3D Integrated circuit is a chip which accommodates two or more layers of active electronic components

They are integrated both horizontally and vertically onto a single circuit.

To reduce wastage of space on the substrate.

To improve interconnections among different wafers.

To reduce the length of interconnections which in turn reduces heat dissipation and also RC delays.

Can be used to accommodate both homogenous and heterogeneous chips.

Thus there is a great urge to switch over from 2D ICs to 3D ICs

•The substrate is divided into blocks

•The similar characterized active components are stacked in the same block.

•This results in ease of interconnection.

•Each block is called a tier.

LOCAL TIERS

•Independent responding blocks

SEMI-GLOBAL TIERS

•Blocks used for intra communication

GLOBAL TIERS

•Inter communicating blocks used for clock and power supply

BEAM RECRYSTALLISATION:

This method involves deposition of polysilicon. This is used to fabricate TFTs which in turn are used in fabrication of 3D ICs.

PROCESSED WAFER BONDING:

This method bonds processed wafers together, and it is independent of temperature.

SOLID PHASE CRYSTALLISATION:

It offers flexibility for fabricating multiple layers, used mostly for stacking SRAM and EPROM.

Timing

Energy performance

Interconnection structures

In current technologies, timing is interconnect driven.Reducing interconnect length in designs can dramatically reduce RC delays and increase chip performance

Wire length reduction has an impact on the cycle time and the energy dissipation

Energy dissipation decreases with the number of layers used in the design

3D Cell PlacementPlacement by min-cut partitioning

3D Global RoutingInter-wafer vias

Circuit layout managementMAGIC

Natural to think of a 3D integrated circuit as being partitioned into device layers or planes

Min cut partitioning along the 3rd dimension is same as minimizing vias

•Routing in 3D consists of routing a set of aligned congruent routing regions on adjacent wafers.

•Wires can enter from any of the sides of the routing region in addition to its top and bottom

•3D router must consider routing on each of the layers in addition to the placement of the inter-waver vias

ILLUSTRATION OF ROUTING AREAS

x

z

y

x

z

y

Detailed routing of net when routing areas are known

LOOSE ROUTING DETAILED ROUTING

MAGIC is an open source layout editor developed at UC Berkeley

It is an extension to MAGIC by providing support for Multi-layer IC design.

The difference is that it has a new Command “bond”.

Bond places inter-layer vias in the design file.

Once Two layers are bonded they are treated as one entity.

The 3D Integrated circuits are a great relief to interconnected IC technologies.

This opens up a new era in chip designing which has many aspects still to be explored and exploited.

These can be used in many facets of our lives like smartphones,microprocessor based memory stacks etc.

Thus it can be concluded that

“3D IC – A GREAT UPLIFTMENT TO IC WORLD”