Solid State Detectors 5 T Bowcock 1 Schedule

Solid State Detectors- 5 T. Bowcock 1

Schedule 1 2 3 4 5 6 Position Sensors Principles of Operation of Solid State Detectors Techniques for High Performance Operation Environmental Design Measurement of time New Detector Technologies 2

Time - the fourth coordinate • Three Reasons time is used – to separate signal from background – particle identification – improvement in resolution 3

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 4

TOF Start time 5

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) 6

TOF K-p p-K 7

E 896 TOF 8

Traditional Methods 9

Scintillation Intrinsically fast<0. 1 ps 10

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

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 12

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

Operation of MCP 14

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

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

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

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 18

Counting Time • Direct clock counting (1 ns) • Digital interpolation of GHz clock (0. 2 ns) • Time Stretcher – best resolution available is about 1 ps • Le. Croy 19

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 20

Intrinsic limit • At 1 ps 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 21

TOF + telescope • Not just used in HEP • Galileo Probe 22

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

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

PIN diodes • Charge may be stored in a pnn+ diode structure • At 4. 2 K trapping time>105 s p+ n-doped --- Intrinsic n+ 25

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

Tunneling from trap Conduction Band Finite Tunneling Probability 27

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

Silicon Drift V V-d. V V-2 d. V V-3 d. V n 29

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 laserinduced charge injection Anode structures around the guard zone allows to study leakage currents in this region Detector is fabricated on 3. 5 k. Ohm/cm NTD N Si 30

ALICE SDD 31

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? 32

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) 33

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 34

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