Texas Instruments Corporation

Iano D'Arrigo

Michael C Smayling

Georges Falessi

Giovanni Santin

Mousumi Bhat

Giulio Giuseppe Marotta

A low voltage flash EEPROM X-Cell includes an array of memory cell transistors (24) that constitute asymmetric floating gate memory cells wherein programming is achieved on only one side of the memory cells (24). The programming side of each of the memory cells (24) is connected to one of a plurality of Column Lines (28) at nodes (30). Each node (30) shares the programming side of two of the memory cells (24) and the non-programming side of two of the memory cells (24). The control gates of each of the memory cells (24) are connected to Word Lines (26) associated with rows of the array. To Flash Write all of the memory cells (24), the Column Lines (38) are connected to a negative medium voltage and the row lines (26) are connected to a positive medium voltage. To selectively erase one of the memory cells (24), the Column Line (28) associated with the programming side of the select memory cell transistor is connected to a positive medium voltage and the associated line (26) is connected to a positive Read voltage. The remaining Word Lines are connected to a negative Read voltage and the remaining Column Lines (28) are connected to a zero volt level.

Low voltage flash EEPROM C-cell using fowler-nordheim tunneling

A non-volatile memory cell 10 is disclosed herein. The cell is formed in a first semiconductor region 12 of a first conductivity type. A second semiconductor region 14 of a second conductivity type formed over the first semiconductor region 12. A third semiconductor region 16 of the first conductivity type formed over the second semiconductor region 14. In the preferred embodiment, the second and third regions 14 and 16 are well regions formed within the first region 12. Other regions such as epitaxially grown layers can also be used. First and second source/drain regions 18 and 20 are formed within the third semiconductor region 16. These second source/drain regions 18 and 20 are separated by a channel region 22. A floating gate 26 overlies at least a portion of the channel region 22 while a control gate 30 overlies the floating gate 26.

Non-volatile memory cell and level shifter

A memory array (10) is provided with a plurality of Flash EEPROM memory cells (24) that are fabricated with a single level poly process. Each of the transistor cells (24) is fabricated from a single poly layer floating gate (40) that extends between a moat region (30) and an implanted region (80), comprising the control gate of the cell (24). The portion of the floating gate (40) overlying the moat forms a channel region and is separated therefrom by a thin tunnel oxide layer (82) to allow the cell to operate in accordance with Fowler-Nordheim tunneling. The portion of the floating gate (40) disposed over the implanted control gate (80) is separated therefrom by a layer of oxide (84). The implant region (80) is contacted by a contact layer (86) to allow voltage to be applied thereto. The transistor is contained within a P-tank (78) which is disposed at a negative voltage, this tank (78) contained within an N-tank (76), which tank ( 76) is disposed at a higher voltage. This assures that no conduction occurs from the region (80) to the tank (78) when negative voltages are applied to the control gate. Negative medium voltages and positive medium voltages are utilized to allow the array to be bit programmed without using separate row select transistors.

Low voltage Fowler-Nordheim flash EEPROM memory array utilizing single

A Flash EEPROM memory array includes a plurality of transistor memory cells (24) arranged in rows and columns. The sources of the transistors (24) are connected to Virtual Ground Lines (29) and the drains thereof are connected to Column Lines (28). The memory cells (24) are programmable by Fowler-Nordheim tunneling. Each cell also includes an isolation structure having a first isolation tank of the first conductivity type material for surrounding each of the floating gate transistor memory devices and a second isolation tank of a second conductivity type material opposite to the first conductivity type surrounding the first isolation tank, allowing application of a negative voltage to the source or drain of the cell. Initially, all of the transistors are erased in the FLASH ERASE operation by disposing the Word Lines at a negative medium voltage and the Bit Lines at a positive medium voltage. Thereafter, selected transistors can be written to by selectively charging the floating gates in the transistors. This is achieved by disposing the Column Lines (28) of a select transistor at a negative voltage of a magnitude less than the programming voltage V.sub. PP and disposing the row line (26) of the select transistor at a positive voltage of a magnitude less than V.sub.PP.

Memory array utilizing low voltage Fowler-Nordheim Flash EEPROM cell

A EEPROM memory array (10) includes a plurality of memory cells (24) which are connected in a symmetric array between row lines (26) and Column Lines (28) and Virtual Ground Lines (29). Each of the memory cells includes a merged pass gate which is connected to a control gate. A non-stacked structure is utilized wherein a floating gate (42) is formed, having two portions that extend over an active region, a tunnel diode portion (44) and a control gate portion (46). The floating gate portion (44) is disposed over a thin tunnel oxide layer (47) to form a tunnel diode which allows Fowler-Nordheim tunneling to occur. The control gate portion (46) is disposed over a much thicker oxide layer such that tunneling does not occur. A control gate layer (50) is disposed over the floating gate (42) such that it overlaps the edges thereof and encloses the floating gate (42). On the one side of the floating gate (42), the control gate extends over the gate oxide layer in an extended portion (52) to form a pass gate structure. The pass gate structure is a merged structure formed in series with the floating gate cell. The merged pass gate has a controllable threshold that allows the floating gate cell to be overerased without causing unwanted conduction when the cell is unselected.

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Cannes, France

Iano D'Arrigo