Nex Ray 2013, Nano-Tera 2013
-
Upload
nanoterach -
Category
Documents
-
view
289 -
download
0
description
Transcript of Nex Ray 2013, Nano-Tera 2013
-
Nexray RTD 2009
2013 | Page 0
Nexray A. DommannA, H. von KnelC, P. GrningB, T. BandiA, S. BeerA,
A. BischofA, R. BergamaschiniD, C. BosshardA, F. CardotA, D. ChrastinaD,
S. CecchiC, H. ElsenerB, C. FalubC, J. FrigerioC, S. GiudiceA, A. GonzalezC,
F. IsaD, G. IsellaD, R. Jose JamesA, R. KaufmannA, C. KottlerA, T. KreiligerC,
R. LongtinB, L. NeumannA, A. MarzegalliD, L. MiglioD, S. MouazizA, A. NeelsA,
P. NiedermannA, A. PezousA, J. SanchezB, G. Spinola DuranteA, Y. ZhaA
A: CSEM C: ETHZ,
B: EMPA D: L-NESS, Politecnico di Milano,
Como, Italy
Bern, 30. 5. 2013
-
2013 | Page 1
Nexray RTD 2009
A System Approach
Source Sample Detector
Contrast mechanism Resolution, Size, Efficiency Spectrum, power,
Coherence, Size
Miniaturized, fast
and programmable
X-ray sources
Phase contrast X-
ray imaging
Direct X-ray
detectors without
bump-bonding
Breakthroughs required in all key building blocks of X-ray systems
-
2013 | Page 2
Nexray RTD 2009
Network of Integrated Miniaturized X-ray Systems Operating in
Complex Environments
Single-photon solid-
state X-ray detection
Si-Ge layers high-
energy X-ray detection
Miniaturized, fast and
programmable X-ray sources
-
2013 | Page 3
Nexray RTD 2009
Novel Concepts of Applications
Large area or pixelated X-ray sources
Pulsed operation of X-ray source (and individual source-pixels)
Smart and economic X-ray detectors, applicable in medical diagnostics
For applications like e.g. static tomography
or X-ray time of flight measurements
-
2013 | Page 4
Nexray RTD 2009
Successful Concept-Proofs for Components
An array of 4 miniaturised sources and
a dental X-ray film proving that X-rays
were emitted
A ground-breaking
semiconductor integration
enabling economic and
smart X-ray detectors
-
Nexray RTD 2009
2013 | Page 5
X-ray Sources
-
2013 | Page 6
Nexray RTD 2009
X-ray Source Concept
-
2013 | Page 7
Nexray RTD 2009
CNT Based X-ray Source Electron Field Emission
EE
AEI
NordheimFowler
5.172
6 1083.6exp
1056.1)(
)1926(
E: Electrical Field
U: Voltage
d: Distance
h: Height of the Tip
r: Radius of the apex
Electron Emission from SWNT
Imax = 25 mA/SWNT
jmax = 100000000 A/cm2
-
2013 | Page 8
Nexray RTD 2009
Developed CNT Cathode Technologies
Coatings with randomly oriented CNTs
a) b)
a) Joining Technology (brazed CVD CNT film)
b) Paste Technology (CNT, graphite, clay paste)
Characteristics of the cathode Only a few electron emitters
Low current cathode (max. 200 mA)
High current density per emitter
Low onset field (high field amplification)
Applications: Display, X-ray source,
mass spectrometer
CNT Arrays
1 mm 10 mm
Characteristics of the cathode Many electron emitters
High current cathode (< 3 mA)
Low current density per emitter
High onset field (low field amplification)
Applications: m-wave Amplifiers, fine focus X-ray source
Plasma Enhanced CVD Process
-
2013 | Page 9
Nexray RTD 2009
Paste based Field Emission Cathode Field enhancement/Emission Stability
Matrix
CNT
As deposited
Mechanically
abraded
Composition of
the CNT Paste 50 wt% Graphite
20 wt% Glass
15 wt% MWNT
7 wt% Clay
High-temperature processable carbon-silicate nanocomposite cold electron cathodes for miniature X-ray sources
R. Longtin, P. Grning, et al., Journal of Materials Chemistry C, published on-line January 2013, DOI:10.1039/c2tc00446a
-
2013 | Page 10
Nexray RTD 2009
1) Brazed CNT Cathode
2) As deposited CNT cathode
1
2
Brazed Electron Field Emission Cathode Optimized electrical CNT/Substrate Contact
CVD CNT Film as deposited
a) b) d) c)
Brazed CNT Field Emission Cathode
Conductive high-temperature resistant carbon nanotube/substrate contacts by active vacuum brazing R. Longtin, P. Grning, in submitted
-
2013 | Page 11
Nexray RTD 2009
Pocket Source Microfabrication: Anode and Spacer
Anode (Diamond window)
Diamond deposition on Si
Litography and etching, releasing Membrane
Metallization: UBM+Au
Diced using a laser
Spacer
Alumina
A hole was drilled using laser
Metallization: UBM/Au both sides
6.3mm
Membrane
-
2013 | Page 12
Nexray RTD 2009
Pocket Source Microfabrication: Grid and Cathode
Grid
Silicon microfabrication
Grid: 125 micron pitch
Metallization: UBM/Au on both sides
Cathode: Flip chip CNT
Ceramic package
CNT integrated using solder
-
2013 | Page 13
Nexray RTD 2009
Test Set-Up for X-ray Generation
cathode
grid
anode+UHV
0V
Igrid
Icathode
Ianode
e-e-
e-
Uextraction
UHV
-Uextraction
high vacuum chamber
CNT source
assembly Lead aperture
with D-hole
X-ray image film
(dental X-ray film) anode
-
2013 | Page 14
Nexray RTD 2009
Source Proof of Concept
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
0 200 400 600 800 1000
em
issi
on
cu
rre
nt
/
A
extraction voltage / V
measurement data(ramp up)
Fit (Fowler-Nordheim)
measurement data(ramp down)
S7: X-ray tube exposure (12kV, 10mA, 30s)
reference
S8: CNT source assembly:
(3.4kV, 0.4A, 20min)
X-ray generation Electron emission
-1.6
-1.4
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0 2000 4000 6000
curr
en
t /
mA
Time / s
measurement (Mo304) voltage (0 to -650V)
0 V
-650 V
CN
T s
ou
rce a
ssem
bly
X-ray
transmitted
through the
lead apperture Emission modulation
-
2013 | Page 15
Nexray RTD 2009
Vacuum Sealing & Getter Activation
Gold-tin eutectic bonding
Without getter and preconditioning
Vacuum level measured limited to 5x10-1 mbar
Trials done with no preconditioning
With getter activation
2mm2 area used
Cannot be done for a long time
Vacuum level is an order of magnitude better 5-8x10-2 mbar measured
With getter activation & preconditioning
2mm2 getter area used
Vacuum level 1x10-3 mbar measured
Getter after and before
activation
Getter
-
2013 | Page 16
Nexray RTD 2009
AuSn Transient Liquid Phase Bonding (TLP)
10um Au thick electroplated layer + eutectic preform
Interface formed of Au/Au-rich intermetallics
High-temperature stability for getter activation (up to 522C)
Reminder:
Getter activation: 15 - 30 min between 350 and 450C
Better sorption capacity when the getter is activated at higher
temperature
-phase
-
2013 | Page 17
Nexray RTD 2009
Vacuum Sealing
Au electroplated ring and AuSn preform
Packages without getter: Variable vacuum level: between 1 - 5 mbar
Packages with ~3mm getter material:
Better vacuum level, below 0.1 mbar (max. sensitivity of -resonators)
Outgassing of the elements influences strongly the vacuum level
(all packages sealed in HV oven under 10-5 mbar)
On-going tests with more sensitive vacuum sensors
-
2013 | Page 18
Nexray RTD 2009
Integration
The final assembly was made using all
the components
Electron emission achieved
Being tested for Xray emission
Lacking of stable UBM on
spacer
-
Nexray RTD 2009
2013 | Page 19
X-ray Detectors
-
2013 | Page 20
Nexray RTD 2009
X-ray Detector Concept
-
2013 | Page 21
Nexray RTD 2009
Breakthrough in Absorber Fabrication
Space-filling array
of Ge-crystals
instead of
continuous layer
Only way to avoid
crack formation!
C.V. Falub et. Al, Science
335, 1330 (2012)
-
2013 | Page 22
Nexray RTD 2009
Quality Control 1: Isolate Single Ge-Crystal
a) Epitaxial growth on
patterned wafer
b) Enlarge gaps by
chemical etching
c) Prepare alignment
marks by FIB
d) Remove neighboring
crystals by
micromanipulation
-
2013 | Page 23
Nexray RTD 2009
Quality Control 2: X-ray Nanodiffraction
X-ray FWHM indicates perfect single crystal far away from the interface!
-
2013 | Page 24
Nexray RTD 2009
Detector with Integrated CMOS Read-Out Unit
Basic principle working but excessive sidewall leakage of as-grown structures
-
2013 | Page 25
Nexray RTD 2009
Eliminating Sidewall Leakage
Ge-crystal growth on unpassivated Si-pillars causes huge leakage currents Dramatic lowering of leakage by sidewall etching
-
2013 | Page 26
Nexray RTD 2009
Diode Characterization Inside SEM
Contacting of single Ge crystal by tungsten manipulator Oxide passivation of sidewalls of Si-pillar leads to lowest
reverse currents
-
2013 | Page 27
Nexray RTD 2009
CMOS Circuit
Pixel block diagram
4000 pulses per pixel,
3000e per pulse:
= 2.9 counts
CSA
RRES
CINT
VREF
VTST_IN
CTST
ITST
Shaper Gm
VTHP
VTHN
Discriminator
Gra
y
Counte
r
ANALOG DIGITAL
VOUT
Regis
ter
Gm
Offset
Calibration
DAC
VREF
VTHRESHOLD
latch enable
DIODE
(not included in test chip)
IPULSE
ITH
IOS
-
2013 | Page 28
Nexray RTD 2009
3D printing a possible solution for the contacting of the pillars
Maskless patterning, compatible
with 3D substrates
Ag layer coating
Bridging of pillars and deposition of
patterned contact
-
2013 | Page 29
Nexray RTD 2009
Device Under Test
CMOS side Ge side
HV
contact
-
2013 | Page 30
Nexray RTD 2009
X-ray Tests
-
2013 | Page 31
Nexray RTD 2009
NEXRAY Summary
-
Nexray RTD 2009
2013 | Page 32
Cosmicmos Add-on Nexray A. DommannA, H. von KnelC, J. FompeyrineB, Mirja RichterB, Emanuele UcelliB,
C. FalubC, R. KaufmannA, A. NeelsA, E. MllerC, A. GonzalezC, Th. KreiligerC, T.
BandiA, F. IsaD, G. Isella D, D. Chrastina D, L. Miglio D, A. MarzegalliD, R.
Bergamaschini D
A: CSEM; B: IBM, C: ETHZ, D:L-NESS, Politecnico di Milano, Como, Italy
Bern, 30. 5. 2013
-
2013 | Page 33
Nexray RTD 2009
- Small mass
- Good thermal conductivity
- Large wafer diameter
- Mainstream technology
- Direct band gap alignment
- High carrier mobility
- Optimum for the development
of optoelectronic devices
Challenges
COSMICMOS
Integration of III-V materials on Si substrates for optoelectronic devices development
Solved by the introduction of Ge intermediate layers
GaAs>Si
Thermal expansion mismatch
(wafer bowing & cracks)
Lattice mismatch
(high TDD)
aSi
MDs
TDs aGaAs>aSi
Anti Phase domains
Why GaAs on Si??
Si GaAs
-
2013 | Page 34
Nexray RTD 2009
34
III-V CMOS : motivation and challenges
G. Dewey et al, IEDM Tech. Dig. 2009
Thermal stability Gate-first process min. 600C
High-k scaling EOT < 1 nm Low leakage current k(average) > 15
Interface trap
density Dit 10
11 eV-1cm-2
At the device level Fully self-aligned Gate first Fully-depleted Scaled devices
At the wafer level III-V on silicon Abundant & cheap n & p-type Available in large size
Bipolar CMOS ?
-
2013 | Page 35
Nexray RTD 2009COSMICMOS GaAs crystals grown on Ge/Si patterned substrates by MOVPE
10 m
10 m
10 m
10 m
10 m 2 m
Ge (LEPECVD)
GaAs (MOVPE)
Si pillars patterned by
Bosch process 10 m
22 m
55 m
1515 m 3015 m
10 m
5 m
Our approach
Combination of different
technological steps
Photolithography + RIE
and growth techniques
LEPECVD + MOVPE
-
2013 | Page 36
Nexray RTD 2009COSMICMOS GaAs crystals grown on Ge/Si patterned substrates by MOVPE: Morphology
Nominal
substrate
Offcut
substrate
Si
2 m
(1-11)
(111) (00
1)
[1-11]
[-113] [001]
[111]
Si Ge
GaAs
[110] 2 m
GaAs
Si Ge 2 m
Evolution towards pyramidal shape
Facet distribution
Offcut substrate:
Pyramidal structure tilt
-
2013 | Page 37
Nexray RTD 2009COSMICMOS GaAs/Ge/Si crystals: growth kinetics
0 2 4 6 8 10
0.4
0.5
Offcut [001]
[001]
Gro
wth
rat
e (n
m/s
)
AlAs marker (#)
[110]
0 2 4 6 8 10
0.2
0.3
0.4
0.5
Offcut [001]
[111]
[113]
Gro
wth
rat
e (n
m/s
)
AlAs marker (#)
[1-10]
Si
Ge
FIB cut along [110]
2 m
2 m
[1-1
0] [110]
Si
Ge
FIB cut along [1-10]
2 m
2 m
[1-1
0] [110]
GaAs
(111)B
GaAs
(111)A
Pyramidal shape: lower growth rate in the
(111) facets compared
with the (001)
Evolution towards
(001): lower growth rate in the
(001) facet compared
with the Offcut (001)
-
2013 | Page 38
Nexray RTD 2009COSMICMOS:
Strain-free GaAs crystals grown on Ge/Si patterned substrates by MOVPE
66.0 66.2 69.0 69.3
GaAsGe
Inte
nsity
(ar
b. u
nits
)
2()
Si
(004)
2 m
5 m
9 m
15 m
20 m
40 m
UP
HRXRD
1.44 1.47 1.50 1.53
2 mm
5 mm
9 mm
15 mm
PL
Inte
nsity
cou
nts(
arb.
uni
ts)
Energy (eV)
GaAs grown on
planar Ge/Si
PL T=5K
GaA
s ba
nd-g
ap
Strain-free
GaAs on Si
Planar 15 9 5 21.46
1.48
1.50
1.52
1.54
PL Energy
Eg (calc.)
Ene
rgy
(eV
)
GaAs
bandgap
Pillar width (m)
0.0 0.3 0.6 0.9 1.2
0.00
0.05
0.10
0.15
0.20
II (
%)
GaAs
FEM calc.
Aspect ratio
-
2013 | Page 39
Nexray RTD 2009
Thank you for your attention