1. Micropattern Gas Detectors
Oleg Bouianov, M.I.T. Cambridge
KEK, Tsukuba, 21 February 2004
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

2. Oleg Bouianov, M.I.T. Cambridge
Outline
Introduction to micropattern gas detectors.
MSGC, GEM, MICORMEGAS, MSHP.
3D simulations of gas detectors.
Limitations of micropattern detectors.
Imperfections of detector fabrication.
µPIC, MDOT.
New materials and fabrication methods.
MIPA.
Trends in micropattern detector development.
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

3. Processes in Gas Detectors
Ionisation
Charge
Transport
Charge
Multiplication
Signal
Formation
-0.015
-0.01
-0.005
0.02
0.04
0.06
0.08
0.1
x 10 -5
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

4. History and introduction to micropattern gas detectors
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

5. MWPC: Multi-Wire Prop. Chamber
Georges Charpak
Nobel Prize in Physics 1992
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

6. Limitations of MWPC
F.Sauli, APS-DPF2000
Counting rate is limited by space charge to ~104 Hz/mm2
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

7. Oleg Bouianov, M.I.T. Cambridge
Aging of MWPC
Anode wire deposits
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

8. Oleg Bouianov, M.I.T. Cambridge
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

9. MSGC: Micro-Strip Gas Chamber
A. Oed, NIM A 263 (1988) 351.
Drift electrode
200 µm
Anode strip
Glass support
Back plane
Cathode strips
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

10. Oleg Bouianov, M.I.T. Cambridge
MSGC vs MWPC
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

11. Oleg Bouianov, M.I.T. Cambridge
MSGC Dimensions
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

12. Oleg Bouianov, M.I.T. Cambridge
MSGC: Discharges
FULL BREAKDOWN
MICRODISCHARGES
F.Sauli, IEEE NSS 2002
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

13. Oleg Bouianov, M.I.T. Cambridge
MSGC: Discharges
F.Sauli, IEEE NSS 2002
For detection of minimum ionizing tracks a gain ~ 3000 is needed
In presence of heavily ionizing particles background, the discharge probability is large
ON EXPOSURE TO a PARTICLES
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

14. Oleg Bouianov, M.I.T. Cambridge
Aging of MSGC
R. Bouclier et al, NIM A381(1996) 289
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

15. Oleg Bouianov, M.I.T. Cambridge
MICROMEGAS
Thin-gap parallel plate chamber
Y. Giomataris et al, Nucl. Instr. and Meth. A376 (1996) 29
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

16. Oleg Bouianov, M.I.T. Cambridge
MICROMEGAS
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

17. GEM: Gas Electron Multiplier
F.Sauli, CERN 1997
GEM Dimensions
45μm
75 μm
140 μm
50 μm
Copper
Kapton
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

18. Oleg Bouianov, M.I.T. Cambridge
GEM operation
Particle traversing the detector volume
Ionization
Drift of primary charges
Avalanche multiplication
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

19. Oleg Bouianov, M.I.T. Cambridge
Cascaded GEM
GEM #1
GEM #2
-0.015
-0.01
-0.005
0.02
0.04
0.06
0.08
0.1
x 10 -5
Pad readout
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

20. Cascaded GEM: Simulated
Strengths of simulations:
Each electron and ion can be individually traced.
Nano-scale study of all major processes.
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

21. Features of GEM-based Detectors
Flexibility.
Charge multiplication and signal formation are separated
Gas gain can be optimised by cascading GEMs
Freedom in selecting a signal readout geometry
Only signal due to electrons is seen.
Ion feedback suppression.
Inexpensive to manufacture in large area.
High-rate operation.
Gain uniformity over large detector areas.
Stability at high gas gains (cascaded).
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

22. Micro-Hole and Strip Plate (MHSP)
A cross between MSGC and GEM
J.M. Maia et al., IEEE Trans. Nucl. Sci. NS-49 (3) (2002) 875
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

23. Oleg Bouianov, M.I.T. Cambridge
MHSP Operation hv
photocathode
Features:
Double-stage amplification
Low ion feedback
Low UV photon feedback
cathode mesh
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

24. 3D Simulation of Gas Detectors
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

25. Why 3D Simulation? 2D: Electric field lines 3D: Field strength
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

26. Why 3D Simulation? 2D: Avalanche 3D: Avalanche and charge sharing
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

27. Oleg Bouianov, M.I.T. Cambridge
Simulation Flow
Simulation Tools
Maxwell
FEM 3D Electric Field Simulator
Garfield
3D drift chambers simulation
Heed
gas ionisation by particles
Magboltz
electron transport properties in gas mixtures
Maxwell
Garfield 3D
Geometry
Model
Generate
Data
Charge
Transport
Magboltz
Mesh
Generation
Gas Data
Track
Particle
Field
Calculation
Heed
Ionisation
Data
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

28. FEM Modelling of e-Field
3D Detector Model
Mesh Generation
FEM Field Calculation
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

29. GEM Simulation Studies
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

30. Early effort on GEM simulations
Setting up simulation environment (1999).
Validation and comparison with published measurement results.
O. Bouianov et al., “Progress in GEM simulation”, Nuclear Instruments and Methods in Physics Research A, 450 (2000),
Study of charge losses.
O. Bouianov et al., “Foil geometry effects on GEM characteristics”, Nuclear Instruments and Methods in Physics Research A, 458 (2001),
Study of gas gain instabilities.
O. Bouianov et al., “Charging-up effects in the gas electron multiplier”, Research reports B24, Laboratory of Computational Engineering, Helsinki University of Technology, 2001, ISBN
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

31. Oleg Bouianov, M.I.T. Cambridge
Studied geometries
(a) cylindrical
(b) biconical
(c) conical
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

32. Oleg Bouianov, M.I.T. Cambridge
Detector modelling
Minimisation of detector volume for various hole distribution patterns:
(a) hexagonal
(b) rectangular
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

33. Study of charge transport in GEM
3D model of GEM.
E-field calculation.
Gas properties.
Primary charge generation.
Propagation of charges (with or without diffusion).
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

34. Deposition of charges (losses)
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

35. Modelling of dielectric charging
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

36. Modelling of dielectric charging
Distribution of electric potentials
in GEM:
initial
modified by charging
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

37. Comparison with measurements
The alteration of the effective gas gain: measured (dots) and simulated (solid curve).
R. Bouclier et al., Nucl. Instr. and Meth. A, 396 (1997), 50.
time constants 1/ 2 =6
total equivalen resistance R≈150∙109 Ω
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

38. Typical characteristics of gaseous micropattern detectors
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

39. Shortcomings of gaseous micropattern devices
discharges at high count rates and gains
low effective gas gain
space-charge effects
time-dependent gain variation (dielectric charging)
slow response due to ions
gain non-uniformity across detector area
aging
limited energy resolution (>20% E/E FWHM) …
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

40. Discharges in micropattern detectors
A. Bressan et al, NIM A 424 (1999) 321
Systematic study of discharges by F.Sauli at CERN.
Irradiation:
high-rate soft X-rays + heavily ionizing alpha particles.
All single-stage micropattern detectors show similar limitation due to discharges at a gain of few thousand.
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

41. Imperfections of detector fabrication
Fabrication process limitations:
Layer-to-layer registration
Photolithography errors
Isotropic etching process
Electrode shape errors (undercut)
Dielectric shape errors
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

42. Oleg Bouianov, M.I.T. Cambridge
GEM: close look
CERN
Imperfections of wet etching and RIE.
CERN
Fuchigami Co
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

43. Modelling of realistic structures
The effect of MPGD fabrication imperfections has been studied.
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

44. Modelling of realistic structures
Smoother electrode structure.
Twofold decrease of the field strength.
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

45. Fabrication techniques: a comparison of results
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

46. MDOT: Micro – Dot Chamber
A remarkable detector with high gain and low discharge rate
Metal electrodes on silicon: microelectronic fabrication process
S. Biagi et al, Nucl. Instr. and Meth. A361 (1995) 72
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

47. Oleg Bouianov, M.I.T. Cambridge
MDOT performance
No discharges observed at high rates with alphas up to the gains 2104
A. Bressan et al, NIM A 424 (1999) 321
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

48. µPIC: Micro Pixel Chamber
New micrpattern detector
Developed at Kyoto University
Similar to MDOT
PCB technology
Discharges at gains of few thousand.
A. Ochi et al., Nucl. Instr. and Meth. A 471 (2001) 264.
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

49. Oleg Bouianov, M.I.T. Cambridge
µPIC vs MDOT
µPIC
MDOT
Technology
Advanced PCB
Microelectronic
Electrode thickness
10 µm
~ 1 µm
Feature tolerances
> 10 µm
~ 0.5 µm
Performance
average
exceptional
Reasons for different performance:
Technology imperfections? …
T.Nagayoshi, Kyoto group
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

50. New Materials and Manufacturing Technologies
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

51. Scale-up: “macropattern”
LC TPC R&D: LEM or Macro-GEM
“Macro-GEM” structure is manufactured and its performance studied at MIT/LNS.
Macro-GEM geometry
Hole pitch
2.5 mm
Max. hole diameter
1.2 mm
Min. hole diameter
0.6 mm
Copper thickness
50 m
Dielectric thickness (G10)
150 m
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

52. Microstructure detectors
Scale-down
Microstructure detectors
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

53. Photoplastics for MEMS
Polyimide
Low aspect ratio (< 3:1)
~80 m thick
SU-8 epoxy PR – popular material for MEMS microfabrication
High UV transparency
High aspect ratio (>10:1)
Straight walls
> 500 m thick spin coated
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

54. Microfabrication with photoplastics
Spin coating
SU-8 process
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

55. Examples of SU-8 microstructures
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

56. Molding of metal structures
Results in precise metal shapes with smooth surfaces.
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

57. Early attempts to produce gas detectors with MEMS techniques
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

58. Oleg Bouianov, M.I.T. Cambridge
MSGC type structures
M. Key CNM, Barcelona
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

59. MIPA: Micro-Pin Array Uses new materials and fabrication processes
Matrix of individual needle proportional counters
P. Rehak et al, IEEE Trans. Nucl. Sci. NS-47(2000)1426
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

60. SU-8 Radiation Hardness
M. Key CNM, Barcelona
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

61. Oleg Bouianov, M.I.T. Cambridge
Not a Conclusion
1928
1988
2000 G e n r a t i o s f g u d c 3 rd
generation 2 nd
generation 1 s t g e n r a i o 4 × 10 2 3 D e t c o r s l u i n , m 5 50
500 S g d a v 1 st
gene-
ration 2 nd
gene-
ration 3 rd
gene-
ration
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge

62. Oleg Bouianov, M.I.T. Cambridge
Thank you …
21 Feb 2004
Oleg Bouianov, M.I.T. Cambridge