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


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


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


Summary of the implant widths and gaps

We tested two different pixel arrays:Test cell sensors (12x92 cells) and FPIX1 sensors (18x160 cells)


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


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


I-V curves before irradiation for oxygenated SINTEF test cell

sensors


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


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


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


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


Leakage current: fluence dependence

cmACT

/107.2 17230

eqTVI

)(


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


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


Depletion VoltageNo difference between oxygenated and standard sensors observed!


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


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


SINTEF wafer layout

We tested two different pixel arrays:1)Test cell sensors (12x92 cells)2) FPIX1 sensors (18x160 cells)


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

Documents

Maria Rita Coluccia Simon Kwan Fermi National Accelerator Laboratory