Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
1999-10-22
2003-01-21
Pham, Long (Department: 2823)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C438S155000, C438S210000, C438S238000, C438S280000
Reexamination Certificate
active
06509217
ABSTRACT:
FIELD OF USE
The invention pertains to the field of RFID tag structures and methods for constructing RFID tags.
RFID tags are passive transceivers which are small, integrated and have RF or electromagnetic receive and transmit capabilities but no batteries (some tags have batteries and these are referred to as active tags with the no battery class referred to as passive tags). Power for the internal operations of a passive tag in receiving RF inquiry transmissions, storing data, reading data and RF reply transmissions is generated by rectifying a received RF inquiry transmission. Such RFID tags have many internal memory cells that can be read only (ROM), write-once-read-many (WORM), or fully rewritable memory such as EEPROM. As such they can store much more data than can be recorded on a bar code tag, and they can have the data recorded thereon changed. Such properties are useful in such environments as tracking of packages for UPS or Federal Express type couriers services, inventory of the contents of pallets (multiple RFID tags can be read simultaneously), tracking baggage in airline operations determining whose bags are on a cart or in a baggage compartment etc. The RFID technology disclosed herein is good for these applications as well as for use in smart cards.
The possible uses of RFID tags are numerous and varied, but one barrier to their use is their expense. Typical RFID tags require an antenna to be formed on a plastic substrate, an RF transceiver and memory circuit to be built in integrated circuit form and then the IC is bonded to the plastic substrate and connections between the IC and the antenna connection pads are wire bonded. Some antennas in the 125 kHz operating frequency band require about 200 turns, whereas antennas for the 13.56 Mhz band require only 4 turns. Antennas can be wire wound, etched photolithographically or silk screened on the substrate. Longer antennas created by the wire winding process give greater operating range, but the wound coil antenna process is typically also the most expensive prior art antenna process.
The most expensive part of the overall RFID process is making the IC itself with costs ranging from between ten and fifty cents. The cost of the wire bonding process is the next most expensive part of the overall process followed by the cost to fabricate the antenna.
In order for RFID tags to become commercially successful with volume in the billions of units per year, the cost of the total tag must be brought down to 5 cents or lower per tag. To reduce costs to this level, the current process for fabrication and the resulting construction cannot be used.
The current form of RFID tag construction is too expensive, and it has reliability problems in high temperature applications. The reliability problems in high temperature applications arise out of the differences in thermal coefficient of expansion between the bulk silicon of the IC substrate and the plastic substrate on which the antenna is formed. The difference in coefficients of expansion lead to stresses in the structure which can fracture the chip or break the wire bond between the transceiver and the antenna. The current separately formed chips are also too expensive. Finally, the structure of prior art RFID tags which have an integrated circuit bonded thereto is not monolithic. This results from the fact that the IC containing the transceiver is about 0.5 mm thick whereas the plastic substrate on which the antenna is formed is much, much thinner. This can be a problem in some applications where, for example, the RFID tag is to be run through a printer to have bar code printed on top of the RFID tag to act as a backup source of information about an article to which the tag is attached.
Therefore, a need has arisen for a structure for an RFID tag which can be made more inexpensively, which is subject to fewer reliability problems by virtue of elimination of the differences in coefficients of thermal expansion, and which has a more planar profile than the prior art RFID tag structures.
SUMMARY OF THE INVENTION
The teachings of the first two classes of embodiments of the invention are equally applicable to both RFID tags and smart cards with RF transponder/processor/memory circuits integrated directly onto the same plastic substrate on which the antenna is formed. Typically the antenna will have two terminals for connection to the RF input/output terminals of the integrated circuit, but in some embodiments, there may be only one terminal for the antenna that is connected directly to the IC with the other terminal connected to a ground plane of conductive material formed on the plastic substrate with the IC having one RF I/O terminal coupled to the antenna and the other coupled to the ground plane. The phrase “integrated on” as used in the claims means an integrated circuit that is formed directly on the plastic substrate by processing the plastic substrate in flat panel display manufacturing or other semiconductor wafer processing machines used for making integrated circuits. The phrase “bonded or otherwised attached to” is intended to describe a plastic substrate upon which is bonded an integrated circuit made on another glass or plastic substrate elsewhere which is then diced and bonded or otherwise physically attached to the plastic substrate.
The ICs that are used to control toys and other equipment that requires cheaply constructed integrated circuits may also be made using the teachings of the invention.
Preferably, the ICs are fabricated on the plastic substrate using the semiconductor processing machines which are used to form thin film transistors at multiple locations on large plastic or glass substrates which are used in manufacture flat panel displays for televisions and computers. These machines operate under the control of data in process configuration or recipe files that define the process temperatures, gas types and composition, RF energy levels etc. that together are the selected one of the process recipes defined herein which are compatible with the substrate selected for the RFID tag or smart card so as not to melt, warp, deform, chemically attack or otherwise damage the substrate. It is easiest to tell the flat panel manufacturing machine manufacturer at the outset which gases are to be used. That way the machine is configured at the factory with the proper gas flow controller since each gas has its own density, and requires a unique flow controller to make sure the right amount of gas is added to the process. However, existing flat panel manufacturing machines can be retrofitted for new gases by changing the flow controller and removing all the old plumbing from the gas supply through the flow controllers to the deposition chambers so that residues of gases previously used in the machine are not inadvertantly added to the process.
In a separate class of embodiments, the ICs are fabricated by the thousands or millions on large plastic or glass substrates using the thin film transistor processing machines used in the flat panel display business, as modified to use process recipes compatible with the substrate selected. “Large” as that term is used herein means larger than the largest diameter semiconductor wafer capable of being processed with the current generation of semiconductor processing equipment.
The invention of the first two classes of embodiments achieves three advantages over the prior art simultaneously. First, by integrating a large number of separate RFID tag transceivers onto large plastic substrates which have a matching number of antennas integrated thereon and dicing the substrate up into individual RFID tags or smart card internal circuits, large cost savings are achieved. This is because the manufacture in bulk of the integrated circuit, which is the largest cost component, saves money on a per unit basis. With the IC formed directly on the same substrate as the antenna, the costs in the prior art process of dicing up the semiconductor wafers into individual transceiver ICs is saved as is the cost of die bonding, wire bonding and flip-c
Fish Ronald Craig
Pham Long
Pham Thanh V
Ronald Craig Fish A Law Corporation
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