Large-Area Flexible Ultrasonic Imaging System With an Organic Transistor Active Matrix

We have successfully fabricated a large-area flexible ultrasonic imaging system by integrating a polymeric ultrasonic-transducer array sheet with an active matrix of organic field-effect transistors. The ultrasonic sheet comprises 8 x 8 ultrasonic sensing cells with an effective size of 25 × 25 cm². The organic transistors exhibit mobility of 0.1 and 0.5 cm²/V ·s at the low operation voltage of 1 mV and in the saturation regime, respectively. When an ac signal is applied between source and drain electrodes for the transistors with a grounded gate, the on/off ratio is larger than 10⁴ at the carrier frequency of 40 kHz. In the linear sensing array comprising eight ultrasonic cells, crosstalk is suppressed sufficiently low, and the on/off ratio exceeds 10⁴. Images in free space are obtained for multiple-target objects over this sheet.