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

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

Characterisation of DSSD interstrip parameters 3Paul Dolejschi What have we tested? Global parameters: –IV-Curve: Dark current, Breakthrough –CV-Curve: Depletion voltage, Total Capacitance Strip Parameters e.g. –strip leakage current I strip –poly-silicon resistor R poly –coupling capacitance C ac –dielectric current I diel 3

Characterisation of DSSD interstrip parameters 4Paul Dolejschi Switching Scheme (Vienna) 4

Characterisation of DSSD interstrip parameters 5Paul Dolejschi Paul Dolejschi Validation of oxide thickness SEM result: 355nmaverage from C_ac measurement: nm Micron average: metal layer implant oxide

Characterisation of DSSD interstrip parameters 6Paul Dolejschi Interstrip measurements 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

Characterisation of DSSD interstrip parameters 7Paul Dolejschi Interstrip Capacitance 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!

Characterisation of DSSD interstrip parameters 8Paul Dolejschi 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…

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

Characterisation of DSSD interstrip parameters 10Paul Dolejschi Comparison of different measurement types Strip length 12cm

Characterisation of DSSD interstrip parameters 11Paul Dolejschi Comparison of different measurement types Strip length 1cm

Characterisation of DSSD interstrip parameters 12Paul Dolejschi Influence of polysilicon resistor High pass filter

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

Characterisation of DSSD interstrip parameters 14Paul Dolejschi 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

Characterisation of DSSD interstrip parameters 15Paul Dolejschi Paul Dolejschi 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

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

Characterisation of DSSD interstrip parameters 17Paul Dolejschi Paul Dolejschi Fit fails sometimes (often) failed fit„Fit ok“

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

Characterisation of DSSD interstrip parameters 19Paul Dolejschi Paul Dolejschi „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

Characterisation of DSSD interstrip parameters 20Paul Dolejschi Paul Dolejschi 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

Characterisation of DSSD interstrip parameters 21Paul Dolejschi Hamamatsu n-sides 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? current

Characterisation of DSSD interstrip parameters 22Paul Dolejschi Hamamatsu n-sides ~50% „Fit ok“

Characterisation of DSSD interstrip parameters 23Paul Dolejschi Hamamatsu n-sides ~50% „Fit ok“

Characterisation of DSSD interstrip parameters 24Paul Dolejschi Hamamatsu n-sides ~96% „Fit ok“

Characterisation of DSSD interstrip parameters 25Paul Dolejschi Other frequently onserved effects Mainly on Micron p- side s „Fit ok“ below 5% (averaged over all sensors from same batch) Well reproduceable

Characterisation of DSSD interstrip parameters 26Paul Dolejschi Statistics

Characterisation of DSSD interstrip parameters 27Paul Dolejschi 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