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Power & Performance: GSS Sees SOI Advantages for FinFETS

Are FinFETs better on SOI? In a series of papers, high-profile blogs and subsequent media coverage, Gold Standard Simulations (aka GSS) has indicated that, yes, FinFETs should indeed be better on SOI.

To those of us not deeply involved in the research world, much of this may seem to come out of nowhere.  But there’s a lot of history here, and in this blog we’ll take a look at what it’s all about, and connect a few dots.

The GSS IEDM ’11 Paper

GSS is a recent spin-off of Scotland’s University of Glasgow – but there’s nothing new to the research community about these folks.  The core GSS-U.Glasgow team has been presenting important papers on device modeling at IEDM (which is one of the most prestigious of our industry’s conferences) and elsewhere for many years.

At the risk of stating the obvious, accurate simulations are incredibly important. Technologists need to be able to predict what results they can expect from different possible transistor design options before selecting the most promising ones.  Then they also need to provide reliable models to designers who will use them before committing chips to silicon.  One of the biggest challenges is predicting variability, which as we all know is getting worse as transistors scale to ever-smaller dimensions.

At IEDM ’11 last December, GSS-U.Glasgow presented Statistical variability and reliability in nanoscale FinFETs.  This covered  “A comprehensive full-scale 3D simulation study of statistical variability and reliability in emerging, scaled FinFETs on SOI substrate with gate-lengths of 20nm, 14nm and 10nm and low channel doping…”.  Essentially they concluded that scaling FinFETs on SOI should be no problem – and in fact the statistical variability of a 10nm FinFET on SOI would be about the same as the industry’s currently seeing in 45nm bulk CMOS.

That paper was based on work that the GSS-U.Glasgow team had done on two major European projects: the EU ENIAC MODERN project, and the EU FP7 TRAMS project.  It’s perhaps worth looking a little more closely at what those projects are about – and who’s involved:

  • A key objective of the MODERN (for Modeling and Design of Reliable, process variation-aware Nanoelectronic devices, circuits and systems) is to develop “effective methods for evaluating the impact of process variations on manufacturability, design reliability and circuit performance”.  Other partners in the project include ST, Leti, NXP, Infineon, Numonyx (now Micron) and Synopsys.
  • The objective of the TRAMS (for ‘Tera-scale Reliable Adaptive Memory Systems’) project is “to investigate in depth potential new design alternatives and paradigms, which will be able to provide reliable memory systems out of highly unreliable nanodevices at a reasonable cost and design effort”. Other partners in the project include Intel, imec, and UPC/BarcelonaTech.

The Blogs

A few months later, when Chipworks published pictures of the (bulk silicon) Intel 22nm FinFETs, the folks at GSS started a series of blogs that caught the attention of major tech pubs such as EE TimesElectronics Weekly and EDN.  For reference, here are the blogs and basically what they concluded:

Specifically, the July 27th blog indicated that if FinFETs are rectangular in shape, drive current would be 12-15% better.  Would that be easier to do on an SOI wafer? Soitec has argued that their “fin-first” SOI-based approach to FinFET manufacturing will save both time & money while getting better results (see Soitec’s Wafer Roadmap for Fully Depleted Planar and 3D/FinFET in Semiconductor Manufacturing & Design).

The GSS blog also reminded readers that the company’s CEO and founder, Asen Asenov (an extremely heavy hitter who’s published over 550 papers), has hinted that “…SOI FinFETs with an almost ideal rectangular shape may be a better solution for future FinFET scaling”.  GSS has noted previously that “FinFETs built on an SOI substrate could have significant advantages terms of simpler processing, better process control and reduced statistical variability”.

Fin shape aside, GSS said that by virtue of the layer of insulation, SOI would give another 5% boost to FinFET drive current.  But perhaps more importantly, that layer of insulation in SOI-based FinFETs would deliver on average 2.5 times less leakage – which would translate into a doubling of battery-life for your cell phone.

Next project

IBM has now entered into an agreement with GSS et al on a project called StatDES, for Statistical Design and Verification of Analogue Systems – see last month’s IBM blog by IBM Research Scientist Dr. Sani Nassif, entitledFins on transistors change processor power and performance”.

Dr. Nassif writes, “IBM, University of Glasgow and the Scottish Funding Council are collaborating on a project to simulate 3D microprocessor transistors at a mere 14 nanometer scale (the virus that causes the common cold is more than twice as large at 32 nanometers). Using a silicon-on-insulator (SOI) substrate, the FinFET (fin field-effect transistor) project, called StatDES, promises to keep improving microprocessor performance and energy conservation.”

The steering group also includes folks from ST, Freescale, Wolfson and Cadence, so one would guess we’ll be hearing more from this project – and others like it, to be sure – in the future, wouldn’t you think?

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ST White Paper Excerpts: Planar Fully-Depleted Silicon Technology to Design Competitive SOCs at 28nm and Beyond

STMicroelectronics recently issued a major white paper detailing the choice of FD-SOI for consumer SOCs at 28nm and beyond. This article excerpts some of the highlights.

From “Planar Fully-Depleted Silicon Technology to Design Competitive SOC at 28nm and Beyond” (White paper by STMicroelectronics and Soitec):

“ FD-SOI Executive Summary

Planar FD is a promising technology for modern mobile and consumer multimedia chips. It combines high performance and low power consumption, complemented by an excellent responsiveness to power management design techniques. The fabrication process is comparatively simple and is a low-risk evolution from conventional planar bulk CMOS – and there is little disruption at the design level, too.

At 28nm, we find that planar FD more than matches the peak performance of “G”-type technology, at the cost and complexity of a low-power type technology, with better power efficiency across use cases than any of the conventional bulk CMOS flavors.

Looking further, for 20nm and 14nm, we believe planar FD will be extremely competitive with respect to alternative approaches in terms of performance and power, while being both simpler and more suited to low-power design techniques. In short, a better choice for the type of SOC we offer.

Planar fully depleted silicon technology will be ready as early as 2012 to compete in the forthcoming superphones era and in many other consumer segments. ”

Having identified that conventional planar bulk CMOS would not meet all the requirements of mobile and consumer multimedia System-on-Chip (SOC) ICs in the coming years, STMicroelectronics assessed alternative options. It is possible to propose a 28nm planar FD solution available as a second generation shortly after readiness of traditional 28nm on bulk silicon, with better time-to-market than waiting for availability of the 20nm node. It is also an excellent learning step to prepare a 20nm planar FD process. Our evaluations show that 20nm planar FD has also a very competitive potential performance-wise vs. FinFET for System-on-Chip applications.

ST Technology Overview

Figure 1: ST’s planar FD device structure features (notional perspective, notional cross-section, TEM cross-section):

  • Immunity to Short Channel Effects and variability (no channel doping, so no Random Doping Fluctuations / RDF)

  • For the 28nm node, the selected BOX thickness is 25nm.

  • Ultra-thin BOX advantages include:

    – further improved electrostatic control and relaxed thinness requirement of the top silicon,

    – enables back-biasing through the BOX,

    – enables the implantation, during the fabrication process, of heavily doped “ground planes” or “back-planes” under the BOX, for improved electrostatics and/or VT adjustment and/or best-efficiency of back-bias,

    – brings the ability, during the fabrication process, to locally remove the top silicon and BOX to reach the base bulk silicon and co-integrate a few (non geometry-critical) devices on Bulk with devices on SOI – with a small step height between an SOI zone and a Bulk zone, compatible with lithography tools.

  • BOX offers total dielectric isolation of the very thin active layer and naturally ultra-shallow junctions, leading to lower source/drain capacitance, lower leakage and latch-up immunity.

Planar FD technology allows several methods for setting the threshold voltage VT, including engineering the gate stack work function, trimming the gate length and other process engineering techniques. Thanks to this, STMicroelectronics’ 28FDSOI technology is capable of offering 3 VTs (HVT, RVT, LVT), as in traditional bulk CMOS technologies.

Circuit-Level Benchmarking

To assess how the improved planar FD-SOI transistor characteristics translate at the circuit level, STMicroelectronics has benchmarked a number of representative IP blocks, including an ARM Cortex-A9 CPU core. To that aim, we have extracted logic critical paths with associated RC parasitics from placed-and-routed designs and have re-characterized them by swapping 28nm traditional bulk CMOS transistor SPICE models with 28nm planar FD SPICE models.

With test chips in our 28nm planar FD technology becoming available, we are demonstrating that

the models predict well the silicon behavior. We are therefore confident that the benchmarks presented below are reliable and will be matched by SOC implementations.

The benchmarks compare the merits at the 28nm node of ST’s planar FD technology (“28FD”) with a state-of-the-art Low-Power technology (“28LP”) and a more performance-oriented, state-of-art General Purpose technology (“28G”). They are all based on evaluation of an ARM Cortex-A9 core. The analysis focuses on the higher end of the range of operating frequencies found in a SOC, since modern mobile and consumer multimedia demand high performance from their master CPU (for example, a Cortex-A9 or the forthcoming A15).

Performance at nominal Vdd : best speed/leakage trade-off: 28FD consistently outperforms both 28LP and 28G (Figure 2).

Figure 2: Best operating frequency for any class of leakage (TT process, 85C)


Excellent
speed/leakage ratio maintained at reduced Vdd : reducing Vdd is a very good way to save dynamic power. It is therefore realistic to envisage building 28FD chips that match 28G or 28LP performance at a fraction of the power consumption.

Leading-edge performance across the full Vdd range: 28FD exhibits outstanding performance at all practical Vdd values. In particular, when maximum circuit speed is sought, only the low- and ultra-low-VT flavors of 28G compare with 28FD LVT; however they are much leakier and more limited in terms of, e.g., Vdd overdrive they can withstand without reliability concerns.

Best Power Efficiency Across Use Cases: the 28FD technology is power-efficient across the full Vdd and target frequency range (Figure 3). Contrary to G-type technology, with 28FD a given logic circuit that is power-efficient with Vdd set to reach a certain operating frequency (say, 2GHz range) remains efficient with Vdd set for a different target frequency range (e.g., sub-1.5GHz).

Figure 3: Power efficiency across all use cases (TT process, WC temp)


Focus on SRAM: 
The bitcells proposed in 28FD technology have very competitive cell current (Icell) vs. standby current ratio, which is representative of the performance/leakage power trade-off for SRAM arrays (Figure 4). This is true for all bit cells flavors: high-density and low-leakage oriented, or high-speed oriented. The footprint of the 4 bitcells proposed in 28FD is the same as that of the 4 bitcells proposed in 28LP.

Figure 4: SRAM memory bit cells performance/leakage. The power supply of 28FD SRAM arrays can be lowered by 100mV from nominal and still match the performance of 28LP SRAM arrays operated at nominal Vdd, while offering a 2x to 5x reduction in leakage power.

Commonalities with 28nm LP Bulk

STMicroelectronics’ strategy when developing the 28nm planar FD technology has been to reuse as much as possible the 28nm low-power bulk CMOS process.

Overall, the Back-End is 100% identical to the traditional 28nm bulk low-power CMOS process, and the Front-End of Line (FEOL) is 80% common with that same process.

The planar FD process saves about 10% of the steps required to fabricate the chips on the wafers. This approximately offsets the cost overhead of the starting wafers. As a result, the 28nm planar FD technology matches the cost of a conventional low-power technology while delivering extremely competitive performance.

Design Considerations

Designing on planar FD requires specific extraction deck and SPICE models. Apart from that, the design flows, methodologies and tools do not need any adaptation that would be specific to planar FD (Figure 5).

Figure 5: ST’s SOC implementation flow outline


SPICE
Models: SPICE compact models have been developed for accurately representing planar FD transistors. The model we use is now integrated in all major commercially available simulators, such as Mentor’s ELDO, Synopsys’ HSPICE and XA or Cadence’ SPECTRE. A model card has been extracted for all transistors and other devices available in our 28nm planar FD technology.

Flow and Design Platform: With adequate SPICE models integrated in the PDK, the design flow is identical to that used with conventional 28nm Bulk CMOS technology. We have developed a full design platform for SOC, re-using work done for 28nm Bulk. It consists of standard cell libraries (multi-channel and multi-VT) with power management elements (power switches, level shifters etc.), embedded memories, analog foundation IP (such as PLLs and the likes) and specialty IP (Antifuse etc.).

A design platform developed for bulk CMOS technology can be ported to planar FD by re-characterization using planar FD SPICE models, which we have done for a variety of back-biasing conditions. Only a limited number of critical IPs need to be tuned or redesigned: Analog IP, IOs, Fuse.

At the SOC level, migrating an existing design from bulk to planar FD represents an effort comparable to half-node migration. It brings very worthwhile benefits at reasonable efforts.

All techniques used in low-power designs are applicable to planar FD. Those that can be enhanced with planar FD include: multi-VT, power switches, reverse and forward body bias, and voltage scaling.

Back-biasing consists of applying a voltage just under the BOX of target transistors. Doing so changes the electrostatic control of the transistors and shifts their threshold voltage VT, to either get more drive current (hence higher performance) at the expense of increased leakage current (forward back-bias, FBB) or cut leakage current at the expense of reduced performance. While back-bias in planar FD is somewhat similar to body-bias that can be implemented in bulk CMOS technology, it offers a number of key advantages in terms of level and efficiency of the bias that can be applied.  Back-biasing can be utilized in a dynamic way, on a block-by-block basis. It can be used to boost performance during the limited periods of time when maximum peak performance is required from that block. It can also be used to cut leakage during the periods of time when limited performance is not an issue. In other words, back-bias offers a new and efficient knob on the speed/power trade-off.

Perspectives

28nm: We expect to sign-off designs breaking the 2GHz barrier under worst-case conditions, in a power-efficient and cost-efficient way. For lower performance targets, there is also the opportunity to design ultra-low-power chips that can fulfill their functional specifications using a very low Vdd, for example in the 0.6-0.8V range. The Process Design Kit (PDK) is available, targeting the technology to be open for risk production by mid-2012.

20nm: We intend to scale our planar FD technology to 20nm, introducing a number of improvements to continue pushing the performance and retain a low power consumption. The objective is to bring up a solution that will improve on what mobile-optimized planar bulk CMOS will achieve, and will be extremely competitive vs. potential FinFET-based approaches for SOC – while keeping a simple and cost-efficient approach. The design rules will be compatible with 20nm bulk CMOS. This technology will bridge the gap to 14nm and provide an interesting alternative to the cost and complexity of introducing Extreme-UV and FinFET structures. Evaluation SPICE models are available, and full PDK is scheduled by end of 2012, with risk production for 13Q3.

14nm: Based on the assessments we have performed, we are confident that the planar FD technology is shrinkable to 14nm. Silicon and buried oxide thickness will need to be reduced to within limits that wafer manufacturers and CMOS process technology can handle.

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Bulk logic designs for mobile apps port directly to FD-SOI

Bulk logic designs can be ported directly to FD-SOI for high-performing, low-power mobile apps.

Fully-depleted (FD)-SOI is a potential alternative to BULK 20nm. But what sort of the impact will that have on the design flow? The short answer is: very little.

Designs for low-power mobile applications in 28nm bulk benefit significantly in terms of increased performance and decreased power when ported to 20/22nm fully-depleted (FD)-SOI. From the designer’s perspective, the port is essentially direct – really no different from any standard port to a smaller geometry.

Interconnects, routing and RC parasitics are identical. Logic, memories, low- and high-voltage I/O and analog parts are handle in the same way as on bulk. Where there are differences, they are more at the device/process level, and do not pose any particular challenges to the designer at this point. This includes SPICE models, antenna effect, ESD protection, I/O and analog, and back-gate bias.

Synopsys Cadence Magma
Synthesis Design Compiler RTL Compiler Talus Design
Place & route IC Compiler SoCE Nanoroute Talus
Timing analysis PrimeTime (NLDM, CCS) ETS (NLDM, ECSM) Talus (NLDM, CCS)
Power analysis PTPX, PrimeRail (NLDM, CCS) EPS, VoltageStorm Talus
Signal integrity PTSI CeltIC Talus
DFT Tetramax
Verification Formality Conformal

ARM uses standard packages from the leading EDA vendors in SOI ASIC design

20nm FD-SOI v. 28nm Bulk

To get some clear figures on power and performance, ARM recently ported a Cortex-M0 from 28nm bulk to 20nm FD-SOI.  We used the Cortex M0 implementation flow that was proven in 22nm SOI. This included:

  • synthesis, place and route, and the same reduced set of standard cells for 20nm FDSOI and 28nm bulk
  • parasitics extraction for interconnects from the routed 22nm SOI M0 core (22nm SOI Back-End Of Line (BEOL) is considered to be the most representative of current bulk/FD-SOI 20nm BEOL)
  • characterization of 20nm FDSOI and 28nm bulk standard cells (typical process corner and room temperature)
  • different voltages to create the corresponding .lib files that would be used for timing and power analysis of the M0 core: 0.7, 0.8, 0.9 and 1V
  • timings and power were compared for the routed M0 core based on 20nm FD-SOI and 28nm bulk characterizations (.lib).
ARM, 2011 IEEE SOI Conference

Source: ARM, 2011 IEEE SOI Conference

In any next-node port, you typically expect to get a 25% improvement in performance, but in porting from 28nm bulk to 20nm FD-SOI, FD-SOI boosted the improvement far beyond the expected 25%. At a Vdd (supply voltage) of 1.0V, we saw a 40% improvement in performance. At 0.9V, we saw 66%. For Vdd of 0.8, we saw an 80% improvement. And for Vdd of 0.7, we saw an improvement of 125%.

Power is consistently reduced by 30%, and leakage holds steady.

Remember, this is a straight port, which gives us a baseline figure. There are several powerful process and design optimization techniques that can boost those numbers even higher without significantly increasing the complication factor.

Existing design, tremendous results

The conclusions we have drawn are that:

  • a standard bulk ASIC design flow can be used for FDSOI – don’t expect any change
  • an existing bulk logic design can be directly ported to FDSOI
  • you just need to check the timing closure – there is no timing variability (this is not PD-SOI)

FD-SOI should give tremendous advantages in terms of both power and performance. These low-voltage, high-performance chips are perfect for low-power applications, with the undoped channel in the low voltage SRAM resulting in higher margins. For some applications, RF features will also be improved if designers choose high-resistivity substrates.

FD-SOI is all a designer needs for high-performing, low-power mobile applications. And happily from the designer’s point of view, FD-SOI is as simple as designing in bulk.

———-

This article was adapted from “FDSOI Design Portability from BULK at 20nm Node”, which was presented at the 2011 IEEE SOI Conference.

ByGianni PRATA

Program Launch: Ready for SOI Technology

The goal is to build a visible, working IP ecosystem to support SOI adoption.

This spring, the SOI Industry Consortium launched its Ready for SOI Technology program, a global initiative to broaden access to energy efficient SOI technology for the electronics industry. This is an important step towards the formation of a complete ecosystem enabling designers to take full advantage of SOI.

A core project team from ARM, Cadence and IBM collaborated within the consortium to lay the foundation for an IP portal on the ChipEstimate.com website. Synopsys and Boeing also contributed key IP to the launch, with an invitation extended to other developers to add to the growing SOI IP ecosystem. Others have quickly followed suite. Read More

ByGianni PRATA

Jump Start SOI Training

Free webcast session now available.

To help IP and chip designers transition to SOI, the Ready for SOI Technology program sponsored an SOI Jump Start Training event. Held in April at the Cadence auditorium, the event is now available as a recorded webcast through the SOI Consortium website.

An international audience representing 75 separate companies, research institutes and universities attended the event to learn how to leverage the benefits of SOI from ARM, Cadence, IBM and SOI Industry Consortium speakers.

(photos: Jeff Wolf)

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Digital implementation with SOI: go with the float

Off-the-shelf solutions eliminate SOI design-time overhead.

Since the drive began to make SOI a more mainstream manufacturing process there has been concern over the cost. These considerations have overshadowed the benefits that the floating body of the SOI process brings, which includes better chip performance per watt, smaller die size, and better scalability at smaller geometries.

The concerns raised were not only regarding the cost of the manufacturing process itself — because any advance comes at a price — but also with the cost of actually implementing cell-based digital designs. The biggest concern: it would take many more man-hours of engineering time to make it through the digital design process as compared to bulk CMOS. Read More

ByGianni PRATA

What’s new

SOI: Simply Greener — The Campaign

This summer, the SOI Industry Consortium launched the “SOI Simply Greener” initiative, encouraging the electronics industry to adopt a broader application of SOI’s energy saving benefits.

Results from two studies offered by consortium members demonstrate both increased performance and reduced power consumption – the magnitude of the benefit applied to each is the designer’s choice.

  • A benchmark analysis was performed by ARM Holdings using a 24-stage interconnect-loaded datapath circuit.  When comparing IBM’s 45nm bulk high performance and 45nm SOI technologies, the SOI implementation resulted in a 25% circuit area reduction, 66% reduction in static power leakage and nearly 22% reduction in dynamic power with 5% higher performance.
  • A consumer product chip design that was migrated from 65nm bulk high performance to IBM’s 45nm SOI technology realized a 50% increase in operating frequency, more than 64% reduction in die area and a 38% reduction in power.

Whether designers put the emphasis on increasing or maintaining performance, significant power savings (as well as area savings) were realized with a move to SOI.

Get the Logo

The Consortium’s SOI: Simply Greener logo is freely available on the website. Members and supporters are encouraged to download it for use in their own presentations.

Industry Support

In support of the press announcement launching the initiative, the Consortium offered citations from industry leaders. A few follow here – you can read all of them on the SOI Consortium website.

“As we detailed in our recent report Semiconductor Technologies: The Potential to Revolutionize U.S. Energy Productivity, semiconductors already are the leading factor behind energy efficiency gains. SOI offers a major advance in the power efficiency of electronics, and with appropriate public policy, investment and usage these semiconductor technology gains can contribute to cumulative net electricity bill savings of $800 billion through 2030 for consumers and businesses in the United States alone, as well as creating an average of 500,000 new jobs per year and reducing energy-related CO2 emissions by more than 400 million metric tons annually over the period 2010 through 2030.”

John A. “Skip” Laitner, lead report author and Director, Economic and Social Analysis, American  Council for an Energy-Efficient Economy (ACEEE)

“UMC has been incorporating the benefits of SOI technology across multiple semiconductor applications such as MEMS, photonics, and our 65nm high-speed process portfolio. The energy efficiency of SOI adds to the attractiveness of the technology and conforms with UMC’s green initiative to provide environmentally friendly processes for our customers. We look forward to further developing SOI to provide customers with solutions that enable more innovative applications for a better and greener planet.”

W.Y. Chen, Senior Vice President, UMC

“The ‘SOI: Simply Greener’ initiative expresses the motivation and values that connect members of the SOI Consortium and foster collaboration around this energy-efficient technology. We welcome like-minded companies to join us in this meaningful work, to bring needed improvements to our industry and quality of life. The ecosystem is ready and accessible, and there is a broad space of opportunities for innovation in all areas: process; planar and 3D device architecture and optimization; digital, analog, RF, and MEMS design; EDA; IP development and optimization; heterogeneous planar and 3D integration; and services.”

Horacio Mendez, Executive Director, SOI Consortium.

“As a leader in low power design, Cadence continues to invest heavily in new technologies and methodologies to provide maximum power efficiency, now a key consideration for all designs. We are pleased to announce our end-to-end support for the SOI process within the Cadence Low Power Design Solution, thereby offering customers an integrated and low-risk path to maximizing the potential SOI benefits on their green designs.”

Dr. Chi-Ping Hsu, Senior Vice President, R&D Implementation Group, Cadence

ByGianni PRATA

Partners In Design: Standard Tools Simplify Rad-Hard SOI Design

Honeywell has worked with the top EDA tool vendors to develop the SOI process design kits (PDKs) needed by both in-house designers and foundry customers. Rick Veres, Honeywell EDA Manager, explains.

ASIC Design With Pilot Flow

For digital rad-hard ASIC design, we worked with Synopsys to adapt the Pilot Design Environment to our process. The environment supports their entire RTL to GDSII flow, including all their synthesis tools, place and route, insertion and so forth—the standard industry flow. Our SOI cell libraries are all radhard optimized for commercial, military or satellite applications.

Analog, Mixed Signal, RF and High Temp

Honeywell provides mixed signal/analog SOI devices and cells to support a broad range of customer’s mixed mode ASICs. The design environment maintains all the digital capabilities while supplying analog cells and SRAM for true mixed signal ASICs. The design flow and associated Design Kits are supported for Cadence mixed signal tools.

For RFIC design and simulation, Honeywell’s SOI fab processes are supported by Cadence (Tality) PDKs, including RF Spectre.

For high temperature SOI CMOS, the Cadence PDK full-custom development library supports Cadence schematic capture, simulation, layout and verification tools.

Calibre for Physical Verification

Mentor Graphics has been very instrumental in helping us develop our SOI capability in their Calibre tool. We use Calibre to verify designs before we run them in the fab. There are some nuances that a user doesn’t see, that as a developer we do. For example, we have twice as many rules we have to implement and check in SOI versus standard bulk. But the complexity is all on the developer side. The user just runs it—it’s transparent to them. Mentor Graphics has done some significant and impressive work for us.

ByGianni PRATA

SOI By Design

The widening availability of tools and services is good news for designers in the fabless/foundry arena considering the move to SOI.

Leading foundries have made the investments in manufacturing on SOI. Those that have taken the final steps – finalizing electrical characterization, constructing SPICE models, integrating design tools and building libraries – are winning business.

Chartered, for example, is producing SOI-based chips for AMD, the Microsoft Xbox®360, Via, and others in partnership with IBM. TSMC, meanwhile has announced an SOI version of its Nexsys 65nm process technology for next year.

For the high-performance fabless community, IBM itself was the first to open SOI doors to its foundry customers. Ghavam Shahidi, Director of Silicon Technology, IBM Research Division, says they see the full range – from customers that do the whole thing themselves, just getting the IBM-specific SOI IP, to those who essentially hand off the whole project to the IBM services group. Asked how big a challenge the move to SOI is, he says, “It’s not a big deal – it seems scarier than it is.”

As far as those low-power customers worried about the added cost of SOI wafers, he suggests that if they were to consider the broader picture and include things like cooling, they might find it a more cost-effective solution.

In the Flow

Design flow involves a series of iterative steps subject to rules and constraints – many of which are different when devices are built in SOI. SOI-specific IP is needed at each step, especially:

• In support of the logic synthesis tools used to transform the high-level RTL design into a gate-level netlist (which is the collection of “standard cells” and their electrical interconnections specific to the foundry that will do the manufacturing).

• And in the placement and routing tools to layout the chip. Either the design team has to develop SOIspecific expertise (a substantial investment), or license intellectual property (IP) from a third party (the foundry or an IP vendor).

By licensing the requisite IP, designing-in SOI becomes a transparent process. As the designer generates netlists and optimizes placement and routing, the SOI IP is applied via standard EDA tools from companies like Cadence, Synopsys and Magna.

TCAD from Synopsys, for example, can model the SOI technology from the process and device simulation standpoint, so performance of SOI and bulk silicon can be compared before choosing the right technology for the design, says a company representative. Also, engineers can optimize the SOI technology by using TCAD simulation before running costly experimental wafers.

Says Francois Thomas, Europe ICD & DFM Field Marketing Director for Cadence Design Systems, “SOI uses nearly standard processes and design but with better performance. The real difference appears for cell creation, analog simulation and DRC and parasitic extraction.”

SOI IP Vendors

Recently three new SOI IP and design services suppliers have helped bring SOI design to a wider community.

Cell layout of SOISIC standard cells library for 90nm SOI process. (Courtesy of Soisic.)

Soisic. Working with companies that pioneered SOI, Soisic developed extensive design expertise and intellectual property (IP), which is now available to any ASIC designer. For a simple licensing fee, a design team can transparently integrate the SOI-specific design considerations into the design flow – without a special understanding of SOI (things like the history effect, for example) and the differences with bulk. No additional investment in time, training or libraries is needed

Innovative Silicon (ISi). ISi has harnessed the SOI “floating body effect” for memory cells that are twice as dense as existing DRAM and five times as dense as existing SRAM. This proprietary “Z-RAM™” (for Zero capacitor DRAM) technology uses standard SOI logic processes without new materials or extra process or masking steps. For most SoC and microprocessor ICs, this results in SOI being a lower-cost solution than bulk silicon. AMD is the first licensee.

CISSOID. As a fabless player, CISSOID designs custom analog, mixed and digital ASICs, with a specialty in SOI-based high temperature components for oil & gas, aeronautics, space and automotive applications. For low-power and RF applications, CISSOID offers design services, IP development and consulting for optimization of SOI analog and RF circuits.

Mixed Signal & RF Choices

For designers of mixed-signal, analog and RF devices, a growing number of major foundries have been actively promoting their SOI services.

For example, Honeywell offers RF SOI foundry services, supported by a comprehensive tool set and optional design services. The company points out that the SOI-enabled integration of mixed signal and high-voltage applications with complex control functions performed at low power on a single chip ultimately reduces cost.

Others like Atmel promote their SOIbased smart power foundry services for automotive, telecommunications and consumer electronics, noting that using SOI cuts the die-area in half compared to standard bulk technology. The X-Fab foundry service offers SOI-based analog/mixed-signal and MEMS.

All things considered, SOI is now well within the grasp of the greater chip design community.