Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length

Definitions

• the present invention relates to an analysis method using porous silicon according to the preamble of claim 1 and an analysis device for such a method according to the preamble of claim 8.
• Porous silicon is a promising material for sensor technology applications (gas sensor, moisture sensor, biosensor) due to its compatibility with the highly developed Si microelectronics and its simple, inexpensive manufacture.
• the large inner surface of the material up to a few 100m cm 3 ) and the microstructure can be used.
• layer systems made of PS are excellently suited for the inexpensive manufacture of optical filters and mirrors as well as waveguides, air being in the pores of the PS and the refractive index of the PS due to substrate doping. Etching current density and composition of the etching solution is determined during manufacture.
• Porous silicon consists of a spongy framework made of silicon crystallites. which is pervaded by pores. The size of the crystallites and the pores varies between a few nanometers and a few micrometers depending on the doping of the silicon and the production conditions. If the wavelength of light is much larger than the size of the structures in PS. the PS appears to light as a homogeneous material ("effective medium") and its properties can therefore be described by specifying an effective refractive index which depends on the refractive indices of the silicon crystallites and the material in the pores.
• Another way to vary the refractive index of the PS is to fill the pores of the PS with another material instead of air to detect substances or to determine their concentration in solutions. This property of PS has not previously been used in the prior art. Selectivity for selected substances can be achieved by using membranes with selective permeability on the surface of the PS.
• the object of the present invention is therefore to provide an analysis method and an analysis device with which the detection of a substance or the determination of its concentration can be carried out using porous silicon.
• the object is achieved according to claim 1 in that a substance or its concentration in a fluid is detected due to the change in the optical property of porous silicon as a function of the refractive index of the substance present in the pore space of the porous silicon or of the fluid containing the substance or is determined.
• a component is at least partially made of porous silicon. whose optical property is dependent on the refractive index of the substance or the fluid containing the substance. a change in the optical property of the porous silicon as evidence of the substance or. can be determined as a determination of the concentration thereof in the pore space of the porous silicon
• Procedure for the analysis according to the invention or. the analysis device according to the invention is proposed. to use the dependence of the refractive index of the PS on the refractive index of the material in the pores. Detect substances or determine their concentration in solutions. For this purpose, the substance advantageously not only has to be deposited irreversibly in the pores (claim 4). but them can also be exchanged during the measuring process in a time-resolved measurement (claim 3) (claim 2).
• Fig. 1 is a schematic representation of a color-selective reflector made of porous silicon. reflecting the spectral dependence of the reflectivity on the refraction of the material in the pores;
• FIG. 3 shows a schematic representation of a photodiode with an interference filter made of porous silicon as a color-selective layer, a liquid to be examined penetrating into the pore space of the porous silicon and changing the refractive index of the porous silicon and thus changing the optical properties of the interference filter:
• FIG. 4 shows a schematic illustration of a waveguide made of porous silicon in cross section, the quality of the adaptation between the core and the cladding of the waveguide varying as a function of the refractive index of the material:
• FIG. 5 shows a schematic illustration of a waveguide interferometer in plan view, the waveguide core and cladding not being shown separately for reasons of simplification;
• Atisration ⁇ ingsfo ⁇ n 1 Color selective mirror
• an interference filter made of PS is illuminated and the reflected portion of the light is measured with a detector.
• the interference filter serves as a reflection filter, the spectral properties of which can be varied by using different PS layers. If the filter is in a liquid and this penetrates into the pores of the PS, the spectral reflectivity of the filter changes.
• FIG. 2 A measurement with such a measurement setup is shown in Fig. 2.
• the lamp and detector are integrated in a white light interferometer.
• the reflection filter used consists of a layer system of the type [HL] 5 [LH] 5 , ie a Fabry-Perot filter with 10 periods of the layer package HL.
• H denotes a layer with a high refractive index
• L denotes a layer with a low refractive index.
• a highly p-doped Si substrate (l * 10 19 c ⁇ r 3 ) and an etching solution with H : 0: HF: C 2 H are used ; OH in the ratio 1: 1: 2.
• an etching current density of 100 mA / cm 2 is used for 0.675 s and 280 mA / cm for the H layer analogously : for 0.478 s.
• the filter frequency of the Fabry-Perot filter is shifted towards longer wavelengths with increasing refractive index of the material in the pores (air 570 nm.
• the reflection spectrum of the interference filter is measured over a wide spectral range, which requires the use of a spectrometer.
• An inexpensive alternative to this is the use of a laser diode as a light source and a photodiode as a receiver.
• the filter frequency of the interference filter must be matched to the wavelength of the laser. Since the laser diode emits monochromatic light, only the change in filter reflectivity for this wavelength is measured, which is sufficient to characterize the material in the pores.
• Embodiment 2 Color selective photodiode
• Interference filters made of PS can, instead of being used as reflection filters as in FIG. 1, also be used as transmission filters as in FIG.
• the interference filter is already integrated in an S, photodiode.
• the photocurrent I Ph is a measure of the transmittance of the filter at this wavelength.
• Embodiment 3 Mismatched waveguide made of PS
• PS is also suitable for the production of waveguides, the properties of which are also influenced by the refractive index of the material in the pores (Fig. 4).
• the loss in light intensity, ie the ratio of the coupled light power I t to the coupled power I 0 depends, among other things, on the adjustment of the refractive indices of the core and cladding of the waveguide.
• the core of the waveguide is made of PS with a larger volume ratio V si-v Lnst & i k JV Po TM than the jacket of the waveguide.
• the refractive index changes less in the core of the waveguide than in the cladding of the waveguide if the refractive index of the material in the pores of the PS is varied.
• the adaptation of the refractive indices of the core and the cladding and thus the losses in the light intensity also change, that is to say when the input power I 0 is fixed, the output power 1 is a measure of the refractive index of the material in the pores of the waveguide.
• Embodiment 4 Asymmetric waveguide interferometer made of PS
• FIG. 5 shows an interferometer made of waveguides, in which the light beam coupled into a waveguide section 1 is split into two partial beams which, after passing through the waveguide sections 2 and 3, are brought together again in a waveguide section 4. This causes the partial beams to interfere, their phase difference being determined by the optical path lengths, that is to say the product of the geometric path length and refractive index.
• Such a structure can be used in two ways:
• Sections 2 and 3 are both made of PS, but have different geometric lengths. If the refractive index of the material in the pores is now varied, the optical path length in sections 2 and 3 changes by the same factor, since the refractive index of the PS changes by same factor changes. The phase difference of the partial beams is not determined by the quotient, but by the difference in the optical path lengths in sections 2 and 3. By varying the refractive index of the material in the pores, the phase difference of the partial beams changes, and in this way the intensity l, of the light, which arises from the interference of the two partial beams.
• Either section 2 or section 3 is made of PS
• the other section is made of a different material (for example SiGe / Si or Si / insulator).
• the length of the sections need not be different. If the refractive index of the material in the pores is now changed, only the optical path length of the PS waveguide section changes, whereas the optical path length of the other section remains constant. In this way, the sensitivity of the component to case a) is increased.
• the change in the refractive index of the PS by 0.001 results in a change in the optical path length of 1 ⁇ m. which corresponds to a full period in the interference signal when using light with a wavelength of 1 ⁇ m.
• Embodiment 5 waveguide interferometer with gate for setting the operating point
• a problem with the operation of the devices of embodiment 4 is that the intensity of the interference signal for a given one
• Pore material is determined by the geometry of the component. In many of the
• the outcoupled light intensity should be maximum for a certain pore material. i.e. the constructive interference of the partial beams should be present. This is possible by placing the component 4b) above the
• Waveguide section without PS a gate is attached. This geometry is in
• Fig.6 shown.
• the refractive index of the underlying waveguide can be varied by the voltage at the gate and the phase difference of the partial beams can thus be set.
• Such a component, but without a variable PS waveguide section, is referred to as a Mach-Zender interferometer. Expansion of embodiments 1 to 5:
• a membrane with selective permeability is applied to the surface of the PS, only those substances for which the membrane is permeable can get into the pores of the PS. Thus, only these substances can lead to a change in the refractive index of the PS. In this way, by selecting a suitable membrane, the components from embodiments 1 to 5 can be selected for individual substances.
• Component according to subsection 2). which are the components light source. Interference filter and light detector included.
• the component can consist of separate components, or several or all of the components can be integrated on one chip.
• Component which contains PS waveguides and in which the transmission of light through the waveguide is varied by the refractive index of the material which is located in the pores of the PS.
• the waveguides do not have to consist entirely of PS.
• Substances can get into the pores, making the component selective for the desired substance.

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• 1996
  • 1996-03-05 DE DE19608428A patent/DE19608428C2/de not_active Expired - Fee Related
• 1997
  • 1997-02-28 JP JP9531335A patent/JP2000506267A/ja active Pending
  • 1997-02-28 CA CA002248723A patent/CA2248723A1/en not_active Abandoned
  • 1997-02-28 EP EP97922810A patent/EP1017990A2/de not_active Withdrawn
  • 1997-02-28 US US09/142,423 patent/US6130748A/en not_active Expired - Fee Related
  • 1997-02-28 WO PCT/DE1997/000361 patent/WO1997033147A2/de not_active Application Discontinuation

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