Polysilicon N-channel TFT have been hydrogenated using the H2 dissociation on a hot tungsten filament. A post-annealing realized at the optimal temperature of 300°C is necessary to obtain interesting electrical TFT characteristics. Different TFT's sizes and geometries have been processed. The analysis of their characteristics shows that hydrogen preferentially diffuses through silicon oxide layer. The enhancement of the current in the ON-state shows that hydrogen atoms have passivated silicon oxide gate / polysilicon interface traps. The important reduction of the dependency of the OFF-state current with the reverse gate voltage shows that hydrogen atoms have passivated grain boundary traps near the interface in the channel region and in the drain sheet resistance region then reducing the trapped carrier emission.

The drift of electrons in the channels of Thin Film Transistors is analysed for discrete grains separated by grain boundaries containing amorphous silicon. The model provides the relationship channel mobility and grain size. The relationship between drain current and the terminal voltages is also predicted. The model relates to normal high current region of transistor operation.

Low Temperature Unhydrogenated in-situ doped polysilicon Thin Film Transistors (LTUTFT) are made through two types of four-mask aluminium gate process. Silicon layers are elaborated by a Low Pressure Chemical Vapor Deposition (LPCVD) method and crystallized by a thermal annealing. Source and drain regions are in-situ doped. An Atmospheric Pressure Chemical Vapor Deposition (APCVD) silicon dioxide ensures the gate insulation. Two structures A and B are fabricated, the difference is that for sample B the undoped/doped polysilicon layer interface is suppressed.

The structure of the polysilicon films is studied using Transmission Electron Microscopy (TEM) and Current-Voltage characteristics of both types of TFTs indicate electrical quality of the polysilicon films.

The best electrical properties are obtained with the B type TFTs: a low threshold voltage (VT=1.2V), a low subthreshold slope (0.7 V/dec), a high On/Off state current ratio (107) for a drain voltage VDS= 1V, and a very high field effect mobility (≥100 cm2 /Vs). It is worth to notice that these good results are obtained without hydrogenation.

The Cl doped amorphous silicon film was deposited from SiH4, SiH2C12 and H2 gas mixture by PECVD process and their properties with various SiH2C12 flow rate is discussed. Controlling the amount of Cl doped was crucial for acquiring high stability TFT without lowering on current. Amorphous silicon and Cl doped amorphous silicon double layer TFT structure, with satisfactory on current and throughput, proved to be more stable than conventional amorphous silicon TFT in photo state and in elevated temperatures.

We have fabricated a new multi-channel polycrystalline silicon thin film transistor (ploy-Si TFT), of which structure may be more effectively hydrogenated than conventional multi-channel poly-Si TFT. The new multi-channel TFT has stripe-cuts in gate electrode so that more hydrogen radicals penetrate into the gate oxide and passivate the active poly-Si layer. After 90 min. hydrogenation of the new device, the electrical characteristics such as threshold voltage and field effect mobility are improved more than those of conventional device.

The new multi-channel poly-Si TFT, which receives more hydrogen radicals thorough gate oxide than the conventional multi-channel TFT, can be hydrogenated effectively in long channel devices. Besides the improvement of the device characteristics, our experimental results show that the dominant hydrogenation path is the diffusion though the gate oxide.

Microwave heating was utilized for the first time for solid phase crystallization of amorphous silicon films. Microwave heating lowered annealing temperature and reduced the annealing time for complete crystallization. For example, the amorphous silicon film deposited at 400 °C was fully crystallized in 3 h at 550 °C below which glass is available as a substrate. On microwave heating, the hydrogen in the amorphous films diffused out very quickly, but there was no change in structural disorder following hydrogen evolution. The lower temperature crystallization of a-Si films compared to conventional furnace annealing is due to the interaction between microwave and silicon atoms. The grain size of the crystallized silicon films was in the range of 0.55 to 0.78 μm, depending on the deposition temperature. These grain sizes are not so small comparing those of Si films by conventional furnace heating, while the crystallization processing time is much shorter.

Conventional and self-aligned processes were developed for 250 °C inverse-staggered bottom gate a-Si:H thin film transistors (TFT's). Tri-layers of silicon nitride, amorphous silicon, and silicon nitride were continuously deposited in a plasma enhanced chemical vapor deposition system (PECVD). A self-alignment technique including back-side exposure and top nitride over etch was developed, which eliminates a masking step and the critical alignment of via opening used in typical TFT processing. Full self-aligned TFT's formed by selective n+ deposition were also fabricated successfully. Transistors show linear mobility ranging from 0.7 to 1.0 cm2/Vs, and current ON/OFF ratios greater than 106 were achieved for all TFT's.

The performance of poly-Si TFTs and CMOS circuits with various active films prepared by different deposition processes and annealing methods, such as SPC(Solid Phase Crystallization) and ELA(Excimer Laser Annealing), have been investigated. We have examined the effects of DC characteristics of poly-Si TFT, such as mobility, threshold voltage and ON- OFF- current level, on the dynamic performance of the CMOS circuits.

We have fabricated poly-Si TFT devices and CMOS circuits with various process conditions, such as active layer preparation source gases, annealing method, film thickness and source/drain impurity doping. The TFTs with ELA active films exhibit much higher field effect mobility and ON/OFF current ratio than those with SPC active film due to low intragranular trap state density. The TFTs with active film deposited using Si2H6 have higher mobility and sub-threshold slope than those with active film deposited using SiH4 because of the large poly-Si grain size and less grain boundary defects. We have observed that the device ON-current, mobility and VTH are the dominant characteristics to control the operation speed of CMOS circuits. We have also found that the effects of active film thickness and source/drain doping process on the performance of CMOS ring oscillator may not be neglected and that it should be optimized for AMLCD applications.

We have proposed the new poly-Si TFT which reduces the leakage current effectively by employing highly resistive a-Si region in the channel. The active layer of proposed device is crystallized selectively by employing excimer laser annealing while the both sides of channel near the source/drain are not recrystallized and remained as a-Si. Unlikely LDD or offset structure, the a-Si region which is designed to reduce the leakage current acts as the conduction channel of carriers under the ON state, so that the ON current is decreased very little. The selectively crystallized active layer can be fabricated by irradiating the excimer laser through ITO film of which transmittance at the wave length of laser is selectively adjusted. In the course of fabricating the proposed device, any additional photo masking step is not necessary and misalign problem is eliminated. The experimental results show that the ON/OFF current ratio of proposed poly-Si TFT is 106 while that of conventional one is 105.

Excimer laser (ECL) crystallization of silicon films on low temperature substrates is one of the most promising technique for large-area polycrystalline silicon films. Crystallization techniques using pulsed-ECL were extensively studied. They are characterized by films with high structural and electrical properties but low uniformity. In this way, the technology using single shot ECL with very large excimer laser (VEL) may be very promising. It was used for the crystallization of amorphous undoped films deposited by PECVD or by LPCVD The LPCVD technique is the most commonly used deposition technique of silicon. It presents numerous advantages and the hydrogen content in the films, known to constitute a drawback in the crystallization process leading to an increased surface roughness, is negligible (∼1 at.%). However, even with these low hydrogen content LPCVD films, high surface roughness is observed after the laser crystallization. Hence surface roughness appears as one of the major problems to be solved in the high performance TFT's realization from laser crystallized films.

In this work, the reduction of the surface roughness, determined from Atomic Force Microscopy observations, is presented. This reduction originated from the use of a surface oxidation and an etch treatment to remove the oxide. The mean height of the roughness is then reduced by about 50%.

Using these low surface roughness polycrystalline films, TFT's are then realized.

We present performance results of 4-inch full-color field emission display (FED) devices which are constructed by using Spindt type arrays with 80,000,000 Mo-metal tips, spacers, uniquely-developed low voltage color phosphors. Spindt type microtips with less than 1.1 urn in hole size are fabricated using a total internal reflection (TIR) holographic lithograpy method. Each color phosphor is electrophoretically deposited on the ITO line. The spacer which is screen-printed is characterized by a 3-dimentional surface analysis system. Electron emission pattern and luminance test of each pixel without cross talk are analyzed under different gate voltages. In addition, the total pressure and residual gas distributions inside the panel are investigated at various gap sizes between the cathode and anode plates.

Total internal reflection (TIR) holographic lithography is studied as a new method for field emitter array (FEA) fabrication. Four basic parameters of the process - scan speed, laser power, focus distance and step distance, are analyzed to optimize the hole patterns. In addition, the characteristics of the Aluminum (Al) parting layer are studied to minimize the stress produced by Molybdenum (Mo) layer during Spindt-type tip formation process.

The band diagram is constructed for diamond on metal and diamond-like carbon on metal emitters, from data for electron affinities, Schottky barrier heights or band offsets. For diamond, there is a large offset for the conduction band at the back-contact, causing this to be the dominant barrier for emission. Nitrogen and perhaps grain boundaries reduce this barrier by forming a depletion layer of ionised donors, which narrows the tunnelling distance. In DLC, there is little conduction band offset at the back-contact, and the dominant barrier is at the surface. Nitrogen now lowers the emission barrier by raising the bulk Fermi level and lowering the work function. Unresolved problems are also pointed out.

A series of tetrahedrally bonded carbon (ta-C) films have been produced using a Filtered Cathodic Vacuum Arc System. The threshold field and current densities achievable have been investigated as a function of sp3/sp2 bonding ratio and nitrogen content. Typical undoped ta-C films have a threshold field of 15–20V/μm and optimally nitrogen doped films exhibit threshold fields as low as ∼ 5 V/μm. Current densities of typically 10-4 A/cm2 at an applied field of 20V/micron were also obtained.

Deposition into micron-sized holes is known to produce cone shapes as supported on substrates. Potential uses for the cones include field-forming devices as field ionizers and field emission cathodes. The application of such devices include flat panel displays and flash x-ray tubes. Process iterations to closely space arrays of sharp cones have been extensively documented during the past two decades using the physical vapor deposition method of evaporation. Sputter deposition is well known as a method to fill holes and trenches but has only recently been demonstrated as an alternative method to produce field emission cathodes. In a further reduction in size, we have been successful in demonstrating the ability to deposit a cone shape into a cavity with a 300nm diameter hole. Through comparison to the results of electron-beam evaporative deposition, a sputter deposited nanocone appears to be suitable for use as a field emission cathode.

This articles describes an investigation of the reactive ion etching of tip-on-post and bottle-neck silicon structures used for fabrication field emission devices. The analytical study for the angular distribution of incident etching ions is presented by the simulation with temporal profile evolution. The surface simulations are compared with experimental results. This comparison shows that numerical expression for the angular distribution could be applied for incident ion flux in case tip-on-post and bottle-neck silicon structures.

A pronounced hysteresis effect was observed in the brightness versus pulse width response of memory electroluminescent (EL) devices driven near the threshold voltage. The use of this effect to address memory EL displays is suggested. A benefit of this technique is that the display is always operated near threshold with a relatively low dielectric stress. Longer device life might be therefore expected.

We have carried out an investigation of the electro-chemical doping (ECD) of porous silicon (PS) with rare earth elements, especially Er was chosen for the main doping element in our work. Under certain conditions, after doping a blue shift was shown in the visible range photoluminescence (PL), and enhancement of PL intensity was observed. We address this that the impurity states in forbidden gap increase the optical probability of trapping carriers and the optical transition probability. Moreover, in the Infrared (IR) range, luminescence is observed around 1.54μm at room temperature and is assigned to the optical transitions from intra-4f energy levels of Er3+. X-ray Photo-electronic Spectroscopy (XPS) showed that at least 3 atomic percen of the rare earth element has been incorporated into porous silicon layer. In conclusion, by choosing suitable electrolyte, we successfully doped rare earth elements into porous silicon by electro-chemical method.

We report on a microscopy and diffraction study of commercially available Cu-doped ZnS powders, along with an optical spectroscopy study of electroluminescent lamps fabricated with these powders. The results allowed us to identify a correlation between the microstructure and the optical properties (i.e. photoluminescence) of the ZnS powders. It is found that the best powders for EL lamps are those displaying a prevalent cubic, i.e. zincblend, structure, while the poor performances of the mixed phase (cubic + hexagonal) are tentatively ascribed to the quenching of luminescence due to defects (stacking faults) introduced into the cubic structure and resulting in a considerable amount of hexagonal phase, as detected by XRD. The mostly cubic powders have been selected to realize EL lamps. The optical properties of these lamps have been investigated by photoluminescence and electroluminescence spectroscopies with the aim to identify the degradation mechanisms leading to a decrease of brightness. The quenching of electroluminescence is primarily ascribed to a deterioration of the electrical contacts. However, the reduced brightness in photoluminescence spectra seems to indicate that additional quenching of luminescence is induced by transformations at the emitting layer of the lamps. This degradation is tentatively ascribed to the presence of voids in the emitting layer, which might induce, acting as traps for moisture, transformations in the optical and electrical properties of the transparent electrode (ITO).

Blue electroluminescent (EL) devices were fabricated with Si nanocrystals produced by ultrasonic fracturing of porous silicon (PSi) as well as silicon and germanium nanocrystals synthesized through a control chemical reaction. The active EL material consists of Si and Ge nanocrystals embedded in various host matrices such as polyvinylcarbazole (PVK), polymethylmethacrylate (PMMA), silica sol-gels and other organic polymers and small organic molecules. Several device configurations were used to induce EL processes that rely on radiative electron-hole recombination within the nanocrystals. We report on the optical and electrical properties of these devices. Applications for these EL devices include highly efficient light emitting devices. The cost and ease of processing of these material systems make them potentially ideal for flat panel display applications.