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FD-SOI: The Best Enabler for Mobile Growth and Innovation

By Handel Jones

The following in-depth analysis, an IBS study entitled How FD-SOI will Enable Innovation and Growth in Mobile Platform Sales, concludes that the benefits of FD-SOI are overwhelming for mobile platforms through Q4/2017 based on a number of key metrics. In fact, FD-SOI has the ability to support three technology nodes, which can mean a useful lifetime through 2020 and beyond for digital designs and through 2030 for mixed-signal designs. Here are some of the highlights from the study.

First, let’s consider the markets we’re addressing.

The unit volume of smartphones and tablet computers is projected to reach nearly 3B units in 2020 worldwide. These mobile platforms need to have access to low-cost and low-power semiconductor products, including application processors and modems. Performance must also be enhanced, but this needs to be done within the cost and power consumption constraints.

Mobile platforms need essentially the same performance as notebook computers, but have to rely on much smaller battery capacity. They also need to support high-performance graphics and ever-greater data rates, including the support of 1Gbps when the 5G protocol is tested in 2018. Better cameras demands high-performance image signal processing. 3-D imaging, now under development, will require multiple image sensors. All of this needs to be accommodated with lower power consumption and lower cost.

It is significant that a high percentage of smartphones and tablet computers will be manufactured byChinese companies. Semiconductor technologies that increase battery lifetime without incurring additional costs or potentially providing lower cost can be very attractive to smartphone vendors.

The market requirements are clear, and our detailed analysis of various technology options, including bulk CMOS at 28nm and 20nm and FinFET at 16/14nm, shows FD-SOI is the best option for supporting the requirements of high-volume mobile platforms.

FinFET Realities

FinFETs have the potential to be in high volume in the future: the key issue is timing. Our analysis indicates that FinFETs have high design costs, along with high product costs. It is not realistic to expect FinFETs to be effective for the low-cost and low-power modems, application processors, and other processor engines for mobile platforms in 2016 and 2017.

FinFETs need to go through two phases in the 2015 to 2016 time frame to reach the point where they are suitable for low power and low cost applications.

In the first phase, they will be used in high-performance products such as processors for servers, FPGAs, graphics accelerators, and other similar product categories. This approach was used in the past for new-generation process technologies, where price premiums were obtained from the initial products. The time frame for the high-performance phase of 16/14nm FinFETs within the foundry environment can be 2015, 2016, and potentially 2017.

The high-performance phase can allow extensive characterization of the 16/14nm process and provide a good understanding of various categories of parasitic so that product yields can become high. There is also the need to establish design flows so that new products can be brought to the market within short design windows. The high priced product phase can position 16/14nm FinFETs to be potentially used in high volume, low cost products at a future time.

The second FinFET phase comprises the ramp-up to high volumes for high end processor engines for mobile platforms. High-end mobile platforms, including tablet computers and smartphones, can provide relatively high volumes for FinFET products if costs are competitive. Modems, application processors, and graphics functionality will be suited to the 16/14nm FinFETs from the foundries in the 2017 to 2018 time frame.

This type of methodical approach in solving the manufacturing challenges at 16/14nm can be applied to 10nm and 7nm FinFETs. There is the need to establish design flows that can yield high gate utilization as well as the ability to obtain high parametric yields. The time frame for the high-volume, low-cost phase of FinFETs can potentially be 2017 or 2018.

With the delays in ramping 16/14nm FinFETs into high volume until potentially 2017 or 2018, an alternate technology is needed to support the next phase of the mobile platform IC product supply, which can give low power consumption and low cost.

FD-SOI: Competitive Positioning

To provide visibly into the options for technology selection, IBS has analyzed projected wafer costs and gate costs for bulk CMOS, FD-SOI, and FinFETs. Considerations include processing steps, masks, wafer costs, die shrink area, tool depreciation and parametric yield. The results are shown in the following figures.

The low cost per gate of 28nm wafers in Q4/2016 and Q4/2017 allows this technology node to have a long lifetime. The performance of 28nm FD-SOI is 30% higher compared to 28nm bulk CMOS, with leakage also being 30% lower. There are, consequently, significant benefits in using 28nm FD-SOI compared to 28nm bulk CMOS for the high volume cost- and power-sensitive applications.

Furthermore, the performance of 28nm FD SOI is 15% better than 20nm bulk CMOS, giving 28nm FD-SOI a potentially even longer lifetime.

The gate cost of 20nm FD-SOI is 20%  lower than 20nm bulk CMOS, while offering 40% lower power. and 40% higher performance. The higher cost per gate of 20nm bulk CMOS compared to 20nm FD-SOI is due to the higher number of processing and masking steps. There are also parametric yield penalties at 20nm because of difficulties in controlling leakage. Fabless companies that choose 20nm bulk CMOS over 20nm FD-SOI (called 14nm by STMicroelectronics) risk to find themselves with a noncompetitive platform.

14nm FD-SOI (called 10nm by STMicroelectronics) has an almost 30% lower cost per gate than 14nm FinFETs (including 16nm FinFETs) in Q4/2017, which is a major advantage in price-sensitive applications. Power consumption and performance are expected to be comparable between two technologies.

Why the hesitation in using FD-SOI?

While we clearly see that the benefits of FD-SOI, we also recognize that there is an expectation in the semiconductor industry that Intel sets the bar, so if Intel is doing FinFETs, everyone else should, too. The financial metrics of Intel are, however, different from those applicable to the fabless-foundry ecosystem. Intel is obtaining large revenues from its data center processors. And even though the company has promoted its 14nm and Tri-Gate processors for mobile platforms, Intel’s success in this arena has not been outstanding to date. Intel has, however, delayed the high-volume production of its 14nm Tri-Gate from Q4/2013 to H1/2015 because of low yields. The yield challenges that Intel is experiencing at 14nm should be a warning to fabless-foundry companies of the difficulties in ramping 16/14nm FinFETs within relatively short time frames.

Nonetheless, the manufacturing ecosystem is committed to making FinFET successful, so the resources that have been committed to FD-SOI have been limited. There is also reluctance to admit that the decision to adopt FinFET was premature and a thorough analysis of the cost penalties was not done. A similar perspective applies to 20nm bulk CMOS in following the industry pattern for not having a thorough review of the cost and performance impact.

FD-SOI for High-Volume Applications

The benefits of FD-SOI are clear, and as the yield and cost problems related to 20nm bulk CMOS and 16/14nm FinFETs become clearer, it is expected that there will be increased momentum to adopt FD-SOI at 28nm, 20nm (14nm by STMicroelectronics), and 14nm (10nm by STMicroelectronics).

To recap, FD-SOI provides the following benefits for high-volume mobile multimedia platforms:

  • At 28nm, FD-SOI has lower gate cost than bulk CMOS HKMG through Q4/2017.
  • 28nm FD-SOI performs 15% better than 20nm bulk CMOS HKMG.
  • At 20nm, FD-SOI has lower power consumption than bulk CMOS and lower cost per gate, (about 20% lower in Q4/2017). FD-SOI also has lower power consumption or higher performance compared to bulk CMOS.
  • Shrinking FD-SOI to 14nm yields about 30% lower gate cost in Q4/2017 than 16/14nm FinFET, with comparable performance and power consumption levels.

At 28nm, 20nm, and 14nm technologies, IBS concludes that FD-SOI is superior to competitive offerings for smartphones and tablet computers, and the advantages of FD-SOI extend through Q4/2017. As the supply base for FD-SOI strengthens, FD-SOI is expected to become a key part of the semiconductor supply chain ecosystem for high-volume applications such as smartphones and tablet computers.

The ecosystem in the semiconductor industry should focus on the technologies that optimize the benefits for customers.

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