High‐mobility ZnO thin films are deposited onto solution‐processed ZrO2 dielectrics in order to investigate the large differences between experimental field‐effect mobility values obtained when ...transparent conductive oxide (TCO) materials are deposited onto high‐k dielectrics as opposed to thermally grown SiO2. Through detailed electrical characterization, the mobility enhancement in ZnO is correlated to the presence of electron traps in ZrO2 serving to provide an additional source of electrons to the ZnO. Furthermore, as a consequence of the general tendency for solution‐processed high‐k dielectrics to exhibit similar behavior, the broad applicability is suggested to other TCO/high‐k material combinations in agreement with experimental observations.
Zinc oxide (ZnO) thin‐films are deposited onto solution‐processed zirconia dielectrics to investigate differences in mobility obtained when transparent conductive oxide semiconductors are deposited onto high‐k dielectrics as opposed to thermally‐grown silica. Through detailed electrical characterization, the mobility enhancement in ZnO is correlated with the presence of electron traps in zirconia—providing an additional source of electrons to the ZnO.
We realize p-type thin film transistors (TFT) with solution-processed channels using a sol-gel route, based on a copper (II) acetate precursor. The sol-gel process initially produces Cu, which is ...then oxidized depending on sintering conditions to produce Cu2O and ultimately CuO. These processes are performed at temperatures no higher than 500 degree C, and are therefore compatible with standard display glass substrates for use in transparent display applications. To control the film morphology of the sol-gel processed copper oxide layer, additional water was added to the precursor solution. As the water to alkoxide ratio is increased, the degree of hydrolysis increased, thus increasing the grain size of CuO and Cu2O. The resulting p-type CuO and Cu2O TFTs exhibited improved thin film transistor performance, including field effect mobilities of 1.010-2 cm2/Vs and 2.010-3 cm2/Vs, respectively, and an on/off ratio of approximately 103.
Solution‐processed mechanically flexible resistive random access memories are fabricated using Ag2Se nanoparticles; the fabricated Ag/Ag2Se/Au memory devices on flexible poly‐ethylene‐naphthalate ...substrates show bipolar switching memory characteristics, with low voltage (<1.5 V) operation, no significant retention loss after 105 s, and no degradation in endurance after 104 switching cycles, with stable operation even under a mechanical strain of 0.38%.
Additive patterning of transparent conducting metal oxides at low temperatures is a critical step in realizing low‐cost transparent electronics for display technology and photovoltaics. In this work, ...inkjet‐printed metal oxide transistors based on pure aqueous chemistries are presented. These inks readily convert to functional thin films at lower processing temperatures (T ≤ 250 °C) relative to organic solvent‐based oxide inks, facilitating the fabrication of high‐performance transistors with both inkjet‐printed transparent electrodes of aluminum‐doped cadmium oxide (ACO) and semiconductor (InOx). The intrinsic fluid properties of these water‐based solutions enable the printing of fine features with coffee‐ring free line profiles and smoother line edges than those formed from organic solvent‐based inks. The influence of low‐temperature annealing on the optical, electrical, and crystallographic properties of the ACO electrodes is investigated, as well as the role of aluminum doping in improving these properties. Finally, the all‐aqueous‐printed thin film transistors (TFTs) with inkjet‐patterned semiconductor (InOx) and source/drain (ACO) layers are characterized, which show ideal low contact resistance (Rc < 160 Ω cm) and competitive transistor performance (µlin up to 19 cm2 V−1 s−1, Subthreshold Slope (SS) ≤150 mV dec−1) with only low‐temperature processing (T ≤ 250 °C).
High‐mobility inkjet‐printed transistors with transparent electrodes are fabricated at below 250 °C exclusively via aqueous ink chemistries. Intrinsic aqueous fluid properties lead to enhanced printing fidelity, high electrical performance, and better ambient stability relative to organic inks. Degenerately doped transparent conductors (CdO:Al) are developed as a low resistance inkjet‐printed contact to an aqueous‐printed InO
x
semiconductor.
In gravure printing, excess ink is removed from a patterned plate or roll by wiping with a doctor blade, leaving a thin lubrication film in the nonpatterned area. Reduction of this lubrication film ...is critical for gravure printing of electronics, since the resulting residue can lower device performance or even catastrophically impact circuit yield. We report on experiments and quantitative analysis of lubrication films in a highly scaled gravure printing process. We investigate the effects of ink viscosity, wiping speed, loading force, blade stiffness and blade angle on the lubrication film, and further, use the resulting data to investigate the relevant lubrication regimes associated with wiping during gravure printing. Based on this analysis, we are able to posit the lubrication regime associated with wiping during gravure printing, provide insight into the ultimate limits of residue reduction, and, furthermore, are able to provide process guidelines and design rules to achieve these limits.
The integration of fully printed transistors on low cost paper substrates compatible with roll‐to‐roll processes is demonstrated here. Printed electronics promises to enable a range of technologies ...on paper including printed sensors, RF tags, and displays. However, progress has been slow due to the paper roughness and ink absorption. This is solved here by employing gravure printing to print local smoothing pads that also act as an absorption barrier. This innovative local smoothing process retains desirable paper properties such as foldability, breathability, and biodegradability outside of electronically active areas. Atomic force microscopy measurements show significant improvements in roughness. The polymer ink and printing parameters are optimized to minimize ink absorption and printing artifacts when printing the smoothing layer. Organic thin film transistors (OTFT) are fabricated on top of this locally smoothed paper. OTFTs exhibit performance on par with previously reported printed transistors on plastic utilizing the same materials system (pBTTT semiconductor, poly‐4‐vinylphenol dielectric). OTFTs deliver saturation mobility approaching 0.1 cm2V–1s–1 and on‐off‐ratio of 3.2 × 104. This attests to the quality of the local smoothing, and points to a promising path for realizing electronics on paper.
Fully printed transistors are demonstrated on paper substrates with performance on par with plastic based devices. Desirable paper properties such as foldability, breathability, and biodegradability are preserved outside of electronically active areas by an innovative locally printed smoothing process. This process is fully compatible with existing paper packaging process flows.
Bioelectronic interfaces require electrodes that are mechanically flexible and chemically inert. Flexibility allows pristine electrode contact to skin and tissue, and chemical inertness prevents ...electrodes from reacting with biological fluids and living tissues. Therefore, flexible gold electrodes are ideal for bioimpedance and biopotential measurements such as bioimpedance tomography, electrocardiography (ECG), electroencephalography (EEG), and electromyography (EMG). However, a manufacturing process to fabricate gold electrode arrays on plastic substrates is still elusive. In this work, a fabrication and low‐temperature sintering (≈200 °C) technique is demonstrated to fabricate gold electrodes. At low‐temperature sintering conditions, lines of different widths demonstrate different sintering speeds. Therefore, the sintering condition is targeted toward the widest feature in the design layout. Manufactured electrodes show minimum feature size of 62 μm and conductivity values of 5 × 10 6 S m−1. Utilizing the versatility of printing and plastic electronic processes, electrode arrays consisting of 31 electrodes with electrode‐to‐electrode spacing ranging from 2 to 7 mm are fabricated and used for impedance mapping of conformal surfaces at 15 kHz. Overall, the fabrication process of an inkjet‐printed gold electrode array that is electrically reproducible, mechanically robust, and promising for bioimpedance and biopotential measurements is demonstrated.
Fabrication of inkjet‐printed flexible gold electrode arrays on plastic substrates is described, with a special focus on laser‐cut freestanding electrodes, low‐temperature sintering, and the methodology used for impedance mapping on conformal surfaces. Taking advantage of low‐cost and large‐area manufacturing techniques, these electrically reproducible and mechanically robust electrode arrays are promising for novel wearable biomedical sensing.
Drop-on-demand inkjet printing of functional inks has received a great deal of attention for realizing printed electronics, rapidly prototyped structures, and large-area systems. Although this method ...of printing promises high processing speeds and minimal substrate contamination, the performance of this process is often limited by the rheological parameters of the ink itself. Effective ink design must address a myriad of issues, including suppression of the coffee-ring effect, proper drop pinning on the substrate, long-term ink reliability, and, most importantly, stable droplet formation, or jettability. In this work, by simultaneously considering optimal jetting conditions and ink rheology, we develop and experimentally validate a jettability window within the capillary number–Weber number space. Furthermore, we demonstrate the exploitation of this window to adjust nanoparticle-based ink rheology predictively to realize a jettable ink. Finally, we investigate the influence of mass loading on jettability to establish additional practical limitations on nanoparticle ink design.
This work employs novel SnO2 gel‐like precursors in conjunction with sol–gel deposited ZrO2 gate dielectrics to realize high‐performance transparent transistors. Representative devices show excellent ...performance and transparency, and deliver mobility of 103 cm2 V−1 s−1 in saturation at operation voltages as low as 2 V, a sub‐threshold swing of only 0.3 V/decade, and Ion/Ioff of 104∼105.
Advances in techniques for recording large-scale brain activity contribute to both the elucidation of neurophysiological principles and the development of brain-machine interfaces (BMIs). Here we ...describe a neurophysiological paradigm for performing tethered and wireless large-scale recordings based on movable volumetric three-dimensional (3D) multielectrode implants. This approach allowed us to isolate up to 1,800 neurons (units) per animal and simultaneously record the extracellular activity of close to 500 cortical neurons, distributed across multiple cortical areas, in freely behaving rhesus monkeys. The method is expandable, in principle, to thousands of simultaneously recorded channels. It also allows increased recording longevity (5 consecutive years) and recording of a broad range of behaviors, such as social interactions, and BMI paradigms in freely moving primates. We propose that wireless large-scale recordings could have a profound impact on basic primate neurophysiology research while providing a framework for the development and testing of clinically relevant neuroprostheses.
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