Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.stsci.edu/stsci/meetings/nhst/talks/OswaldSiegmund.pdf Äàòà èçìåíåíèÿ: Tue Apr 15 23:44:51 2003 Äàòà èíäåêñèðîâàíèÿ: Sun Dec 23 05:09:42 2007 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: arp 220

Advances in microchannel plate detectors for Advances in microchannel plate detectors for UV/visible Astronomy UV/visible Astronomy
Dr. O.H.W. Siegmund
Space Sciences Laboratory, U.C. Berkeley

Advances in:Photocathodes (GaN, Diamond, GaAs) Microchannel plates (Silicon MCP's) Readouts (Cross strip) Are changing the tools and performance of photon counting imaging detectors available for future UV missions achieving better QE, lower background, higher resolution, better uniformity, linearity and better lifetimes.
Work funded by NASA grants, NAG5-8667, NAG5-11547, NAG-9149
Space Sciences Lab, UC Berkeley, CA, USA 1 April 11, 2003


EUV Photocathodes, 100å - 2000å
Alkali Halide UV Photocathodes have improved substantially as a result of better fabrication techniques and geometrical optimization
0.7 CsI CsI CsI CsI CsI CsI 1985 30° 1985 20° #3 2/99 20° #3 2/99 30° #2 1/99 20° #2 1/99 30°

1

0.6

0.5

0.4

Qua ntum Effi ci e ncy

QDE

0.1

0.3

CsI
KI
KBr

0.2

0.1

0 0 500 1000 1500 2000

0.01 0 500 1000 1500 2000

Wavelength (å)

Opaque Alkali Halide Photocathodes - MCP substrate

W a ve le ngth (A)
Opaque Alkali Halide Photocathodes - metal substrate

Space Sciences Lab, UC Berkeley, CA, USA

2

April 11, 2003


EUV Photocathodes, 100å - 2000å
Diamond Photocathodes on Silicon and Si MCP's Polycrystalline boron doped diamond, band gap - 5.47 eV (227 nm) - Solar blind. Hydrogenated and cesiated diamond exhibit NEA. Cathodes are air stable (<10% drop in 18 hours)and are very mechanically robust. Can be ultrasonic cleaned in water and alcohol. Re-hydrogenation restores QE.
1

Diamond coated Silicon MCP

0.1

QDE

0.01

#2 #1 #5 #8 21201 Si MCP 20801 20501 0 500

Pre-hydrogenated values
1000 1500 2000

0.001

Diamond photocathode UV efficiency
Space Sciences Lab, UC Berkeley, CA, USA

Diamond Photocathodes on Silicon and Si MCP's
3 April 11, 2003

Wavelength (å)


EUV Photocathodes, 100å - 2000å
Diamond cathodes have been grown on Si MCP's, appropriately for EUV sensors Activation of diamond indicates that very high EUV DQE's are possible

Diamond Photocathode on Silicon MCP (Nanosciences)

At smaller incidence angles than 90° the QE improves significantly for planar layers

Space Sciences Lab, UC Berkeley, CA, USA

4

April 11, 2003


GaN Photocathodes, 1000- 4000å
Potentially high UV QE and cutoffs from 350nm to 450nm Basic strategy is to achieve NEA using Cs activation. Material, cleaning & activation processes all under study. Working with Northwestern U. (Ulmer, Wessels).
1
T samples processed by Nanosciences 2003

Quantum Detection Efficiency

0.1

0.01

0.001 100

150

200

Wavelength (nm)

250

300

350

400

Early GaN photocathode comparisons [Ulmer 2001]
Space Sciences Lab, UC Berkeley, CA, USA 5

Opaque GaN photocathodes on Sapphire UCB supplied samples, Nanosciences processing
April 11, 2003


GaN UV Photocathodes, 1000- 4000å
1
JG238/T/TT samples 2003 Ulmer et al 2001

GaN Opaque Photocathodes Opaque First tests showed poor QE with Cs activation - except at short wavelength. Initial sealed photodiode tubes were slightly better, and showed no degradation over > 6 months.

Quantum Detection Efficiency

0.1
Early sealed tube, MgF window
2

JG238 early attempt

Improvements in processing have improved the QE substantially. Cutoff is quite sharp at 370-390nm. As NEA improves the longer wavelength QE and enhances the cutoff characteristics.

0.01

0.001 150

200

250

Wavelength (nm)

300

350

400

450

Development of opaque GaN photocathodes on sapphire substrates, with Cs activation
Space Sciences Lab, UC Berkeley, CA, USA 6

~40% QE for < 250nm is significantly better than CsI or CsTe, and shows promise for further >250nm improvements.
April 11, 2003


GaAs Visible and NIR Photocathodes
GaAs has high visible/NIR QE (50%), and noise is 10 events/sec at -20°C. Can adjust bandpass blue end response. Photon counting with time response ~1ns. No cosmic ray background effects. Can combine with high spatial resolution large area imaging MCP readouts. Astronomy - interferometry, time resolved spectroscopy and imaging.

GaAs photocathode efficiency (courtesy ITT)
Space Sciences Lab, UC Berkeley, CA, USA 7

GaAs photocathode blue variants (courtesy ITT)
April 11, 2003


Silicon MCP Developments
Silicon MCP's
Silicon MCP's are made by photo-lithographic methods Photolithographic etch process - very uniform pore pattern No multifiber boundaries & array distortions of glass MCP's Large substrate sizes (100mm) OK, with small pores (5µm) High temperature tolerance - CVD and "hot" processes OK UHV compatible, low background (No radioactivity) Development in collaboration with Nanosciences. Typical Silicon microchannel plates in test program 25mm diameter (75mm currently feasible) 40:1 to 60:1 L/D (>100:1 possible) 7µm pore size, hexagonal and square pore ~2° bias and 8° bias, resistances ~G, to <100M possible Working on processing techniques to improve uniformity Techniques for gain & QE enhancement under investigation
8cm Si MCP on 100mm substrate
Space Sciences Lab, UC Berkeley, CA, USA 8 April 11, 2003

Hexagonal pore Si MCP with ~7µm pores, >75% open area


Silicon MCP Performance Characteristics
Many Si MCP's of 25mm diameter with ~7µm pores have been tested The performance is improving as production is being refined. Gain is similar to glass MCP's. Open area ratio is up to >75% for hexagonal pores Gain decrease during scrub is smaller and faster than glass MCP's
1.00E+05
Si 208

CVD 105-1

Glass MCP

CVD107-5

1.00E+04

CVD106-1

CVD120-2

CVD114-1-c

CVD122-2

1.00E+03
Gain

CVD122-4

CVD122-4-BEO

CVD134-1

CVD134-4

1.00E+02

CVD139-2

CVD139-4

ITT Glass MCP

CVD169-3

1.00E+01

1.00E+00 0 500 1000 Voltage (V) 1500 2000

Gain evolution of single Si MCP's
Space Sciences Lab, UC Berkeley, CA, USA 9

MCP gain as a function of extracted charge, for one Si MCP.
April 11, 2003


Silicon MCP Performance Characteristics
Gain and pulse height very similar to glass MCP's, stacks of Si MCP's (4) with gain up to 10 Quantum detection efficiency is similar to good bare glass MCP's (COS, EUVE, 12/10/6µm) The background rate is lower (0.02 events cm-2 sec-1) than normal or low background glass Gain and response uniformity are reasonably good. No "hex" modulation!
0.2
6

12/10µm COS
Si MCP Bare glass Si Hex MCP

0.15

6µm pore MCP

0.1

0.05

0 200

400

600

800

1000

1200

1400

Wavelength (å) QDE for Si & bare glass MCP's vs Wavelength
Space Sciences Lab, UC Berkeley, CA, USA

Contrast enhanced image of the fixed pattern response to a Hg vapor lamp with a stack of 4 Si MCP's. ~14mm area, 107 counts, ~50µm resolution XDL.
10 April 11, 2003


Cross strip anode readout

32mm x 32mm XS anode, 0.5mm period
Cross strip is a multi-layer cross finger layout. Fingers have ~0.5mm period on ceramic. Charge spread over 3-5 strips per axis, Event position is derived from charge centroid. Can encode multiple simultaneous events. Fast event propagation (few ns). Anodes up to 32 x 32mm have been made Signals are routed to anode backside by hermetic vias Packaging can be compact with amp on anode backside Overall processing speed should support >> MHz rates Compact and robust (900°C).

Bottom fingers

Space Sciences Lab, UC Berkeley, CA, USA

11

April 11, 2003


Cross Strip Anode Electronics Chain
Basic encoding sequence
X Fingers
16

Preamp

16

Shaper

16

50 Ohm Driver

16

ADC

Small, low power ASIC encoding with sparsification reduces data throughput requirements
Discriminator

16

DIGITAL INTERFACE

Cross strip anode position encoding electronics test-bed system. All signals amplified and digitized. Can choose up to 12 bits per signal.

Anode backside showing connectors for the external board where preamplifier chips are mounted. Currently amplifiers have ~600e- rms noise.
12 April 11, 2003

Space Sciences Lab, UC Berkeley, CA, USA


Cross Strip Anode Readout
~7µm pores are resolved, <3 µm electronic resolution with 10 bit encoding electronics Image linearity is ~1µm level and shows pore misalignments and multi-fiber boundaries Gain required is <4 x 105, allows higher local event rates than normal readouts Lower gain means longer overall MCP lifetime due to reduced scrubbing

Outstanding Spatial Resolution/Linearity

Similar image of 7µm pore MCP pair at 2 x 106 Gain .

Flood image of 12µm pore MCP pair at 4 x 10 Gain, 1mm square area.
Space Sciences Lab, UC Berkeley, CA, USA

6

13

April 11, 2003


Resolution of Cross Strip MCP Sensors Resolution of Cross Strip MCP Sensors
Gain 1.3 x 10
6

4 x 10 1.1 x 10
6

5

1.8 x 10

5

7µm pore MCP pair
Space Sciences Lab, UC Berkeley, CA, USA 14

10µm pore MCP pair
April 11, 2003


Advanced MCP Sensors for Astrophysics Advanced MCP Sensors for Astrophysics Developing Detector Prospects Developing Detector Prospects
High QE cathodes (Diamond, GaN, GaAs) with ~50%QE covering 20nm - 850nm Si MCP's with low fixed pattern noise, <5µm pores, background 0.02 events cm-2 sec Cross-strip readouts with <5µm resolution, >50mm formats, >10k x 10k "resels" Packaging is shrinking while spatial resolution & QE are increasing dramatically.
-1

GALEX 65mmsealed tube XDL detector
Space Sciences Lab, UC Berkeley, CA, USA 15

COS 2 x 85mm XDL detector
April 11, 2003