Static information storage and retrieval – Read/write circuit – Having fuse element
Reexamination Certificate
1999-12-22
2001-09-18
Zarabian, A. (Department: 2824)
Static information storage and retrieval
Read/write circuit
Having fuse element
C365S189120, C365S096000
Reexamination Certificate
active
06292422
ABSTRACT:
TECHNICAL FIELD
The present invention relates to electrical fuses, and more particularly to a system and method for programming an electrical fuse chain that includes read and write protection capabilities.
BACKGROUND OF THE INVENTION
Laser blown fuses historically have been used in logic processes for memory redundancy control and die identification. In some technologies the laser blown fuses are being replaced by electrically programmable fuses. An electrical programmable fuse cell contains an electrically programmable element and sense circuit such that its output may be permanently set to a logic ‘1’ instead of its natural unprogrammed state, a logic ‘0’ or vice-versa. These electrically programmable fuse cells could be used for not only memory redundancy control and die identification, but also for analog trimming control, customer owned configuration bits, encryption key coding, in addition to a variety of other applications.
Presently, electrically programmable fuses have to be customized to a particular application. For example, if a manufacturer wants to provide a set of write protected fuses for die identification, the manufacturer will integrate the fuses into a design and provide a probe pad that is not coupled to an external pin when the wafer is packaged into an integrated circuit. This prohibits the customer from overwriting the fuse data. Customer specific fuses will then be provided via a separate pin on the integrated circuit for programming by the customer. In another situation, a manufacturer may want to provide fuses with confidential information for use by the device within which the fuses have been integrated. The manufacturer would have to fabricate custom fuses into the device that include outputs accessible to circuitry within the device and not the customer to provide read protection of the information. Although this has been sufficient for programming a limited number of electrically programmable fuses, it becomes quite cumbersome when programming a large number of electrically programmable fuses across different devices that may be integrated into a single integrated circuit. In addition, providing multiple pads and pins wastes die and board space. Furthermore, in certain applications, such as calibration, it is undesirable to be limited to either a pad or pin programming method because of changes in parameters from the wafer stage to the package stage.
The present art has not provided an electrically programmable fuse arrangement that provides the manufacturer and customer with read protect, write protect, and test capabilities. The present art also has not provided an electrically programmable fuse arrangement that can be utilized across multiple devices in a large scale application, while allowing for either pin or pad access programming. Accordingly, there is a strong need in the art for a system and/or method for providing a programmable electrical fuse device that allows for write and/or read protection across a variety of different applications.
SUMMARY OF THE INVENTION
According to a preferred embodiment of the present invention, a system and method is provided for storing data values by implementation of electrical fuses. The present invention provides for a combination of electrical fuse cells, control, and connectivity which enables the programming and use of electrical fuses for diverse product applications, such as memory redundancy control, analog trimming control, customer owned configuration bits, die identification, encryption key coding, etc. The electrical fuses are provided in a fuse array and are broken up into one or more fuse chains which are addressable by a control logic circuit. The control logic circuit provides control signals for serially loading data values into the fuse chains. The control logic circuit also provides control signals for testing and programming of the loaded data values in addition to subsequently reading the programmed data values. A fuse chain may also include a plurality of sub-chains. Each fuse chain or sub-chain includes an optional write protection fuse cell, an optional read protection fuse cell and at least one data fuse cell.
Each data cell in a fuse chain or sub-chain includes a first flip flop or shift register element that allows for programming of the sub-chain by serially loading the data downstream through the chain or sub-chain. Once each of the protection cells and data cells are loaded in the chain or sub-chain, a high program enable bit (“1”) is propagated through a second flip flop or shift register element disposed in each cell. Propagation of the high bit ensures that the high current necessary for programming of a cell fuse is provided to each cell in the chain or sub-chain one at time, so that undesirable constraints are not placed on the system power source or signal routing resistance. Preferably, the optional write protection fuse cell is located first in the chain or sub-chain and the optional read protection fuse cell is located last in the chain or sub-chain. Programming of the optional write protection fuse cell prohibits subsequent programming of downstream fuses in the chain or sub-chain, while programming of the optional read protection cell prohibits serial reading of upstream fuses in the chain or sub-chain. Additionally, each data cell is provided with an output that is optionally readable by a host system or device within which the chain or sub-chain is integrated.
The present invention allows a manufacturer to program a manufacturing code into a fuse sub-chain that cannot be accessed or altered in any way by a customer. The customer can then program a customer code in a different fuse sub-chain which can subsequently be protected against further modification. The data can also be programmed to not be accessible to anyone other than a host device. This allows for not only programming of the fuse values in integrated circuits by wafer probing, but allows for the same security in an integrated circuit package form. Due to the fact that the fuse data values are serially loaded, tested, programmed, and read, a fuse chain can be implemented across a variety of devices integrated onto a single integrated circuit or device. In addition, the electrical fuse is designed to be universal in that it requires no additional photomasks for a basic single gate oxide CMOS process. The laser fuse process typically requires an additional photomask.
Thus, according to one aspect of the present invention, an electronic system is provided that includes an electronic device and a fuse chain integrated into the electronic device. The fuse chain includes at least one protection fuse cell and at least one data fuse cell operably coupled to the at least one protection fuse cell.
In accordance with another aspect of the present invention, a circuit is provided for storing a data value. The circuit includes an optional write protection fuse cell, an optional read protection fuse cell and at least one data fuse cell disposed between and operably coupled to the optional write protection fuse cell and the optional read protection fuse cell.
In accordance with yet another aspect of the present invention, a data storing methodology is provided. The methodology includes the steps of providing a fuse chain including at least one protection fuse cell and at least one data fuse cell, loading a data value serially into the fuse chain and programming the loaded data value into the fuse chain.
In accordance with yet another aspect of the invention, a method is provided for storing a data value. The method includes the steps of providing a plurality of fuse cells, each fuse cell including a data shift register element and a program enable shift register element wherein the data shift registers of each cell are electrically coupled serially and the program enable shift registers of each cell are electrically coupled serially. The method further includes loading a data value serially into the data shift registers of the plurality of fuse cells and propagating an enable bit serially through the program enabl
Brady W. James
Mosby April M.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
Zarabian A.
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