Solid State Detectors- 5

T. Bowcock

2

Schedule

1 Position Sensors

2 Principles of Operation of Solid State

Detectors

3 Techniques for High Performance Operation

4 Environmental Design

5 Measurement of time

6 New 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 velocity22

221 /)(1667 pmmLdt

(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-multiplierOften made of glasscan 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 glasslimits 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>105s

- - -

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 1m

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

Al

-V

-V

p

p

29

Silicon Drift

V V-dV V-2dV V-3dV

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