1. Field of the Invention
The present invention relates generally to semiconductor components, and more particularly, to protection against electrostatic discharge for semiconductor devices. An electrostatic charge, applied inadvertently to a semiconductor circuit, can not only effect the operation of the semiconductor components, but can damage the semiconductor components themselves.
2. Description of the Related Art
Referring to
The operation of the circuit of
As will be clear to those skilled in the art,
While the circuit shown in
A need has been felt for apparatus and an associated method having the feature of improving the protection against electrostatic discharge in semiconductor circuits. It would be another more particular feature of the apparatus and associated method to provide the electrostatic protection circuit with a mechanism for extending the period of electrostatic-origin current removal from the circuit.
The aforementioned and other features of the apparatus and associated method are accomplished, according to the present invention, by enclosing the typical electrostatic protection circuit in an electrically isolated well that prevents the migration of electrons, inserted into the substrate, from migrating away from the electrostatic protection circuits. The conduction of the virtual transistor associated with the second transistor is stronger and of longer duration.
Other features and advantages of the present invention will be more clearly understood upon reading of the following description along with the accompanying figures and claims.
1. Detailed Description of the Drawings
Referring to
2. Operation of the Preferred Embodiment
The operation of the present invention can be understood as follows. The typical electrostatic protection circuit includes a transistor for pumping charge into the substrate and a transistor applying charge to a pin, the pin conducting the charge away from the integrated circuit. The charge in the substrate results in increased flow of electrons by the biasing of a parasitic bipolar transistor, the parasitic transistor resulting from the two n-wells and the intervening p-substrate for the associated field effect transistor. The charge in the substrate results in the additional current flow between the two p-wells. However, the charge in the substrate is short-lived because of the migration of the inserted charge into other regions of the substrate. By electrically isolating the portion of the substrate into which the charge is pumped from the remainder of the substrate, the activation of the parasitic transistor is stronger and longer lasting than in the absence of the electrical isolation. Consequently, the electrostatic charge is removed more efficiently.
Although the present invention has been described with respect to the preferred embodiment and drawings of the invention, it will be apparent to those skilled in the art that various adaptations, modifications, and alterations may be accomplished without departing from the spirit and scope of the present invention. Accordingly, it is to be understood that the accompanying drawings as set forth hereinabove are not intended to limit the breadth of the present invention, which should be inferred only from the following claims and their appropriately construed legal equivalents.
This Application claims the benefit of Provisional Application 60/846,795, filed Sep. 22, 2007.
Number | Date | Country | |
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60846795 | Sep 2006 | US |