Status and future measurements on Micron detectors

Outline:

Irradiation and measurement in dry atmosphere

Measurements in vacuum

Irradiation and measurement in dry atmosphere

Motivation: test of the oxide charge as possibly shorting the read-out strips after heavy irradiation. Oxide charge build-up favoured by irradiation under bias. Test ability to stand high voltage in dry air.

Is there a saturation oxide charge concentration? Our p-spray: 1.1 1012 ± 0.3 B cm-2

Possible scenario: strips could be shorted if oxide charge > p-spray.

But: evidences from other works (MPI) that after irradiation strips are insulated also with p-spray doses < p-spray. Tentative explanation is that insulation is given by interface states.

Monitoring the irradiation

Irradiation was performed in the ATLAS cool box, in nitrogen atmosphere.

Detector was vertical in the beam. The irradiated area is ~ 2x2 cm2, maximum fluence > 2 1015 p cm-2.

Typical Irrad 7 fluence horizontal profile

(to be rescaled to max ~2.2 1015 cm-2).

0

10

20

30

40

50

60

70

80

20 30 40 50 60 70 80

Position from Ref [mm]

Me

as

ure

d f

lue

nc

e [

x1

013

cm

-2]

Reverse bias current during irradiation

0.0E+00

2.0E-05

4.0E-05

6.0E-05

8.0E-05

1.0E-04

1.2E-04

1.4E-04

1.6E-04

1.8E-04

2.0E-04

3.1509E+09 3.1510E+09 3.1511E+09 3.1512E+09 3.1513E+09 3.1514E+09

Time (s)

Cu

rre

nt

(A)

0.0E+00

5.0E-05

1.0E-04

1.5E-04

2.0E-04

0.0E+00 2.0E+07 4.0E+07 6.0E+07 8.0E+07 1.0E+08

SEC counts

Cu

rre

nt

(A)

Bias changed from 100V to 200V.

Measurements foreseen with the irradiated device:

•CCE(V) measurement of the irradiated area (to determine, if possible, the irradiation profile).

•Measurement of strip insulation (charge spread over multiple strips) with laser light injection next to a strip as a function of the fluence.

•Possible estimation of the maximum survival limit (fluence on the detector varies from 0 to > 2 1015 cm-2)

Measurements in vacuum

A LHCb VELO phi measuring detector, PR02 version has been put in vacuum (~10-2 mb) and left under 250V for 6 days (it’s still running at present). The reverse current (initially 0.8 µA) didn’t vary significantly over this period (small variations due to temperature variation where in the order of ± 2%.