Fig. 2. A P-FCB inductor and its frequency response

Planar-Fabric Circuit Board and Silicon-on-Clothes for Wearable Healthcare Applications

Jerald Yoo Microsystems Engineering

Masdar Institute of Science and Technology Masdar City, Abu Dhabi, United Arab Emirates

jyoo@masdar.ac.ae

Abstract— This paper introduces two emerging wearable technologies: Planar-Fabric Circuit Board (P-FCB) and Silicon-on-Clothes (SoC). P-FCB enables fabric itself to become a circuit board and it maximizes wearer’s comfort and safety. Discrete components and dry fabric electrodes made out of P-FCB is discussed and their electrical characteristics are shown. SoC directly integrates silicon chip onto P-FCB to form a system. With these technologies, an example patch sensor is also presented.

Keywords-Planar-Fabric Circuit Board (P-FCB), Silicon-on-Clothes, Wearable Electronics, Wearable Healthcare

I. INTRODUCTION Nowadays, chronic diseases are becoming more and more

threat to society. As it is very difficult to completely cure the chronic diseases, the goal of chronic disease treatment is to stop it from getting worse, or, preferably, to prevent diseases in the first place. To do so, continuous health monitoring is necessary, and wearable healthcare is a one of prospective solutions [1].

To realize wearable healthcare during everyday life, it should be safe and convenient to use, especially over an extended period of time. Conventional approaches to implement wearable electronics include using 1) conductive yarn [2]-[4], 2) electrical wire integrated with clothes, or 3) flexible printed circuit board (FPCB) [5]. They are all effective in making wearable sensors, but they require additional process of special stitching or soldering, which is difficult to integrate into today’s fabric or clothes production facilities for mass production.

In this paper, two emerging wearable technologies called Planar-Fabric Circuit Board (P-FCB) and Silicon-on-Clothes

(SoC) are introduced: they provide a practical wearable healthcare at low cost.

II. PLANAR-FABRIC CIRCUIT BOARD Planar-Fabric Circuit Board (P-FCB) [6],[7] exploits

already-widely-used screen printing process to form a circuit board directly on clothes (Fig. 1). No additional process to current clothes production facilities is necessary, and therefore mass production becomes possible at low cost. By P-FCB, we can easily make passive elements as well as fabric electrodes.

A. Passive Elements Fig. 2 shows an inductor formed with P-FCB: a 4-turn

inductor with 30mm diameter measures to have L=0.98μH with self resonant frequency of 122.9MHz. Capacitors and resistors can be easily made as shown in [6]. Electrical properties of each element may not be as good as off-the-shelf components, and therefore, proper circuit compensation or tuning is necessary. However, strength of P-FCB comes from superior comfort and flexibility over conventional wearable technology.

B. Fabric Electrodes An electrode plays a major role in capturing physiological

signals. Commonly used electrode types are wet and dry type surface electrodes [7]. Especially when it comes to continuous health-related signal monitoring over an extended period of time, such as electrocardiogram (EKG) in Holter Monitor system, wet electrode may not be the best solution, as wet types might result in skin irritation [7]-[9]; the wet type (Fig. 3(a)) is more suitable for clinical usage where precise recording is required, whereas the dry type (Fig. 3(b)) is preferred for long-term monitoring at the cost of slightly degraded signal quality

This research work was jointly sponsored by the Masdar Institute of Science and Technology, Abu Dhabi, United Arab Emirates, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA, and the Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea.

Fig. 1. Planar-Fabric Circuit Board (P-FCB)

978-1-4244-8132-3/10/$26.00 ©2010 IEEE

Fig. 3. Electrodes: (a) wet type and (b) dry fabric P-FCB type

Fig. 4. Skin-electrode impedance over frequency

Fig. 5. Silicon-on-Clothes: direct integration of silicon onto P-FCB

Fig. 6. An example wearable band-aid sensor.

due to increased electrode-skin impedance.

Fig. 4 is the skin-electrode impedance over frequency of various-sized P-FCB and wet type electrodes. We can observe that typically the P-FCB electrodes have up to orders of magnitude larger impedance compared to wet type. Another factor that we must consider in using a dry electrode is that the dry type typically requires settling time. This measurement was done 20min. after the electrode was attached to the skin. We therefore can conclude that dry fabric electrode is more suitable for long term, continuous monitoring, which is the case for continuous wearable healthcare.

III. SILICON-ON-CLOTHES In order to implement a wearable healthcare system in

small form-factor, not only the passive element with the fabric circuit board, but also silicon chip integration is necessary: attaching a chip package to the fabric too bulky and inconvenient to a wearer. Silicon-on-Clothes (SoC) [6],[8]-[10] solves this problem by directly attaching silicon die onto

fabric (Fig. 5). Either wire bonding or flip-chip bonding can be used. SoC combined with P-FCB enables powerful wearable healthcare applications such as wearable band-aid EKG patch [8],[9] (Fig. 6).

IV. CONCLUSION Two emerging wearable technologies are introduced. The

Planar-Fabric Circuit Board (P-FCB) makes fabric itself to become a circuit board or passive elements, and the Silicon-on-Clothes (SoC) directly integrates silicon chip onto P-FCB to form a truly wearable system. These techniques are applicable to many wearable healthcare applications.

ACKNOWLEDGMENT The author acknowledges Prof. Hoi-Jun Yoo (KAIST) for

his fruitful comments in consolidating ideas, and providing the facilities. The author also thanks Mr. Long Yan, Mr. Yongsang Kim and Ms. Seulki Lee (all from KAIST) for their help in making the electrodes and the sensors.

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978-1-4244-8132-3/10/$26.00 ©2010 IEEE