Solid State Detectors- 5 T. Bowcock

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 Time - the fourth coordinate Three Reasons time is used –to separate signal from background –particle identification –improvement in resolution

4 Using time Could use t to measure velocity directly –good spatial resolution easier to achieve In practice we tend to use it only for particle identification

5 TOF Start time

6 Time of Flight The momentum of a particle is measured using its curvature in a magnetic field Its velocity is related to its momentum From time we can calculate velocity (ps m)

7 TOF  -K K-p

8 E896 TOF

9 Traditional Methods

10 Scintillation Intrinsically fast<0.1ps

11 TOF technology Normally use scintillator and photomultiplier tubes Resolution can be down to 100ps Solid State Detectors?

12 Timing with Si Signal rise time in our diode detectors was very slow few ns rise time –very high fields increase mobility –shallower detectors –impossible electronics

13 Microchannel plates Solid state photo-multiplier Often made of glass can be made of solid Si etching

14 Operation of MCP

15 MCP Can be made of Glass or Si Typical transit time about 50ps Resolutions of order 100ps or better –thin holes(down to 5 microns) –high fields –perhaps as low as 10ps –electronics

16 MCP Use either by themselves or in conjunction with scintillator Highly expensive Commercial product –night vision –time of flight systems for ion beams

17 Compare with Spark Chambers Cylindrical Spark Chamber (Pestov style) Resistive glass limits discharge

18 Note Calculation of tof usually requires precision tracking (mm or better) MCP could be used with r/o with high granularity –BUT –fine t resolution large distances –large distance imply large areas –cost becomes inhibitive

19 Counting Time Direct clock counting (1ns) Digital interpolation of GHz clock (0.2ns) Time Stretcher –best resolution available is about 1ps LeCroy

20 Time Stretching Time to Amplitude converter –starts a ramp on a signal –stops when it receives another Wilkinson type “converter” –discharge by a constant current Second stage of TAC –final digitisation Factor of 500 attainable

21 Intrinsic limit At 1ps are we getting close to limit –waveguide on chips –sizes critical ps electronics not at all compact? Can’t put at Time stretcher on every channel Large dead time

22 TOF + telescope Not just used in HEP Galileo Probe

23 Streak Camera Can also be used as part of a streak camera

24 Other uses for timing information More “usefully” We can also use solid state detectors as drift detectors –remember gaseous drift detectors

25 PIN diodes Charge may be stored in a pnn+ diode structure At 4.2K trapping time>10 5 s p+ n+ n-doped Intrinsic

26 PIN diodes Stored charged can be released by application of a few V/  m At 2V/  m trapping time is only 10ps Capture happens at a characteristic distance of 1  m

27 Tunneling from trap Conduction Band Finite Tunneling Probability

28 Silicon Drift Chamber Depleted from side over long distance Until depletion “median line” conducts n Al -V p p

29 Silicon Drift V V-dV V-2dV V-3dV n

30 SSD Operation Basic detector characteristics: Rectangular active region 50 x 67 mm 9% of dead region (guard structures) Implanted P+ resistor HV divider Drift length 2 x 33.5 mm 200 anodes on each side of the detector (anode pitc 250 um) 3 lines of MOS, N+ and N+(AC) charge injection structures Precise openings in metalization for laser- induced charge injection Anode structures around the guard zone allows to study leakage currents in this region Detector is fabricated on 3.5 kOhm/cm NTD N Si

31 ALICE SDD

32 SDD Many experiments use SDD –timing vital –drift possible –an extension of previous methodology Difficult to fabricate –double sided processing –handling Why not use strips?

33 Summary The time coordinate not used in comparison with x,y,x –space gives momentum and topology Time most useful for background rejections –c.f. emulsions –triggering (coarse requirement)

34 Summary cont’d Time TOF –particle ID –solid state only used as part of the system(MCP) –pulses in diodes are slow Time can be used to give spatial information

35 New Technologies Si developments –Oxygenated Si –p-type Si Diamond Polymer diodes Deep Sub-Micron Processing Nanotechnologies Physics