Why 28nm is a Half Node of 32nm:
Incremental Scaling:
The transition from 32nm to 28nm represents a modest reduction in feature size, typically achieved through an optical shrink or process optimizations rather than a complete overhaul of the manufacturing process.
This is characteristic of a half node, where the improvements are incremental rather than a full leap to a new node (like 32nm to 22nm).
Process Characteristics:
The 28nm node, as developed by foundries like TSMC, often used similar manufacturing techniques as 32nm (e.g., high-k metal gate technology and 193nm immersion lithography) but with refinements to improve transistor density, power efficiency, or performance.
For example, TSMC’s 28nm process was a refinement of the 32nm process, offering ~10-15% better power efficiency and slightly higher transistor density without major changes to the underlying technology.
Industry Context:
In the semiconductor industry, half nodes like 28nm are used to extend the life of a process technology, providing chip designers with better performance or efficiency while the foundry prepares for the next full node (e.g., 22nm or 20nm).
The 28nm node was particularly significant because it was widely adopted and remained a workhorse node for many years due to its cost-effectiveness and maturity.
Not a Full Node Jump:
A full node transition (e.g., 32nm to 22nm) typically involves a significant reduction in feature size (roughly 0.7x scaling), new materials, or transistor architectures (e.g., moving from planar to FinFET).
In contrast, 28nm was more of an evolutionary step from 32nm, with smaller tweaks to lithography, design rules, or process optimizations, fitting the definition of a half node.
Example:
TSMC’s 32nm and 28nm processes both used planar transistor technology and high-k metal gate (HKMG) processes. The 28nm node improved on 32nm by tightening design rules and optimizing the process, resulting in better power efficiency and performance without a major architectural shift.
This contrasts with the jump from 28nm to 20nm or 16nm, which involved more significant changes (e.g., introduction of FinFETs in 16nm).
Summary:
Yes, 28nm is considered a half node of 32nm because it represents a refined, incremental improvement over the 32nm process, focusing on better density, power, or performance without the major technological leap of a full node.
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