189
Noise in Strain-Engineered Devices
Figure 6.36 shows the average normalised drain current noise spectral density S I
/
Id
d
2 at f = 10 Hz as a function of the drain current I d at constant V ds of
–50 mV, with varying gate voltage for both n- and p-type SNWTs with different gate lengths and channel orientations. The normalised variations S I
/
Id
d
2
vs. I d exhibit a slope close to −1, which shows that the mobility fluctuation 1/f
noise model is dominant according to Equation (6.29). If the 1/f noise is due
to the carrier number fluctuations, S I
/
Id d
2 would have been independent of
the drain current, and S I
/
Id d
2 becomes proportional to (g m /I d ) 2 per Equation
(6.20). In the inset of Figure 6.36, a large slope deviation between S I
/
Id d
2 and
(g m /I d ) 2 in the subthreshold region further confirms the mobility fluctuation
mechanism. A similar form of Equation (6.26) depicting the empirical relation of the mobility fluctuation model [13] is given by
S f
I
fN
( )
Id
d
H
2
=
α
(6.54)
with α H being Hooge’s parameter and N the total number of carriers under the
gate. In the subthreshold region N is very small, and in SNWT it is typically
less than 20. The study is centred on the 1/f noise in the subthreshold region.
10
–5
Slope = –1
10 –6
10
–9
10
–9
10
–8
10
–7
10
–6
10
–8
10
–7
10
–7
d
2
> (Hz
–1
)
d
2
>
10
–8
10
–8
10
–7
10
–6
10
–5
I d (A)
I d (A)
~ (g m /I d )
2
, N
~ (g m /I d )
2 , P
L = 90 nm, <110>
L = 130 nm, <110>
L = 180 nm, <110>
L = 90 nm, <010>
FIGURE 6.36
Average normalised drain current spectral density at |V ds | = 50 mV and f = 10 Hz vs. drain current for both n- and p-type SNWTs with L = 90, 130, and 180 nm, respectively. The noise data of
90 nm n- and p-type SNWTs are compared with the corresponding (constant × (g m /I d ) 2 ) in the
inset. Open symbols, p-type; solid symbols, n-type; solid line, fitted by Equation (6.63). (After
Wei, C., Y.-Z. Xiong, X. Zhou, N. Singh, S. C. Rustagi, G. Q. Lo, and D.-L. Kwong, IEEE Electron
Dev. Lett., 30, 668–671, 2009. With permission [43].)
Noise in Strain-Engineered Devices
Figure 6.36 shows the average normalised drain current noise spectral density S I
/
Id
d
2 at f = 10 Hz as a function of the drain current I d at constant V ds of
–50 mV, with varying gate voltage for both n- and p-type SNWTs with different gate lengths and channel orientations. The normalised variations S I
/
Id
d
2
vs. I d exhibit a slope close to −1, which shows that the mobility fluctuation 1/f
noise model is dominant according to Equation (6.29). If the 1/f noise is due
to the carrier number fluctuations, S I
/
Id d
2 would have been independent of
the drain current, and S I
/
Id d
2 becomes proportional to (g m /I d ) 2 per Equation
(6.20). In the inset of Figure 6.36, a large slope deviation between S I
/
Id d
2 and
(g m /I d ) 2 in the subthreshold region further confirms the mobility fluctuation
mechanism. A similar form of Equation (6.26) depicting the empirical relation of the mobility fluctuation model [13] is given by
S f
I
fN
( )
Id
d
H
2
=
α
(6.54)
with α H being Hooge’s parameter and N the total number of carriers under the
gate. In the subthreshold region N is very small, and in SNWT it is typically
less than 20. The study is centred on the 1/f noise in the subthreshold region.
10
–5
Slope = –1
10 –6
10
–9
10
–9
10
–8
10
–7
10
–6
10
–8
10
–7
10
–7
d
2
> (Hz
–1
)
d
2
>
10
–8
10
–8
10
–7
10
–6
10
–5
I d (A)
I d (A)
~ (g m /I d )
2
, N
~ (g m /I d )
2 , P
L = 90 nm, <110>
L = 130 nm, <110>
L = 180 nm, <110>
L = 90 nm, <010>
FIGURE 6.36
Average normalised drain current spectral density at |V ds | = 50 mV and f = 10 Hz vs. drain current for both n- and p-type SNWTs with L = 90, 130, and 180 nm, respectively. The noise data of
90 nm n- and p-type SNWTs are compared with the corresponding (constant × (g m /I d ) 2 ) in the
inset. Open symbols, p-type; solid symbols, n-type; solid line, fitted by Equation (6.63). (After
Wei, C., Y.-Z. Xiong, X. Zhou, N. Singh, S. C. Rustagi, G. Q. Lo, and D.-L. Kwong, IEEE Electron
Dev. Lett., 30, 668–671, 2009. With permission [43].)