Threshold voltage tuning and printed complementary transistors and inverters based on thin films of carbon nanotubes and indium zinc oxide

Carbon nanotubes (CNTs) have emerged as an important material for printed macroelectronics. However, achieving printed complementary macroelectronics solely based on CNTs is difficult because it is still challenging to make reliable n-type CNT transistors. In this study, we report threshold voltage (V_th) tuning and printing of complementary transistors and inverters composed of thin films of CNTs and indium zinc oxide (IZO) as p-type and n-type transistors, respectively. We have optimized the V_th of p-type transistors by comparing Ti/Au and Ti/Pd as source/drain electrodes, and observed that CNT transistors with Ti/Au electrodes exhibited enhancement mode operation (V_th < 0). In addition, the optimized In: Zn ratio offers good n-type transistors with high on-state current (I_on) and enhancement mode operation (V_th > 0). For example, an In: Zn ratio of 2:1 yielded an enhancement mode n-type transistor with V_th ~ 1 V and I_on of 5.2 μA. Furthermore, by printing a CNT thin film and an IZO thin film on the same substrate, we have fabricated a complementary inverter with an output swing of 99.6% of the supply voltage and a voltage gain of 16.9. This work shows the promise of the hybrid integration of p-type CNT and n-type IZO for complementary transistors and circuits.