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data matrix barcodes for visual basic 3.fm Page 94 Friday, January 18, 2002 9:00 AM in Microsoft Office Generation ECC200 in Microsoft Office 3.fm Page 94 Friday, January 18, 2002 9:00 AM

chapter3.fm Page 94 Friday, January 18, 2002 9:00 AM using none tocreate none for asp.net web,windows applicationdata matrix vb.net THE DEVICES Java Reporting Library-Jasper Reports 3 . 0.9 0.85 0.

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4 - 2.5. The effect of the well bias none none on the threshold voltage of an NMOS transistor is plotted in for typical values of . 2 F. = 0.6 V and = 0.4 V0.

5. A none none negative bias on the well or substrate causes the threshold to increase from 0.45 V to 0.

85 V. Note also that VSB always has to be larger than -0.6 V in an NMOS.

If not, the sourcebody diode becomes forward biased, which deteriorates the transistor operation.. V (V). Effect of body-bias on threshold. Example 3.5 Threshold Voltag e of a PMOS Transistor An PMOS transistor has a threshold voltage of -0.4 V, while the body-effect coefficient equals -0.

4. Compute the threshold voltage for VSB = -2.5 V.

2 F = 0.6 V. Using Eq.

(3.19), we obtain VT(-2.5 V) = -0.

4 - 0.4 ((2.5+0.

6)0.5 - 0.60.

5) V = -0.79 V, which is twice the threshold under zero-bias conditions!. Resistive Operation Assume n none for none ow that VGS > VT and that a small voltage, VDS, is applied between drain and source. The voltage difference causes a current ID to flow from drain to source (Figure 3.15).

Using a simple analysis, a first-order expression of the current as a function of VGS and VDS can be obtained.. VGS S G VDS D + L x n+ ID V(x). p-substrate B Figure 3.15 voltages. NMOS transistor with bias At a point x along the chann none for none el, the voltage is V(x), and the gate-to-channel voltage at that point equals VGS V(x). Under the assumption that this voltage exceeds the threshold voltage all along the channel, the induced channel charge per unit area at point x can be computed..

chapter3.fm Page 95 Friday, January 18, 2002 9:00 AM Section 3.3 The MOS(FET) Transistor Q i ( x ) = C ox [ V GS none none V ( x ) V T ] Cox stands for the capacitance per unit area presented by the gate oxide, and equals ox C ox = -----t ox. (3.20). (3.21). with ox = 3.97 o = 3.5 10-11 F/m the oxide permittivity, and tox is the thickness of the oxide.

The latter which is 10 nm (= 100 ) or smaller for contemporary processes. For an oxide thickness of 5 nm, this translates into an oxide capacitance of 7 fF/ m2. The current is given as the product of the drift velocity of the carriers n and the available charge.

Due to charge conservation, it is a constant over the length of the channel. W is the width of the channel in a direction perpendicular to the current flow. ID = n ( x )Q i ( x )W (3.

22). The electron velocity is rel none for none ated to the electric field through a parameter called the mobility n (expressed in m2/V s). The mobility is a complex function of crystal structure, and local electrical field. In general, an empirical value is used.

n = n ( x ) = n dV dx Combining Eq. (3.20) Eq.

(3.23) yields I D dx = n C ox W ( V GS V V T )dV (3.24) (3.

23). Integrating the equation ove r the length of the channel L yields the voltage-current relation of the transistor. V DS 2 V DS 2 I D = k"n W ( V GS V T )V DS -------- = k n ( V GS V T )V DS ----------2 2 L k"n is called the process transconductance parameter and equals n ox k" n = n C ox = -----------t ox (3.26).

(3.25). The product of the process t ransconductance k"n and the (W/L) ratio of an (NMOS) transistor is called the gain factor kn of the device. For smaller values of VDS, the quadratic factor in Eq. (3.

25) can be ignored, and we observe a linear dependence between VDS and ID. The operation region where Eq. (3.

25) holds is hence called the resistive or linear region. One of its main properties is that it displays a continuous conductive channel between source and drain regions. NOTICE: The W and L parameters in Eq.

(3.25) represent the effective channel width and length of the transistor. These values differ from the dimensions drawn on the layout due to effects such as lateral diffusion of the source and drain regions (L), and the encroachment of the isolating field oxide (W).

In the remainder of the text, W and L will.
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