NL1040186C2 - On-silicon integrated antenna with horn-like extension. - Google Patents

Description

TITEL: ON-SILICON INTEGRATED ANTENNA WITH HORN-LIKE EXTENSION

STATE OF THE ART

Analog or digital Integrated circuits (ICs) are designed and layed out on (BiCMOS or CMOS) silicon, GaAs, GaN or SiGe processes. These are mass-produced on for instance 8 or 12 inch wafers. After production of the wafer, the wafer is sawed (or diced) to separate the ICs from each other.

The sawing or dicing process is a very rough process: a diamond saw cuts through the silicon. As silicon is quite brittle cracks due to sawing process can easily form and extend into the electronic circuitry an thus destroy electrical performance.

The standard way of preventing cracks forming into the electronic circuitry is by placing a "seal-ring" around all circuitry. A seal-ring is a ring consisting of (nearly) all doping- and metal-layers placed around the electronic circuitry. Silicon-nitride is usually placed as last layer on top of all circuitry (except bump-pads and bond-pads as they need to be electrically connected to the outside world) to prevent moisture getting into the silicon. The seal-ring also has an opening in the silicon-nitride as a silicon-nitride layer is also quite brittle (similar to glass), again to prevent cracks from entering the IC.

This seal-ring is therefore an essential part of the mass-production process of silicon chips in order to realize a high reliability and a high yield.

When integrating RF electronics on silicon, people have started thinking of implementing antennas on-silicon. Antennas are used in all electronic equipment (from GSM, GPS, DECT, Bluetooth to radar systems) to convert electrical energy to electromagnetic energy and vice-versa. However, when these antennas are placed inside the seal-ring they will short the electromagnetic field of the antenna and thus reduce the radiation efficiency and negatively influence the radiation pattern of the antenna. Some antenna-on-silicon designs simply ignore the production process requirements by leaving out the seal-ring, resulting in lower yields or reliability problems or breakdown after some time in the application. Other designs implement antennas in special post-production processes thus increasing overall costs.

Modern IC processes require a minimum and maximum use of metal per given silicon-area for reproducibility of the etching process and the chemical-mechanical-polishing used in the back-end processing. Usually a defined metal-filling (called tiling) using minimum sized structures fulfils the metal density requirement without disturbing overall performance too much.

When antennas are placed on the silicon, testing becomes an issue as DC-voltage, output power and matching can no longer be measured.

When the abovementioned problems are solved, antennas can be integrated side-to-side a complete radar. Even if the antenna is not integrated on the silicon but in the package the overall" module" can be seen as a single device. Antennas usually have a size close to lambda/4 or lambda/2, where lambda is the wavelength in the material or in free-space. For 60 GHz the free-space wavelength is 5 mm, and antenna can thus be 1.25 mm or smaller pending the dielectric constant of the material. An example of the silicon IC with integrated antennas is shown in Figure 5. Single antennas usually have a relatively wide radiation pattern, which can be as wide as ±60 degrees in azimuth and ±60 degrees in elevation. For some applications this beam-width is too wide. Narrower beam-widths can be realized with antenna arrays: multiple antennas in a row, column or matrix driven with the proper phase and amplitude for each antenna. This can be done on the silicon, but results in a new design (usually resulting in a much larger silicon area to accommodate the extra antennas) and thus a new, expensive mask-set. Economy of scales may be difficult to reach if the market consists of a large number of application with low quantities. It would be much nicer if a low-cost, easy to mass-produce, auto-aligned structure can be made that allows to define the radiation pattern after the silicon is produced.

Parabolic dish antennas and horn antennas have been known to provide well defined gains and (narrow) beam-widths. A special heavy and expensive launcher is required to launch the electromagnetic wave into a waveguide or horn antenna, see Figure 6. For optimum performance the waveguide should also be aligned with the horn antenna.

The topic of quasi-integrated horn antennas has been discussed in literature, see Reference [1-3].

Reference [1] discusses a quasi-integrated horn antenna. The design of the horn starts by anisotropic etching of the silicon attached to a machined small flare-angled pyramidal section. The difficulty in such designs is that you have to know in advance which antenna radiation pattern you want, and specifically prepare you silicon design for that. This does not lead to cheap solution.

Reference [2] discusses an array of antennas, each with its own diode-receiver whereby several rings are etched into the silicon-substrate, together forming a round horn. Also here the problem is that you have to define and manufacture the silicon again for each new application.

Reference [3] shows the design of a 100 pm thick quartz superstrate (on top of the standard silicon) with horn-extensions. Also here, modification to the standard silicon-die are required to implement the antenna. Each antenna element has its own patch antenna exited by a feed-line, and each antenna has its own horn. This limits the freedom of location of the antennas and increases the complexity in an application.

This patent application explains how to avoid influence on the electro-magnetic-field while still implementing a seal-ring for high yield and high reliability, while also being able to test the complete solution. This patent application also demonstrates a low-cost, easy to manufacture way of off-chip/off-package definition of the overall antenna radiation pattern without having to redefine the silicon or package.

FIGURES

Figure 1 shows an example of an IC layout that use the basis of our invention.

Figure 2 shows a 3D view of the antenna connection through the seal-ring to the bond-pad.

Figure 3 shows a close-up of the antenna connection through the seal-ring.

Figure 4 shows the same antenna, but now the close up is from the inside of the first seal-ring to the outside of the first seal-ring.

Figure 5 shows a one-chip-radar, where all radar functionality is integrated on a single piece of silicon.

Figure 6 shows a standards 60 GHz launcher for a wave-guide or horn-antenna. Figure 7 shows a first horn together with its measured radiation pattern.

Figure 8 shows a second horn together with its measured radiation pattern.

Figure 9 shows a third horn together with its measured radiation pattern.

Figure 10 shows the monopulse characteristic.

Figure 11 shows the preferred way of mounting the IC, horn and PCB together.

DETAILED DESCRIPTION

Figure 1 shows an example of an IC layout 4 with three antennas (number 1,2 and 3 in the figure), 1 at the top, and 2 and 3 at the bottom. The IC may contain any amount of analog and/or digital circuitry. Antennas 1 is connected to the center-bond-pad 10, antenna 2 is connected to center-bond-pad 11 and antenna 3 is connected to center-bond-pad 12. The left and right outer bond-pads are connected to ground and the inner seal-ring 5. Together with the outer seal-ring 6 these two seal-rings minimize cracks that could harm the analog/digital circuits. The two seal-rings are clearly outlined in the figure. The first seal-ring (number 5 in the figure) contains all doping-layers in combination with all metal layers and an opening in the top-metal and its associated via-layer for the passing of the antenna connection and the opening in the nitride layer as presented in the figure with numbers 7, 8 and 9. The second seal-ring (denoted with number 6 in the figure) consists of all metal layers (except in the keep-out areas (dashed-line around antennas 1,2 and 3)) and an opening in the nitride layer.

Figure 2 shows a close-up of the connection of the antenna 1 through the first sealring 11 at location 8 to the bond-pad 3. The two ground bond-pads are given by 2 and 4 and are connected to the seal-ring 11. The openings in the top-metal layer are denoted by number 6 and 7. The active circuit of the IC is at area 5. Tiling is denoted in areas 9 and 10.

Figure 3 shows another view. Antenna 1 is (AC- or DC-coupled) to bond-pad 2 in the top-metal layer. Aground bond-pad 3 is located at the left side. The opening 4 and 5 in the top-metal layer are clearly visible. Tiling is shown in area 6. The opening in the nitride layer is denoted with number 7. The other layers in the seal-ring 8 are unchanged and continue their path under antenna 1.

Figure 4 shows yet another view, this time from inside the IC towards the outside.

The antenna 1 is connected to bond-pad 4 through seal-ring 3. The opening in the top-metal layer and the via-layer below the top-metal layer is visible at location 5.

The nitride-opening is denoted by 2.

For testing purposes we envision several possibilities. A first solution is to add of bond-pads and/or bump-pads for probing the output and/or input. By standard IC testing methods, probes can be landed on these pads and DC levels can be measured. RF quantities (frequency, voltage/power, spurious components) can be measured but will be influenced by the radiation of the antenna. Correlation of reference measurements and probed measured results show functionality and performance of the device-under-test.

A second method uses on-chip measurements circuits. The DC voltage can be measured with an on-chip ADC (via the proper isolation circuit, as not to influence the RF performance). The frequency of the RF signal can be measured indirectly by implementing a frequency divider circuits on the 1C and measuring the frequency of the frequency-divided signal. The output power can be measured by adding a power sensor on-silicon. When using a power sensor with a high bandwidth, any amplitude modulated spurious component within the bandwidth of the sensor will become measurable. Matching to the load can be measured by on-chip measurement of the power reflected by the antenna.

Due to the size of the antennas, the number of antennas is still limited. In Figure 5 three antenna 1,2 and 3 are shown, taking up a similar silicon area as the analog/digital design 4. The 2 receivers allow the calculation of the angle-of-arrival of reflections in a radar-mode setup. The radiation patterns of these antennas is quite wide; ±60 degrees. In order to minimize silicon cost it is preferred to realize off-chip/off-package structures that can modify the radiation pattern. Usually a launcher is used (see Figure 6 for the mechanical drawing) to convert signals from a cable assembly to a waveguide assembly. These launcher are quite large (order of centimeters) are unpractical in our application. Therefore we invented horn-like structures that are capable of doing this. Several of these horn-like extensions are shown in Figure 7a, 8a, and 9a. These horn have been made by hand using standard copper-plated FR4 epoxy. Several other materials combinations can be used as well: any (combination of) metal, plastic coated with metal, 3D-printed forms consisting of metals or plastics with a metal coating, plastics coated with a metal-tape or metal-spray, etc. The measured radiation diagram are shown in 7b, 8b and 9b. Curve 1 shows the azimuth while curve 2 shows the elevation, the curves clearly show that the radiation pattern can be modified by the external horn-like structure. The hand-made horns shown in Figure 7-9 are hand-aligned with the IC for optimum performance. Automatic alignment and robustness are still required for consumer like products. Robustness is determined by the combination of weight and size of the horn and the 1C soldered on a PCB. For instance the 1C weights less than 1 gram. A plastic metal-coated horns has a similar weight.

Measurements have also shown that angle-of-arrival functionality is also present for the combination of the single-chip radar and the horn. This is illustrated in Figure 10 showing a monopulse radar characteristic obtained with the sum-and-difference method; curve 3 shows the measured characteristic, while curve 4 shows the theoretical one. Axis 1 shows the difference pattern while axis 2 denotes the angle from which the reflection is received.

Figure 11 shows a preferred way of mounting the horn together with the IC. The IC 5 is soldered to the PCB 6. The horn-like structure is mounted onto the PCB with screws (3 and 4) or clips. The complete construction can be attached to the housing in the application by means of screws (1 and 2) or clips from the PCB or from the horn-structure. Alignment of the horn to the IC is done by the design of the plastic of the horn.

Basic antenna theory on horn-antennas shows that the product of the antenna aperture (the width of the horn) and (3 dB) beam-width of the antenna is constant (see for instance the Antenna Handbook by Balanis). This hold both for azimuth and for elevation. Calculating the aperture-beam-width product for the horns as measured and shown in Figure 6-9 indeed shows the expected constant. So by changing the aperture we can modify the beam-width without having to modify the silicon.

Instead of making a horn as a open horn, the horn can also be filled with a dielectric material. A metal coating or spray can then be added to the outside of the horn. The shape of the dielectric filling material can be used to act as a lens-like structure, thus even improving beam-forming further.

In the figures above only rectangular horns are shown. It is clear to the experienced engineer that round, elliptical, hexagonal, octagonal or any other type of horn-like structure is just as feasible.

In the examples used in this text only three antennas have been used. It is clear that another number of antennas can also be used as well.

The discussion above is equally valid for different polarizations: horizontal, vertical, circular polarization or any combination.

Inserts in the back of the horn can be used to modify the polarization; from vertical or horizontal or circular polarization.

The horns can be fabricated hand-made as shown here, with standard plastic mold fabrication, of with 3D-printing.

Although the ideas presented here have been used for radar applications they are just as well applicable for communication or communication-like systems, i.e. any applications where the antenna are integrated on-silicon or in the package.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings and figures, the disclosure, and the appended claims. In the claims, the word " comprising" does not exclude other elements or steps, and the indefinite article "a " or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

REFERENCES

[1] G.V. Eleftheriades, G.M. Rebeiz, "Design and Analysis of Quasi-Integrated Horn Antennas for Millimeter and Sub-Millimeter-Wave Applications", IEEE Transactions on Microwave Theory and Techniques, Vol.41, No. 6/7, June/July 1993.

[2] V. Douvalis, Y. Hao, C.G. Parini, "A Monolithic Active Conical Horn Antenna Array for Millimeter and Submillimeter Wave Applications ", IEEE Transactions on Antennas and Propagation, Vol.54, No. 5, May 2006.

[3] Y. Ou, and G.M. Rebeiz, "On-Chip Slot-Ring and High-Gain Horn Antennas for Millimeter-Wave Wafer-Scale Silicon Systems", IEEE Transactions on Microwave Theory and Techniques, Vol.59, No. 8, August 2011.

Claims (14)

A device with the characteristics of an integrated transmitter-receiver intended for communication or radar applications in which one or more antennas are integrated on the semiconductor material, wherein one or more sealing rings are applied, wherein in the first sealing ring more or less all doping layers and more or less all metal layers are used, and a second sealing ring in which more or less all doping layers and more or less all metal layers are used in one part of the integrated circuit and no conductive in another part of the integrated circuit (semiconductor and / or metal) layers are used, and in which one or more antennas are realized between the first and second sealing ring, and wherein the antennas are connected to the electronic circuits within the first sealing ring by using a hole in the first sealing ring consisting of (preferably) a hole in a single metal layer (and the associated frame) (via layer or layers) by means of a metal connecting track, whereby the desired antenna radiation pattern is realized in its entirety, while also the desired reliability and yield of the standard semiconductor processing remain possible. A device according to any one of the preceding claims wherein filling is applied to the integrated circuit. A device according to any one of the preceding claims wherein the antenna is connected to a bond pad so that a high frequency signal can be measured or injected to test the whole. A device according to any one of the preceding claims wherein additional measuring circuits are added to enable measurement of direct voltage / current and / or high-frequency voltage / current / power, frequency and / or reflection / adaptation on one or more antenna ports. A device characterized in that an integrated transmitter-receiver with one or more antennas are combined on the integrated circuit chip or in the housing in combination with a horn-like structure that directs the antenna radiation pattern. A device according to any one of the preceding claims wherein the horn-like structure is metal. A device according to any one of the preceding claims wherein the horn-like structure is made of plastic and is covered with a metal or metal-like structure. A device according to any one of the preceding claims wherein additional flanges and / or reinforcement ribs and / or mounting holes are added to the horn-like structure for an improvement of the stiffness and robustness and for ease of mounting. A device according to any one of the preceding claims wherein the overall structure is used in a radar system. A device according to any one of the preceding claims wherein at least two receivers with antennas are used such that the angle of reception of a reflection can be determined. A device according to any one of the preceding claims, wherein the metal covering layer is provided on the outside of the horn-like structure. A device according to any one of the preceding claims wherein the horn-like structure is filled with a material having a dielectric constant and having a lens-like shape. A device according to any of the preceding claims wherein a matrix of integrated circuits is mounted on a PCB in combination with a matrix of horn-like structures that is mounted on top of the integrated circuits. A device according to any of the preceding claims wherein the semiconductor material is silicon, silicon germanium, gallium arsenide or gallium nitride.