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In this study, a simple method of fabricating a thin-film transistor (TFT) with a double-layered channel using indium–zinc-oxide (IZO) films was proposed. Two IZO films used as channel layers were consecutively deposited via sputtering without stopping the vacuum and only by changing the volumetric fraction of the additive O2 gas during the deposition. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis showed a large difference in the depth profiles of the InO− and InO2− ions between the two IZO layers. Compared to the conventional single-IZO-channel TFT, the double-IZO-channel TFT that was fabricated using the proposed two-step deposition method showed greatly improved electrical characteristics: the on/off-state current ratio was increased from 1.30 × 105 to 1.03 × 106, and the field effect mobility was enhanced from 1.2 to 9.3 cm2/Vs.

The effect of adding hydrogen gas (H2) when depositing a zinc oxide (ZnO) thin film in a thin film transistor (TFT) using the ZnO as the channel layer on the electrical characteristics of the ZnO-TFTs, particularly the change in the characteristics according to long-term exposure to air, was investigated. As the amount of added H2 gas was increased, the resistivity of ZnO films was monotonously decreased and their crystallinity was weakened. Compared with the TFT using a ZnO without H2 addition, the threshold voltage (Vth) decreased and the on/off current ratio (Ion/Ioff) greatly increased, if the amount of H2 entry was small (≤ 0.3 sccm). However, when an excessive (≥ 0.5 sccm) amount of H2 was added, the TFT's properties deteriorated. In addition, the ZnO TFTs showed a positive Vth-shift with increased air exposure time. The analysis using the X-ray photoelectron spectroscopy (XPS) confirmed that this was attributed to the reduction of oxygen vacancies due to air exposure. It was noticed that the TFTs that were manufactured using ZnO films with H2 addition showed significant suppression of the Vth-shift according to air exposure.

Presented in this study are the results of an experiment that was performed regarding the effects of plasma post-treatment on the material properties of amorphous indium zinc oxide (a-IZO) films, and on the device characteristics of the thin film transistor when an a-IZO film is used as the channel layer. Prior to the source/drain deposition, post-treatment was performed on the area that was not covered by photoresist (PR), using Ar and H2 plasma. The electrical resistivity of a-IZO films was dramatically reduced when they were plasma-treated. The creation of an oxygen vacancy and the formation of hydroxyls in the a-IZO film due to plasma treatment were identified via X-ray photoelectron spectroscopy (XPS) analysis. The change in the field effect mobility (μFE) due to the plasma post-treatment was inversely proportional to the change in the contact resistance (RC) of the plasma-treated a-IZO layer. The prolonged (> 1 min) treatment using H2 plasma caused deep electron traps and surface damages, resulting in the increased RC (or decreased μFE) of the a-IZO TFT. In addition, for the a-IZO TFT that underwent H2 plasma treatment, the VT monotonically decreased whereas the VT of the a-IZO TFT that was Ar-plasma-treated remained almost the same as that of the untreated a-IZO TFT.

A zinc oxide (ZnO) thin film as a channel layer in an oxide thin film transistor (TFT) has been characterized by investigating the effects of additive gases (such as hydrogen and oxygen) during growth and plasma treatment (using argon or hydrogen) after growth on its electrical, optical, and structural properties. By decreasing the additive gas ratio of O 2 /H 2 or by increasing the treatment time of hydrogen plasma, the electrical resistivities of ZnO films were significantly reduced, and their transmittances and optical bandgap energies were blue-shifted in wavelength. These results were considered to be closely related to the passivation of oxygen vacancies as well as the formation of shallow donors that were induced by the injection of hydrogen in ZnO via gas addition and plasma treatment. In addition, the injection of hydrogen-including additive gas resulted in a decrease in grain size and crystallinity of ZnO films, whereas the plasma treatment hardly affected their crystalline structures.

Both negative and positive substrate bias effects on structural and field-emissive properties of carbon nanotubes (CNTs) are investigated. The CNTs are grown on Ni catalysts employing an inductively coupled plasma chemical vapor deposition (ICP-CVD) method by varying substrate bias from −550 to 400 V. Characterization using various techniques, such as field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), Auger spectroscopy (AES), and Raman spectroscopy, shows that the physical dimension as well as the crystal quality of grown CNTs can be changed and controlled by the application of substrate bias during CNT growth. It is for the first time observed that the prevailing growth mechanism of CNTs which is either due to tip-driven growth or based-on-catalyst growth may be influenced by the application of substrate bias. It is also seen that negative bias would be more effectual for vertical-alignment of CNTs compared with positive bias, whereas the CNTs grown under positive bias display much better electron emission capabilities than those grown under negative bias or without bias. The reasons for all the measured data regarding the structural properties of CNTs are discussed to confirm the correlation with the observed field-emissive properties.

A simple process is presented with which a bottom-gate-type oxide thin-film transistor (TFT) can be fabricated by using two photomasks. The active channel, the source-drain electrode, and the pixel electrode layers were simultaneously formed via a single photolithography using a gray-tone mask (GTM). In particular, the gray-tone profiles of the photoresist were carefully observed to ensure process feasibility with the GTM. From the transparent-oxide TFTs fabricated in this letter, functional indices, such as threshold voltage VT = 4.13 V (at VDS = 10 V), subthreshold swing S = 0.59 V/dec, field-effect mobility μFE = 12.41 cm2/V·s, on-off current ratio lesser than 8 ×106, and transmittance higher than 85%, were obtained.

We present, for the first time, a prototype active-matrix field emission display (AMFED) in which an amorphous silicon thin-film transistor (a-Si TFT) and a molybdenumtip field emitter array (Mo-tip FEA) were monolithically integrated on a glass substrate for a novel active -matrix cathode (AMC) plate. The fabricated AMFED showed good display images with a low-voltage scan and data signals irrespective of a high voltage for field emissions. We introduced a light shield layer of metal into our AMC to reduce the photo leakage and back channel currents of the a-Si TFT. We designed the light shield to act as a focusing grid to focus emitted electron beams from the AMC onto the corresponding anode pixel. The thin film depositions in the a-Si TF Ts were performed at a high temperature of above 360 ° C to guarantee the vacuum packaging of the AMC and anode plates. We also developed a novel wet etching process for n + -doped a-Si etching with high etch selectivity to intrinsic a-Si and used it in the fabrication of an inverted stagger TFT with a very thin active layer. The developed a-Si TFTs performed well enough to be used as control devices for AMCs. The gate bias of the a-Si TFTs well controlled the field emission currents of the AMC plates. The AMFED with these AMC plates showed lowvoltage matrix addressing, good stability and reliability of field emission, and good light emissions from the anode plate with phosphors.

We have designed and monolithically integrated amorphous silicon thin-film transistor (a-Si TFT) with Mo-tip field emitter arrays (FEAs) on glass substrate for active-matrix cathodes (AMCs) in field-emission display (FED) application. In our AMCs, a light shield layer of metal was introduced to reduce the photo leakage and back channel currents of a-Si TFT. The light shield was designed to have the role of focusing grid to focus emitted electron beams from the AMC on the corresponding anode pixel by forming it around the Mo-tip FEAs as well as above the a-Si TFT. The thin film depositions in a-Si TFTs were performed at a high temperature of above 360/spl deg/C to guarantee the postvacuum packaging process of cathode and anode plates in FED. Also, a novel wet etching process was developed for n/sup +/-doped-a-Si etching with high etch selectivity to intrinsic a-Si and good etch controllability and was used in the fabrication of inverted stagger TFT with a very thin active layer. The developed a-Si TFTs had good enough performance to be used as control devices for AMCs with Mo-tip emitters. The fabricated AMCs exhibited very effective aging process for field emitters.

Fine-pitched carbon nanotube (CNT) pixels for field emitter arrays were patterned using a lift-off process. Compared with the conventional screen-printing method, this lift-off process provides a small feature size of 195 µm×80 µm pixels in emitter arrays. The field emission properties of patterned pixels are highly dependent on surface morphology. The buried carbon nanotubes from the surface barely contribute to field emission in a low electric field range. By using a proper formulation of carbon nanotube slurry for emitters in the patterning layer, we were able to obtain carbon nanotube pixels in which most of carbon nanotubes protruded from the surface layer of patterns after a final heat treatment, to burn out the organic binders at 300°C. Their turn-on field was determined to be less than 2.2 V/µm and the current density was 3.2 mA/cm2 at 3.7 V/µm. This lift-off process has the potential for use as an inexpensive patterning method for fine-pitched emitter array on a large substrate.

Amorphous silicon thin‐film transistors (a‐Si TFTs) were incorporated into Mo‐tip‐based triode‐type field emitters and diode‐type ones of carbon nanotubes for an active‐matrix cathode (AMC) plate of field emission displays. Also, we developed a novel surface‐treatment process for the Mo‐tip fabrication, which gleatly enhanced in the stability of field emission. The field emission currents of AMC plates on glass substrate were well controlled by the gate bias of a‐Si TFTs. Active‐matrix field emission displays (AMFEDs) with these AMC plates were demonstrated in a vacuum chamber, showing low‐voltage matrix addressing, good stability and reliability of field emission, and highly uniform light emissions from the anode plate with phosphors. The optimum design of AMFEDs including a‐Si TFTs and a new light shield/focusing grid is discussed.

Carbon nanotubes (CNTs) emitters were successfully patterned in small pixels (50×50 μm2) by using photolithography process on a hard metal electrode for field emission displays (FEDs) application. The CNTs particles in the patterned pixels were uniformly distributed on 2-inch diagonal substrates. The maximum diameter of CNTs particles could be controlled less than 20 μm. After patterning and heat treatment process below 300°C, most of CNTs bundles on the cathode electrode were aligned perpendicular to the substrates. The threshold electric field of emission for patterned CNTs was about 4.2 V μm−1 and the field enhancement factor derived from the Fowler–Nordheim plots of the electron emissions was about 100 000 in the high voltage region. This newly developed process can be applicable to field emitter arrays for high resolution FEDs.

A novel patterning technology of fine-pitched carbon nanotube (CNT) pixels on a thin metal has been developed by lift-off process for field emitter arrays (FEAs). The lift-off method provides even smaller CNT pixels compared with those made by conventional screen-printing and photolithography processes. SEM images demonstrated that the smallest pitch and the size of patterned pixels were 15 μm × 15 μm and 7 μm × 7 μm, respectively. After patterning and heat treatment process at 300°C, most of CNT bundles on the cathodes were aligned perpendicular to the substrate. The density of CNT bundles in the patterned pixels was 10–20/μm2. The turn-on field of patterned CNTs was less than 2.5 V/μm and the current density was 3.2 mA/cm2 at 3.5 V/μm.