Chao-Lung Wang

Effects of crystallization mechanism on the electrical characteristics of green continuous-wave-laser-crystallized polycrystalline silicon thin film transistors

Thin film transistors (TFTs) with amorphous silicon films crystallized via continuous-wave green laser at a wavelength of 532 nm exhibit very different electrical characteristics in various crystallization regions, corresponding to the Gaussian energy density distribution of the laser beam. In the center region subjected to the highest energy density, the full melting scheme led to the best crystallinity of the polycrystalline silicon film, resulting in the highest field-effect mobility of 500 cm2 V−1 s−1. In contrast, the edge region that resulted in solid phase crystallization exhibited the worst mobility of 48 cm2 V−1 s−1 for the polycrystalline silicon TFTs.

High-Performance Polycrystalline-Silicon Nanowire Thin-Film Transistors With Location-Controlled Grain Boundary via Excimer Laser Crystallization

High-performance polycrystalline-silicon (poly-Si) nanowire (NW) thin-film transistors (TFTs) are demonstrated using excimer laser crystallization to control the locations of grain boundaries two-dimensionally. Via the locally increased thickness of the amorphous-silicon (a-Si) film as the seeds, the cross-shaped grain boundary structures were produced among these thicker a-Si grids. The NW TFTs with one primary grain boundary perpendicular to the channel direction could be therefore fabricated to achieve an excellent field-effect mobility of 346 cm2/V · s and an on/off current ratio of 3 × 109. Furthermore, the grain-boundary-location-controlled NW TFTs also exhibited better reliability due to the control of grain boundary locations. This technology is thus promising for applications of low-temperature poly-Si TFTs in system-on-panel and 3-D integrated circuits.

Reliability improvement of InGaZnO thin film transistors encapsulated under nitrogen ambient

The nitrogen ambient encapsulation (NAE) technique is introduced to improve the reliability issue for the amorphous InGaZnO (a-IGZO) thin-film transistors under positive gate bias stress (PGBS). For the NAE devices, the threshold voltage (Vth) shift is significantly decreased from 1.88 to 0.09 V and the reduction of saturation drain current is improved from 15.75 to 5.61 μA as compared to the bare a-IGZO counterparts after PGBS. These improvements are attributed to the suppression of negatively charged oxygen adsorption on the a-IGZO backsurface and thereby well maintain the channel potential of NAE devices, which in turn sustain the Vth during PGBS.

A Novel SONOS Memory With Recessed-Channel Poly-Si TFT via Excimer Laser Crystallization

A silicon-oxide-nitride-oxide-silicon memory with recessed-channel (RC) polycrystalline-silicon (poly-Si) thin-film transistors (TFTs) via excimer laser crystallization (ELC) has been demonstrated to achieve a high mobility of ~ 400 cm2/V · s and a large ON/OFF current ratio of ~ 108. Such a high performance is because the RC poly-Si TFTs possess only one perpendicular grain boundary (GB) in the channel and the corresponding protrusion at this GB. In addition, the proposed devices also exhibited the largest memory window of 2.63 V in 10 ms with respect to 2.37 and 1.31 V for the conventional-ELC and solid-phase-crystallized ones, respectively. Since the silicon grain growth could be artificially controlled, the device-to-device uniformity could be significantly improved. Therefore, such a simple scheme is promising for applications of low-temperature poly-Si TFTs in 3-D ICs and system on panel.

The recovery mechanism of the light-induced instability of the amorphous InGaZnO thin film transistors

The recovery mechanism of the light-induced instability of amorphous InGaZnO thin-film transistors was examined. Following light illumination, the bare devices displayed more dark recovery of the threshold voltage (Vth) shifts than the ones encapsulated in nitrogen ambient. This was attributed to the adsorption of more oxygen (O2) in the back channel of the bare devices. Further, much more recovery was also observed for the bare devices than the nitrogen-encapsulated ones under positive gate bias. This implied the recovery effect under gate bias could be further enhanced because the induced electrons could greatly increase the adsorption of more O2 for the bare devices.

Location-Controlled Single-Crystal-Like Silicon Thin-Film Transistors by Excimer Laser Crystallization on Recessed-Channel Silicon Strip With Under-Layered Nitride

High-performance Si thin-film transistors (TFTs) on the recessed-channel Si strips with the under-layered nitride film have been fabricated using excimer laser crystallization (ELC). A nitride film was added as a light absorption layer to suppress solidification along the edge of the Si strip. Thus, only one primary grain boundary perpendicular to the Si strip formed in the middle of the recessed region during ELC. The single-crystal-like Si TFTs fabricated on one-half of the recessed region are capable of excellent field-effect mobility of 640 cm2/V-s, with only minor deviation.

The mechanism of the surface morphology transformation for the carbon nanotube thin film irradiated via excimer laser

In this paper, the surface morphology transformation of the sprayed carbon nanotube (CNT) thin film irradiated with the excimer laser has been systematically investigated. Under the excimer-laser irradiation, two phenomena, including the annealing and ablation effects, were found to be dependent on the incident laser energy and overlapping ratios. Moreover, the extremely high protrusions would be produced in the interface between the annealing and ablation regions. The mechanism of the CNT thin film under the excimer laser irradiation was, therefore, proposed to derive the surface morphology modifications and the further reinforced crystallinity with proper laser energy densities and overlapping ratios.

High Sensitivity of Dry-Type Nanowire Sensors With High-

Dry-type poly-Si nanowire pH sensors with high-<i>k</i> dielectrics have been demonstrated with the aid of novel focus ion beam engineered capillary atomic force microscopy (C-AFM) tip. By means of this C-AFM tip coating technique, the relatively few testing solutions can be transferred onto the surface of a nanowire, preventing the sensor device from the immersion in the liquid and therefore suppressing the possible leakage current from the testing solution. As compared with the TEOS SiO₂, the pH sensors comprising Al₂O₃, TiO₂, and HfO₂ high- <i>k</i> materials exhibit the better sensitivities due to their enhanced capacitances. The best sensitivity (138.7 nA/pH) and linearity (99.69%) for a HfO₂ dielectric can be ascribed to the higher <i>k</i> value and larger bandgap with respect to the Al₂ O₃ and TiO₂, accordingly. Consequently, the C-AFM tip coating technique incorporating with HfO₂ dielectric suggests the potential for the detection of a minute quantity of biomedicines.

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A high-performance poly-Si TFT with bottom-gate structure and a top-gate poly-Si TFT were vertically stacked for three dimensional integrated circuit. Consequently, the n-channel poly-Si TFTs with bottom-gate structure on the bottom layer showed considerably improved electrical characteristics, such as a high field effect mobility of 390 cm2/V-s due to the large lateral grain formed in the channel. The vertically stacked p-channel poly-Si TFTs with top-gate structure on the top layer showed a high field effect mobility of 131 cm2/V-s. Therefore, the proposed structure is very suitable for future 3D-IC and nano-device application.

Dielectrics for pH Detection via Capillary Atomic Force Microscope Tip Coating Technique

In this work, a novel gate-all-around (GAA) low-temperature poly-Si (LTPS) junctionless (JL) silicon–oxide–nitride–oxide–silicon (SONOS) nonvolatile memory device with a field-enhanced nanowire (NW) structure has been proposed to improve the programing/erasing (P/E) performance. Each nanowire has three sharp corners fabricated by a sidewall spacer formation technique to obtain high local electrical fields. Owing to the higher carrier concentration in the channel and the high local electrical field from the three sharp corners, such a JL SONOS memory device exhibits a significantly enhanced P/E speed, a larger memory window, and better data retention properties than a conventional inversion mode NW-channel memory device.