Week-15-DC-Testing-2

Week-15-DC-Testing-2 - Electrical Characterization of the...

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10/06/09 Dr. Kian Kaviani - Spring 2009 EE4 1 Electrical Characterization of the Finished Wafers Part – II Dr. Kian Kaviani Hsieh Ming Electrical Engineering USC Viterbi School of Engineering
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10/06/09 Dr. Kian Kaviani - Spring 2009 EE4 2 Metal Oxide Semiconductor Field Effect Transistors (MOSFETs)
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10/06/09 Dr. Kian Kaviani - Spring 2009 EE4 3 Assumptions used for MOSFET Model 1. We assume that we have long channels (L > 5 micrometer) 1. We assume the mobility of electrons is constant in the channel. 3. We assume that the shape of the channel (same as the MOS inversion layer) as a function of the drain – source bias changes linearly ( g radual c hannel a pproximation , GCA ). 4. Furthermore, we assume the electric along the channel is the dominant electric field and the component of electric perpendicular to the channel inside the semiconductor is negligible. For long channel MOSFETs this is a fairly good approximation.
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10/06/09 Dr. Kian Kaviani - Spring 2009 EE4 4 I – V Characteristics of MOSFETs
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10/06/09 Dr. Kian Kaviani - Spring 2009 EE4 5 Square Law Model: Linear Regime where: Ids : Drain – to - source current [A] μ : Average mobility of carriers in the channel [cm 2 /V.sec] C 0 : Capacitance per unit area of the MOS structure [F/cm 2 ] W : MOSFET Width ( μ m) L : MOSFET Gate Length ( μ m) V gs : Gate –to-Source Voltage [V] V th : Threshold Voltage [V] V ds : Drain-to-Source Voltage [V]
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10/06/09 Dr. Kian Kaviani - Spring 2009 EE4 6 Linear – Saturation Transition The above relationship represent the “linear region” of the MOSFET I – V characteristic, shown in the figure. In the regime of Vds > (V ds ) sat , where (V ds ) sat = V dss represent the drain – to-source voltage, beyond which any increase in the value of V ds would not bring about any further increase in the I ds . This regime is called saturation regime.
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10/06/09 Dr. Kian Kaviani - Spring 2009 EE4 7 Saturation Region Saturation regime is the most important
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Week-15-DC-Testing-2 - Electrical Characterization of the...

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