Optics: measuring and testing – By particle light scattering – With photocell detection
Patent
1998-09-04
2000-10-10
Turner, Samuel A.
Optics: measuring and testing
By particle light scattering
With photocell detection
356361, G01B 902
Patent
active
061307483
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to an analytic process using porous silicon for producing a variable refractive index, as well as to an analytic device for such a process according to the introductory part of claim 8.
2. The Prior Art
Porous silicon (PS) is a promising material for applications in sensorics (gas sensors, humidity sensors, bio-sensors) because of its compatibility with highly developed Si-microelectronics as well as simple manufacturability at favorable cost, whereby use is made of the large inner surface of the material (up to a few 100 m.sup.2 /cm.sup.3) and the microstructure. Furthermore, layered systems made from PS are excellently suitable for producing optical filters and mirrors as well as wave conductors at favorable cost, whereby air is present in the pores of the PS and the refractive index of the PS is fixed in the course of production by substrate doping, the density of the etching current and the composition of the etching solution.
Porous silicon (PS) consists of a sponge-like structure of silicon crystallites, which is traversed by pores. The size of the crystallites and of the pores varies depending on the doping of the silicon and the manufacturing conditions between a few nanometers and a few micrometers. If the wavelength of light is very much greater than the size of the structures in the PS, the PS appears to the light as a homogeneous material ("effective medium") and its properties therefore can be described by specifying an effective refractive index, which is dependent upon the refractive indices of the silicon crystallites and of the material in the pores.
The structuring of PS by CMOS-compatible process steps has already been demonstrated. Interference filters made from PS, especially Bragg-reflectors and Fabry-Perot filters have already been manufactured as well and are known from M. G. Berger, M. Thonissen, R. Arens-Fischer, H. Munder, H. Luth, M. Arntzen and W. Theiss, Thin Solid Films 255 (1995), pp 313-316. It has been possible already to integrate Bragg-reflectors in a silicon photodiode as a color-selective layer. Furthermore, the conduction of light waves in wave conductors made from PS has been demonstrated.
Now, another possibility to vary the refractive index of the PS consists in filling the pores of the PS with another material instead of air in order to detect substances or to determine their concentration in solutions. This property of the PS has not been put to use heretofore in the state of the art. By using diaphragms with selective permeability on the surface of the PS it is possible to achieve selectivity versus selected substances.
Therefore, the problem of the present invention is to create an analytic process and an analytic device by which a substance can be detected or its concentration can be determined with the use of porous silicon.
SUMMARY OF THE INVENTION
An object according to claim 1 in that a substance is detected or its concentration in a fluid is determined based on the change in the optical property of porous silicon as a function of the refractive index of the substance present in the pores of the porous silicon, or of the fluid containing the substance.
Furthermore, this object is achieved according to the invention in that provision is made for a component which is at least partly made of porous silicon, the optical property of which is dependent upon the refractive index of the substance or of the fluid containi-g the substance, whereby a change in the optical property of the porous silicon can be measured to indicate detection of the substance or to determine the concentration of such substance in the pores of the porous silicon.
For the analytic process as defined by the invention, or for the analytic device as defined by the invention it is proposed that the dependence of the refractive index of the PS upon the refractive index of the material in the pores be put to use for detecting substances or for determining their concentration in solutions. For this purpose
REFERENCES:
patent: 5082629 (1992-01-01), Burgess, Jr. et al.
patent: 5120131 (1992-06-01), Lukosz
patent: 5377008 (1994-12-01), Ridgway et al.
patent: 5453624 (1995-09-01), Sailor et al.
patent: 5874047 (1999-02-01), Schoning et al.
Gauglitz, et al. "Optische Chemo- und Biosensoren fur die Umwelt- und Bioanalytik" Spektrum der Wissenschaft, Jan. 1994, pp. 92-97.
Bjorklund, et al. "Color Changes In Thin Porous Silicon Films Caused By Vapor Exposure" Applied Physics Letters, Nov. 1996, pp. 3001-3003.
Homola, et al. "A New Optical Fiber Sensor For Humidity Measurement" pp. 245-248.
Arens-Fischer "Strukturbeeinflussung von Porosem Silicium fur Optoelektronische Anwendungen" pp. 83-91.
Arens-Fischer Rudiger
Berger Michael
Kruger Michael
Luth Hans
Thonissen Markus
Forschungszentrum Julich GmbH
Turner Samuel A.
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