VTT ASSEMBLY 5 CHARACTERISATION KATE DOONAN & RICHARD BATES 2012

SETUP ROIC is 200um thick, no special thin device treatment during the re-flow process VTT Assembly 5 was operated: in the dark at -100V and at room temperature (20C) INITIAL TESTS Analog and Digital scans looked good Noise occupancy scan and subsequent mask revealed noisy pixels in the 2 right hand columns which were to be masked

TUNING DONE WITH THRESHOLD TARGET OF 3200ELECTRONS Prim list was: IF TUNE GDAC (note in STControl version 3.0 need to run Fast_GDAC) TDAC FDAC TDAC Repeating the FDCA, TDAC loop three times improves the uniformity of the Vth 50% point.

AFTER 1 ST TDAC/FDAC/TDAC TUNE CYCLE THRESHOLD SCANNOISE - Very non-Gaussian threshold – misses target value of 3200electrons Mean = Sigma = 7.0 Mean = 3314 Sigma = 349.8

AFTER 2 ND TDAC/FDAC/TDAC TUNE CYCLE THRESHOLDNOISE Mean = 3194 Sigma = Mean = 134 Sigma = 6.54 Significant improvement in threshold distribution

AFTER 3 RD TDAC/FDAC/TDAC CYCLE THRESHOLDNOISE Still a slight tail to lower thresholds for several columns Slight improvement in the target but probably not worth the extra tune cycle Mean = Sigma = 6.36 Mean = 3200 Sigma = 26.91

HUNTING FOR NON-BONDED PIXELS Perform threshold scans with and without Detector HV With HV on, sensor is depleted and there is low noise on all pixels With HV off, disconnected pixels will exhibit just the noise of the bare FE (around 120e) Small bump can be seen around 120e

Zoomed in noise plot There are a number of pixel which appear to be unbonded They are in the top corner sections of the assembly Number of un-bonded pixels is /26,400 = % is too high Data to be fed back to VTT to understand how to over come bow problem DISCONNECTED PIXELS

CROSSTALK SCAN: MERGED BUMPS With high voltage off, crosstalk is seen due to the bulk of the sensor being undepleted With high voltage on, any crosstalk is due to merged bumps This happens at columns 0, 78 and 79 which are masked out No merged pixels are visible

AMERICIUM-241 SOURCE SCAN Columns 0, 78 and 79 masked Full sensor illumination achieved with 12million events Strange pattern seen at corners identified in previous scans Placed source over each corner to investigate

CORNER BEHAVIOUR Scan of 12million events at top right hand corner shows a dark section where full illumination is expected

Scan of 4million events at top left hand corner shows similar effects CORNER BEHAVIOUR

CONCLUSION There is some form of disconnection at the corners of the sensor They do not perform as well in the threshold noise scan Analysis on going They show much less illumination in the source scan although the source is placed directly over these corners Analysis on going 2% disconnected bumps at the corners probably due to ROIC bow during the reflow process