High density flash memory architecture with columnar substrate coding
First Claim
1. A flash memory comprising:
- a semiconductor substrate;
a plurality of trenches separating the semiconductor substrate into a plurality of columnar active substrate regions;
a plurality of flash memory cells formed in each of the columnar active substrate regions; and
circuitry for providing independent electronic access to each of the columnar active substrate regions, where the semiconductor substrate includes a multiple well structure, and the trenches extend for an entire depth of a top well of the triple well structure.
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Abstract
Instead of using a common substrate (101) for each sector of a flash memory, trenches are used to isolate columnar active substrate regions (304) of the substrate (101), and independent access to each of these columnar regions (304) is provided. First, the independent access to each of these columnar regions (304) provides a capability for achieving more precise control over the voltage on the floating gates (106). For example, flash memory in accordance with the present invention is better suited for multi-level storage (storing of more than 1 bit of information per cell). Second, the independent access to each of these columnar regions (304) also provides a capability for areas of flash memory smaller than an entire sector to be erased at one time. Finally, since both programming and erasing is achieved by way of cold electron tunneling from the columnar active substrate region (304), no high voltages need to be applied to either the drain (102) or source (104). This is advantageous in that the minimum distance required by cell punchthrough is reduced. Hence, higher densities of flash memory may be achieved.
15 Citations
22 Claims
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1. A flash memory comprising:
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a semiconductor substrate;
a plurality of trenches separating the semiconductor substrate into a plurality of columnar active substrate regions;
a plurality of flash memory cells formed in each of the columnar active substrate regions; and
circuitry for providing independent electronic access to each of the columnar active substrate regions, where the semiconductor substrate includes a multiple well structure, and the trenches extend for an entire depth of a top well of the triple well structure. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
floating gates of the flash memory cells;
a set of wordlines including control gates of the flash memory cells;
drain contacts through oxide to drains of the flash memory cells;
a set of drain lines connecting to the drain contacts;
a set of source lines connecting to sources of the flash memory cell;
substrate contacts through oxide to the columnar active substrate regions; and
a set of substrate lines connecting to the substrate contacts, the set of substrate lines providing for the independent electronic access to each of the columnar active substrate regions.
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18. The flash memory of claim 17, where the set of source lines comprise a local interconnect layer.
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19. The flash memory of claim 18, where the local interconnect layer comprises tungsten.
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20. The flash memory of claim 17, where
the set of source lines comprise a local interconnect layer; -
the set of drain lines comprise a first metal layer;
the floating gates comprise a first polysilicon layer;
the set of wordlines comprise a second polysilicon layer; and
the set of substrate lines comprise a third polysilicon layer.
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21. The flash memory of claim 17, where the set of drain lines comprise a first set of bitlines, and the set of substrate lines comprise a second set of bitlines.
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22. The flash memory of claim 21, where the first set of bitlines is used to provide access to the flash memory cells during read operations, and the second set of bitlines is used to provide access to the flash memory cells during program and erase operations.
Specification