In the quaint Belgian town of Leuven, a short distance from the town center and just a few miles from Brussels, sits IMEC, an extraordinary microelectronics research center. In a country famous for cuisine that rivals that of France, exquisite linens, and wonderful chocolate, the Center delves into leading-edge semiconductor R&D programs. Funded by the Flemish government, several European technology agencies, and many companies around the world, IMEC’s research projects comprise technology and methodology that enable current and future system-on-a-chip (SoC) designs.
Founded in 1984, IMEC is currently the largest European independent research center for microelectronics, nano-technology, and design methods and technologies for information and communication technology (ICT) systems. The Center has a two-fold missionto strengthen the local economy and to do scientific investigation and research 3-10 years ahead of industrial needs. IMEC has a staff of over 1200 employees, including 350 industrial residents and guest researchers, operates with a budget around 120M euros, and collaborates with more than 450 partners. Along with their Leuven headquarters, the Center has offices in San Jose, CA and Shanghai, China.
IMEC Research Overview
The organization’s current research projects, undertaken with leading university and industrial partners, include those covering:
- Semiconductor processing and packaging technologies, including material and photolithographic programs down to 65 nanometers (0.065 microns)
- System-on-a-chip (SoC) design methodologies
- Embedded-system design techniques
- Microelectromechanical Systems (MEMS)
- Biotechnology, including biosensors
- Solar cells
- Reconfigurable SoCs
- Wireless communications.
Key contributing factors to IMEC’s success are the center’s R&D microelectronic programs and co-research laboratories with several Flemish universities, including:
- Ghent University (broadband communication, microdisplays, and advanced interconnection and packaging technologies)
- University of Brussels (image compression, communication systems, and optical and optoelectronic components)
- Higher Polytechnical School of Bruges-Ostend (analog design)
- University of Limburg (ferroelectric, semi-conducting polymer, and broad-bandgap materials such as thin-film diamond)
- University of Antwerp (electrical transport in low-dimensional semiconductor structures; ultra-fast switching and relaxation processes in III-V semiconductor devices; concentration-depth profiles of semiconductor structures; organic semiconductors and light-emitting semiconductors; and TEM and TOF-SIMS analysis methods)
- University of Leuven (millimeter-wave and microwave circuits and systems; parallel VLSI architectures; DSP algorithms and architectures for digital communication systems; micro-system design methodology; software environments for real-time emulation of complex DSPs; and solar cells).
IMEC has also put in place several types of cooperative programs, covering various types of the Center’s research activities. Included in these programs are:
- Industrial Affiliation Programs Generic research
- Bilateral Collaborations Pre-competitive or competitive programs
- Technology Transfers Collaboration in the areas of training, information transfer, and installation support
- License Agreements Intellectual property given in either a non-exclusive or an exclusive way to a partner for commercialization
- Setting up Spin-Off Companies .
The technical subjects covered by IMEC’s Industrial Affiliation Programs are vast and include the following:
- Process Technology Development (optical lithography; ultra-clean processing; low-k dielectrics, copper interconnect, silicides, and shallow junctions for 65 nm technology and below; and high-k dielectrics and metal transistor gates for sub-90 nm technology)
- Device and Package Technology (emerging alternative devices, BiCMOS process integration, advanced Flash memory, and wafer-level packaging)
- Design Technology (object-oriented SoC design)
- System Technology (MPEG-4, integrated transceiver design for wireless multimedia communications, and reconfigurable systems).
Some ‘Hot Technology’ Programs at IMEC
IMEC’s MEMS development is targeted towards the goal of true SoC chipsthose that include electrical, mechanical, optical (including infrared), and biochemical functionality on the same semiconductor. The Center’s MEMS research encompasses design, processing, packaging, and reliability. IMEC uses the term system-in-a-package (SiP) for MEMS-enabled devices. SiP technology is targeted towards several applications, including wireless systems, optoelectronics, magneto-electronics, and biotechnology.
Wireless applications are particularly “hot” at this time for MEMS development, since MEMS components can offer distinct performance, cost, and ruggedness advantages over strictly electronic wireless components. Applications for wireless MEMS devices include mobile communications, WLANs, satellite communications, automotive electronics, radar, and military defense systems.
Since MEMS comprise multiple technology domains, their design and processing requires complex multi-domain design, which uses analytical models and highly accurate 3D analysis tools. IMEC uses several MEMS design tools, including those from Coventor. IMEC’s MEMS processing capabilities include bulk and surface micromachining technologies. Bulk micromachining forms the basis for devices such as micro-calorimeter arrays. IMEC uses surface micromachining on both poly-SiGe and metal materials, with poly-SiGe offering thermal, electrical and mechanical advantages over poly-Si. Applications for the poly-SiGe devices include pixel detectors in linear and 2D bolometer arrays. RF-MEMS switches use metal surface-micromachined devices, such as those made with aluminum, since poly-SiGe’s resistance is too high for RF switches.
Another critical part of MEMS development is packaging the devices. You can use existing or modified chip packages for the final product, but due to their vulnerability during wafer processing, MEMS need wafer-level encapsulation (also known as zero-level packaging) to protect the individual die during separation and assembly. The encapsulation also provides hermetic protection of the MEMS against moisture and ambient atmosphere.
Current MEMS zero-level packaging techniques are not well suited for certain types of MEMS devices, such as RF switches or micro-bolometers. Figure 1 shows a poly-SiGe IR Bolometer Linear Array. The processing of these MEMS require hermetic vacuum packaging, to protect the devices from high process temperatures and other process-related problems. IMEC has developed alternative techniques, such as indent reflow solder (IRS), using solder and BCB (benzyocyclobutenea planarization interlayer for vertically integrated MEMS) seals. The IRS technique provides cavity-seal hermeticity and cavity-ambient controllability, both necessary features for MEMS packaging. IMEC chose a die-to-wafer approach, instead of the traditional wafer-to-wafer approach, that is fully compatible with standard IC-packaging equipment. The Center has used this technique for packaging RF-MEMS devices and micro-relays.
Figure 1: A poly SiGe IR Bolometer Linear Array
MEMS reliability is another area getting a lot of IMEC attention. MEMS reliability issues comprise chip-like issues (such as oxide charging and breakdown, mechanical stress, hot carriers, and electromigration), and MEMS-specific issues (such as fracture, wear, stiction, fatigue and creep, hermeticity, heater stability, and contact integrity). IMEC has focused their MEMS-reliability research primarily on stiction, stress effects, and instrumentation.
A key failure mode in MEMS is auto-adhesion, or stiction, of two surfaces. IMEC has developed a theoretical model in which the interaction energy between surfaces and the probability that stiction will appear is calculated as a function of humidity, taking into account the MEMS surface roughness. Using micro-Raman spectroscopy to study the local mechanical stress in a pressure sensor bonded to a glass wafer, IMEC showed that this technique is valuable for local stress analysis in silicon MEMS.
To study the reliability of MEMS containing moving parts, IMEC is building a MEMS optical system (MOPS) for in-situ monitoring of the out-of-plane movement of MEMS (for example, switches, tunable capacitors, membranes, and other devices) up to MHz frequencies. A second system detects the switching-induced change in capacitance of RF-MEMS switches with fF sensitivity. By monitoring the difference as a function of the number of switching cycles, you can use the system to study switching-induced degradation effects such as creep, fatigue and stiction.
Biosensor research at IMEC has the goal of developing sensors for “monitoring, protecting, or improving human health.” The Center’s activities are based on microelectronic transducers using planar silicon technology, allowing such sensors to be, ultimately, integrated on an SoCso-called “labs on a chip.”
Biosensors use a chemically or biologically enabled sensing surface along with circuitry that can interpret what the sensor is detecting. These sensors find use in various chemical, pharmaceutical, medical, biotechnical, and other applications. Examples of biosensor use are reliable substance measurements in cell cultures or biological fluids, environmental monitoring in air or water, and cell-parameter measurements for medical applications.
At the center of a biosensor system is a biosensor module, or BioSiP (Biosensor-System-in-a-Package), comprising microfluidics, a transducer, and a biological top layer. The BioSiP includes transducer configuration, organic surface chemistry, and an optimized biochemical probe, packaged in a durable, simple and inexpensive cartridge. For BioSiPs, IMEC has identified two key areas of interest:
- The development of an adequate biological recognition layer based on self-assembled monolayers (as an interface between the electrical transducer and the biological probes)
- The development of novel transducers, based on microelectronics technology.
A key challenge in biosensor development is attaching the organic (biological) receptors to the inorganic transducer. Developers have focused attention on affinity biosensors that use the binding of antibodies to antigens, cell receptors to their ligands, and DNA and RNA to nucleic acids with a complementary sequence. These techniques require the development of so-called immobilization techniques to attach these bio-molecules (antibodies, cell receptors, DNA, and RNA) to the transducer.
IMEC is working on the covalent and oriented immobilization of antibodies on Au and oxide materials (mainly on SiO2 and tantalum pentoxide, Ta2 O5 ). Self-assembled monolayers (SAMs) of thiols (similar to alcohols but containing a sulfur rather than an oxygen molecule) on Au and of silanes on oxide materials are made as a first step in the immobilization process. Specifically, Ta2 O5 is a promising material for affinity biosensors, especially for capacitive- or impedimetric-based devices, due to the oxide’s high dielectric constant and chemical stability. IMEC has used different analytical techniques to evaluate the quality of these so-called ‘linking layers’, investigating the density, distribution, and activity of the bio-molecules and the type and stability of binding between the coupled molecules and a gold or oxide substrate. SAMs have shown enhanced qualities for the immobilization of bio-molecules.
The second area of biosensor interest for IMEC is the development of novel transducers and transducer applications based on microelectronic technology. Applications for these transducers span a wide variety of fields, from medical diagnostics and analytical chemistry to environmental monitoring and industrial process-control. IMEC is developing several types of transducers for biosensor applications:
- A polymer-based ChemFET (chemically modified field-effect transistor) for pH monitoring and the detection of neutral compounds. By modifying an organic transistor, you enable the development of detectors for different analyte species, since you can monitor both the charged and uncharged chemical species by the field-induced current variation in the transistor channel if an appropriate recognition layer is added to the transistor to provide chemical specificity. The detection principle is generic and can be used in biosensing systems based on enzymes or cells by adding a layer with a specific functionality onto the organic transistor.
- An acoustic-based biosensor, using SAW (surface acoustical wave) technology, for the detection of very low concentrations of the prostate-specific antigen (PSA). The biosensor’s surface is covered with antibodies that exclusively bind PSAs. The antibodies are attached to a gold plate using SAMs of thiols or silane to immobilize the bio-molecules on, respectively, gold and oxide. Interdigitated structures on both sides of the gold plate generate and detect the electromechanical wave. When PSAs attach to the biosensors’ antibodies, you can detect a difference in mass loading, electrical properties, viscoelastic, and mechanical properties of the antibodies with high sensitivity.
- An interdigitated electrode-based sensor for the detection of specific DNA sequences. IMEC’s development of an innovative production technique allows low-cost production of arrays of interdigitated electrode (IDE) structures. The resulting polymer chips enable a new type of diagnostic device for the impedimetric detection of either DNA hybridization or affinity binding of antibody/antigen combinations.
- A micro-calorimetry tool for drug screening. The generic technology measures temperature changes that have potential commercial use for drug screening. The system comprises miniaturized calorimeters on a single substrate along with integrated temperature sensors using microsystem technology. The integrated temperature sensors measure the temperature change between the test well with the potential drug, and a reference well with a reference sample. A change in temperature between the neighboring wells indicates drug activity.
Figure 2 shows several types of biosensor-enabled devices for biomedical and related applications.
Another interesting biotechnology application IMEC is investigating is the use of magnetic labels on bio-molecules. On-chip magnetic gradients can manipulate the labels to direct the attached bio-molecules to a chip’s surface or to specific locations on a chip. You can detect the presence of the magnetic labels to monitor, for example, hybridization results. IMEC has implemented a proof-of-principle demonstrating the manipulation and detection of magnetic particles in aqueous solution using a spin-valve magnetic sensor and integrated current conductors.
A third area of IMEC expertise and development effort is embedded-computing platforms using instruction-set processors (ISPs) with reconfigurable hardware. The Center is working on design technology for programming heterogeneous reconfigurable platforms that is as easy to use as current design technology for general-purpose processors. One focus of this technology development is networked portable multimedia appliances.
Such reconfigurable platforms should have the following attributes: be powerful, flexible, energy-efficient, and inexpensive. IMEC feels that these attributes can be accomplished using a combination of ISPs with FPGA-based reconfigurable hardware. However, there are several challenges facing those who develop these platforms concerning architecture development, how to accomplish hardware multi-tasking, an appropriate RTOS, middleware for platform abstraction and QoS-aware rescheduling, and how to efficiently map applications onto a heterogeneous reconfigurable platform.
IMEC’s view of a heterogeneous-reconfigurable-platform architecture is one that can handle multiple microprocessors (of multiple types), additional silicon cores, and reconfigurable-hardware components. In addition, the architecture must support true hardware/software multitasking. Dynamic partial reconfiguration of FPGAs can take care of hardware reconfiguration. In addition, IMEC will also use a fixed-interconnect network on the FPGA to isolate the different tasks. The network is accomplished by dividing the FPGA in tiles, which allows easy removal and creation of tasks, and should aid in communication between different tasks.
IMEC will develop a hardware/software RTOS unifying communications between hardware tasks, software tasks, and between hardware and software. The RTOS should be able to handle both software and hardware scheduling, the latter controlling the partial reconfiguration of the reconfigurable hardware. In addition, the RTOS should also include a supervisory function regarding which tasks are implemented in software and hardware, and manage the interconnection network. The research issues for these tasks include memory organization, which allows data sharing between software and hardware tasks eliminating the need to explicitly copy live data during context switching; algorithms to identify good context switch points; and translation of states and live data between hardware and software.
IMEC is looking at a middleware layer that can distribute the tasks on the available resources in a way that provides the best tradeoffs to the user. Taking into account the QoS of each application running on the platform, the middleware will be able to reschedule the different tasks in order to maximize the global QoS of the terminal. Once the physical platform is available and the basic programming infrastructure is developed, the final challenge is in mapping high-level application behavior in an efficient way on these architectures.
IMEC has developed three demonstration vehicles using reconfigurable computing for multimedia applications:
- Go4Net A standalone network camera, designed in OCAPI-xl, IMEC’s C++ design environment, for capturing and translating live images on the Internet (for a description of IMEC’s C++ design environment, see SoC++: A Unified Design Method from Concept to Implementation)
- Cam-E-Leon An Internet camera combining reconfigurable hardware and embedded software implementing a VPN with 3-DES encryption
- Gecko A portable multimedia device using hardware/software multi-tasking to run a video decoder and 3D game.
Gecko comprises a StrongARM 32-bit RISC core in a Compaq iPAQ PDA with a Xilinx Virtex FPGA linked to the iPAQ through an expansion bus. A soft interconnect packet-switched network on top of the FPGA allows uses partial reconfiguration of the FPGA to create and delete tasks. Hardware tasks can also use the network to communicate with other hardware or software tasks.
Figure 3: Gecko comprises a StrongARM 32-bit RISC core in an iPAQ PDA with a Virtex FPGA linked to the iPAQ through an expansion bus
Silicon Valley without the Hassle
With all of IMEC’s leading-edge research programs, it is easy to visualize the Center as a little bit of Silicon Valley transported to a small Belgian city. However, there are some significant differencesless crowding, fewer cars, and much more affordable housing. IMEC is a good example of how you can achieve significant downstream technological benefits with successful cooperation between government, industry, and academia.