Micro Channel Cooling at the GTK

Georg Nüssle & Alex Kluge

NA62 Gigatracker demands

The NA62 experiment proposes to study a very rare Kaon decay at the CERN SPS. In order to track the high intensity Kaon beam before its decay a set of three high precision silicon pixel detector planes has been proposed (GigaTracKer - GTK). In the current layout three hybrid silicon pixel detector layers will be operated in a high fluence environment and provide precise tracking and timing information. The GTK modules will operate in vacuum and under high radiation, which will damage the sensor. So it has to be replaceable with a reasonable effort on a yearly base. This requires an efficient cooling system, which however must be very low mass inorder to avoid degradation in the performance and efficiency of the detector.The highest allowable operation temperature for the readout chip has been set to 5°C. A lower operation temperature is desirable. The use of microchannel cooling directly on the chip or on the cooling/support plate seems very promising.

NA62 Gigatracker demandsCooling/Support plate

Readout Chip

Sensor

The GTK module will consist of:• one silicon pixel sensor (60x200 mm)• bump bonded to 2 x 5 readout chips (12.5 x

20 mm), heat dissipation ca. 3.2 W per chip• a carbon cooling/support plate with high

heat conduction • support and alignement structure outside of

the beam areaschematic sketch of the GTK module

Micro-Evaporators: Basic Geometry and Flow Stabilization

(a) (b)

Examples of (a) silicon micro-evaporator with micro-channels etched on the chip silicon die and (b) copper micro-evaporator test section made by electro-erosion with an inlet orifice insert.

EPFL Lausanne, Prof. Thome

Si microchannel evaporator:• Channel widths: 200, 100, and 50 microns• Manifolds: 1 inlet/1 outlet or 1 inlet/2 outlets• Slits at inlet create orifices that prevent flow

instabilities and generates bubbles to avoid temperature overshoot

• Can be bonded to top of microprocessor

Cobra Heater on backside of silicon chip:• Simulates heat dissipated by a

microprocessor• Better measurement accuracy • Lower thermal resistance to evaporation

surface• 5 RTD sensors along channel length, span

across 1/3rd of width(red arrow) Channel Orientation on backside of chip

LTCM/IBM Micro-Evaporator Test Section in Silicon

EPFL Lausanne, Prof. Thome > 200 W/cm2

GTK-Cooling with Microchannels

schematic sketch of the GTK module

Microchannels in Si supportplate:• Channel cross section: 50 x 50 microns• Manifolds: inlet and outlet outside the sensor

area• In sensor area channels are covered by a thin

foil • Thermal contact to readout chips via thermal

grease or ‘liquid metal’ (liquifies under electricity)

A 3D computer chip with integrated cooling system is expected to:

- Overcome the limits of air cooling- Compress ~1012 nanometer sized functional units (1 Tera)

into one cubic centimeter - Yield 10 to 100 fold higher connectivity- Cut energy consumption and CO2 emissions drastically

• A new $4million consortium project lead by Prof. Thome

• Work ongoing at EPFL in two institutes– LTCM, Heat and Mass Transfer Laboratory– Microsystems laboratory

• CERN DT

Advantages Micro channel cooling

• Uniform temperature distribution in the sensor area• Less thermal stress• Technology known at EPFL, Transfer to our application has to be done• Support by CERN PH-DT to develop this technology

Component Material Thickness [μm] X0 [%]

Sensor Si 200 0.21

Bump Bonds Pb-Sn ~25 0.001

Readout Chip Si 100 0.11

Thermal contact ? ~20 ?

Support Plate, coolant, foil

Si ~150 ~0.15

Sum ~0.47

Radiation length for sensor

The total material budget (material in the beam) allowed fot the GTK module is 0.5% X0(radiation length). In the current proposed layout the material inside the beam area will consist of the ones listed in the table with values for the radiation length and hence their thickness.

Cooling proposals and simulations until nowconvective cooling in a vessel:

HEAT

FL

UX

COO

LIN

G PL

ATE

PCB

VESSEL FRAME

VESSEL WALL

DETECTOR ELECTRICALCONNECTIONS

GTK module will be encapsulated in a vessel and will be cooled via a gas flow of cold nitrogen. The vessel will have Kapton windows for the beam to pass through.

• good cooling• gas leakage into beam

vacuum?• high flow rate >

vibrations?

Cooling proposals and simulations until now

• non-uniform temperature distribution

• thermal stress in the module?

• known technology in vacuum

MAX

THE

RMAL

CO

NDU

CTIV

ITY

GTK module will be cooled via a carbon plate with high heat conduction. On the carbon plate the heat will be extracted outside of the beam area by a pipe with liquid or two-phase cooling.

conductive cooling via a carbon plate: