Published on November 07th, 2011

MEMS and Packaging Hold Keys to Radio Connectivity

Building on Intel’s Rattner introduction to the future of mobile computing, IMEC’s Liebet Van der Perre recently spoke about the need for ultra-low-power, ultra-high-speed, versatile radios. Dr. Van der Perre is the director of the Green Radios Program at IMEC. What follows is a summary of her presentation.

Building on Intel’s Rattner introduction to the future of mobile computing, IMEC’s Liebet Van der Perre recently spoke about the need for ultra-low-power, ultra-high-speed, versatile radios. Dr. Van der Perre is the director of the Green Radios Program at IMEC. What follows is a summary of her presentation.

The prerequisite technology to achieve context-aware mobile computing is improved connected devices—from smartphones and smart buildings to smart devices and displays. This technology is supported by growth numbers, which project that the number of wireless devices will reach beyond 10 billion units in the next few years.

The continued growth in wireless devices brings with it the predictable need for greater bandwidth, connectivity, and mobility. What is far less predictable is the associated user behavior, desired applications, and business models needed to support the market. No one is quite sure what connectivity applications will excite future users. Who could have predicted the rise of Facebook? This is why user-experience-based design has taken on new urgency.

The one certain trend is that all of the technical aspects that support future connectivity will take place in “the cloud”—connecting machines, users, content providers, governments, and everything imaginable. Dr. Van der Perre highlighted machine-to-machine (M2M) connectivity via the cloud with a picture of a Twittering plant. Using simple electronics and low-power wireless connectivity, the plant tells the farmer when it needs more or less water. The name of the platform tells it all: Botanicalls (; see Figure 1). I recently covered an unusual Hollywoodstyle application of low-power, wireless cloud connectivity (see “Embedded World Illuminates TRON,”

In addition to unpredictable user demands and applications, such future connectivity brings enormous technical complexity and uncertainty. The best way to address certain technical crossroads is still being defined in areas ranging from lithography, EUV, and patterning types to interconnect, air gap, 3D, and packaging issues.

Where is certainty to be found in all of this unpredictability? For wireless devices, the requirements are clear: Decrease power consumption with every increase in performance. But this tradeoff between power and performance is old news. The one new requirement for future connectivity is the versatility of the radios.

Versatile radios can operate in small heterogeneous cells. Furthermore, they can exploit all spectral resources—from today’s crowded 6-GHz ranges to future huge-capacity, unused, and free 60-GHz bandwidths (see Figure 2). The challenge for smaller cells is that they must operate with increasing capacity while radiating less and consuming less energy. Conversely, larger cells will need to achieve greater mobility while increasing transmission coverage areas.

The versatility requirement translates to spectral agility for existing 0-to-6-GHz radios, which now must support 17+ bands for fourth-generation (4G) communications. IMEC has reconfigurable analog-front-end (Scaldio) and digital-baseband (Cobra) systems-on-a-chip (SoCs) that address these requirements.

It’s one thing to have a sophisticated RF front end to handle 17+ bands. But you also must have an equally versatile antenna interface. Reconfigurable surfaceacoustic- wave (SAW) filtering with radio-frequency (RF) microelectromechanical-systems (MEMS) technology provides the most promising answer to the antenna bottleneck issue. RF MEMS also could be tightly integrated within the front-end and baseband chip packages.

In fact, one idea is to integrate the RF MEMS and related passives (like low-loss inductors) into a portion of diepackaging interposer substrate. Using the interposer would provide several benefits, ranging from low-loss antenna filtering to integrated CMOS power amplifiers and lowphase- noise voltage-controlled amplifiers (VCOs).

RF MEMS also could be used to integrate a switchedcapacitor MEMS array within a single software-definedradio (SDR) package. The MEMS for the array might be located above the integrated circuit (IC) or directly on the interposer.

For the currently uncrowded, free 60-GHz spectrum, versatility will require improved radio platforms to meet the need for cheap, small, and low-power modules for the consumer markets. This means using leading-edge, 40-nm, low-power CMOS processes. Phased-array radio transmitters and receivers will be needed as well as new beamforming functionality. Power consumption must be low: 260 mW for the multiple receivers and 420 mW for the transmitters. Standards bodies have been formed to address this new technology—including a group within the IEEE and the Wireless Gigabit Alliance (WGA).

As always, the big question boils down to balancing performance (speed) and power. How can we design ultra-high-speed, versatile radios that consume ultra-low power? The good news is that we can. The bad news is that it takes a comprehensive, co-designed approach that requires system, architecture, and technology consideration.

At a system level, the challenge is to move from a performance and coverage mindset to one of capacity and energy. Meeting this challenge will mean connecting via the shortest and best direct link. Designs will need to enable the versatility to determine—on the fly—what type of link is the best for any given connectivity scenario.

Architecturally, connectivity platforms must be multi-mode and scalable. Improved designs will be needed for the next generation of power-efficient transmitters. Technology will help through further process scaling below 40 nm and with more heterogeneous integration of chip dies and related structures, such as MEMS and interposers.

From a wireless perspective, all of these challenges and solutions will welcome a future of very versatile radio devices that can operate at ultra-low power over a variety of heterogeneous networks. These platforms will then provide the technology upon which a sensor-rich, context-aware, user-experience-driven world can exist. Whether it proves to be more beneficial or distracting for most of us remains to be experienced.

John Blyler is the Editorial Director of Extension Media, which publishes Chip Design and Embedded Intel® Solutions magazine, plus over 36 EECatalog Resource Catalogs in vertical market areas.

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