Inkjet Printed Single Walled Carbon Nanotubes As Active Semiconductors in Thin-Film Transistors and Circuits

Inkjet printed single walled carbon nanotubes (SWCNTs) can be incorporated as active layers in thin-film transistors with promising performance.  When the channel length is much larger than the average nanotube length (~ 1 mm), charge transport takes place through a network of nanotubes and the SWCNT film behaves like an effective medium with a mobility in excess of 25 cm²/V-s, which makes them suitable for a number of applications.  In such devices, the on/off current ratio can be very high (> 10⁵). In devices with channel length less than individual nanotube dimensions, we can get high transconductance devices which can be either p- channel or ambipolar depending on the details of the device structure. We will describe in detail characteristics of both types of SWCNT Transistors.

The materials combination of inkjet-printed single-walled carbon nanotubes (SWCNTs) and zinc tin oxide (ZTO) is very promising for large-area thin-film electronics. We compare the characteristics of conventional complementary inverters and ring oscillators measured in air (with SWCNT p-channel Thin-film transistors (TFTs) and ZTO n-channel TFTs) with those of ambipolar inverters and ring oscillators comprised of bilayer SWCNT/ZTO TFTs. This is the first such comparison between the performance characteristics of ambipolar and conventional inverters and ring oscillators. The measured signal delay per stage of 140 ns for complementary ring oscillators is the fastest for any ring oscillator circuit with printed semiconductors to date. We also demonstrate novel voltage controlled ring oscillators which are promising for analog to digital conversion circuits.