CDF-II ISL (Intermediate Silicon Layers)

The ISL is composed of five barrels in total, each barrel being composed of single layer of double-sided Si microstrip sensors. An elevation view of the CDF-II detector is here. The barrels are positioned at radius of 22.6/23.1 cm (central barrel), 19.7/20.2 cm (forward/backward inner barrels) and 28.6/29.0 cm (forward/backward outer barrels) such that there are coordinate measurements at two (one) positions for forward (central) tracks. Each barrel is made up from ladders, each ladder consisting of 6 Si mircrostrip sensors which are ganged into two 3-sensor groups so that signals are read out from either end of the ladder. The Si sensor is AC coupled and double sided having two planes with 112 micron pitch readout strips. The strips are running at a stereo angle of ~1.2 deg. The main function of the ISL is to measure the particle momentum in the forward regions where the outer tracker, COT, can not fully cover and to provide anchor hit points from which track segments in SVX-II/ISL detector are searched for.

CDFnote on B class sensors
Production delivery
Long-term stability
Ladder construction procedure
Co-60 irradiation of Class B sensors
Probing of Production ISL Sensors

  • Design of the ISL and the sensor
  • Details of the ISL sensor
  • Leak current from individual strip (prototype)
  • Poly-Si resistance and dead C_coupl fraction(prototype)
  • Total leakage current (prototype)
  • Bulk capacitance (prototype)
  • Interstrip capacitance (prototype)
  • Radiation resistance
  • Testbench system

    ISL page at Fermilab (access limited)
    ISL page at Pisa
    ISL page at Purdue
    ISL page at Karlsruhe

    Design of the ISL and the sensor

    An isometric view of the ISL barrels is here ( GIF view ). The microstrip sensors are processed on 4" or 6" wafers. The dimensions of 4" prototype sensors from Hamamatsu ( GIF view) is determined to utilize the maximum available area. The dimensions of 4" SEIKO sensors are similar (the outer dimensions are identical). Six of such sensors are aligned to construct a ladder.

    The strips run along the beamline for the n-side and at a small stereo angle of 1.207deg for the p-side. This angle is determined such that the stereo strips are aligned on a line when the neighboring sensors are positioned at a gap space of 100 microns ( GIF view ).
    The phi-acceptance of ISL barrels is plotted here ( GIF view). The plot shows how the acceptance is degraded with increasing the number of stereo strips which are not read out. 12 strips at the corner are short and not readout, though they are biased so that the field at the corner is not distorted. Wirebonding three sensors, 36 strips at the corner are not read out per half ladder. The plot shows the phi acceptance is not degraded at all - we have enough overlapping between the sensors.

    The specifications of 4" prototype sensors are summarized in this list ( PS file). The pad position is shown here( GIF view ). A constraint concerning the pad position is the wire length be shorter than 3 mm. A scheme of staggering the pads is avoided to simplify the wirebonding procedure.

    Details of the structure of the 4" ISL sensor

    The design of the sensor is based on the various studies carried out in designing Hamamatsu SVX-II sensors. The implant strip width is 22 microns to match the strip pitch of 112 microns. The Al electrode width is set to 16 microns so that the Al electrodes are recessed by 3 microns from the implant strips, thus suppressing the micro-discharge. The drawings above are for the SEIKO prototype. The main differences between the two manufactures are the materials at the coupling capacitance and the passivation. The differences are shown here ( GIF view , EPS file ).

    Performance of the 4" ISL prototypes

    The QC items by each manufacturer are summarized in these tables, Hamamatsu ( GIF view: EPS file) and SEIKO ( GIF view: EPS file). The characteristics plots include:

    33 strips per side and bias lines are wirebonded on a test printed board . Main characteristics measured at University of Tsukuba are:

    Performance related to Co-gamma irradiation

    Co irradiation was performed on January 26, 1998 for two sensors each for Hamamatsu and SEIKO.

    Testbench system

    Production Sensors

    Co-60 irradiation of Class B sensors

    Three sensors H0196-198 were irradiated with Co-60 gammas to 0.2 Mrad. Individual strip currents were compared before and after the irradiation. The post irradiation measurements were made 2-4 days after (The sensors are still underway of annelaing). The average leakage current of good strips increased from 1 nA to 50 nA. Leaky strips (>100 nA or so) remain to be leaky but there is no radiation induced increase in the leakage current nor the neighboring strips are affected.

    Long-term stability

    In total seven sensors are kept biased at 120V in a thermostat chamber where the temperature is controlled at 20degC. The total leakage current of these sensors are measured at 120 and 150V. The bias was raised to 150V for a period of ca.1min for this measurement. Th seven sensors are of grade A (199,200,201), of grade B (195,202) and of grade C (203,204) in terms of the IV characteristics (they fail dead channel fraction, though). See the IV curves measured by HPK (at 25degC).

    We note the leakage current of 203 at 120V droped substantially in a couple of days. To see what happened to this and to other sensors, the IV characteristics was measured 5 days after biasing .
    Comments: sensors 195 and 199 have been probed at Tsukuba. No instabilities are seen for these sensors, instabilities being expected if the sensors are damaged.

    Ladder construction procedure

    The sensors are assembled into half-ladders, each consisting of 3 sensors. Two half ladders are glued together, making a full ladder. The assembling is performed at Fermilab with using assembling jigs constructed by Karlsruhe group.

    Production Sensors Delivery

    The original plan and current status of the delivery as of December 23, 1999

    Delivery history in plot
    Class B sensors pass relaxed specs defined in Jan 99
    Class C sensors are for electrical checks delivered to U. of Tsukuba
    Oct.98 Nov.98 Dec.98 Jan.99 Feb.99 Mar.99 Apr.99 May.99 Jun.99 Jul.99 Aug.99 Sep.99 Oct.99 Nov.99 Dec.99
    Original plan 60 60 60 60 60 60 60 60 70
    Delivered 0 20 4 27+18B 34+15B 40+32B 28+10B 8+6B 0 19 39 87+15B 13+2B 31+7B 37+8B -
    +ClassC 0 3C 1C 0 0 10C 0 0 0 11C 0 0 0 0 0 -
    Accepted 0 20 4 27+13B 34+12B 39+22B 28+10B 8+5B 0 19 39 87+15B 13+2B 31+7B 37+8B
    Use as C 0 0 0 3B 3B 11B 0 1B 0 0 0 0 0 0 0 -
    Returned 0 0 (1) 3 0 0 0 0 0 0 0 0 0 0 0 -
    Skipped serial# 0 0 0 0 0 0 0 0 2 0 0 1 0 0 0 -
    Accept sum 0 20 23 51+11B 85+23B 124+45B 152+55B 160+60B 160+60B 179+60B 218+61B 305+75B 318+77B 349+84B 386+92B -