Weibing Gu

Fabrication and electrical properties of all-printed carbon nanotube thin film transistors on flexible substrates

In this manuscript, we developed a high-performance, printable and water-based semiconducting SCNT ink, and fabricated all-printed chemically functionalized CoMoCat 76 SCNT thin film transistors (TFTs) on flexible substrates via a suite of printing technologies. The metallic species in the pristine CoMoCat 76 SCNTs were effectively eliminated by organic radicals, and the functionalized SCNTs were characterized by UV-Vis-NIR spectroscopy and Raman spectra. The high quality, printable and water-based functionalized SCNT inks were obtained by tuning the ink ingredients, such as the concentrations of surfactants and additives. The printing methods we investigated include inkjet printing, aerosol jet printing and a hybrid with nanoimprinting. Large area source and drain electrode patterns were first fabricated on flexible substrates by a hybrid printing method, and then the optimal SCNT ink was printed on the channel of the TFT devices by ink-jet printing. Subsequently, the silver side-gate electrode and ion gel dielectric layer were deposited by aerosol jet printing. The all-printed flexible TFTs exhibited an effective mobility up to 1.5 cm2 V−1 s−1 and an on/off ratio up to 4 × 103. This work opens up a way to fabricate scalable and all-printed flexible electronics, and it is of benefit to generalize the practical applications of flexible electronics in the future.

Synthesis, properties, and structures of functionalized peri-xanthenoxanthene.

Three types of alkylated peri-xanthenoxanthene (PXX) have been synthesized employing efficient synthetic routes. These heteroaromatic compounds exhibited different electronic and crystal structures according to UV-vis spectra, electrochemical measurements, and X-ray structural analyses. Among them, 1,7-DOPXX has been demonstrated as an active material for organic field-effect transistors with promising mobility and a high on/off ratio simultaneously.

Selective Conversion from p-Type to n-Type of Printed Bottom-Gate Carbon Nanotube Thin-Film Transistors and Application in Complementary Metal–Oxide–Semiconductor Inverters

The fabrication of printed high-performance and environmentally stable n-type single-walled carbon nanotube (SWCNT) transistors and their integration into complementary (i.e., complementary metal-oxide-semiconductor, CMOS) circuits are widely recognized as key to achieving the full potential of carbon nanotube electronics. Here, we report a simple, efficient, and robust method to convert the polarity of SWCNT thin-film transistors (TFTs) using cheap and readily available ethanolamine as an electron doping agent. Printed p-type bottom-gate SWCNT TFTs can be selectively converted into n-type by deposition of ethanolamine inks on the transistor active region via aerosol jet printing. Resulted n-type TFTs show excellent electrical properties with an on/off ratio of 106, effective mobility up to 30 cm2 V-1 s-1, small hysteresis, and small subthreshold swing (90-140 mV dec-1), which are superior compared to the original p-type SWCNT devices. The n-type SWCNT TFTs also show good stability in air, and any deterioration of performance due to shelf storage can be fully recovered by a short low-temperature annealing. The easy polarity conversion process allows construction of CMOS circuitry. As an example, CMOS inverters were fabricated using printed p-type and n-type TFTs and exhibited a large noise margin (50 and 103% of 1/2 Vdd = 1 V) and a voltage gain as high as 30 (at Vdd = 1 V). Additionally, the CMOS inverters show full rail-to-rail output voltage swing and low power dissipation (0.1 μW at Vdd = 1 V). The new method paves the way to construct fully functional complex CMOS circuitry by printed TFTs.

The elastic microstructures of inkjet printed polydimethylsiloxane as the patterned dielectric layer for pressure sensors

A direct inkjet printing process was developed to fabricate patterned elastic microstructures for pressure sensors using n-butyl acetate diluted polymethylsiloxane (PDMS). The diluted PDMS precursor mixture with a cross-linker exhibited a controllable viscosity below 14 cP in 48 h at 25 °C, and the PDMS film had lower elastic modulus and hardness values than the non-diluted PDMS precursor after curing. The capacitor using the printed PDMS film as the microstructured dielectric layer showed a very high pressure sensitivity of up to 10.4 kPa−1 under the pressure below 70 Pa, and the pressure sensitivity would be dramatically decreased to 0.043–0.052 kPa−1 under the pressure between 2 and 8 kPa. Furthermore, the triboelectric sensors could be structured with an inkjet printed PDMS film and controllably generate the voltage signals up to 1.23 V without any amplification. The results suggest that mechanical properties and patterned elastic microstructures play the key roles in PDMS-based sensor devices, and th...

Printed stretchable circuit on soft elastic substrate for wearable application

In this paper, a flexible and stretchable circuit has been fabricated by the printing method based on Ag NWs/PDMS composite. The randomly oriented Ag NWs were buried in PDMS to form a conductive and stretchable electrode. Stable conductivity was achieved with a large range of tensile strain (0–50%) after the initial stretching/releasing cycle. The stable electrical response is due to the buckling of the Ag NWs/PDMS composite layer. Furthermore, printed stretchable circuits integrated with commercial ICs have been demonstrated for wearable applications.

Printed flexible and stretchable hybrid electronic systems for wearable applications

In this work, we report the use of printing strategy applied to the fabrication of flexible and stretchable circuit. The prepared Ag NWs paste was printed on glass substrate to form conductive circuit via screen printing, and liquid PDMS was casted on top of the printed Ag NWs circuit and cured to peel off the substrate. The randomly oriented Ag NWs were buried in PDMS to form conductive and stretchable circuit. We studied the influence of the diameter of Ag NWs on the surface morphology of Ag NWs/PDMS circuit during strain process and further analyzed the relationship between the surface microstructure and electrical property of Ag NWs/PDMS conductor. The results showed that the cracks happened on the surface of circuit with Ag NWs of smaller diameter in stretching process, while the buckling structure appeared after pre-tension strain of 100% with Ag NWs of larger diameter. The buckling of Ag NWs/PDMS layer resulted in the stable resistance of stretchable circuit in the strain range of 0-50%. We also demonstrate the printed stretchable circuit integrated with LED array under bending, twisting and even stretching deformation. The printing method may provide a new step towards the development of stretchable strategies for conductive circuit and other wearable electronics.