Updated: Tue Aug 9 22:11:19 UTC 2022

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All you need to know about 3D Integrated Circuits

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Repeated waves of major technological change and accompanying business realignment have defined the history of electronic design. Many businesses have failed as a result of their inability to anticipate and adjust to these powerful forces of change. 

3D integration, a new technology, is being used to design multi-core microprocessors and memory integration.

Everything You Need To Know About 3D Integrated Circuits

Vertically stacking integrated circuits (ICs) or circuitry has emerged as a viable solution for meeting device requirements such as higher performance, increased functionality, lower power consumption, and a smaller footprint in the world of semiconductors and microelectronics. 3D integration technologies mention the various methods and processes used to accomplish this.

Three-dimensional integrated circuits are made up of two or more layers of circuitry in a single package. The layers are interconnected both vertically and horizontally. Multi-layer chips are typically created by fabricating separate layers, stacking, and thinning them. 

Advantages of 3D Integrated Circuits

  • Faster Signal Transitions: The total capacitance of a vertical interconnect is lower than that of a horizontal interconnect because these designs use shorter interconnects. Interconnect signals will have a lower RC time constant and transition between ON and OFF states faster as a result of this. Furthermore, because total parasitic capacitance on an interconnect is lower, the signal delay is reduced, resulting in faster switching from inputs to outputs. These factors allow for higher serial data rates with digital signals.
  • Space Saving: The most obvious benefit is that package sizes are smaller, resulting in space savings. When compared to spreading circuit blocks out over the surface of a semiconductor die, vertically stacked 3D integrated circuits can be kept very thin. More components and features are often crammed onto one PCB as a result, allowing higher-density designs with advanced packages.
  • Lower Power Consumption: Since the late 1990s, lower power consumption has prompted smaller package sizes and novel interconnects designs. Stacking the design in 3D was once the only way to get smaller package sizes in an integrated circuit. Due to lower DC resistive losses over the length of an interconnect, the shorter interconnect length allows for lower power consumption. This is critical as technology nodes have shrunk, necessitating thinner interconnects with higher DC resistance.
  • Analog and Digital Integration: With 3D integration, analog and digital circuit blocks can be integrated into the same package with fewer signal integrity concerns and without significantly increasing the package size. The digital and analog blocks can be separated in a planar arrangement in these packages. Even so, more features can be added vertically to each block without significantly increasing the package size. Crosstalk and noise coupling are easier to control and will not cause major signal problems in these designs by isolating blocks into their regions.
  • Heterogeneous Integration: The layers of a 3D integrated circuit are manufactured separately and can be assembled in a variety of ways. This is more important than it appears! The process of making a die has an impact on the behavior of the components on that die: one process produces better capacitors, another produces faster transistors, and so on. Even more intriguing, the layers could be built at various process nodes, implying that the size of the electronic components could vary. This has an impact on the cost, complexity, and performance of each layer. Different material layers can even be stacked on top of one another. A 3D IC can combine the simplest of every process, node, and substrate with all of those options, without sacrificing some components to form room for others.
  • Speed: A 3D chip’s dies are stacked much closer together than chips on a circuit board. Electronic signals can travel faster from one component to another due to the shorter distances. When compared to comparable 2D solutions, 3D stacked devices have shown up to a 5x speed improvement.
  • Footprint: Stacking multiple dies on top of one another obviously results in a chip that is smaller than if the dies were placed side by side. A multi-layer 3D-IC can be no thicker than a traditional 2D chip if the layers are aggressively thinned. In miniaturized devices such as cell phones and IoT applications, 3D-ICs’ small size is extremely valuable.

New Challenges

Despite its benefits, the 3D-IC poses new challenges:

  • Thermal Issues: 3D-ICs have a higher power density than 2D-ICs because several layers of power-dissipating electronic components are stacked vertically. This could cause thermal issues. Furthermore, the oxide layer (between the silicon layers) has a low thermal conductivity, which reduces heat transfer to the environment. This exacerbates the problems with the 3D-heat IC. It’s possible that 3D-ICs will require new cooling solutions.
  • Design Challenges: The dimension introduces a further control variable during the planning of the electronic system. 2D technology is the focus of traditional design software. New EDA tools are required for 3D-ICs.
  • Cross-Talk Between Layers: It is possible to connect the metal wires on the top layer to the device on the active layer above it. Furthermore, in heterogeneous integration, the RF signal can affect the logic and memory in other layers.
  • TSV Induced Overheads: Thousands of TSVs are utilized in 3D-ICs for interlayer communication also as power/ground delivery.  These TSVs are taking up extra overhead space. TSVs cause thermal-mechanical stress due to the heat expansion mismatch between silicon and the TSV filling material. Thermal stress can cause reliability issues such as cracking as well as timing violations because transistor delay is affected by thermal stress.
  • Cost: While cost has been identified as a barrier to 3D IC commercialization in mainstream consumer applications, it is an advantage over scaling. Efforts are being made, however, to address this problem. Despite the fact that 3D printing is a relatively new and complex technology, the cost of the manufacturing process when broken down into the activities that make up the entire process is surprisingly simple. The combination of activities that make up the foundation can be used to identify cost drivers. Once the cost drivers have been identified, determining where the majority of the cost originates, and, more importantly, where cost can be cut, becomes much easier.

Conclusion

By reducing delay and interconnection losses, 3D ICs will be the first in a new generation of dense, low-cost chips that will eliminate the need for traditional storage and recording media.

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