IMPACT OF THE TRANSMISSION-LINE PROPERTIES OF A METAL ULTRATHIN SILICON DIOXIDE SEMICONDUCTOR FIELD-EFFECT TRANSISTOR ON THE EXTRACTED INVERSION-LAYER THICKNESS

The effective thickness of the inversion layer, expressed in terms of the inversion charge centroid, is determined by capacitance measuremen ts in the weak, moderate and strong inversion regimes using a new mode l for the gate-to-channel capacitance which takes into account quantum and transmission line effects in all the regimes. It is shown that th e extracted inversion-layer thickness, using the capacitance-voltage m ethod in a typical frequency range of 10-100 kHz, is unambiguous only for short channel metal-silicon dioxide-semiconductor field effect tra nsistors with channel length L-m less than 1 mu m. For long channel de vices having L-m>(5-10) mu m the extraction is very difficult due to t he dominant impact of the transmission line effect on the measured cap acitance value. The effective inversion-layer thickness is found to fo llow a 1/N-inv(m) law where N-inv is the inversion-layer concentration (m congruent to 1/3 in the weak inversion regime, m=1/2-1 in moderate inversion regime and m=1/3 in the strong inversion regime). In the st rong inversion regime the effective inversion-layer thickness is exact ly equal to the real inversion-layer centroid which can be rather accu rately described, as is shown, using the electric quantum limit approx imation. In the moderate and weak inversion regimes the dependence can be explained in terms of the real average charge centroid and an effe ctive conducting area under the gate which is smaller than the real ar ea due to fluctuations of the surface potential. The surface potential fluctuation can be attributed to dopant distribution fluctuations. (C ) 1998 American Institute of Physics.