Introduction to radiation-resistant semiconductor devices and circuits

g m / I d
g m / I d
30
20
10
0
20
10
0
10 -4 10 -3 10 -2 10 -1 10 0
I d / W [A/m]
NMOS: 0 Mrad
NMOS: 5 Mrad
10 1
10 2
Figure 7 shows the normalized transconductance gm/Id vs. Id/W before and after
irradiation. (36) For the selected channel length this representation allows direct
scaling to any device width at a given current density. For example, to operate a
1.2 μm NMOS transistor in moderate inversion one might choose a normalized
drain current Id /W= 0.3 A/m, yielding Id= 0.3 mA for a 1 mm wide transistor. The
normalized transconductance gm /Id= 15.4 V -1 or gm= 4.6 mS. After exposure to
5 Mrad gm /Id= 11.8 V -1 or gm= 3.5 mS. Typically, the NMOS devices suffer a 20
to 30% degradation, whereas the PMOS devices are quite insensitive to radiation,
with only a few percent decrease in transconductance at 5 Mrad. About half of the
observed change at 5 Mrad occurred before attaining a dose of 1 Mrad.
Extensive noise measurements have been performed at the University of
Pennsylvania (38) and by a UCSC/LBNL group. (36) In the latter, spectral noise
density was measured over a frequency range of 10 kHz to 10 MHz before and
g m / I d
g m / I d
40
30
20
10
0
30
20
10
0
L= 1.2
L= 2.2
L= 3.2
10 -4 10 -3
10 -2 10 -1
I d /W [A/m]
PMOS: 0 Mrad
PMOS: 5 Mrad
FIGURE 7. Normalized transconductance g m / I d vs. drain current I d /W for NMOS and
PMOS transistors with channel lengths of 1.2, 2.2 and 3.2 μm before and after 60 Co
irradiation to 5 Mrad (Si).
10 0
10 1
17
10 2