Very-large-scale integration (VLSI) refers to the complex circuitry on integrated electronic chips. Over the past few decades, VLSI technology has advanced at an incredible pace, enabling the development of more powerful and efficient chips. The continuous scaling down of transistors based on Moore’s law has allowed chip designers to pack billions of transistors onto a single silicon die. This advancement in vlsi hardware design technology has fueled innovations across various industries and transformed our daily lives.
However, as chip features approach atomic scales, traditional silicon-based VLSI technology is facing significant challenges. Chip designers must navigate these challenges to develop more powerful and energy-efficient chips for futuristic applications like artificial intelligence, autonomous vehicles, augmented reality, etc. This article discusses some of the cutting-edge VLSI technologies that can help overcome scaling challenges and power futuristic chips.
3D chip stacking is an important technology that allows continuing the trend of increasing transistor density, even as traditional silicon scaling reaches its limits. In 3D chip stacking, multiple layers of silicon chips are stacked vertically on top of each other using advanced integration techniques. This allows chip designers to build up chips with many layers of transistors stacked over each other, rather than just spreading them out on a single silicon wafer plane. This vertical stacking enables a 10-100 times increase in the number of transistors that can be integrated into a chip as compared to traditional planar chip design. Where earlier chips were constrained by the surface area of the silicon wafer, 3D stacking helps overcome that limitation by utilizing volume. Multiple silicon layers can be efficiently integrated into a single chip footprint through this approach.
Core vlsi physical design in usa like monolithic 3D and through-silicon vias play a key role in enabling 3D chip stacking. Monolithic 3D allows different transistor layers to be built directly on top of each other on the same wafer. TSVs provide high density vertical interconnects between the stacked layers through holes that pass through the silicon. This helps establish dense wiring for high-speed communication between different layers. The high density of transistors achieved through 3D stacking makes it particularly useful for developing chips for futuristic applications that require tremendous processing power. Advanced multicore processors, high-bandwidth memory stacks, and heterogeneous system-on-chips for applications can benefit from 3D stacking technology. It is enabling the industry to create 3D stacked chips with over 10 billion transistors, powerful enough to enable next-generation technologies.
Non-Silicon Materials
As silicon-based CMOS technology approaches its scaling limits, researchers are exploring alternative channel materials that can enable continued transistor scaling as per Moore’s Law. Some promising non-silicon materials being researched are germanium, III-V compound semiconductors, graphene, and two-dimensional (2D) materials like molybdenum disulfide and black phosphorus. 2D materials have unique properties that make them
well-suited for next-generation post-silicon chips. Molybdenum disulfide (MoS2) and black phosphorus are two important 2D materials being researched for their electrical and optical characteristics.
MoS2 is a semiconductor with a direct bandgap, enabling its usage in optoelectronic devices. It has a high on/off current ratio and can complement silicon in digital applications. Black phosphorus also has a thickness-dependent direct bandgap, making it suitable for applications such as infrared photodetectors. It demonstrates high hole mobility, making it promising for complementary metal-oxide-semiconductor (CMOS) applications. Both these 2D materials offer thickness-tunable bandgaps as well as the ability to stack different 2D layers vertically or horizontally. This enhances opportunities for developing novel heterostructure devices.
The electrical and optical properties of 2D materials like MoS2 and black phosphorus provide advantages over conventional bulk materials. Their integration into CMOS fabrication processes could enable new functionalities and help extend Moore’s Law beyond the limitations of silicon-based technology. This makes them important candidates for further research towards developing future post-silicon chips.
Non-Von Neumann Architectures
The von Neumann architecture that separates processing and memory units is inefficient for parallel workloads like AI. New non-von Neumann architectures optimize hardware for specific applications. Neuromorphic chips mimic neural networks in biology using novel in-memory computing approaches. These are highly efficient for AI tasks but general-purpose processing.
Other novel architectures include spatial architectures that distribute processing across a large grid of processor tiles and tensor processing units optimized for deep learning matrix operations. Research is ongoing in developing specialized architectures for quantum computing, probabilistic computing, cognitive computing, etc. Novel architectures combined with new materials can fulfill the high performance and low power needs of futuristic applications.
Emerging Memory Technologies
Modern chips rely on power-hungry SRAM and DRAM for memory. Novel non-volatile memories like phase-change memory, resistive RAM, and spin-transfer torque MRAM can replace them. These emerging memories offer attributes like high density, fast access, non-volatility, and better scalability.
3D XPoint is a breakthrough non-volatile memory developed by Intel-Micron that sits between NAND flash and DRAM. It provides 1000x faster access than NAND and 10x denser capacity than DRAM. Novel memories will play a key role in developing universal memory capable of replacing different existing memory types. This can help overcome the von Neumann bottleneck.
Heterogeneous Integration
Combining different materials, devices, and even foundries onto a single chip or package is known as heterogeneous integration. It allows integrating analog, memory, photonic, and other components with digital CMOS to develop system-on-chips. For example, integrating photonics enables optical I/O for high-speed chip-to-chip communication.
Advanced packaging technologies like 2.5D/3D stacking, silicon interposers, and embedded multi-die interconnect bridges help realize heterogeneous integration. They overcome interconnect limitations between separately manufactured components. This approach helps optimize designs for diverse workloads through hardware specialization and achieve performance, power, and area targets for futuristic applications.
Conclusion
As CMOS scaling slows down, chip designers must leverage disruptive technologies of semiconductor design services to continue powering innovation. Novel 3D architectures, new materials, specialized processors, emerging memories, and heterogeneous integration provide pathways to overcome scaling challenges. By navigating these cutting-edge VLSI technologies, the industry can develop highly integrated, application-specific chips with unprecedented capabilities. This will fuel innovations across domains and help realize the promise of futuristic technologies for a smarter world. Continuous research and cross-industry collaboration are crucial to make Moore’s law a reality for generations to come.
