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Indium–gallium–zinc-oxide (IGZO) thin-film transistors (TFTs) gated with sputtered silicon dioxide dielectric were fabricated. Under different sputtering pressures of silicon dioxide, the device is able to produce transfer curves from clockwise hysteresis to anticlockwise hysteresis, corresponding to different operation modes and thus adding complementary performance by the same material system and device structure. In the interface trapping mode, the transistor exhibited inhibitory synaptic spiking behavior induced by positive stimuli. In the electric double-layer coupling mode, positive stimuli led to excitatory synaptic spiking behavior, while negative stimuli resulted in inhibitory synaptic spiking behavior. All the transistor and synaptic spiking behaviors are conducted within ±1 V range. Enriched functionality and ultralow operation voltage make sputtered SiO2-gated IGZO TFTs promising candidate for neuromorphic applications.

The lack of a sizeable band gap has so far prevented graphene from building effective electronic and optoelectronic devices despite its numerous exceptional properties. Intensive theoretical research reveals that a band gap larger than 1 eV can only be achieved in sub-3 nm wide graphene nanoribbons (GNRs), but real fabrication of such ultranarrow GNRs still remains a critical challenge. Herein, we demonstrate an approach for the synthesis of ultranarrow and photoluminescent semiconducting GNRs by longitudinally unzipping single-walled carbon nanotubes. Atomic force microscopy reveals the unzipping process, and the resulting 2.2 nm wide GNRs are found to emit strong and sharp photoluminescence at ∼685 nm, demonstrating a very desirable semiconducting nature. This band gap of 1.8 eV is further confirmed by follow-up photoconductivity measurements, where a considerable photocurrent is generated, as the excitation wavelength becomes shorter than 700 nm. More importantly, our fabricated GNR field-effect transistors (FETs), by employing the hexagonal boron nitride-encapsulated heterostructure to achieve edge-bonded contacts, demonstrate a high current on/off ratio beyond 105 and carrier mobility of 840 cm2/V s, approaching the theoretical scattering limit in semiconducting GNRs at room temperature. Especially, highly aligned GNR bundles with lengths up to a millimeter are also achieved by prepatterning a template, and the fabricated GNR bundle FETs show a high on/off ratio reaching 105, well-defined saturation currents, and strong light-emitting properties. Therefore, GNRs produced by this method open a door for promising applications in graphene-based electronics and optoelectronics.

The human brain is capable of short- and long-term memory with retention times ranging from a few seconds to several years. Electrolyte-gated transistors have drawn attention for their potential to mimic synaptic behaviors in neuromorphic applications, but they generally operate at low voltages to avoid instability and, hence, offer limited tunability. Sputtered silicon dioxide electrolytes are utilized in this work to gate indium-gallium-zinc-oxide thin-film transistors, which offer robust operation at much higher voltages. The synaptic memory behavior is studied under single and multiple pulses and under mild (1 V) and strong stimuli (up to 8 V). The devices are found to be capable of providing an extremely wide range of memory retention time from ∼2 ms to ∼20 000 s, over seven orders of magnitude. Furthermore, based on the experimental data on individual transistors, pattern learning and memorizing functionalities are conceptually demonstrated.

The graphene ballistic rectifier uses the ultra-high carrier mobility of graphene to rectify ballistic carriers in an asymmetric nanostructure, and has been previously shown to operate beyond 650 GHz. Unlike conventional diodes and transistors, it does not require a bandgap. Building on the previously developed extended Buttiker-Landauer formula for semiconductors, we derive an analytical theory suitable for coexistence of electrons and holes in semi-metal graphene. Four ballistic rectifier designs are fabricated and compared. The developed theory fits their characteristics well, with derived parameters showing good agreement with device geometries. We also predict achievable responsivities of at least 50,800 V/W and noise-equivalent powers of 0.51 pW/Hz1/2 using these designs, far better than has so far been achieved. Importantly, this theory predicts increased responsivities with a large difference in carrier mobilities. Using the theory presented here, other graphene based ballistic nanodevices may be designed and optimized.

The use of amorphous InGaZnO (IGZO) has become more and more popular especially in display technologies because of its high mobility, excellent large area uniformity, and low-temperature processability. However, unlike Si-based thin-film transistors (TFTs), the top channel surface of IGZO TFTs is extremely sensitive to air, resulting in a degraded device performance, particularly when a very-thin channel layer is used. To avoid such detrimental effects and improve the device performance, a top surface treatment such as encapsulation is necessary. In this work, very thin, 1 V IGZO TFTs with top surface modified by a self-assembled monolayer (SAM) were studied. The electrical performance of the presented TFTs was significantly enhanced after the SAM modification because of a much reduced desorption–adsorption effect on the IGZO surface. The importance of top surface condition on TFTs with ultrathin channel layers was discussed. TFTs with a 5 nm thick IGZO channel layer showed a carrier mobility almost tripled plus an 18% decrease of total trap density after the SAM treatment. The treated devices also showed a superb air stability with negligible change of electrical performance after being stored in ambient air for a year. Considering the high cost of indium, this approach has a high potential to significantly reduce the manufacturing cost of IGZO-based electronics.

Although graphene can operate in the ballistic transport regime at room temperature, there are very few devices harnessing this property. Here we present a novel device called the ballistic rectifier which circumvents the problem of opening a bandgap in graphene. Based on the device theory, we propose four different asymmetric planar structures. All devices are working and show responsivity higher than 1,000 V/W at room temperature, with noise-equivalent power as low as 4.16 pW/Hz$^{\mathbf {1/2}}$. These properties make GBRs a suitable candidate for THz detection.

Here we present theory and measurements for a bridge rectifier formed from arrays of graphene self-switching diodes (GSSDs). Graphene’s extremely high carrier mobility allows GSSDs to work at THz frequencies, with the bridge rectifier structure allowing for full wave rectification of an AC signal. We derive an equation for the voltage output of a GSSD bridge rectifier, predicting a quadratic dependence on input current. This relationship is confirmed using AC and DC measurements. The fabricated rectifier has a high room temperature intrinsic responsivity of 3,230 V/W at low frequency and a low noise equivalent power of 7.0 pW/Hz1/2. Moving forward, similar devices using CVD graphene have been tested and shown to function with high responsivity.

Thin-film Schottky diodes are one of the key elements in large-area flexible electronics. In such devices, a highly uniform semiconductor film is vital for the device performance. Here, we propose a novel solution-based anodization method to form a conformal oxide semiconductor layer for Schottky diodes. The thickness of the anodized TiO2 layer varied from 12 to 22.5 nm. The optimized Pt/TiO2/Ti Schottky diode demonstrated a large barrier height of 1.19 eV, an ON/OFF ratio as high as ${3.5} \times {10}^{{6}}$ at ± 2 V, and an ideality factor of 1.5. The average breakdown electric field was 5.5 MV/cm, which is higher than typical values of conventional solution processed TiO2. The diode with a 15-nm-thick TiO2 layer also showed good rectification properties up to 0.7 MHz.

Solution-processed high-к gate dielectrics, such as Al2O3 and HfO2, show great potential for use in low-cost electronics. However, high-temperature treatments are generally needed to cure the film, limiting the use in flexible electronics. Here we use anodization, a simple, low-cost, solution-based method, to form thin, conformal, high quality HfOx layers at room temperature. Several anodization voltages were studied and the relative quantity of Hf-O bonding was found to increase by 10% when increasing anodization voltage from 2 to 3 V, while maintaining almost the same when further increasing the anodization voltage. Conduction mechanisms were analyzed, showing that Schottky emission dominates even for the thinnest oxides. HfOx layers formed by anodization voltages of 2, 3 and 4 V show high capacitance density of 1290, 1160 and 1060 nF/cm2, which are equivalent to 2.68, 2.97 and 3.26 nm of thermally grown SiO2. Using such high capacitance density insulators, InGaZnO (IGZO) thin-film transistors (TFTs) were fabricated at room temperature, showing a low operating voltage of 0.5 V, one of the lowest for oxide-semiconductor-based TFTs. TFTs gated with HfOx anodized at the optimal voltage, 3 V, show a high current on/off ratio of > 105, a mobility approaching 10 cm2/Vs, and a subthreshold swing as low as 69 mV/dec, close to the theoretical limit at 300 K. The interface trap density was found to be highly related to the quality of the HfOx film, showing a 50% decrease with the increase of anodization voltage from 2 to 3 V. The devices show negligible change after storage in air for 6 months, and favorable stability under both positive and negative gate bias stress. Finally, we demonstrate TFTs on plastic substrates, maintaining high quality performance even under a bending radius of 9 mm. As a result, such devices have potential applications in low-cost, low-voltage-operation, low-power electronics.

Despite being a standard process in fabrication of organic thin-film transistors(TFTs) to reduce interface trap density and decrease surface energy, self-assembled monolayer (SAM) treatment of gate dielectrics is rarely used in oxide-semiconductor-based TFTs due to possible damage to the SAM during semiconductor deposition. Here, by studying the dependence of plasma damage to SAM on the deposition conditions of InGaZnO (IGZO) 2 semiconductor thin films, the feasibility of enhancing the performance of oxide TFTs usingoctadecyltrichlorosilane (OTS)-treated, ultra-thin AlxOy gate dielectrics is explored. It is discovered that under optimized conditions, the TFTs can be significantly improved, showing a reduction of interface trap density by 50% and an increase of carrier mobility and current on/off ratio by a factor of 2.3 and 76, respectively. The effects on bias stress stability also show substantial improvement after the SAM interface treatment. Finally, such an optimizedcondition is found to also work for IGZO TFTs gated with OTS-treated HfOx, showing an increase of mobility from 7.8 to 16 cm2 V-1 s-1 compared with the untreated devices. As a result, this simple and yet effective interface treatment method and the resulting devices may have potential applications in future low-cost, low-power electronics.

Here, we present theory and measurements for a bridge rectifier formed from arrays of graphene self-switching diodes (GSSDs). Despite graphene's lack of a bandgap and high carrier concentration causing a reduced rectification ratio, the extremely high carrier mobility will allow GSSDs to work at frequencies well into the THz region. Compared with a single SSD array, the bridge rectifier structure allows for full-wave rectification of an AC signal. Here we derive an equation for the voltage output of a bridge rectifier formed from GSSDs, which predicts a quadratic relationship between output voltage and input current. This relationship is confirmed using AC and DC measurements. The fabricated rectifier is found to have a high room temperature intrinsic responsivity of [Formula: see text] at low frequency and a low noise equivalent power of [Formula: see text].