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Characterisation of DSSD interstrip parameters

This study by Paul Dolejschi delves into the detailed characterisation of interstrip parameters in DSSD, focusing on capacitance, resistance, and oxide thickness validation using innovative measurement techniques and analysis methods.

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Characterisation of DSSD interstrip parameters

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  1. Characterisation of DSSD interstrip parameters Paul Dolejschi BELLE II SVD-PXD Meeting

  2. QTC-Setup switching-system LCR-meter (measurement of capacitance) 2 SMUs (Bias-Voltage, Resistance) electrometer (current) needles, chuck, table LabView-software Completley automated setup Paul Dolejschi Paul Dolejschi 2

  3. What have we tested? Global parameters: IV-Curve:Dark current, Breakthrough CV-Curve:Depletion voltage, Total Capacitance Strip Parameters e.g. strip leakage current Istrip poly-silicon resistor Rpoly coupling capacitance Cac dielectric current Idiel Paul Dolejschi 3

  4. Switching Scheme (Vienna) Paul Dolejschi 4

  5. Validation of oxide thickness metal layer oxide implant SEM result: 355nm average from C_ac measurement: 354.2 nm Micron average: 391.8 13.4.2011 Paul Dolejschi Paul Dolejschi 5

  6. Interstrip Capacitance Comparison of Frequency dependent measurements on Hamamatsu barrel sensors CMS-test structure Interstrip Resistance Hamamatsu Barrel sensors 4 batches Micron Wedge sensors 2 batches, p-stop/p-spray Interstrip measurements Paul Dolejschi

  7. Capacitance between Implants (p+/n+) Charge Sharing Metal layers (Al) Cross Talk, Signal to noise Metal layer and implant (AC coupling) Separates strip leakage current from readout electronics → Electrical Network! Interstrip Capacitance Paul Dolejschi

  8. Interstrip Capacitance • Different measurement methods • Contacting Implants only (via DC pads) • Contacting metal layer only (via AC pads) • Contacting both implants and metal layer • Additional option: Measuring 1, 2 or 4 neighbouring strips • Slightly different result for each method and/or sensor type • AC or DC coupled structures, different strip length, bias-resistor,… • Try to distinguish different contributions of capacitances, restistors etc… Paul Dolejschi

  9. Frequency dependent interstrip capacitance measurement LCR-meter measures impendance and phase at the same time and then computes capacitance with chosen equivalent circuit. Paul Dolejschi

  10. Comparison of different measurement types Strip length 12cm Paul Dolejschi

  11. Comparison of different measurement types Strip length 1cm Paul Dolejschi

  12. Influence of polysilicon resistor High pass filter Paul Dolejschi

  13. Frequency dependent interstrip capacitance measurement Unknown effect of implants in low frequency region High frequency: no contribution of implants if strips are long Low frequency: no contribution of metal layer because of high pass filter Paul Dolejschi

  14. Conclusion • High Frequencies: • Above a certain frequency only a small length of the implant contributes to the capacitance • The capacitance between the metal layers dominates the observed value when both AC and DC pads are contacted • Low Frequencies: • Presence of a polysilicone resistor influences low frequency region  high pass filter for metal layers if R_poly is low • Unknown effect of implants in low frequency region Paul Dolejschi

  15. Interstrip Resistance - Measurement Principle DC pad #X kept on ground, voltage applied to DC pad #X+1, electromenter measures current on pad #X Don‘t want to measure series connection of poly-resistances R-poly can be measured at the same time Strip X Strip X+1 Paul Dolejschi Paul Dolejschi 15

  16. Usually five voltage steps, slope of the IV curve represents 1/R Typical ΔI: 5-20pA Typical R_int: 50-200GΩ Intersection of R-poly curve at y=0 reveals current of next strip Paul Dolejschi Paul Dolejschi 16

  17. Fit fails sometimes (often) „Fit ok“ failed fit Paul Dolejschi Paul Dolejschi 17

  18. Measurement with 3rd SMU for compensation Keeping electrometer in lowest possible range (200 pA)! introduces current for I_strip compensation Paul Dolejschi 18

  19. „Ideal stripscan“ Interstrip resistance and polysilicon resistor measured at same time Value plotted for each strip More than 90% „fit ok“ in this exapmple Measurement success Paul Dolejschi Paul Dolejschi 19

  20. Hamamatsu n-sides n-side Similarity in shape new measurement method using 3rd SMU for I_strip-compensation (+guarded positioners) - no improvement Measurement accuracy high enough to measure >1TΩ Similarity between Hamamatsu sensors (all 4 batches) Independent of „direction“ of stripscan HPK #4 HPK #80 Paul Dolejschi Paul Dolejschi 20

  21. The higher the strip number, the higher the resistance „mean dI“: after the voltage is applied, it takes some time (sec) until current is stable Difference between first and final value = „mean dI“ Can be positive or negative „responsible“ for higher resistance? Hamamatsu n-sides current Paul Dolejschi

  22. Hamamatsu n-sides ~50% „Fit ok“ Paul Dolejschi

  23. Hamamatsu n-sides ~50% „Fit ok“ Paul Dolejschi

  24. Hamamatsu n-sides ~96% „Fit ok“ Paul Dolejschi

  25. Mainly on Micron p-sides „Fit ok“ below 5% (averaged over all sensors from same batch) Well reproduceable Other frequently onserved effects Paul Dolejschi

  26. Statistics Paul Dolejschi

  27. Conclusion • The overall detector performances (dark current, depletion voltage, radiation hardness,…) are ok, but interstrip resistance measurement is not fully understood • Reproducable effects on Hamamatsu n-sides and Micron p-sides • Improvement with growing batch number • Measurement impossible on noisy strips • Effects possibly caused by pn-junction effects, simulation required Paul Dolejschi

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