Maria Rita Coluccia Simon Kwan Fermi National Accelerator Laboratory
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Transcript of Maria Rita Coluccia Simon Kwan Fermi National Accelerator Laboratory
Characterization of prototype BTeV silicon pixel sensors
before and after irradiation
Maria Rita ColucciaSimon Kwan
Fermi National Accelerator Laboratory
2001 IEEE Nuclear Science Symposium, San Diego 3-10 Nov Friday, Nov 8, 2001
Maria R. Coluccia - Fermilab 2
Outline
• BTeV SINTEF pixel sensor prototypes• Proton Irradiation at IUCF• Characteristics before and after irradiation• Conclusions
Maria R. Coluccia - Fermilab 3
BTeV SINTEF silicon pixel sensor prototypes tested
• n+/n/p configuration that allows them to operate partially depleted• Sensor thickness: 270 um• Low resistivity material: 1.0-1.5 KOhmxcm• P-stop electrode isolation technique• Oxygenated and non-oxygenated wafers• Various guard ring configurations
Maria R. Coluccia - Fermilab 4
P-stop sensorCommon p-stop Individual p-stop
n implantp implant gap between n and pgap between adjacent p
p implant n implantgap between n and p
bump pad
Maria R. Coluccia - Fermilab 5
Summary of the implant widths and gaps
We tested two different pixel arrays:Test cell sensors (12x92 cells) and FPIX1 sensors (18x160 cells)
Maria R. Coluccia - Fermilab 6
P-side guard ring designsThree different designs.
For the test cell sensors: 10 guard rings 18 guard rings
For the FPIX1 sensors: 11 guard rings
active area
10 GR 11-18 GR
metal
p-implant
Maria R. Coluccia - Fermilab 7
I-V curves before irradiation for standard SINTEF test cell
sensors
• 7 wafers tested • A few sensors had bad performance (high leakage current, low breakdown voltage) but this doesn’t depend on the p-stop layout
Maria R. Coluccia - Fermilab 8
I-V curves before irradiation for oxygenated SINTEF test cell
sensors
Maria R. Coluccia - Fermilab 9
I-V curves before irradiation for standard SINTEF FPIX1 sensors
For all these sensors we have a Vbreak of 300 V.This is due to the different p-implant width:1. For FPIX1_SIP (single individual p-stop) the gap between 2
adjacent p-stop rings is 3 um compared to 5 um in the test cell sensors
2. For FPIX1_SCP (single common p-stop) the p-implant width is 3um compared to 9um in the test cell sensors
Maria R. Coluccia - Fermilab 10
Breakdown Voltage Distribution
•Very high values (700 V) without significant differences between individual and common p-stop sensors and between oxygenated and standard sensors•Very high yield for the SINTEF wafers
Maria R. Coluccia - Fermilab 11
Irradiation test at IUCF (Indiana University Cyclotron Facility) with a 200 MeV proton beam
• 2 test cell standard sensors (individual and common p-stop) with 8 x 1013 p/cm2 • 4 FPIX1 sensors with 2 x 1014 p/cm2 : 2 oxygenated (individual and common p-stop) and 2 standard (individual and common p-stop)• 4 test cells sensors with 4 x 1014 p/cm2: 2 oxygenated (individual and common p-stop) and 2 standard (individual and common p-stop)Irradiation was done in air at room temperature.After irradiation the tested devices have been kept at –15 oC
Maria R. Coluccia - Fermilab 12
Leakage current: temperature dependence
After irradiation Ileak significantly increases, but the problem associated with the large current can be minimized by operating at reduced temperature.
)2
(2 Tk
E
leakB
g
eTI
Fluence: 8 x 1013 p/cm2
Maria R. Coluccia - Fermilab 13
Leakage current: fluence dependence
cmACT
/107.2 17230
eqTVI
)(
Maria R. Coluccia - Fermilab 14
I-V curves after irradiation with various fluences
We see no breakdown Voltage below 500 V for the test cell sensors.
standard sensors oxygenated sensors
Maria R. Coluccia - Fermilab 15
Capacitance: temperature and frequency dependence after
irradiation
A logarithmic change in frequency gives the same pattern of C-V’s as a linear change in temperature.
23 oC 40 KHz
Individual p-stop sensor (10 GR) fluence: 4 x 1014 p/cm2
Maria R. Coluccia - Fermilab 16
Depletion VoltageNo difference between oxygenated and standard sensors observed!
Maria R. Coluccia - Fermilab 17
Guard Rings: Voltage Distribution Before and After
Irradiation
Innermost guard ring
FPIX1_SCP oxygenated (11 GR)before after
Measurements performed with the innermost guard ring floating.We have a potential drop across the device edges after type inversion.
Innermost guard ring
29 V
Maria R. Coluccia - Fermilab 18
Conclusions•Excellent results for the SINTEF sensors•Very high yield•No significant difference between common and individual p-stop layout•Important effects introduced by different p- implant widths•No difference between oxygenated and standard sensors before and after irradiation for SINTEF sensors•More investigations needed for the guard ring structures•Next step: to study performance of the sensors bonded to ROC and charge collection efficiency before and after irradiation
Maria R. Coluccia - Fermilab 19
SINTEF wafer layout
We tested two different pixel arrays:1)Test cell sensors (12x92 cells)2) FPIX1 sensors (18x160 cells)
Maria R. Coluccia - Fermilab 20
After DicingWe diced several wafer:
• Some sensors present different result after dicing (high Ileak, low Vbreak)• Cleaning carefully the surface and the edges of the sensors we can restore the performances that we had before • All the sensors with three guard rings present performances degradation after dicing