Crystallized Monolayer Semiconductor for Ohmic Contact Resistance, High Intrinsic Gain, and High Current Density

Abstract

The contact resistance limits the downscaling and operating range of organic field‐effect transistors (OFETs). Access resistance through multilayers of molecules and the nonideal metal/semiconductor interface are two major bottlenecks preventing the lowering of the contact resistance. In this work, monolayer (1L) organic crystals and nondestructive electrodes are utilized to overcome the abovementioned challenges. High intrinsic mobility of 12.5 cm2 V−1 s−1 and Ohmic contact resistance of 40 Ω cm are achieved. Unlike the thermionic emission in common Schottky contacts, the carriers are predominantly injected by field emission. The 1L‐OFETs can operate linearly from VDS = −1 V to VDS as small as −0.1 mV. Thanks to the good pinch‐off behavior brought by the monolayer semiconductor, the 1L‐OFETs show high intrinsic gain at the saturation regime. At a high bias load, a maximum current density of 4.2 µA µm−1 is achieved by the only molecular layer as the active channel, with a current saturation effect being observed. In addition to the low contact resistance and high‐resolution lithography, it is suggested that the thermal management of high‐mobility OFETs will be the next major challenge in achieving high‐speed densely integrated flexible electronics.

Sub-thermionic, ultra-high-gain organic transistors and circuits

“…It is important to note that the overall improvement of transistor performance ( g m , r 0 , A i , SS ) is accomplished by systematic optimization, including high mobility material, monolayer channel, clean contact interface and ferroelectric dielectrics. To verify the importance of monolayer channel, we fabricated devices with thicker channel and observed inferior SS , on-current and g m due to poor electrostatics and contact resistance 35 , 41 (Supplementary Fig. 8 ).…”

Scalable High-Speed Hybrid Complementary Integrated Circuits based on Solution-Processed Organic and Inorganic Transistors

“…Figure S8. The p-channel TFT exhibited µlin, µsat, Ioff, and and Ion/Ioff ratio of 4.4 cm 2 V −1 s −1 , 1.1 cm 2 V −1 s −1 , as low as 10 −13 A, and 10 8 , respectively, while the corresponding values for the n-channel TFT were 1.6 cm 2 V −1 s −1 , 1.9 cm 2 V −1 s −1 , as low as 10 −13 A, and 10 9 respectively; additionally, for the nchannel TFT, Von ~ 0 V. The µsat value observed for the p-channel TFT may be attributed to an early pinch-off phenomenon, which is often observed in short-channel TFTs based on OSCs 49 .…”

“…The electrical performance of the pand n-channel TFTs recorded under these conditions is shown in FigureS8. The p-channel TFT exhibited µlin, µsat, Ioff, and and Ion/Ioff ratio of 4.4 cm 2 V −1 s −1 , 1.1 cm 2 V −1 s −1 , as low as 10 −13 A, and 10 8 , respectively, while the corresponding values for the n-channel TFT were 1.6 cm 2 V −1 s −1 , 1.9 cm 2 V −1 s −1 , as low as 10 −13 A, and 10 9 respectively; additionally, for the nchannel TFT, Von ~ 0 V. The µsat value observed for the p-channel TFT may be attributed to an early pinch-off phenomenon, which is often observed in short-channel TFTs based on OSCs49 .The VTC of a single inverter with a supply voltage of 10 V (Figure6(b)) suggests that even those inverters with short channel lengths exhibit a full rail-to-rail swing, symmetric transition of VM ~ 5 V for both forward and backward voltage sweep, and a high noise margin with an NMH of 3.2 V and NML of 2.9 V. The output signal at a VDD of 10 V is shown in Figure6(c).…”

Flexible, high mobility short-channel organic thin film transistors and logic circuits based on 4H–21DNTT

“…( d ) Schematic illustration of solution shearing set-up. ( e ) Literature overview of OTFT effective mobility for short channel length devices for channel length in range of 300 nm–50 μm 12 – 20 , 41 – 43 , 45 – 65 and for 4H–21DNTT OTFT theoretical effective mobility (μ sat_theoretical ) calculation; μ int_avg = 12.5 cm 2 V −1 s −1 and R c W = 1 kΩcm.

Figure 2 Characterization of 4H–21DNTT films deposited from solution shearing at different blade scanning speed ( a – c ) Polarized microscopy images of 4H–21DNTT film at 0.1 wt% concentration in o-DCB solution ( d – f ) Polarized microscopy images of 4H–21DNTT film at 0.09 wt% concentration in o-DCB solution.

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“…( d ) Schematic illustration of solution shearing set-up. ( e ) Literature overview of OTFT effective mobility for short channel length devices for channel length in range of 300 nm–50 μm 12 – 20 , 41 – 43 , 45 – 65 and for 4H–21DNTT OTFT theoretical effective mobility (μ sat_theoretical ) calculation; μ int_avg = 12.5 cm 2 V −1 s −1 and R c W = 1 kΩcm.…”