Coating processes – Direct application of electrical – magnetic – wave – or... – Electrical discharge
Reexamination Certificate
2000-03-23
2002-01-15
Pianalto, Bernard (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Electrical discharge
C427S058000, C427S109000, C427S162000, C427S165000, C427S166000, C427S167000, C427S249100, C427S249150, C427S255110, C427S255180, C427S255280, C427S255395, C427S255700, C427S294000, C427S419700, C427S585000
Reexamination Certificate
active
06338882
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to multi-layer structures containing liquid-crystal layers. In particular, the present invention relates to a process for applying an absorption layer of an optically addressable spatial light modulator (OASLM).
RELATED TECHNOLOGY
OASLMs are used for various areas of optical telecommunications. An example that may be mentioned is that of level balancing in WDM multi-channel systems, as described in W. P. Beard et al., “
AC Liquid Crystal Light Valve”,
Appl. Phs. Lett., Vol. 22, No. 3, 90-92 (1973).
Other applications relate to the local attenuation of strong light sources as glare protection, as well as applications for preventing halation of the image in video cameras, video spectacles, pilot spectacles etc.; see W. P. Bleha, L. P. Lipton, E. Winere, Opt, Eng., Vol 17, No.4, Appl. Phys. Lett, V, Opt. Eng., V, 371-384 (1978).
Particularly important for the optical parallel processing of images is the conversion of optical, incoherent images into the coherent beam path of the optical correlator. Used for this purpose are OASLMs in which the writing and read-out beam paths are optically separated from each other. In the event that the read-out light overlaps spectrally with the sensitivity curve of the photoconductor, it must be completely separated from the writing beam path, because otherwise there are great losses in terms of the sensitivity, resolution and grey-scale range of the OASLM due to this parasitic illumination.
Only in relatively rare cases is it possible to optically separate the writing and read-out beam paths solely through the spectral composition of writing and read-out light, by employing photoconductors which absorb exclusively in the blue light range, while red or infrared light is used for the read-out.
None of the conventional reflecting layers made of metal films or dielectric films have a sufficiently low transmission in order to separate the two beam paths and to prevent the penetration of the read-out light into the photoconductor.
An appreciable improvement in light separation can be achieved by additional absorbing layers between the photoconductor and the reflecting layer of the read-out beam path. A semiconductor layer can be used as the absorbing layer if the band gap is smaller than that of the photoconductor.
Known from W. P. Beard et al., “
AC Liquid Crystal Light Valve”,
Appl. Phs. Lett., Vol. 22, No. 3, 90-92 (1973), W. P. Bleha, L. P. Lipton, E. Winere, Opt. Eng., Vol. 17, No.4, Appl. Phys. Lett, V, Opt. Eng., V, 371-384 (1978) and U. Efron, J. Grinberg, P. O. Braatz, M. J. Little, P. G. Reif and R. N. Schwarts, “
The silicon liquid
-
crystal light valve
”, J. Appl. Phys., Vol. 57, No. 4, 1356-1368 (1985) is the use of a cadmium-telluride layer CdTe as a light-blocking layer. Therein described is a cadmium-telluride layer CdTe of 2&mgr; thickness, a surface resistance of 10
11
&OHgr;cm and an absorption coefficient not less than 10
5
cm
−1
at 525 nm in structures which used cadmium-sulfide CdS as photoconductor. The same light-blocking layer was also employed to improve the properties of light valves on the basis of liquid crystals with amorphous silicon (&agr;-Si) as photoconductor. The CdTe layer was applied between the dielectric mirror (based on titanium oxide) and a special adhesive layer (to improve the adhesion of the CdTe to the photoconductor). The adhesive layer included 4 films:
1) an SiO
2
film applied in an argon atmosphere,
2) an SiO
2
film applied in an argon-oxygen atmosphere,
3) a CdTe film likewise applied in an argon-oxygen atmosphere, and
4) a CdTe film applied once again in an argon atmosphere.
Amorphous carbon &agr;-C and amorphous hydrogenated carbon &agr;-C:H as such are known as thin films with high light absorption. These materials can be applied by sputtering or vaporization of carbons or by chemical vapor deposition (CVD), with hydrocarbons as precursor; see A. V. Balakov, E. A. Konshina, “
Methods of production and properties of diamond
-
like carbon films
”, Sov. J. Opt. Technol.”, Vol. 49, No. 9, 591-599(1982) and A. Bubenzer, B. Dischler, G. Brandt, P. Koidl, “
Optical properties of hydrogenated hard carbon thin films
”, Thin Solid Films, Vol. 91, 81-87 (1982). Used for this purpose are plasma discharges in the radio-frequency range and magneton gas discharge; see A. Bubenzer, B. Dischler, A. Nyaiesh, “
RF
-
plasma deposited amorphous hydrogenated hard carbon thin films. Preparation, properties and applications
”, J. Appl. Phys., Vol. 54, 4590-454595 (1983), and D. R. McKenzie, R. C. McPhedran, N. Savvides, “
Analysis of films prepared by plasma polymerization of acetylene in a d. c. magnetron
”, Thin Solid Films, Vol. 108, 247-256 (1983).
It is also possible to employ direct ion-beam and dual-beam deposition, as well as laser erosion from the carbon target. The optical constants of amorphous carbon layers and amorphous, hydrogenated carbon layers depend characteristically on the deposition and on the parameters of the condensation process; see F. W. Smith, “
Optical constants of a hydrogenated amorphous carbon film
”, J. Appl. Phys., Vol. 55, 764-771 (1984).
The described carbon layers are used as reflecting layers or as protective layers in IR optics. Optically visible carbon layers with an absorption in the visible spectral range are employed for selective solar applications and as contrast-intensifying layers for crystal displays.
A carbon-containing film of very complex structure of silicon, germanium and carbon is known from K. Takizawa, T. Fuijii, M. Kawakita, H. Kikuchi, H. Fuijkake, M. Yokozawa, A. Murata and K. Kishi, “
Spatial light modulators for projection displays
”, Applied Optics, Vol. 36, No. 23, 5732-5747 (1997). The layers described therein had a great thickness of 3.5 &mgr;m and more, in order to provide the required absorption and the necessary resistance in an OASLM based on thick (250 &mgr;m) BSO photoconductor layers and polymer-dispersed nematic liquid crystals.
For &agr;-Si:H and &agr;-Si:C:H photoconducting layers, these blocking layers are too thick to be able to optimize the basic parameters of the OASLM. A further disadvantage is that these complex compositions of Si, Ge and C are too expensive in manufacture.
SUMMARY OF THE INVENTION
The present invention provides a process for applying a light-blocking layer between a photoconducting layer and a mirror when manufacturing an optically addressable spatial light modulator OASLM using the CVD process. The light-blocking layer (
4
) and the photoconducting layer (
3
) are applied in a shared process step in which both the thickness and composition of the photoconducting layer (
3
) to be applied to the transparent electrode (
2
), as well as the thickness and composition of the light-blocking layer (
4
) to be applied to the photoconducting layer (
3
) are determined by a time-related change of the variation of the gas composition during the deposition process. The silanes are continuously replaced by hydrocarbons in the gas atmosphere of the CVD reactor, with the result that a layer sequence composed of photoconducting layer (
3
) and light-blocking layer (
4
) is produced, having the desired specific resistances.
The process of the present invention relates to the decoupling of the writing and read-out beam paths of an optically addressable spatial light modulator (OASLM) in reflection mode by applying a light-blocking layer between the writing and read-out beam paths. In order to determine and optimize the properties of the light valve, it should be possible during the process to selectively adjust, within narrow limits, the specific resistances of the layers and therefore the conductivity of the layer sequence of transparent electrode ITO, photoconducting layer and light-blocking layer. At the same time, one should be able to implement the process as simply and cost-effectively as possible.
Transparent electrode ITO
2
is applied onto the class or quartz-glass substrate
1
according to already known process steps of the CVD process in a CVD reactor. According t
Beresnev Leonid
Dultz Wolfgang
Haase Wolfgang
Konshina Elena
Onokhov Arkadii
Deutsche Telekom AG
Kenyon & Kenyon
Pianalto Bernard
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