Stmicroelectronics S.r.l.

Alberto Modelli

Roberto Bez

Federico Pio

Guido Torelli

Alessandro Manstretta

Enrico Gomiero

Paola Paruzzi

David Esseni

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

A method for correction of errors in a word stored in multi-bit memory cells includes associating a full error code, which includes bit error codes and a set error code, for each set of bits of the word stored in a single memory cell. The method includes associating, with each single error, a bit error code which is not associated with other errors and which is indicative of a position of the bit in the word. The set error code is computed based on the bit error codes associated with the bits in the set. The method also checks to make sure that the full error code for the set has not already been associated with other errors. If the error code has already been used for another error, then the method changes both the set error code and at least one of the bit error codes.

Method for correction of errors in a binary word stored in multi-level memory cells, with minimum number of correction bits

When programming, for each programming pulse, a threshold voltage whose value is increased with respect to the previous programming pulse is applied to the gate terminal of each cell to be programmed. After an initial step, the increase of threshold voltage of the cell being programmed becomes equal to the applied gate voltage increase. In order to reduce the global programming time, keeping a small variability interval of threshold voltages associated with each level, to pass from a threshold level to a following one, each cell to be programmed is supplied with a plurality of consecutive pulses without verify, until it is immediately below the voltage level to be programmed, and then a verify step is performed, followed by subsequent programming and verify steps until the cell to be programmed reaches the desired threshold value.

Method for programming multi-level non-volatile memories by controlling the gate voltage

A test structure is formed by an array of memory cells connected in parallel and including each a memory transistor and a select transistor connected in series. The gate terminals of the select transistors of all memory cells are biased to a value next to the threshold voltage of the select transistors. Therefore, in each memory cell, the drain current is limited by the memory transistor for control gate voltages below the threshold voltage of the memory transistor, and by the select transistor at higher voltages; for high control gate voltages, the drain current is clamped to a constant maximum value. Since the clamping effect of the select transistors acts on each memory cell, the total maximum current of the test structure may be held below a value causing a limitation in the current generated by the entire array because of the resistance in series to the output of the test structure. Thus also the right side of the threshold distribution may be evaluated and the presence of defective cells causing injection of electrons in the floating gate of the memory transistors may be detected.

Nonvolatile memory test structure and nonvolatile memory reliability

A memory device comprising a semiconductor material substrate with a dopant of a first type; a first semiconductor material well with a dopant of a second type formed in the substrate; a second semiconductor material well with a dopant of the first type formed in said first well; an array of memory cells formed within said second well. Each memory cell comprises a first electrode and a second electrode respectively formed by a first and a second doped regions with dopant of the second type formed in said second well, and a control gate electrode. The memory array comprises a first plurality of strips of conductive material extending over said second well in a first direction and forming rows of memory cells, a second plurality of strips of conductive material extending over said second well in a second direction substantially orthogonal to said first direction and forming columns of memory cells, each strip of said second plurality electrically contacting the first electrodes of a respective group of memory cells, a third plurality of strips of conductive material extending over said second well in said second direction and intercalated to the strips of the second plurality, electrically contacting the second electrodes of the cells. A fourth plurality of strips of conductive material is provided extending over said second well in said second direction and intercalated to the strips of said second and third pluralities, electrically contacting the second well in a succession of contact points distributed longitudinally to each strip of said fourth plurality.

Memory device with a memory cell array in triple well, and related

A memory device comprising a semiconductor material substrate with a dopant of a first type, a first semiconductor material well with a dopant of a second type formed in the substrate; a second semiconductor material well with a dopant of the first type formed in the first well, an array of memory cells formed within the second well. Each memory cell comprises a first electrode and a second electrode respectively formed by a first and a second doped regions with dopant of the second type formed in the second well, and a control gate electrode. The memory array comprises a first plurality of strips of conductive material extending over the second well in a first direction and forming rows of memory cells, a second plurality of strips of conductive material extending over the second well in a second direction substantially orthogonal to the first direction and forming columns of memory cells, each strip of the second plurality electrically contacting the first electrodes of a respective group of memory cells, a third plurality of strips of conductive material extending over the second well in the second direction and intercalated to the strips of the second plurality, electrically contacting the second electrodes of the cells. A fourth plurality of strips of conductive material is provided extending over the second well in the second direction and intercalated to the strips of the second and the third pluralities, electrically contacting the second well in a succession of contact points distributed longitudinally to each strip of the fourth plurality.

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Milan, Italy

Alberto Modelli