Jens Janssen Diploma Thesis - Prof. Dr. Norbert Wermes ...

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probability of 50%. Mathematically, the probability P hit is given by convolutingthe Heaviside step function with a normal (or Gaussian) distribution:A BP hit (Q inj ) = hit(Q inj ≠ Q thr ) ¢ exp ≠ Q2 inj2‡ noise2 (5.7a)= 1 3 42 erfc Qthr ≠ QÔ inj. (5.7b)2‡noiseThe solution of the convolution is a complementary error function erfc(x) =(2/ Ô fi) ´ Œxexp(≠t2 )dt, where‡ noise is the equivalent noise charge 7 [46]. ‡ noiseis proportional to the slope of the S-curve at P hit = 50% and is typically in theorder of 160 e - (for planar sensors and for a pixel size of 50 ◊ 400 µm 2 ). Thethreshold setting should be well above the overall noise to avoid fake hits dueto noise.By plotting the threshold histogram, the mean threshold and threshold dispersion‡ thr (root mean square, RMS) can be obtained assuming a normaldistribution. The threshold dispersion of an untuned FE-I3 readout chip isabout 600 e - and for a tuned chip it is less than 40 e - . The dispersion of thepixel-to-pixel threshold has a similar e ect as noise, but it can be treated asa time-independent noise source [11]. The contribution to overall noise can beneglected in the case of a tuned chip.Neither the threshold dispersion nor the noise depends on the target threshold[6]. But both are characteristic for the sensor type attached to the FE-I3readout chip. In case of the noise there is also dependence on the reverse-biasingof the sensor (see next chapter).5.7 Bias Scan SetupThe purpose of the bias scan is to measure the leakage current of the entire pixelmatrix and pixel-wise (MONLEAK), noise, threshold, threshold dispersion andcrosstalk depending on the reverse-biasing voltage applied to the sensor.The measurement was done using the Primitive List (often referred to asPrim List) functionality that is implemented in STcontrol. A Primitive List is alist of scans (e. g. Threshold Scan) and actions (e. g. setting the voltage, waitingfor a given amount of time) that defines the procedure of the scan. Items in thePrimitive List are processed in a sequence. The Primitive List used for the biasscan contains following steps:1. Setting the reverse-biasing voltage2. Waiting 5 (30) minutes3. MONLEAK Scan4. Configuring the readout chip5. Waiting 1 minute7 In High Energy Physics applications, the equivalent noise charge (ENC) is a convenientway to express the noise-to-signal ratio of a charge sensitive amplifier and is given by theratio of root mean square (RMS) noise voltage V RMS to the signal pulse height V max(q e) forachargesignalofasingleelectron:ENC = V RMS /V max(q e).58
Figure 5.6: Source scan setup: The Single Chip Card (SCC) is mounted on anacrylic board. Above the SCC is the metal collimator with acrylic core, belowthe plastic scintillator. The signal output of the scintillator is connected to thetrigger logic unit (TLU, not shown).6. Measuring the leakage current7. Threshold Scan8. Crosstalk ScanAll steps listed above are repeated every bias voltage step. After setting thereverse-biasing voltage, a waiting time of 5 minutes was added to stabilize theleakage current. In case of irradiated sensors, the waiting time was increasedto 30 minutes. The waiting time before measuring the leakage current is todissipate heat from the sensor that was accumulated by the MONLEAK Scan.Before reading out the leakage current the readout chip is configured (writingpixel and global register data as stored in the tuning file). Global and pixelregister (especially pixel masks), which were changed by previous scans, canhave an influence on the leakage current.5.8 Source Scan SetupThe aim of the Source Scan is the characterization of the sensor using highenergyparticles. The Source Scan in the laboratory provides a first impression ofthe overall performance of the sensor. Of greater interest is the charge collectione ciency (charge collecting distance) and the amount of charge sharing betweenadjacent pixels.High energy- -particles can penetrate the entire thickness of the detector.By placing the- -source on the one side and a scintillation detector on the otherside of the detector,- -particles can be used to generate a trigger signal. AssumingMIPs, a homogeneous charge distribution throughout the entire thicknessof the sensor can be achieved. By using the Landau theory (see section 3.4.1),it is possible to calculate the amount of deposited charge.The beam of- -particles, which is coming from a 90 Sr source (12 MBq floodsource), is perpendicular to the detector surface. The detector is placed so59
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Universität BonnPhysikalisches Ins
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Chapter 1IntroductionThe ATLAS expe
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Chapter 2The LHC Experiment2.1 The
Page 11 and 12: Figure 2.3: Cut-away view of the in
Page 13 and 14: The electromagnetic calorimeter use
Page 15 and 16: Chapter 3Silicon Pixel Detectors3.1
Page 17 and 18: Figure 3.2: Layout and interconnect
Page 19 and 20: (a) (b)Figure 3.4: On top view of t
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Page 24 and 25: Figure 3.8: The digital block of th
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Page 28 and 29: Stopping power [MeV cm 2 /g]100101L
Page 30 and 31: The free charge carriers need to be
Page 32 and 33: The first point particularly concer
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Page 36 and 37: few µm compared to a few 100 µm).
Page 38 and 39: Figure 4.1: The USBpix test system
Page 40 and 41: e accessed through a 20-bit wide ad
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Page 44 and 45: 100Scan overlaythreshold80604020MSC
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Page 96 and 97: [37] Backhaus, M. et al.: Developme
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Jens Janssen Diploma Thesis - Prof. Dr. Norbert Wermes ...

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