164
Strain-Engineered MOSFETs
at a compressive stress level of 200 MPa. The noise PSDs increase for both of
the two measurements, as shown in Figure 6.8(b).
To obtain more accurate PSD data (as there are high uncertainties in PSD
measurements), a more averages are taken. More averaging is required to
differentiate even a few percent of change in the noise PSD. Since the drain
current 1/f noise PSD generally follows the following frequency dependence,
S f
S
Hz
f
( )
(1 )
I
I
D
D
=
γ
(6.38)
the noise magnitude and exponent can be extracted by a least-squares fit
(LSF) of the noise spectrum on a log-log plot. Over the frequency range
0
10
–19
10
–20
–2
4
0 MPa
189 MPa
2
0
∆I
D (σ)/I
D (0) (%)
∆I
G (σ)/I
G (0) (%)
S
ID (A
2
/Hz)
–4
–6
0
5 0
100
Stress (MPa)
Frequency (Hz)
(a)
(b)
150
200
80
90
100
FIGURE 6.7
n-MOSFET under compressive stress: (a) relative changes in drain and gate tunneling currents and (b) comparison of drain current noise PSDs for different stresses. (After Lim, J.-S.,
Strain Effects on Silicon CMOS Transistors: Threshold Voltage, Gate Tunneling Current, and
1/f Noise Characteristics, PhD thesis, University of Florida, 2007.)
12
10 –18
10 –19
10 –20
9
0
0 MPa
–0.8 V
–0.6 V
–0.6 V
–0.8 V
189 MPa
–1
–2
∆I
D (σ)/I
D (0) (%)
∆I
G (σ)/I
G (0) (%)
S
ID (A 2
/Hz)
3
0 0
5 0
100
Stress (MPa)
Frequency (Hz)
(a)
(b)
150
200
80
90
100
FIGURE 6.8
p-MOSFET under compressive stress: (a) relative changes in drain and gate tunneling currents and (b) comparison of drain current noise PSDs for different stresses. (After Lim, J.-S.,
Strain Effects on Silicon CMOS Transistors: Threshold Voltage, Gate Tunneling Current, and
1/f Noise Characteristics, PhD thesis, University of Florida, 2007.)