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ATLAS Tracker Upgrade UK Workshop Coseners House, 8.07.08

Electrical characteristics of un-irradiated ATLAS07 mini strip sensors A.Chilingarov, Lancaster University. ATLAS Tracker Upgrade UK Workshop Coseners House, 8.07.08. Outline. Sensors C-V, I-V measurements Punch-through voltages Interstrip resistance Interstrip capacitance Summary

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ATLAS Tracker Upgrade UK Workshop Coseners House, 8.07.08

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  1. Electrical characteristics of un-irradiated ATLAS07 mini strip sensorsA.Chilingarov,Lancaster University ATLAS Tracker Upgrade UK Workshop Coseners House, 8.07.08

  2. Outline • Sensors • C-V,I-V measurements • Punch-through voltages • Interstrip resistance • Interstrip capacitance • Summary • Conclusions A.Chilingarov, ATLAS07 mini sensors

  3. Available versions (“Zones”) of the ATLAS07 mini-SSDs. Here we report the results for zone 1 (no isolation structure) and for zone 3 (baseline option) sensors. Each zone may additionally have a thin lightly p-doped layer on the surface (“p-spray”). PTP means Punch-Through Protection structure. A.Chilingarov, ATLAS07 mini sensors

  4. Backplane Cs to LCR meter . . . . . e Rs Rb Bias rail A CV – IV measurements Both C-V and I-V measurements are made simultaneously. The impedance is measured between the backplane and the bias rail by the LCR meter in Cs-Rs mode (standard frequency is 10kHz). The Cs represents the total capacitance between the strips and the backplane, while the Rs is the average bias resistor divided by the number of strips. A.Chilingarov, ATLAS07 mini sensors

  5. Five out of 7 sensors can withstand 1000V bias, two develop a breakdown above 800V. Typical current is below 10 nA (for ~1cm2 area). Depletion voltage values lie between 150 and 180V. Resistance agrees with expectation within a factor of ~1.5 A.Chilingarov, ATLAS07 mini sensors

  6. e A Rstr Rb Rdyn Punch-through resistance measurements Negative DC potential, U, varying from 0.5 to 50 V is applied to a strip implant and the resulting current, I, is measured. The slope dU/dI gives the value of effective resistance, Reff, between the strip and the bias rail. Reff represents the bias resistor, Rb, with Rdyn + Rstr in parallel. Here Rdyn is the dynamic resistance of the punch-through gap quickly decreasing with U above the break-through voltage and the Rstr is the strip implant resistance (if the punch-through gap is at the strip end opposite to the contact point). A.Chilingarov, ATLAS07 mini sensors

  7. As expected, zone 1 sensors have a relatively low break-through voltage of ~5 or ~15V. For zone 3 sensors the break-through is also observed above 45 V. For all sensors this voltage decreases with time under bias. Note that the strip bias resistors can tolerate up to ~50V voltage drop across them without being burnt. A.Chilingarov, ATLAS07 mini sensors

  8. U1 Io Uo e Ris V A Rb Bias rail Interstrip resistance measurements A “master” DC potential U0 is applied to a strip implant and the “slave” potential U1 induced at the neighbouring strip implant is measured by a high impedance voltmeter. The U0 is varied by a few volts around zero and the resulting current I0 is measured. The slope dU0/dI0 gives the value of effective resistance between the strip and the bias rail, R0. The slope dU1/dU0 allows calculation of the effective interstrip resistance, Ris, using an assumption of bias resistor, Rb, being the same at both strips. A.Chilingarov, ATLAS07 mini sensors

  9. Typical dependence of the induced voltage (Uslave) vs. the voltage applied to the neighbouring strip (Umaster). Normally the slope dU1/dU0 is ~1mV/V which means Ris ~ 106 Rbias i.e. ~1000 GOhm. The spread of the points around the linear fit determines the Ris error. A.Chilingarov, ATLAS07 mini sensors

  10. For zone 3 sensors the interstrip resistance Ris does not depend on bias in the range 10-200V and doesn’t change after sensor remaining at 200V bias during 3 hours. Typical Ris value is ~1000 GOhm. A.Chilingarov, ATLAS07 mini sensors

  11. For fresh zone 1 sensors with p-spray the Ris also doesn’t depend on bias in the range 10-200V but after 3 hour biasing by 200V it decreases and becomes slightly bias dependent with Ris value of ~500 GOhm above 100V bias. For zone 1 sensors without p-spray the Ris behaviour is more complicated. Nevertheless above 100V bias the Ris remains above 100 GOhm even after 3 hours at 200V bias. A.Chilingarov, ATLAS07 mini sensors

  12. to LCR meter Interstrip capacitance measurements The capacitance is measured between an aluminium outer strip and two its nearest neighbours connected together. The LCR meter operates in Cp-D mode. Standard measurement frequency is 100 kHz. The strips are grounded through ~1 MW resistors to keep their DC potential fixed. A.Chilingarov, ATLAS07 mini sensors

  13. Interstrip capacitance Cis vs. Ubias Below 300V the Cis has a complicated behaviour with bias but above 300V it almost flattens and gradually converges to a value of ~0.6 pF for all sensor types. Our results are in a reasonable agreement with KEK measurements. A.Chilingarov, ATLAS07 mini sensors

  14. Interstrip capacitance Cis vs. time at Ubias = 600V At 600V bias the Cis further converges with time to a common value of ~0.61 pF for all sensor types. The measurements were made at ~22oC temperature and 35-45% relative humidity. A.Chilingarov, ATLAS07 mini sensors

  15. The strip length, L, is 8000 mm for zone 3 sensors and 8060 mm for zone 1 sensors. Assuming the whole measured capacitance being scalable with L the capacitance per unit length was calculated. No systematic difference due to the sensor type or the p-spray presence was observed. The average Cis value is 0.758+-.003 pF/cm where the error is the points r.m.s. spread. A.Chilingarov, ATLAS07 mini sensors

  16. Comparison with the SCT sensors The observed Cis/L agrees well with the data measured for the SCT sensors. An absolute LCR meter uncertainty of 0.01 pF is also shown in the error. Thus the Cis in ATLAS07 minis can be regarded as simply geometrical one. A.Chilingarov, ATLAS07 mini sensors

  17. Frequency dependence of the Cis For the frequencies above 100kHz the Cis for the mini SSDs is by ~10% higher. However for the SCT sensors there is <1% difference between the Cis values in the range from 100kHz to 1MHz. Measurements with longer strips are necessary to distinguish between the changes with frequency due to the whole strip (scalable with L) and to the strip edges (independent of L). A.Chilingarov, ATLAS07 mini sensors

  18. Summary of the results presented in this talk Note: the interstrip resistance values are given at 200V bias and after 3 hours where appropriate. A.Chilingarov, ATLAS07 mini sensors

  19. Conclusions • Typically ATLAS mini SSDs show a stable behaviour up to at least 800 V. More than a half of them can be operated up to 1000V bias. The depletion voltage values are below 200V. • The punch-through protection structure implemented in zone 1 sensors operates according to expectations with a break-through voltage below 15 V. • For all sensor types the interstrip resistance exceeds 100 GOhm for bias voltage above 100V. • The interstrip capacitance values for all sensor types are very similar and agree with those for ATLAS SCT sensors scaled by the length. • The bias resistors have the value in the range 1.2 - 1.3 MOhm. They are able to withstand up to ~50V voltage drop across them without thermal destruction. A.Chilingarov, ATLAS07 mini sensors

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