development of a 10-inch hpd with integrated readout...

Beaune 2002, C. Joram / CERN

Development of a 10-inch HPD

with Integrated Readout Electronics

A. Braem, E. Chesi, C. Joram, J. Séguinot, P. WeilhammerCERN

M. Giunta , N. Malakhov, A. Menzione, R. Pegna, A. Piccioli, F. Raffaeli INFN Pisa

1. CLUE – an air shower Cherenkov experiment2. The 5-inch Pad HPD3. Development of a 10-inch HPD4. Rb2Te photocathode5. Self triggering readout electronics


CLUE = Cherenkov Light Ultraviolet Experiment

Imaging Air Cerenkov Telescopewith 9 detector units

40 m Single unit" F/1 Parabolic Mirror, 1.8 m Ø" UV Detector in focal plane

e-

quartzgas

+ TMAE

segmented cathode

…………………..Npe ~ ∫ QE·Tquartz · TO2 dE

now futureMWPC 10” HPD

× 20


1 step back: The 5-inch Pad HPD

hν

e-

Si sensor

Focusing electrodes

Indium joint

127 mm

• Bialkali K2CsSb cathode on UV extended borosilicate window (schott 8337)

• 114 mm active diameter• Si sensor, 2048 channels, 1 × 1 mm2

• Integrated readout electronics (IDEAS VA2, VA-prime)

• Nominal operational voltage: 20 kV

• Originally developed for LHCbRICH detectors

• Since January 2000 continued as independent R&D project

• Fountain focusing optics• D ~ 2.4 à segmentation on cathode 2.4 × 2.4 mm2

VA2 chips Ceramic with 2 signallayers

Si detectorWire bonds


QE and uniformity (K2CsSb cathode)

Radial dependence of the quantum efficiency of HPD PC68 for λ=230, 290 and 350 nm.Non-uniformity (±10%) mainly due to reflections from Si and electrodes.

200 300 400 500 600

lambda (nm)

0

4

8

12

16

20

24

28

32

Q.E

. (%

)

HPD PC87(produced Easter Sunday 2001)

trans

pare

ncy

of w

indo

w

“one of the best”

Peak QE in the range 25±3% is routinely reached !


15 16 17 18 19 20

Ucathode (kV)

7.0E-004

8.0E-004

9.0E-004

1.0E-003

1.1E-003

1.2E-003

1.3E-003

1.4E-003

1.5E-003

nois

e / p

ad /

trig

ger cut pedestal noise at nσ = 4

HPD PC100

2 3 4 5 6 7 8 9 10 11

pedestal cut nσ

1.0E-004

1.0E-003

1.0E-002

nois

e / p

ad /

trigg

er

Ucathode = 20 kV

HPD PC100

total noise

electronics noise

HPD 'proper' noise

-2 -1 0 1 2point spread function (on silicon) (mm)

0

10

20

30

40

50

60

70

80

90

100

coun

ts

σ = 0.45 mm

20 kV, cos(θ), 1.5 eV

Simulation SIMION 7.0

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60r cathode (mm)

-25

-15

-5

5

15

25

r sili

con (m

m)

Linear demagnificationD = 2.60

HPD PC100


0 2 4 6 8 10 12 14 16 18 20 22Ucathode (kV)

0

5

10

15

20

25

sign

al a

mpl

itude

(A

DC

cha

nnel

s)

E0 = 1.5 keV

HPD PC100

0 10 20 30 40 50 60 70 80 90 100

signal amplitude (ADC channels)

0

20

40

60

80

100

120

140

160

coun

ts

HPD PC100

20 kV VA' chip set (350 ns shaping time)

<signal> = 23.13σ = 2.74

4 σ

cut


LHCb beam test with aerogel radiator (May 2001)

Courtesy of LCHb/RICH group

Use Pad HPDsPC84 / 85 / 86 / 87

See separate poster(Tito Bellunato et al.)


The 10-inch HPD

Characteristics of the final version

• Rb2Te cathode, 4-7 eV, “solar blind”

• Quartz or UV ext. borosilicate window

• Demagnification ca. 4

• Segmentation on cathode level ca. 4 x 4 mm2

• Integrated self triggering electronics

• Envelope originally designed and fabricated for the AQUARICH prototype experiment (T. Ypsilantis et al.)


HPD’s development and production at CERN

1998 – 2001 à HPD 5”• Optimised for RICH

applications (LHCb)

• K2CsSb photocathode

• UV extended window

• 2048 readout pads

• Optimised for Cherenkov based air shower detectors

• UV extended (or quartz) window

• Rb2Te photocathode

2001 - 2003 à HPD 10”


U = -20 / -19.6 / -16. / -13.5 / -7 kV

Electron optical simulations(SIMION 7.0)


D ~ 4

0 5 10 15 20 25 30R silicon (mm)

0

20

40

60

80

100

120

R c

atho

de (

mm

)

-5 -4 -3 -2 -1 0 1 2 3 4 5

xsilicon (mm)

-5

-4

-3

-2

-1

0

1

2

3

4

5

y silic

on (

mm

)

Electron optical simulations (cont’d)

Linear demagnification up to R=120 mm

Electron distribution on silicon for pointsource at xcathode = ycathode = 0

projection

-5 -4 -3 -2 -1 0 1 2 3 4 5point spread function (mm)

0

20

40

60

80

100

120

140

160

RMS = 1.3 mm

Ucathode = -20 kV

<Ekin> = 1.5 eV, cos(θ) distributed emission


The Rb2Te photocathode

200 250 300 350 400 450 500

λ (nm)

0.00001

0.00010

0.00100

0.01000

0.10000

1.00000

10.00000

Q.E

. (%

)

Cs2Te

Rb2Te

Hamamatsu….Rb2Te has similar

characteristics than the well known ‘solar blind’ Cs2Te cathode.

However, very important for our application: the response of Rb2Te above 300 nm is ~10-100 times lower.

Resistivity of cathode is very high: > 1010 O/•Conductive under-coating required to allow for reasonable photocurrents and uniform cathode response.


Indium Tin Oxide (ITO) ïð Chromium as transparent conductive layers

Our standard layer:

• ITO film thickness : 3.2nm• Vacuum evaporated + post oxidation in air at 300ºC for 8 hours

Measured transmission of UV extended glass (Schott 3337) coated with ITO

0

0.2

0.4

0.6

0.8

1

200 300 400 500 600Lambda [nm]

Tra

nsm

issi

on

window

window + ITO

Resistance versus average transmission (200 - 400nm) of ITO and Cr thin films on Quartz

0.40

0.50

0.60

0.70

0.80

0.90

1.0E+03 1.0E+05 1.0E+07 1.0E+09 1.0E+11Resistance [ohm/square]

Tra

nsm

issi

on

Cr 1.9nm Cr 3nmCr 5.5 ITO 1.6nmITO 2.6nm ITO 3.2nmITO 3.9nm ITO 4.8nmITO 5.9nm ITO 6.3nm

Cr

ITO

3.2 nm


The Rb2Te co-evaporation process

Turbo Pump

monochromator(200-800 nm)

Te Rb

• Excellent vacuum after bake-out (160ºC, tube at 300ºC)

p ~ 5•10-9 mbarpH2O ~ 1•10-9 mbar

• Tank + substrate at T ~ 70ºC

• Permanent monitoring of Iphoto, all other essential parameters (p, T, Isource)

• Start with evaporation of Rb only à Iphoto ~ few pA

• Co-evaporate Rb and Te

• Stop when Q.E. (250 nm) reaches maximum


The HPD development plant

• Coat substrates up to φ 10”

• Adapted to UV–VIS PCs, from 200 to 800 nm

• Press mechanism for cold indium encapsulation (2.5 tons)

• Production capacity limited to~ 1.5 HPD / week


200 240 280 320 360 4000

2

4

6

8

10

12

14

16

18

20

QE

(%

)PC99, Rb

0

10

20

30

40

50

60

70

80

90

100

T H

PD

(%

)

λ (nm)

Direct measurement

Extrapolation to quartz window

200 240 280 320 360 400

λ (nm)

0.001

0.010

0.100

1.000

10.000

QE

(%),

extra

pola

ted

to q

uartz

win

dow

HPD PC101

HPD PC99 HPD PC101

Two HPDs produced

Ref. Hamamatsu


Side discovery: Under-layer has strong influence on cathode growth.

0

8

16

24

32

Q.E

. (%

)

PC 92 (ITO, 3nm)

250 350 450 550 650

λ (nm)

PC 87

PC90 (ITO, 3nm)

PC 93

ITO seems not work for K2CsSb cathodes !

200 220 240 260 280 300 320 340 360 380 400

λ (nm)

0

1

2

3

4

5

6

7

Q.E

. (%

)

hemiphere with ITO

hemisphere without ITO

no correction for transparency of borosilicate window

Photocathode PC96

º»Half of HPD window coated with ITO (3 nm)

ITO noITO

2 bialkali photocathodes with ITO2 bialkali photocathode without ITO


Set-up for holding and heating the 10” envelope during evaporation

All components machined in Pisa, most of them now finished.

Heater consisting of 3 spiral heating

elements.

2

3

1

envelope


preamp slowshaper

S&H

silicon diode

hold

Vthr

trigger out

silicon diode Vthr

rea

do

ut

log

ic (

se

ria

l o

r s

pa

rse

)

gainfastshaper discr. monostable

128 channels

differential analog out

200 ns

3 µs

Electronics: IDEAS VaTagp3 - a self triggering analogue chip

Sparse readout scheme allows readout rates > 100 kHz.

Existing chip:

= 3 µs

= 150 ns

noise ~ 350 e- (ENC)

slowpeakτfastpeakτ

Faster chip under design

= 1 µs,

= 35 ns

slowpeakτfastpeakτ


Summary and outlook

The 5-inch Pad HPD works up to specifications. Development practically finished.

The ingredients for the fabrication of a 10-inch solar-blind HPD are being developed

• Co-evaporation process è Excellent Rb2Te (ITO) photocathodes

• Two 5” HPD with Rb2Te cathodes (borosilicate window) produced and characterized

• Electron-optics of 10” tube studied

• Most of the mechanical components for the evaporation plant available

Time plan

• Still in 2002: First 10” HPD with bialkali cathode on glass window, VA-prime electronics

• Summer 2003: First 10” HPD with Rb2Te cathode on quartz window, VaTagp electronics

In our spare time we dream of another nice gadget…


Development of a proximity focused HPD

• Optimized for medical applications

• K2CsSb photocathode

• Flat Sapphire window

• Ceramic rectangular body

• Very high active area fraction

development of a 10-inch hpd with integrated readout...

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