Characterization of prototype BTeV silicon pixel sensors before and after irradiation

1. Characterization of prototype BTeV silicon pixel sensors before and after irradiation Maria Rita Coluccia Simon Kwan Fermi National Accelerator Laboratory 2001 IEEE Nuclear Science Symposium, San Diego 3-10 Nov Friday, Nov 8, 2001

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 sensor Common p-stop Individual p-stop p implant n implant n implant p implant gap between n and p gap between n and p gap between adjacent 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 designs Three different designs. For the test cell sensors: 10 guard rings 18 guard rings For the FPIX1 sensors: 11 guard rings metal active area p-implant 10 GR 11-18 GR 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: • 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 • 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 Fluence: 8 x 1013 p/cm2 After irradiation Ileak significantly increases, but the problem associated with the large current can be minimized by operating at reduced temperature. Maria R. Coluccia - Fermilab

13. Leakage current: fluence dependence Maria R. Coluccia - Fermilab

14. I-V curves after irradiation with various fluences standard sensors oxygenated sensors We see no breakdown Voltage below 500 V for the test cell sensors. Maria R. Coluccia - Fermilab

15. Capacitance: temperature and frequency dependence after irradiation Individual p-stop sensor (10 GR) fluence: 4 x 1014 p/cm2 23 oC 40 KHz A logarithmic change in frequency gives the same pattern of C-V’s as a linear change in temperature. Maria R. Coluccia - Fermilab

16. Depletion Voltage No difference between oxygenated and standard sensors observed! Maria R. Coluccia - Fermilab

17. Guard Rings: Voltage Distribution Before and After Irradiation FPIX1_SCP oxygenated (11 GR) before after Innermost guard ring Innermost guard ring 29 V Measurements performed with the innermost guard ring floating. We have a potential drop across the device edges after type inversion. 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 Dicing • We 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 Maria R. Coluccia - Fermilab