Semiconductor memory device having electrically floating body transistor, semiconductor memory device having both volatile and non-volatile functionality and method or operating
A semiconductor memory cell includes a floating body region configured to be charged to a level indicative of a state of the memory cell; a first region in electrical contact with said floating body region; a second region in electrical contact with said floating body region and spaced apart from said first region; and a gate positioned between said first and second regions. The cell may be a multi-level cell. Arrays of memory cells are disclosed for making a memory device. Methods of operating memory cells are also provided.
1. A semiconductor memory cell comprising:
a substrate;
a floating body region configured to store volatile memory;
a stacked gate nonvolatile memory comprising a floating gate adjacent said substrate and a control gate adjacent said floating gate such that said floating gate is positioned between said control gate and said substrate; and
a select gate positioned adjacent said substrate and said floating gate.
2. The semiconductor memory cell of claim 1 , wherein said floating body is exposed at a surface of said substrate, said cell further comprising:
first and second regions each exposed at said surface at locations other than where said floating body region is exposed; wherein said first and second regions are asymmetric, wherein a first area defines an area over which said first region is exposed at said surface and a second area defines an area over which said second region is exposed at said surface, and wherein said first area is unequal to said second area.
3. The semiconductor memory cell of claim 2 , wherein one of said first and second regions at the surface has a higher coupling to said floating gate relative to coupling of the other of said first and second regions to said floating gate.
4. The semiconductor memory cell of claim 2 , further comprising a buried layer buried in a bottom portion of said substrate, said buried layer having a conductivity type different from a conductivity type of said floating body region.
5. The semiconductor memory cell of claim 4 , wherein said floating body is bounded by said surface, said first and second regions and said buried layer.
6. The semiconductor memory cell of claim 1 , further comprising insulating layers bounding side surfaces of said substrate.
7. The semiconductor memory cell of claim 2 , further comprising a buried insulator layer buried in a bottom portion of said substrate.
8. The semiconductor memory cell of claim 7 , wherein said floating body is bounded by said surface, said first and second regions and said buried insulator layer.