IV measurement
IV measurement:
There are several parameters could extraxted from IV measurement such as threshould voltage and resistance :

Threshould voltage:
The threshold voltage is a significant parameter for MOSFET. It is defined as a voltage when
the device turns on, where the surface potential is equal to twice the Fermi potential
Φs= 2Φf
Vt= Vfb+2Φf + (2qksϵ0NA2Φf /Cox)^{0.5}
^{
}
There are several methods to extract Vt, such as extrapolation in the linear region method,
transconductance extrapolation method in the linear region, secondderivative method, ratio
method, transition method, second derivative logarithmic method; nonlinear optimization
method and integral method .All of these methods give slightly different values of Vt. the transconductance extrapolation method, which uses a
transconductance (gm) versus gate voltage curve. Vt is the gate voltage maximum slope at the point as shown in following figure

Subthreshold slope (S.S):
This parameter determines how fast the device switches off and it is extracted from the slope of log Id versus Vg curve .The theoretical value is given by the following equation:
S.S= [ d(logId)/dVG]^{1
}=2.3 kBT (1+Cdm/Cox)/q
Cdm depletion layer capacitance. The theoretical minimum value for a MOSFET is 60mV/dec. next figure illustrate the curve between drain current and gate voltage whereit could determine subthershold slope .

Resistance:
Series resistance becomes more important with the down scaling of MOS devices, since in long channel devices the channel resistance is much larger than the contact resistance. From equation 23 the channel resistance could be define by
Rch = Leff / µeff CoxWeff (VgVt)
Leff= LΔL
The total resistance is channel resistance and source –drain resistance
Rm= Vds/Ids= Rsd +Rch
Rm = Rsd +A (L ΔL)
Where A= (µeff CoxWeff (VgVt))^{1}
By drawing the relation between channel length and resistance for different gate voltage the channel resistance is the y value where the lines are intersecting and the x value is ΔL.This
method is not accurate .Therefore, another method have been used to get more accurate value.
Terada and Muta pointed out another method to extract channel resistance which define
Rch=ƍ Leff/W ƍ channel sheet resistance
Rm = Rsd + ƍ /W (L ΔL) Rm= A + (ƍ/W) L
By drawing this equation for different gate voltages A is the intercept point, and the slop is ƍ/W. The slope of the relation between ƍ/W and A is ΔL and the intercept is the source drain
resistance.
 Kazuo Terada and Hiroki Muta ,A new method to determine effective MOSFET channel length , Japaness Journal of applied physics Vol.18,No,5,May1979.
 K. Terada and H. Muta. "A New Method to Determine Effective MOSFET Channel Length". Jap. J. of Appl. Phys., 18:953{959, 1979.
 A. OrtizCondea , F.J. Garc ,S a ancheza, J.J. Liou b,1, A. Cerdeira c,M. Estrada c, Y.Yue d ,A review of recent MOSFET threshold voltage extraction methods,
Microelectronics eliability 42 (2002) 583–596.