Minimization in variation of output characteristics of a SOI MOS due to Self Heating Sahil M. BansalD.Nagchaudhuri B.E. Final Year, Professor, Electronics & Electrical Commn.DA-IICT, Punjab Engineering CollegeGandhinagar, Gujarat Chandigarh, INDIAINDIA

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 !!!

SOI MOS Less Capacitance … Faster … Less Power … High Device Temperatures !!!

Effects of Self Heating on the Id – Vds plot

FTGSOIMOS – Feedback Thermal Gradient SOI MOS

FTGSOIMOS response to change in temperature

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

A look at the BSIM SOI 3 Model Ids, MOSFET = {I ds0 ( 1+ ( V ds V dseff )/V A )}\ ( 1 + R ds I ds0 /V dseff ) U 0( T ) = U 0( T nom) (T/T nom )^ ute V th( T ) = V th( T nom) + ( T/T nom – 1 ) * { K T1 + ( K tl1/ L eff) + K T2* V bseff} K T1, K tl1, K T2 and ute determine the response of Vth and mobility to change in temperature

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

Controlling the change in Vth and Mobility

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

An idea to be explored If Values of K T1, K tl1, K T2 and ute can 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..???

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 [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.

[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 [9] Groesenken G. et al “Temperature dependence of threshold voltage in thin-film SOI MOSFETS” IEEE Electron Devices letters Pg , Volume 11 Aug 1990.

Thank you !!