Showing papers by "Helena Gleskova published in 1996"

Electrophotographic patterning of thin film circuits

Abstract: Amorphous silicon thin-film transistors on glass foil are made using exclusively electrophotographic printing for pattern formation, contact hole opening, and device isolation. Toner etch masks are applied by feeding the glass substrate through a laser printer or photocopier, or from laser-printed patterns on transfer paper. This all-printed patterning is a low-cost, large-area circuit processing technology, suitable for producing backplanes for active matrix liquid crystal displays.

Electrographically patterned thin-film silicon transistors

Abstract: The authors made amorphous silicon thin-film transistors on glass foil using exclusively electrophotographic printing for pattern formation, contact hole opening and device isolation. Toner masks were applied by feeding the glass substrate through a photocopier, or from laser-printed patterns on transfer paper, This all-printed patterning is an important step toward demonstrating a low-cost large-area circuit processing technology.

a-Si:H TFTs patterned using laser-printed toner

Abstract: We fabricated top-gate amorphous silicon thin-film transistors (a-Si:H TFTs) on alkali-free glass foil, for the first time using laser-printed toner for the patterning of each layer. The toner for the first mask level was applied by feeding the glass foil through a laser printer, and for the following mask levels from patterns laser-printed on transfer paper. The transistors have off currents from ~ 10−12 A to ~ 10−11 A and on-off current ratios of ~ 106. Thus we have demonstrated a technology for the patterning of TFT circuits by printing.

Equilibration and stability in undoped amorphous silicon

Abstract: The annealing of structure and defect density in silicon-implanted non-hydrogenated and hydrogenated amorphous silicon, a-Si and a-Si:H, is compared. In both materials, the annealing follows equilibrium-like trajectories of defect density versus Urbach energy. A comparison of implanted, as-grown, and light-soaked a-Si:H shows that these three materials are strained on an intermediate, extended, and local scale, respectively. Similar defect annealing rates in ion-implanted and light-soaked a-Si:H point to the same mechanism for relaxation, which most likely is associated with the diffusion of an atom or defect. Hydrogen is the most likely candidate, but more quantitative verification is needed.

On the lack of observable light-induced H diffusion near room temperature

Abstract: A 5-day, high-intensity (9 W cm−2), red-light soak of a-Si:H at 65°C yields no detectable H diffusion in a tracer experiment. A new upper bound to the light-induced diffusion coefficient at a temperature so low that thermal diffusion is negligible is found. The null result found here is incompatible with models in which H emission from SiH bonds is proportional at all times to both the light intensity and the metastable defect creation rate. However, this result is compatible with the model proposed by Santos et al. in which both H emission and metastable defect creation are proportional to the product of the free electron and hole densities. In this model, this result implies that fewer than 500 H emissions occur per created metastable defect.

In-plane photoconductivity in amorphous silicon doping multilayers

Abstract: We prepared amorphous Si p-i-p-i and n-4-n-i doping multilayers to study their in-plane carrier transport and interfacial defect densities. The structures were grown using glow discharge or electron-cyclotron-resonance-enhanced chemical vapour deposition. We measured the following: composition by secondary-ion mass spectrometry; transport by dark conductivity SsGd and its thermal activation energy, by continuous-wave photoconductivity SsGph as a function of intensity and wavelength, and also by photoconductive decay; defect density by photothermal deflection spectroscopy (PDS) and the constant-photocurrent method (CPM). SsGd is dominated by the doped layers. The intensity dependence of SsGph suggests that it also is controlled by the doped layers. The fast component of the photoconductivity response time is comparable with that of the doped bulk. The PDS spectra of the multilayers are nearly identical with those of the bulk doped hydrogenated amorphous silicon. The pronounced wavelength dependenc...

Recovery kinetics of phosphorus ion-implanted a-Si:H

Abstract: Hydrogenated amorphous silicon was implanted with phosphorus ions to a uniform concentration of 3 {times} 10{sup 20} cm{sup {minus}3} and defect saturation. The implants were annealed isochronally up to 400 C in the dark or under additional illumination. This illumination had no effect on recovery. The Urbach energy remains higher than that of silicon-implants. The midgap defect density anneals to {approximately}10{sup 18} cm{sup {minus}3}, typical of gas-phase doped samples. The dark conductivity remains lower and its thermal activation energy higher than in gas-phase doped samples. The authors surmise that the Si-Si network absorbs some of the donor electron-induced defect density by forming strained Si-Si bonds. These strained bonds widen the band tails, and thus reduce the effective electron mobility and pin the Fermi level.