HELIX_128_1
irradiation
-
One HELIX 128 chip in the AMS 0.8u CMOS technology, has been
irradiated at NMI in Utrecht Netherlands.
-
The radiation comes from a 7krad/hour Co 60 source. The irradiated
area was 2 x 2 cm.
-
The chip is irradiated in steps of about 30kRad over night,
and then measured over day.
HELIX bias
conditions :
|
bias
|
normal
|
after irr.
|
|
|
Ipipe
|
20
|
19
|
uA
|
|
Ilev
|
-3
|
-3
|
uA
|
|
Isha
|
200
|
200
|
uA
|
|
Ibuf
|
100
|
100
|
uA
|
|
Idrv
|
300
|
300
|
uA
|
|
Isf
|
20
|
20
|
uA
|
|
Ipre
|
200
|
300
|
uA
|
|
Vsf
|
1.5
|
0
|
V
|
|
Vfp
|
-0.3
|
-0.6
|
V
|
|
Vd
|
500
|
650
|
mV
|
|
Vdcl
|
1.2
|
1.45
|
V
|
The measurements are done like this:
-
For noise measurements 1000 "events" are read out
-
For the analog data , dummy_out and analog_out
are measured with a dual channel oscilloscope. The analog values are determined
by averaging 100 samples (2Gs/s) in the "plateau" area of the analog signal.
-
The test pulse is given to the internal test capacitors of
the chip.
-
For the dynamic range measurements 6 external capacitors
are used which connect to 6 channels. This allows us to scan through the
-20 to +20MIP input range. The input voltage is generated by a LeCroy pulse
generator.
measurement plots:
test pulse on input TP and notTP:
3.3V swing.
-
raw
data : (analog(t)-dummy(t))-(analog(t-1)-(dummy(t-1)), the blue line
is the pedestal (see data)
-
data
: raw data - pedestal.
RESULTS :
-
The chip is irradiated up to 160 krad.
After that two other points in each graph show the result of two extra
measurement. One after 2 days, and one after adjustment of the bias settings
(new optimum). The point at the dashed red line is at the last irradiation
step.
-
Results of current monitoring :
-
Result of gain measurements:
-
Results of noise determination:
-
Results on maximum frequency measurement:
-
Results on pulse shape scan :
The vertical line shows the sampling
point of the analog pipeline. This line is determined from the values measured
with the noise measurement with the use of the internal test signal. This
plot shows only the +3.5MIP result of the internal test pulse (average
of 32 channels).. It shows that the pulse shape is changing during irradiation
(becomes faster) and therefor the sample point is not anymore at the top
of the amplifier output signal.
The adjusted (black) line with
new bias setting has a different offset, but the amplitude and peak are
comparable with the non irradiated pulse. The small "pulse" is a measurement
error.
Note that the pulse shape is
not representative for the pulse shape of an individual signal.
The way the internal pulse is generated causes this behaviour. A pulse
to a individual channel gives a "clean" signal without the undershoot shown
here.
