Exynos 5 Octa also turned out to be a rather powerful piece of silicon, besting every mobile processor currently on the market in synthetic benchmark tests, even the new Snapdragon generation by Qualcomm, which is powering phones like the HTC One or LG Optimus G Pro. Then why is Samsung not using it in its flagship Galaxy S4 more, despite that there is clearly a version of it with Exynos 5 Octa making the rounds in benchmarks and that will be sold in certain markets?
At first we thought it might be because of LTE compatibility. Qualcomm's processor are a veritable system-on-a-chip (SoC) endeavor, as they have the broadband radios built into the chipset, instead of tacked on later, like with the Exynos series. It is not easy to develop a compact and frugal LTE chip with all the filters to avoid band interference, and make it play well with the other elements of a mobile processor without affecting battery life more than needed. Qualcomm has mastered this process, making it a breeze for manufacturers to just leave the Texans take care of everything related to processing and connectivity, and focus on design and added features.
What's the holdup? Well, it turns out that Samsung went with the simpler and cheaper way to design 28nm chips like the Exynos 5 Octa, called gate-first, while the competing foundry TSMC designed its production capacity with the harder to implement gate-last process, developed by Intel. The problem stems from the fact that gate-first might be easier to transition to, but gives yield problems later on, especially with complex SoCs, and that's exactly what seems to be happening with Exynos 5 Octa.
Here's the more scientific citation, eventually explained by one of Samsung's chip customers in the Silicon Valley:
Gate-first HKMG is easier to implement as a transition from a traditional poly/SION structure. The construction of the gate and transistor remain the same, though the materials are different (i.e., a high-k gate oxide instead of oxynitride); a metal gate is inserted, and then poly on top of that—and the rest of the flow is "basically the same as previous generation structures."
Gate-first also is "much simpler" to implement from a process migration standpoint in terms of IP implementation, and fewer restrictive design rules (gate-last requires CMP around the gate structure). "We can maintain 50% shrink from 45nm to 32nm because there's not as many restrictive design rules," Ana Hunter (VP foundry at Samsung Semiconductors) said. This makes the process particularly good for mobile applications, as it's cost-effective and "very good on gate leakage—a >100× improvement from 45nm to 32nm."
Long story short, it might be a while before Samsung ramps up enough 28nm yield for Exynos 5 Octa to be implemented on a broader scale throughout its portfolio of mobile gadgets. Granted, only performance geeks would care about the benchmark difference between the Snapdragon 600 and Exynos 5 Octa chips, as today's mobile processors are already more powerful than Android needs, but this little episode might be a hint that the touted 14nm and even 20nm chips that Samsung says it has tapped out already, might remain in the labs longer than we thought, of which the main beneficiary will likely be TSMC, exactly where Apple is heading to build its proprietary A6 and A7 chipsets.
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