ISSCC 2009 / SESSION 28 / TD: DIRECTIONS IN COMPUTING AND SIGNALING / 28.3
28.3

A Stretchable EMI Measurement Sheet with 8×8 CoilArray, 2V Organic CMOS Decoder, and -70dBm EMI
Detection Circuits in 0.18µm CMOS

Koichi Ishida1, Naoki Masunaga1, Zhiwei Zhou1, Tadashi Yasufuku1,
Tsuyoshi Sekitani1, Ute Zschieschang2, Hagen Klauk2,
Makoto Takamiya1, Takao Someya1, Takayasu Sakurai1
1

University of Tokyo, Tokyo, Japan
Max Planck Institute for Solid State Research, Stuttgart, Germany

2

Electromagnetic interference (EMI) is a serious issue degrading the dependability of electronic devices. The issue is complicated by the following technology trends: 1) RF signals and clock pulses of digital ICs are in the same frequency range. 2) The increase of LSI power consumption causes an increaseof noise emission. 3) Electronic devices have 3D-structures and packaging isdense. These trends also make the root cause analysis of EMI difficult. For
example, it is difficult to find the EMI generation points in electronic devices
such as cell-phones and PDAs.
Typical frequencies of concern with respect to EMI issues is from 30MHz to
1GHz as specified by CISPR, International Special Committee on RadioInterference. Although the noise power is specified by electric field strength ingeneral, magnetic field probes with X-Y scanning equipment and spectrum
analyzers are used as an easy EMI measurement method. The conventional
method is, however, not applicable to 3D-structure devices since the scanningequipment can only move in a flat plane.
To solve the problem, an EMI measurement sheet is proposed, which enables
the measurement of the EMI distribution on the surface of the electronic
devices by wrapping the devices with a sheet like “furoshiki”.
Figure 28.3.1 shows the photograph and block diagram of the EMI
measurement sheet. The 12cm×12cm sheet has a 4×4 PCB array and 2
organic circuits (decoder and selector). The PCBs and the organic circuits areconnected by stretchable interconnects [1, 2] including carbon nanotubes,
and the whole system is covered with a rubber sheet, which enables the sheet
to be stretched. Each PCB has a 2×2 coil array picking up EMI, an LSI, and 6
stretchable interconnects. The 4 coils share the LSI. The coils are made on arigid PCB, since coils on a flexible film cause unstable antenna characteristics.
In such large-area array structures, a low-cost and large-area decoder isrequired to reduce the number of interconnects and organic transistors are
suitable for the decoder [3]. Figure 28.3.1(c) shows the photograph of theorganic CMOS 3-to-8 decoder on polyimide film. In the conventional organic
design, only PMOS was available and the power supply voltage was 40V [4].
The low gain circuits in the PMOS only design and the high voltage makes thefusion of the organic circuits and LSIs difficult. To solve the problem, 2V
organic CMOS technology enabled by the 2.1nm thick gate insulator [5] andorganic semiconductor [6] for NMOS were developed. As shown in Fig.
28.3.1(d), the diameter of the coil on the PCB is 9.8mm. Figure 28.3.1(e)shows the 40% stretchable interconnect.
The 2V organic CMOS technology allows direct signal transmission between
organic circuits and LSIs, which eliminates the level shifters [4]. Figure28.3.2(a) shows the circuit of the 3-to-8 organic CMOS decoder. A key part ofthe decoder was fabricated on a silicon substrate and Fig. 28.3.2(b) shows thephotograph. Figure 28.3.2(c) shows the measurement setup for the direct
signal transmission between the organic circuits and an LSI. The power
supply voltage for both the organic circuits and the LSI is 2.0V. The organiccircuits and the LSI are connected by 12cm-stretchable interconnect. The
width is 1mm, the thickness is 500µm, the resistance is 48Ω, and theresistivity is 0.02Ω cm. Figure 28.3.2(d) shows the measured waveform ofboth the input and output of the organic circuits and the LSI. The organic
CMOS decoder successfully drives the LSI. Both the rise time and fall time ofthe output of the organic decoder are 0.5s, which is very slow but acceptablein this application.
Figure 28.3.3 depicts the circuit diagram of the proposed LSI. The circuit
consists of four-stage amplifiers, an NMOS rectifier, sample and hold, and acomparator. The circuit handles differential signals from the antenna coil to472• 2009 IEEE International Solid-State Circuits Conference

measure magnetic fields rather than electric fields [7]. To capture the noise
waveform up to 1GHz digitally, the bandwidth of a comparator should be
10GHz or higher, which is not reasonable. The system, therefore, detects theEMI noise power as a DC voltage level with an NMOS rectifier and a sampleand hold. The noise power is observed as a function of reference voltage ofthe comparator. The rectifier relaxes comparator design of both speed andresolution. In fact, the comparator can operate at 100kHz. EMI noise of-70dBm, equivalent to 45µV with 50Ω input resistance, is picked up by the coiland raised to proper level by amplifiers that connect to the rectifier. The fourstage amplifiers have a gain of around 80dB. The bandwidth of the final stage
amplifier can be changed by simply cutting off some parallel transistors. The
EMI noise frequency can be roughly estimated by this selectable bandwidth
amplifier.
Figure 28.3.4 shows measurement configuration of the proposed silicon chipand measurement result of the minimum detectable EMI noise power anddynamic range. Input noise is emulated by using a signal generator and a coil,and its magnetic field strength is monitored with a magnetic field probe (NECCP-2S) and a spectrum analyzer. EMI noise power is plotted as a function of
the reference voltage of the comparator. The measurement result
demonstrates that the proposed system can detect minimum noise power of-70dBm with 25dB dynamic range and a maximum detectable frequency of
1GHz.
Figure 28.3.5 demonstrates that the proposed circuit can roughly estimate
EMI noise frequency by changing the bandwidth of the amplifier. 900MHz EMI
noise was measured. The left image in Fig. 28.3.5 shows the density of a highpulse output from the comparator is 71% with a wide bandwidth setting, and100MHz cutoff frequency, and the right image shows a density of 24% of ahigh pulse output with a narrow bandwidth setting. This result indicates themeasured EMI noise frequency is high. If the measured EMI noise frequency
is low (e.g., 100MHz), the difference of the high pulse density is small whenchanging the bandwidth of the amplifier.
Figure 28.3.6 demonstrates the correlation of EMI measurement between themagnetic field probe and the proposed scheme. EMI noise around a memory
module in a notebook PC is measured. The output spectrum by the magnetic
field probe includes a peak noise power of -50dBm at 267MHz and its
harmonic tones. On the other hand, the output bit stream by the proposed EMI
measurement system shows a high pulse density of 81% at the same place.
Without any EMI noise, the output bit stream includes no high pulses asshown in Fig. 28.3.6. Thus, the proposed system successfully detects theactual noise emitted by the electronic device.
Figure 28.3.7(a) shows the die micrograph and the layout. The LSI is
implemented in a 0.18µm CMOS process and the core area is 0.18mm2. Keyfeatures of the LSI for the EMI measurement are summarized in Fig. 28.3.7(b).
Co-integration of silicon CMOS technology, 2V organic CMOS technology, andstretchable interconnect including carbon nanotubes makes a stretchable EMI
measurement sheet possible, and the proposed LSI demonstrates EMI noise
measurement up to 1GHz by using an NMOS rectifier and a comparator
operating at only 100kHz.
Acknowledgement:This work was partially supported by CREST/JST, the Grant-in-Aid for Scientific
Research, Special Coordination Funds for Promoting and Technology, and NEDO.
References:[1] H.C. Ko, et al., “A hemispherical electronic eye camera based on compressible silicon
optoelectronics,“ Nature, vol. 454, pp. 748-753, Aug. 2008.
[2] T. Sekitani, et al., “A rubberlike stretchable active matrix using elastic conductors,”
Science, vol. 321, pp. 1468-1472, Sept. 2008.
[3] T. Someya, et al., “Cut-and-paste organic FET customized ICs for application to artificial skin,” ISSCC Dig. Tech. Papers, pp. 288-289, Feb. 2004.
[4] M. Takamiya, et al., “Design solutions for multi-object wireless power transmission
sheet based on plastic switches,” ISSCC Dig. Tech. Papers, pp. 362-363, Feb. 2007.
[5] H. Klauk, et al., “Ultralow-power organic complementary circuits,” Nature, vol. 445,
pp. 745-748, Feb. 2007.
[6] H. E. Katz, et al., “A soluble and air-stable organic semiconductor with high electronmobility,” Nature, vol. 404, pp. 478-481, Mar. 2000.
[7] S. Kazama, K. Arai, “Adjacent electric field and magnetic field distribution measurement system,” IEEE Int. Symp. on Electromagnetic Compatibility, vol. 1, pp. 395-400,Aug. 2002.

978-1-4244-3457-2/09/$25.00 ©2009 IEEE

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Figure 28.3.3: Circuit diagram of the LSI in the proposed EMI measurement sheet.

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Figure 28.3.2: (a) Organic CMOS 3-to-8 decoder. (b) Photograph of the decoder on Si
substrate. (c) Measurement setup for direct connection of organic CMOS and LSI. (d)Measured waveforms in (c).

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Figure 28.3.4: Measurement configuration and measured EMI noise power.

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DFigure 28.3.7: (a) Die micrograph and layout. (b) Summary of key features of LSI forEMI measurement.

• 2009 IEEE International Solid-State Circuits Conference

978-1-4244-3457-2/09/$25.00 ©2009 IEEE