Method of maintaining the state of semiconductor memory having electrically floating body transistor
Methods of maintaining a state of a memory cell without interrupting access to the memory cell are provided, including applying a back bias to the cell to offset charge leakage out of a floating body of the cell, wherein a charge level of the floating body indicates a state of the memory cell; and accessing the cell.
1. A semiconductor memory cell comprising:
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, located at a surface of said floating body region; and
a second region in electrical contact with said floating body region, located below said floating body region, configured to inject charge into said floating body region to maintain said state of the memory cell;
wherein an amount of charge injected into said floating body is a function of a charge stored in said floating body region.
2. The semiconductor memory cell of claim 1 , wherein said floating body has a first conductivity type selected from a p-type conductivity type and an n-type conductivity type;
said first region has a second conductivity type selected from said p-type and n-type conductivity types, said second conductivity type being different from said first conductivity type; and
said second region has said second conductivity type.
3. The semiconductor memory cell of claim 2 , further comprising a third region having said second conductivity type, said third region being spaced apart from said first region.
4. The semiconductor memory cell of claim 1 , further comprising a gate region above said floating body.
5. The semiconductor memory cell of claim 1 , further comprising:
a terminal connected to said first region; and
a back bias terminal connected to said second region.
6. The semiconductor memory cell of claim 1 , wherein applying a voltage to said second region offsets charge leakage out of said floating body.
7. The semiconductor memory cell of claim 6 , wherein said voltage applied to said second region is a constant positive voltage bias.
8. The semiconductor memory cell of claim 6 , wherein said voltage applied to said second region is a periodic pulse of positive voltage.
9. A semiconductor memory array comprising:
a plurality of semiconductor memory cells arranged in a matrix of rows and columns, wherein each said 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;
wherein a back-bias region is commonly connected to at least two of said memory cells, and when a first memory cell of said at least two of said memory cells is in a first state and a second memory cell of said at least two of said memory cells is in a second state, application of a bias via said back-bias region maintains said first memory cell in said first state and said second memory cell in said second state.
10. The semiconductor memory array of claim 9 , wherein each said first region has a first conductivity type selected from a p-type conductivity type and an n-type conductivity type;
each said floating body region has a second conductivity type selected from said p-type and n-type conductivity types, said second conductivity type being different from said first conductivity type;
each said second region has said first conductivity type; and
said back bias region comprises a substrate having said first conductivity type.
11. The semiconductor memory array of claim 9 , wherein said back-bias region is commonly connected to all of said memory cells in said memory array.
12. The semiconductor memory array of claim 9 , wherein said back-bias region is segmented to allow independent control of bias applied to a selected portion of said memory array.
13. The semiconductor array of claim 9 , wherein application of voltage to said back bias region maintains current states of each said memory cell connected thereto.
14. The semiconductor array of claim 13 , wherein said application of voltage is applied as a constant voltage bias.
15. The semiconductor array of claim 13 , wherein said application of voltage is applied as a periodic pulse of voltage bias.
16. The semiconductor array of claim 9 , wherein a maximum potential that can be held by any one of said memory cells connected to said back bias region is increased by said application of voltage to said back bias region, resulting in a relatively larger memory window.
17. A semiconductor memory cell comprising:
a bipolar device having a floating base region, a collector, and an emitter, wherein:
a state of said memory cell is stored in said floating base region,
said collector is located below said floating base region;
said state of said memory cell is maintained through a back-bias applied to said collector.
18. The semiconductor memory cell of claim 17 , wherein said floating base region has a first conductivity type selected from a p-type conductivity type and an n-type conductivity type;
said emitter has a second conductivity type selected from said p-type and n-type conductivity types, said second conductivity type being different from said first conductivity type; and
said collector has said second conductivity type.
19. The semiconductor memory cell of claim 17 , wherein said back-bias applied to said collector is a constant voltage bias.
20. The semiconductor memory cell of claim 17 , wherein said back-bias applied to said collector is a periodic pulse of voltage.