Gap waveguide structures for THz applications

Abstract

A microwave/millimeter device having a narrow gap between two parallel surfaces of conducting material by using a texture or multilayer structure on one of the surfaces is disclosed. The fields are mainly present inside the gap, and not in the texture or layer structure itself, so the losses are small. The microwave/millimeter wave device further includes one or more conducting elements, such as a metallized ridge or a groove in one of the two surfaces, or a metal strip located in a multilayer structure between the two surfaces. The waves propagate along the conducting elements. At least one of the surfaces is provided with means to prohibit the waves from propagating in other directions between them than along the ridge, groove or strip. At very high frequency, the gap waveguides and gap lines may be realized inside an IC package or inside the chip itself.

Claims

1. A scalable production method for fabrication of a microwave/millimeter wave device, said microwave/millimeter wave device operating at frequencies in the entire range of or one or more subranges of the frequency range between 1 GHz and 100 THz, and comprising the step of providing a metamaterial on a surface of said microwave/millimeter wave device, wherein the step of providing said metamaterial on said surface of the microwave/millimeter wave device involves the use of at least one polymer to fabricate a high-resolution structure, and subsequent metallization of the high-resolution structure.

2. The method of claim 1, wherein the microwave/millimeter wave device comprises two opposing surfaces of conducting material arranged to form a narrow gap there between, wherein at least one of the surfaces is provided with at least one conducting element, and wherein at least one of the surfaces is provided with said metamaterial, thereby stopping wave propagation in other directions inside the gap than along said conducting element.

3. A microwave/millimeter wave device, said microwave/millimeter wave device operating at frequencies in the entire range of or one or more subranges of the frequency range between 1 GHz and 100 THz, wherein the microwave/millimeter wave device comprises a metamaterial arranged on at least one surface thereof, said metamaterial being based on mushroom-shaped or inverted-pyramid-shaped pillars, wherein the metamaterial acts as a perfect magnetic conductor in the operating frequency range.

4. The method of claim 1, wherein the at least one polymer comprises a patterned photosensitive high-aspect ratio polymer.

5. The method of claim 1, wherein at least one of said at least one polymers is formed by at least one of: a micromolding process or hot embossing.

6. The method of claim 1, wherein the metallization is applied by at least one of sputtering, evaporation and chemical vapor deposition.

7. The method of claim 6, wherein the metallization is subsequently improved by at least one of electroplating and electroless plating.

8. The method of claim 1, wherein one fabricated part of the microwave/millimeter wave device is a lid.

9. The method of claim 1, wherein the metamaterial is formed on a flange on said microwave/millimeter wave device.

10. The method of claim 1, wherein the microwave/millimeter wave device is at least one of: a waveguide, a transmission line, a waveguide circuit, a transmission line circuit, a resonator/filter, a flange, a splitter, a shielding and a packaging.

11. The method of claim 2, wherein the at least one conducting element is selected from the group consisting of: a conducting ridge provided on the surface, a groove with conducting walls provided on the surface, and a conducting strip arranged within a multilayer structure of the surface.

12. A scalable production method for fabrication of a microwave/millimeter wave device, said microwave/millimeter wave device operating at frequencies in the entire range of or one or more subranges of the frequency range between 1 GHz and 100 THz, and comprising the step of providing a metamaterial on a surface of said microwave/millimeter wave device, wherein the step of providing said metamaterial on said surface of the microwave/millimeter wave device involves a Lithographie, Galvanoformung, Abformung (Lithography, Electroplating and Molding, LIGA) process.

13. A scalable production method for fabrication of a microwave/millimeter wave device, said microwave/millimeter wave device operating at frequencies in the entire range of or one or more subranges of the frequency range between 1 GHz and 100 THz, and comprising the step of providing a metamaterial on a surface of said microwave/millimeter wave device, wherein at least one part of said microwave/millimeter wave device is fabricated using freeforming or 3D forming in metals or other conducting material or metalized non-metals.

14. The method of claim 13, wherein the fabrication using freeforming or 3D forming in metals or other conducting material or metalized non-metals is applied by at least one of sputtering, evaporation and chemical vapor deposition.

15. The method of claim 14, wherein the fabrication using freeforming or 3D forming in metals or other conducting material or metalized non-metals is improved by electroplating or electroless plating.

16. The device of claim 3, wherein the at least one conducting element is selected from the group consisting of: a conducting ridge provided on the surface, a groove with conducting walls provided on the surface, and a conducting strip arranged within a multilayer structure of the surface.

17. The device of claim 3, wherein the microwave/millimeter wave device comprises two opposing surfaces of conducting material arranged to form a narrow gap there between, wherein at least one of the surfaces is provided with at least one conducting element, and wherein at least one of the surfaces is provided with said metamaterial, thereby stopping wave propagation in other directions inside the gap than along said conducting element.

18. The device of claim 3, wherein the metamaterial is provided on a flange of said microwave/millimeter wave device.

19. The device of claim 3, wherein the microwave/millimeter wave device is at least one of: a waveguide, a transmission line, a waveguide circuit, a transmission line circuit, a resonator/filter, a flange, a splitter, a shielding and a packaging.

20. The device of claim 3, wherein said device is produced in accordance with a scalable production method for fabrication of a microwave/millimeter wave device, comprising the step of providing the metamaterial on a surface of said microwave/millimeter wave device.

21. The method of claim 1, wherein said microwave/millimeter wave device operates in a the frequency range above 100 GHz.

Description

DRAWINGS

(1) The invention will now be discussed in more detail by means of embodiments, and with reference to the enclosed drawings, on which:

(2) FIG. 1 shows a two-way power divider or combiner as an example of a component that is an embodiment of the invention. The component is realized by using ridge gap waveguides between metal surfaces. The upper metal surface is shown in a lifted position to reveal the texture on the lower surface.

(3) FIGS. 2a and 2b show a cut along the input line of a 90 deg bend in a ridge gap waveguide according to an embodiment of the invention, both in a perspective view (2a), and in a cross sectional view (2b).

(4) FIGS. 3, 4, and 5 show the cross sections of three examples of groove gap waveguides according to embodiments of the invention.

(5) FIGS. 6a-e shows various stages in a process plan as an example of a fabrication process that is an embodiment of the invention.

(6) FIGS. 7a and 7b show exemplary embodiments according to the present invention, wherein FIG. 7a is a ridge gap waveguide, and FIG. 7b is a ridge gap resonator.

(7) FIG. 8 is a diagram illustrating results of measurement and simulation of an exemplary resonator made in accordance with an embodiment of the present invention.

(8) FIGS. 9 and 10 are illustrations of a contactless pin-flange adapter in accordance with an embodiment of the present invention. FIG. 9 is a design of the pin-flange surface, and FIG. 10 is a pin-flange-adapter prototype.

(9) FIG. 11 is a SEM picture of micromachined pillars performed by the proposed process and formed in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE FIGURES

(10) In the following, the present invention will be discussed in relation to these types of embodiments, and it is to be appreciated by someone skilled in the art that specific advantageous features and advantages discussed in relation to any of these embodiments are also applicable to the other embodiments.

(11) FIG. 1 shows a two-way power divider or combiner as an example of a component that is an embodiment of the invention. There are two metalized pieces providing the upper 1 and lower 2 conducting surfaces. The upper surface is smooth, but the lower surface is structured. Surrounding the structure/texture, forming a metamaterial, there is a surrounding rim 3 to which the upper surface can be fixed, and a region which is lower than the rim and thereby provides a gap 4 between the upper and lower surfaces when the upper surface is mounted. The metalized ridge 5 is forming a two-armed fork, and around the ridge there are metalized posts 6 providing cut-off conditions for all waves propagating between the lower and upper surfaces except the desired waves along the ridge 5. The metalized posts here forms a metamaterial, as discussed in the foregoing. The posts work similar to a perfect magnetic conductor (PMC) within the operating frequency band. There are screw holes 8 in the upper metal piece that is used to fix it to the metal rim 3 of the lower metal piece, and there are matching screw holes 7 in this rim. The mounting is shown with screws, but other methods, more common in micromechanical fabrication can be used, such as silicon fusion bonding, eutectic bonding, anodic bonding, adhesive bonding.

(12) FIGS. 2a and 2b show how the wave stop surface is located to stop waves approaching the 90 deg bend from continuing to propagate straight forward. The waves are indicated as wave shaped arrows pointing in the propagation direction. The lengths of the arrows indicate the amplitudes of the different waves. The approaching wave may instead either be reflected (undesired) or turn left (desired). The desired turn of the wave can be achieved by properly cutting the corner of the bend as shown.

(13) FIGS. 3, 4 and 5 show different groove gap waveguides, but it may also be in the upper surface, or there may be two opposing grooves in both surfaces. The groove 20 is provided in the lower surface. The groove supports a horizontally polarized wave in FIGS. 3 and 4, provided the distance from the top surface to the bottom of the groove is more than typically 0.5 wavelengths in FIG. 3, and 0.25 wavelengths in FIG. 4. The groove in FIG. 5 supports a vertically polarized wave when the width of the groove is larger than 0.5 wavelengths. The widths of the grooves in FIGS. 3 and 4 should preferably be narrower than 0.5 wavelengths, and the distance from the bottom of the groove in FIG. 5 to the upper surface should preferably be smaller than effectively 0.5 wavelengths (may be even smaller depending on gap size), both in order to ensure single-mode propagation. The lower surfaces in FIGS. 3 and 5, and the upper surface in FIG. 4 are provided with a wave stop surface 14. The wave stop surface can have any realization that prevents the wave from leaking out of the groove 20.

(14) FIG. 6 shows various sequential stages in a process plan as an example of a fabrication process that is an embodiment of the invention. In a first step, illustrated in (a), a 0.5 μm layer of Al is sputtered over the surface. In a second step, illustrated in (b), a thin photoresist layer is spun onto the Al layer. In a third step, illustrated in (c), the photoresist is developed and the exposed Al is etched. In a fourth step, illustrated in (d), deep reactive ion etching is used to define the pillars, after the Al and remaining resist is stripped. In a final step, illustrated in (e), gold is sputtered (seed layer) and electroplated.

(15) As experimental confirmation, an exemplary micromachined ridge gap waveguide and resonator for 220-325 GHz will now be discussed in more detail. As discussed in the foregoing, a ridge gap waveguide is a fundamentally new high-frequency waveguide, which does not need any electrical contact between the split blocks, and which gives it an advantage compared to the rectangular waveguide, which is the standard today. Rectangular waveguides are often fabricated by milling. However, there are issues when constructing waveguides above 100 GHz. As has already been discussed, it has now been discovered that MEMS technology can offer high-precision fabrication and thus enables the path for new types of high-frequency components.

(16) MEMS here related to “Microelectromechanical systems” (also written as micro-electro-mechanical, MicroElectroMechanical or microelectronic and microelectromechanical systems) is the technology of very small devices; it merges at the nano-scale into nanoelectromechanical systems (NEMS) and nanotechnology. MEMS are also referred to as micromachines, or micro systems technology—MST. MEMS are typically made up of components between 1 to 100 micrometers in size (i.e. 0.001 to 0.1 mm), and MEMS devices generally range in size from 20 micrometers (20 millionths of a meter) to several millimeters (i.e. 0.02 to 10 mm).

(17) In the example to be discussed in the following, a ridge gap waveguide and a ridge gap resonator have been fabricated for the frequencies 220-325 GHz using MEMS technology. Support packages have been designed to enable device measurements.

(18) Two devices were fabricated forming a bent-line waveguide and a resonator, as shown in FIGS. 7a and 7b. The principle of the waveguide is based on having a Perfectly Electrically Conductive (PEC) surface parallel to a Perfectly Magnetically Conductive (PMC) surface with an electrically conductive ridge embedded into it. The PMC is obtained by a pin surface that forms a metamaterial, as discussed in P.-S. Kildal, E. Alfonso, A. Valero-Nogueira, and E. Rajo-Iglesias “Local metamaterial-based waveguides in gaps between parallel metal plates”, IEEE Antennas and Wireless Propagation letters (AWPL), Vol. 8: pp. 84-87, 2009, said document hereby being incorporated in its entirety by reference.

(19) The wave is prohibited from propagating away from the ridge by the pin surface. Packages were milled to support the silicon chip during measurements. The packages act as an interface and transition from the ridge gap waveguides to standard rectangular waveguides.

(20) Simulations show that the reflection coefficient for the ridge gap waveguide is below −15 dB between 240 and 340 GHz. Two resonance peaks were measured, as is seen in FIG. 8, at the frequencies 234 GHz and 284 GHz for the ridge gap resonator with unloaded Q-values of 336 and 527 respectively. Both the ridge gap waveguide and resonator have the potential to obtain similar performances as the rectangular waveguide without strict requirement on electrical contact, allowing simplified fabrication and assembly technique.

(21) In another example, a contactless pin-flange adapter based on gap waveguide technology is considered for high-frequency measurements, as shown in FIGS. 9 and 10. Here, FIG. 9 shows a design of the pin-flange surface and FIG. 10 shows the pin-flange-adapter prototype. Conventionally standard (WR) flanges are used, these require good electrical contact and are sensitive to small gaps. The pin-flange adapter has been fabricated and demonstrated for the frequency range 220-325 GHz and does not need electrical contact and will still show similar or better results than a standard flange or a choke flange.

(22) FIG. 11 illustrates an advantageous geometry and shape of the metamaterial, here in the form of posts/pillars, obtainable by the above-discussed methods. As is clearly seen in this SEM picture, mushroom-shapes or inverted-pyramid-shaped posts/pillars are obtained, i.e. posts/pillars having a smaller cross-sectional dimension at the end connected or integrated with the surface, and a larger cross-sectional dimension at the opposite end.

(23) The invention is not limited to the embodiments shown here. In particular, the microwave/millimeter wave device is useable for many types of high-frequency devices, in addition to the ones discussed above. Further, different realizations of the metamaterial, such as posts, pillars, patches, nails, etc, and having different geometry, shapes etc, are feasible. Further, the metamaterial may be arranged on either one of the two surfaces, or even on both surfaces. Further, the two surfaces may be connected in various ways, and the cavity need not be closed, but may be open at one or several sides. Further, the conducting surfaces need not be mechanically fastened to each other, and also, many alternative options for mechanical interconnection, apart from the examples discussed above, are feasible. Still further, other types of MEMS and micromachining are useable to obtain similar results to the ones discussed above. Such and other related modifications should be considered to be within the scope of the patent, as it is defined in the appended claims.