Stmicroelectronics S.r.l.

Micron Technology Incorporated

David Esseni

Paolo Giuseppe Cappelletti

Roberto Bez

Alberto Modelli

Bruno Ricco

Luca Selmi

The memory cell is formed in a body of a P-type semiconductor material forming a channel region and housing N-type drain and source regions at two opposite sides of the channel region. A floating gate region extends above the channel region. A P-type charge injection region extends in the body contiguously to the drain region, at least in part between the channel region and the drain region. An N-type base region extends between the drain region, the charge injection region, and the channel region. The charge injection region and the drain region are biased by special contact regions so as to forward bias the PN junction formed by the charge injection region and the base region. The holes thus generated in the charge injection region are directly injected through the base region into the body, where they generate, by impact, electrons that are injected towards the floating gate region.

Nonvolatile memory cell with high programming efficiency

In order to optimize writing of the cell, the latter is written in a condition of equilibrium between an injection current I,and the displacement current C,V,. In this way, during writing, the voltage of the floating gate region V,remains constant, as does the drain current and the rise in the threshold voltage. In particular, both for programming and for soft-writing after erasure, the substrate of the cell is biased at a negative voltage V,with respect to the source region, and the control gate region of the cell receives a ramp voltage V,with a selected predetermined inclination V,satisfying an equilibrium condition V,<I,/C,.

Controlled hot-electron writing method for non-volatile memory cells

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Monterenzio, Italy

David Esseni