SOI lateral bipolar for integrated-injection logic SRAM
View Patent ↗A static random access memory (SRAM) cell is provided. The SRAM cell consists of two cross coupled integrated-injection logic (I 2 L) inverter devices. Each inverter device contains two lateral bipolar transistors (e.g., NPN- and PNP-type lateral bipolar transistors). Each of the inverter devices, and hence each lateral bipolar transistor, is formed on a surface of an insulator layer of a semiconductor-on-insulator (SOI) substrate.
1. A static random access memory (SRAM) cell comprising:
a first inverter device containing a first PNP-type lateral bipolar transistor and a first NPN-type lateral bipolar transistor; and
a second inverter device containing a second PNP-type lateral bipolar transistor and a second NPN-type lateral bipolar transistor, wherein each lateral bipolar transistor is present on an insulator layer and contains an emitter terminal, a base terminal and a collector terminal, and wherein
said collector terminals of said first PNP-type lateral bipolar transistor and said second NPN-type lateral bipolar transistor are electrically connected, and said collector terminals of said first NPN-type lateral bipolar transistor and said second PNP-type lateral bipolar transistor are electrically connected,
said collector terminal of said first PNP-type lateral bipolar transistor is electrically connected to said base terminal of said first NPN-type lateral bipolar transistor and said collector terminal of said second PNP-type lateral bipolar transistor is electrically connected to said base terminal of said second NPN-type lateral bipolar transistor,
a first wordline electrically connecting said emitter terminal of said first NPN-type lateral bipolar transistor to said base terminal of said first PNP-type lateral bipolar transistor, and a second wordline electrically connecting said emitter terminal of said second NPN-type lateral bipolar transistor to said base terminal of said second PNP-type lateral bipolar transistor, and
a first bitline electrically contacting said emitter terminal of said first PNP-type lateral bipolar transistor, and a second bitline electrically contacting said emitter terminal of said second PNP-type lateral bipolar transistor.
2. The SRAM cell of claim 1 , wherein said second NPN-type lateral bipolar transistor is located laterally adjacent said second PNP-type lateral bipolar transistor, and said first PNP-type lateral bipolar transistor is located laterally adjacent said first NPN-type lateral bipolar transistor.
3. The SRAM cell of claim 2 , wherein said collector terminals of said first PNP-type lateral bipolar transistor and said second NPN-type lateral bipolar transistor are in direct physical contact within each other and said collector terminals of said second PNP-type lateral bipolar transistor and said first NPN-type lateral bipolar transistor are in direct physical contact with each other.
4. The SRAM cell of claim 3 , wherein a metal semiconductor alloy is located on said collector terminals of each of said first PNP-type lateral bipolar transistor, said second NPN-type lateral bipolar transistor, said second PNP-type lateral bipolar transistor and said first NPN-type lateral bipolar transistor.
5. The SRAM cell of claim 4 , wherein a conductor within a first metal level provides said electrical connection between said collector terminal of said first PNP-type lateral bipolar transistor and said base terminal of said first NPN-type lateral bipolar transistor, and another conductor in said first metal level provides said electrical connection between said collector terminal of said second PNP-type lateral bipolar transistor and said base terminal of said second NPN-type lateral bipolar transistor.
6. The SRAM cell of claim 5 , wherein said first wordline and said second wordline are located in a second metal level, and wherein said first bitline and said second bitline are located in a third metal level.
7. The SRAM cell of claim 6 , wherein said SRAM cell has a size of from 7F×4F.
8. The SRAM cell of claim 1 , wherein said collector terminals of said first PNP-type lateral bipolar transistor and said second NPN-type lateral bipolar transistor are spaced apart from each other and said collector terminals of said second PNP-type lateral bipolar transistor and said first NPN-type lateral bipolar transistor are spaced apart from each other.
9. The SRAM cell of claim 8 , wherein a first metal level containing a conductor is located on said collector terminals of said first PNP-type lateral bipolar transistor and said second NPN-type lateral bipolar transistor that are spaced apart from each other, and wherein another first metal level containing a conductor is located on said collector terminals of said second PNP-type lateral bipolar transistor and said first NPN-type lateral bipolar transistor that are spaced apart from each other.
10. The SRAM cell of claim 9 , wherein said conductor of said first metal level provides said electrical connection between said collector terminals of said first PNP-type lateral bipolar transistor and said second NPN-type lateral bipolar transistor, and between said collector terminals of said first NPN-type lateral bipolar transistor and said second PNP-type lateral bipolar transistor.
11. The SRAM cell of claim 9 , wherein said first wordline and said second wordline are located in a second metal level, and wherein said first bitline and said second bitline are located in a third metal level, and wherein a conductor within said second metal level provides said electrical connection between said collector terminal of said first PNP-type lateral bipolar transistor and said base terminal of said first NPN-type lateral bipolar transistor, and said another conductor in said first metal level provides said electrical connection between said collector terminal of said second PNP-type lateral bipolar transistor and said base terminal of said second NPN-type lateral bipolar transistor.
12. The SRAM cell of claim 11 , wherein said SRAM cell has a size of from 9F×4F.
13. The SRAM cell of claim 1 , wherein a bottommost surface of each of said collector terminals, said base terminals and said emitter terminals is in direct physical contact with a topmost surface of said insulator layer.
14. A method of forming a static random access memory (SRAM) cell, said method comprising:
providing a first inverter device containing a first PNP-type lateral bipolar transistor and a first NPN-type lateral bipolar transistor, and a second inverter device containing a second PNP-type lateral bipolar transistor and a second NPN-type lateral bipolar transistor, wherein each lateral bipolar transistor is present on an insulator layer and contains an emitter terminal, a base terminal and a collector terminal;
first electrically connecting said collector terminals of said first PNP-type lateral bipolar transistor and said second NPN-type lateral bipolar transistor together and said collector terminals of said first NPN-type lateral bipolar transistor and said second PNP-type lateral bipolar transistor together;
second electrically connecting said collector terminal of said first PNP-type lateral bipolar transistor to said base terminal of said first NPN-type lateral bipolar transistor and to electrically connect said collector terminal of said second PNP-type lateral bipolar transistor to said base terminal of said second NPN-type lateral bipolar transistor;
forming, in a metal level, a first wordline to electrically connect said emitter terminal of said first NPN-type lateral bipolar transistor to said base terminal of said first PNP type lateral bipolar transistor and a second wordline to electrically connect said emitter terminal of said second NPN-type lateral bipolar transistor to said base terminal of said second PNP-type lateral bipolar transistor; and
forming, in another metal level, a first bitline to electrically contact said emitter terminal of said first PNP-type lateral bipolar transistor and a second bitline to electrically contact said emitter terminal of said second PNP-type transistor.
15. The method of claim 14 , wherein said collector terminals of said first PNP-type lateral bipolar transistor and said second NPN-type lateral bipolar transistor are in direct physical contact within each other and said collector terminals of said second PNP-type lateral bipolar transistor and said first NPN-type lateral bipolar transistor are in direct physical contact with each other.
16. The method of claim 15 , wherein said first electrically connecting comprising forming a metal semiconductor alloy on said collector terminals of each of said first PNP-type lateral bipolar transistor, said second NPN-type lateral bipolar transistor, said second PNP-type lateral bipolar transistor and said first NPN-type lateral bipolar transistor.
17. The method of claim 16 , wherein a trench isolation structure is formed separating said first inverter device from said second inverter device.
18. The method of claim 14 , wherein said collector terminals of said first PNP-type lateral bipolar transistor and said second NPN-type lateral bipolar transistor are spaced apart from each other and said collector terminals of said second PNP-type lateral bipolar transistor and said first NPN-type lateral bipolar transistor are spaced apart from each other.
19. The method of claim 18 , wherein said first electrically connecting comprises forming a first metal level containing a conductor on said collector terminals of said first PNP-type lateral bipolar transistor and said second NPN-type lateral bipolar transistor that are spaced apart from each other, and forming another first metal containing a conductor on said collector terminals of said second PNP-type lateral bipolar transistor and said first NPN-type lateral bipolar transistor.
20. The method of claim 19 , wherein a trench isolation structure is formed separating said first inverter device from said second inverter device.