micromachined thermoelectric generator chip for energy har- vesting from body heat, and an interwoven antenna concept for. RFID labels for the identification of ...
ISSCC 2003 / SESSION 22 / TD: EMBEDDED TECHNOLOGIES / PAPER 22.1
22.1
Enabling Technologies for Disappearing Electronics in Smart Textiles
Stefan Jung, Christl Lauterbach, Marc Strasser, Werner Weber Infineon Technologies AG, Laboratory for Emerging Technologies, Munich, Germany Today, the interaction of individual humans with electronic devices demands specific user skills. In future, improved user interfaces can largely alleviate this problem and push the exploitation of microelectronics considerably [1]. In this context the vision of smart clothes promises greater user-friendliness, user-empowerment, and more efficient services support. Wearable electronics recognizes and responds to the presence of individuals in a more or less invisible way. It serves the human individual in his needs thus making life much easier [2]. We believe that today, the cost level of important microelectronic functions is low enough and enabling key technologies are mature enough to exploit this vision to the benefit of society. In the following we present a packaging and interconnect technology for deep textile integration of electronics, a silicon-based micromachined thermoelectric generator chip for energy harvesting from body heat, and an interwoven antenna concept for RFID labels for the identification of textiles. An interconnect and packaging technology is demonstrated using a polyester narrow fabric with several warp threads replaced by copper wires which are coated with silver and polyester. Six of those parallel conductive warp threads form one lead. For the electrical connections the coating of the wires and the surrounding textile material is removed by laser treatment. The resulting holes in the fabric are then soldered with tiny contact plates and thin bonding wires before the module is encapsulated for mechanical protection (Fig. 22.1.1). Alternatively, the bonding wires and contact plates are replaced by a thin flexible printed circuit board (PCB), shown in Fig. 22.1.2. Here, the substrate material of the PCB is attached to the polyester fabric before soldering. The complete unit is molded forming a hermetically sealed casing protecting it against mechanical and chemical stresses caused by wearing and cleaning the textile [3]. As a demonstration a speech-controlled MP3 player system is realized which is based on a DSP/µC-two-processor system [4]. The demonstration system architecture shown in Fig. 22.1.3 is composed of four units, all connected via the conductive textiles. The audio module is a miniaturized PCB containing the audio chip and several auxiliary elements. A detachable module contains a rechargeable Li-Ion battery and a MultiMediaCard for data storage, an earphone and microphone module, and a capacitive keyboard module. The user can control the music player either by speaker-independent voice recognition or by means of the keypad. When integrating the proposed system into clothing, special care is necessary for the textile design. The materials are chosen according to maximum wear comfort and environmental compliance. E.g., the audio module has been fully covered by garment, so that the wearer still feels a textile touch. A number of wearable devices such as small remote wireless sensor units for medical applications dissipate only a small amount of power. The human body produces several tens of watts of heat. Miniaturized thermoelectric generators can harness part of this energy and convert it into electrical power. These generators are built of a large numbers of thermocouples, electrically connected in series and arranged to make best use of a given area. They consist of bars of different materials joined at one end. Due to the Seebeck effect, a temperature difference between both ends generates a voltage and an electrical current through a connected
• 2003 IEEE International Solid-State Circuits Conference
load. Most available thermogenerators are realized using compound semiconductors such as bismuth telluride. However, those are difficult to produce, not compatible with standard silicon chip fabrication processes and non-disposable. They are thus not for low cost applications such as wearables. In line with these arguments silicon appears to be a better choice. Figure 22.1.4 shows a cross-section revealing the micromachining technology [5]. Recently, a chip with 16,000 thermocouples on a silicon chip measuring 7.0mm2 has been realized. Figure 22.1.5 shows the output power measured as a function of the temperature difference between both sides of the chip. A quadratic dependence of the output power versus the temperature difference ∆T occurs. In order to obtain a large difference between the body and ambient temperature, a generator is integrated directly into the fabric of the clothes with good thermal contact to the skin. It has been found that an effective ∆T of up to 5K can be achieved [6]. For this value an output power of 1.6µW/cm2 is obtained and is sufficient to power devices such as a wrist watch. The concept of a transponder system using an RF ID chip and a woven antenna coil structure is proposed. Applications include the item management in laundries or in logistics supply chains, and the protection of branded goods. Since RF ID tags are selfcontained systems that have only an antenna coil and a small silicon chip connected to it, a hermetically sealed package can be realized which has excellent properties in withstanding elevated temperatures, pressures, chemicals, and mechanic stress. A reader device emits electromagnetic waves at a specific frequency that is received and modulated by the tag. However, existing RF ID antenna structures are not suited for the rough environment in textile applications. A conducting spiral can be realized by connecting orthogonally oriented conductive warp and weft threads in a fabric as in Fig. 22.1.6. By this means, the antenna structure is fully embedded into the fabric in an unobtrusive and robust way. The chip can be mounted by one of the integration methods described above. In conclusion, the convergence of microelectronics into novel appliances such as 'wearable electronics' requires the development of enabling key technologies. Three technology demonstrators are proposed which consistently aim for improving the interaction between the human individual and information technology. They open the way to promising scenarios like pervasive computing that may lead to a completely new market of microelectronic technologies in just a few years time. References [1] F. Boekhorst, "Ambient Intelligence, the Next Paradigm for Consumer Electronics: How Will it Affect Silicon?,” ISSCC Digest of Technical Papers, 2002. [2] W.D. Hartmann et al, "High-tech-fashion,” Heimdall Verlag, 2000. [3] S. Jung et al., “A Digital Music Player Tailored for Smart Textiles: First Results,” Avantex Symposium, 2002. [4] B. Burchard et al, "Devices, Software, their Applications and Requirements for Wearable Electronics,” ICCE, 2001. [5] M. Strasser et al, "Miniaturized Thermoelectric Generators Based on Poly-Si and Poly-SiGe Surface Micromachining,” S&A A, 2002. [6] C. Lauterbach et al, "Smart Clothes Self-Powered by Body Heat,” Avantex Symposium, 2002.
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©2003 IEEE
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Figure 22.1.1: Wire bonding concept for textile integration in a polyester fabric.
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