Presentation on theme: "Solid State Detectors- 3 T. Bowcock 2 Schedule 1Position Sensors 2Principles of Operation of Solid State Detectors 3Techniques for High Performance Operation."— Presentation transcript:
2 Schedule 1Position Sensors 2Principles of Operation of Solid State Detectors 3Techniques for High Performance Operation 4Environmental Design 5Measurement of time 6New Detector Technologies
3 Techniques for High Performance Operation Strip Detectors –Design and Fabrication Issues What to avoid!
4 Review... In the p-strip in n-bulk (“p-in-n”) detectors V dep =100V Energy to create electron hole pair is –3.6eV ( not 1.1eV-why? ) Average energy lost/ m –39keV (108eh/ m) Al Si -V + -
5 Drift Electric field in Depleted region linear –300 m detector –at 100V E=3.0keV/cm Diffusion/Drift by multiple collisions Takes 7ns for e’s, 20ns for holes Higher diffusion at low temps!
6 Ballistic Deficit Charge lost is known as the ballistic deficit Collection time
7 Strip Pitch and Readout Pitch and resolution Select it: d Single strip has d/ 12 d/10
8 Choosing the Pitch Why not make it infinitely small –transverse diffusion 10-20 microns –construction –readout electronics! Readout pitch –not necessarily the same as diode pitch (cost$$$) 75 m readout (25 m diode)
9 Intermediate Strips Work by capacitive coupling –induced current/charge is that seen by the electrons and holes (not a post-facto charge sharing!) Why no broader strips ? –Interstrip capacitance <1pF Need field map!
10 Intermediate Strips? Loose signal An option if –limited by resources –little noise in electronics (slow e’s) Optimal choice is –readout each strip pitch and width evaluated by FEA –pitch between 20 microns and 100 microns
11 Performance 50 m with intermediate strip 25 m readout
12 Resolution Test your resolution –series of particles of known position testbeam telescope cosmic telescope longwavelength laser
13 Checking Resolution Tests –laser problems? transparancy –cosmics slower –testbeam expensive labour intensive Optical fiber Focus to 5 m 1064nm Si transparent
14 Two Track Resolution Reconstruction position as a function of proximity of one track to another
15 Occupancy Best to reduce occupancy –1% considered the benchmark 10% too high Reduce the length of strips –usually about 6cm –reduce to 1cm for example
16 AC Coupling Revisited =0.34pF/cm 200nm oxide –10pF/cm Greater than Interstrip capacitance Electronics at ground!
17 + - Double Sided Needs AC coupling! Correlation of signals Strips can run opposite directions –2D style r/o + 0V -V
18 Double Sided Detector Would like electronics at one end Can get correlated measurement (E) giving x/y measurement Reduces fakes Punchthrough
19 Double Metal Add another routing layer more processing via Expense can double Built in stresses in SiO2 can warp Si wafer badly
20 Double Metal Can also use to route on single sided detectors
39 Noise Hybrid is often a source of noise –bad grounding for electronics –bad grounding for supplies to detector –sensor,analog and digital all connected The detector, f/e electronics and the hybrid should be regarded as one unit or MODULE
43 Offline Analysis Can give improvement in resolution d w x R L Only true if charge uniform and if the width of the cluster matches the strip width In general we have a Gaussian distribution of width determined by the diffusion coefficient (for normal incidence)
44 Offline Corrections for the angle of the track and the known (measured) charge sharing can give great improvement –20 to 30% in the case of 25 microns pitch detectors Good software must accompany good hardware Removal of deltas
45 7 things to avoid Picking the wrong technology Picking the wrong manufacturer($) Not enough Quality Control Bad design limiting operation Noise in system Treating sensor and hybrid separately Bad analysis
46 Summary We have all the elements now to think about real detectors in real environments –design issues –noise problems See how we design a detector for LHCb