Chapter 4 Four-port RF MOSFET Model Parameter Extraction
4.3 Extraction and analysis of parameters in linear region
arameters extraction of four-port devices operating in linear region. For four-port devic
uation (4.2), the subscript value represents the port number for the measurement respectively. In this study, port1, 2, 3, and 4 represent that gate, source, drain, and body respectively. The result shows that the extracted parasitic RL is not the frequency independent parameters, it may be has a high frequency term without considered in the equivalent circuit, and common part of the resistance is smaller than the resistances come from metal connection between metal3 and metal8, the parasitic RL parameters are extracted at low frequency.
4.3 Extraction and analysis of parameters in linear region
In this section, we will discuss that p
es, when gate voltage is smaller than the threshold voltage and Vds=0V, the equivalent circuit of four-port devices with parasitic
RL parameters and substrate network components can be shown in Fig. 4.5. The differentiation between two-port and four-port devices is the substrate networks that connection of the body and DNW terminal is not tied together in four-port devices.
4.3.1 Extraction of parameters in linear region
The capacitances of the equivalent circuit are extracted from the intrinsic Y parameters at low frequency conventionally, the circuit is very simple, we assume that
extraction quation.
For the four-port MOSFET, Ward-Dutton description leads to a total of 16 ed as follows in a 4x4 matrix
(4.3)
terminal current does not contain any conductive current component. The elements in each column and low must sum to zero owing to the constraints imposed by charge conservation. As gate capacitances for example, the gate capacitances relationship cab be represented as
the components between gate and the other terminals can be considered as purely capacitances, the terminals resistance is finite in the frequency of our consideration, and it will be smaller than the impedance of the captaincies, according to the assumption, Rs and Rd can be neglected at low frequency to simplified the
e
transcapacitances. This set of 16 elements can be organiz .
⎥
⎥ ⎥
⎤
⎢
⎢ ⎢
⎡
=
bb bd
bs bg
db dd
ds dg
sb sd
ss sg
gb gd
gs
gg
C C C
C C
In this bias condition, there is not current flow through the devices, so that
⎥
⎥
⎢ ⎦
⎢
⎣ C C C C
C C
C C
C C
C C
gb gd
gs
gg
C C C
C = + +
(4.4) performing the Y parameter analysis of the equivalent circuit, the Y11 Bycomponent cab be derived as
bulk gb
R C j C
Following the Y parameter analysis, the components of Yxy(x=1~4, y=1~4) also can be derived, under the assumption
ω
2Rbulk2 Cgb2 <<1, the capacitances extraction equation can be simplified as bellow:( ) ( ) / ω Im ( ) / ω
The proposed de-embedding method is simpler than that of two-port 4T devices, and the capacitances can be extracted form the intrinsic Y matrix at low frequency directly, especially source junction capacitance, it is hardly to extract Cjs in a
ected together.
, the equivalent circuit is plotted in Fig. 4.6, extraction of capacitance at Vg=0V (4.6) to be suitable for use at this c
traditional two-port 3T CS MOSFET because source and body conn
The substrate resistance extraction tends to use the method discussed in the two-port CS configuration devices, the 2x2 matrix will be obtained by using the port reduction method that discussed in session 2.2.3, the remaining parameters Rs_diff, Rd_diff, and Cdnw also can be extraction by the reduced 2x2 Y matrix that bias at Vg=Vd=Vs=Vb=0V in other words.
Similarly, when MOSFETs operate at the strong inversion region and at Vd=Vs=Vb=0V
ondition, and the channel resistance will be extracted in the 2x2 matrix that reduce from the 4x4 matrix.
4.3.2 Analysis of parameters in linear region
The extracted capacitances are plotted as a function frequency in Fig.4.7 and Fig.
4.8, the extracted capacitances Cgg, Cgs and Cgs have weak frequency dependence at low frequency, and will be increase with the frequency increasing, there are some inductances without de-embedding completely to cause the behavior at high frequency
e of the existence of Rblk in equivalent circuit.
capacitances are well proportioned to the NF. As gate voltage increases, the channel charges build up to increase the intrinsic component of the extracted capacitances and Cgs is larger than the Cgd at Vgs=1.2V
there
.
rain to channel rather than body in the strong inversion region, the whole Cgb capacitance which through the active channel area to source/drain region is very small and can be neglected, the value of the Cgb is close to zero at Vg=1.2V. The extracted junction capacitances also show that the value of Cjs is larger than that of Cjd, becaus
junction than the drain and gate bias independent almost.
The geometry dependence of the optimizing resistances is shown in Fig. 4.11, it is known that R
. Conversely, the extracted capacitances Cgb, Cjs, and Cjd will be decease as the frequency increase, Cgb is extracted from the imaginary part of the intrinsic Y parameters in equation (4.6), and there is a frequency component in the denominator with the RC component, In other words, the capacitances Cgb, Cjs, and Cjd will be decrease as frequency increasing becaus
The geometry dependence of the optimizing capacitances are shown in Fig. 4.9 and Fig. 4.10, it shows that the
, because are one source junction than the drain, the extrinsic capacitances with gate bias dependency of source is more than drain
When the channel charge can be supplied by source/d
e there is one source
g_poly is gate bias insensitively and dominate the total resistance in
shorter devices, it also show that RG is well proportional to reciprocal function of NF.