Nex Ray 2013, Nano-Tera 2013

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A first application is for the extraction of depth information from an X-ray image without the need to do tomography. With X-ray time-of-flight measurements based on Compton backscattering, the depth inside objects where scattering occurs can be precisely measured. This calls for an intensity-modulated X-ray signal in the MHz range which can be achieved with CNT based cold emitters. An obvious application would be the detection of buried landmines: the Compton backscattering signal can indeed indicate the landmine position with much better accuracy than metal detectors.Another key application is in the area of tomographic imaging, making use of the fact that both the X-ray source and the X-ray detector are pixelated. Since the X-ray source is built as a matrix of micro X-ray sources that can also be addressed and controlled individually, the combination of pixelated X-ray sources and detectors brings up completely new imaging capabilities, in particular the possibility to do static tomographic imaging and therefore reduce costs or increase throughput.

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