The 3D ICs are believed to be best way to keep Moore's Law ticking.
On an average , a chip holds over one billion transistors today. Intel's 10-core Xeon Westmetre-EX packs 2.6 billion transistors into a 512 mm2 using 32 nm technology. The thirst for more features and processing power is unquenchable, but how much more can you pack into a chip? If transistors get any smaller, their reliability could become questionable. Plus, if you need to make the chip denser, the fabrication costs might also become unreasonably high. Such issues have led to the development of 3D IC technology, wherein two or more dice are stacked atop of each other.
Benefits of 3D chips :
|3D IC stacking|
1. 3D chips saves space. Dice that used to be centimetres apart on a chip can now be placed millimetres apart, and that too vertically.
2. Since the dice are close by, the interconnect length is significantly smaller. This results in low latency and high performance.
3. Stacking helps overcome the memory-to-processor performance bottleneck that plagues 2D ICs.
4. 3D interconnects permit data to be moved both horizontally and vertically. This helps boost performance
by 30 to 40percent.
5. Bandwidth is much higher as it is possible to have a large number of vertical vias between the layer.
6. 3D chips consumes 30 to 40 percent less power than traditional ICs.
7. 3D stacking permits heterogeneity, since the dice arranged one above the other need not be similar.
Techniques for stacing the dice in a 3D chip:
There are several ways to stack the chips, Gilies Peckham, EMEA director-Marketing, Xilinx, explains ost common ones:
1. Connecting two stacked chips to a flip chip at the bottom of the stack. Examples are SoCs where a dynamic Random Access memory (DRAM) is placed on top of the Central Processing unit (CPU).
|Xilinx Stacked Silicon Interconnect technology|
2. Using TSV, where the dice are place on the top each other and connected through vertical copper channels. An example of TSV usage is the super-density DRAMs used in camera CMOS sensors.
3. Making use of silicon transposer, which connects two or more chips together - much like transposers used in AMD graphics cards.