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Principles of Semiconductor Devices ( 집적 회로 소자 ) Principles of Semiconductor Devices ( 집적 회로 소자 ) Hanyang University Division of Electronics & Computer Engineering Semiconductor Lab Han Sub Yoon
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Figure 8.1 (a) Schematic cross section and (b) the circuit symbol of an N-channel MOSFET.
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Figure 8.2 Types of MOSFETs.
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Figure 8.3 Cross-sectional illustrations of a MOSFET in (a) off and (b) on modes, along with (c) the corresponding current voltage characteristics.
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Figure 8.4 Two-dimensional energy-band diagram for the semiconductor part of an N-channel MOSFET in the flat-band condition. The two different colors in the conduction band indicate the two different types of doping: N type in the source and drain regions, and P type in the body. Darker colors indicate higher carrier concentration, and the nearly white areas indicate the depletion region.
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Figure 8.5 Two-dimensional energy-band diagrams for an N-channel MOSFET acting as a switch in (a) off mode and (b) on mode. The two colors in the conduction band indicate the concentrations of electrons and holes: darker colors correspond to higher carrier concentrations, whereas the nearly white areas indicate depleted regions. Note that the depleted regions correspond to the areas with sloped energy bands and therefore with existence of built-in and externally applied electric field.
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Figure 8.6 (a) The circuit of CMOS inverter. (b) Typical input/output signals.
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Figure 8.7 Illustration of the body effect. (a) V SB voltage increases the barrier between the electrons in the source and the drain. (b) The surface potential of 2 F does not reduce the barrier sufficiently for the electrons to be able to move into the channel. (c) The surface potential needed to form the channel is 2 F V SB.
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Figure 8.8 (a) Cross section of a MOSFET in the saturation region. (b) The corresponding I D V DS characteristics.
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Figure 8.9 Two-dimensional energy-band diagrams for an N-channel MOSFET in saturation due to channel pinch off. A comparison of the smaller V DS bias in (a) to the larger V DS value in (b) shows that the channel is shortened by the increased drain-to-source bias, but the concentration of electrons in the channel is not changed. As in the waterfall analogy, the drain current is limited by the concentration of the electrons in the channel and not by the height of the fall.
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Figure 8.10 (a) Output and (b) transfer characteristics of a MOSFET.
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Figure 8.11 Output characteristics corresponding to SPICE LEVEL 1 model. Solid lines, Eq. (8.20); dashed lines, saturation current.
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Figure 8.12 N-channel MOSFET diagram, indicating the surface potential at the source and the drain ends of the channel.
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Figure 8.13 Comparison of LEVEL 1, LEVEL 2, and LEVEL 3 models.
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Figure 8.14 Influence of mobility reduction with gate voltage on (a) transfer and (b) output characteristics.
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