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Has SOI’s Turn Come Around Again?

Monday, October 10th, 2016


By David Lammers, Contributing Editor

When analyst Linley Gwennap is asked about the chances that fully-depleted silicon-on-insulator (FD-SOI) technology will make it in the marketplace, he gives a short history lesson.

First, he makes clear that the discussion is not about “the older SOI,” – the partially depleted SOI that required designers to deal with the so-called “kink effect.” The FD-SOI being offered by STMicroelectronics and Samsung at 28nm design rules, and by GlobalFoundries at 22nm and 12nm, is a different animal: a fully depleted channel, new IP libraries, and no kink effect.

Bulk planar CMOS transistor scaling came to an end at 28nm, and leading-edge companies such as Intel, TSMC, Samsung, and GlobalFoundries moved into the finFET realm for performance-driven products, said Gwennap, founder of The Linley Group (Mountain View, Calif.) and publisher of The Microprocessor Report, said,

While FD-SOI at the 28nm node was offered by STMicrelectronics, with Samsung coming in as a second source, Gwennap said 28nm FD-SOI was not differentiated enough from 28nm bulk CMOS to justify the extra design and wafer costs. “When STMicro came out with 28 FD, it was more expensive than bulk CMOS, so the value proposition was not that great.”

NXP uses 28nm FD-SOI for its iMX 7 and iMX 8 processors, but relatively few other companies did 28nm FD-SOI designs. That may change as 22nm FD-SOI offers a boost in transistor density, and a roadmap to tighter design rules.

“For planar CMOS, Moore’s Law came to a dead end at 28nm. Some companies have looked at finFETs and decided that the cost barrier is just too high. They don’t have anywhere to go; for a few years now those companies have been at 28nm, they can’t justify the move on to finFETs, and they need to figure out how they can offer something new to their customers. For those companies, taking a risk on FD-SOI is starting to look like a good idea,” he said.

A cautious view

Joanne Itow, foundry analyst at Semico Research (Phoenix), also has been observing the ups and downs of SOI technology over the last two decades. The end of the early heyday, marked by PD-SOI-based products from IBM, Advanced Micro Devices, Freescale Semiconductor, and several game system vendors, has led Itow to take a cautious, Show-Me attitude.

“The SOI proponents always said, ‘this is the breakout node,’ but then it didn’t happen. Now, they are saying the Fmax has better results than finFETs, and while we do see some promising results, I’m not sure everybody knows what to do with it. And there may be bottlenecks,” such as the design tools and IP cores.

Itow said she has talked to more companies that are looking at FD-SOI, and some of them have teams designing products. “So we are seeing more serious activity than before,” Itow said. “I don’t see it being the main Qualcomm process for high-volume products like the applications processors in smartphones. But I do see it being looked at for IoT applications that will come on line in a couple of years. And these things always seem to take longer than you think,” she said.

Sony Corp. has publicly discussed a GPS IC based on 28nm FD-SOI that is being deployed in a smartwatch sold by Huami, a Chinese brand, which is touting the long battery life of the watch when the GPS function is turned on.

GlobalFoundries claims it has more than 50 companies in various stages of development on its 22FDX process, which enters risk production early next year, and the company plans a 12nm FDX offering in several years.

IP libraries put together

The availability of design libraries – both foundation IP and complex cores – is an issue facing FD-SOI. Gwennap said GlobalFoundries has worked with EDA partners, and invested in an IP development company, Invecas, to develop an IP library for its FDX technology. “Even though GlobalFoundries is basically starting from scratch in terms of putting together an IP library, it doesn’t take that long to put together the basic IP, such as the interface cells, that their customers need.

“There is definitely going to be an unusual thing that probably will not be in the existing library, something that either GlobalFoundries or the customers will have to put together. Over time, I believe that the IP portfolio will get built out,” Gwennap said.

The salaries paid to design engineers in Asia tend to be less than half of what U.S.-based designers are paid, he noted. That may open up companies “with a lower cost engineering team” in India, China, Taiwan, and elsewhere to “go off in a different direction” and experiment with FD-SOI, Gwennap said.

Philippe Flatresses, a design architect at STMicro, said with the existing FDSOI ecosystem it is possible to design a complete SoC, including processor cores from ARM Ltd., high speed interfaces, USB, MIPI, memory controllers, and other IP from third-party providers including Synopsys and Cadence. Looking at the FD-SOI roadmap, several technology derivatives are under development to address the RF, ultra-low voltage, and other markets. Flatresses said there is a need to extend the IP ecosystem in those areas.

Wafer costs not a big factor

There was a time when the approximately $500 cost for an SOI wafer from Soitec (Grenoble, France) tipped the scales away from SOI technology for some cost-sensitive applications. Gwennap said when a fully processed 28nm planar CMOS wafer cost about $3,000 from a major foundry, that $500 SOI wafer cost presented a stumbling block to some companies considering FD-SOI.

Now, however, a fully-processed finFET wafer costs $7,000 or more from the major foundries, Gwennap said, and the cost of the SOI wafer is a much smaller fraction of the total cost equation. When companies compare planar FD-SOI to finFETs, that $500 wafer cost, Gwennap said, “just isn’t as important as it used to be. And some of the other advantages in terms of cost savings or power savings are pretty attractive in markets where cost is important, such as consumer and IoT products. They present a good chance to get some key design wins.”

Soitec claims it can ramp up to 1.5 million FD-SOI wafers a year with its existing facility in 18 months, and has the ability to expand to 3 million wafers if market demand expands.

Jamie Schaeffer, the FDX program manager at GlobalFoundries, acknowledges that the SOI wafers are three to four times more expensive than bulk silicon wafers. Schaeffer said a more important cost factor is in the mask set. A 22FDX chip with eight metal layers can be constructed with “just 39 mask layers, compared with 60 for a finFET design at comparable performance levels.” And no double patterning is required for the 22FDX transistors.

Technology advantages claimed

Soitec senior fellow Bich-Yen Nguyen, who spent much of her career at Freescale Semiconductor in technology development, claims several technical advantages for FD-SOI.

FD-SOI has a high transconductance-to-drain current ratio, is superior in terms of the short channel effect, and has a lower fringing and effective capacitance and lower gate resistance, due partly to a gate-first process approach to the high-k/metal gate steps, Nguyen said.

Back and forward biasing is another unique feature of FD-SOI. “When you apply body-bias, the fT and fmax curves shift to a lower Vt.  This is an additional benefit allowing the RF designer to achieve higher fT and fmax at much lower gate voltage (Vg) over a wider Vg range.  That is a huge benefit for the RF designer,” she said. Figure 1 illustrates the unique benefit of back-bias.

Figure 1. The unique benefit of back-bias is illustrated. Source: GlobalFoundries.

“To get the full benefit of body bias for power savings or performance improvement, the design teams must consider this feature from the very beginning of product development,” she said. While biasing does not require specific EDA tools, and can be achieve with an extended library characterization, design architects must define the best corners for body bias in order to gain in performance and power. And design teams must implement “the right set of IPs to manage body biasing,” such as a BB generator, BB monitors, and during testing, a trimming methodology.

Nguyen acknowledged that finFETs have drive-current advantages. But compared with bulk CMOS, FD-SOI has superior electrostatics, which enables scaling of analog/RF devices while maintaining a high transistor gain. And drive current increases as gate length is scaled, she said.

For 14/16 nm finFETs, Nguyen said the gate length is in the 25-30 nm range. The 22FDX transistors have a gate length in the 20nm range. “The very short gate length results in a small gate capacitance, and total lower gate resistance,” she said.

For fringing capacitance, the most conservative number is that 22nm FD-SOI is 30 percent lower than leading finFETs, though she said “finFETs have made a lot of progress in this area.”

Analog advantages

It is in the analog and RF areas that FD-SOI offers the most significant advantages, Nguyen said. The fT and fMAX of 350 and 300 GHz, respectively, have been demonstrated by GlobalFoundries for its 22nm FD-SOI technology. For analog devices, she claimed that FD-SOI offers better transistor mismatch, high intrinsic device gain (Gm/Gds ratio), low noise, and flexibility in Vt tuning. Figure 2 shows how 22FDX outperforms finFETs for fT/fMax.

Figure 2. 22FDX outperforms finFETs for fT/fMax. Source: GlobalFoundries.

“FDSOI is the only device architecture that meets all those requirements. Bulk planar CMOS suffers from large transistor mismatch due to random dopant fluctuation and low device gain due to poor electrostatics. FinFET technology improves on electrostatics but it lacks the back bias capability.”

The undoped channel takes away the random doping effect of a partially depleted (doped) channel, reducing variation by 50-60 percent.

Analog designers using FD-SOI, she said, have “the ability to tune the Vt by back-bias to compensate for process mismatch or drift, and to offer virtually any Vt desired. Near-zero Vt can also be achieved in FD-SOI, which enables low voltage analog design for low power consumption applications.”

“If you believe the future is about mobility, about more communications and low power consumption and cost sensitive IoT chips where analog and RF is about 50 percent of the chip, then FD-SOI has a good future.

“No single solution can fit all. The key is to build up the ecosystem, and with time, we are pushing that,” she said.

IoT Demands Part 2: Test and Packaging

Friday, April 15th, 2016

By Ed Korczynski, Senior Technical Editor, Solid State Technology, SemiMD

The Internet-of-Things (IoT) adds new sensing and communications to improve the functionality of all manner of things in the world. Solid-state and semiconducting materials for new integrated circuits (IC) intended for ubiquitous IoT applications will have to be extremely small and low-cost. To understand the state of technology preparedness to meet the anticipated needs of the different application spaces, experts from GLOBALFOUNDRIES, Cadence, Mentor Graphics and Presto Engineering gave detailed answers to questions about IoT chip needs in EDA and fab nodes, as published in “IoT Demands:  EDA and Fab Nodes.” We continue with the conversation below.

Korczynski: For test of IoT devices which may use ultra-low threshold voltage transistors, what changes are needed compared to logic test of a typical “low-power” chip?

Steve Carlson, product management group director, Cadence

Susceptibility to process corners and operating conditions becomes heightened at near-threshold voltage levels. This translates into either more conservative design sign-off criteria, or the need for higher levels of manufacturing screening/tests. Either way, it has an impact on cost, be it hidden by over-design, or overtly through more costly qualification and test processes.

Jon Lanson, vice president worldwide sales & marketing, Presto Engineering

We need to make sure that the testability has also been designed to be functional structurally in this mode. In addition, sub-threshold voltage operation must account for non-linear transistor characteristics and the strong impact of local process variation, for which the conventional testability arsenal is still very poor. Automotive screening used low voltage operation (VLV) to detect latent defects, but at very low voltage close to the transistor threshold, digital becomes analog, and therefore if the usual concept still works for defect detection, functional test and @speed tests require additional expertise to be both meaningful and efficient from a test coverage perspective.

Korczynski:  Do we have sufficient specifications within “5G” to handle IoT device interoperability for all market segments?

Rajeev Rajan, Vice President of Internet of Things (IoT) at GLOBALFOUNDRIES

The estimated timeline for standardization availability of 5G is around 2020. 5G is being designed keeping three classes of applications in mind:  Enhanced Mobile Broadband, Massive IoT, and Mission-Critical Control. Specifically for IoT, the focus is on efficient, low-cost communication with deep coverage. We will start to see early 5G technologies start to appear around 2018, and device connectivity,

interoperability and marshaling the data they generate that can apply to multiple IoT sub-segments and markets is still very much in development.

Korczynski:  Will the 1st-generation of IoT devices likely include wide varieties of solution for different market-segments such as industrial vs. retail vs. consumer, or will most device use similar form-factors and underlying technologies?

Rajeev Rajan, Vice President of Internet of Things (IoT) at GLOBALFOUNDRIES

If we use CES 2016 as a showcase, we are seeing IoT “Things” that are becoming use-case or application-centric as they apply to specific sub-segments such as Connected Home, Automotive, Medical, Security, etc. There is definitely more variety on the consumer front vs. industrial. Vendors / OEMs / System houses are differentiating at the user-interface design and form-factor levels while the “under-the-hood” IC capabilities and component technologies that provide the atomic intelligence are fairly common. ​

Steve Carlson, product management group director, Cadence

Right now it seems like everyone is swinging for the fence. Everyone wants the home-run product that will reach a billion devices sold. Generality generally leads to sub-optimality, so a single device usually fails to meet the needs and expectations of many. Devices that are optimized for more specific use cases and elements of purchasing criteria will win out. The question of interface is an interesting one.

Korczynski:  Will there be different product life-cycles for different IoT market-segments, such as 1-3 years for consumer but 5-10 years for industrial?

Rajeev Rajan, Vice President of Internet of Things (IoT) at GLOBALFOUNDRIES

That certainly seems to be the case. According to Gartner’s market analysis for IoT, Consumer is expected to grow at a faster pace in terms of units compared to Enterprise, while Enterprise is expected to lead in revenue. Also the churn-cycle in Consumer is higher / faster compared to Enterprise. Today’s wearables or smart-phones are good reference examples. This will however vary by the type of “Thing” and sub-segment. For example, you expect to have your smart refrigerator for a longer time period compared to smart clothing or eyewear. As ASPs of the “Things”come down over time and new classes of products such as disposables hit the market, we can expect even larger volumes.​

Jon Lanson, vice president worldwide sales & marketing, Presto Engineering

The market segments continue to be driven by the same use cases. In consumer wearables, short cycles are linked to fashion trends and rapid obsolescence, where consumer home use has longer cycles closer to industrial market requirements. We believe that the lifecycle norms will hold true for IoT devices.

Korczynski:  For the IoT application of infrastructure monitoring (e.g. bridges, pipelines, etc.) long-term (10-20 year) reliability will be essential, while consumer applications may be best served by 3-5 year reliability devices which cost less; how well can we quantify the trade-off between cost and chip reliability?

Steve Carlson, product management group director, Cadence

Conceptually we know very well how to make devices more reliable. We can lower current densities with bigger wires, we can run at cooler temperatures, and so on.  The difficulty is always in finding optimality for a given criterion across the, for practical purposes, infinite tradeoffs to be made.

Korczynski:  Why is the talk of IoT not just another “Dot Com” hype cycle?

Rajeev Rajan, Vice President of Internet of Things (IoT) at GLOBALFOUNDRIES

​​I participated in a panel at SEMICON China in Shanghai last month that discussed a similar question. If we think of IoT as a “brand new thing” (no pun intended), then we can think of it as hype. However if we look at the IoT as as set of use-cases that can take advantage of an evolution of Machine-to-Machine (M2M) going towards broader connectivity, huge amounts of data generated and exchanged, and a generational increase in internet and communication network bandwidths (i.e. 5G), then it seems a more down-to-earth technological progression.

Nicolas Williams, product marketing manager, Mentor Graphics

Unlike the Dot Com hype, which was built upon hope and dreams of future solutions that may or may not have been based in reality, IoT is real business. For example, in a 2016 IC Insights report, we see that last year $63.4 billion in revenue was generated for IoT systems and the market is growing at about 20% CAGR. This same report also shows IoT semiconductor sales of over $15 billion in 2015 with a CAGR of 21.1%.

Jon Lanson, vice president worldwide sales & marketing, Presto Engineering

It is the investment needed up front to create sensing agents and an infrastructure for the hardware foundation of the IoT that will lead to big data and ultimately value creation.

Steve Carlson, product management group director, Cadence

There will be plenty of hype cycles for products and product categories along the way. However, the foundational shift of the connection of things is a diode through which civilization will only pass through in one direction.

IoT Demands Part 1: EDA and Fab Nodes

Thursday, April 14th, 2016

The Internet-of-Things (IoT) is expected to add new sensing and communications to improve the functionality of all manner of things in the world:  bridges sensing and reporting when repairs are needed, parts automatically informing where they are in storage and transport, human health monitoring, etc. Solid-state and semiconducting materials for new integrated circuits (IC) intended for ubiquitous IoT applications will have to be assembled at low-cost and small-size in High Volume Manufacturing (HVM). Micro-Electro-Mechanical Systems (MEMS) and other sensors are being combined with Radio-Frequency (RF) ICs in miniaturized packages for the first wave of growth in major sub-markets.

To meet the anticipated needs of the different IoT application spaces, SemiMD asked leading companies within critical industry segments about the state of technology preparedness:


*  Electronic Design Automation (EDA) – Cadence and Mentor Graphics,

*  IC and complex system test – Presto Engineering.

Korczynski:  Today, ICs for IoT applications typically use 45nm/65nm-node which are “Node -3″ (N-3) compared to sub-20nm-node chips in HVM. Five years from now, when the bleeding-edge will use 10nm node technology, will IoT chips still use N-3 of 28nm-node (considered a “long-lived node”) or will 45nm-node remain the likely sweet-spot of price:performance?

Timothy Dry, product marketing manager, GLOBALFOUNDRIES

In 5 years time, there will be a spread of technology solutions addressing low, middle, and high ends of IoT applications. At the low end, IoT end nodes for applications like connected smoke

detectors, security sensors will be at 55, 40nm ULP and ULL for lowest system power, and low cost. These applications will be typically served by MCUs <50DMIPs. Integrated radios (BLE, 802.15.4), security, Power Management Unit (PMU), and eFlash or MRAM will be common features. Connected LED lighting is forecasted to be a high volume IoT application. The LED drivers will use BCD extensions of 130nm—40nm—that can also support the radio and protocol-MCU with Flash.

In the mid-range, applications like smart-meters and fitness/medical monitoring will need systems that have more processing power <300DMIPS. These products will be implemented in 40nm, 28nm and GLOBALFOUNDRIES’ new 22nm FDSOI technology that uses software-controlled body-biasing to tune SoC operation for lowest dynamic power. Multiple wireless (BLE/802.15.4, WiFi, LPWAN) and wired connectivity (Ethernet, PLC) protocols with security will be integrated for gateway products.

High-end products like smart-watches, learning thermostats, home security/monitoring cameras, and drones will require MPU-class IC products (~2000DMIPs) and run high-order operating systems (e.g. Linux, Android). These products will be made in leading-edge nodes starting at 22FDX, 14FF and migrating to 7FF and beyond. Design for lowest dynamic power for longest battery life will be the key driver, and these products typically require human machine Interface (HMI) with animated graphics on a high resolution displays. Connectivity will include BLE, WiFi and cellular with strong security.

Steve Carlson, product management group director, Cadence

We have seen recent announcements of IoT targeted devices at 14nm. The value created by Moore’s Law integration should hold, and with that, there will be inherent advantages to those who leverage next generation process nodes. Still, other product categories may reach functionality saturation points where there is simply no more value obtained by adding more capability. We anticipate that there will be more “live” process nodes than ever in history.

Jon Lanson, vice president worldwide sales & marketing, Presto Engineering

It is fair to say that most IoT devices will be a heterogeneous aggregation of analog functions rather than high power digital processors. Therefore, and by similarity with Bluetooth and RFID devices, 90nm and 65nm will remain the mainstream nodes for many sub-vertical markets, enabling the integration of RF and analog front-end functions with digital gate density. By default, sensors will stay out of the monolithic path for both design and cost reasons. The best answer would be that the IoT ASIC will follow eventually the same scaling as the MCU products, with embedded non-volatile memories, which today is 55-40nm centric and will move to 28nm with industry maturity and volumes.

Korczynski:  If most IoT devices will include some manner of sensor which must be integrated with CMOS logic and memory, then do we need new capabilities in EDA-flows and burn-in/test protocols to ensure meeting time-to-market goals?

Nicolas Williams, product marketing manager, Mentor Graphics

If we define a typical IoT device as a product that contains a MEMS sensor, A/D, digital processing, and a RF-connection to the internet, we can see that the fundamental challenge of IoT design is that teams working on this product need to master the analog, digital, MEMS, and RF domains. Often, these four domains require different experience and knowledge and sometimes design in these domains is accomplished by separate teams. IoT design requires that all four domains are designed and work together, especially if they are going on the same die. Even if the components are targeting separate dice that will be bonded together, they still need to work together during the layout and verification process. Therefore, a unified design flow is required.

Stephen Pateras, product marketing director, Mentor Graphics

Being able to quickly debug and create test patterns for various embedded sensor IP can be addressed with the adoption of the new IEEE 1687 IP plug-and-play standard. If a sensor IP block’s digital interface adheres to the standard, then any vendor-provided data required to initialize or operate the embedded sensor can be easily and quickly mapped to chip pins. Data sequences for multiple sensor IP blocks can also be merged to create optimized sequences that will minimize debug and test times.

Jon Lanson, vice president worldwide sales & marketing, Presto Engineering

From a testing standpoint, widely used ATEs are generally focused on a few purposes, but don’t necessarily cover all elements in a system. We think that IoT devices are likely to require complex testing flows using multiple ATEs to assure adequate coverage. This is likely to prevail for some time as short run volumes characteristic of IoT demands are unlikely to drive ATE suppliers to invest R&D dollars in creating new purpose-built machines.

Korczynski:  For the EDA of IoT devices, can all sensors be modeled as analog inputs within established flows or do we need new modeling capability at the circuit level?

Steve Carlson, product management group director, Cadence

Typically, the interface to the physical world has been partitioned at the electrical boundary. But as more mechanical and electro-mechanical sensors are more deeply integrated, there has been growing value in co-design, co-analysis, and co-optimization. We should see more multi-domain analysis over time.

Nicolas Williams, product marketing manager, Mentor Graphics

Designers of IoT devices that contain MEMS sensors need quality models in order to simulate their behavior under physical conditions such as motion and temperature. Unlike CMOS IC design, there are few standardized MEMS models for system-level simulation. State of the art MEMS modeling requires automatic generation of behavioral models based on the results of Finite Element Analysis (FEA) using reduced-order modeling (ROM). ROM is a numerical methodology that reduces the analysis results to create Verilog-A models for use in AMS simulations for co-simulation of the MEMS device in the context of the IoT system.

Tallness Makes Reliable Spindt Tip Cold Cathodes

Monday, November 30th, 2015


By Ed Korczynski, Sr. Technical Editor

MIT researchers have seemingly found a solution to a half-century-old engineering challenge:  how to make a reliable cold cathode array for vacuum electronic devices. While solid-state technology continues to replace vacuum tubes for most electronic applications—the most recent being light emitting diode (LED) luminaires replacing both incandescent and fluorescent light bulbs—there are still applications where vacuum-based devices provide unmatched performance. At the IEEE’s upcoming annual International Electron Devices Meeting (IEDM, Stephen Guerrera will present paper number 33.1 entitled “High Performance and Reliable Silicon Field Emission Arrays Enabled by Silicon Nanowire Current Limiters” on behalf of his team. Since these field emission arrays (FEA) are built in silicon, they can be integrated as cold cathodes with silicon ICs to function as compact RF amplifiers and as sources of terahertz, infrared, and X-ray energy.

Figure 1 shows a 3D illustration of the FEA structure, along with scanning electron microscope (SEM) close-up images of one tip cross-section and the tip array. The array of cold cathodes can be considered as a group of nanoscale electron guns. Each 10µm tall and 100-200nm diameter vertical silicon nanowire is topped by a 6-8nm diameter conical emitter tip.

FIGURE 1: (top) 3D schematic of the FEA device structure showing 50:1 aspect-ratio silicon nanowires, and (bottom) left-side SEM image of one tip cross-section, and right-side plan-view SEM of gate holes showing 1µm spacing and a gate aperture of 350nm.

As can be seen in the bottom left of Figure 1, the researchers used a variation on the now-standard “Bosch” deep reactive ion etch (DRIE, process to form the nanowires. The Bosch process uses vertical etching with side-wall dielectric deposition in alternating sequences such that cross-sections appear with characteristic scalloped profiles. It appears that the other unit-processes used by the MIT team to create this new device are likewise similar to industry standards.

However, while based on standard processes, the cost of using a Bosch etch and the other steps needed to fabricate the 50:1 aspect-ratio (AR) of these 200nm diameter wires is inherently high. In constrast, 5:1 AR structures can be formed using much less expensive processes, while 1:1 AR cones as used in original Spindt tips can be very inexpensive to make. Why do these nanowires need to be so tall?


Decades before organic light emitting diode (OLED) technology was to be the future of flat panel display (FPD) manufacturing, Field Effect Display ( FED) technology was explored as a more efficient replacement for liquid crystal displays (LCD). FED have typically been built using “Spindt Tip” Arrays, named after Charles A. Spindt who developed the technology for SRI International as originally published as “A thin-film field-emission cathode,” Journal of Applied Physics, vol. 39, no. 7, pages 3504-3505, 1968. Figure 2 shows how FED use multiple redundant Spindt Tips to light up the phosphor in each color sub-pixel. With ten or more connected in parallel, if one tip fails then the remaining tips in the sub-pixel cluster only have to handle a 10% increase in current…under another tip fails…and another tip will fail over time without a way to limit current.

FIGURE 2: Cross-sectional schematic of a pixel in a field effect display (FED), showing multiple redundant Spindt Tips driving a single phosphor dot.

Though inherently prone to reliability issues, the original Spindt Tip design is extraordinarily manufacturable. After layers of blanked film depositions, the top gate is patterned with uniform holes which serve as masks for both the etching of cavities and the deposition of tips. Each resulting cone-shaped tip concentrates the current to the point, allowing for efficient low voltage operation. The problem with concentrating current is that over time it tends to find a weak spot in grain boundaries resulting in decreased electrical resistance on one side of a tip, such that current flow over-concentrates and run-away heating causes the tip to fail.

In 2002 and still with SRI International, Spindt was co-author on “Spindt cathode tip processing to enhance emission stability and high-current performance” published by the American Vacuum Society [DOI: 10.1116/1.1527954]. The paper describes using the extracted field emission current to controllably heat and recrystallize the surface of Spindt tips to drive off impurities and smooth the tip surface, thereby producing more uniform physical arrays for more reliable functionality.

While alloys and anneals can improve the reliability, the run-away over-heating effect remains an inherent issue with conical tips. Dean et al. from Motorola worked on FEDs for many years, and found that individual tips emit from multiple nano-scale features with fluctuating current levels [DOI: 10.1109/IVMC.2001.939681]. It only takes one of these nano-scale features to preferentially line-up with a grain-boundary for it to draw relatively more current, and with electro-migration the feature can grow from the surface to be relatively closer to the gate compared to the rest of the tip. A protruding nano-spike create an extremely concentrated electrical field, which further concentrates the current flowing to the protrusion until it tends to physically explode.


Having exhausted all easier solutions, it now appears that using DRIE to create 50:1 AR vertical nanowires is the way to make reliable FEA. The nanowires act as current limiters to protect each emitter tip from run-away heating and arcing, and thereby design-in reliability unlike simple Spindt Tip cones. Since high-quality silicon epitaxial layers with controlled dopant levels to ensure uniform electrical resistivity can be commercially sourced, the resistance of nanowire arrays etched from such an epi-layer can be easily controlled. These device reportedly exhibit long lifetimes and low-voltage operation.

The team built emitter arrays as large as 1,000 x 1,000, and have shown ability to handle current density of >100 A/cm2, more than a hundredfold greater than any other field-emission cathode operated in continuous wave mode. These new devices combine the positive aspects of solid state semiconductors (high gain and low noise) with those of vacuum electronics (high power and efficiency). While not likely to appear in commercial FPDs, there seems to be demand for this technology in diverse communications, defense, and healthcare applications.


SOI: Revolutionizing RF and expanding in to new frontiers

Friday, April 17th, 2015

By Peter A. Rabbeni, Director, RF Segment Marketing and Business Development, GLOBALFOUNDRIES

Faster connections and greater network capacity for wireless technologies such as LTE, WiFi, and the Internet of Things is driving the demand for more complex radio circuit designs and multi-band operation.  In addition the emergence of wirelessly connected smart wearables is not only driving localized high performance processing power but also extended battery life, two goals which are often in conflict. The predicted explosion in the IoT is shown in Figure 1.

Figure 1. More than 30 billion devices are forecast to be connected to the internet by 2018 (Source: BI Intelligence).

The rapid growth in smartphones and tablet PCs and other mobile consumer applications has created an opportunity and demand for chips based on RF-SOI technology, particularly for antenna interface and RF front end components such as RF switches and antenna tuners.  As a low cost and more flexible alternative to expensive gallium arsenide (GaAs) technologies, the vast majority of RF switches today are built on RF-SOI.

To address the highly complex, multi-band and multi-standard designs, RF front-end modules (RF FEM) require integration of multiple RF functions like power amps, antenna switches, and transceivers, as well as digital processing and power management. Today these functions are addressed by different technologies. The RF SOI process technology enables design flexibility by integrating multiple RF functions like power amps, antenna switches, and transceivers, as well as digital processing and power management to be integrated—all on the same die. The benefit of integrated radios is they consume   less power and smaller area than traditional radios. Therefore, mobile devices that exploit radio integration using RFSOI can offer more functions with better RF performance at competitive cost.

Mobile devices that implement RF SOI for RF Front End module functions benefit from higher levels of integration that combine with improved linearity and insertion loss, which translates to better transmitter efficiency and thus longer battery life enabling longer talk times (lower power) and faster downloads (higher signal-to-noise ratio).

Emerging technologies like RF-SOI and even FD-SOI have unique properties and capabilities beneficial in enabling RF circuit innovation and integration levels never before seen in silicon-based technologies.  Device ft, gm/I, well bias control and inherent isolation of the substrate all contribute to improved system level performance over competing technology resulting in the ability to achieve higher linearity, lower power, low loss, and low cost/small size.

Innovative solutions

An innovative technology that is currently addressing the ever-increasing challenges of RF front-end design is UltraCMOS 10 (Figure 2). This customer specific process, co-developed by GLOBALFOUNDRIES and Peregrine Semiconductor, demonstrates SOI’s ability to create highly integrated and reconfigurable mobile radio antenna interface solutions. For designers, it dramatically reduces the required engineering and validation time. And, for the end-user, they benefit from longer battery life, better reception, faster data rates and wider roaming range. With the qualification process complete, UltraCMOS 10 technology is now a fully qualified technology platform.

Figure 2. UltraCMOS 10 technology demonstrates SOI’s ability to create highly integrated and reconfigurable mobile radio antenna interface solutions (Source: Peregrine Semiconductor).

High speed digital-to-analog converters (DAC) are an essential component for direct-to-RF conversion architectures. Faster converter sampling speeds and greater peak-to-peak signal fidelity hold high promise in moving mobile digital signal processing closer to the antenna. It has been demonstrated that DACs on fully depleted SOI, achieve high linearity and very low power for nyquist bandwidths as wide as 5.5GHz. The RF architecture with a high-performance DAC results in lower power dissipation while synthesizing very wideband signals (Figure 3). This further demonstrates SOI ability to move high frequency digital sampling and processing closer to the antenna.

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Figure 3. Low power RF DAC demonstrates SOI ability to move high frequency digital sampling and processing closer to the antenna [1

Agile radio architectures are another key area that can address mobile architecture challenges and cost. Today, the analog RF frontend duplicates much of the circuitry for each band. To simplify, new advancements (Figure 4) in tunable structures and filters are being made to provide a single radio for multi-band/multi-mode frequency. SOI technology offers the possibility to develop tunable/reconfigurable RF FEMs to improve RF performance at competitive cost.


Figure 4. Cutting-edge developments in tunable filters [2

Creating an Ecosystem to Extend SOI to RF

As RF FEM architectures and design challenges become more and more complex, it becomes necessary to relieve some of the increased burden at all levels of the value chain. In order to provide better RF products—from system design and RF integrated circuits down to engineered substrate design—development teams can no longer expect to design in silos and be successful. Collaboration and co-optimization are becoming much more important as a result of the changing dynamics of the design-technology landscape.

Investing in the future is critical to address certain RF challenges such as radio architecture design in multiband, multimode mobile radios and ultra-low power (ULP) wireless devices. Successful collaboration will require adherence to standards to enable interoperability, otherwise, in this fragmented market, the industry won’t see the full benefit of all of the technology innovation. To succeed, we need collaboration at different levels, from R&D to ensure we have the world’s best talent trying to solve all of these problems, all the way through to business models.

There is no doubt that demand on our networks will continue grow and there are advanced chip technology challenges the industry needs to address to enable a higher level of integration and lower power consumption for future wireless communication. GLOBALFOUNDRIES is committed to enabling an SOI portfolio and ecosystem—from process, device, and circuit through system level IP— to lower customer design barriers and complexity and introduce new RF architectures that leverage SOI-based technologies.


1. E. Olieman, A.-J. Annema and B. Nauta, “A 110mW, 0.04mm2, 11GS/s 9-bit interleaved DAC in 28nm FDSOI with >50dB SFDR across Nyquist,,” in VLSI Circuits Digest of Technical Papers, 2014 Symposium on , Honolulu, 2014.

2. Joeri Lechevallier, Remko Struiksma, Hani Sherry, Andreia Cathelin, Eric Klumpernik, Bram Nauta, “A Forward-Body-Bias Tuned 450MHz Gm-C 3rd-Order Low Pass Filter in 28nm UTBB FD-SOI with >1VdBVp IIP3 over a 0.7 to 1V Supply”, ISSCC, San Francisco, 2015.

MicroWatt Chips shown at ISSCC

Thursday, March 5th, 2015


By Ed Korczynski, Sr. Technical Editor

With much of future demand for silicon ICs forecasted to be for mobile devices that must conserve battery power, it was natural for much of the focus at the just concluded 2015 International Solid State Circuits Conference (ISSCC) in San Francisco to be on ultra-low-power circuits that run on mere microWatts (µW). From analog to digital logic to radio-frequency (RF) chips and extending to complete system-on-chip (SoC) prototypes, silicon IC functionality is being designed with evolutionary and even revolutionary reductions in the operational power needed.

The figure shows a multi-standard 2.4 GHz radio that was co-developed by imec, Holst Centre, and Renesas using a 40nm node CMOS process. This was detailed in session 13.2 when Y.H. Liu presented “A 3.7mW-RX 4.4mW-TX Fully Integrated Bluetooth Low-Energy/IEEE802.15.4/Proprietary SoC with an ADPLL-Based Fast Frequency Offset Compensation in 40nm CMOS.” It uses a digital-intensive RF architecture tightly integrated with the digital baseband (DBB) and a microcontroller (MCU), and the digital-intensive RF design reduces the analog core area to 1.3mm2, and the DBB/MCU/SRAM occupies an area of 1.1mm2. This is an evolution of a previous 90nm RF front-end design that results in a reduced supply voltage (20 percent), power consumption (25 percent), and chip area (35 percent).

Ultra-low-power multi-standard 2.4 GHz radio compliant with Bluetooth Low Energy and ZigBee, co-developed by imec, Holst Centre, and Renesas. (Source: Renesas)

“From healthcare to smart buildings, ubiquitous wireless sensors connected through cellular devices are becoming widely used in everyday life,” said Harmke De Groot, Department Director at imec. “The radio consumes the majority of the power of the total system and is one of the most critical components to enable these emerging applications. Moreover, a low-cost area-efficient radio design is an important catalyst for developing small sensor applications, seamlessly integrated into the environment. Implementing an ultra-low power radio will increase the autonomy of the sensor device, increase its quality, functionality and performance and enable the reduction of the battery size, resulting in a smaller device, which in case of wearable systems, adds to user’s comfort.”

When most ICs were used in devices and systems that were powered by line current there was no advantage to minimizing power consumption, and so digital CMOS circuits could be designed with billions of transistors switching billions of times each second resulting in sufficient brute-force power to solve most problems. With power-consumption now a vital aspect of much of the demand for future chips, this year’s ISSCC offered the following tutorials on low-power chips:

  • “Ultra Low Power Wireless Systems” by Alison Burdett of Toumaz Group (UK),
  • “Low Power Near-threshold Design” by Dennis Sylvester of University of Michigan, and
  • “Analog Techniques for Low-Power Circuits” by Vadim Ivanov of Texas Instruments.

Then on Thursday the 26th, an entire short course was offered on “Circuit Design in Advanced CMOS Technologies:  How to Design with Lower Supply Voltages.” with lectures on the following:

  • “A Roadmap to Lower Supply Voltages – A System Perspective” by Jan M. Rabaey of UC Berkeley,
  • “Designing Ultra-Low-Voltage Analog and Mixed-Signal Circuits” by Peter Kinget of Columbia University,
  • “ACD Design in Scaled technologies” by Andrea Baschirotto of University of Milan-Bicocca, and
  • “Ultra-Low-Voltage RF Circuits and Transceivers” by Hyunchoi Shin of Kwangwoon University.

µW SoC Blocks

Session 5.10 covered “A 4.7MHz 53µW Fully Differential CMOS Reference Clock Oscillator with -22dB Worst-Case PSNR for Miniaturized SoCs” by J. Lee et al. of the Institute of Microelectronics (Singapore) along with researchers from KAIST and Daegu Gyeongbuk Institute of Science and Technology in Korea. While many SoCs for the IoT are intended for machine-to-machine networks, human interaction will still be needed for many applications so session 6.7 covered “A 2.3mW 11cm-Range Bootstrapped and Correlated-Double-Sampling (BCDS) 3D Touch Sensor for Mobile Devices” by L. Du et. al. from UCLA (California).

As indicated by the low MHz speed of the clock circuit referenced above, the only way that these ICs can consume 1/1000th of the power of mainstream chips is to operate at 1/1000th the speed. Also note that most of these chips will be made using 90nm- and 65nm-node fab processes, instead of today’s leading 22nm- and 14nm-node processes, as evidenced by session 8.3 covered “A 10.6µA/MHz at 16MHz Single-Cycle Non-Volatile Memory-Access Microcontroller with Full State Retention at 108nA in a 90nm Process” by V.K. Singhal et al. from the Kilby Labs of Texas Instruments (Bangalore, India). Session 18.3 covered “A 0.5V 54µW Ultra-Low-Power Recognition Processor with 93.5% Accuracy Geometric Vocabulary Tree and 47.5 Database Compression” by Y. Kim et al. of KAIST (Daejeon, Korea).

In the Low Power Digital sessions it was natural that ARM Cortex chips were the basis for two different presentations on ultra-low power functionality, since ARM cores power most of the world’s mobile processors, and since the RISC architecture of ARM was deliberately evolved for mobile applications. Session 8.1 covered “An 80nW Retention 11.7pJ/Cycle Active Subthreshold ARM Cortex-M0+ Subsystem in 65nm CMOS for WSN Applications” by J. Myers et al. of ARM (Cambridge, UK). In the immediately succeeding session 8.2, W. Lim et al. of the University of Michigan (Ann Arbor) presented on the possibilities for “Batteryless Sub-nW Cortex-M0+ Processor with Dynamic Leakage-Suppression Logic.”

nW Beyond Batteries

Session 5.4 covered “A 32nW Bandgap Reference Voltage Operational from 0.5V Supply for Ultra-Low Power Systems” by A. Shrivastava et al. of PsiKick (Charlottesville, VA). PsiKick’s silicon-proven ultra-low-power wireless sensing devices are based on over 10 years of development of Sub-Threshold (Sub-Vt) devices. They are claimed to operate at 1/100th to 1/1000th of the power budget of other low-power IC sensor platforms, allowing them to be powered without a battery from a variety of harvested energy sources. These SoCs include full sensor analog front-ends, programmable processing and memory, integrated power management, programmable hardware accelerators, and full RF (wireless) communication capabilities across multiple frequencies, all of which can be built with standard CMOS processes using standard EDA tools.

Extremely efficient energy harvesting was also shown by S. Stanzione et al. of Holst Centre/ imec/KU Leuven working with OMRON (Kizugawa, Japan) in session 20.8 “A 500nW Battery-less Integrated Electrostatic Energy Harvester Interface Based on a DC-DC Converter with 60V Maximum Input Voltage and Operating From 1μW Available Power, Including MPPT and Cold Start.” Such energy harvesting chips will power ubiquitous “smarts” embedded into the literal fabric of our lives. Smart clothes, smart cars, and smart houses will all augment our lives in the near future.


RF and MEMS Technologies to Enable the IoT

Friday, October 24th, 2014


By Ed Korczynski, Sr. Technical Editor, Solid State Technology and SemiMD

The “Internet of Things” (IoT) has been seen as the next major market that will demand high volumes of integrated circuits (IC). The IoT can be loosely defined as a network of small, low-cost, ubiquitous electronic devices where sensing data and communicating information occurs without direct human intervention. Each device would function as a “smart node” in the network by doing some low-level signal processing to filter signals from noise, and to reduce the bandwidth needed for node-to-node communications. The nodes will need to communicate up to some manner of a “cloud” for secure memory storage and to bounce actionable information down to humans.

Figure 1 shows a conservative forecast of the global IoT market that was recently published by IDC. IDC expects the worldwide IoT installed base to experience a compound annual growth rate (CAGR) of 17.5% from 2013 to 2020, starting from 9.1 billion smart nodes installed at the end of 2013 and growing to 28.1 billion units by 2020.

FIGURE 1: Forecast for global IoT applications revenue 2013-2020. Note that smart node “intelligent systems/devices” provide the foundation for this huge growing market. (Source: IDC)

Due to the anticipated elastic-demand for IoT devices that would come from cost reductions, the forecasts for the number of IoT nodes ranges to 50 billion or even 80 billion by the year 2020, as documented in the recent online Pete’s Post “Don’t Hack My Light Bulb, Bro”. The post also provides an excellent overview of recent discussions regarding the host of additional technology and business challenges associated with the enterprise infrastructure and security issues surrounding the integration of vast streams of new information.

As shown in Figure 1, the smart nodes form the foundation for the whole IoT. Consequently, the world will need low-cost high-volume manufacturing (HVM) technologies to create the different functionalites needed for smart nodes. Sensor- and logic-technologies to enable IoT smart nodes will generally evolve from existing IC applications, while R&D continues in Radio Frequency (RF) communications and in Micro Electro-Mechanical Systems (MEMS) energy harvesting.

RF Technology

IoT smart-nodes will use wireless RF technologies to communicate between themselves and with the “cloud.” In support of rapid growth in the 71-86 GHz RF “E-band” telecom backhaul segment—which transports data from cell sites in the peripheral radio access network (RAN) to the wireless packet core—Presto Engineering recently announced a non-captive production-scale testing service for 50µm-thin gallium arsenide wafers.

Silicon-On-Insulator (SOI) substrate supplier Soitec has excellent perspective on the global market for RF chips, since it’s High-Resistivity SOI (HR-SOI) wafers are widely used in commercial fabs. Bernard Aspar, senior vice president and general manager of the Communications and Power business unit of Soitec, explained to SemiMD in an exclusive interview why the market for RF chips is growing rapdily. RF front-end module unit sales are forecasted to increase at a CAGR of ~16% over the period of 2013-2017, while the area of silicon needing to be delivered could actually increase at ~30% CAGR. RF chips are increasing in average size due to the need to integrate multiple standards for wireless communications and multiple antenna switches. “The first components to be integrated in silicon were the antenna switches, moving from 70% on GaAs in 2010 to more than 80% on SOI in 2014,“ said Aspar.

Soitec claims that >80% of smart-phones today use an RF chip built on a wafer from the company, based on sales last year of >300k 200mm HR-SOI wafers. Due to anticipated future growth in RF demand, the company has plans to eventually move HR-SOI production to 300mm diameter wafers. Most of the anticipated demand will be for the company’s new variant of HR-SOI called eSI (“enhanced Signal Integrity”previously called “Trap Rich”) with a measured effective resistivity as high as 10 kOhm-cm for improved device performance.

This high-resistivity characteristic, which is conserved after a full CMOS process, translates to very low RF insertion loss (< 0.15 dB/mm at 1 GHz) and purely capacitive crosstalk similar to quartz substrates. HR-SOI substrates in general demonstrate reduced harmonics compared with standard SOI substrates, and the eSI wafers reduce harmonics to the point that they can be considered as lossless. Soitec was recently given a Best Partnership Award by Sony Semiconductor for supplying RF substrates.

“We’re also adding value to the substrate because it allows for simplification of the fab processing,” said Aspar. The eSI wafers enable much higher linearity and isolation, helping designers to address some of the most advanced LTE requirements at competitive costs. These substrates also provides benefits for the integration of passives, such as the quality factor of spiral inductors or tunable MEMS capacitors.

Vibrational Energy Harvesting

IoT smart nodes will need electrical power to function, and batteries that must be replaced or charged by an external source create issues for ubiquitous always-on small devices. In principle the ambient energies of the environment can be harvested to power smart nodes, and to do so we may consider using thermoelectric, photovoltaic, and piezoelectric properties of thin-films. Thermoelectric and photovoltaic devices both require somewhat specialized ambients for efficient energy harvesting, while piezoelectric devices can extract energy from subtle vibrations almost anywhere in the world (Fig. 2).

FIGURE 2: Schematic cross-section of piezoelectric cantilever with end mass, depicted in connection to an energy-harvesting circuit. (Source: Science)

Researchers in the Energy Harvesting and Mechatronics Research Lab at Stony Brook University, New York, recently published an excellent overview of the potential for 1 W to 100 kW piezoelectronic energy harvesting in building, automobiles, and wearables electronics in the Journal of Intelligent Material Systems and Structures 24(11) 1405-1430. However, the largest forecasted growth in the IoT is for small devices that would consume µW to mW of active power.

For low-cost and low-power consumption, the logic chips for IoT smart nodes are expected to be made using a 65nm “trailing edge” fab process. For example, CAST Inc. has developed a 32-bit BA20 embedded processor core that can deliver 3.41 CoreMarks/MHz at a maximum frequency of 75 MHz. Using TSMC’s 65nm Low Power fab process, it occupies only 0.01 mm2 of silicon area while consuming 2 µW/MHz. Thus, at maximum speed the chip core would consume just 150µW.

MicroGen Systems, Inc. (MicroGen) is a privately held company developing thin piezoelectric energy harvesters, based on technology from Cornell University’s NanoScale Science and Technology Facility. Founded in 2007, MicroGen has headquarters and R&D in the Ithaca and Rochester, NY areas, and volume manufacturing with X-FAB in Itzehoe, Germany. Figure 3 shows one of the company’s ~100 mm2 area chips featuring an aluminum nitride (AlN) peizoelectric thin-film on a cantilever that produces alternating current (AC) electricity in response to external vibrations. Different cantilever designs allow for harvesting energy from either single-frequency or broadband vibrations. At resonance the AC power output is maximized, so it can be ~100 µW at 120Hz and 0.1g, or ~900 µW at 600Hz and 0.5g.

FIGURE 3: BOLT™-R0600 energy-harvesting chip without packaging. The green-silver trapezoidal area is a 25-100µm thick cantilever (with several thin-film layers including an AlN piezoelectric) attached to grey rectangular end mass (silicon). A fixed-frequency device, at resonance of ~600Hz it can produce ~900 µWatts of AC power. (Source: MicroGen Systems)

For any piezoelectric energy harvester there are basic materials properties that must be optimized, including the piezoelectric strain constant as well as the electromechanical coupling factor of the thin-film to the moving mass. Lead-zirconium-titanate (PZT) has been the most studied piezoelectric thin-film due to high strain constant and ability to couple to a substrate though the use of buffer layers.

S. H. Baek, et al. showed “Piezoelectric MEMS with Giant Piezo Actuation” in Science 18 November 2011, Vol 344 using lead-manganese-niobate with lead-titanate (PMN-PT) layers epitaxially grown on a strontium-titanate (STO) buffer layer over 4°-off-axis(001)Si. Figure 4 shows both the transverse piezoelectric coefficient (C/m2) and the energy-harvesting figure of merit (GPa) for this and other thin-films. Note that to acheive stable “giant” piezoelectric effects the PMN-PT layer had to be grown epitaxially with precise control over the STO grain orientation.

FIGURE 4: Transverse piezoelectric coefficient (C/m2) and the energy-harvesting figure of merit (GPa) for PMN-PT (“this work”) and other piezoelectric thin-films. (Source: Science)


RF Substrate Technologies for Mobile Communications

Monday, May 23rd, 2011

Two Soitec Group managers — Eric Desbonnets and Stéphane Laurent — describe how SOI wafers support RF technology development.