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Nexray
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Nexray RTD 2009 May 13, 2011 | Page 1 Nexray A. Dommann A , H. von Känel C , P. Gröning B , N. Blanc A , C. A. Bosshard A , A. D. Brenzikofer A , S. Giudice A , R. Jose James A , R. Kaufmann A , C. Kottler A , C. Lotto A , A. Neels A , P. Niedermann A , P. Seitz A , G. Spinola Durante A , C. Urban A , H.R. Elsener B , O. Gröning B , B. Batlogg C , C.V. Falub C , K. Mattenberger C , E. Müller C , P. Wägli C Bern, 13. 5. 2011 A: CSEM; B: EMPA, C: ETHZ Network of integrated miniaturized X-ray systems operating in complex environments
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This project targets the development of novel pocket X-ray sources and X-ray direct detectors that will be combined in a distributed network to solve important tasks, for example in the field of security, by ensuring reliable and real-time monitoring of failure sensitive parts in large manufacturing plants or in public transportation.The miniaturized X-ray sources are based on multi-wall carbon nanotube (CNT) cold electron emitters and advanced microsystems technology. The electron field emission properties of CNTs, with their high current densities, make them prime candidates for cold emitter cathodes. Using CNT cold electron emitters will make it possible to miniaturize the whole X-ray source. Additionally, as opposed to classical thermionic emission, field electron emission of the CNT is voltage-controlled which allows for high modulation frequencies up to GHz level. The X-ray direct detectors in turn are based on crystalline germanium absorption layers grown directly on a CMOS sensor chip yielding high resolution and high sensitivity X-ray detectors. Single photon detection will allow for a significant improvement of contrast for applications in security, health care and nondestructive testing.
Transcript of Nexray
Nexray RTD 2009
May 13, 2011 | Page 1
Nexray
A. DommannA, H. von KänelC, P. GröningB, N. BlancA, C. A. BosshardA, A.
D. BrenzikoferA, S. GiudiceA, R. Jose JamesA, R. KaufmannA, C.
KottlerA, C. LottoA, A. NeelsA, P. NiedermannA, P. SeitzA, G. Spinola
DuranteA, C. UrbanA, H.R. ElsenerB, O. GröningB, B. BatloggC, C.V.
FalubC, K. MattenbergerC, E. MüllerC, P. WägliC
Bern, 13. 5. 2011
A: CSEM; B: EMPA, C: ETHZ
Network of integrated miniaturized X-ray systems operating in complex environments
May 13, 2011 | Page 2
Nexray RTD 2009
A system approach
Source Sample Detector
Contrast mechanism Resolution, Size, EfficiencySpectrum, power, Coherence, Size
Miniaturized, fast and programmable X-ray sources
Phase contrast X-ray imaging
Direct X-ray detectors
Breakthroughs in all key building blocks of X-ray systems:Sources, Contrast mechanism and Detectors
May 13, 2011 | Page 3
Nexray RTD 2009
Network of integrated miniaturized X-ray systems operating in complex environments
Single-photon solid-state X-ray detection
Si-Ge layers for high-energy X-ray detection
Phase contrast X-ray imaging
Miniaturized, fast and programmable X-ray sources
May 13, 2011 | Page 4
Nexray RTD 2009
Static Computed Tomography
• Array of sources replaces
moving parts in CT-systems
• Sequencial operation of sources,
also with alternating high voltage
Detector
Source
May 13, 2011 | Page 5
Nexray RTD 2009
Novel Concepts of Applications
Large area X-ray sources
Pixelated X-ray sources
Pulsed operation of X-ray source (and individual source-pixels)
Highly efficient sensors, applicable in medical diagnostics
Energy resolved X-ray image detection
Source Detector
High frequency source modulation compatible with ToF-technology
Allows for distance measurement to object in reflexion geometry
May 13, 2011 | Page 6
Nexray RTD 2009
Medicine and Nondestructive Testing
• Static CT for emergency medicine
• Miniaturised X-ray systems for monitoring purposes during
surgery, e.g. for cardiovascular or brain surgeries
• Large area sources for radiation therapies
• Fast static CT for in-line product inspection
• Imaging of fast phenomena due to high switching frequency of
cold electron emitters
• Depth measurements inside objects due to TOF operation mode
May 13, 2011 | Page 7
Nexray RTD 2009
A system approach
Source Sample Detector
Contrast mechanism Resolution, Size, EfficiencySpectrum, power, Coherence, Size
Miniaturized, fast and programmable X-ray sources
Phase contrast X-ray imaging
Direct X-ray detectors
May 13, 2011 | Page 8
Nexray RTD 2009
X-ray source microfabrication
Extraction Anode
Emission Cathode
Diamond X-ray Window
May 13, 2011 | Page 9
Nexray RTD 2009
Plasma Enhanced-CVD growth of CNTs
Utilization of a Plasma during deposition allows the growth of vertically oriented CNTs
Ni dot of Da = 70 nm → catalyst for growth of straight CNTsTiN for homogenisation of CNTs electron emission
May 13, 2011 | Page 10
Nexray RTD 2009
X-ray source packaging aspects
• Research on multilayer UBM stable at high
temperature for CNT deposition (600°C)
Annealing, bonding and hermeticity tests
with different combinations of evaporated
thin films
• Tests based on AuSn for high vacuum
packaging
10-5 mbar required for functioning of
CNTs
Tests with AuSn bonding processes
allowing getter integration and activation
Pt UBMAu UBM
Au UBM showing good hermeticity
ζ phase
Eutectic gold tin
May 13, 2011 | Page 11
Nexray RTD 2009
High vacuum sealing of test vehicle
• Goal :
- Tests with all the developed elements together and characterization
- Increase in melting point of solder and getter activation during life time
- Vacuum level measurement and finer hermeticity test with µPirani
CNT substrateThin film getter
µPiraniAuSn solder ring
May 13, 2011 | Page 12
Nexray RTD 2009
X-ray source experimental platform: The concept
Vacuum pump system (<10-7mbar)HiCube Eco, Pfeiffer Vacuum
ISO-K 63
Grid electrode
Cathode electrode
HV
Vacuum gauge
Mechanical support
Exit windowCNT source assembly
High vacuum recipient
May 13, 2011 | Page 13
Nexray RTD 2009
Silicon chips for cathodes
• For development of high
vacuum hermetic packaging
• Different variants of Pt and
Au based UBM metal stacks
• 2 wafer runs
Metal layer ~ 200 nm
SiO2 2 µm
Cavity 50 µm
Si
May 13, 2011 | Page 14
Nexray RTD 2009
Microfabricated grids
Diced wafer
2 x 2 mm grid
10 µm grid lines
May 13, 2011 | Page 15
Nexray RTD 2009
Emission characteristics: longtime-stability
Applied elec. field
20, 100, 500 µA
Longtime measurement: 13 hDistance: 20 µmEmission current: 50 µA (constant) I-V measurement after longtime test
May 13, 2011 | Page 16
Nexray RTD 2009
A system approach
Source Sample Detector
Contrast mechanism Resolution, Size, EfficiencySpectrum, power, Coherence, Size
Miniaturized, fast and programmable X-ray sources
Phase contrast X-ray imaging
Direct X-ray detectors
May 13, 2011 | Page 17
Nexray RTD 2009
Low-Energy Plasma-Enhanced CVD (LEPECVD)
Primary coil
Plasma source
Primary coil
Turbo pump
“Wobblers”
“Wobblers”
Load lockArgon plasma
Anode plate
Wafer stage
Wafer
Gas inlet
• Electrons emitted by a hot filament sustain a DC plasma• Low (~10eV) ion energy – no ion damage• Discharge confined by a magnetic field (~1 mT)• Deposition rates 0.01-10nm/s depending on gas flow and plasma density
• Gas phase precursors: SiH4, GeH4
May 13, 2011 | Page 18
Nexray RTD 2009
CHALLENGES: Mismatched Epitaxy, e.g. Si-Ge
Si
Ge cracksSiSi
GeGe
TD
MD
Ge
Si
• Lattice mismatch (strain = 4.2 %).
• Mismatch of thermal expansion coefficients.
High density of misfit (MD) and threading dislocations (TD), wafer bowing and cracks, which can significantly degrade the performance of a device.
May 13, 2011 | Page 19
Nexray RTD 2009
Problems related to Si:Ge Epitaxy
LATTICE MISMATCH (aSi = 0.543095 nm, aGe = 5.564613 nm a/a = 4.2 % compressive)
Ge
% Si
Ge
Only 4 monolayers of Ge (~ 2.2. nm) can be grown epitaxially on Si ! Plastic Deformation (i.e. relaxation) by misfit (M) and threading (T) dislocations: bad qualityStrained Ge on Si substrate
strained Ge
bulk Si
a ┴>
a S
i
a║ = aSi
relaxed Ge
bulk Si
Misfit
Relaxed SiGe on Si substrate
a0
a0
Threadingdislocations
Misfit
Threading
May 13, 2011 | Page 20
Nexray RTD 2009
Monolithic Integration on CMOS Wafers Demonstrated
• Monolithic integration of
Ge photodetectors on CMOS demonstrated
for infrared applications (2 µm layer thickness)
• 64 x 64 pixel NIR image sensor exists
• Optimisation of process is going on
May 13, 2011 | Page 21
Nexray RTD 2009
INNOVATION: Self-aligned epitaxial Ge crystals
Micromachined Si pillars Epitaxial Ge pillars on Si
GeGeSiSi
5 m
GeGe
~30 m~30 m No limitation for layer thickness!
May 13, 2011 | Page 22
Nexray RTD 2009
INNOVATION: Selective Epitaxy on pre-patterned Si
Ge fullyrelaxed
Ge partially strained(0.14%)
Perfect crystal structure despite lattice strain!
Perfect basic understanding
of the growth morphology
Simulations Experiment
May 13, 2011 | Page 23
Nexray RTD 2009
Defect free Pillars
May 13, 2011 | Page 24
Nexray RTD 2009
Nexray detector technology & chip schematic concept
· Si pillar patterning· Si pillar sidewall&bottom passivation· Ge/Ge+/Si epi growth· Ge sidewall passivation· Ge etch· Hole filling & etchback? (not shown)· Metallisation (shadowmask?)
guard
pixel pixel pixel
chip edge
Ge thickness: 50 µmSi thickness: 50 µmVoltage: ~100VPixel size:Chip size:
n- Si
1 Pixel
n+p+
- HV
depletedarea
electricfieldlines
CMOS circuit
X-ray
p- Ge
e h
May 13, 2011 | Page 25
Nexray RTD 2009
SiGe Pillars
RSMs on Ge/Si(004) and Ge/Si(115) – measured on patterned part of the wafer
-100-50 0 50 100Qx*10000(rlu)
7050
7100
7150
7200
7250
7300
7350
7400
Qy*10000(rlu)
0 0 4Omega 33.750002Theta 67.50000
Phi 0.00Psi 0.00
X 0.00Y 0.00Z 0.000
56560_Ge-004-RSM-Pillars.xrdml
1.3
1.9
2.8
4.0
5.8
8.4
12.3
17.8
25.9
37.6
54.5
79.2
115.0
167.1
242.6
352.3
511.7
743.1
1079.2
1567.3
2276.1
Relaxed Ge
2400 2450 2500 2550 2600 2650 2700Qx*10000(rlu)
8800
8900
9000
9100
9200
Qy*10000(rlu)
1 1 5Omega 30.456902Theta 92.50000
Phi 0.00Psi 0.00
X 0.00Y 0.00Z 0.000
56560_Ge-115-RSM-Pillars.xrdml
1.3
1.8
2.5
3.4
4.8
6.7
9.4
13.1
18.4
25.7
35.9
50.2
70.1
98.0
137.1
191.6
267.9
374.5
523.6
732.0
1023.3
(115) (004)
Si-Substrate
Patterned: Very small mosaicity. No tilt compared to #56558.
May 13, 2011 | Page 26
Nexray RTD 2009
Photon Counting Circuits
Cs
Rr
sense node
• X-ray quantum counting:
Every single X-ray photon is counted
• Test-chip exists
• Low noise circuit with band-pass filtering
• Measured noise limit of 12 e- RMS
at 1 µs pulse length
• X-ray energy resolution possible
with pulse-height measurements
May 13, 2011 | Page 27
Nexray RTD 2009
THANK YOU FOR YOUR ATTENTION
