Standalone VeloPix Simulation Jianchun Wang 4/30/10.
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Standalone VeloPix Simulation Jianchun Wang 4/30/10
Introduction VeloPix performance after irradiation affects our current design. We want to create tools to study these effects. As a first step I modify the standalone simulation package and look at performance of pixel detector before irradiation. More features are to be added. More sophisticated electric field based ISE-TCAD simulation. Charge trapping. Finite integration time. Disclaim: Some of the electronics properties may be too good to be true. If it is need, more realistic parameters can be added to provide input to other studies. 04/30/10Jianchun Wang2 Besides of many interesting features, I am particular interested in: The charge collection efficiency will be reduced due to insufficient bias and/or charge trapping, etc. Reconstruction of angled tracks are biased due charge collection inefficiency. Non-uniform irradiation dose on a single chip/sensor makes it difficult bias. …
Sensor and Electronics Properties Silicon sensor Thickness = 150 m. Charge carrier = electron Pixel size = 55 m x 55 m. Full depletion voltage = 30 V Bias HV = 50 V Electronics Charge collection efficiency= 100% Noise= 100 e Gain uncertainty= 10 % Crosstalk between adjacent pixels= 0 Threshold= 1000 e Non-uniformity of thresholds= 0 % ADC (TDC) bits= 8 ADC range= 1000 – 24000 e Non-linearity= 0 04/30/10Jianchun Wang3 More realistic parameters will be added when they are available
Normal Incident Tracks 04/30/10Jianchun Wang4 Track: 20 GeV Row X, Column Y With VeloPix detector row and column have same pitches. Angle X = 0 Angle Y = 0 =1.55 =1.26 MPV ~ 11 Ke Above ADC range
Eta Correction 04/30/10Jianchun Wang5 Pixel border Linear charge weighting ~75%, no charge sharing info available ~25%, very narrow after eta correction partially due to small portion eta correction
Tracks At Different Angles 04/30/10Jianchun Wang6 Tracks at 0 degree in Y/column direction For threshold = 1000 e, the best resolution is at 18 – 20 degree.
With Plane Tilted 04/30/10Jianchun Wang7 Tracks at 0 or 20 degree in Y/column direction There are more charge sharing in column direction, thus slightly less charge sharing for normal incident track in X direction.
Different Thresholds and Noise 04/30/10Jianchun Wang8 Threshold = 1000 e Noise = 100 e Threshold = 2000 e Noise = 100 e Threshold = 1000 e Noise = 300 e Just to show how thresholds and noise affect the resolution. With increasing of noise, the resolution is affected the most at small angles where the shared charges are less. Threshold affects the resolution, especially for thin detector. Trim DAC in each cell may be necessary to reduce the non-uniformity of threshold, and thus reduce the overall threshold level.
Plan Use more realistic electronics parameters from TimePix studies, and generate inputs for other studies. Add irradiation dose dependent effects More sophisticated electric field based ISE-TCAD simulation. Charge trapping. Finite integration time. … May integrate it to more general simulation, depending CPU consumption ( ~10ms /hit ). More interesting studies. 04/30/10Jianchun Wang9
Telescope Configuration 11 Type Thickness ( m) Size (mm 2 ) HVComment TelescopeN-type Si300 ? 16 x 24 32 x 16 220 DUT sCVD5004x 4250 At 0 , 10 , & 20 , HV scan at 20 MCZ Si300 ?16 x 24500 0 , threshold scan Purdue 3D2008x8403d_4e_wb5_8, failed 2008x8403d_2e_wb216_6, HV & threshold scan 2858x8403d_2e_wb5_2, HV & threshold scan DUT YY 120 GeV proton beam Scint X Z Y XX YY : –22 : +22 : +22 : –22 : 0, –10 , –20 Lab frame 04/30/10Jianchun Wang
Diamond HV Scan at Angle What we want to extract from the testbeam for different bias HVs: Total charge collected per particle hit in terms of MPV of the Landau distributions. For a fixed threshold how the charge sharing information the detector can deliver, in terms of number of rows, or columns per particle hit cluster. Spatial resolution. Shift of spatial position measurement due to partial charge collection and tracks at angle. This can give us some ideas on effective depth, and charge trapping. Status of each task: Need more work on readout electronics gain and pedestal calibrations. It is difficult to compare the absolute charge before that. Numbers of pixels per hit vs bias HV qualitatively agree with expectation. We need to obtain precise thresholds from bench test for MC simulation. Then we can have quantitative comparison to test our understanding. Current resolution is not as good as expectation. Need more work on gain curve and telescope alignment. Shift of center residual shows correct trend. It will be revised after the spatial measurement optimization. 04/30/1012Jianchun Wang
Diamond Sensor Charge Sharing vs HV Number of Columns per Cluster Number of Rows per Cluster HV = -250 V Sensor rotated to ~ 20 in row direction. More charge collected with higher bias HV till saturation. Need more work on gain calibration to extract the absolute charge (MPV of Landau distribution). 04/30/1013 Preliminary Jianchun Wang
Diamond Sensor Residual Center vs HV Tracks are at ~ 20 with respect to normal of sensor plane in row direction. Use the same set of telescope spatial configuration parameters. With low bias HV, charges generated near readout electronics have more chance to be collected, equivalent to thinner effective sensor. Thus the residual center shifts. In extreme case, the maximum possible shift ~ tan( )*d/2 ~ 90 m. 04/30/1014 Preliminary Jianchun Wang
Diamond Sensor Charge Sharing vs Angle Diamond sensor is biased at -250 V. Sensor was perpendicular to beam, or rotated by ~10 & ~20 in row direction. Gain and threshold of the electronics are different from that of HV scan. 04/30/1015 Preliminary Jianchun Wang
Problem with Diamond Gain Calibration 04/30/10Jianchun Wang17 sCVD DUT Charge (Ke) Double peaks belong to different cluster sizes, suggesting there is offset issue. The difference between two peaks is too big. The offset would have to be ~ –13 in order to have the same MP. And the MP would be ~ –3. So this is not a correct hypothesis. MP=9.8 MP=22.7 Charge (Ke)
Diamond Residual Distribution 04/30/10Jianchun Wang18 X recon – X track ( m)Y recon – Y track ( m) = 30.5 m = 46.7 m Tracks are at ~20 in X direction wrt the diamond. Charging sharing information is not fully used yet due to calibration issues. In comparison 100/ 12 = 28.9, 150/ 12 =43.3.
Summary We had tested radiation hard sensors: diamond, MCZ silicon & 3D. Some interesting results are produced from diamond test. Gain calibration somehow becomes bottle neck. We provide offline analysis and alignment program for this testbeam system as our promised contribution. We may use the telescope to test our own sensors. 04/30/10Jianchun Wang19