Flexible, Print-in-Place 1D-2D Thin-Film Transistors Using Aerosol Jet Printing

In this work, we overcome temperature constraints and demonstrate 1D−2D thin-film transistors (1D−2D TFTs) in a low-temperature (maximum exposure ≤80 °C) full print-in-place process (i.e., no substrate removal from printer throughout the entire process) using an aerosol jet printer. Semiconducting 1D CNT channels are used with a 2D hexagonal boron nitride (h-BN) gate dielectric and traces of silver nanowires as the conductive electrodes, all deposited using the same printer. The aerosol jet-printed 2D h-BN films were realized via proper ink formulation, such as utilizing the binder hydroxypropyl methylcellulose, which suppresses redispersion between adjacent printed layers. In addition to an ON/ OFF current ratio up to 3.5 Å~ 105, channel mobility up to 10.7 cm2·V-1·s-1, and low gate hysteresis, 1D−2D TFTs exhibit extraordinary mechanical stability under bending due to the nanoscale network structure of each layer, with minimal changes in performance after 1000 bending test cycles at 2.1% strain. It is also confirmed that none of the device layers require high-temperature treatment to realize optimal performance. These findings provide an attractive approach toward a cost-effective, direct-write realization of electronics

Inkjet printed circuits with two-dimensional semiconductor inks for high-performance electronics

Air-stable semiconducting inks suitable for complementary logic are key to create low-power printed integrated circuits (ICs). High-performance printable electronic inks with two-dimensional materials have the potential to enable the next generation of high performance, low-cost printed digital electronics. Here we demonstrate air-stable, low voltage (< 5 V) operation of inkjet-printed n-type molybdenum disulfide (MoS2) and p-type indacenodithiophene-co-benzothiadiazole (IDT-BT) field-effect transistors (FETs), estimating a switching time of {\tau} ~ 3.3 {\mu}s for the MoS2 FETs. We achieve this by engineering high-quality MoS2 and air-stable IDT-BT inks suitable for inkjet-printing complementary pairs of n-type MoS2 and p-type IDT-BT FETs. We then integrate MoS2 and IDT-BT FETs to realise inkjet-printed complementary logic inverters with a voltage gain |Av| ~ 4 when in resistive load configuration and |Av| ~ 1.36 in complementary configuration. These results represent a key enabling step towards ubiquitous long-term stable, low-cost printed digital ICs

Inkjet printed circuits with two-dimensional semiconductor inks for high-performance electronics

Air-stable semiconducting inks suitable for complementary logic are key to create low-power printed integrated circuits (ICs). High-performance printable electronic inks with two-dimensional materials have the potential to enable the next generation of high performance, low-cost printed digital electronics. Here we demonstrate air-stable, low voltage (< 5 V) operation of inkjet-printed n-type molybdenum disulfide (MoS2) and p-type indacenodithiophene-co-benzothiadiazole (IDT-BT) field-effect transistors (FETs), estimating a switching time of {\tau} ~ 3.3 {\mu}s for the MoS2 FETs. We achieve this by engineering high-quality MoS2 and air-stable IDT-BT inks suitable for inkjet-printing complementary pairs of n-type MoS2 and p-type IDT-BT FETs. We then integrate MoS2 and IDT-BT FETs to realise inkjet-printed complementary logic inverters with a voltage gain |Av| ~ 4 when in resistive load configuration and |Av| ~ 1.36 in complementary configuration. These results represent a key enabling step towards ubiquitous long-term stable, low-cost printed digital ICs

Charge Transport in and Luminescence from Covalently Functionalized Carbon Nanotube Networks

Their high ambipolar charge carrier mobilities and narrowband emission in the near-infrared make semiconducting single-walled carbon nanotubes (SWCNTs) a promising material for optoelectronic devices. The controlled low-level decoration of SWCNTs with covalently bound sp3 defects gives rise to red-shifted luminescence and single-photon emission, thus strongly expanding their application potential. While the spectroscopic properties of sp3-functionalized SWCNT dispersions under optical excitation are already well-understood, little research efforts have been directed at the impact of luminescent defects on charge transport as well as defect population and emission in thin films and under electrical excitation. A fundamental understanding of these aspects is a prerequisite for the realization of light-emitting devices based on functionalized SWCNTs. This thesis demonstrates high ambipolar charge carrier mobilities and red-shifted defect-state electroluminescence in light-emitting field-effect transistors with randomly oriented networks of functionalized SWCNTs as active layers. The results imply that luminescent defects act as shallow trapping potentials for charge carriers that still allow for fast detrapping at room temperature, thus explaining the moderate decrease in network mobilities upon functionalization. Time-resolved terahertz spectroscopy corroborates the impact of these defects on the intrinsic nanotube conductivity and provides further evidence that charge transport in semiconducting SWCNT networks, as opposed to the widespread belief, is not solely determined by the inter-nanotube junctions. To achieve better control over the spectroscopic properties of SWCNT thin films deposited on surfaces, substrate passivation with a cross-linked polymer is demonstrated to reduce peak broadening and suppress sideband emission that is assigned to the uncontrolled formation of lattice defects through nanotube–substrate interactions. The realization of pristine and sp3-functionalized SWCNT network transistors with near-intrinsic electroluminescence on passivated substrates showcases the compatibility of the developed method with standard semiconductor processing steps and device fabrication. Moreover, the selective introduction of luminescent defects with a larger spectral red-shift pushes the electroluminescence from SWCNT networks further towards telecommunication wavelengths and highlights their potential for optoelectronic applications such as electrically-pumped single-photon sources

Field-effect transistors based on Zinc oxide nanoparticles

This work reports the development of field-effect transistors (FETs), whose channel is based on zinc oxide (ZnO) nanoparticles (NPs). Using screen-printing as the primary deposition technique, different inks were developed, where the semiconducting ink is based on a ZnO NPs dispersion in ethyl cellulose (EC). These inks were used to print electrolyte-gated transistors (EGTs) in a staggered-top gate structure on glass substrates, using a lithium-based polymeric electrolyte. In another approach, FETs with a staggered-bottom gate structure on paper were developed using a sol-gel method to functionalize the paper’s surface with ZnO NPs, using zinc acetate dihydrate (ZnC4H6O4·2H2O) and sodium hydroxide (NaOH) as precursors. In this case, the paper itself was used as dielectric. The various layers of the two devices were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform Infrared spectroscopy (FTIR), thermogravimetric and differential scanning calorimetric analyses (TG-DSC). Electrochemical impedance spectroscopy (EIS) was used in order to evaluate the electric double-layer (EDL) formation, in the case of the EGTs. The ZnO NPs EGTs present electrical modulation for annealing temperatures equal or superior to 300 ºC and in terms of electrical properties they showed On/Off ratios in the order of 103, saturation mobilities (μSat) of 1.49x10-1 cm2(Vs)-1 and transconductance (gm) of 10-5 S. On the other hand, the ZnO NPs FETs on paper exhibited On/Off ratios in the order of 102, μSat of 4.83x10- 3 cm2(Vs)-1and gm around 10-8 S

Electronic transport of graphene devices

Ph.DDOCTOR OF PHILOSOPH

Enhancement of the Dynamic Performance of Electrolyte-Gated Transistors: Toward Fast-Switching, Low-Operating Voltage Printed Electronics

University of Minnesota Ph.D. dissertation. June 2019. Major: Chemistry. Advisor: Daniel Frisbie. 1 computer file (PDF); ix, 148 pages.A transistor is an electrical circuit element which acts as a switch, can tune the current in an electrical circuit, and can amplify input signals. Fast switching with low-operating voltage and high amplification are desired characteristics for transistors but are not readily achieved by printed electronics. Electrolyte-gated transistors (EGTs) are a specific class of transistors with an electrolyte as the gate dielectric. Using electrolyte as the gate dielectric enables low-operating voltage, high amplification (gain), and relaxed fabrication requirements. Electrolytes have a huge capacitance which is thickness independent thanks to the formation of electrical double layers (EDL) at the interfaces of the electrolyte with the electrodes. Ion gel is a type of electrolyte consisting of an ionic liquid and a triblock copolymer. The polymer is responsible for providing mechanical integrity, whereas the ionic liquid is responsible for the gating mechanism with great electrical, physical, chemical, and electrochemical properties. Ion gels pave the way for miniaturizing EGTs and their use in printed electronics. Despite all the promising properties of printed EGTs including low-operating voltage, ease of printing, flexibility, and low-toxicity, fast EGTs have not yet been demonstrated. Similarly, higher EGT gain is also required to improve the sensitivity and computational power of devices. In this thesis, the EGT working principles have been investigated, as well as the effects of EGT architectures, materials, components, printing resolution, and precision on the EGT operating speed and gain. New architectures have been designed to produce fast and high-performance EGTs. Modification of EGT architectures and components enabled us to achieve 5 MHz operation with an order of magnitude increase in gain and amplification. In order to fabricate different architectures, a variety of techniques including inkjet, aerosol-jet, and screen printing have been employed. Screen-printed, UV-cured ion gels with a line width resolution of 10 µm have been demonstrated. In conclusion, in this thesis, the performance of printed ion gel-based electrolyte-gated transistors has been investigated and improved by relating the device dynamic and static characteristics to its material components and architecture