1. Design and Analysis of A Novel 8T SRAM Cell December 14, 2010 Department of Microelectronic Engineering & Centre for Efficiency Oriented Languages University College Cork, Ireland & Synopsys, Ireland Jiaoyan Chen, Dilip Vasudevan, Emanuel Popovici, Michel Schellekens, Peter Gillen Email: chenj@ue.ucc.ie

2. Contents  Motivation  Architectures of 6T SRAM, 9T SRAM and our 8T SRAM  Adiabatic and Non-Adiabatic Operations  SNM Comparison  Dynamic Power  Static Power  Conclusion

3. Motivation Roadmap –Cell Area Trend(ITRS 2008) Consumer Portable Power Consumption Trend (ITRS 2008 update) SOC Consumer Stationary Power Consumption (2008) SRAM consumes a lot of power and area in chips. Our aim is to built an efficient SRAM.

4. Conventional 6T SRAM 4 Technology: 90nm,65nm,45nm, 28nm… Stability: Static Noise Margin (SNM) is getting Down. Leakage Power: a) Subthreshold leakage current b) Gate oxide leakage current

5. 9T SRAM 9T SRAM 5 Features: a) 2 sub-circuits: Upper : Writing Lower: Reading b) Minimal Sizing for the upper part c) SNM is much better d) Lower leakage Power (in super cut-off mode) Z. Liu and V. Kursun, “Characterization of a novel nine-transistor sram cell,” IEEE Trans. Very Large Scale Integr. Syst., vol. 16, no. 4, pp. 488–492, 2008

6. Proposed 8T SRAM 6 Features: a) 2 sub-circuits: Upper :1. No GND Connection 2. Add One Sharing transistor Lower: Using PMOS b) Half swing BL and BL’ return to VDD/2 after writing or reading.

7. Adiabatic Operations: Writing PMOS P3 is used to meet the Adiabatic Principle: No voltage difference before the transistor turns on

8. Adiabatic Operations: Reading

9. Simulation Waveforms

10. SNM Comparison (45nm) Proposed 8T SRAM Conventional 6T SRAM

11. Dynamic Power Comparison (1) Dynamic Power Comparison (1) 8*8 Array 1 Bit Cell

12. Dynamic Power Comparison (2) 62% 67%

13. Leakage Power Analysis

14. Temperature Variation >90%

15. Process Variation (65nm) – TOX, VTH, U0 >90%

16. Process Variation (45nm) – TOX, VTH, U0 90%

17. Conclusion Summary  Efficient 8T SRAM architecture  Improved SNM compared with 6T SRAM  Very Low Dynamic and Leakage power Future work  Use 36nm, 28nm…Check performance particularly for leakeage  Further Enhance the Stability  Fabricate and validate the proposed architecture

18. Thank You Questions?