The implementation of High Bandwidth Memory (HBM) in a 2.5D System-in-Package (SiP) is a highly intricate task, involving multiple stages, from architecture definition to rigorous system-level validation. This process requires designing an interposer channel that guarantees reliability, and ensuring robust testing of the entire data path. Each phase presents unique challenges, especially when working with advanced memory technologies like HBM4.
The first critical step in the design process is planning the architecture. It’s essential to define the necessary bandwidth, latency, and power requirements to ensure the system meets its performance goals. In modern designs, a monolithic chip can be broken down into smaller modules, known as chiplets. This disaggregation offers improved flexibility, power efficiency, and scalability.
Another significant aspect is the interposer design, which is a crucial link between the memory and compute die. The interposer can be made from silicon or organic material and features multiple metal layers to manage high-density routing. The introduction of HBM4, building upon the advancements of HBM3E, seeks to further enhance data rates, memory density, and energy efficiency. However, the increased I/O density presents challenges, particularly in routing and managing the physical layer (PHY). Proper routing, power distribution, and grounding are essential to prevent issues like signal interference and to ensure the system meets HBM4E specifications. Alphawave Semi is working on a test vehicle designed to assess the integrity of data signals across the entire path, incorporating both HBM4E memory and interposer components.
To maintain signal integrity (SI) at the high data rates of HBM4E, several techniques are employed. These include impedance matching, shielding, and minimising crosstalk between adjacent traces. The interposer is analysed for insertion loss, reflection loss, and power sum crosstalk, which all contribute to the channel’s overall performance. Additionally, the I/O architecture is upgraded to include equalisation techniques, ensuring the highest signal integrity and optimal performance.
Equally important is the power delivery network (PDN). Effective power distribution requires careful selection of decoupling capacitors, low-impedance paths, and dedicated power planes for sensitive signals. Every component within the system, from the motherboard to the interposer and silicon die, contributes to the overall noise budget. By controlling the impedance of the power delivery network, it is possible to minimise interference and ensure efficient operation.
Testing is another critical phase, with both signal integrity and power integrity needing to be thoroughly validated. Extensive testing at the system level ensures that all components in the data path meet the required performance standards. By analysing the effects of jitter, crosstalk, and rise-fall time degradation, issues can be identified and addressed early in the design process, optimising both layout and I/O architecture.
While HBM4 offers many advantages in terms of performance and lower latency, it also presents a range of technical challenges in system architecture, interposer design, and testing. Alphawave Semi is well-equipped to tackle these challenges, driving the development of high-performance, reliable HBM4 implementations. These innovations are crucial for advancing AI and data centre applications, where the demand for more sophisticated memory solutions continues to grow. Custom HBM4 implementations that allow deeper integration with compute dies and custom logic could provide a significant performance boost, making their complexity worthwhile.
Alphawave IP Group plc (LON:AWE) is a semiconductor IP company focused on providing DSP based, multi-standard connectivity Silicon IP solutions targeting both data processing in the Datacenter and data generation by IoT end devices.
