Exynos 7420: First 14nm Silicon In A Smartphone

This generation more than any generation in recent memory has been a time of significant movement in the SoC space. We were aware of the Exynos 7420 well before it was announced in the Galaxy S6, but for the most part I expected to see Snapdragon 810 in at least a few variants of the Galaxy S6. It was a bit surprising to see Samsung drop Snapdragon SoCs completely this generation, and judging by the battery life of the Galaxy S6 it seems that Samsung had their reasons for doing this.

For those that are unfamiliar with the Exynos 7420, this SoC effectively represents the culmination of their efforts in semiconductor manufacturing and integrated circuit design. On the foundry side, Samsung is leveraging their vertical integration to make the first SoC on their 14nm LPE (Low Power Early) process, which seems to be solely for Systems LSI until they can no longer use all production capacity.

We previously mentioned that Samsung’s 14nm process in general will lack any significant die shrink due to almost unchanged metal interconnect pitch, but this assumption was in comparison to their 20nm LPM process from which the 14nm LPE process borrows its BEOL (back end of line) from. Opposite to what we thought, the Exynos 5433 was manufacturered on a 20LPE process which makes use of a quite larger metal layer. The result is that one can see a significant die shrink for the 7420 as it is, according to Chipworks, only 78mm² and a 44% reduction over the Exynos 5433's 113mm². This is considerable even when factoring in that the new SoC had two added GPU shader cores. Beyond the swap from a LPDDR3 memory controller to a LPDDR4 capable one, the only other at first noticeable major functional overhaul on the SoC seems to be that the dedicated HEVC decoder block has been removed and HEVC encoding and decoding capability has been merged into Samsung's MFC (Multi-Function Codec) media hardware acceleration block.


Galaxy S6 PCB with SoC and modem in view (Source: Chipworks)

The move from a planar to FinFET process is crucial. Although this is covered in more detail in previous articles, the short explanation is that planar processes suffer from increasing power leakage at smaller process nodes as the bulk of the silicon becomes relatively more massive than the gate that controls the flow of current. This causes decreased power efficiency as the power source of the transistor starts to act as a gate itself. FinFET solves this problem by attempting to isolate the transistor from the bulk of the silicon wafer, wrapping the gate around the channel of the transistor to ensure that it retains strong control over the flow of current compared to a planar transistor design.

The effective voltage drop allowed by the process can be substantial. We can have a look at some voltage excerpts of common frequencies available on both the Exynos 5433 and 7420:

Exynos 5433 vs Exynos 7420 Supply Voltages
  Exynos 5433 Exynos 7420 Difference
A57 1.9GHz (ASV2) 1287.50mV 1056.25mV -234.25mV
A57 1.9GHz (ASV9) 1200.00mV 975.00mV -225.00mV
A57 1.9GHz (ASV15) 1125.00mV 912.50mV -212.50mV
A57 800MHz (ASV2) 950.00mV 768.75mV -181.25mV
A57 800MHz (ASV9) 900.00mV 687.50mV -224.50mV
A57 800MHz (ASV15) 900.00mV 625.00mV -275.00mV
A53 1.3GHz (ASV2) 1200.00mV 1037.50mV -162.50mV
A53 1.3GHz (ASV9) 1112.50mV 950.00mV -162.50mV
A53 1.3GHz (ASV15) 1062.50mV 900.00mV -162.50mV
A53 400MHz (ASV2) 862.00mV 743.75mV -118.25mV
A53 400MHz (ASV9) 787.50mV 656.25mV -131.25mV
A53 400MHz (ASV15) 750.00mV 606.25mV -143.75mV
GPU 700MHz (ASV2) 1125.00mV 881.25mV -243.75mV
GPU 700MHz (ASV9) 1050.00mV 800.00mV -250.00mV
GPU 700MHz (ASV15) 1012.50mV 750.00mV -262.50mV
GPU 266MHz (ASV2) 875.00mV 750.00mV -125.00mV
GPU 266MHz (ASV9) 800.00mV 668.75mV -131.25mV
GPU 266MHz (ASV15) 762.50mV 606.25mV -156.25mV

The ASV (Adaptive Scaling Voltage) numbers represent the different type of chip bins, a lower value representing a worse quality bin and a higher one a better quality one. Group 2 should be the lowest that is found in the wild, with group 15 representing the best possible bin and group 9 the median that should be found in most devices. As one can see in the table, we can achieve well up to -250mV voltage drop on some frequencies on the A57s and the GPU. As a reminder, power scales quadratically with voltage, so a drop from 1287.50mV to 1056.25mV as seen in the worst bin 1.9GHz A57 frequency should for example result in a considerable 33% drop in dynamic power. The Exynos 7420 uses this headroom to go slightly higher in clocks compared to the 5433 - but we expect the end power to still be quite lower than what we've seen on the Note 4.

On the design side, Systems LSI has also done a great deal to differentiate the Exynos 7420 from the 5433. Although the CPU architectures are shared, the A53 cluster is now clocked at 1.5 GHz instead of 1.3 GHz, and the A57 cluster at 2.1 GHz rather than 1.9 GHz. The memory controller is new and supports LPDDR4 running at 1555MHz. This means that the Galaxy S6 has almost double the theoretical memory bandwidth when compared to the Galaxy Note 4 Exynos variant, as we get a boost up to 24.88GB/s over the 5433's 13.20GB/s. We still need to test this to see how these claims translate to practical performance in a deep dive article in the future, as effective bandwidth and latency can often vary depending on vendor's memory settings and SoC's bus architecture. 

Outside of the memory controller, LSI has also updated the 7420 to use a more powerful Mali T760MP8 GPU. Although the Exynos 5433 had a Mali T760 GPU as well, it had two fewer shader cores which means that achieving a given level of performance requires higher clock speeds and higher voltages to overcome circuit delay. This new GPU is clocked a bit higher as well, at 772 MHz compared to the 700 MHz of the GPU in the Exynos 5433. We see the same two-stage maximum frequency scaling mechanism as discovered in our Note 4 Exynos review, with less ALU biased loads being limited to 700MHz as opposed to the 5433's 600MHz. There's also a suspicion that Samsung was ready to go higher to compete with other vendors though, as we can see evidence of an 852 MHz clock state that is unused. Unfortunately deeply testing this SoC isn’t possible at this time as doing so would require disassembling the phone.

Introduction and Design Battery Life and Charge Time
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  • FlushedBubblyJock - Friday, April 24, 2015 - link

    so the pictures go by default to internal memory - that's one red herring out with the bathwater ...

    lag and power drain - I guess android is so stupid the 1st thing it does when you touch your metal feel, is scan the sd card for desperately needed data, right ?

    yes, twin babies out with the bathwater fella - right out the window an onto the sidewalk below
  • h3ck - Friday, May 8, 2015 - link

    How is removing the sdcard more "iPhone-like" when Google Android Standard is no sdcard? The flagship Vanilla Android Nexus line is all sans sdcard. I think we often forget that and quickly point to Apple. Also, with increasing harddisk sizes and the ease of using a microsd to microusb adapter (see Dash Micro device), I think the sdcard argument is weak.
  • Daniel S. Buus - Friday, July 17, 2015 - link

    Those were my gripes as well. However, as I've learned that the battery is still replaceable, and the charge is $45 for such a replacement done by Samsung, the battery issue doesn't bother me anymore. Then the storage thing — I've previously bought my share of SD cards to augment my phones. The largest card I've bought was a 64GB one, though, which was sufficient in my Note 3 to satisfy my hunger for filming 1080p60 when travelling. I just ordered the S6 128GB version on sale for the same price as the 32GB version, and it's plenty plenty plenty for my needs. I may have to unload some stuff in the evening to an external storage device if I go crazy with my filming, but that's it. Reading this review and seeing the impressive speed of the storage just makes me even happier that I finally chose this phone :)
  • beehofer - Friday, April 17, 2015 - link

    Nice Phone. There's nobody who won't take one if it were offered. But since we have to pay, ppl will decide on the things that set it apart from the pack. Samsung had an "edge" with SD cards and removable batteries and for some of us it will be a deciding factor. The battery, OK I'll get an extra charger for the car or office but the SD is inexcusable. This has ALWAYS been a blow against Apple and now it can be said against Samsung. I'll keep my S5 or wait.
  • name99 - Friday, April 17, 2015 - link

    Samsung probably ALSO have sw installed on the phone that tells it when an SD card has been installed and the battery replaced, and is well aware that <1% of their phones ever went through either operation.
    I suspect Samsung's idea of what matters to the market is rather more accurate than your idea...
  • FlushedBubblyJock - Friday, April 24, 2015 - link

    I believe you are referring to the NSA, and thus, with no removable battery, the phone can never really be "turned off" and no removable SD means Homaleand Security and the NSA can access you and everything you've done at any time....

    So, it's truly and upgrade because you of course have nothing to hide
  • akeemcharles - Friday, April 17, 2015 - link

    Nice photos
  • Uxi - Friday, April 17, 2015 - link

    I have an S5 with wireless charging using original Samsung covers, so wireless charging is not N/A on the S5, but I admit it was an add-on purchase.
  • DanNeely - Friday, April 17, 2015 - link

    What is the "obvious" defect on the S6 screen picture? Is it one of the things that looks like a fingerprint smudge, the horizontal blue bar that looks like a reflection, or something that isn't obvious to me from looking at the picture?
  • nerd1 - Friday, April 17, 2015 - link

    I have a phone with exactly the same display (Galaxy S5 cat.6 model) and couldn't see any 'obvious' defects at all.

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