A few weeks ago, I got to look into a crystal ball to see what kinds of novel IC products were being enabled by tomorrow’s process technologies. In a nutshell, some of the things we can look forward to include: denser ICs using vertical integration, wearable medical devices with body area networks (BANs), more applications for software defined radio (SDR), and hotter SiGe bipolars.
This came out of a visit to imec, the global research consortium headquartered in Leuven, Belgium. imec (small initial “I”), started out as “Interuniversity Microelectronics Centre,” but a couple of years ago, they re-branded. Every year, imec invites representatives of the international technology media to visit them in Belgium, and this year, I was privileged to attend for Electronic Design.
Stacking MEMS and Logic with SiGe
Many of the presentations at imec dealt with the organization’s “More than Moore” push, which laughs in the face of anxieties about Moore’s law running out of steam. One aspect of “More than Moore” involves going vertical with chip stacking and more sophisticated packaging. But in one case, it was about extending the process technology to create a MEMS device directly on top of the analog circuitry it works with. This is not trivial, because the heat required for fabricating the MEMS device using today’s processes would affect the underlying circuit. imec attacked the problem, with, of all things, silicon germanium, which does not introduce as much heating during the fabrication process.
For the project reported at the conference, imec described an integrated poly-SiGe-based piezoresistive pressure sensor directly fabricated above their own 0.13-µm copper (Cu) -backend CMOS technology. This is breakthrough stuff. The successful fabrication of the sensor represents not only the first integrated poly-SiGe pressure sensor directly fabricated above its readout circuit, but also the first time that a poly-SiGe MEMS device was processed on top of Cu-backend CMOS.
In detail, the top-layer sensor comprises a surface-micromachined piezoresistive pressure sensor, with a poly-SiGe membrane and four poly-SiGe piezoresistors, and an instrumentation amplifier fabricated using imec's 0.13-μm standard CMOS technology, with copper interconnects (two metal layers), oxide dielectric, and tungsten-filled vias. In performing the above-CMOS integration, imec kept the maximum processing temperature of the complete sensor, including the poly-SiGe piezoresistors, below 455º C.
Heart-Monitoring on the Go
A different sensor-plus-analog (plus microcontroller) breakthrough is a body-patch that combines a complete electrocardiograph (ECG), MEMS accelerometer, and Bluetooth Low Energy (BLE) body-area-network radio that will run for as long as a month on a battery charge.
The system integrates components from imec and Holst Centre’s Human++ R&D program. It was designed in collaboration with DELTA which supplied its ePatch skin-mountable wireless platform. (Holst Centre is a separate imec R&D lab in Eindhoven, Netherlands, that develops generic technologies for wireless autonomous sensor technologies and flexible electronics. DELTA Microelectronics is a Danish research firm.
The ECG patch measures one, two, or three ECG “leads” (signals). (It also uses tissue-contact impedance to monitor the integrity of the sensor connection.) In addition, the ePatch includes a 3D-accelerometer for monitoring physical activity.
The ECG readings are processed and analyzed locally, and relevant events and information are transmitted through the BLE radio. Largely thanks to BLE, the entire system only consumes 280 µA at 2.1 V, and can run continuously for a month on a 200-mAh Li-Po battery if it’s simply transmitting heart data. It can run for a week if it is also collecting and sending accelerometer data.
The custom ECG System-On-Chip (SoC), is a mixed signal ASIC. Using the accelerometer data it runs algorithms for motion-artifact reduction (based on adaptive filtering or principal component analysis) and beat-to-beat heart rate computations (based on discrete or continuous wavelet transforms). It has sufficient additional computation power to run more application-specific algorithms such as epileptic seizure detection, energy expenditure estimation or arrhythmia monitoring. In a neat compression trick, its integral 12-bit ADC samples QRS waves (the big spike in the middle of the pulse waveform) at high frequency, and the slower R and T waves before and after the spike at a lower frequency, achieving compression ratios up to five.
IR-UWB for Body-Area Networking
In order to deliver fade-“resilient” and interference-free communication for battery-operated mobile and sensing applications such as BANs (but not limited to them), imec also disclosed details of an ultra low-power, impulse-radio ultra-wideband (IR-UWB) chip for the 6-10-GHz band.
Researcher Kathleen Phillips said some potential applications include short-range video streaming, and around-the-body audio streaming (e.g. between a headset and a smartphone).
I hadn’t heard of IR-UWB. It’s a mode intended for short-range (sub-20-meter) communication and for precise positioning within small areas. In those applications, wide bandwidth provides better resilience against fading than more narrowband radios, which tend to lose signals when there are a lot of reflective surfaces that create multi-path effects. Also, modulating information over a wide bandwidth decreases the power spectral density at any particular frequency, helping to meet regulatory interference requirements and lowering the probability of interception.
Curiously, the way reflections of IR-UWB’s wide-band signal tend to cancel out makes this mode uniquely suited for positioning sensors; it allows for centimeter-range position precision.
imec’s prototype consists of a transmitter, receiver front-end, and receiver digital baseband processor. The transmitter delivers 13 dBm peak power, with an average power consumption of 3.3 mW. The receiver front-end shows -88-dBm sensitivity at 1 Mbit/s. A digital synchronization algorithm enables real-time duty cycling, resulting in a mean power consumption of 3 mW.
SDR for TV Standards
According to another presentation, today’s digital TV broadcasting environment is hampered by a plethora of differing regional standards, especially in Europe. To deal with this, software-defined radio (SDR) solutions are becoming attractive.
Recognizing the potential in this, imec applied its reconfigurable ADRES processor to the development of a reconfigurable receiver that uses algorithm-architecture co-optimization to accommodate the DVB-T, ISDB-T and ATSC digital video broadcasting standards.
The imec SDR SoC combines better area efficiency than the best current reference - dedicated ASICs that are designed to provide similar versatility. The optimizations came out of imec and Panasonic's partnership in imec's green-radio research program.
Pushing the Envelope on SiGe Bipolars
More in the tradition of advances in process technology, imec introduced a high performance SiGe:C heterojunction bipolar transistor (HBT) device for enhanced imaging systems for automotive radar and security, medical and scientific applications. (C is carbon added to the transistor base during fabrication to moderate the diffusion of boron dopant atoms during later high-temperature stages of fabrication.) The transistors demonstrated an fT/fMAX of 245-GHz/450-GHz. Other characteristics include a BVCEO of 1.7V and a sharp transition from the saturation to the active region in the IC-VCE output curve. imec said that, despite the aggressive scaling of the sub-collector doping profile, the collector-base capacitance values did not increase much. Moreover, the current gain is well defined, with an average around 400 and the emitter-base tunnel current, visible at low VBE values, is limited as well.
According to the presentation, compared to III-V HBT devices, SiGe:C HBT’s high-density and low-cost integration, make them more likely candidates for consumer applications. Such high-speed devices can open up new application areas, working at very high frequencies with lower power dissipation, or applications which require a reduced impact of process, voltage and temperature variations at lower frequencies for better circuit reliability.
The devices self-align emitter, base and collector, and implement an optimized collector doping profile.
There was more, like the demos of an electroencephalograph apparatus that simply drops on a patients head like a bike helmet, and a point-of-care molecular diagnostic platform that can detect extremely low concentrations of molecules in tiny samples of body fluids. There were also tours of imec’s own fabs, including a new, multidisciplinary lab merging microelectronics, biotechnology, and neurology for the investigations of fundamental brain mechanisms.
Leveraging Public Money to Create Jobs
What makes this all the more remarkable is that these efforts are largely self-funding. What government support there is, comes from the six million or so people of Flanders (I’ve found that “Flanders” is hard to define, except as the part of Belgium where most of the people speak Dutch at home), supplemented by an additional amount from the Netherlands.
Commercially, however, in 2010, imec took in €285 million, of which, only €49 million were subsidies from the Flemish Region and The Netherlands. At the end of the year, after paying taxes, the salaries of 1,900 employees, and the usual overhead, the organization came out about €1.9 million to the good, while refining dozens of new technologies that Electronic Design will be writing about for decades to come.
All jobs-creation endeavors should be so successful.