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Abstract

A semiconductor structure for long-term learning includes a p-type silicon substrate or well having first and second spaced apart n-type regions formed therein. A polysilicon floating gate is separated from the surface of the silicon substrate by a layer of gate oxide. One edge of the polysilicon floating gate is aligned with the edge of the first n-type region such that the polysilicon floating gate does not appreciably overly the n-type region. The second n-type region lies beyond the edge of the polysilicon floating gate. The first n-type region, the silicon substrate, and the second n-type region form the collector, base, and emitter, respectively, of a lateral bipolar transistor. An alternate embodiment of a semiconductor long-term learning structure includes an n-type silicon substrate having a p-well region formed therein. An n-type region is formed within the well region. A polysilicon floating gate is separated from the surface of the silicon substrate by a gate oxide and is positioned above the well region. One edge of the polysilicon floating gate is aligned with the edge of the n-type region within the well region such that the polysilicon floating gate does not appreciably overly the n-type region. The substrate, the well, and the n-type region, respectively, form the emitter, base, and collector of a bipolar transistor.

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