Articles | Volume 15
Adv. Radio Sci., 15, 123–130, 2017
https://doi.org/10.5194/ars-15-123-2017
Adv. Radio Sci., 15, 123–130, 2017
https://doi.org/10.5194/ars-15-123-2017

  21 Sep 2017

21 Sep 2017

Design of a CMOS readout circuit on ultra-thin flexible silicon chip for printed strain gauges

Mourad Elsobky1, Yigit Mahsereci1, Jürgen Keck2, Harald Richter1, and Joachim N. Burghartz1 Mourad Elsobky et al.
  • 1Institut für Mikroelektronik Stuttgart – IMS CHIPS, Allmandring 30a, 70569 Stuttgart, Germany
  • 2Hahn-Schickard, Allmandring 9B, 70569 Stuttgart, Germany

Abstract. Flexible electronics represents an emerging technology with features enabling several new applications such as wearable electronics and bendable displays. Precise and high-performance sensors readout chips are crucial for high quality flexible electronic products. In this work, the design of a CMOS readout circuit for an array of printed strain gauges is presented. The ultra-thin readout chip and the printed sensors are combined on a thin Benzocyclobutene/Polyimide (BCB/PI) substrate to form a Hybrid System-in-Foil (HySiF), which is used as an electronic skin for robotic applications. Each strain gauge utilizes a Wheatstone bridge circuit, where four Aerosol Jet® printed meander-shaped resistors form a full-bridge topology. The readout chip amplifies the output voltage difference (about 5 mV full-scale swing) of the strain gauge. One challenge during the sensor interface circuit design is to compensate for the relatively large dc offset (about 30 mV at 1 mA) in the bridge output voltage so that the amplified signal span matches the input range of an analog-to-digital converter (ADC). The circuit design uses the 0. 5 µm mixed-signal GATEFORESTTM technology. In order to achieve the mechanical flexibility, the chip fabrication is based on either back thinned wafers or the ChipFilmTM technology, which enables the manufacturing of silicon chips with a thickness of about 20 µm. The implemented readout chip uses a supply of 5 V and includes a 5-bit digital-to-analog converter (DAC), a differential difference amplifier (DDA), and a 10-bit successive approximation register (SAR) ADC. The circuit is simulated across process, supply and temperature corners and the simulation results indicate excellent performance in terms of circuit stability and linearity.

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Short summary
A flexible Hybrid System-in-Foil (HySiF) is designed to be used as an electronic skin for robotic applications. At IMS CHIPS, we believe that the future of flexible electronics relies on the integration of multiple electronic components on a single substrate. Our system comprises of an array of printed strain gauges and ultrathin flexible silicon chips, which demonstrates the complementary benefits of combining the low-cost printed electronics and the high performance silicon technologies.