Ultra-thin ion-sensitive field-effect transistors chips with bending-induced performance enhancement

Flexible multifunctional sensors on skin or wearables are considered highly suitable for next-generation noninvasive health care devices. In this regard, the field-effect transistor (FET)-based chemical sensors such as ion-sensitive FETs (ISFETs) are attractive as, with the ultrathin complementary metal oxide semiconductor technology, they can enable a flexible or bendable sensor system. However, the bending-related stress or strain could change the output of devices on ultrathin chips (UTCs), and this has been argued as a major challenge hindering the advancement and use of this technology in applications such as wearables. This may not be always true, as with drift-free ISFETs, we show that bending could also enhance the performance of UTCs. Through fine control of bending radius in the micrometer scale, the mechanically flexible RuO2-based ISFETs on UTCs (44.76 μm thickness) are shown to reproducibly enhance the performance even after 1000 bending cycles. The 1.3 orders of magnitude improved stability (the drift rate changed from −557 nA/min to −28 ± 0.16 nA/min) is observed over a time period of 417.3 s (∼7 min) at fixed biasing and temperature conditions and under different pH conditions. Finally, a compact macromodel is developed to capture the bending-induced improvements in flexible ISFETs. The performance enhancement by controlled bending of devices could generally benefit the rapidly growing field of flexible electronics.