Huang-Chung Cheng

Field emission from quasi-aligned SiCN nanorods

We report on the preparation and field emission properties of quasi-aligned silicon carbon nitride (SiCN) nanorods. The SiCN nanorods are formed by using a two-stage growth method wherein the first stage involves formation of a buffer layer containing high density of nanocrystals by electron cyclotron resonance plasma enhanced chemical vapor deposition and the second stage involves using microwave plasma enhanced chemical vapor deposition for high growth rate along a preferred orientation. It should be noted that growth of the SiCN nanorods is self-mediated without the addition of any metal catalyst. Scanning electron microscopy shows that the SiCN nanorods are six-side-rod-shaped single crystals of about 1–1.5 μm in length and about 20–50 nm in diameter. Energy dispersive x-ray spectrometry shows that the nanorod contains about 26 at. % of Si, 50 at. % of C, and 24 at. % of N. Characteristic current–voltage measurements indicate a low turn-on field of 10 V/μm. Field emission current density in excess of ...

A new pixel circuit for driving organic light-emitting diode with low temperature polycrystalline silicon thin-film transistors

A new pixel circuit design for active matrix organic light-emitting diode (AMOLED), based on the low-temperature polycrystalline silicon thin-film transistors (LTPS-TFTs) is proposed and verified by SPICE simulation. Threshold voltage compensation pixel circuit consisting of four n-type TFTs, one p-type TFT, one additional control signal, and one storage capacitor is used to enhance display image quality. The simulation results show that this pixel circuit has high immunity to the variation of poly-Si TFT characteristics.

High current density field emission from arrays of carbon nanotubes and diamond-clad Si tips

Arrays of carbon nanotubes (CNT) and diamond-clad Si tips were grown by microwave plasma-enhanced chemical vapor deposition. The former ones were grown directly on prepatterned cobalt-coated silicon substrate, while the latter ones were grown on Si-tip arrays. Each array contains 50×50 emitting cells and each individual cell is 3 μm square. A maximum effective emission current density of about 17 A/cm2 (at a macroscopic field of 17.5 V/μm) has been demonstrated, while a macroscopic emission current density of 10 mA/cm2 with operating fields around 10 V/μm can be routinely achieved from an array of CNT emitters. In contrast, operating fields above 20 V/μm were needed to draw a comparable emission current density from all of the diamond-clad Si tips arrays. Emission stability test performed at 40 mA/cm2 for CNT arrays also showed little sign of degradation. Due to the high efficiency of electron emission, simple sample process, and large area growth capability, field emitter arrays based on CNT are attracti...

Novel Gate-All-Around Poly-Si TFTs With Multiple Nanowire Channels

The novel gate-all-around (GAA) poly-Si thin-film transistors (TFTs) with multiple nanowire channels (MNCs) have been, for the first time, fabricated using a simple process to demonstrate high-performance electrical characteristics and high immunity to short-channel effects (SCEs). The nanowire channel with high body-thickness-to-width ratio (TFin/WFin), which is approximately equal to one, was realized only with a sidewall-spacer formation. Moreover, the unique suspending MNCs were also achieved to build the GAA structure. The resultant GAA-MNC TFTs showed outstanding three-dimensional (3-D) gate controllability and excellent electrical characteristics, which revealed a high on/off current ratio ( > 108), a low threshold voltage, a steep subthreshold swing, a near-free drain-induced barrier lowering, as well as an excellent SCE suppression. Therefore, such high-performance GAA-MNC TFTs are very suitable for applications in system-on-panel and 3-D circuits.

The effects of NH 3 plasma passivation on polysilicon thin-film transistors

The NH/sub 3/ plasma passivation has been performed for the first time on the polycrystalline silicon (poly-Si) thin-film transistors (TFTs). It is found that the TFTs after the NH/sub 3/ plasma passivation achieve better device performances, including the off-current below 0.1 pA//spl mu/m and the on/off current ratio higher than 10/sup 8/, and also better hot-carrier reliability as well as thermal stability than the H/sub 2/-plasma devices. These improvements were attributed to not only the hydrogen passivation of the grain-boundary dangling bonds, but also the nitrogen pile-up at SiO/sub 2//poly-Si interface and the strong Si-N bond formation to terminate the dangling bonds at the grain boundaries of the polysilicon films. >

The Instability Mechanisms of Hydrogenated Amorphous Silicon Thin Film Transistors under AC Bias Stress

Hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) with silicon nitride (SiNx) gates have been stressed under various AC biases to investigate the instability mechanisms. The state creation is dominant at low stress voltage although the charge trapping also occurs in SiNx gates, and such cases have also been found under the DC bias stress. In addition, the degradations of a-Si:H TFTs are found to be independent of the AC frequency for the positive polarity but show frequency dependence for the negative polarity due to the RC effect. Furthermore, the threshold voltage shift is associated with the duty ratio due to the accumulation of stress time. Finally, the degradation of the a-Si:H TFTs under bipolar AC bias stress is also introduced. It is found that the instability mechanisms of devices are composed of different charge compensations in SiNx and redistributions of defect states in the a-Si:H layer.

Effect of SiH4/CH4 flow ratio on the growth of β‐SiC on Si by electron cyclotron resonance chemical vapor deposition at 500 °C

β‐SiC (3C–SiC) films were deposited on silicon substrates by electron cyclotron resonance chemical vapor deposition from SiH4/CH4/H2 mixtures at 500 °C. The crystalline structure and chemical composition of the deposited film were found to depend on the SiH4/CH4 flow ratio. With a sufficient energy supply from microwave power and a SiH4/CH4 flow ratio of 0.5 and lower, stoichiometric SiC could be deposited on Si substrates. Microcrystalline β‐SiC was grown at a SiH4/CH4 flow ratio of 0.5, whereas amorphous SiC was obtained at the SiH4/CH4 flow ratios lower than 0.5. When the SiH4/CH4 flow ratio was above 0.5, only polycrystalline Si could be deposited.

Instability mechanisms for the hydrogenated amorphous silicon thin‐film transistors with negative and positive bias stresses on the gate electrodes

The hydrogenated amorphous silicon (a‐Si:H) thin film transistors (TFTs) with silicon nitride as a gate insulator have been stressed with negative and positive bias to realize the instability mechanisms. It is found that the threshold voltages of the a‐Si:H TFTs are positively shifted under low negative bias stress and then negatively shifted for large negative gate bias. The positive threshold voltage shift is ascribed to the increased states in the band gap near the conduction band by the negative gate bias. As the negative bias continuously increases, the hole trapping in the silicon nitride or at the a‐Si:H/silicon nitride interface will become dominant, resulting in the negative threshold voltage shift. A similar turnaround phenomenon is also observed with respect to the stress time. On the other hand, for the TFTs stressed with positive gate bias, the monotonic increase of the threshold voltage shift with stress time is attributed to the state creation. Nevertheless, the distributions of the created...

High-performance low-temperature poly-Si TFTs crystallized by excimer laser irradiation with recessed-channel structure

High-performance low-temperature poly-Si (LTPS) thin-film transistors (TFTs) have been fabricated by excimer laser crystallization (ELC) with a recessed-channel (RC) structure. The TFTs made by this method possessed large longitudinal grains in the channel regions, therefore, they exhibited better electrical characteristics as compared with the conventional ones. An average field-effect mobility above 300 cm/sup 2//V-s and on/off current ratio higher than 10/sup 9/ were achieved in these RC-structure devices. In addition, since grain growth could be artificially controlled by this method, the device electrical characteristics were less sensitive to laser energy density variation, and therefore the uniformity of device performance could be improved.

pH Sensing Characteristics of Extended-Gate Field-Effect Transistor Based on Al-Doped ZnO Nanostructures Hydrothermally Synthesized at Low Temperatures

The pH sensing properties of an extended-gate field-effect transistor (EGFET) with Al-doped ZnO (AZO) nanostructures are investigated. The AZO nanostructures with different Al dosages were synthesized on AZO/glass substrate via a simple hydrothermal growth method at 85°C . The pH sensing characteristics of pH-EGFET sensors with an Al dosage of 1.98 at% can exhibit a higher voltage sensitivity of 57.95 mV/pH, a larger linearity of 0.9998, and a wide sensing range of pH 1-13, attributed to the well-aligned nanowire (NW) array, superior crystallinity, less structural defects, and better conductivity. Consequently, the hydrothermally grown AZO NWs demonstrate superior pH sensing characteristics and reveal the potentials for flexible and disposable biosensors.