1. Silicon Detectors and DAQ principles for a physics experiment Masterclass 2011, 7-11 February 2011 Alessandro Scordo

3. Telescopes

4. Human eyes

5. Microscope

6. Accelerators

7. Detectors

8. But where does it all start from?

9. Electronic properties of materials Atoms are made of proton, neutrons (nucleus) and electrons Valence and conduction electrons are responsible for the principal characteristics of different atoms

10. Electronic properties of materials Everyone wants to be noble !!! Water is a good example….

11. Electronic properties of materials Atomic levelsMolecular bands

12. Semiconductors -For low temperature, valence band is full and conduction band is empty -At higher temperatures, thermal excitations promote some electrons from valence to conduction band Definition of semiconductor

13. If some electron is promoted in the conduction band, what may occur? 1)Drift: an external field can move these electrons 2)Multiplication; if the field is strong enough 3)Recombination: if nothing happens, electrons fall back to valence band What happens then? How can we describe the situation?

14. Physicians must be smart and clever…. holes !!! h+h+ h+h+ h+h+ h+h+

15. ....and do a smart use of drugs!!! n dopingp doping Why ?

16. p-n Junctions Fermi level definition Electrons and holes diffusion Non equilibrium situation Donors and acceptors ions field plays against diffusion and equilibrium is reached Equilibrium !!! … ?

17. p-n Junctions Equilibrium is reached when the two Fermi levels are at the same energy A sort of slope is then created, hard to climb up and easy to roll down! Equilibrium does not mean immobility!!!

18. p-n Junctions Equilibrium means that electrons and holes diffusions are compensating each other! A depletion region is formed where no charge carriers are present, and if some charged particles are created there they can be detected The new slide shape of the bands can be used to improve this detection!

19. Direct polarization of the junction reduce (or reverse) the potential barrier, electrons are provided from the external voltage and current flows in the device Reverse polarizaton increase the potential barrier and in principle no current flows! If the reverse bias is big enough, multiplication may occur and inverse breakdown let current flow in the device‏ p-n Junctions

20. Breakdown voltage V br Junctions are the basic devices for all semiconductor detectors!

21. Particles through matter How can we detect them?

22. Energy loss; particle interacting with matter Bethe - Bloch

23. Particles’ measurements A particle passes through a silicon thickness, generating e-h pairs e - and h + are collected by anode and cathode (be aware of recombination…) An electric field causes electron flow through the device and created charge can be collected (by capacitor for ex.)

24. SDD, a clever anti- recombination device An electric field leads electrons, generated by particle flow (x- Rays or ionizing) to a small collector anode. At the same time holes are immediately removed from electron’s path by cathode strips.

25. Position measurements: strips !

26. We got the charge... and now what?

27. Analog – Digital conversion Digital signal; signal is a function of discrete numbers, F(N) Analog signal; signal is a function of continuous numbers, usually time, F(t) The world is analogic but Pc and analysis software can only work with digital informations….. Analog signal have to be converted to digital signals!

28. Analog – Digital conversion SamplingQuantization

29. Analog – Digital conversion channels

30. Analog – Digital conversion In this world….. ….this is poker !!!

31. Analog – Digital conversion Converting analog signals into digital signals, some information may be lost … but are they really necessary?

32. From analog signals to files and histograms: Data AQuisition methods

33. DAQ What are we interested in ? Which information can we get? ChargeTimingRates

34. DAQ : Discriminators

35. DAQ : QDC (charge to digital converter) QDC values (integer numbers) Histograms

36. DAQ : TDC (time to digital converter)

37. DAQ : Scaler 4 events in 10 seconds Rate = 0,4 Hz

38. A real example!

39. MPPC (Multi Pixel Photon Counters) detectors Each pixel acts like a p-n junction Breakdown current is used Output signals are summed

40. MPPC (Multi Pixel Photon Counters) detectors

41. MPPC Signal coming out from the detecor is then: QDC spectrum is then composed by several pixes with fixed distance

42. Dark Count‏ 0 ph 1 ph 2 ph 3 ph 0 ph 1 ph 2 ph 3 ph Thermal generated faked signals

43. New physicists? Questions?