The document discusses the challenges and methods of heat mitigation in three-dimensional integrated circuits (3D ICs), highlighting the advantages of 3D architecture over traditional 2D circuits. It presents a comparative study of various active and passive cooling techniques, specifically focusing on the use of Peltier elements and innovative cooling methodologies like micro-channel liquid cooling. Effective thermal management is deemed crucial for enhancing performance and reliability as device density and clock speeds increase in modern chip designs.

1. Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)
30 – 31, December 2014, Ernakulam, India
216
ACTIVE COOLING TECHNIQUE USING PELTIER
ELEMENT FOR EFFICIENT HEAT MITIGATION IN 3
DICS-A COMPARATIVE STUDY
AlfinJohny K1
, GnanaSheela2
, Gifty K Baby3
1, 2, 3
Toc.H Institute of Science and Technology Kerala, India
ABSTRACT
Three Dimensional IC technology is recent in IC fabrication technology. A three-dimensional integrated circuit
(3D IC) is a chip in which two or more layers of active electronic components are integrated both vertically and
horizontally into a single circuit. Mitigation of heat generated in different layers is a challenging problem in 3D-IC
fabrication process. Many methods like passive and active methods are introduced to address this problem. This paper
compares different methods used for heat mitigation. It is rapidly becoming one of the most challenging issues in high-
performance chip design due to ever increasing device count and clock speed. Thermal problems have important
implications for performance and reliability. The 3-D architecture offers unique advantages both in terms of circuit
performance (lower RC delay), and on-chip integration of digital, analog, and mixed signal circuits. With the growing
menace of RC delay in 2-D circuits, the 3-D architecture is being viewed as a potential alternative that can not only
maintain chip performance but also become a vehicle for System on-a-Chip (SoC) design in the near future. Hence,
careful thermal design of 3-D ICs is central to their development.
Keywords: Peltier Effect, Peltier Element, System on-a-chip, Thermal Through Silicon Via (TTSV).
1. INTRODUCTION
A three-dimensional integrated circuit is a chip in which two or more layers of active electronic components are
integrated both vertically and horizontally into a single circuit. It is not yet widely used; this technology saves space by
stacking separate chips in a single package.
3 DICs promise many significant benefits, including:
• Footprint: More functionality fits into a small space
• Cost: Large chip is partitioned into multiple smaller dies, which helps to reduce fabrication cost if individual dies
are tested separately.
• Heterogeneous integration: Circuit layers can be built with different processes, or even on different types of
wafers.
• Shorter inter connect: The average wire length is reduced (10 -15%).
• Power: Shorter wires also reduce power consumption by producing less parasitic capacitance reducing the
power budget leads to less heat generation, extended battery life, and lower cost of operation.
• Bandwidth: 3D integration allows large numbers of vertical vias between the layers. This allows construction
of wide bandwidth buses between functional blocks in different layers.
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2. Proceedings of the International Conference on Emerging Trends in
Because this technology is new it carries new challenges, including:
• Yield: Each extra manufacturing step adds a risk for defects.
• Heat: Simulations show that a 10°C raise in temperature can double a 3D IC chip’s heat density, degrading
performance by more than one-
issue as electrical proximity correlates
managed.
• Design complexity: Taking full advantage of 3D integration requires sophisticated design techniques and new
CAD tools.
3D IC integration technology is recent in IC
problem in 3D IC technology. Various techniques are introduced to mitigate heat dissipated in different IC layers. They
are classified as active and passive cooling techniques. Many shortco
active method of cooling, which uses peltier element to mitigate heat.
2. LITERATURE SURVEY
Sungjun et al[1] showed by Full Chip Thermal Analysis of Planar (2
Performance ICs [1] showed that interconnect Joule heating in advanced technology nodes can strongly impact the
magnitude of the maximum temperature within 2
thermal analysis of vertically integrated (3
simulations. Full chip thermal analysis of 2
numerical simulations shown that thermal de
considered during their early design phase. It has also been shown that interconnect Joule heating and low thermal
conductivity of dielectric materials will strongly impact the magn
with significant implications for reliability and performance.
Arifur Rahman et al [2] examined thermal issues in 3
analytical and numerical modeling of device
comparable system performance in 2-D and 3
integration due to lower capacitance associated with interconnec
ICs is higher (compared to that of 2-D ICs), chip temperature could reach an unacceptable level. The chip temperature is
generally limited by the heat removal capability of the packaging technology. T
for reliable operation of devices and interconnects, innovative package
Thermal vias, Cu bonding layer for 3-D integration, etc. could also be beneficial for heat remova
2.1. PASSIVE METHODS OF COOLI
2.1.1. INTER-TIER INTEGRATED M
Mohamed M. Sabry et al [3] proved that conventional back
cooling and micro channel cold-plates prove to
heat from multi-processor 3D ICs.
Fig1:
Inter-tier liquid cooling is a potential solution to address the high temperatures in 3D MPSoCs.
being developed by the CMOSAIC Nano
the tiers of a 3D stack. This cooling technology scales with
vertical interconnects (through silicon vias or TSVs), which are needed to connect the different electrical components in
the 3D processing architectures. Main Advantages of this method is that Micro channel
International Conference on Emerging Trends in Engineering and Management (ICETEM14)
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217
Because this technology is new it carries new challenges, including:
: Each extra manufacturing step adds a risk for defects.
Simulations show that a 10°C raise in temperature can double a 3D IC chip’s heat density, degrading
-third. Heat building up within the stack must be dissipated. This is an inevitable
issue as electrical proximity correlates with thermal proximity. Specific thermal hotspots must be more carefully
Taking full advantage of 3D integration requires sophisticated design techniques and new
3D IC integration technology is recent in IC fabrication process. Heat mitigation is the one of the challenging
problem in 3D IC technology. Various techniques are introduced to mitigate heat dissipated in different IC layers. They
are classified as active and passive cooling techniques. Many shortcomings of passive cooling techniques got solved in
active method of cooling, which uses peltier element to mitigate heat.
Sungjun et al[1] showed by Full Chip Thermal Analysis of Planar (2-D) and Vertically Integrated
Performance ICs [1] showed that interconnect Joule heating in advanced technology nodes can strongly impact the
magnitude of the maximum temperature within 2-D chips despite negligible change in the chip power density. Detailed
of vertically integrated (3-D) ICs has been carried out using analytical modeling and numerical
simulations. Full chip thermal analysis of 2-D and 3-D high performance chips, performed using analytical models and
numerical simulations shown that thermal design issues are going to be critical for both 2-D and 3
considered during their early design phase. It has also been shown that interconnect Joule heating and low thermal
conductivity of dielectric materials will strongly impact the magnitude of the maximum temperature within these chips,
with significant implications for reliability and performance.
Arifur Rahman et al [2] examined thermal issues in 3-D ICs by system-level modeling of power dissipation and
ng of device- and package-level heat removal. The results obtained shows that
D and 3-D ICs, 20% - 25% reduction in power dissipation can be achieved by 3
integration due to lower capacitance associated with interconnects and clock networks. If the system performance in 3
D ICs), chip temperature could reach an unacceptable level. The chip temperature is
generally limited by the heat removal capability of the packaging technology. To reduce the chip temperature in 3
for reliable operation of devices and interconnects, innovative package-level cooling technologies will be necessary.
D integration, etc. could also be beneficial for heat remova
ING
MICRO CHANNEL LIQUID COOLING
Mohamed M. Sabry et al [3] proved that conventional back-side heat removal strategies like heat sinks, air
plates prove to be insufficient for 3D ICs. Inter-tier liquid cooling is capable of removing
: 3D Stacked IC with inter layer channel cooling.
tier liquid cooling is a potential solution to address the high temperatures in 3D MPSoCs.
being developed by the CMOSAIC Nano-Tera.ch RTD project, involves injecting water through micro
the tiers of a 3D stack. This cooling technology scales with the number of dies and it is compatible with area
vias or TSVs), which are needed to connect the different electrical components in
processing architectures. Main Advantages of this method is that Micro channel
Engineering and Management (ICETEM14)
31, December 2014, Ernakulam, India
Simulations show that a 10°C raise in temperature can double a 3D IC chip’s heat density, degrading
third. Heat building up within the stack must be dissipated. This is an inevitable
with thermal proximity. Specific thermal hotspots must be more carefully
Taking full advantage of 3D integration requires sophisticated design techniques and new
fabrication process. Heat mitigation is the one of the challenging
problem in 3D IC technology. Various techniques are introduced to mitigate heat dissipated in different IC layers. They
mings of passive cooling techniques got solved in
D) and Vertically Integrated (3-D) High
Performance ICs [1] showed that interconnect Joule heating in advanced technology nodes can strongly impact the
D chips despite negligible change in the chip power density. Detailed
D) ICs has been carried out using analytical modeling and numerical
D high performance chips, performed using analytical models and
D and 3-D ICs, and must be
considered during their early design phase. It has also been shown that interconnect Joule heating and low thermal
itude of the maximum temperature within these chips,
level modeling of power dissipation and
level heat removal. The results obtained shows that
25% reduction in power dissipation can be achieved by 3-D
ts and clock networks. If the system performance in 3-D
D ICs), chip temperature could reach an unacceptable level. The chip temperature is
o reduce the chip temperature in 3-D ICs
level cooling technologies will be necessary.
D integration, etc. could also be beneficial for heat removal in 3-D ICs.
side heat removal strategies like heat sinks, air
tier liquid cooling is capable of removing
tier liquid cooling is a potential solution to address the high temperatures in 3D MPSoCs. This technology
water through micro-channels between
the number of dies and it is compatible with area-array
vias or TSVs), which are needed to connect the different electrical components in
processing architectures. Main Advantages of this method is that Micro channel-based liquid cooling is a

3. Proceedings of the International Conference on Emerging Trends in
promising cooling technology solution to overcome the ther
intelligent control of the coolant flow rate is needed to avoid
when the system is under-utilized.
2.1.2. THERMAL VIA PLACEMENT
Brent Goplen et al [4] proposed a method of in
promising way of mitigating thermal issues by lowering the thermal
take up valuable routing space, and therefore, algorithms are needed
where they would make the greatest impact.
Fig 2: Th
2.1.3. IMPACT OF THERMAL THROUGH
TEMPERATURE PROFILE OF MUL
Shiv Govind Singh et al [6] presented IC performance is predominantly governed by
smaller wire cross-section, wire pitch and longer lines that t
capacitance hence signal latency of these lines. Material solutions
interconnects delay time as pitch is scaled down further. 3
to overcome this scaling barrier as it replaces long
interconnects. Thermal dissipation in present 2
device reliability in a negative manner. This problem is expected to be exacerbated further in 3
by every silicon layers must now be dissipated
the power density and is a potential show
Fig
The schematic of 3-D stack with TTSV is depicted in Figure 3. In this proposed model, heat is
device power and interconnects joule heating. The heat flux is generated by device is
and is in the range of 0.3 W/mm2 to 0.7 W/mm2. This power density
we also assume that interconnects joule heating is
interface between two chips.
This method also compared the temperature variation along the vertical distance from the top of
substrate) in Figure 3. TTSV reduces temperatures of all layers. Additionally, the impact
different IC layers has also been investigated. This allows one to
layer temperature. Another consideration is the
Figure 5, as the TTSV extends further into substrate, the temperature of IC1 at a point immediate to TTSV decreases
sharply and saturates when TTSV is about 10 m and further into substrate. On the other hand, IC1 temperature at a
distant point (>90 m) is not affected by the TTSV extension length. Thermal aware design is imperative
success and must be considered at early phase of design. The model presented in this work
International Conference on Emerging Trends in Engineering and Management (ICETEM14)
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218
promising cooling technology solution to overcome the thermal challenges of 3D MPSoCs in HPC architectures. But
intelligent control of the coolant flow rate is needed to avoid wasted energy consumption for over
T IN 3D ICS.
Brent Goplen et al [4] proposed a method of incorporating thermal vias into integrated
promising way of mitigating thermal issues by lowering the thermal resistance of the chip itself. However, thermal vias
therefore, algorithms are needed to minimize their usage while placing them in areas
would make the greatest impact.
Thermal mesh or 3DIC, with thermal via regions
OUGH SILICON VIA (TTSV) ON THE
LTI-LAYER 3-D DEVICE STACK
Shiv Govind Singh et al [6] presented IC performance is predominantly governed by
section, wire pitch and longer lines that traverse across larger chips. These increase the resistance and
capacitance hence signal latency of these lines. Material solutions such as Cu/low-κ is no longer able to reduce
interconnects delay time as pitch is scaled down further. 3-D ICs with multiple active Si layers is a promising technique
to overcome this scaling barrier as it replaces long inter-block global wires with much shorter vertical inter
present 2-D circuits is known to significantly impact interconnect, performance and
a negative manner. This problem is expected to be exacerbated further in 3
every silicon layers must now be dissipated through a smaller 3-D chip foot print. This results in a sharp
the power density and is a potential show-stopper to 3-D ICs if left unmanaged
ig 3: The schematic of 3-D stack with TTSV
D stack with TTSV is depicted in Figure 3. In this proposed model, heat is
device power and interconnects joule heating. The heat flux is generated by device is homogeneous across the entire chip
and is in the range of 0.3 W/mm2 to 0.7 W/mm2. This power density is applied at the top of each Si layers. In addition
we also assume that interconnects joule heating is homogeneous across the entire chip and is applied at the bonding
This method also compared the temperature variation along the vertical distance from the top of
substrate) in Figure 3. TTSV reduces temperatures of all layers. Additionally, the impact of various TTSV diameters on
different IC layers has also been investigated. This allows one to determine the required TTSV diameter given a desire
layer temperature. Another consideration is the impact of TTSV extension length into silicon substrate. As can be seen in
further into substrate, the temperature of IC1 at a point immediate to TTSV decreases
saturates when TTSV is about 10 m and further into substrate. On the other hand, IC1 temperature at a
distant point (>90 m) is not affected by the TTSV extension length. Thermal aware design is imperative
success and must be considered at early phase of design. The model presented in this work can be applied to understand
Engineering and Management (ICETEM14)
31, December 2014, Ernakulam, India
MPSoCs in HPC architectures. But
wasted energy consumption for over-cooling the system
corporating thermal vias into integrated circuits (ICs) is a
resistance of the chip itself. However, thermal vias
to minimize their usage while placing them in areas
Shiv Govind Singh et al [6] presented IC performance is predominantly governed by interconnects delay due to
chips. These increase the resistance and
κ is no longer able to reduce
tiple active Si layers is a promising technique
block global wires with much shorter vertical inter-layer
D circuits is known to significantly impact interconnect, performance and
a negative manner. This problem is expected to be exacerbated further in 3-D ICs as power generated
D chip foot print. This results in a sharp increase in
D stack with TTSV is depicted in Figure 3. In this proposed model, heat is generated due to
homogeneous across the entire chip
is applied at the top of each Si layers. In addition,
homogeneous across the entire chip and is applied at the bonding
This method also compared the temperature variation along the vertical distance from the top of IC1 layer (i.e.
of various TTSV diameters on
determine the required TTSV diameter given a desired
impact of TTSV extension length into silicon substrate. As can be seen in
further into substrate, the temperature of IC1 at a point immediate to TTSV decreases
saturates when TTSV is about 10 m and further into substrate. On the other hand, IC1 temperature at a
distant point (>90 m) is not affected by the TTSV extension length. Thermal aware design is imperative for 3-D ICs
can be applied to understand

4. Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)
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219
the thermal behavior for different functional and stacking configurations of logic, memory, RF or sensors. Our simulation
results show that TTSV acts very effectively as a mean to remove heat generated in device layers and to mitigate thermal
challenges facing 3-D ICs.
2.1.4. TARGETED COOLING WITH CVD DIAMOND AND MICRO-CHANNEL TO MEET 3-D IC HEAT
DISSIPATION CHALLENGE
It is shown that by inserting electrically isolated thermal through silicon via (TTSV) having Cu core and CVD
diamond as a liner shell that extends across the layers to substrate, significant temperature reduction up to (103K) 62%
can be achieved which also reflected through almost 60% reduction in thermal resistivity. Additionally simple micro
channel integration with IC 3 layer and allowed fluid flow through the channel show transient temperature reduction.
TTSV is also shown to be effective in mitigating severe heat dissipation issue facing 3-D IC bonded "face down" and
logic layer stacked on memory substrate.
The dielectric liner of TTSV provides electrical insulation between Si and Cu core and its property is extremely
important in heat dissipation. Besides SiO2, polyimide and CYD diamond (CYDD) are also evaluated. Due to its high
thermal conductivity and electrical resistivity which allow to conduct heat from Si substrate to TTSV (earlier block by
poor thermal conductivity of Si02 or polymide liner), CVDD liner makes TTSV extremely effective in cooling.
By using CVDD at any selected IC layer, one can provide greater cooling to layers which are at higher
temperature. TTSV, when coupled with CYDD, reduces the effective thermal resistance significantly by more than 60%
as compared no TTSV. Targeted and bulk thermal modeling of 3 IC layers stack has been carried out and observed that
chip temperature can go very high without managing it. It is observed that TTSV with conductive liner such as CYD
diamond is very useful to mitigate heat from different IC levels. We have observed about 120 K temperature difference
after application of CVDD as a liner material which is about 52% reduction in temperature. In heterogeneous integration
of logics and memories was also evaluated and found that with the help of targeted cooling using CVD Diamond MML
or MLL configuration can be used for stacking for future application as it turns out best shielded with thermal and
electrical affects. We have observed that due to CVD D liner in TTSV reduced the temperature by 51 K in case of MML
configuration. Present results will be useful to design the TTSV as well arrangement of stacking of Memories and logic
for future application.
2.2. ACTIVE COOLING TECHNIQUE FOR EFFICIENT HEAT MITIGATION IN 3D-ICS
Many passive cooling techniques were introduced to solve heat mitigation problem in 3D-IC. However due to
their nature performance is already saturated. In the newly proposed method of active cooling, Peltier element is used.
Peltier Effect.
The Peltier effect is the presence of heating or cooling at an electrified junction of two different conductors.
When a current is made to flow through a junction between two conductors A and B, heat may be generated (or
removed) at the junction. This technique uses the Peltier element to mitigate the heat at different IC layers. To
demonstrate the advantages of this technique, thermal simulation of a stack consisting of three IC layers bonded face up
is performed and extensive case studies are carried out using finite element modeling. It has been observed that by
inserting an electrically isolated peltier element that extends across IC layers to substrate reduced the temperature by
150◦ K. The initial temperature difference between top IC layer and sink is reduced from 172◦ K to 16◦ K i.e a reduction
of 90 % compared to 61.7 % with TTSV. A voltage difference of 50mV (0.7mA) is applied across the Peltier element.
The cooling effect of Peltier element reduced temperature which is almost 150◦ K. Thermal analysis has also been carried
out for different combinations of stacking, having a Peltier element with and without copper ring, two Peltier elements
with one on another and one beside another.
Over the years to relieve the heating problem in 3-D ICs various passive cooling techniques were proposed.
However due to their passive nature, performance is already saturated. So a new technique is proposed to overcome this
limitation, called as active cooling technique. This technique uses the Peltier element to mitigate the heat at different IC
layers. It has been observed that by inserting an electrically isolated peltier element that extends across IC layers to
substrate reduced the temperature by 150◦ K. The initial temperature difference between top IC layer and sink is reduced
from 172◦ K to 16◦ K i.e a reduction of 90 % compared to 61.7 % with TTSV.
A thorough thermal analysis of a vertically integrated stack consists of three IC layers bonded “back to face”
(face up) having Peltier element is carried out using commercially available FEM tool. The Peltier effect was first
observed in 1834 by the Frenchman Jean C.A. Peltier. It describes the heat current that arises as a result of an electric
current through the interface of two different conductors. In the proposed technique instead of a copper TTSV with liner,
a Peltier element is formed through the silicon via. A voltage difference of 50mV (0.7mA) is applied across the Peltier
element. The cooling effect of Peltier element reduced temperature which is almost 150 ◦ K. Thermal analysis has also
been carried out for different combinations of stacking, having a Peltier element with and without copper ring, two
peltier elements with one on another and one beside another.
Simulations are done for Peltier cooling for different combination of logical and memory layer to study impact
of cooling on heterogeneous integration. By varying diameter and depth of TTSV layer from top of IC, we observed

5. Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)
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220
better cooling is achieved by increasing diameter of Peltier element and no significant variation with depth. Better heat
reduction is seen for multiple Peltier elements than single peltier element of same area. It also provides approximately
lesser variation in temperature profile across the top IC layer. It is shown that for heterogeneous integration irrespective
of their stacking combination, temperature can be reduced at any IC layer.
3. COMPARATIVE ANALYSIS
Different methods of cooling in IC technology, both active and passive methods are compared.
Table 1: Comparative analysis of cooling techniques in IC
4. CONCLUSION
Management of thermal issues is central to the development of future generation microprocessors, integrated
networks, and other highly integrated systems. It is rapidly becoming one of the most challenging issues in high-
performance chip design due to ever increasing device count and clock speed. Thermal problems have important
implications for performance and reliability. Different cooling techniques are introduced to eliminate heat problem in
3D-IC. Passive methods are less used because their performance is already saturated.
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[3] Mohamed M. Sabry, “Towards Thermally-Aware Design of 3D MPSoCs with Inter-Tier Cooling”.
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Author Year Method Advantage Disadvantage
Lee et al 2000 Thermal via island. Simple process. Use of Si area which can be
used for new functionality.
Rahman et al. 2001 Thermal via made of Cu. More heat reduction. Use of Si area which can be
used for new functionality
Singh et al 2009 TTSV. Significant reduction
of top level heat.
Technique is passive in nature
Aftab et al 2012 Use of Conductive CVD
diamond as a liner.
Further heat reduction
of∼103 ◦K.
Technique is passive in nature
Pramod et alJ 2014 Active cooling technique
with the use of Peltier
element
Further heat reduction
of∼150 ◦K.
Active method of cooling.
Performance is not saturated.