Hydrogenated amorphous carbon (a-C:H), deposited by the if-plasma enhanced chemical vapour deposition (rf-PECVD) technique, is a promising material for large area electronic and interlayer dielectric applications. The structural and electronic properties of rf-PECVD a-C:H, deposited at room temperature from CH4/He and CH4/Ar gas mixtures, are shown to be sensitive to the substrate on which the thin film is deposited. The choice of substrate (c-Si or C7059 glass), and the existence and geometrical dimensions of any metallic pattern on the substrate surface, can result in significant spatial variations in the a-C:H adhesion and material properties. The observed effects are attributed to potential variations across the metal patterned substrates which influence the ‘local’ dc self-bias. This leads to spatial variations in the growth conditions and hence material properties. For electronic device and dielectric isolation applications this effect can result in significant variations in operating performance. The nature of the substrate and any overlying metallisation pattern are therefore important considerations.

A planar electron emitter was fabricated employing chemical vapor deposited (CVD) diamond thin films. This device is composed of CVD diamond films selectively deposited on a pair of patterned Au/Cr films separated 2 micrometers from each other. When the driving voltage (Vd) was applied between the Au/Cr films, the extremely low threshold emission from diamond film was observed (Vd ∼ 10 V). Furthermore, by applying high voltage on anode screen placed above this device, part of emitted current was drawn to the anode and the luminescence from phosphors was clearly seen under Vd = 50V. The mechanism of electron emission from the diamond films used in this device was also discussed by comparing with the electron emission from isolated diamond particles. It was found that the effective work functions differ between the isolated particles and the continuous films. This result suggests a difference in the emission site of electrons.

The work function is one of the most fundamental properties of a metal surface. To clarify frictional electrification phenomena, the effects of frictional damage on the contact potential difference (CPD), which is defined by the difference between the work functions of two contacting surfaces, were investigated. Au(111) and Si(111) surfaces were scratched in an ultrahigh vacuum under a light load with the Si cantilever tip of an atomic force microscope. The contact potential difference between the scratched surface and the tip whose work function was known was measured using an ultrahigh vacuum scanning Kelvin probe force microscope (SKPM). Simultaneously, the noncontact atomic force microscope (NC-AFM) images were observed in situ. The CPD images showed clear changes between the areas with and without scratching, corresponding to the scratching track on the NC-AFM images.

We have studied different metal-silicon-metal (MSM) Schottky barrier photodiodes for the detection of visible and infrared light. We investigated the different Schottky barriers from Ti, Cr and Pt. At infrared wavelengths, the Schottky contacts provide electrons and holes by “internal photoemission” into the Si. The lowest Schottky barrier determines the long wavelength cutoff and the current noise. The temporal response was measured byultrashort (100 fs) laser pulses from a Ti:A1203 laser, which were converted by an optical parametric oscillator to a wavelength of 1.1 to 1.6 μm. The measurements were performed between 30 K and room temperature. The best detectors show a pulse width of 3.2ps FWHM at 1.25 μm wavelength and room temperature. To our knowledge this is the fastest infrared response for silicon based diodes ever reported.

New approach to control the lateral growth mechanism through the opportune spatial modulation of the absorbed laser energy and with a two-pass excimer laser crystallization process is presented. In the first pass, spatial modulation of the light intensity has been obtained by irradiating the sample through a patterned mask in contact with the sample. Lateral growth is triggered when the irradiated regions are fully melted and a lateral extension of the grains in excess to 1 μm has been observed for samples irradiated at RT. In order to homogeneously crystallize the sample, the film can be re-irradiated (second pass) without the mask. By using opportune energy densities it can be induced a complete melting of the residual a-Si regions (masked areas during the first pass), while partially melting the polysilicon regions (unmasked areas during the first pass). Different mask geometries have been investigated and for optimized conditions, the sample area can be fully covered with laterally grown grains. The proposed novel technique can be rather attractive for polysilicon TFT fabrication, being characterized by only a two laser-shot process and wide energy density windows.

We have proposed a new excimer-laser crystallization system based on an optical projection concept. In the proposed system, a collimated excimer-laser light pulse is irradiated to Si thin-films on a glassy substrate, through a phase-shift mask and an optical lens system. Using oneand two-dimensional phase-shift masks, we have examined feasibility of the proposed method.

The liquid-solid interface motion and the temperature history of thin Si films during excimer laser annealing are observed by in-situ experiments combining time-resolved (∼Ins) electrical conductance, optical reflectance/transmittance at visible and near-IR wavelength, and thermal emission measurements. The existence of partial and complete melting regimes is elucidated. In the partial melting regime, the maximum temperature remains close to the melting point of aSi, since the laser energy is consumed on the latent heat of phase-change. In the complete melting regime, substantial supercooling, followed by homogeneous nucleation is observed. These phase transformations are consistent with the recrystallized poly-Si morphologies.

We investigated the properties of polycrystalline silicon (poly-Si) films oxidized in inductively coupled plasma (ICP) and the characteristics of poly-Si thin film transistors (TFTs) with an ICP/LPCVD gate oxide. The ICP oxidation reduced the interface traps and passivated dangling bonds by hydrogen incorporation. The ICP oxidation did not change the roughness of the Si/SiO2, while thermal oxidation increased the roughness largely. The characteristics of the TFTs with ICP/LPCVD oxide were improved due to the reduced interface trap density.

We present a new technique for the spatially selective deposition, or “printing”, of materials such as Si and Al. This transfer is effected by irradiating a hydrogenated amorphous silicon film deposited on a quartz substrate and coated with the material to be transferred with an excimer laser pulse. The resulting release and accumulation of hydrogen at the film/substrate interface generates pressures sufficient to propel the silicon, as well as any overlying material, onto an adjacent glass receptor wafer. Transient optical transmission measurements performed during the transfer of Si indicate that the amorphous film is melted by the laser pulse and breaks into droplets during ejection. These droplets travel towards the host substrate with a velocity of about 800 m/s and coalesce upon arrival. For fluences above 400 mJ/cm2, the resulting films adhere well to the receptors and can be smoothed using a second laser irradiation. We fabricated thin film transistors (TFTs) in the printed-and-smoothed Si using conventional lithography. The resulting devices show consistent switching behavior. We have also printed Si and Al lines with widths 5 to 15 µm by patterning the laser beam using a reflective grating mask defined on the target substrate. These lines are straight, show few discontinuities, and have sharp edges.

Defect creation mechanisms during solid phase crystallization (SPC) of Si thin films were investigated with PECVD amorphous precursor samples produced with various deposition temperatures and thicknesses. These precursor films were implanted with dopant and then crystallized to obtain both SPC and dopant activation. The doping efficiency was found to decrease with the tensile stress level as measured by Raman shift. The stress shows a decrease as the precursor deposition temperature and thickness are lowered. Furthermore, a lower level of stress is induced by rapid thermal annealing when the annealing temperature is high enough to soften the glass substrate on which the films were deposited. We show that by control of stress during the SPC step, intragrain defect density can be lowered and electronic quality of the resulting polycrystalline Si films can be improved. Based on these observations, we propose the following tentative model to explain the defect creation: during SPC, tensile stress evolution is considered to result from the volumetric contraction of Si film when it transforms from the amorphous to crystalline phase. This contraction is retarded by the substrate, which imposes a tensile stress on the film. A high level of stress leads to formation of structural defects inside the grains of the resulting polycrystalline material. These defects trap carriers or complex with the dopant reducing doping efficiency.

We report the design, fabrication, and characterization of an indium tin oxide/hydrogenated amorphous silicon (ITO/a-Si:H) Schottky photodiode based on room temperature deposition of ITO. The optical transmittance of the ITO is larger than 80% in the visible light range and its resistivity is less than 6 x 10-4 Ω-cm. The fabricated photodiode exhibits low leakage current and stable I-V characteristics. The leakage current is 7x10-10 A/cm2when biased at -2 V and the shift in leakage current stabilizes to a value less than 9% after 2 seconds of biasing at -2 V. The improvement in performance can be attributed to the high integrity ITO/a-Si:H interface achieved with the low temperature deposition.

A TCO/ μc-p-i-n Si:H/AI imager is presented and analyzed. The μc-p-i-n Si:H photodiode acts as a sensing element. Contacts are used as an electrical interface. The image is acquired by a scan-out process. Sampling is performed on a rectangular grid, and the read-out of the photogenerated charges is achieved by measuring simultaneously both transverse photovoltages at the coplanar electrodes. The image representation in gray-tones is obtained by using low level processing algorithms. Basic image processing algorithms are developed for image enhancement and restoration.

Polyimide substrates are of interest because of their thermal stability, light weight, and good mechanical characteristics. This paper reports thermal control multilayer deposition experiments which have strongly affected the properties of the image sensor structure (TFT + photodiode). Particularly TFT properties have been studied with respect to difficulties of obtaining of good quality a-SiNx:H films at temperature below 120°C. We characterize the structural properties using infrared absorption, refractive index measurements, small angle x-ray diffraction and the optoelectrical measurements of the TFT and PIN diode structure. The linear image sensor consisting of two rows, 40 pixels per row, with dimensions 0.6 mm2was made on the polyimide foil.

This contribution describes the preparation of a single crystalline Si thin-film separable from a reusable Si wafer. The method relies on: i) etching of a porous silicon layer ii) high-temperature annealing and iii) transfer of the recrystallized film to a foreign substrate. As a result of the process we obtain 1 to 30 μm thick monocrystalline Si films that contain voids with a size of several 100 nm. Due to its “swiss-cheese-like” structure the material is termed as “quasi-monocrystalline Si”. Sub micrometer thin layers are almost compact, while in several micron thick films voids cause scattering of incident light. This effect increases the effective absorption coefficient by light trapping and seems promising for the application of our quasi-monocrystalline films in thin film solar cells. Quasi-monocrystalline p-type silicon reaches a hole mobility of 78 cm2/ Vs measured by room-temperature Hall-effect. High carrier mobility and adjustable optical characteristics make these films suitable for display and photovoltaic applications. Quasi-monocrystalline films are processed using conventional high-temperature Si processing; finished devices can be transferred to a foreign substrate such as glass, while the starting wafer can be reused several times.

Polycrystalline silicon thin-film transistors (TFTs) have been fabricated on glass substrates using a low temperature top-gate self-aligned process. The interface between the polysilicon active layer and the silicon dioxide oxide gate dielectric is of vital importance in order to achieve good thin-film transistor electrical characteristics. Carrier transport takes place within 10nm of this interface, and any roughness in this region, corresponding to the initial surface roughness of the polysilicon layer, causes scattering of the carriers and a higher density of interface traps. Chemical-mechanical polishing has been used to reduce the initial surface roughness of the polysilicon. Electrical parameters of polished TFTs, such as mobility and threshold voltage, show a marked improvement compared to unpolished devices.

Chemical bath deposition is a thin film technique in which semiconductor thin films of typically 0.02 – 1 μm thickness are deposited on substrates immersed in dilute baths containing metal ions and a source of sulfide or selenide ions. Many I–VI, II–VI, IV–VI, and V–VI semiconductors are included in the list of materials deposited by this technique, II–VI compounds CdS, CdSe, ZnS and ZnSe being the most investigated. However, a mathematical model describing the growth mechanism of these films still remains to be established. The deposition process consists of a nucleation phase, growth phase, and a terminal phase, each of which depends on the concentration of the ions in the deposition bath, its temperature, dissociation constants of the metal complex ions, etc. In this paper we propose a mathematical model, which can qualitatively account for most of the features of the experimental growth curves of chemically deposited semiconductor films.

Large area polymer photodiode arrays were designed and fabricated for full-color imaging applications. These sensor arrays are of high photosensitivity, low dark current, large dynamic range and fast response time. The red, green and blue color primaries were achieved by coupling a set of color filters with the polymer sensor pixels with broad response covering entire visible spectrum. Image recovery process from the pixel photocurrent data was developed, which is suitable generally to image arrays with power-law light intensity dependence and with finite pixel dark current. Large sensing length photodiode arrays (2.5”5”) were fabricated with pixel densities from 40 to 100 dot-per-inch. They were used as the sensing elements in page size document scanners. Voltage switchable polymer photodetectors were developed. Their photosensitivity can be switched on and off with external bias. These devices can be used as the sensing elements in x-y addressable two-dimensional sensor matrices. The high on/off switching ratio and high photocurrent/dark-current ratio allow such two-dimensional, passive photosensor matrices be used for image sensing applications.

A novel sensor concept for detecting the fundamental components of the visible light has been developed. The multi-channel sensors based on three stacked amorphous thin film detectors are color moiré or color aliasing free due to their vertical integration. The four terminal devices enable the generation of three or six linearly independent spectral response curves at the same spatial position. The 3-channel sensor based on three stacked pin-diodes generates a red-green- blue signal with one shot, whereas the 6-channel sensor with three stacked pinip structures allows the detection of up to six linearly independent spectral response curves. The reproducibility of the complex layer sequences is enhanced by introducing a textured TCO-layer in the rear part of the device, which leads to a distinct scattering of the incoming light for longer wavelengths.

In order to gain information on how to improve the sensor performance, the sensors are characterized. The presented characterization model facilitates the quantification of color errors with regard to the human perception. Furthermore, the color errors of amorphous thin film sensors are compared with a commercial color CCD camera and a BiCMOS color-sensor.

We present a novel sensor concept comprising a new contacting scheme for voltage-bias con- trolled thin film photodiode arrays on CMOS readout chips. Our unilateral contact structure greatly facilitates manufacturing of the sensor system. Moreover, the novel contacting scheme most efficiently suppresses crosstalk between neighboring pixels. The respective devices are ready for operation and testing directly after deposition of the amorphous silicon based sensor layers. No extra transparent front contact is needed, no patterning and no connection between the topmost layer of the thin film stack and the underlying readout chip. Due to the lack of a metal oxide front contact, contamination of CMOS manufacturing equipment with tin, zinc or similar materials is definitely avoided. Thus, for the first time, a sensor concept with complete CMOS process compatibility is demonstrated. Our new sensor structure allows for a considerable reduction in manufacturing cost of high performance optical detection systems. As a proof of concept, we present detailed investiga- tions on current-voltage characteristics, dynamic behavior and spectral response of 0.1-inch test structures. Down-scaling to pixel sizes in the micron range is evaluated by semi-empirical numerical modeling and proves easily feasible.