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S. G. Kandlikar and A. Ganguly
Communication channels across the cooling layer are realized through wireless
links. For this purpose, each layer is logically divided into subnetworks or subnets,
such that a particular switch in each subnet is equipped with a wireless interface (WI).
The WIs are deployed in a switch at the center of the subnets to avoid long multi-hop
paths from all cores in its subnet, assuming any core can transmit inter-subnet data
at some point during the operation of the system. This WI deployment strategy has
been shown to provide the minimum average distance (MAD) between all switches
in an intra-chip NoC in [42]. All cores that need to send data across a cooling layer
access the wireless channel through the WI in its subnet. The WIs are connected in
an all-to-all fashion using the shared wireless band as discussed in Sect. 3.3. The
data is transferred to the WI in the subnet of the destination core from where it is
routed to the final destination. In order to improve performance, data transfer within
the same layer or in adjacent layers not separated by a cooling layer can also use the
WIs depending on the adopted routing policy as discussed in Sect. 3.4. In this way,
a hybrid hierarchical 3D wireless, wireline and TSV based NoC architecture (3DHiWiNoC) is formed. Figure 13.1b shows the top view of one active layer (vertical
TSVs are not shown).
13.6.4.2 Physical Layer of the 3D WiNoC
Several alternative technologies exist for realizing on-chip and off-chip wireless
interconnections [30, 31, 37, 42]. We envision the use of on-chip embedded miniature
antennas that can be fabricated within the chip to establish direct communication
channels between the internal switches. The chosen on-chip antenna has to provide
the best power gain for the smallest area overhead. Several on-chip antenna designs
in the mm-wave bands have been investigated [43–45]. A linear dipole occupies a
large area proportional to the wavelength of the carrier frequency. A patch antenna
is directional mostly radiating perpendicular to its plane. A log-periodic antenna can
have higher power gains but is highly directional. We intend the chosen antenna to be
compact as well as not directional. This is because we want to communicate between
antennas that are located in different layers of the 3D IC and potentially at different
angles with respect to each other’s axes.
A metal mm-wave zigzag antenna as shown in Fig. 13.6, has been demonstrated
to possess these characteristics as they are more compact compared to a linear dipole
due to the zig-zag folding of the arms. In addition, such mm-wave antennas fabricated using top layer metals are CMOS process compatible [44]. Therefore, to realize
such wireless channels, we choose on-chip metal zig-zag antennas which have been
shown to be effective in establishing on-chip communication [44] This antenna also
has negligible effect of rotation (relative angle between transmitting and receiving
antennas) on received signal strength, making it most suitable for on-chip wireless
interconnects, as each antenna has to communicate with other WIs in multiple directions. Such mm-wave 60 GHz antennas are shown to have a bandwidth of 16 GHz
for on-chip communications links [44]. The antennas are placed at the center of each
subnet being fed from the WIs of its respective subnet in each layer.
S. G. Kandlikar and A. Ganguly
Communication channels across the cooling layer are realized through wireless
links. For this purpose, each layer is logically divided into subnetworks or subnets,
such that a particular switch in each subnet is equipped with a wireless interface (WI).
The WIs are deployed in a switch at the center of the subnets to avoid long multi-hop
paths from all cores in its subnet, assuming any core can transmit inter-subnet data
at some point during the operation of the system. This WI deployment strategy has
been shown to provide the minimum average distance (MAD) between all switches
in an intra-chip NoC in [42]. All cores that need to send data across a cooling layer
access the wireless channel through the WI in its subnet. The WIs are connected in
an all-to-all fashion using the shared wireless band as discussed in Sect. 3.3. The
data is transferred to the WI in the subnet of the destination core from where it is
routed to the final destination. In order to improve performance, data transfer within
the same layer or in adjacent layers not separated by a cooling layer can also use the
WIs depending on the adopted routing policy as discussed in Sect. 3.4. In this way,
a hybrid hierarchical 3D wireless, wireline and TSV based NoC architecture (3DHiWiNoC) is formed. Figure 13.1b shows the top view of one active layer (vertical
TSVs are not shown).
13.6.4.2 Physical Layer of the 3D WiNoC
Several alternative technologies exist for realizing on-chip and off-chip wireless
interconnections [30, 31, 37, 42]. We envision the use of on-chip embedded miniature
antennas that can be fabricated within the chip to establish direct communication
channels between the internal switches. The chosen on-chip antenna has to provide
the best power gain for the smallest area overhead. Several on-chip antenna designs
in the mm-wave bands have been investigated [43–45]. A linear dipole occupies a
large area proportional to the wavelength of the carrier frequency. A patch antenna
is directional mostly radiating perpendicular to its plane. A log-periodic antenna can
have higher power gains but is highly directional. We intend the chosen antenna to be
compact as well as not directional. This is because we want to communicate between
antennas that are located in different layers of the 3D IC and potentially at different
angles with respect to each other’s axes.
A metal mm-wave zigzag antenna as shown in Fig. 13.6, has been demonstrated
to possess these characteristics as they are more compact compared to a linear dipole
due to the zig-zag folding of the arms. In addition, such mm-wave antennas fabricated using top layer metals are CMOS process compatible [44]. Therefore, to realize
such wireless channels, we choose on-chip metal zig-zag antennas which have been
shown to be effective in establishing on-chip communication [44] This antenna also
has negligible effect of rotation (relative angle between transmitting and receiving
antennas) on received signal strength, making it most suitable for on-chip wireless
interconnects, as each antenna has to communicate with other WIs in multiple directions. Such mm-wave 60 GHz antennas are shown to have a bandwidth of 16 GHz
for on-chip communications links [44]. The antennas are placed at the center of each
subnet being fed from the WIs of its respective subnet in each layer.