Ingrid devicesfor UV photon detection
Joost MelaiMESA+ institute for Nanotechnology, University ofTwente, the Netherlands
in collaboration with the Weizmann Institute of Science,
Rehovot, Israel
and NIKHEF, Amsterdam, the Netherlands

May 12, 2010

KEK visit - j.melai@utwente.nl

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Overview• Post-Processing on CMOS
• InGrid concept and technology• InGrid performance• Photon detection, photocathodes on InGrid• Experimental results– Charge pulses– Imaging• Summary and outlook

May 12, 2010

KEK visit - j.melai@utwente.nl

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The beginning of Moore’s law
Source:www.intel.com

CMOS
Oxide
Metal
N+

Metal

N+

P

P+

P+

N

Semiconductor
NMOS

May 12, 2010PMOS

KEK visit - j.melai@utwente.nl

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The state of the art: CMOS
IBM

IBM
IBM
Intel

• Nanometer precision• Sub-ppm materials purity

May 12, 2010

KEK visit - j.melai@utwente.nl

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The state of the art: DRAM
• 58-nm DRAM technology
Qimonda (Infineon)

SAMSUNG• Nanometer precision• Sub-ppm materials purity
May 12, 2010

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Moore’slaw
More Moore and More than Moore
Source: ENIAC
Industry &academia

Industry
Industry &academia

May 12, 2010

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Post-processing CMOS
• Chip fabrication: standard,at any regular (CMOS) fab
a. Chip fabricationb. Post-processingc. Wafer dicing

May 12, 2010

• Post-processing: special,in a custom CR laboratory• Wafer dicing, packaging: specialized
work like MEMS packaging, e.g.
Amkor, Boschman
KEK visit - j.melai@utwente.nl

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Pros and cons
• We do not interfere with the(CMOS) fab process• We can buy good quality chips
a. Chip fabrication• We can use any lab for this• We must keep the CMOS intact
b. Post-processing• We have to think the final stages
through very carefully!
c. Wafer dicing

Flexible for R&D; potential for mass-scale manufacturing
May 12, 2010

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Example: Liquid-Crystal-on-Silicon

Cover glass
ElectrodeLiquid crystal
Reflector
CMOS

May 12, 2010

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Example: Digital MicroMirror™

Texas Instruments (1987), used in every DLP projector
May 12, 2010

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Samsung CMOS image sensor
Micro lenses and color filters

May 12, 2010

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Rohmcorp.: CIGS image sensor on
CMOS (IEDM 2008)

May 12, 2010

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CMOS on top of CMOS!
3D integration

A. W. Topol et al.,IBM J. Res. & Dev. 50 (4/5) 491

T ≤ 450 °C

B. Rajendran et al.,IEEE Trans. El. Dev. 54 (4) 707.

Stacking of activedeviceregions
new technology

I. Brunets et al.,IEEE Trans. El. Dev. 56 (8) 1637
May 12, 2010

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CMOS post-processing
Careful treatment of the underlying CMOS:• Temperature ≤ 450 °C• Mild (or no) plasmas• Maintain the H balance in the MOSFET• Limited mechanical stress• Prevent material contamination (spec.
metals)The CMOS properties must be unchanged:
then the standard infrastructure can be used
May 12, 2010

KEK visit - j.melai@utwente.nl

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Overview• Post-Processing on CMOS
– Can we also miniutarize the MWPC?
– Can we use CMOS as the readout anode?
(multiple) GEM

Particle

IntegratedMicromegas

Anode wire
Externalelectronics

Cathodeplaneschip
Patterned anode(μ-PIC, MHSP etc)

InGrid concept and technology
InGrid performance
May 12, 2010

KEK visit - j.melai@utwente.nl

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Overview• Post-Processing on CMOS
– Can we also miniutarize the MWPC?
– Can we use CMOS as the readout anode?

InGrid concept and technology
InGrid performance
IntegratedMicromegaschip• Detector elements– The chip: Timepix– The MPGD: grid and pillars
May 12, 2010

KEK visit - j.melai@utwente.nl

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TimePixvariation of Medipix2,
designed by the Medipix2
collaboration headed by CERN

• 256×256 pixels of 55×55 μm2, charge sensitive• Different readout modes:– MediPix mode: nr of hits per pixel– TimePix mode: time of arrival within shutter window– TOT mode: estimation of total charge per pixel• 0.25 μm CMOS, size 14×16 mm• Post-processing done on chip level or multi-chip cluster levelMay 12, 2010

KEK visit - j.melai@utwente.nl

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SiRN:New anti-spark material••••

Sparks cause permanent damage
Originally a-Si:H, now Si-rich Nitride
Si3N4typical anti-scratch layer on CMOSSiRN, excess of Si to tune resistivity andmechanical stress• Deposited by PECVD at 300 °C or lower

May 12, 2010

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19Spark protection• Protection layer quenches discharges,
removing the built up E-field• Signal still fast by induced mirror charge• Timepix with 7.2 μmSiRN + InGrid• Operation in Ar/Iso 80/20,withalphaparticles
induce sparks• No damage observed, spark protection iseffective
Courtesy of Victor Blanco
Carballo
May 12, 2010

KEK visit - j.melai@utwente.nl

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InGrid: postprocessedMicromegas
•
•
•
•
•

Metal grid (Al) supported by insulating pillars (SU-8)
Pillars in the middle of four pixels
Perfect alignment hole to pixel, pillar to pixel
Arbitrary hole geometry
Integrated MPGD: Micro Patterned Gaseous Detector

May 12, 2010

KEK visit - j.melai@utwente.nl

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InGrid: Integrated Grid

1) Pre-processchip2) Spin SU-8

3) UV exposure4) Deposit metal

5) Pattern metal

6) Develop resist

May 12, 2010

KEK visit - j.melai@utwente.nl

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SU-8 material• Negative tone photoresist (developed by IBM Research)• Polymer based (EPON SU-8 from Shell Chemical)• Available in many viscosities• Thickness ranges from 1 to 1000 µm• Processing similar to normal UV lithography
May 12, 2010

KEK visit - j.melai@utwente.nl

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Examples of SU-8 use• Permanent, high aspect ratio structures

Krijnen et al.,MESA+, UT

Conradie et al.,(Cambridge univ.)
J. Micromech. andMicroeng. 12 (2002)

May 12, 2010

KEK visit - j.melai@utwente.nl

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Examples of SU-8 use• Bio compatibility: lab-on-a-chip applications

B. Xuet al., (Univ.
Shanghai)Sensors andActuators A 132(2006)• Multiple layers of patterned SU-8 alternative
to bonding
May 12, 2010

KEK visit - j.melai@utwente.nl

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Examples of SU-8 use• SU-8 removal using a lift-off layer• A stencil mask made in SU-8
G. Kim et al.
(MESA+, UT),
Sensors andActuators A 107(2003)• SU-8 as plating mold  cheap, fast, UV LIGA
L. Jian et al.
(Louisiana State
Uinv.),SPIE vol. 4979
(2003)

May 12, 2010

KEK visit - j.melai@utwente.nl

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DS of SU-8 mesa capacitor structures

SiO2:
0.8–1 kV/µm

8
VBD [kV]

metal
SU-8
metal

HV
A

SU-8: 443 ± 16 V/µm

6

Kapton-N: 270 V/µm

4

MCP: ≤ 100 V/µm2

MPGD: ≤ 10–20 V/µm

0
0

5

10

15

20

SU-8 thickness [µm]May 12, 2010

KEK visit - j.melai@utwente.nl

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Outgassing from SU-8

T=150 °C• Outgassing rate comparable to Kapton• 20–30 min Hard-Bake efficient pre-conditioning• Components directly linked to resist formulation
May 12, 2010

KEK visit - j.melai@utwente.nl

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Overview• InGrid, integrated MPGD

Window(Kapton orquartz)

cathode bias (HV)
grid bias (HV)and pulsedetection

chip

chip bias
and readout
gas ambient

Capabilities of InGrid
InGrid for photon detection
May 12, 2010

KEK visit - j.melai@utwente.nl

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Chip bonding• Finish post-processing• Attach chip (w/ InGrid) to board• Wirebonding of connections• Mount chamber onto board

May 12, 2010

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InGrid performance• High single e− collection efficiency (> 90% at G=104), set
by field-ratio• Good energy resolution (11.7% FWHM for 55Fe in Ar/CH4)• 2D and 3D tracking of MIPs etc• Different device designs, Micromegas, GEM, multiple
electrodes

May 12, 2010

KEK visit - j.melai@utwente.nl

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Gain in Ar/iso-Butane mixtures

Typicalthresholdlevel,
2–3∙103

From the thesis of Max Chefdeville (NIKHEF)
May 12, 2010

KEK visit - j.melai@utwente.nl

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Homogeneous response

SeperatleymountedMicromegasPost-processedInGrid

Microlithography  alignment tolerance (few μm)
 alignment between pixels and grid (55 μm pitch) no more Moiré patterns
May 12, 2010

KEK visit - j.melai@utwente.nl

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Two 90Sr tracks in a B field
Recorded with a 3 cm Timepix TPC

Courtesy: Martin Fransen and Lucie de Nooij, NIKHEF
May 12, 2010

KEK visit - j.melai@utwente.nl

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InGrid for photon detection• Aim: complete integration of a UV photon
sensitive detector• Based on InGrid technology• High resolution, high sensitivity, high rate
• Photocathode deposited after chip bonding
CsIphotocathodechip

May 12, 2010

KEK visit - j.melai@utwente.nl

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Set-up for photon detection

•
•
•
•

Si-nitride spark protection of 8 μm
Typical InGrid: 80 μm gap, 25 μm holes (OT: 19%)GOSSIP/NEXT chamber, USB readout
CsI is deposited by thermal evaporation, after chip is
processed and mounted on board
May 12, 2010

KEK visit - j.melai@utwente.nl

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Operation principle of alight sensitive InGrid

Steel mesh
Low field:
transfer

Al grid,
200 nm CsIHigh field:
multiplication

pillars

readout

TimePix chippixel nMay 12, 2010

pixel n+1

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Extraction of primary electrons
into He/isobutane
Ar/isobutane(90/10)Ar/CH4 (95/5)

Ar
He/isobutane(80/20)He@ atm. pressure• He shows increased backscattering (compared to Ar)• Addition of quencher (isobutane) restores yield (partially)• High concentration of isobutane leads to UV absorption
May 12, 2010

KEK visit - j.melai@utwente.nl

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IBF

Ion Back Flow (IBF) measurement
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0.00

IBF:
Fraction of anode current
that flows back to cathode(as ions)
Ions can damage
photocathode(surface reactions)0

100 200 300 400
Grid bias voltage [V]500

Options for reduction• Optimization of geometry, field ratio, gas
Saclay (Colas et al.) reported IBF ~ 0.001• Multistage structures (IBF not known)
May 12, 2010

KEK visit - j.melai@utwente.nl

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UV pulses measured on grid
UV or Fe 55 irradiation−HV

Increasing V

mesh cathodegrid with PC
Timepix

Pulse readout(MCA)• He/isobutane (80/20), Al grid with 200 nm CsI• Distribution G(Q) ∝C∙1/G∙exp(−Q/G)• Fit to distribution extract G(V)May 12, 2010

KEK visit - j.melai@utwente.nl40

Gain of InGrid device with PC
UV or Fe 55 irradiation−HVmesh cathodegrid with PC
Timepix

Pulse readout(MCA)• He/isobutane (80/20),Al grid with 200 nm CsI,
80 μm gap height, 25 μm hole size
• slope ≈ 100–110 V/dec, max. gain ≈ 7∙104
May 12, 2010

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Spectra with and without CsI No increase in (photon) feedback
May 12, 2010

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Determining spatial resolution usingslanted edge method
Select ROICorrect using open frame

May 12, 2010

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Determining spatial resolution usingslanted edge method
Select ROICorrect using open frame
Find edge using derivation for alllines and fit a line
Shift line data accordingly

May 12, 2010

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Determining spatial resolution usingslanted edge method
Select ROICorrect using open frame
Find edge using derivation for alllines and fit a line
Shift line data accordingly
Resample into 1 ESF
Calculate LSF
Determine resolution
May 12, 2010

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Determining spatial resolution usingslanted edge method

Fit to LSF:
• Gaussian with σ = 0.48 pixel = 26.4 μm• FWHM = 1.13 pixel = 62.2 μm
Fourier transformation of LSF  MTF
May 12, 2010

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MTF calculated from LSF• MTF50 = 0.4 lp/pixel (≈ 7 lp/mm)• Limit ≈ 0.8 lp/pixel (≈ 14 lp/mm)• Resolution < pixel size (MTF = 0.32 @ fNyquist)
May 12, 2010

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Influence of cathode mesh
Mesh modulates light  non-uniform response,
but also indication of resolution−HV

Pixel pitch = 55 μm

May 12, 2010

Fine mesh (56 μm)
 Moiré pattern
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Coarse mesh (500 μm)
 Mesh is imaged
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More images
Vertical stripes

Siemens star

Fingerprint on
window

Logo of the Universityof Twente
May 12, 2010

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Conclusions• Post processing combines CMOS strengths
with MEMS flexibility• SU-8 pillars and Al grid allow integration of
MPGD on CMOS readout• CsIdeposition on InGrid successful,
CsIPC works on InGrid• Timepix fully operational with PC

May 12, 2010

KEK visit - j.melai@utwente.nl

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Conclusions
Successful integration of MPGD and PC on
CMOS imaging chip:• No photon feedback observed• IBF ≈ 0.02
• Max gain ≈ 7∙104• UV photon imaging capability demonstrated,
external cathode mesh
• Spatial resolution is very good, FWHM of LSF
is 62 μm, resolution limit above fNyquist
May 12, 2010

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Outlook• Qualitative measurement of QE• Multistage structures for better IBF• Otherphotocathodes• Spectroscopic capabilities of Timepix TOT
readout-mode• Other grid materials (spark protection)• Technological limits, alignment and featuresize

May 12, 2010

KEK visit - j.melai@utwente.nl

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Acknowledgement
Weizmann Institute of Science, Rehovot, Israel:
Amos Breskin, Marco Cortesi, Moshe Klin andAlexeyLyashenko
NIKHEF, Amsterdam, the Netherlands:
Victor Blanco Carballo, YevgenBilevych, Max
Chefdeville, Martin Fransen, Harry van derGraaf,
Fred Hartjes, JoopRövekamp, Jan Timmermans
and Jan Visschers
MESA+, University of Twente, the Netherlands:
Cora Salm, Jurriaan Schmitz, Sander Smits, andRob Wolters
This project is sponsored by Dutch Technology
Foundation STW
May 12, 2010

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Questions

May 12, 2010

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Dependence on drift field• TOT count of full frame (in cps)
May 12, 2010

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Gain curve based on TOT count• Fe55: 99 V/dec; TOT: 117 V/dec
May 12, 2010

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TwinGrid
multistage structure to reduce IBF, increase gain

May 12, 2010

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Detector geometries• Hole pitch variation:
20 - 32 - 45 - 58 μm• 20 & 32 μm pitch: pillars insideholes• 45 & 58 μm pitch: pillars between
holes• Hole pitch/diameter variation:
ratio 1.5 - 2.0 - 3.0(hole sizes from 7 - 38 μm)• Amplification gap set by SU-8
thickness, variable with spin speed

May 12, 2010

KEK visit - j.melai@utwente.nl

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