U.S. patent application number 13/025199 was filed with the patent office on 2011-06-09 for methods for coupling an rfid chip to an antenna.
This patent application is currently assigned to BAE Systems Information and Electronic Systems Integration Inc.. Invention is credited to Roland A. GILBERT, Zane LO, Court E. ROSSMAN, John A. WINDYKA.
Application Number | 20110133896 13/025199 |
Document ID | / |
Family ID | 44081465 |
Filed Date | 2011-06-09 |
United States Patent
Application |
20110133896 |
Kind Code |
A1 |
ROSSMAN; Court E. ; et
al. |
June 9, 2011 |
Methods For Coupling An RFID Chip To An Antenna
Abstract
A method for mounting multiple small RFID chips onto larger
antenna. The chips are mechanically aligned with an interdigitated
gap at the feed point of the antenna by electrostatic or magnetic
techniques. In an alternate embodiment RF field coupling between
the chips and the antenna is employed.
Inventors: |
ROSSMAN; Court E.;
(Merrimack, NH) ; LO; Zane; (Merrimack, NH)
; GILBERT; Roland A.; (Milford, NH) ; WINDYKA;
John A.; (Amherst, NH) |
Assignee: |
BAE Systems Information and
Electronic Systems Integration Inc.
Nashua
NH
|
Family ID: |
44081465 |
Appl. No.: |
13/025199 |
Filed: |
February 11, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11918696 |
Oct 17, 2007 |
7911343 |
|
|
13025199 |
|
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Current U.S.
Class: |
340/10.1 |
Current CPC
Class: |
G06K 19/07756 20130101;
G06K 19/07786 20130101 |
Class at
Publication: |
340/10.1 |
International
Class: |
H04Q 5/22 20060101
H04Q005/22 |
Claims
1. A method for coupling a Radio Frequency Identification (RFIC)
chip to an antenna having a feed region comprising the step of
effecting coupling of the chip to the antenna by means of RF field
coupling.
2. The method of claim 1, wherein the RF field coupling includes a
field coupling loop integrated into the RFID chip.
3. The method of claim 1, wherein a small RFID chip is made from a
wafer, the chip then being mounted onto a small coil, the chip and
coupling coil then mounted onto the antenna.
4. The method of claim 3, wherein the antenna is mounted on an
item.
5. A method for coupling a Radio Frequency Identification (RFID)
chip to an antenna having a feed region comprising the steps of:
patterning conductive ink on a surface to form the antenna having a
gap at the feed region; and, self-aligning the chip across the
gap.
6. The method of claim 5, wherein the RFID chip is self-aligned by
means of an electrostatic free charge.
7. The method of claim 5, wherein the RFID chip is self-aligned by
means of electrostatic dielectric polarization.
8. The method of claim 5, wherein the RFID chip is self aligned by
means of magnetostatic permanent and soft magnetism.
9. A method providing a Radio Frequency Identification (RFID) tag
to an item, comprising the steps of: patterning an antenna at the
item; and, depositing microradio RFID chips at the feed point of
the antenna using xerographic techniques in which the antenna is
imaged onto photoconductive material and in which multiple
microradios are deposited over the imaged antenna.
10. The method of claim 9, wherein the pattern of the antenna
imaged onto the photoconductive material corresponds to a charged
image.
11. The method of claim 10, wherein the pattern of microradios that
are deposited over the photoconductive material exist only in the
region of the charged image pattern.
12. The method of claim 11, wherein the pattern of microradios on
the photoconductive material is placed adjacent to and aligned with
the patterned antenna, and further including the step of
transferring the microradio pattern from the photoconductive
material to the patterned antenna.
13. A method for coupling an RFID integrated circuit chip to the
feed point of an antenna, comprising the steps of: providing a
coupling loop to the RFID integrated circuit chip, with the size of
the loop being commensurate with the size of the chip; providing
neck-down antenna material at the feed point of the antenna; and,
locating the RFID integrated circuit chip and the coupling loop
within the neck-down portion of the feed point of the antenna,
whereby the focused magnetic field region associated with the
neck-down portion of the antenna is commensurate in size with the
size of the loop.
Description
RELATED APPLICATIONS
[0001] This Application is a divisional application of U.S.
application Ser. No. 11/918,696 filed Oct. 17, 2007 and claims
rights under 35 USC .sctn.119(e) from U.S. Application Ser. No.
60/711,218 filed Aug. 25, 2005, the contents of which are
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates to the use of Radio Frequency
Identification (RFID) tags for tracking items during shipping,
receiving the items at final destination and inventory control of
items, and more specifically to methods for mounting the RFID chip
onto a larger antenna.
BACKGROUND OF THE INVENTION
[0003] RFID tags have been utilized extensively to be able to trace
pallets from a point of shipment through a destination, with the
RFID tags being passive devices that are read out with RF energy,
usually in the 900 MHz range. These passive devices are
parasitically powered by the energy impinging upon the antenna of
the tag that powers the integrated circuits within the tag, with
the result that the tag transmits the identity of the pallet in
response to a probing signal.
[0004] While such RFID tags are now mandated for pallets in some
industries, there is increased level of interest in item-level
tagging, which involves placing a tag on the item itself as opposed
to on a pallet of items.
[0005] However, in order to be able to make such tagging strategies
possible for low-value items such as toothpaste and the like,
techniques are required to be able to manufacture and deposit the
tags on items at an overall cost of no more than 5 cents per
item.
[0006] The relatively low price for the tagging of items is not so
important in high-value items such as pharmaceuticals, where the
tag price may be as much as 25 or 50 cents from start to finish.
Rather, mass merchants are interested in keeping track of how much
material is on their shelves for inventory control.
[0007] This means that, for short ranges, an individual carries a
reader with him- or herself and probes the individual items, either
in a walk-by scenario or as the items come into the facility, for
instance on a conveyor belt.
[0008] Note that RFID technology is not merely a bar code
technology, but rather one that can store data and, upon request
from a reader, output data to a global database. The data can be as
simple as a product ID code.
[0009] The desideratum using item-level RFID tags is that the whole
shipment history of a product from the time it leaves the
manufacturing plant to its final destination can be tracked through
various hands such as shippers, importers, wholesalers and
warehousemen.
[0010] If in its simplest embodiment the RFID tag merely contains
an identification number, this number is read out along the way
during shipment such that the transport history of the item can be
ascertained.
[0011] It is noted that the current tags are passive tags in that
they do not require or have a battery. This is useful because in
item-level tagging there is no real estate available for batteries
and battery shelf life is not a problem.
[0012] With respect to tagging of a pallet, it is noted that a
pallet is usually placed on a forklift truck and is driven, for
instance, into a warehouse where it passes through the warehouse
door at which a reader is located. The reader sends out RF energy
that charges up the passive tag by transferring energy to the
integrated circuits within the tag. The reader then transmits a
special code that interrogates the RFID electronics so as to output
the tag ID and any other related information stored by the tag.
[0013] These passive devices have a range of approximately 30 feet,
given the fact that the Federal Communications Commission limits
the amount of radiated power from the reader to be 1 watt.
[0014] As to the size of the tags that are currently placed on
pallets, they are on the order of 2 inches by 2 inches, with the
antenna dimensions being the dominating factor. It is noted that
the larger the antenna, the greater the range, since a larger tag
antenna can capture more energy from a reader. For short-range
applications such as monitoring pill bottle inventories, the
antenna can be indeed quite small.
[0015] Note that with small antennas the amount of energy available
for the integrated circuits making up the tag is limited, with the
energy being derived from a so-called rectenna that rectifies the
RF energy and stores it on a capacitor. In these cases the energy
from the capacitor is utilized to power up the circuitry that
includes some kind of logic or even a microcomputer as well as a
transmitter. Note that once the circuit is powered up the
information is transmitted back to the reader.
[0016] Using the above tags to identify pallets is commonplace.
However, the integrated circuits are relatively expensive, with the
integrated circuit tending to be the most expensive part. Secondary
to the expense of the integrated circuit itself is the cost
involved in building the tag.
[0017] If pallets, for instance, are high value, one can afford a
50- or 75-cent tag. However, for item level tags the cost needs to
be kept under 5 cents.
[0018] Moreover, for item-level tags, the output of the transmitter
of the RFID tag is in general in the microwatt range due to the
small size antenna required. However, with sufficient size
reduction there should be a concomitant cost reduction at least of
the integrated circuits. If one could make the integrated circuits
very, very small, in the micron or tens of micron size, the cost
per IC die goes down dramatically. This is because if one can
utilize large wafers, one can make millions of individual dies per
wafer. With processing costs constant and sufficient yields, one
can reduce the cost of the tag under 5 cents.
[0019] For item-level tags, for instance on individual pill
containers, one can arrange to have antennas that are perhaps a
quarter of an inch on a side, with a tiny integrated circuit on
them. However, even if one could make the micron-sized RFID tags,
one is faced with a significant challenge in how to locate an RFID
integrated circuit on the associated antenna at its feed point.
[0020] In an effort to reduce the cost of the individual chips,
manufacturing large numbers of them on a large-size wafer while
theoretically reducing the cost of these chips, the individual
chips are extremely hard to test and hard to handle. What is
conventionally done now, at least for item-level RFID tags, is to
use pick-and-place machines and size the individual integrated
circuits to be at least large enough to enable the pick-and-place
operation. Thus, the integrated circuits must be of a size that
they can be taken off some kind of dispensing apparatus and
physically moved where they can be deposited on and electrically
connected to the antenna.
[0021] However, pick-and-place machines currently are limited to
integrated circuits that are larger than a millimeter on a
side.
[0022] If one could break through the barrier imposed by
pick-and-place machines, for instance utilizing different
deposition techniques, then one could garner the cost savings of
manufacturing millions of integrated circuits on a single wafer. It
would therefore be extremely useful in reducing the overall price
of the RFID tag to be able to have integrated circuits as small as
a 10.sup.th of a millimeter on a side. Manufacturing of such small
integrated circuits is possible with standard 90-nanometer
integrated circuit technology. Even 65-nanometer technology in high
volume applications is now state of the art.
[0023] However, just because one can lay down patterns that have
90-nanometer line widths or less, a serious limitation is the
ability to be able to scribe and break the individual ICs apart
from the die. Note that various scribing, breaking, and sawing
techniques have been used in the past to separate out individual
integrated circuits.
[0024] Taking sawing for instance, the saw itself defines the curf,
which is the material that the saw blade requires in the removal of
material. Note that in most cases the curf is larger than the
desired size of the chips.
[0025] As to laser scribing, one can go to finer and finer pitches,
but one has thermal issues that limit this type of scribing
technique.
[0026] There is, however, a unique chemical etching process that
limits undercutting in which microscopic dies can be formed
utilizing standard CMOS processes.
[0027] Assuming that one can actually separate out the microscopic
dies, as illustrated in U.S. Pat. No. 6,864,570 and licensed to
Alien Technology, mounting of the dies to an antenna can be
accomplished through the use of a shaped die and a specially shaped
receiver cavity. In a self-assembly method, these shaped dies are
squeegeed over in a slurry across a substrate that has receiver
cavities that are adapted to uniquely hold the specially-shaped
dies.
[0028] This type of self-assembly method requires a match between
the orientation of the die and the receptacle. Thus the specially
shaped ICs have to match the corresponding cavities and if they are
randomly oriented in the slurry, they will either not enter the
cavity or not be appropriately positioned in the cavity.
[0029] The result is that the reliability of the RFID tags when
manufactured in this and other processes oftentimes results in
failure rates of 5 to 10% that are wholly unacceptable. In order to
eliminate those RFID tags that are inoperative, one must test the
tag before applying it to a package, which is another
time-consuming and costly procedure that may not be totally
successful when microscopic integrated circuit-type tags are
involved.
[0030] What is therefore needed is first a manufacturing technique
for manufacturing RFID tags that reduces the cost of the individual
integrated circuit by reducing the size of the integrated circuits;
and secondly a technique for coupling the integrated circuits to
the feed points of antennas in a way that virtually guarantees a
100% yield while at the same time eliminating the use of
pick-and-place machines.
[0031] Of particular importance in the provision of RFID tags are
techniques to connect microradio size integrated circuits to
corresponding antennas so that the circuits can be parasitically
powered, programmed, probed and read out. While a co-pending
application describes one method for coupling RFID circuits to an
antenna at its feed point, there is a requirement for more
efficient manufacturing methods and to obtain maximum gain and
maximum output for the tag.
SUMMARY OF INVENTION
[0032] According to the present invention, there are various
methods for coupling an RFID chip to an antenna. One, direct dc
contact between the chip and the antenna, using a grid of
interdigitated fingers at the feed region. Two, a single gap is
used at the feed region, and the chip is approximately positioned
but then centered and aligned across the gap using
magnetic/electric techniques. Three, field coupling is achieved
(without DC contacts) when the chip contains a small antenna, and
this assembly is then positioned at the appropriate region of the
main antenna, preferably a narrowed region that concentrates
magnetic fields surrounding the chip. An intermediate loop can be
used for stronger coupling. Also, field coupling can be achieved
using capacitive pads, which overlay the feed region of the
antenna.
[0033] The first method uses an interdigitated antenna feed that
presents a large number of positions for a randomly oriented
microradio to connect to, thus increasing the likelihood of a good
connection across an antenna feed point gap. In one embodiment the
microradio is provided with dual-sided or 3D bonding pads,
integrated onto the RFID chip (as opposed to 2D pads) to allow
placement of the chip on the antenna and connection to its feed
point regardless of orientation and position of the microradio
chip. Note, the chip is made for direct connection to the feed
region of, for example, a spiral, dipole, or loop antenna. For
quick and inexpensive placement of the chip, the chip can be
carried in a slurry that is deposited over the interdigitated gap
for the antenna feed, where the gap is made the same size as the
length of the chip, i.e., separation between the two pads on the
chip. Chip and interfinger dimensions can be made quite small to
permit the IC cost savings associated with microradio chips. This
placement method is probabilistic in that there is a high
probability that one microradio will be properly connected across
at least one gap in the interdigitized antenna feed due to its many
tines and its interdigitated design.
[0034] When the interdigitated structure is formed utilizing
conductive ink, the resistivity of the ink can sometimes cause
problems. In order to increase the conductivity and decrease the
resistance, after a microradio is deposited across the tines of the
interdigitated structure, a conductive adhesive and/or solder can
be deposited over the tines to either side of the tines across
which the microradio is connected. This substantially increases the
line width of the tines to eliminate the above-mentioned problems
with the resistivity of the conductive ink.
[0035] To determine correct placement and orientation of the RFID
chip onto the antenna, the RFID response can be tested using the
standard RFID functionality. For single chip placements, if there
is an incorrect placement, another chip is added until success is
achieved. For multiple chips in a slurry, there is a high
likelihood that at least one chip will be properly placed across
adjacent feed point fingers.
[0036] For electrical contact, the pads or the antenna may have
electrically conductive adhesive applied. Additional methods are
disclosed in the referenced patent entitled "RFID Tag and Method
and Apparatus for Manufacturing Same."
[0037] What has been described above is the utilization of the
interdigitated antenna feed structure to provide numbers of
contacts for randomly oriented microradios however they are
deposited on or positioned on the antenna feed.
[0038] In order to make sure that the microradios are properly
positioned transverse to the longitudinal center line of the tines
of the interdigitalized feed, it is possible to orient the
microradios as they are deposited through a self-aligning
procedure, which is either electrostatic in which the microradio is
provided with charges on either end that are opposite and an
external field is applied or voltages are applied to the
alternating tines of the interdigitated structure so that with like
charges repelling and unlike charges attracting, the microradios,
when they arrive in the vicinity of the tines of the interdigitated
structure, will align themselves up in a preferred transverse
direction to the longitudinal axis of the tines.
[0039] The microradios themselves can be polarized before being
deposited in the vicinity of the feed structure, or they can be
electrostatically charged by applying a differential voltage to
adjacent tines, with the result being the same and that being that
the microradios with the spaced charge structure will line up due
to electrostatic attraction and repulsion. Moreover, an E-field may
be utilized external of the interdigitated structure to align the
microradios.
[0040] In an alternative embodiment, the microradio may be provided
with a ferromagnetic material that in essence embeds a permanent
magnet in the microradio. The alignment procedure is by providing a
permanent magnet to either side of the interdigitated structure
such that when the microradios are deposited in the vicinity of the
interdigitated structure, they are magnetically aligned.
[0041] One of the ways that the microradios are deposited is by
embedding the microradios in a nonconductive fluid and inkjetting
or depositing the fluid in the vicinity of the interdigitated
structure. Another way, akin to xerography, is to for instance
imprint or provide a metallized antenna on an item to be tagged and
then to image that antenna onto a photoconductive material, which
results in a pattern on the photoconductive material that
corresponds to the image of the metallized antenna on the item.
[0042] With the image on the photoconductive material, multiple
microradios are deposited on top of the image and stick to the
pattern, where the image is not discharged. It is noted that the
image is discharged when light impinges on the photoconductive
material, with the dark areas of the imaged metallized antenna not
discharging the photoconductive material.
[0043] The result is the photoconductive material having a pattern
of microradios corresponding to the pattern of the antenna feed
point, which may be the interdigitated structure noted above.
[0044] When the photoconductive material is aligned with and
pressed against the metallized antenna on the item, the microradios
will be aligned with and adhere to the proper feed points on the
antenna.
[0045] Alternatively, instead of imaging a previous interdigitated
metallized feed region of the antenna, an alternative would be to
leave the feed region on the antenna un-metallized and let the
stamping process from the photoconductor simultaneously define the
interdigitated tines and also apply the RFID chip. This would avoid
precise mechanical orientation issues.
[0046] It will be appreciated that this type of photoconductive
process is an alternative to the aforementioned inkjet printing
system previously described.
[0047] This general technique to mount the RFID chip can apply to
any case where a chip must be mounted onto an antenna. For example,
the antenna can be ink-jetted onto the consumer item, and the chip
applied directly to the consumer item. Alternatively, the antenna
can be separately made on an adhesive plastic, and the chip mounted
onto this antenna. The antenna and chip structure are then applied
to the consumer item.
[0048] In summary, an interdigitated structure is provided as a
feed point to an antenna on an RFID tag, with microradios deposited
over the interdigitated structure such that at least one of the
microradios is either directly connected to the interdigitated
structure in the appropriate orientation or in which the
orientation of the deposited microradios can be aligned utilizing
electrostatic means or magnetic means so that the microradios with
contacts on either end have an axis transverse to the longitudinal
axis of the tines of the interdigitated structure. As an
alternative to depositing the microradios utilizing a printing
process involving conductive inks, in an alternative embodiment a
xerography-type deposit of microradios on the interdigitated
structure utilizes photoconductive materials onto which the
microradios are initially dispersed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] These and other features of the subject invention will be
better understood in connection with the Detailed Description, in
conjunction with the Drawings, of which:
[0050] FIG. 1 is a perspective view of an RFID chip that serves as
a microradio, showing, inter alia, metallized ends that function as
electrical pads for the connection of the chip to the feed point of
an antenna;
[0051] FIG. 2 is a block diagram of an RFID chip microradio and its
connection to a dipole antenna through the connection of the RFID
chip metallized pads to the feed point of the antenna;
[0052] FIG. 3 is a diagrammatic illustration of an interdigitated
feed for a loop antenna, illustrating the deposit of large numbers
of microradios, some of which will be properly positioned across
adjacent interdigitated tines or fingers so as to be connected to
the antenna;
[0053] FIG. 4 is a diagrammatic illustration of a microradio of
FIG. 3 properly connected across adjacent tines or fingers of an
interdigitated feed point for an antenna;
[0054] FIG. 5 is a diagrammatic illustration of an interdigitated
feed printed by conductive ink on a substrate showing a microradio
bridging adjacent interdigitated tines or fingers, showing the use
of conductive fill to either side of the fingers or tines to which
the microradio is attached, thereby to add conductivity in excess
of that associated with conductive ink to eliminate the effects of
the resistivity of the conductive ink;
[0055] FIG. 6 is a diagrammatic illustration of the proper location
of a microradio RFID chip having a chip axis that is orthogonal to
the tine or finger axis, with such alignment being optimal for the
connection of the microradio to the interdigitated feed structure
of the antenna;
[0056] FIG. 7 is a diagrammatic illustration of the electrostatic
free charge that can be provided for the RFID chip in which a
potential is applied across the electric pads of the RFID chip,
with the RFID chip having insulating material between the pads,
whereby the microradio is given a differential charge across the
chip;
[0057] FIG. 8 is a diagrammatic illustration of one method of
aligning the microradio of FIG. 7 by virtue of the fact of the
electrostatic free charge orienting a microradio deposited across
the tines of the interdigitated antenna feed, illustrating the
application of a voltage across the dipole so as to provide an
attractive force for the portions of the microradio having opposite
polarity charge thereon;
[0058] FIG. 9 is a schematic diagram of a microradio that
incorporates polarizable material such as tantalum oxide or any
other high-dielectric material as a substrate for the integrated
circuit. When a polarizable material is used, the external aligning
E fields can also be the resonant RF field of the antenna;
[0059] FIG. 10 is a diagrammatic illustration of the alignment of
the microradio of FIG. 9 through the application of a differential
voltage across the tines of the interdigitated feed for the antenna
in which not only does the applied voltage polarize the material
but further assists in the alignment of the polarized microradio
after polarization;
[0060] FIG. 11 is a diagrammatic illustration of the utilization of
a small magnet running along the longitudinal axis of the radio,
indication north and south poles thereof;
[0061] FIG. 12 is a diagrammatic illustration of the alignment of
the microradio of FIG. 11 through the utilization of a permanent
magnet having north and south poles that attract the corresponding
south and north poles of the microradio, thereby to align the
microradio across the tines of the interdigitated antenna feed;
[0062] FIG. 13 is a diagrammatic illustration of the utilization of
an external E-field to align a polarized microradio so that its
axis lies transverse to the longitudinal axis of the tines of an
interdigitated antenna feed;
[0063] FIG. 14 is a diagrammatic illustration of an antenna feed
point that has a neck-down portion where currents are high and the
utilization of an RFID chip having an integral coupling loop
antenna illustrating the application of a magnetic field at the
neck-down portion of the antenna feed point, with the neck-down
portion providing a focus magnetic field region to more efficiently
couple RF energy into and out of the RFID chip and antenna from the
external antenna, thereby to achieve RF coupling between the
two;
[0064] FIG. 15 is a diagrammatic illustration of a feed point of an
antenna in which there is no significant neck-down portion, which
results in a non-focused magnetic field region of a large extent
and requires that the RFID chip be connected to a much larger
antenna/coupling loop, in an intermediate process, so as to
efficiently couple the output of the RFID tag to the antenna and
vice versa in an efficient manner, the RFID chip being mounted onto
the coupling loop in an intermediate process, which may be more
reliable and controlled in some instances, than mounting the chip
directly onto the inventory item;
[0065] FIG. 16 is a diagrammatic illustration of an alternative to
the utilization of inkjet printing utilizing a conductive ink in
which a xerography-type printing is utilized in which a
photoconductive material has an image of a metallized antenna
focused on its surface, after which multiple microradios are
distributed across the exposed photoconductor, with microradios
sticking where the image is not discharged corresponding to the
metallized antenna pattern, followed by the step of aligning the
photoconductive material substrate with the appropriately patterned
microradios against the metallized antenna where the alignment of
the substrate and pattern with the antenna causes the microradios
carried by the photoconductive material substrate to adhere to the
metallized antenna at the appropriate feed portions thereof;
and,
[0066] FIG. 17 is a diagrammatic illustration of a capacitive
coupling technique for coupling an RFID chip to an antenna.
DETAILED DESCRIPTION
[0067] By way of further background, RFID tags are becoming a
well-established method for tracking materials during shipping and
storage. In many applications they replace the printed bar code
labels on items because they do not require a close proximity for
the automatic reader. RFID tags that conform to the ISO/IEC 18000
standard also can contain significantly more data than a printed
bar code label and can be modified en route to include waypoint or
other information.
[0068] Present RFID tags cost about SUS 0.50 (50 cents) and are
usually fabricated by electrically bonding a custom integrated
circuit (IC) to a substrate containing a printed circuit antenna.
The usual fabrication method, well known in the electronics
industry is flip-chip bonding. An electrically conductive solder
paste is applied to the appropriate places on the antenna. A "pick
and place" machine picks up the IC die and places it onto the
substrate in the proper location with respect to the antenna
connections. The assembly is then heated to cure the solder and
mechanically bond the structure. The substrate may have an adhesive
backing for eventual manual or machine application to the end
item.
[0069] The common wisdom in the RFID industry as of 2005 is the
cost of the tags must be less than SUS 0.05 (5 cents) for the
widespread adoption. Cost is the key driver for the application.
With the economy of scale of integrated circuits, the cost of an
individual RFID die of the required size can be very low. The cost
of the antenna on the substrate can also be very low. The primary
cost is the tag manufacturing process and the application of the
tag to the end item.
[0070] As mentioned hereinbefore, methods for fabricating the tag
such as "strap-mounting" have been proposed by Alien Technology and
Avery Dennison. Self-assembly methods, such as that disclosed in
U.S. Pat. No. 6,864,570 "Method and Apparatus for Fabricating
Self-Assembling Microstructures" have been also been proposed for
tag manufacture.
[0071] The components of a passive RFID tag are typically an
antenna, and a chip containing a rectenna circuit, an
energy-storage capacitor, a controller and a memory. In operation,
an RF field is transmitted to the tag from a programming device or
a reader. The energy received by the tag antenna is coupled to the
chip where it is rectified and transformed to a higher voltage
using a voltage multiplier circuit. This energy is stored in a
capacitor. When sufficient voltage has been achieved in the energy
storage device, the rest of the chip is able to function.
[0072] For programming the tag, data specific to an end item is
sent from the programmer to the tag and stored into memory. Query
of the tag is done by a reader which functions in a similar way,
except now the stored data is sent back to the reader. In
applications where additional data is to be added to tag during
transit, the same process used to program the tag may be used to
store new information.
[0073] Referring now to FIG. 1, a microradio 10 in the form of an
RFID chip is manufactured having an integrated circuit 12 located
on a substrate 14 with the integrated circuit chip being connected
to metallized ends 15 and 16 at opposite ends of a rectilinear chip
structure. In one embodiment the ratio of length to width is 2:1 to
establish proper connection to an interdigitated antenna feed
structure.
[0074] It is noted that there is a longitudinal axis 18 for such a
microradio chip, a lateral axis 20 and a vertical axis 22 as
illustrated.
[0075] Thus in a preferred embodiment the chip has a two-to-one
aspect ratio, with the metal ends manufactured as a modification of
conventional chip manufacturing techniques. The chip can be mounted
face-up or facedown and achieve contact with the antenna for the
tag. Alternatively, a chip can be mounted in a "capsule" fabricated
utilizing three-dimensional etch techniques. The capsule would then
have large metal caps on the ends to provide the pads.
[0076] In one embodiment the RFID chip is composed of several
sublayers of integrated circuit materials and conductive materials,
not shown in this figure. The insulating layer is normally applied
over the chip area except for the metal pad regions. It is noted
that the smaller the RFID chip that can be fabricated, the more
chips that can be manufactured on a single wafer and the lower the
part cost for each chip.
[0077] It is noted that the structure in FIG. 1 is a
three-dimensional contact structure in which the contact pads are
not on a single XY plane but also have contact material in the Z
direction with respect to the chip. As will be seen, the purpose of
this when these microradios are deposited over an antenna feed is
that they can make electrical contact to the antenna feed,
sometimes regardless of the orientation of the microradio to the
antenna feed. For instance, it is not necessary to have the
microradio have its contacts on a single plane, which must be then
married to the contact pads of the feed of the antenna.
[0078] Rather, the attachment of randomly oriented microradios can
be established in accordance with the technique described in a
patent application entitled "RFID Tag and Method and Apparatus For
Manufacturing Same" by Ken Erickson and assigned to the assignee
hereof and incorporated herein by reference. In this patent
application, randomly oriented microradios can be attached to an
antenna feed by having one end of the microradio be attached to one
feed point and an insulating layer placed on top of it followed by
a conductive printed layer to attach the other end of the
microradio to the other feed point of the antenna.
[0079] This technique is described in Provisional Patent
Application Ser. No. 60/711,217 filed Aug. 25, 2005.
[0080] The following describes a number of methods for coupling an
RFID chip microradio to an antenna.
[0081] However, prior to describing the coupling of the RFID chip
microradio to an antenna, and referring now to FIG. 2, an RFID tag
48 includes inter alia an antenna 50 designed according to
well-known principles. This antenna is responsive to RF energy in
the chosen frequency band for the tag. As described below, this
antenna is fabricated utilizing electrically conductive ink in one
embodiment or any type of metallizing structure on an item to be
tagged.
[0082] An integrated circuit microradio with conductive surfaces 36
and 38 contains a programmable device 54 together with an RF
interface 56. Also included are an energy storage device 58, a
controller 60 and a memory 62. The functions of the RF interface,
energy storage, controller and memory are typical of passive RFID
tags to provide the performance described hereinbefore.
[0083] Here it can be seen that it is important to be able to
connect the RFID chip 10 to antenna 50 by virtue of the direct DC
contact of pads 36 and 38 to feed points 64 and 66 of antenna
50.
Method One: Interdigitative Feed
[0084] As part of the subject invention and referring to FIG. 3, an
antenna 68, which is in this case a loop antenna, is provided with
an interdigitated feed 70 that contains a series of tines 72
connected at feed point 70 to a portion 74 of antenna 68.
[0085] Likewise, interdigitated tines 76 are interdigitated between
tines 72 and are electrically connected to a portion 78 of antenna
68.
[0086] Thus the feed region 70 of the antenna has a large
interdigitated gap. For quick and inexpensive placement of a chip,
the chip can be randomly placed on the interdigitated gap at the
antenna feed, where the gap is made the same size as the separation
between the two pads on the chip. Chip dimensions should be
minimized for economy of manufacture, with the chip dimensions also
being determined by RF components and pad dimensions. The 2:1
aspect ratio of the chip allows only those chips that are correctly
placed to make contact with the antenna by bridging the gap between
the interdigitated tines or fingers.
[0087] In general, the chip should be long enough to cross the two
disconnected adjacent tines. However, they should not be so long as
to cross three tines because the chip could potentially make
contact with two tines on the same side of the antenna feed, and
the chip will be ineffective. The dimensions of the interdigitated
tines can be optimized for the dimensions of the chip, or the chip
can be optimized for the dimensions of the tines. In either case,
there should be approximately equal spacing for the tines and for
the pads on the chip. The pad structure on the chip can be narrower
with a high aspect ratio, or triangular, to maximize probability of
contact. Each individual pad should not be large enough to cause
shorting across the gap.
[0088] Here microradios 80 are randomly deposited over the tines of
the interdigitated feed so that at least one chip will be properly
aligned across the gap between the tines, thereby establishing a
direct DC connection of the microradio across the tines of the feed
point of the antenna.
[0089] The chips can be painted on, blown on or dispensed similar
to inkjet printing. The last method is disclosed in the referenced
patent entitled "RFID Tag and Method and Apparatus For
Manufacturing Same." As will be seen, this method is probabilistic.
This means that it is highly probable given a large number of
microradios dispensed on the interdigitated structure that at least
one microradio will be properly positioned across the adjacent
tines of the interdigitated feed structure.
[0090] To determine correct placement and orientation of the RFID
chip onto the antenna, the RFID response can be tested utilizing
standards RFID functionality. If incorrect placement, another chip
may be added until success is achieved. For electrical contact,
either the pads require electrically conductive adhesive, or the
antenna interdigitated feed structure must have conductive adhesive
thereon.
[0091] This method does not require precise orientation and
positioning of the chip on the feed region if one or more chips are
used. As will be described hereinafter, magnetostatic,
electrostatic or photoconductive orientation methods may be used to
ensure orientation and positioning of the chips.
[0092] Referring to FIG. 4, what is seen is the proper orientation
of chip 10 across adjacent tines 72 and 76, with conductive ends 82
and 84 directly attached to the opposed tines.
[0093] Prior to discussing the ability to orient microradios
dispersed over an interdigitated antenna feed structure, if the
antenna is printed utilizing conductive inks, and if as shown in
FIG. 5 microradio 10 bridges opposed tines 72 and 76, the
connection to antenna regions 74 and 78 can be more robustly
established by filling in the adjacent interdigitated tines with a
conductive fill 90 such that, for instance, tine 72' is robustly
connected to adjacent tine 72'', whereas tine 76' is robustly
connected to adjacent tines 76'' and 76'''. It is noted that the
conductive fill not only covers the adjacent tines for which a gap
is not needed, area 92 connects all of the tines associated with it
to area 78 at the antenna feed, whereas conductive fill at 94
attaches the associated tines to region 74.
[0094] In this manner, assuming that one can have a single
microradio across the interdigitated tine structure and assuming
that the interdigitated tine structure as well as the antenna is
made of conductive ink that may have a non-optimal resistivity, the
resistivity between the ends of microradio 10 and the associated
tines and consequently the associated portions of the antenna at
the feed can be made more robust by the filling of the
interdigitated tines as illustrated.
[0095] This constitutes a parallel grid feed, which is another
implementation of the interdigitated feed gap that is utilized to
avoid losses due to thin fingers and non-optimal conductivity of
the thin fingers themselves.
[0096] The gap is composed of parallel conductive lines that are
isolated from each other by a gap. The RFID chip is dispensed onto
the parallel grid and contact is made across two of the lines or
fingers or tines. The extra gaps between other parallel lines are
filled in with conductive material and the final result is a
single, very small feed gap, with the RFID chip robustly coupled to
the antenna. The advantage of this method is less conductor loss at
the feed.
[0097] Note that if the antenna is created utilizing inkjet
printing, then the chip can be deposited before the ink has
stabilized. Any gaps can be filled in by smearing the other
parallel tines with conductive material or by adding conductive in
with the inkjet dispenser.
Self-Positioning
[0098] As mentioned in connection with FIG. 3, the interdigitated
structure is useful for providing more contact points or areas when
multiple chips are deposited across the antenna feed. However, the
random positioning of these microradios does not provide for the
most robust signal connections into and out of the chip.
[0099] Referring now to FIG. 6, an antenna 100 with an
interdigitated feed zone 102 has fingers 104 and 106 that lie
essentially along a finger axis 108 as illustrated.
[0100] For most robust coupling of the microradios to the antenna
feed structure, the chip axis 110 is to be perpendicular to the
finger axis 108. How this is accomplished in various embodiments is
now described.
[0101] Referring to FIG. 7, in an electrostatic free charge
embodiment, an RFID chip microradio 112 with conductive ends 114
and 116 is fabricated with an insulating material 118 between the
two ends.
[0102] An electrostatic free charge is generated by applying a
voltage 120 with the negative terminal applied to conductive pad
114' and with the positive side coupled to conductive pad
114''.
[0103] As can be seen, negative charges flow into pad 114', whereas
holes [holes/wholes?] or positive charges flow out of pad 114''
whereby the microradio is provided with electrostatic charge
different at opposite ends.
[0104] Referring to FIG. 8, if a voltage as illustrated at 122 is
applied for instance across the dipole antenna 124 having an
interdigitated feed region 126, then as can be seen, finger or tine
128 of feed 126 has negative charges on it, whereas tine 130 has
positive charges on it.
[0105] If the microradio 112 of FIG. 7 happens to land
approximately with its longitudinal axis 132 perpendicular to the
longitudinal axis 134 of the tines, then the negative charges will
attract the positive charges on end 114'', whereas the positive
holes will attract the negative charges 114' so as to align a
microradio transverse to the longitudinal axis of the fingers.
[0106] This self-alignment technique is mimicked in FIG. 9, where
the microradio itself, here illustrated at 140, is provided with
polarizable material 142 that has a high dielectric constant. Such
a material is tantalum oxide.
[0107] If, as illustrated in FIG. 10, microradio 140 is deposited
over tines 142 and 144 and assuming a voltage 146 is applied as
illustrated, then there will be a negative charge on tine 142,
which will cause a migration of holes in the polarizable material
to migrate to an end 148 of microradio 140.
[0108] Likewise holes at tine 144 will cause negative particles to
migrate towards end 150 of microradio 140. The result is a
self-alignment of microradio 140 along transverse axis 152 likewise
perpendicular to the longitudinal axis of tines 142 and 144.
[0109] As illustrated in FIG. 11, a microradio 160 may be provided
with an internal magnet 162 having the indicated north and south
ends.
[0110] As illustrated in FIG. 12, when this microradio 160 is
deposited over the tines 164 and 166 constituting the feed point
168 of antenna 170, with the application of an external magnetic
field as shown by magnet pole pieces 172 and 174, then the magnetic
field provided by these pole pieces attracts the opposite
north-south ends of internal magnet 162, thus to align microradio
160 along transverse axis 176.
[0111] Referring now to FIG. 13, if a voltage 180 is applied across
conductive plates 182 and 184, alignment of a polarized or
electrostatically free charge microradio 186 will cause the
microradio 186 to align along the transverse axis 188, which is
transverse to the longitudinal axis of tines 190 and 192.
[0112] The result of all of these self-alignments is that the
contact pads for the microradios can be appropriately positioned
across adjacent tines and in a self-aligning procedure to give the
highest probability of success for at least one microradio to be
properly connected across adjacent tines in the feed region of the
associated antenna.
[0113] In summary, the orientation and positioning methods
mentioned above include: [0114] 1) Electrostatic Free Charge: A
charge is placed on the pads during or before the dispensing
process, using various methods such as corona discharge. Hence an
electrostatic dipole moment exists on the RFID chip. A static
voltage is placed across the antenna feed gap using electrical
contacts to the antenna. The RFID chip moves toward the gap and
aligns itself across the gap. This is the state of minimum energy.
[0115] 2) Electrostatic Dielectric Polarization: An isotropic
dielectric material will polarize in the direction of an external E
field. If the chip is longer in one dimension, the material will
have the largest electrostatic polarization and lowest energy when
the long dimension is oriented across the gap. Hence the RFID chip
moves toward the gap and aligns itself across the gap. [0116] 3)
Magneto-static permanent and soft magnetism: If the antenna has
soft magnetic material embedded in the metal, then this material
can attract magnetic flux across the gap. If the RFID chip contains
a material with either permanent or induced magnetization, then the
chip will move toward the gap and align itself across the gap.
Field Coupling, No DC Contact
[0117] As illustrated in FIG. 14, it is possible to couple an RFID
chip 200 and an integral coupling loop 202 to the feed point of an
antenna 204, here shown as a dipole.
[0118] The feed should be at the center of the dipole and in this
case the dipole has a neck-down portion 206 where currents are
high.
[0119] Field coupling is used to couple the RFID chip to the
antenna, removing the DC contact failure mode. In one embodiment,
the chip is dc mounted onto an intermediate-sized loop (diameter
.about. 1/20 wavelength), for enhanced bandwidth (.about.10%), and
this loop/chip assembly is mounted as one unit onto the antenna. A
very small coupling loop (diameter .about. 1/100 wavelength), on
the scale of the chip, integrated into the chip, has bandwidth
limitations (.about.%3%).
[0120] Because of the neck-down portion of the antenna feed, there
is a focused magnetic field region 210 that is relatively small to
permit small coupling loops to efficiently couple the RFID chip to
its associated antenna. Thus, passive field coupling is possible.
Coupling is enhanced if a dipole is made with a very thin metal
region in the middle. This permits a small coil to be located in
this thin region that will couple to the dipole utilizing magnetic
fields. The field coupling method has the advantage that the DC
contact is not a failure mode and this field coupling method is
easier and cheaper when trying to couple an RFID chip to its
associated antenna. In one embodiment, the field coupling loop is
integrated into the RFID chip and results in a coupling, albeit
narrower in bandwidth than direct coupling.
[0121] Of course field coupling is also possible as illustrated in
FIG. 15 in which a feed portion of the antenna 212 is not
noticeably neck-down. This results in a non-focused magnetic field
region 214 as illustrated by the dotted line.
[0122] In this embodiment, field coupling is possible by utilizing
a larger antenna loop 216 coupled to the RFID tag chip 218.
[0123] As an alternative, field coupling may be accomplished
through the use of a capacitive coupling in which a capacitor plate
coupled to the microradio capacitively couples the output of the
RFID chip to the interdigitated antenna feed point.
Photocopying Technology
[0124] Referring to FIG. 16, there is an alternative method of
positioning and applying microradios to the feed points of an
antenna. As can be seen in this figure, an item 300 is provided
with a metallized antenna 302 on the item itself. This may be by
providing a conductive ink pattern or by fabricating a metallized
structure and adhering it to item 300. In this method a xerography
printing system is employed that includes imaging of the metallized
antenna onto a photoconductive material 304 through the utilization
of a lens 306. This provides a charge pattern image on the surface
of the photoconductive material as illustrated at 308.
[0125] Thereafter, multiple microradios 310 are deposited over the
surface 312 of the photoconductive material 304 in which the
photoconductive material has a charge pattern image.
[0126] It is a feature of the photoconductive material that it is
discharged when light impinges on the photoconductive material.
When the photoconductive material is discharged at various pattern
places, it is noted that the microradios 310 only stick to the
photoconductive material 304 where the photoconductive material is
not discharged.
[0127] This leaves a pattern of microradios on the surface 320 of
the photoconductive material.
[0128] When this photoconductive material is aligned with the
metallized antenna 302 and, for instance, pressed into place, the
microradios will be deposited at the appropriate places on the
metallized antenna where they adhere to the particular antenna feed
points.
[0129] The photocopy technique can be alternatively described as a
way to mix the conductive ink and the chip onto a stamp, and then
push this "stamp" against the feed region of the antenna. In
general, conductive ink for the antenna is patterned onto an
application surface, a "stamp". An RFID is mounted onto the feed
gap and self-aligns/centers using magnetic/electric techniques
listed above. Ink and chip are then pressed onto the item, and
either heat or adhesive bonds the antenna/chip to the surface. The
larger bulk of the antenna could be made using a foam stamp, dipped
in ink, for quick application. Note that the region around the feed
requires more precision than is available with the foam stamp.
However, this interdigitated feed for the antenna can use this
photocopy technique.
[0130] In summary it will be appreciated that the advantages of the
embodiments described herein enables the application of very small
RFID chips to an antenna feed region utilizing an interdigitated
antenna feed. The subject invention also facilitates the use of
printing of complete RFID tags at the point of application to an
end item such as a container of pills or a box containing the item
to be tracked.
[0131] Moreover, and as discussed above, precision handling of
individual RFID chips during fabrication and application is
eliminated, the result being a major cost savings.
Capacitive Coupling
[0132] Referring now to FIG. 17, while what has been described
above is field coupling utilizing a loop at the feed point of an
antenna as a substitute for direct DC coupling, in FIG. 17 what is
shown is a capacitive coupling of an RFID chip 330 to an antenna
feed point having portions 332 and 334 overlaid by capacitive pads
336. These capacitive pads are provided with an interdigitated
structure 338 such as that described above. At least one RFID chip
330 is shown connected across the interdigitated tines 340 and 341,
which couples the output of the chip through the capacitive pads to
the associated antenna.
[0133] Thus, rather than utilizing inductive coupling to connect
the chip through the interdigitated structure to the tag antenna,
one can capacitively couple the RFID chip output to the tag
antenna.
[0134] Note that antenna portions 332 and 334 may be part of a
standalone antenna structure or may be a conductive inkjet pattern
printed on the item itself.
[0135] While the present invention has been described in connection
with the preferred embodiments of the various figures, it is to be
understood that other similar embodiments may be used or
modifications and additions may be made to the described embodiment
for performing the same function of the present invention without
deviating therefrom. Therefore, the present invention should not be
limited to any single embodiment, but rather construed in breadth
and scope in accordance with the recitation of the appended
claims.
* * * * *