Kenji Nakazawa

Recrystallization of amorphous silicon films deposited by low‐pressure chemical vapor deposition from Si2H6 gas

This paper investigated the recrystallization of low‐pressure chemical vapor deposition amorphous silicon (a‐Si) films deposited using Si2H6 gas at various substrate temperatures. The grain size of recrystallized films formed from Si2H6 is larger than that formed from SiH4. The maximum grain size is obtained at the substrate temperature of 460 °C, where the nucleation rate is minimum due to the maximum structural disorder of the Si network. The structural disorder is increased not only by lowering the substrate temperature but also by increasing the deposition rate. The field effect mobility of thin‐film transistors (TFTs) using the recrystallized films reaches 120 cm2 V−1 s−1, even though the highest temperature during the TFT fabrication process is only 600 °C.

Effect of substrate temperature on recrystallization of plasma chemical vapor deposition amorphous silicon films

The effect of substrate temperature on the recrystallization of plasma chemical vapor deposition amorphous silicon films is investigated. The grain size of polycrystalline silicon films recrystallized at 600 °C increases as the substrate temperature decreases. The enlargement in the grain size is attributed to the decrease in the nucleation rate. The nucleation rate is suppressed by an increase in structural disorder of the Si network. Electrical properties of recrystallized films are improved by the increase in the grain size.

Characteristics of field-induced-drain (FID) poly-Si TFTs with high on/off current ratio

The characteristics of polycrystalline silicon thin-film transistors (poly-Si TFTs) with a field-induction-drain (FID) structure using an inversion layer as a drain are investigated. The FID structure not only reduces the anomalous leakage current, but also maintains a high on current. An off current of 1.5 pA/ mu m and an on/off current ratio of 10/sup 7/ (V/sub d/=10, V/sub g/=-20 V) are successfully obtained. These characteristics result from good junction characteristics between the p channel and n/sup +/ inversion layer. Reducing the threshold voltage of the FID region allows a simple circuit configuration for the FID TFTs. >

Characteristics of narrow-channel polysilicon thin-film transistors

The effect of channel width on the characteristics of polysilicon thin-film transistors (TFTs) was investigated. n-channel TFTs with a channel length L of 20 mu m and a channel width W ranging from 20 to 0.5 mu m were fabricated and characterized. The most prominent effect of reducing the TFT channel was found to be a drastic decrease in threshold voltage when W was reduced to less than 5 mu m. This decrease was found to be correlated with the decrease in grain-boundary trap density. >

Role of Hydrogen and Fluorine in Amorphous Silicon as Elucidated by NMR and ESR

Results of NMR measurements on H and F have been compared with those of ESR, IR and photoconductivity measurements in various kinds of a-Si films. The density of dangling bonds is found to have a close correlation with the content of dispersed H atoms contributing to the narrow component of NMR spectra, indicating that dispersed H atoms mainly play a role in decreasing the density of dangling bonds. Gathered H and F atoms contributing to the broad component of NMR spectra appear to play a role in decreasing the mobility.

Hydrogen Incorporation Scheme in Amorphous-Microcrystalline Mixed-Phase Si: H Films

Silicon-hydrogen alloy films containing both microcrystalline phase and amorphous phase (µc-Si: H) are prepared by sputtering, magnetron sputtering and glow-discharge methods. Results of NMR measurements for hydrogen in µc-Si: H are qualitatively similar to those in amorphous silicon-hydrogen alloy films except that hydrogens are easy to move and exhibit the motional narrowing effect. There seems to be little possibility of presence of a large amount of non-bonded hydrogens such as hydrogen molecules or atomic hydrogens.

Polycrystalline Silicon Film Formation at Low Temperature Using a Microcrystalline Silicon Film

Polycrystalline silicon (polysilicon) films are formed from the recrystallization of microcrystalline silicon films with different crystalline nucleus densities. The films are deposited by plasma CVD using a gas mixture of SiH2F2, SiH4, and H2. The SiH2F2 flow rate can successfully control the crystalline nucleus density of an as-deposited film. The recrystallization is carried out by annealing at 600°C. The TEM observation shows that recrystallization proceeds from the nucleus until the neighboring grains face each other. Therefore, the grain size in the annealed films and the field effect mobility of thin film transistors using polysilicon films completely depend on the crystalline nucleus density in the starting films. The largest grain sizes and highest field effect mobilities can be obtained from microcrystalline silicon films with the lowest nucleus densities.

A New 3-D Display Method Using 3-D Visual Illusion Produced by Overlapping Two Luminance Division Displays

We are developing a simple three-dimensional (3-D) display method that uses only two transparent images using luminance division displays without any extra equipment. This method can be applied to not only electronic displays but also the printed sheets. The method utilizes a 3-D visual illusion in which two ordinary images with many edges can be perceived as an apparent 3-D image with continuous depth between the two image planes, when two identical images are overlapped from the midpoint of the observers eyes and their optical-density ratio is changed according to the desired image depths. We can use transparent printed sheets or transparent liquid crystal displays to display two overlapping transparent images using this 3-D display method. Subjective test results show that the perceived depths changed continuously as the optical-density ratio changed. Deviations of the perceived depths from the average for each observer were sufficiently small. The depths perceived by all six observers coincided well.

Depth-fused 3D (DFD) display with multiple viewing zones

A new depth-fused 3-D (DFD) display for multiple users is presented. A DFD display, which consists of a stack of layered screens, is expected to be a visually comfortable 3-D display because it can satisfy not only binocular disparity, convergence, accommodation, but also motion parallax for a small observer displacement. However, the display cannot be observed from an oblique angle due to image doubling caused by the layered screen structure, so the display is applicable only for single-observer use. In this paper, we present a multi-viewing-zone DFD display using a stack of a see-through screen and a multi-viewing-zone 2-D display. We used a film, which causes polarization-selective scattering, as the front screen, and an anisotropic scattering film for the rear screen. The front screen was illuminated by one projector, and the screen displayed an image at all viewing angles. The rear screen was illuminated by multiple projectors from different directions. The displayed images on the rear screen were arranged to be well overlapped for each viewing direction to create multiple viewing zones without image doubling. This design is promising for a large-area 3-D display that does not require special glasses because the display uses projection and has a simple structure.

Reduction of power consumption in compact DFD display by using FS color technology

A method to drastically reduce the power consumption of the backlight in a compact depth-fused three-dimensional display, which consists of a stack of two liquid crystal (LC) panels, is proposed and experimentally validated. To remove the color filters in the LC panels, we introduced the field-sequential technique for color display. The transmittance of the display could be improved by more than one order. Therefore, the luminance of the backlight could be reduced to less than that of a two-dimensional LC display.