Minimization in variation of output characteristics of a SOI MOS due to Self Heating

1. Minimization in variation of output characteristics of a SOI MOS due to Self Heating Sahil M. Bansal D.Nagchaudhuri B.E. Final Year, Professor, Electronics & Electrical Commn. DA-IICT, Punjab Engineering College Gandhinagar, Gujarat Chandigarh, INDIA INDIA

2. Overview • SOI Technology – Benefits and Drawbacks • Self heating results in increase in operating temperature • Background - efforts to minimize the effect of Self heating • Circuit Level – Feedback technique • Studying the response of Vth and mobility to change in temperature • An idea !!!

3. SOI MOS • Less Capacitance … Faster … Less Power … High Device Temperatures !!!

4. Effects of Self Heating on the Id – Vds plot

5. FTGSOIMOS – Feedback Thermal Gradient SOI MOS

6. FTGSOIMOS response to change in temperature

7. FTGSOIMOS – Advantages and Drawbacks • Useful in circuits with large values of drain current. • Variation with temperature is nearly zero • Increase in Area Overhead. • Not Applicable to modern day circuits with thousands of gates

8. A look at the BSIM SOI 3 Model • Ids,MOSFET = {Ids0( 1+ ( Vds Vdseff)/VA)}\ ( 1 + RdsIds0/Vdseff) U0(T) = U0(Tnom) (T/Tnom)^ ute Vth(T) = Vth(Tnom) + (T/Tnom – 1 ) * {KT1 + (Ktl1/ Leff) + KT2*Vbseff} KT1, Ktl1, KT2 and ute determine the response of Vth and mobility to change in temperature

9. Contradictory effects of change in Vth and mobility on Drain Current • An increase in T results in less values for Vth and mobility • Reduced mobility = Reduced Drain Current • Reduced Vth = Increased Drain Current

10. Controlling the change in Vth and Mobility

11. Advantages • No area overhead problems • Constant Id-Vds plot over a relatively large range of Vds at small device geometries Disadvantages • Controlling the parameters governing the temperature response of Vth and mobility may hamper performance

12. An idea to be explored • If Values of KT1, Ktl1, KT2 and utecan be controlled at the technology level then we can have a temperature independent performance of the SOI MOS !!! • What effects would altering the values of these parameteres have on other device characteristics ..???

13. References: • [1] Su Lisa T. et al “Measurement & Modeling of Self-Heating in SOI NMOSFET’s” • IEEE Transaction on Electron Devices, Vol 41 Jan 1994, Pg 69-75. • [2] Pellela M.M et al “On the performance advantage of PD/SOI CMOS with floating • bodies” IEEE Transactions on Electron Devices, Vol 49 Jan 2002, Pg 96 – 104. • [3] Yu-Ming F. et al “Modeling of Thermal Behavior in SOI structures” IEEE • Transactions on Electron Devices, Vol 51 Jan 2004, Pg 83 – 91.

14. [4] Jeon D.S., Burk D.E. “A Temperature Dependent SOI MOSFET Model for High • Temperature application (27C - 300C)” IEEE Transactions on Electron Devices, Sept • [5] Berger M. et al “Estimation of Heat transfer in SOI MOSFET’s” IEEE Transactions • on Electron Devices Pg 871 – 875, Vol 38, Apr 1991 • [6] Nooshabadi et al “A MOS Transistor thermal sub-circuit for the SPICE circuit • simulator” 1998 Microelectronics Journal. • [7] BSIMSOI 3.1 User’s Manual • [8] Sherony M.J. et al “Minimization of Threshold Voltage variation in SOI MOSFETS” • Proceedings of 1994 IEEE International SOI conference Pg 131-132 • [9] Groesenken G. et al “Temperature dependence of threshold voltage in thin-film SOI • MOSFETS” IEEE Electron Devices letters Pg 329-331, Volume 11 Aug 1990.

15. Thank you !!