1 marco ferrero with nicolo’ cartiglia, francesca cenna, fabio ravera, universita’ degli studi...
TRANSCRIPT
PRELIMINARY STUDY TO DETERMINE THE DOPING
PROFILE OF LGAD DETECTOR
1
Marco Ferrero
With Nicolo’ Cartiglia, Francesca Cenna, Fabio Ravera,
Universita’ degli Studi di Torino & INFN
TREDI2015 WORKSHOP - TRENTO
OUTLINE
• THEORY OF EXTRAPOLATION OF DOPING PROFILE FROM CAPACITANCE-VOLTAGE CURVES
• LABORATORY SETUP
• DESCRIPTION OF THE METHOD FOR DETECTORS WITHOUT GAIN
• PRESENTATION OF THE RESULTS
• FUTURE GOALS2
Mar
co F
erre
ro, U
nive
rsita
’ Di T
orin
o, IN
FN, T
redi
2015
Measuring doping profile of a pn junction using the Capacitance-Voltage Curve
p type n+ typeD
eple
ted
Zone
Depleted zone can be considered as a
Parallel Plate Capacitor
Case of NA << NDCapacitance depends upon the area and
width of depleted zone
Width of depleted zone depends upon Voltage bias and doping concentration
3
Mar
co F
erre
ro, U
nive
rsita
’ Di T
orin
o, IN
FN, T
redi
2015
Detector as a Trapeziodal Parallel Plate Capacitor
x
Plate A
Plate B
Plate A
Plate B
Parallel plate capacitor
Trapezoidal parallel plate
capacitor
Plate A ≠ Plate B
n++ impiantation
p substrate
Detector CNMRun 6474
W9B6-Gain 1
4
Mar
co F
erre
ro, U
nive
rsita
’ Di T
orin
o, IN
FN, T
redi
2015
Capacitance of a Trapezoidal parallel plate capacitor
a side of n-implantationb side of b substrated width of detector
By the Gauss’ Theorem
Additional contributionconstant that depends upon the geometry of the detector
parallel plate capacitor
5
x
Plate A
Plate B
Mar
co F
erre
ro, U
nive
rsita
’ Di T
orin
o, IN
FN, T
redi
2015
Capacitance-Voltage Curve Setup
Device
Laboratory PC
Power supplyKeithley 2410
LCR MeterAgilent E4980A
6
Mar
co F
erre
ro, U
nive
rsita
’ Di T
orin
o, IN
FN, T
redi
2015
Setup test: measurement of a known capacitor
RESONANCEVerify the setup using a
known capacitor
Good frequency range of measurement [10 kHz ; 2 MHz]
CORRECT Value
(~ 34pF)
Scan in frequency from
50 Hz to 2 MHz
34 pF
7
Mar
co F
erre
ro, U
nive
rsita
’ Di T
orin
o, IN
FN, T
redi
2015
By scanning in frequency at fixed Voltage, a variation of the detector’s capacitance
is observed
Capacitance-Frequency curve
Capacitance-frequency curve shows a variation of
detector’s area
The sensor acts as a low pass RC filter
The detector is an extended network of resistors and capacitors
Due to a smaller effective Area
8
Mar
co F
erre
ro, U
nive
rsita
’ Di T
orin
o, IN
FN, T
redi
2015
Capacitance-Frequency curves at different Voltage
C-f (2 Volt)
C-f (25 Volt)
C-f (36 Volt)
We need to find a frequency that works well at every bias voltage.The measurements should follow the known relation between C and V.
9
Mar
co F
erre
ro, U
nive
rsita
’ Di T
orin
o, IN
FN, T
redi
2015
Fit Equation
30kHz is a good frequency to work
Fit to the C-V curves with the expected dependencyto select the good working frequency
Voltage [V]
Capa
cita
nce
[F]
0 10 20 30 40 50 60 700
1E-11
2E-11
3E-11
4E-11
5E-11
6E-11
7E-11
f(x) = 3.10648070008886E-11 x^-0.275762571429319
f(x) = 5.03967362522733E-11 x^-0.392076898306343
f(x) = 8.8015913525478E-11 x^-0.518119141651436
Frequency of 30kHzFrequency of 30kHzFrequancy of 500kHzFrequency of 500kHzFrequancy of 1MHzFrequency of 1MHz
10
Mar
co F
erre
ro, U
nive
rsita
’ Di T
orin
o, IN
FN, T
redi
2015
Effect of the Trapezoidal correction
0 20 40 60 80 100 120 140 160 1800
5E+021
1E+022
1.5E+022
2E+022
2.5E+022
No Cg correctionCg correction
Voltage Bias [V]
1/C2 [
F-2]
For a parallel plate capacitor:1/C2 vs Vbias should be a straight line
11
Mar
co F
erre
ro, U
nive
rsita
’ Di T
orin
o, IN
FN, T
redi
2015
For detector W9B6-Gain 1Cg is about 4,69 pF
Parallel plate
Trapezoidal plate
Capacitance-Voltage and 1/(C2)-Voltage curve
1/(C2)-V Curve acquired at 30 kHz(Cg Corrected)
Above 120 V the measurement is hard to understand
12
Mar
co F
erre
ro, U
nive
rsita
’ Di T
orin
o, IN
FN, T
redi
2015
Width of the depleted zone
Note: 360 um is too large
It’s necessary improve the absolute
scale, i.e. precise knowledge of the Cg
correction
0 20 40 60 80 100 120 140-20
30
80
130
180
230
280
330
380f(x) = 36.9236595482781 x^0.502534631985136
Fit Equation:
Wid
th o
f dep
lete
d zo
ne [u
m]
Voltage Bias [V]
Respected the relationship between width of depleted zone and Voltage bias
13
Mar
co F
erre
ro, U
nive
rsita
’ Di T
orin
o, IN
FN, T
redi
2015
Extraction of the Doping profileN
A [c
m-3
]
w [um]
To extrapolate the doping profile: calculate the derivative of 1/(C2)-V curve
8.98134439052327
9.74682860025615
13.2389244704591
19.0830722845919
24.9675892540797
31.3157837860146
38.1323733264888
45.5555147206352
48.4120125393613
55.2540970739535
62.7938868820074
70.7943118760032
79.0653147844596
88.2621182301991
97.2175237857759
107.421349587852
117.937277643519
128.3458738289450.00E+005.00E+111.00E+121.50E+122.00E+122.50E+123.00E+123.50E+124.00E+12
Due to the Built-in Voltage, the depth is already 9 microns at Voltage Bias=0 14
Mar
co F
erre
ro, U
nive
rsita
’ Di T
orin
o, IN
FN, T
redi
2015
VALUE CONSISTENT WITH EXPECTATIONS
Study of LGAD Detector
0 20 40 60 80 100 1200
2E-11
4E-11
6E-11
8E-11
1E-10
1.2E-10
1.4E-10
1.6E-10
1.8E-10
2E-10
Capa
cita
nce
[F]
Voltage [V]
In LGAD detectors, the value of capacitance is increasing with Voltage.
Why??
It’s necessary to study and better understand the Capacitance-Voltage
curve of a Detector with gain.
15
Mar
co F
erre
ro, U
nive
rsita
’ Di T
orin
o, IN
FN, T
redi
2015
p
n++p+
SUMMARY
The CV method illustrated allows the measurement of the doping profile in silicon sensors.The method gives the correct doping concentration for standard pin diods
Application of the method on LGAD sensors under study
Need to improve the Cg correction to the capacitance for a better width absolute scale
16
Mar
co F
erre
ro, U
nive
rsita
’ Di T
orin
o, IN
FN, T
redi
2015