Memory device having electrically floating body transistor
A semiconductor memory cell includes a floating body region configured to be charged to a level indicative of a state of the memory cell selected from at least first and second states. A first region of the memory cell is in electrical contact with the floating body region. A second region of the memory cell is spaced apart from the first region and is also in electrical contact with the floating body region. A gate is positioned between the first and second regions. A back-bias region is configured to generate impact ionization when the memory cell is in one of the first and second states, and the back-bias region is configured so as not to generate impact ionization when the memory cell is in the other of the first and second states.
1. 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 selected from at least first and second states;
a first region in electrical contact with said floating body region; and
a back-bias region configured to maintain a charge in said floating body region;
wherein said first region, said floating body region, and said back-bias region form a bipolar transistor where the product of forward emitter gain and impact ionization efficiency of said bipolar transistor approaches unity;
wherein said back bias region is commonly connected to at least two of said memory cells, and
wherein said back bias region has a lower band gap than said floating body region.
2. The semiconductor memory array of claim 1 , wherein said back-bias region is configured to generate impact ionization when the memory cell is in one of said first and second states, and wherein said back-bias region is configured so as not to generate impact ionization when the memory cell is in the other of said first and second states.
3. The semiconductor memory array of claim 1 , wherein each said semiconductor memory cell further comprises a second region in electrical contact with said floating body region and spaced apart from said first region.
4. The semiconductor memory array of claim 1 , wherein each said semiconductor memory cell further comprises a gate region positioned above said floating body region.
5. The semiconductor memory array of claim 1 , further comprising a substrate region, wherein said back-bias region is positioned between said substrate region and said floating body region.
6. The semiconductor memory array of claim 1 wherein said first and second states are stable states.
7. The semiconductor memory array of claim 1 , wherein said floating body region comprises first and second subregions, wherein said first subregion has a first doping concentration level and said second subregion has a second doping concentration level, and wherein said first doping concentration level is different from said second doping concentration level.
8. The semiconductor memory array of claim 1 , comprising a fin structure extending from a substrate.
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 selected from at least first and second states; and
a back-bias region located below said floating body region;
wherein said back-bias region acts as a collector region of a bipolar transistor that maintains the state of said memory cell and has a lower band gap than said floating body region, and
wherein said back bias region is commonly connected to at least two of said memory cells.
10. The semiconductor memory array of claim 9 , wherein said first and second states are stable.
11. The semiconductor memory array of claim 9 , wherein a product of forward emitter gain and impact ionization efficiency of said bipolar transistor that maintains the state of said memory cell approaches unity when said memory cell is in one of said first and second states, and wherein impact ionization, when said memory cell is in the other of said first and second states is less than the impact ionization when said memory cell is in said one of said first and second states.
12. The semiconductor memory array of claim 9 , wherein current flow through said bipolar transistor is larger when said memory cell is in one said first and second states than when said memory cell is in the other of said first and second states.
13. The semiconductor memory array of claim 9 , wherein said memory cell states are maintained through impact ionization.
14. The semiconductor memory array of claim 9 , wherein said back-bias region is configured to generate impact ionization when the memory cell is in one of said first and second states, and wherein said back-bias region is configured so as not to generate impact ionization when the memory cell is in the other of said first and second states.
15. The semiconductor memory array of claim 9 , comprising a fin structure extending from a substrate.
16. 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 storing a charge or lack of charge indicative of a state of the memory cell selected from at least first and second states;
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;
a back-bias region commonly connected to at least two of said memory cells,
wherein said back bias region has a lower band gap than said floating body region; and
wherein 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 back bias via said back-bias region generates impact ionization in one of said first and second memory cells, and not in the other of said first and second memory cells.
17. The semiconductor memory array of claim 16 , further comprising a substrate region, wherein said back-bias region is positioned between said substrate region and said floating body region.
18. The semiconductor memory array of claim 16 , wherein said floating body region comprises first and second subregions, wherein said first subregion has a first doping concentration level and said second subregion has a second doping concentration level, and wherein said first doping concentration level is different from said second doping concentration level.
19. The semiconductor memory array of claim 16 , where said first and second states are stable states.
20. The semiconductor memory array of claim 16 , comprising a fin structure extending from a substrate.