Over a hundred chip designers packed the room for the SOI Consortium’s recent FD-SOI Design Techniques Tutorial Day. Five professors and scientists from top institutions covered design techniques with real examples in digital, mixed-signal, analog, RF, mmW and ULV memory.
Although it was in Silicon Valley, people actually flew in from all over the world to be there. During the Q&A at the end, most everyone prefaced their questions by saying, “Thank you. I really learned a lot today.”
Many of the questions pertained to body biasing, which prompted STMicroelectronics Fellow and Professor Andreia Cathelin to state what may well have been the take-away of the day. “Body biasing is not an obligation,” she said. “It’s an opportunity.”
The tutorial, sponsored by both Samsung and GlobalFoundries, was hosted by Samsung at their San Jose headquarters. But as this was a paying event, the presentations are only available to those who attended. Having had the good fortune to attend, I can give you a quick recap of some of the highlights.
Professor Cathelin set the stage with a basic overview of FD-SOI design for analog, mixed-signal and mmW.
FD-SOI is a perfect match for the many up and coming SOCs that are often half analog and/or RF and mmW. She explained how FD-SOI makes the analog designer’s life much easier (no small feat, since analog can seem rather like blackbox magic to those on the digital side). FD-SOI improves: performance (even at high frequencies), noise, short device efficiency and brings in a new very efficient transistor knob through the Vt (threshold voltage) tuning range. She also explained and gave numerous real examples implemented in ST’s 28FDSOI on how:
For mmW design, the transistor should operate at Lmin, and hence you get excellence performance in terms of both transition frequency (Ft – set by the technology node) and maximum frequency (Fmax – what the designer can really get in the gain vs. speed trade-off). This can be conjugated with the fact that the back-end of line, despite the very fine nm node, takes advantage of the SOI features and brings in very decent quality factors.
For mixed-signal/high-speed design, she showed how and why FD-SOI gives you improved variability, a fantastic switch performance, and reduced parasitic capacitance. All these permit state of the art results in high-speed data converters, or, for example, lower frequency implementations which do not need any specific calibration for best in class linearity and ENOB (effective number of bits).
She also presented details on the CEA-Leti electrical models which are now the reference stand point (Leti-UTSOI2) for any FDSOI technology, and are implemented in several industrial Design Kits such those from ST.
Next on tap was a very lively talk with almost 60 slides by Professor Sorin Voinigescu of U. Toronto. He focused on how to use the main features of FD-SOI for efficient design of RF, mm-wave and broadband fiber-optic SOCs. We’re talking high-speed/high-frequency here, and he had real examples of chips fabbed in ST’s 28FDSOI and some simulated in GlobalFoundries’ 22FDX technology.
He examined layout issues and gave measurement tips and tricks, noting that there are a lot of things you can do in FD-SOI that you can’t do in bulk. It’s also easier to get high linearity in FD-SOI – yet another reason that he really likes it. Plus he sees it as competitive in terms of scaling even past 7nm.
Professor Joachim Rodrigues of Lund University in Sweden (the largest university in Scandinavia) talked about Design Strategies for ULV memories in 28nm FD-SOI (ST’s FD-SOI technology). Noting that SRAMs eat a lot of area in an SOC, he first proposed a standard cell-based memory (SCM) in 28nm FD-SOI that cut memory area by 35% and reduced leakage by 70%.
He then talked about other chips he and his team have presented at the world’s top chip conferences, including an ultra-low voltage (ULV) SRAM. For that chip they lay claim to having the best write performance in ULV in sub-65nm (15MHz at 240mV), and the best performing read capability across all technologies (30MHz at 240mV). In each case, he explained the fundamental design considerations, concepts and trade-offs.
Professor Borivoje “Bora” Nikolic of UC Berkeley is an expert in body-biasing for digital logic. He and his team have designed ten chips in ST’s 28nm FD-SOI, and they’re now working on their 8th generation of energy-efficient SOCs. During his 90-slide (!) tutorial, Energy-Efficient Processors in 28nm FDSOI, he covered: digital logic (including implementation and adaptive tuning of cores for optimal energy efficiency); SRAM and caches (design scenarios and results compared to bulk); supply (generating, switching and analog assists); back bias (how it’s generated and how to use it). He finished with (60 slides of!) design examples and the results they got for power (including adaptive voltage scaling) and performance. He said to be on the lookout for upcoming publications on (even more!) chips, as well as new work on 22nm designs.
Even if you don’t know anything about mixed-signal design, you can walk away from an hour-long lecture by Professor Boris Murmann of Stanford with a good understanding of what it’s all about. In his talk, Pushing the Envelope in Mixed-Signal Design Using FD-SOI, he explained how a mixed-signal person thinks about FD-SOI, and how the different metrics and sweetspots vary depending on what you’re working on. From there it was the deep dive, as he got into the heart of his talk: simulated transition frequency vs. gm/lD. He explained that while some things might seem counter intuitive (like long channels are more efficient for very low Ft requirements), it’s all related to electrostatics. It’s not yet well explained in the literature, he said, but it should be a big deal. And he explained why with FD-SOI, you don’t have to design for the worst case. He then talked about where he sees things going – he sees a very bright future indeed for FD-SOI and analog as computing moves into very low-power neural networks. In the end, he said, it all boils down to the FD-SOI performance benefits with respect to better gate control. This translates into “significant improvements” for many mixed-signal/RF building blocks.
All in all, it was a really terrific day. BTW, this tutorial day followed a full-day FD-SOI Symposium in Silicon Valley. Click here to read about that.
Would you like to better understand FDSOI-based chip design? If you’re in Silicon Valley, you’re in luck. On April 14th, the SOI Consortium is organizing a full day of FDSOI tutorials for chip designers. This is not a sales day. This is a learning day.
On the agenda are FD-SOI specific design techniques for: analog and RF integration (millimeter wave to high-speed wireline), ultra-low-power memories and microprocessor architecture, and finally energy-efficient digital and analog-mixed signal processing designs.
The courses will be given by top professors at top universities (including UC Berkeley, Stanford, U. Toronto and Lund). These folks not only know FDSOI inside and out, they’ve all spent many years working closely with industry, so they truly understand the challenges designers face. They’ve helped design real (and impressive) chips, and have stories to tell. (In fact, all of the chips they’ll be presenting were included in CMP’s multiproject wafer runs – click here if you want to see and read about some of them on CMP website.)
The FD-SOI Tutorial Day, which will be held in San Jose, will begin at 8am and run until 3pm. Each professor’s course will last one hour. Click here for registration information.
(The Tutorial Day follows the day after the annual SOI Silicon Valley Symposium in Santa Clara, which will be held on April 13th.)
Here’s a sneak peak at what the professors will be addressing during the FDSOI Tutorial Day.
If you know anything about FDSOI, you know ST’s been doing it longer than pretty much than anyone. Professor Cathelin will share her deep experience in designing ground-breaking chips.
She’ll start with a short overview of basic FDSOI design techniques and models, as well as the major analog and RF technology features of 28nm FDSOI technology. Then the focus shifts to the benefits of FD-SOI technology for analog/RF and millimeter-wave circuits, considering the full advantages of wide-voltage range tuning through body biasing. For each category of circuits (analog/RF and mmW), she’ll show concrete design examples such as an analog low-pass filter and a 60GHz Power Amplifier (an FDSOI-aware evolution of the one featured on the cover of Sedra/Smith’s Microelectronics Circuits 7th edition, which is probably on your bookshelf.) These will highlight the main design features specific to FD-SOI and offer silicon-proof of the resulting performance.
Particularly well-known for his work in millimeter wave and high-speed wireline design and modeling (which are central to IoT and 5G), Professor Voinigescu has worked with SOI-based technologies for over a decade. His course will cover how to efficiently use key features of FD-SOI CMOS technology in RF, mmW and broadband fiber-optic SoCs. He’ll first give an overview at the transistor level, presenting the impact of the back-gate bias on the measured I-V, transconductance, fT and fMAX characteristics. The maximum available power gain (MAG) of FDSOI MOSFETs will be compared with planar bulk CMOS and SiGe BiCMOS transistors through measurements up to 325 GHz.
Next, he’ll provide design examples including LNA, mixer, switches, CML logic and PA circuit topologies and layouts that make efficient use of the back-gate bias to overcome the limitations associated with the low breakdown voltage of sub-28nm CMOS technologies. Finally, he’ll look at a 60Gb/s large swing driver in 28nm FDSOI CMOS for a large extinction-ratio 44Gb/s SiPh MZM 3D-integrated module, as a practical demonstration of the unique capabilities of FDSOI technologies that cannot be realized in FinFET or planar bulk CMOS.
Having started his career as a digital ASIC process lead in the mobile group at Ericsson, Professor Rodrigues has a deep understanding of ultra-low power requirements. His tutorial will examine two different design strategies for ultra-low voltage (ULV) memories in 28nm FD-SOI.
For small storage capacities (below 4kb), he’ll cover the design of standard-cell based memories (SCM), which is based on a custom latch. Trade-offs for area cost, leakage power, access time, and access energy will be examined using different read logic styles. He’ll show how the full custom latch is seamlessly integrated in an RTL-GDSII design flow.
Next, he’ll cover the characteristics of a 28nm FD-SOI 128 kb ULV SRAM, based on a 7T bitcell with a single bitline. He’ll explain how the overall energy efficiency is enhanced by optimizations on all abstraction levels, from bitcell to macro integration. Degraded performance and reliability due to ULV operation is recovered by selectively overdriving the bitline and wordline with a new single-cycle charge-pump. A dedicated sense-amplifierless read architecture with a new address-decoding scheme delivers 90MHz read speed at 300mV, dissipating 8.4 fJ/bit-access. All performance data is silicon-proven.
Considered by his students at Berkeley as an “awesome” teacher, Professor Nikolic’s research activities include digital, analog and RF integrated circuit design and communications and signal processing systems. An expert in body-biasing, he’s now working on his 8th generation of energy-efficient SOCs. During the FDSOI tutorial, he’ll cover techniques specific to FDSOI design in detail, and present the design of a series of energy-efficient microprocessors. They are based on an open and free Berkeley RISC-V architecture and implement several techniques for operation in a very wide voltage range utilizing 28nm FDSOI. To enable agile dynamic voltage and frequency scaling with high energy efficiency, the designs feature an integrated switched-capacitor DC-DC converter. A custom-designed SRAM-based cache operates in a wide 0.45-1V supply range. Techniques that enable low-voltage SRAM operation include 8T cells, assist techniques and differential read.
If you’ve ever attended a talk by Professor Murmann, you know that he’s a really compelling speaker. His research interests are in the area of mixed-signal integrated circuit design, with special emphasis on data converters and sensor interfaces. In this course, he’ll look at how FD-SOI technology blends high integration density with outstanding analog device performance. In same-generation comparisons with bulk, he’ll review the specific advantages that FD-SOI brings to the design of mixed-signal blocks such as data converters and switched-capacitor blocks. Following the review of such general benchmarking data, he’ll show concrete design examples including an ultrasound interface circuit, a mixed-signal compute block, and a mixer-first RF front-end.
With five manufacturing sites around the world and 72,000 wafer starts/month, X-Fab is a leading pure-play analog/mixed-signal and specialty foundry for automotive, industrial and medical applications. ASN recently had the opportunity to talk to Tilman Metzger, Product Marketing Manager for the X-Fab Group, about when customers choose an SOI-based offering.
Advanced Substrate News (ASN): Can you give us an overview of the SOI offering at X-Fab?
Tilman Metzger (TM): X-FAB offers a range of SOI solutions from 1µm to 0.18µm. We support high voltage (HV) requirements from 20V to 650V. X-FAB also targets very high temperature applications of up to 225˚C.
Our latest addition to the SOI family is XT018, our first 0.18µm SOI solution. The modular XT018 platform combines a state-of-the-art 180nm mixed-signal process with benefits of a robust SOI HV technology. XT018 supports voltages up to 200V and targets next generation automotive and industrial applications.
ASN: When did X-Fab first start offering SOI and why?
TM: We started more than 15 years ago with a 2µm HV SOI process. Our first SOI development was driven by specific customer requirements for an HV motor driver application.
ASN: What sorts of chips are currently being manufactured by X-Fab using SOI?
TM: X-FAB solely focuses on analog and high-voltage SOI applications. We do not target RF-SOI or high density SOCs like CPUs etc.
Typical products include high-side gate pre-driver ICs, motor driver ICs, ultrasound driver ICs, solid state relays, optocoupler and analog switch arrays.
ASN: For X-Fab, what are the traditional SOI markets (both in terms of end-markets and geography)? How do you see it evolving?
TM: Historically, we have seen demand for SOI-based technologies mainly from the industrial sector. That said, we expect to see more automotive customers adopt our SOI solutions in the future.
Geographically, our SOI customer base mostly originates from North America, Europe and Japan. Customers from Greater China and South Korea are generally slower in adoption but gaining momentum.
ASN: When and why do your customers choose an SOI-based process?
TM: Typically, we see two types of SOI customers:
ASN: Can you expand on the time-to-market (TTM) issue a bit?
TM: Since SOI substrates are more expensive than normal bulk wafers, the average wafer price is also higher. Typically customers look at a straight cost-per-die calculation when evaluating the business case for their product. But there’s also the aspect related to ease of design – with SOI, design is easier, so the design cycle might be faster and less costly in terms of engineering time. As a result, if customers can launch their product faster, they can grab more market share and increase their profits.
ASN: What kind of support do you offer designers for SOI-based chips? Is it different from the sort of support for bulk processes?
TM: Generally, for our SOI technologies we offer the same comprehensive support as for our bulk solutions. In addition, we provide SOI application notes that discuss SOI related design considerations. With the exception of XI10, the SOI material we are using is “thick film” SOI, where the device layer is up to 55µm thick, so the behavior of active devices is similar to those on non-SOI substrate. Let’s consider the designers doing high-voltage analog: in bulk, they do standard junction isolation, but in SOI they use deep trench isolation, which actually comes with fewer parasitics, so it’s easier to simulate and design.
ASN: Would you say the SOI ecosystem is well established in the markets X-Fab serves?
TM: There are no special SOI ecosystem requirements for X-FAB’s SOI solution. We use established SOI wafer suppliers and support all major EDA platforms (Cadence, Mentor, Synopsys, Tanner). with complete design kits. Analog and high voltage is all about customization. In the analog world, there are some generic IPs, but most of it is specialized. We offer basic IPs for SOI solutions including I/O and standard cell libraries and memories such as OTP, SRAM etc. which is similar to our offering for non-SOI processes..
ASN: Can you tell us more about X-Fab’s SOI offerings?
TM: X-Fab has two one-micron SOI ultra-high-voltage process offerings for 650 Volt and 350 Volt which are used by customers for applications that plug directly into the grid. There is also a big market for 600V IGBT and MOSFET driver ICs. Some customers select these processes for their inherent robustness in applications like avionics and aerospace. (We do not offer specific radiation-hardened solutions, but our customers use these when they have particular reliability requirements.)
Our one-micron process XI10 targets very high-temperature applications: it offers different metallization schemes, and can support up to 225°C.
XT06 is a 0.6µm SOI technology that supports voltages up 60V and is popular across a range of industrial applications.
XT018 is our latest SOI solution. As mentioned earlier it not only targets industrial and medical applications, but also next generation automotive products. An example is the new CAN FD** standard which is more complex and challenging to implement. XT018 offers the right process options to address these requirements. X-FAB has a long successful track record of serving the automotive market. This is also reflected by the fact that the automotive segment accounts for more that 50 percent of our total revenue.
ASN: For MEMS, when and why do your customers opt for an SOI-based solution? Do you see any growth in interest in putting MEMS on SOI?
TM: For MEMS, we definitely see the opportunity to take advantage of SOI material. In general, SOI wafers are interesting for the formation of highly uniform silicon membranes or other mechanical structures, especially if we prefer to use SOI’s mono-crystalline properties rather than depositing poly silicon. The top device layer is ideal for defining silicon features with thicknesses from a few microns to several tens of microns, without the effort of very long silicon deposition times. The buried oxide (BOX) layer acts as a natural etch-stop layer during silicon etching, at the etching either from the front or from the back of the wafer. Stopping at the BOX layer mitigates any non-uniformity for the deep silicon etch and allows for great process control.
For instance, at X-FAB, we use SOI wafers to manufacture our open-platform gyro sensor / accelerometer process. We use the SOI wafer’s device layer to make single-crystal masses with uniform thickness for predictable and robust performance. In this case the buried oxide layer not only acts as an etch stop when etching the silicon but is also a sacrificial material to remove from underneath silicon structures such as inertial masses and comb-drives.
We also have our newer three-axis gyro / accelerometer process where X-FAB is making its own SOI substrate with buried cavities. In other cases, we etch a pattern all the way through the back side of the wafer to leave thin membranes on the front side of the wafer. Again, the etch is well-controlled, stopping on the buried oxide and the remaining oxide / device layer silicon membrane could be used on its own or with further layers and structuring to form a variety of device types such as pressure sensors, force sensors, thermopile structures or microphones.
ASN: Do you see SOI becoming a more important part of X-Fab’s offering? If so, why?
TM: Yes. One of the factors that we foresee to drive SOI based designs is the increasing challenges of automotive systems and ICs. This is largely driven by newer standards like CAN FD. While SOI is is still a relatively small part of our business, we see opportunities, especially with our XTO18 offering, which may open new high-volume markets.
We have customers that require a stable supply of their product over a long period in time, often for a decade or more. In the automotive industry, those customers are using a 10-year old process. We need to be able to guarantee that those processes will be available for ten to fifteen years.
We have customers in consumer markets using SOI – either because they’ve tried and failed on bulk, or they’re looking for long-term solutions. They see the benefits in the ease and speed of design, which helps them ensure that they don’t miss windows of opportunity. But they need to crunch the numbers themselves. SOI will give them a smaller chip size, but there is not a “one fits all” approach – it depends on the design topology.
ASN: Will the SOI-based processes offered by X-Fab evolve? If so, how and why?
TM: Remember, analog and mixed-signal is not a linear shrink like for digital. The node at 0.18 microns is the leading edge for high-voltage. We can add more functionality and more voltage classes. We’ll continue to add features and modules where we see opportunities for increased performance or new markets. That said, for the five platforms in our current SOI offering, the mature ones won’t change too much except for increasing performance. The markets are evolving, but they’re also very conservative.
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X-Fab has organized a series of design webinars, including a number that cover SOI-related topics. Click here to access the list.
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* EMI = electromagnetic interference; EMC = electromagnetic compatibility; ESD = electromagnetic discharge
**CAN stands for controller area network, a protocol that allow microcontrollers and other devices to communicate without a CPU. It is used extensively in automotives for connecting electronic control units (ECUs) and in industry for factory automation. CAN FD is CAN with Flexible Data rates.
RF-SOI will play a key role in the IoT plans of analog and mixed-signal specialist MagnaChip (read the press release here). The company has launched a task force to address IoT. The statement says, “MagnaChip also offers 0.18 micron and plans to offer 0.13 micron Silicon on Insulator (SOI) RF-CMOS technologies, which is suitable for use in antenna switching, tuner and Power Amplifier (PA) applications. Switches and tuners are core components of wireless Front-End-Modules (FEMs) for cellular and Wi-Fi connectivity in IoT devices. MagnaChip’s CMOS based FEMs reduce manufacturing cost and time to market while providing competitive performance for multiband and multimode smartphones, tablets and other IoT devices.”
Commenting on the IoT opportunity, YJ Kim, MagnaChip’s interim Chief Executive Officer, said, “We believe there is tremendous growth opportunity in the IoT market and our participation is part of our overall strategy to broaden our product portfolio in new markets. MagnaChip’s IoT task force and business consortium with key business partners will reinforce our position as a key manufacturing service provider in the expanding IoT market.”