Low material budget microfabricated cooling devices for particle detectors

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Oct 24, 2013 (4 years and 20 days ago)

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Low material budget
microfabricated

cooling devices for particle detectors

P. PETAGNA and A. MAPELLI

On behalf of:


CERN PH/DT


The NA62 Collaboration


EPFL


LMIS4


EPFL


LTCM


UCL


ELEC/DICE (SOI & MEMS)

30 Sep 2010

1

P. Petagna & A. Mapelli

Outline of the talk

30 Sep 2010

2

P. Petagna & A. Mapelli




Why micro
-
channel cooling for HEP?




A first application: local cooling for the NA62 GTK




Proposed solution and approach to the problem




Micro
-
fabrication process




Structural analysis




Thermo
-
fluid dynamics simulations




First tests on a full
-
scale prototype




Layout optimization





Next steps and beyond


Why
m
-
channelcooling?

30 Sep 2010

3

P. Petagna & A. Mapelli

Radiation length (X
0
): mean distance over which the energy of a
high
-
energy electron is reduced to 1/e (0.37) by
bremsstrahlung

1



Minimization

of

material

budget

(Dahl, PDG)

More readily usable quantity:
X
0
= X
0
/
r

[cm]

Cu: 1.436 cm

Steel: ~1.7 cm

Al alloy: ~8.9 cm

Ti: 3.56 cm

Si: 9.37 cm

C
6
F
14

@
-
20

C
: 19.31 cm

K13D2U 70%
vf
: 23 cm

CO
2
(liquid) @
-
20

C
: 35.84 cm

Minimize material budget Minimize x[cm] / X
0
[cm]

(i.e. use material with high X
0

and minimize thickness)

m
-
channel cooling naturally addresses this issue through the use of Si
cooling plate and tiny (PEEK?) pipes in extremely reduced thickness

Why
m
-
channelcooling?

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P. Petagna & A. Mapelli

Material budget of the CMS Si
-
strip tracker (10 layers)

Material budget of the CMS Si
-
Pixel tracker (2 layers)

Present LHC large Si trackers (ATLAS and CMS) ~ 2% X
0

per layer


SLHC “phase II” upgrade: “significant” reduction needed


Future trackers at ILC ~ 0.1
÷

0.2% X
0

per layer

Why
m
-
channelcooling?

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P. Petagna & A. Mapelli

2



Cooling

power

enhancement

Newton’s law for convective heat flux:

Heat transfer coefficient for m
-
channel system:

Hydraulic diameter
~ 10
-
4
m or less

Nusselt

number = 3.66
÷

4.36 for fully
developed laminar flow

Fluid thermal conductivity
= 0.05
÷

0.11 W/
mK

for
low temperature fluids

~10
3
W/m
2
K


m
-
channelcooling:veryhighhea琠瑲ans晥rcoe晦fcien瑳⡶ery
small
D
h

possible) and very high heat flux (large
S

available)

Why
m
-
channelcooling?

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P. Petagna & A. Mapelli

3



Reduction

of

D
T

between

heat

sorce

and

heat

sink

With a standard cooling
approach, the
D
T between the
module and the fluid ranges
between 10 and 20

C (small
contact surface + long chain
of thermal resistances)

With an integrated
m
-
channelcoolingapproach,瑨elargesr晡ceavailable
景r瑨ehea琠exchange⡣oldpla瑥
vs.

cold pipe) and the natural minimization
of the thermal resistance between the source and the sink effectively
address the issue of the
D
Tbe瑷een瑨e晬idand瑨eelemen琠瑯becooled

Lower temperatures are envisaged for the future Si
-
trackers at SHLC. This
has non
-
negligible technical impacts on the cooling plants

An example of future potential use

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P. Petagna & A. Mapelli

Concept of module for a “level
-
0 trigger” layer @ SHLC (courtesy of A. Marchioro)

Sensor

RO chips

m
-
channel cooling plate

Manifolds

Interconnect

A first application: the NA62 GTK

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P. Petagna & A. Mapelli

A first application: the NA62 GTK

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P. Petagna & A. Mapelli

A first application: the NA62 GTK

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P. Petagna & A. Mapelli

Vacuum tank

Mag2

Mag3

Mag4

Mag1

GTK1

GTK3

GTK2

Cedar

selects particles

with 75
GeV/c

sees

kaons

only

Achromat

250 m

beam: hadrons,

only 6
%

kaons
-
> only 20% decay in the vacuum tank into a
pion

and 2
neutrinos
-
> out of which only 10
-
11

decays are of interest

straw chambers

RICH

hit correlation via matching of arrival times


100
ps

RICH

identifies pions

straw chambers

measure position

GTK sees

all particles

A first application: the NA62 GTK

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P. Petagna & A. Mapelli


Sensor & bonds: 0.24% X
0


(~200 µm Silicon)


RO chip: 0.11% X
0

(~100 µm Silicon)


Passive or active cooling plate

Final target: 0.10


0.15 % X
0


Priority: minimize X
0


Acceptable DT over sensing area ~ 5
°
C


Dimension of sensing area: ~ 60 x 40 mm


Max heat dissipation: ~ 2 W/cm
2



Target T on Si sensor ~
-
10
°
C


Support structure outside acceptance region: ~ FREE


18 000 Pixels / station (300 x 300
m
m, 200
m
m thick)


10 ASICS chips bump
-
bonded to the sensor

Proposed solution

30 Sep 2010

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P. Petagna & A. Mapelli

Schematic of the layout of the proposed
m
-
channel
cooling plate the coolant will enter and exit the
straight channels via manifolds positioned on top
and bottom. The channels, distribution manifold and
openings for the inlet and outlet connectors are
etched into a silicon wafer, which is then coupled to
a second wafer closing the hydraulic circuit.

The final goal is to have
both wafers in silicon
bonded together
by
fusion bonding
to produce a monolithic cooling element

An alternative design, in case of technical difficulties with the fusion bonding process, relies on a
flat Pyrex
cover 50 µm thick anodic
-
bonded to the silicon wafer

carrying the hydraulic circuit. On top of this flat plate,
an additional silicon frame (surrounding the beam area) will be again anodic
-
bonded. In this way the global
structure of the cooling wafer will be symmetric, the effects of coefficient of thermal expansion (CTE)
mismatching between silicon and Pyrex will be minimized and the same resistance to pressure and
manipulation as in the baseline case will be attained


Approach to the problem

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P. Petagna & A. Mapelli

Take advantage of recent results obtained in two different fields of development:


m
-
channel cooling devices have started to be actively studied for future
applications for
high power computing chips or 3D architectures
.


Thin and light
m
-
fluidic devices in silicon are largely in development for
bio
-
chemical applications
.

Anyway for the first case, where the power densities are extreme, the mass of
the device (hence its
material budget
) is an irrelevant parameter. In the second
case the typical values of the
flow rate and pressure
are much lower.
Furthermore, the presence of a
low temperature fluid
and possibly of a
high
radiation level
is unique to the HEP detector case.

dedicated R&D is nevertheless unavoidable
for the specific application under study.

Approach to the problem

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P. Petagna & A. Mapelli

The procedure followed to tackle the different challenges and to converge in a limited time
on a single device satisfying all the requirements is to move in parallel along different lines
of R&D in a “matrix” approach, where the intermediate results of one line are used to steer
the parallel developments.

F
abrication
technique studies

Thermo
-
fluid

dynamic
simulations

Numerical
structural
simulations

Experi
mental tests

Common
specs

Possible
layouts

Optimal
layout

Pressure
limits

m
-
fabrication process

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P. Petagna & A. Mapelli

START:
Czochralski

silicon wafer polished on both sides (4′′ diameter, 380
μm

thick, 0.1
-
0.5 ohm
-
cm p
-
type).


(a)
A layer of 1 µm of oxide (SiO
2
) is grown on both sides of the wafer

(b)
Clariant

AZ
-
1512HS
photoresist

is spin coated on one side of the wafer at
2000 rpm and lithography is performed to obtain an image of the channels
in the
photoresist

(c)
Dry etching of the top layer oxide is used to transfer the micro
-
channels
pattern

(d)
A second lithography is performed with
frontside

alignment to image two
fluid transfer holes, 1.4 mm diameter, for fluid injection and collection from
the two manifolds.

(e)
Deep Reactive Ion Etching (DRIE) is used to partially etch the access holes
down to 280 µm

(f)
The
photoresist

is stripped in
Microposit

Remover 1165 at 70
°
C

(g)
and DRIE is used to
anisotropically

etch 100
μm

deep channels separated
by 25 µm wide structures in silicon

(h)
Subsequently the oxide layers are removed by wet etching in BHF 7:1 for
20 min at 20
°
C

(i)
At present, the processed Si wafer and an unprocessed Pyrex wafer (4”
diameter and 525 µm thick) are then cleaned in a Piranha bath (H
2
SO
4

+
H
2
O
2
) at 100
°
C and anodic bonding is performed to close the channels with
the Pyrex wafer

m
-
fabrication process

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P. Petagna & A. Mapelli

Scanning Electron Microscope image of the
cross
-
section of 50 x 50
m
mc桡湮els etc桥搠
in silicon bonded to a Pyrex wafer

Finally, PEEK connectors (
NanoPort
®
assemblies from Upchurch Scientific) are
aligned, together with a gasket and a
preformed adhesive ring to the inlet and
outlet on the silicon and clamped. They
undergo a thermal treatment at 180
°
C for 2
hours to develop a complete bond between
the connectors and the silicon substrate.

The anodic bonding is performed at ambient
pressure and T is raised to 350
°
C then lowered to
320
°
C. At this stage a constant voltage of 800 V is
applied between the Si and Pyrex wafer.

In the final production both the processed and the
unprocessed wafers will be in 525 µm thick silicon.

The bonded wafer undergoes a further processing:
this includes a final local etching to obtain a thinner
region in the beam acceptance area

The resulting wafer is diced according to alignment
marks previously etched in Si to obtain a cooling
plate with precise external references for integration
into the electromechanical assembly

1 mm

....

30 mm

Structural analysis

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P. Petagna & A. Mapelli

“Sacrificial” samples with different manifold width
are produced and brought to collapse by gradually
increasing pressure under a high speed camera in
order to determine the limit pressure and the exact
breaking mechanics.

60

3

0.05

0.025

varying width

1



Experiments

Structural analysis

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P. Petagna & A. Mapelli

2



Numerical

simulations

vs
.

tests

Yield
stress
~25
MPa

[ICES 2009
]

A simplified ANSYS 2D parametric model has been
developed and calculations are checked against
experimental results in order to validate the model for
further forecasts, including the effect of wall thinning or
of geometrical variations

0
20
40
60
80
0.0
0.5
1.0
1.5
2.0
P
int

(bar)

Manifold width (mm)

Pyrex rupture
Connector detachment
ANSYS model
Structural analysis

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P. Petagna & A. Mapelli

0
50
100
150
200
250
300
350
400
450
0
0.5
1
1.5
2
Pi
nt

(Bar)

Manifold Width (mm)

Rupture Pressure for
Silicon

Cover (165
Mpa
)

tp=50µ
tp=200µ
tp=350µ
tp=525µ
0
20
40
60
0.0
0.5
1.0
1.5
2.0
P
int

(bar)

Manifold width (mm)

tp=50µ
tp=200µ
tp=350µ
tp=525µ
Rupture Pressure for
Pyrex

Cover (25
Mpa
)

3



Extrapolations

Thermo
-
fluid dynamics simulations

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The choice of the cooling fluid circulating in the micro
-
channels has naturally been oriented towards
perfluorocarbon

fluids (C
n
F
2n+2
), which are widely used as coolant medium in LHC detectors. They exhibit
interesting properties for cooling applications in high radiation environment such as thermal and chemical
stability, non
-
flammability and good dielectric behaviour. In particular C
6
F
14

is liquid at room temperature
and is used as single phase cooling fluid in the inner tracking detectors of CMS.

Properties

C
6
F
14

@

-
25
°
C

Density

r

[kg/m
3
]

1805

Viscosity

n

[
10
-
7

m
2
/s]

8
.
2

Heat

capacity

c
p

[J/(kg

K)]

975

Thermal

conductivity

l

[
10
-
2

W/(m

K)]

6
.
275

Based on the properties of C
6
F
14
, a mass flow of
7.325*10
-
3
kg/s is required to extract the heat dissipated
by the readout chips (~32 W) with a temperature
difference of 5K between the inlet and outlet temperature
of the coolant

The results from the analytical calculations performed
indicate that the suited range of the micro channel
geometry is the following:


Width: between 100
m
mand150
m
m


Height: between 80
m
mand120
m
m


Fin width: between 25
m
mand75
m
m


Between 300 and 500 channels to cover the area

Flow rate
attained with 2
bar
D
p

vs.
channel width
for a fixed
height of 90
m
m

First tests on a full
-
scale prototype

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P. Petagna & A. Mapelli

1mm

Inlet

Outlet

manifold

depth

1
00
m
m


Channel
cross

section

10
0
m
m x 100
m
m


Power
density

1 W/cm
2

(
50% nominal
)


Mass

flow

3,66 x 10
-
3

kg/s (
50% nominal
)


Inlet

temperature

18

C


Outlet

pressure

1bar


Laminar
flow

Test

sample

and

numerical

model

First tests on a full
-
scale prototype

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Simulated

vs
.

experimental

pressure

drop

First tests on a full
-
scale prototype

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P. Petagna & A. Mapelli

Thermal

visualization

IN

OUT

Thermograph before
injection

Thermograph at
injection

IN

OUT

Thermograph after few
seconds of coolant circulation

Heat load
simulated by a
Kapton

heater of
suited resistance
and geometrical
dimension

First tests on a full
-
scale prototype

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P. Petagna & A. Mapelli

Steady

state

D
T

bet睥en

inlet

and

srface

probes

1

2

3

4

5

6

4

5

6

3

2

1

Layout optimization

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P. Petagna & A. Mapelli

Outlet

Wedged

manifold
,
depth

150
m
m,280
m

and

㐰4
m
m

Optimized

geometry

for

uniform

and

minimal

D
m

CFD models of the geometry presently under tests have been successfully validated. Further
optimization of the manifold geometry and of the channel cross section can then be performed
through CFD analysis in order to reduce the amount of samples to be produced for testing purposes

Inlet

Layout optimization

30 Sep 2010

P. Petagna & A. Mapelli

26

Effect

of

inlet

manifold

geometry

on

D
m

Rectangular

manifold, 1 mm wide,
100
m

thick, central inlet & outlet

Wedged

manifold, 1.6 mm
Max width,
150
m

thick,
opposed inlet & outlet

Wedged
manifold, 1.6 mm
Max width,
280
m

thick,
opposed inlet & outlet

Wedged

manifold, 1.6 mm
Max width,
400
m

thick,
opposed inlet & outlet

Layout optimization

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P. Petagna & A. Mapelli

Layout optimization

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two inlets

two inlets

two inlets

two inlets

two inlets

Summary

table

Next steps and beyond

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P. Petagna & A. Mapelli

Immediate

future

1.
Perform full
-
scale thermal tests in cold (vacuum vessel)

2.
Define the details and properties of the Si
-
Si fusion bonding
process (industrial partnership), fix the final thickness and verify
with a new series of tests

3.
Complete the detailed study of the integration in the GTK module

1.
Study
m
-
channelsincombina瑩onwi瑨CO
2

evaporative cooling

2.
Challenge the system aspects for larger and more complex
detectors (e.g. ATLAS IBL? CMS PIX?
LHCb

VeLo
?)

Next steps and beyond

30 Sep 2010

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P. Petagna & A. Mapelli

Next

year

Two
-
phase CO
2

vs.

single phase C
6
F
14
:
D
P and
D
T in a 50 x 50
m
m channel

Two
-
phase flows comparison:
D
P and
D
T in a 50
x 50
m
m channel plate under the same heat and
mass flow for CO
2

, C
3
F
8

and C
2
F
6

Next steps and beyond

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P. Petagna & A. Mapelli

Sensor

Chips

Embedded
m
-
channels!

A

long
-
term

dream?