Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Fusible link or intentional destruct circuit
Reexamination Certificate
2000-12-28
2002-07-09
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Fusible link or intentional destruct circuit
C327S053000
Reexamination Certificate
active
06417720
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a sensing and programming circuit for programming a fuse cell, and more particularly, to a sense circuit that can operate with high programming voltage.
BACKGROUND OF THE INVENTION
In CMOS integrated circuits, it is often desirable to be able to permanently store information, or to form permanent connections on the integrated circuit after it is manufactured. Fuses or other devices forming fusible links are frequently used for this purpose. Fuses can be used to program redundant elements to replace identical defective elements, for example.
Fuse devices are selectively programmed to provide the capabilities described above. Where one or more fuses is used for information storage purposes, a sensing circuit it typically used to determine whether the associated fuse has been programmed or not, i.e., a sensing circuit is used to determine the value “stored”. Sensing circuits operate to distinguish between programmed and unprogrammed (or burned and unburned) fuses, usually by detecting a change in the resistance of the fuse device from a low to a high value.
An issue arises because of the smaller geometries provided by modem process technologies. Smaller geometries include smaller line widths and device sizes. At reduced geometries, the resistance of the fuse device is more difficult to control. In some cases, the difference in a resistance between a burned fuse and an unburned fuse maybe so small that the difference is difficult to detect with prior fuse sensing circuits.
Furthermore, as processes move to lower supply voltages, the voltage available to program fuses is decreased. As the fuse programming voltage is lowered, the number of “marginally burned” fuses increases. Fuses are considered to be marginally burned when, after programming, the resistance of the fuse remains low enough that there is an unacceptable risk that the fuse might be identified as being unprogrammed when its state is sensed. Therefore, marginally burned fuses may compromise the functionality of quality of circuit that uses the fuse. This is particularly true where the state of the single fuse determines that state of a fuse based storage cell. Additional or redundant fuses have previously been provided for this type of cell, but each redundant fuse takes up valuable space.
Thus, it is preferred to have fuses that can be programmed using a higher voltage supply. The use of a higher voltage supply insures that the number of marginally burned fuses is minimal. However, in order to use high voltages to program the fuse cells, a high voltage sensing circuit must be developed.
REFERENCES:
patent: 4730129 (1988-03-01), Kunitoki et al.
patent: 5731733 (1998-03-01), Denham
patent: 5959445 (1999-09-01), Denham
patent: 6208549 (2001-03-01), Rao et al.
Blakely , Sokoloff, Taylor & Zafman LLP
Cunningham Terry D.
Intel Corporation
Tra Quan
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