Explain how heterogeneous integration techniques, such as chiplet-based designs and 2.5D/3D packaging, can be used to overcome the limitations of monolithic GPU designs and enable future performance scaling.
Heterogeneous integration, encompassing techniques like chiplet-based designs and 2.5D/3D packaging, has emerged as a crucial strategy to overcome the limitations of monolithic GPU designs and pave the way for future performance scaling. Monolithic GPUs, where all components are fabricated on a single silicon die, face several challenges as technology advances.
*Limitations of Monolithic GPU Designs:
1. *Yield Issues: As GPU die sizes increase, the probability of defects also increases, leading to lower yields and higher manufacturing costs. A single defect on a large monolithic die can render the entire chip unusable.
2. *Design Complexity: Designing and verifying increasingly complex monolithic GPUs becomes extremely challenging and time-consuming. The complexity of the design process scales non-linearly with the number of transistors.
3. *Reticle Size Limits: The size of a monolithic die is limited by the reticle size of the lithography equipment. Exceeding this limit requires stitching multiple reticles together, which can introduce alignment errors and increase manufacturing costs.
4. *Memory Bandwidth Bottleneck: Integrating memory directly onto the GPU die is limited by area and thermal constraints. Off-chip memory solutions, such as GDDR6, provide limited bandwidth compared to the computational power of modern GPUs.
5. *Specialized Process Technologies: Different components of a GPU, such as compute units, I/O interfaces, and memory controllers, may benefit from different process technologies. Fabricating all components on a single die requires compromising on the optimal technology for each component.
*Heterogeneous Integration Techniques:
*Chiplet-Based Designs:
Chiplet-based designs involve partitioning a large monolithic GPU into smaller, independent dies called chiplets. These chiplets are then interconnected using a high-bandwidth, low-latency interconnect fabric. This approach offers several advantages:
1. *Improved Yield: Smaller chiplets have a higher yield than large monolithic dies, reducing manufacturing costs. Only known-good die (KGD) chiplets are integrated into the final product, further improving yield.
2. *Increased Design Flexibility: Chiplets can be designed and fabricated independently, allowing for greater design flexibility and faster time-to-market. Different chiplets can be designed using different process technologies, optimizing performance and power consumption.
3. *Scalability: Chiplet-based designs are highly scalable. The number of chiplets can be increased to improve performance, allowing for a wide range of GPU configurations.
4. *Die Reuse: Proven chiplet designs can be reused in multiple products, reducing design costs and time. This modularity allows for rapid product iteration and customization.
*2.5D and 3D Packaging:
2.5D and 3D packaging techniques involve vertically stacking multiple dies on top of each other and connecting them using through-silicon vias (TSVs) or other high-density interconnects. These techniques offer several advantages:
1. *Increased Interconnect Density: 2.5D and 3D packaging allows for a much higher density of interconnects between dies compared to traditional side-by-side packaging. This significantly improves bandwidth and reduces latency.
2. *Shorter Interconnect Lengths: The vertical stacking of dies reduces the length of interconnects, minimizing signal propagation delays and power consumption.
3. *Heterogeneous Integration: 2.5D and 3D packaging enables the integration of dies fabricated using different process technologies, optimizing performance and power consumption. For example, a GPU die can be stacked on top of a memory die (HBM) to provide high-bandwidth, low-latency memory access.
*Examples:
*AMD's Instinct MI