Three dimensional non-volatile storage with asymmetrical vertical select devices
View Patent ↗A three-dimensional array adapted for memory elements that reversibly change a level of electrical conductance in response to a voltage difference being applied across them. Memory elements are formed across a plurality of planes positioned different distances above a semiconductor substrate. Bit lines to which the memory elements of all planes are connected are oriented vertically from the substrate and through the plurality of planes.
1. A non-volatile storage system, comprising:
a substrate;
a monolithic three dimensional memory array of memory cells positioned above and not in the substrate;
word lines connected to the memory cells;
a plurality of vertically oriented bit lines above and not in the substrate, the vertically oriented bit lines are connected to the memory cells;
a plurality of global bit lines;
a plurality of asymmetrical vertically oriented select devices that are above and not in the substrate, the asymmetrical vertically oriented select devices are connected to the vertically oriented bit lines and the global bit lines, the asymmetrical vertically oriented select devices have a first gate interface and a second gate interface; and
a plurality of select lines connected to the select devices, each asymmetrical vertically oriented select device has one of the select lines connected to the first gate interface for the respective asymmetrical vertically oriented select device and another of the select lines connected to the second gate interface for the respective asymmetrical vertically oriented select device.
2. The non-volatile storage system of claim 1 , wherein:
each asymmetrical vertically oriented select device includes a channel that is asymmetrically doped.
3. The non-volatile storage system of claim 1 , wherein:
each asymmetrical vertically oriented select device includes an asymmetrical channel.
4. The non-volatile storage system of claim 1 , wherein:
each asymmetrical vertically oriented select device includes a channel with a first side at the first gate interface and a second side at the second gate interface, the first side has a different threshold voltage than the second side.
5. The non-volatile storage system of claim 1 , wherein:
each asymmetrical vertically oriented select device includes a first gate oxide at the first gate interface and a second gate oxide at the second gate interface, the first gate oxide has a different thickness than the second gate oxide.
6. The non-volatile storage system of claim 1 , wherein:
each asymmetrical vertically oriented select device is asymmetrical due to a gate material work function difference.
7. The non-volatile storage system of claim 1 , wherein:
a first side of a asymmetrical vertically oriented select devices that includes the first gate interface will act like depletion mode transistors and a second side of the asymmetrical vertically oriented select devices that includes the second gate interface will act like enhancement mode transistors.
8. The non-volatile storage system of claim 1 , wherein:
each asymmetrical vertically oriented select device includes an enhancement mode side and a depletion mode side.
9. The non-volatile storage system of claim 1 , wherein:
each of a plurality of the select lines are positioned between and in communication with gate interfaces for two neighboring asymmetrical vertically oriented select devices, applying a selection signal to the select lines only causes one of two neighboring asymmetrical vertically oriented select devices to turn on.
10. The non-volatile storage system of claim 1 , wherein:
the asymmetrical vertically oriented select devices are active thin film transistors with vertically oriented channels.
11. The non-volatile storage system of claim 1 , wherein:
the word lines include groups of word lines, each group of word lines includes multiple word lines connected together; and
each select line is connected to a set of the asymmetrical vertically oriented select devices that are connected to a set of the vertically oriented bit lines that are connected to memory cells also connected to only one word line of a particular group of word lines.
12. The non-volatile storage system of claim 1 , wherein:
the memory cells in combination with the vertically oriented bit lines and the word lines form a continuous mesh.
13. The non-volatile storage system of claim 1 , further comprising:
row select line drivers, the memory cells are arranged in blocks, the memory array includes gaps between blocks, and each row select line driver includes multiple components that are distributed in different gaps between blocks.