Ambipolar thin-film transistors and inverter circuits based on mixed-dimensional bilayer heterostructures

Among a large number of layered materials family, molybdenum disulfide (MoS₂) has been the most representative semiconducting channel material for electronic devices due to its exceptional electrical performance with a monolayer thickness. However, quite complicated fabrication processes, such as multiple transfer and alignment of individual flakes, have usually been required to implement integrated complementary circuits with MoS₂ which typically exhibits n-type behavior. In particular, MoS₂ flakes with large lateral sizes grown by chemical vapor deposition (CVD) often result in high surface coverage, which restricts layout flexibility and poses challenges for the fabrication of complementary circuits. Therefore, more straightforward methods of fabricating complementary circuits based on low-dimensional semiconductors such as MoS₂ have to be sought. In this work, we demonstrate complementary-like circuits using ambipolar thin-film transistors (TFTs) whose channel comprises a bilayer heterostructure of n-type MoS₂ and p-type single-walled carbon nanotubes (SWCNTs). SWCNTs are inkjet printed directly onto the desired areas of a monolayer of MoS₂ grown by CVD, where both inkjet printing and CVD are regarded as fully scalable fabrication methods, so that complementary-like circuits are readily fabricated without patterning of MoS₂. The resulting ambipolar TFTs exhibit typical ambipolar behavior, such as V-shaped transfer characteristics, with reasonably balanced current levels in both n- and p-branches, as well as an I_on/I_off ratio greater than 10³. The complementary-like inverter, where a bilayer ambipolar TFT and another n-type MoS₂ TFT are employed as a pull-up and a pull-down TFTs, shows clear inverting operations at a low operating voltage of 2 V in both DC and AC measurements. Our results provide more flexibility in integrating low-dimensional semiconductor-based circuits.