ATLAS Detector Qualification Tests

Tests listed in this document are Cambridge proposals and have not yet been formally approved by ATLAS.

Overview

In order to qualify as a candidate for ATLAS production orders, detectors from each designated manufacturer must be demonstrated to satisfy the ATLAS specifications on delivery, as well as after irradiation to 3x10**14 p.cm-2 as part of the 1998 ATLAS irradiation program.

Several new designs from different manufacturers are becoming available this summer, and before inclusion in the irradiation program they should first be checked to ensure that detector and test-structure electrical properties are consistent with required ATLAS specifications. These checks should include the following:

• Interstrip capacitance (strip metal to neigbours) should be measured at 150V bias. The measurement requires at least a 5-point contact (strip to nearest two neighbours either side). ATLAS specs require C < 1.2pF/cm.
• Coupling capacitance measured from either the detector or test-structure. Specs require C > 20pF/cm.
• Interstrip resistance at 150V bias (strip implant to a nearest neighbour). Specs require interstrip resistance >> biassing resistance, ie measured R ~ 2 x Rpoly.
• Depletion from either detector or diode CV measurements. ATLAS specs require Vdep < 150V.
• Series resistance of strip metal, from either the detector or from the test-structure. Specs require R < 15ohms/cm.
• Resistance of poly biassing from either the detector or from the test-structures (easiest to do this with the test-structure). Specs require R= 1.5+/-0.5 Mohm.
• Sheet resistance of n- and p-implants from test-structures or the detector if possible. Specs require < 400ohm/sq.
• Flat band voltage from CV MOS (no spec reqiurement, but useful for processing consistency check)

For detector designs satisfying the above criteria, proposed pre- and post-irradiation tests are listed below:

Tests on every detector before irradiation

• Delivery inspection. Visual check with the detector placed on the probestation chuck.
• IV characteristic measured up to 350V. This measurement requires the detector to be placed on the chuck of a probestation and the IV characteristic measured using a computer controlled current meter and voltage source. Detectors should be rejected if current exceeds 6uA at 150V or 20uA at 350V.
• CV at 1kHz to check detector depletion.

Tests on a detector batch subset before irradiation

• All 768 strips will be probed to quantify strip losses due to metal shorts/opens and oxide pinholes. The detector is placed on the chuck of an automatic probestation, and each strip metal is probed under computer control. Continuity across the strip oxide is determined by a measure of current between the strip metal and backplane at 100V bias; opens and shorts between strip metals are determined by measuring capacitance between strip metal and backplane. An example of the scheme currently in use at Cambridge is illustrated here. This test requires a computer controlled probestation, voltage source, current meter and LCR meter, and takes about 1.25 hours. Specs require >98% good strips.
• Detector current at 150V should be monitored over 24 hours in an inert (nitrogen) atmosphere. Several detectors may be measured in parallel by use of a switching matrix, though this will probably require the detectors to be mounted into frames. Detectors with current increasing by more than 2uA in 24hours do not satisfy the ATLAS spec and the remainder of the detector batch will also require testing.

Pre-Irradiation detector preparations

Before irradiation the detectors should be glued (or clamped?) to ceramic support cards and bonded to pitch adaptors for compatibility with readout with both binary and analogue chips. The glue type should be araldite 2011. The IV test described in the previous section should be repeated to check the effects of the glue. It would also be to great advantage if the detector can be bonded to readout chips for an analysis of the strip noise distribution, as this is helpful in the interpretation of post-irradiation studies.

Post-irradiation detector tests

• IV (require <1mA at 350V at -10degC)
• CV at 100Hz for estimate of depletion volts (require plateau at < 350V).
• IV stability over 24 hours at 350V.
• Oxide punch-throughs measured by automatic probestation. This test will require the detector to be warmed to room temperature. A simple continuity test across the strip oxides requires only a few volts, and the pitch adaptors can be probed instead of the detector for conveniance.
• Detectors will be bonded to readout chips for an analysis of strip noise distributions across the full detector width. Bad strips should be quantified. We require the pre-irradiation condition of >98% good strips (taking into account both oxide punchthroughs as well as noisy strips) to be maintained.
• A sample of irradiated detectors to be bonded to analogue chips to determine the onset of the plateau in charge collection efficiency, for use as a cross check on the CV depletion measurement
• Multi-function test-structures evaluated (**NB none yet have been irradiated, so this is only relevent to future irradiations).

Equipment Required

The following is considered to be the minimal list of equipment required for the unirradiated detector tests listed in this proposal document.

• Automatic (computer controlled) probestation, eg Wentworth AWP-1050, Summit 10K, Alessi 6100 etc
• Voltage source up to 500V or more, both polarities, eg Keithley 487, Keithley 6517 etc
• Picoammeter, sensitive from <1nA to >=2mA, eg Keithley 487, Keithley 6517 etc
• LCR meter, from 100Hz to 1kHz or higher, eg Wayne Kerr 6425, HP 4263B etc
• Switching matrix 2 x n where n=10 or more, eg Pickering 20-360, Keithley etc, for IV stability tests of several detectors in parallel.
• Bonding machine, manual or automatic.
• Networked PC with GPIB card and appropriate control software (eg LabView)

• Binary chip hybrids with re-bondable support frame (eg ABCD or LBIC/CDP)
• Analogue chip hybrid(s) with re-bondable support frame (eg SCT128 or FELIX)
• Ru-106 beta source (activity 185kBq/5uC is ideal) for triggering
• Trigger counters (Hamamatsu model H5783 is ideal)
• PC or workstation equiped with appropriate control and monitoring software for irradiation module readout

Go back to main Cambridge Silicon Web Page