of the input power to each antenna side 1902, 1904 with the same phase. A negligible amount of power can couple to the first port 1910. The surface current distribution of an embodiment of monopole mode on the antenna arms 1902, 1904 at 60 GHz is plotted in
An embodiment of a wire-grid array 2900 is shown in
Embodiments of MEMS antennas have been presented. These embodiments include MEMS antennas with ground plane isolation from the feeding circuitry using single silicon wafer without the need for any wafer bonding or hybrid integration. Beneficially, this reduces the fabrication cost dramatically while maintaining superior electromagnetic performance at the same time. Additionally, embodiments of a method for fabricating the proposed category of MEMS antennas has been described. In one embodiment, the method may be performed in as little as three processing steps. Embodiments of the MEMS antennas offer diversity in polarization and radiation characteristics, such as: single element for linear polarization, single element for circular polarization, reconfigurable single element for radiation pattern diversity, and a wire-grid antenna array.
Embodiments of the three single antenna elements appear to exhibit very high radiation efficiency (≅94%) and high gain (≅8 dBi) on high-resistivity silicon. These remarkably high figures may be achieved at high operation frequency, specifically 60 GHz. The high radiation efficiency may lead to long battery life-time, while high gain results in enlarged range of communication. On the other hand, the three single elements on low-resistivity silicon are showing significantly less radiation efficiency (≅35%) and gain (≅3.5 dBi). This gain value is suitable for short range communication such as in-door wireless systems. For such systems, the low-resistivity silicon solution is very attractive as it is much cheaper and more compatible with the driving electronics as compared to the high-resistivity silicon solution. As for embodiments of the wire-grid array, the gain is significantly higher, 13 dBi and 7.6 dBi on high- and low-resistivity silicon, owing to the increased directivity. This enlarges the communication range of the embodiments of the wire-grid array making it sufficient for several applications even if the array is fabricated on low-resistivity silicon.
Bandwidth of embodiments of the MEMS antennas on high- and low-resistivity silicon have been observed to be around 2 GHz and 5 GHz, respectively, which are considered sufficient for the majority of applications. However, for applications require significantly large information capacity, the bandwidth of all the proposed antennas may be enhanced by adding parasitic elements in the vicinity of the driven ones. An example of this is done for the linearly polarized antenna whose bandwidth is enhanced by about 2.5% by adding parasitic elements. Various other embodiments may also benefit from the use of parasitic elements. Embodiments of such elements show one side radiation characterized by front-to-back ratio in the order of 15 dB. This value indicates that the proposed ground-plane isolation technique is functional and minimum interference between the antenna and the driving circuit can be achieved. The polarization purity of all antennas may be as high as characterized by cross-polarization level in the range of −30 dB.
All of the devices and methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the apparatus and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. In addition, modifications may be made to the disclosed apparatus and components may be eliminated or substituted for the components described herein where the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope, and concept of the invention as defined by the appended claims.
This application is a national phase application under 35 U.S.C. § 371 of International Application No. PCT/IB2010/003487 filed 18 Dec. 2010, which claims priority to U.S. Provisional Application No. 61/287,876 filed 18 Dec. 2009. The entire contents of each of the above-referenced disclosures is specifically incorporated herein by reference without disclaimer.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2010/003487 | 12/18/2010 | WO | 00 | 10/17/2012 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2011/073802 | 6/23/2011 | WO | A |
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| Number | Date | Country | |
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| 20130044037 A1 | Feb 2013 | US |
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| 61287876 | Dec 2009 | US |
