1. FE-I4 irradiated chip tests at low temperature M. Menouni, P. Breugnon, A. Rozanov (CPPM - Aix-Marseille Université)

2. September 9, 2013irradiated FE-I4 tests at low temperature2 Introduction  The FE-I4-B chip number 162 was irradiated in 2012 at CERN PS with 24 GeV protons close to the region of end of columns  It received a total dose of 1200 Mrad (800 Mrad + 400 Mrad)  Tests at room temperature  Analog Tests  Threshold level measurement and adjustment  Threshold Scan and difficulties to tune  Partial Tune results  Tests at low temperature (-26 °C)  Out1 DC levels measurements  PrmpVbp I(V) measurements  Conclusion

3. September 9, 2013irradiated FE-I4 tests at low temperature3 Analog Test  Configuration parameters : Amp2Vbn=79 Amp2Vbp=85 Amp2VbpFoll=26 Amp2Vbpf=40 PrmpVbp=43 PrmpVbpf=100 Vthin_AltFine=120 TDACVbp =150  Power : Ivddd=219 mA and Ivdda= 422 mA Analog Test with Amp2Vbpf=40 and Vcal=400Analog Test with Amp2Vbpf=40 and Vcal=1000

4. Effective Threshold measurement  DC levels measurements through OABUF  The effective threshold value becomes high because of irradiation  For the default value of Vthin_Altfine (= 120)  Chip 162 : The mean value of measured VthEff is 0.85V  Measured VthEff around 1.15 V for the chip 165  Decreasing the Vthin_Altfine to the minimum value does not help well  The threshold still high  >30000 e- beam spot center region  In order to decrease the effective threshold:  TDACVbp is set to the highest allowed value 255 instead of the standard value of 150  The Vtheff is increased to 0.933 V.  The resultant threshold is ~6000 e-  Drawback : increase the TDAC step  For TDACVbp=255, the Analog test is OK with VCAL=400 September 9, 2013irradiated FE-I4 tests at low temperature4

5. September 9, 2013irradiated FE-I4 tests at low temperature5 Threshold Scan  Threshold histogram before tuning  Mean value=6269 e- and Sigma =840 e-  The majority of pixels have a reasonable noise : 150 e- RMS  This noise reaches 900 e- RMS in the beam spot center region (most irradiated region)  Many pixels in 2 columns 15 and 16 are always at 1 (counting of 100%) Broken Columns : 15 and 16

6. September 9, 2013irradiated FE-I4 tests at low temperature6 TDAC Tune  DAC TUNE launched with a target threshold of 6500 e-  A strange resultant TDAC map. Only 2 values 16 and 24 are used for tune  Most of TDAC values are set to 16  TDAC = 24 in the beam spot center region  High disparity between thresholds in high and low irradiated regions makes the tuning failed  In order to make the TDAC Tune possible :  Regions with a very high threshold are disabled  DC number 16 to 28 are disabled  The 2 columns in the left-middle of the chip are also disabled  DC number 8 to 9 disabled

7. September 9, 2013irradiated FE-I4 tests at low temperature7 TDAC Tune results  Threshold Scan at room temperature  Threshold histogram after tuning : Mean value=5511 e- Sigma =143 e-  The tuning resolution is high because of the high threshold difference before tuning (and TDACVbp = 255 ?)  Noise : 143 e- RMS

8. TDAC Map  TDAC value at 16 : disabled pixels  High TDAC values for pixels near the beam spot center region  Values from 0 to 8 not used during tuning  Tuning could be re-optimized September 9, 2013irradiated FE-I4 tests at low temperature8

9. Test at Low Temperature (-26°C)  Same configuration file at -26 °C as for room temperature  Threshold Scan shows a global mean value of 3612 e-  Individual Scurves show a threshold above 10000 e- in the beam center region  The noise value is similar to the value at room temperature (150 e- RMS).  It reaches 700-800 e- RMS near the center region  Columns 15 and 16:  many pixels are always counting 100%. Level stuck to "1" September 9, 2013irradiated FE-I4 tests at low temperature9

10. TDAC Tune at low temperature (-26°C)  Tune with 4000 e- as target value  TDAC Tune failed for the whole array  Partial Tune :  DC 8-9 and DC 18->26 disabled  After tuning  Threshold Mean value=3959 e-  Sigma =237e-  The tuning resolution is high because of the high threshold disparity before tuning September 9, 2013irradiated FE-I4 tests at low temperature10

11. TDAC Map  TDAC value at 16 for disabled pixels  High TDAC values for pixels near the beam center region September 9, 2013irradiated FE-I4 tests at low temperature11

12. DC level of out1  DC levels measured for out1, out2 and vtheff through the OABUF  The out1 DC values are higher for the chip 162  Lowest value for the chip 162 : 356 mV  Lowest value for the chip 165 is 230 mV  LBL measurements on the chip Ch27 show a lower DC value (80mV to 120 mV)  The chip 162 and 165 can be partially tuned even for the PrmpVbp value of 43 September 9, 2013irradiated FE-I4 tests at low temperature12 LBL Ch27 chip Chip 165 Chip 162

13. September 9, 2013irradiated FE-I4 tests at low temperature13 PrmpVbp I(V)  We don’t observe the high gate leakage current behavior for both irradiated chips (165 and 162)  PrmpVbp I(V) measurements show an increase in the threshold voltage for the pmos transistors. This increase is especially high for the chip 162

14. September 9, 2013irradiated FE-I4 tests at low temperature14 Conclusion  The chip 162 irradiated to a dose level of 1200 Mrad can be tuned partially at room and at low temperature  The whole array tune is failed because of the high disparity on the thresholds for high and low irradiated regions  Configuration parameters to set in order to reduce this disparity ?  An optimal Bias for the preamplifier and amplifier  The effective threshold voltage can not be set to a low values for the irradiated chip 162  TDACVbp set to 255  Other parameters to change ?  High gate leakage current behavior is not observed for the irradiated chip 165 (400 Mard) or for the irradiated chip162(1200 Mrad)