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Ultra-thin piezoelectric strain sensor array integrated on flexible printed circuit for structural health monitoring

In this paper, we present a novel sensor array manufacturing process that involves transfer printing methods using a chip mounter with a vacuum collet. We have successfully fabricated 5× 5 array of MEMS-based very fragile ultra-thin piezoelectric strain sensors on a polyethylene naphthalate (PEN) flexible printed circuit (FPC) with etched Cu pattern. Twenty five of the piezoelectric strain sensors made of ultra-thin 2-μm-thick Pb(Zr, Ti)O3 (PZT)/3-μm-thick Si plate were transfer printed onto the PEN FPC with adhesive layer by the chip mounter. PZT and Cu pattern were wired with Ag paste by screen printing. Since output voltage corresponding to the magnitude of the strain from the developed 5× 5 sensor array was generated, it was confirmed that ultra-thin sensors could be integrated to the PEN FPC substrate by these transfer and screen printing techniques without damage. We succeeded in strain distribution display by color mapping method using the data from the sensor array.