Active solid-state devices (e.g. – transistors – solid-state diode – Integrated circuit structure with electrically isolated... – Passive components in ics
Reexamination Certificate
1999-02-26
2001-09-11
Crane, Sara (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Integrated circuit structure with electrically isolated...
Passive components in ics
C257S529000
Reexamination Certificate
active
06288437
ABSTRACT:
TECHNICAL FIELD
The present invention concerns integrated-circuit wiring, particularly programmable electrical connections, such as fuses and antifuses, and methods of making them.
BACKGROUND OF THE INVENTION
Integrated circuits, the key components in thousands of electronic and computer products, are interconnected networks of electrical components fabricated on a common foundation, or substrate. Fabricators typically use various techniques, such as layering, doping, masking, and etching, to build thousands and even millions of microscopic resistors, transistors, and other electrical components on a silicon substrate, known as a wafer. The components are then wired, or interconnected, together to define a specific electric circuit, such as a computer memory.
Because of the difficulties of making and interconnecting millions of microscopic components, fabricators expect that one or more parts of an integrated circuit will fail to operate correctly. However, rather than discard the entire integrated circuit because of a few defective parts, fabricators sometimes include extra, or redundant, parts in integrated circuits to selectively replace defective parts. For example, memory fabricators sometimes include redundant memory cells to replace defective memory cells in an integrated memory circuit. Fabricators can then test the memory circuit for defective cells and activate one or more of the redundant cells to save the integrated circuit.
Activating a redundant part often entails opening or closing, that is, programming, one or more programmable electrical connections between the redundant part and the rest of the integrated circuit. In general, there are two types of programmable electrical connections: fuses and antifuses. A fuse is a normally closed electrical connection which can be opened typically using a laser to melt and vaporize a portion of the fuse. An antifuse, on the other hand, is normally open and requires some action to close the connection, that is, to electrically connect one end of the antifuse to the other.
Antifuses typically include a thin, insulative layer sandwiched between two conductors. Closing, or programming, an antifuse generally requires applying a large voltage across the two conductors. The large voltage creates an electric field which exceeds the breakdown strength of the insulative layer, thereby rupturing the insulative layer and electrically connecting the two conductors.
Unfortunately, antifuses based on the breakdown or rupturing of an insulative layer perform poorly. Specifically, the resulting electrical connections often have high electrical resistances which ultimately waste power and slow down the transfer of electrical signals through integrated circuits. Moreover, these high resistances tend to vary significantly over time and thus make it difficult for integrated circuits to perform consistently as they age. Additionally, the rupturing process inevitably varies significantly from antifuse to antifuse within the same integrated circuit, introducing undesirable differences in the electrical traits of various parts of the circuit and thus compromising circuit performance. These and other performance concerns have ultimately led some fabricators to avoid using antifuses.
Accordingly, there is a need for better antifuses and antifuse programming techniques.
SUMMARY OF THE INVENTION
To address these and other needs, the inventors devised an integrated antifuse structure that includes two conductive elements and a programming mechanism for selectively moving one of the elements relative to the other, to, for example, bring them into electrical contact with each other. More specifically, one embodiment forms a chamber in an integrated circuit, with two conductive elements overhanging the top of the chamber and a third conductive element lying on the bottom of the chamber. The bottom of the chamber includes a chemical compound that when heated sufficiently rapidly evolves, or releases, a gas, such as hydrogen, nitrogen, or oxygen. The rapid release of gas into the chamber creates a force that moves the third element, like a piston, from the bottom of the chamber to contact the two elements overhanging the top of the chamber, thereby completing an electrical connection. The exemplary embodiment uses copper elements and ultimately promises better performance than conventional rupture-based antifuses because the copper elements have reproducible electrical resistances that remain stable during antifuse programming and subsequent aging.
Other facets of the invention include methods of making and operating antifuses and several integrated-circuit applications for antifuses in accord with the invention. For example, one integrated-circuit application is a programmable logic array, and another is an integrated memory circuit having redundant memory cells. The invention, however, can be applied to any integrated circuit where a programmable electrical connection, such as a fuse or antifuse, is desirable.
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Eldridge Jerome M.
Forbes Leonard
Crane Sara
Drake Eduardo E.
Micro)n Technology, Inc.
Schwegman Lundberg Woessner & Kluth P.A.
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