Rigorous Surface-Potential Solution for Undoped Symmetric Double-Gate MOSFETs Considering Both Electrons and Holes at Quasi Nonequilibrium

Xing Zhou, Senior Member, IEEE, Zhaomin Zhu, Subhash C. Rustagi, Senior Member, IEEE, Guan Huei See, Student Member, IEEE, Guojun Zhu, Shihuan Lin, Chengqing Wei, and Guan Hui Lim, Student Member, IEEE

IEEE Transactions on Electron Devices, Vol. 55, No. 2, pp. 616-623, Feb. 2008.
(Manuscript received May 22, 2007; revised  October 15, 2007.)

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This paper presents a rigorously-derived analytical solution of the Poisson equation with both electrons and holes in pure silicon, which is applied to the analysis of undoped symmetric double-gate transistors.  An implicit surface-potential equation is obtained that can be solved by a second-order Newton–Raphson technique along with an appropriate initial guess.  Within the assumption of holes at equilibrium that is being used in the existing literature, the new results, when compared with the models based on one carrier, reveal that missing the other carrier in the formulation results in a singularity in the gate capacitance exactly at flatband, which may give trouble for high-frequency analysis, although the errors in surface potentials are below the nano-volt range for all gate voltages.  However, the solution without assuming constant hole imref, as presented in this paper for the first time, further pinpoints the inadequacy in existing theories of surface-potential solutions in double-gate MOSFETs with undoped thin bodies, although its application to transport solutions of terminal current/charge models depends highly on the type of source/drain structures and contacts.



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