EP2255174A1

EP2255174A1 - Device and method for determining an index of refraction of a measured object

Info

Publication number: EP2255174A1
Application number: EP09721047A
Authority: EP
Inventors: Wladimir Tschekalinskij; Norbert Weber; Stephan Junger
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date: 2008-03-14
Filing date: 2009-03-16
Publication date: 2010-12-01
Also published as: DE102008014335A1; DE102008014335B4; WO2009112288A1

Abstract

A system (30) for determining an index of refraction (n (object)) of a measured object (31), comprising a light source (32) for issuing light (33) of a pre-defined wavelength, an integrated sensor element (35) with an optoelectronic sensor (36) and a layered structure (37) with at least one structured metal layer (44) wherein the optoelectronic sensor (36) and the layered structure (37) are commonly integrated on a semiconductor substrate (38), a device (39) for holding the measured object (31) between the integrated sensor element (35) and the light source (32) so that the layered structure (37) is disposed between the measured object (31) and the optoelectronic sensor (36), and so that an output signal from the optoelectronic sensor (36) to the light (33) with the pre-defined wavelength changes depending on the index of refraction (n(object)) of the measured object (31), and a device (40) for determining the index of refraction (n(object)) of the measured object (31) based on the output signal of the optoelectronic sensor (36).

Description

Apparatus and method for determining a refractive index of a DUT

description

The present invention relates to apparatus and methods for determining a refractive index of a measuring object.

The refractive index n is a good indicator for many chemical and biological applications. The refractive index n can be calculated according to n = Co / c = ∈ _r μ _r , where Co is the speed of light in a vacuum and c is the speed of light of a material whose refractive index is to be determined. Furthermore, ε _r denotes the dielectric conductivity or permittivity and μ _r the magnetic conductivity or permeability of the material. The refractive index n changes, for example, depending on the concentration of substances dissolved in a liquid. A large field of application of refractometers is the determination of the concentration and presence of a particular substance in a chemical solution, such as the original wort of beer or the water or sugar content of honey. Biological investigations of dangerous viruses and bacteria are also applications of refractometers or devices for determining the refractive index.

Type and concentration of solutes breaks light differently. This manifests itself as a refractive index change. The construction principle of optical refractometers has been known for a long time and is still used today in almost unchanged form. A conventional refractometer is shown schematically in FIG.

The refractometer 10 comprises a monochromatic light source 11, a measuring prism 12, on which total reflection occurs. stands, a receiving part 13, 14, which registers a position of a reflected light beam and converted into a refractive index n.

The refractometer shown in Fig. 1 is generally referred to as Abbe refractometer. From the light source 11 outgoing beam 15, 16, 17 meet an interface 18 of the prism 12 with the refractive index n (l) where a liquid to be examined with a refractive index n (2) is applied. The beam 17 continues in the medium with refractive index n (2), resulting in a beam 17 '. For the beam 16, total reflection occurs. The beam 15 is reflected from the boundary surface 18 of the prism 12 to the object to be measured 19 to a black painted surface 20 (15 ') - Due to this light distribution creates two fields that are light or dark. The image 21 of these fields is viewed using the optical system 13 with the eye 22 or registered with a photoreceiver and further processed with an electronics 14. The value of the critical angle A is used in the Abbe refractometer to determine the refractive index n (2). After measuring the critical angle A at which total reflection occurs, one can calculate the unknown refractive index n (2) according to Sin (A) = n (l) / n (2), assuming that the refractive index n (l) is known. The main part of the refractometer 10 is therefore a high-resolution optical angle sensor which determines the angle A.

In a known Abbe refractometer, a viewing of a working field and the angle measurement through an eyepiece with the eye. Such a device has a thermostabilization of the measuring range with a digital thermometer and operates with only a measuring wavelength of 590 nm. The measuring range for the refractive index n (2) is between 1.3 and 1.72.

There are also portable, fully automatic refractometers whose measurement process is so automated that no visual channel is needed. In such devices For example, the position of the light / dark boundary (shadow line) is automatically evaluated. Such a fully automatic refractometer may, for example, have two thermostats - one for the test sample and a second one to keep the light source, the optics and a photodiode array constant at a certain temperature.

In the published patent application DE 3909143 a method is described in which the functional principle of the refractometer is based on the so-called surface plasmon resonance. Samples to be tested are placed in a surface plasmon field and scanned by surface plasmon microscopy. As the sensor element, a prism having a metal layer is used, and the field after the sample is examined by a surface plasmon microscope.

Another possibility is, for example, the use of near field microscopes which measure changes in the dielectric constant of the samples or objects to be examined. An example of the underlying operating principle is the scanning of an object surface with an optical probe. This comprises a single-mode fiber, at the end of which there is a diaphragm with a hole diameter of about 40 nm. The light emerging from this waveguide strikes the object plane, thereby changing its evanescent field. An evanescent field is generally a non-propagating component of a light field that is close to an object to be examined, the so-called near field. The evanescent field exponentially decays to the surface normal of the radiating body. Each illuminated object thus generates an evanescent and a propagating field. A purely evanescent field can be observed, for example, in the case of total reflection. If an incident light beam is totally reflected at an interface of an optically denser medium to an optically thinner medium, the field may be due to the continuity condition on the side of the optically thinner medium not abruptly zero, but it falls exponentially in the half-space of the optically thinner medium. In general, the evanescent field has already disappeared at a distance of approximately λ / 2 from the interface of the two optical media. A remote receiver with signal processing system can register changes in the evanescent field, from which the refractive index n can be calculated. Various methods for measuring the near field are described, for example, in the dissertation "A high-resolution optical near-field probe for fluorescence measurements on biological samples" by Heinrich Gotthard Frey.

In recent years, several simulations and experiments have been published which confirm refractive index selectivity of structures composed of array-shaped sub-wavelength openings in metal layers. The dependence of transmission on the dielectric constant of a material in the vicinity of sub-wavelength structured layers is described in two articles: "The Optical Properties of Metal Nanoparticles: The Influence of Size, Shape, and Dielectric Environment" by K. Lance Kelly, Eduardo Coronado, Lin Lin Zhao, and George C. Schatz and in "Light transmission through a high index dielectric hole in a metal film surrounded by surface corrugations" by Juuso Okkonen and Kari Kataja.

Conventional refractometer assemblies based, for example, on the Abbe refractometer, require optical systems of multiple elements that must be positioned very accurately against each other. Furthermore, a very high measurement accuracy is required to measure the critical angle of total reflection. A measurement with several wavelengths at the same time is not possible. Furthermore, it is necessary to thermostatize the measurement object or even the entire optical system from the light source to the receiver. Conventional refractometers measure the refractive index only at a predetermined wavelength, such as 590 nm. The plasmon-polariton resonance is strongly dependent on a light incidence angle. The evanescent field at the interface of two optical media decreases exponentially. This means that the field to be measured soon becomes small after a small distance. Therefore, individual photons must be counted, thereby requiring a very sensitive photoreceiver, and / or a high power light source must be used. Producing a probe with the nano-aperture at the tip (40 nm diameter) is complicated and poorly reproducible. This method is therefore not suitable for mass production. In order to produce a two-dimensional refractive index profile, in the conventional near-field detection in which only a one-point measurement is possible, a scanning of the measurement object is required.

Due to the great expense and the high costs, it is hardly conceivable to build a cost-effective disposable system with conventional refractometer systems. In conventional systems, electronics and optics are always disconnected. Due to their complexity, a real-time measurement to determine dynamic refractive index changes is not possible.

Therefore, the object of the present invention is to provide improved devices and methods for determining a refractive index of, for example, optical media by refractometry, compared with the prior art.

This object is achieved by a system having the features of claim 1 and a method for determining a refractive index of an optical medium according to claim 23.

The realization of the present invention is that, for constructing a refractometer system, an integrated component with an optoelectronic sensor and structured layers of metal and / or polycrystalline semiconductor material of a layer structure which has a dependence of transmission on electromagnetic shear radiation from the dielectric constant of a test object or material in an environment of the structured layers of metal and / or polycrystalline semiconductor material can be used.

In this case, the measurement object can be arranged, for example, in direct contact with a surface of the integrated sensor element. That is, a measurement object whose refractive index is to be determined is arranged above the layer structure of the integrated sensor element. Preferably, the measurement object is arranged directly on a passivation, ie a non-metallic protective layer, of the integrated sensor element or of the sensor chip. For this purpose, a holding device for the measurement object is provided on the sensor chip according to embodiments. The measurement object can be irradiated with monochromatic light of a predetermined wavelength, so that the light can strike the integrated sensor element through the measurement object. The light which has passed through the measurement object with the desired refractive index and which strikes the layer structure of the integrated sensor element can generate electromagnetic fields in the layer structure which can be detected by the optoelectronic sensor located below the layer structure. The detected electromagnetic fields are dependent on the refractive index of the measurement object, which is located on the chip surface of the integrated sensor element. That is, an output signal of the optoelectronic sensor, such as a photocurrent of a photodiode, is dependent on the desired refractive index. By means of the output signal and a calculation rule can be concluded that the refractive index of the under investigation ^■ measurement object. In a pre-calibration, a measurement is performed with a Kalibriermessobjekt with a known refractive index, so that component tolerances play little role.

Embodiments of the present invention provide a system for determining a refractive index of a measurement object, with a light source for emitting light of a predefined wavelength, an integrated sensor element with an opto-electronic sensor and a layer structure with at least one structured layer of metal or polycrystalline semiconductor material, wherein the optoelectronic sensor and the layer structure are integrated together on a semiconductor substrate. Furthermore, the system comprises a device for holding the measurement object between the integrated sensor element and the light source, so that the layer structure is arranged between the measurement object and the optoelectronic sensor, so that an output signal of the optoelectronic sensor is dependent on the refractive index of the measurement object changes. In the system, a device for determining the refractive index of the measurement object is also provided based on the output signal of the optoelectronic sensor.

According to exemplary embodiments, the layer structure of the integrated sensor element may have properties of a photonic crystal. A photonic crystal is to be understood below to mean a three-dimensional periodic structure whose periodically arranged structural elements have dimensions and distances from one another which are of the order of a predetermined wavelength range for electromagnetic radiation which transmits through a photonic crystal to an optoelectronic sensor assigned to it can be. Photonic crystals comprise structured metals, semiconductors, glasses or polymers and force electromagnetic radiation, in particular light, by means of their specific structure to propagate in the medium in the manner necessary for a component function. According to the exemplary embodiment, periodic dielectric and / or metallic structures whose structural period length is set such that they influence the propagation of the electromagnetic radiation, in particular light, in a similar manner as the periodic potential in semiconductor crystals influence the propagation of electrons. This leads to, that electromagnetic radiation or light of certain wavelengths can not propagate in the photonic crystal. These wavelengths are then effectively forbidden. The spectral filtering effect of photonic crystals has been known for some years and confirmed by experiments. The spectral properties of periodically structured layers of metal and / or polycrystalline semiconductor material are highly dependent on the shape of the individual structural elements. The layer structures have structure or microelements whose dimensions and distances from each other are of the order of the predetermined wavelength, in particular the wavelength of the monochromatic light of the light source, for which the integrated spectral filter structure is in the form of at least one photonic crystal , The microelements of the structured layers of metal and / or polycrystalline semiconductor material may be periodically arranged three-dimensionally. According to embodiments, adjacent microelements of adjacent layers are formed identically for the predetermined wavelength and lie on a common optical axis. Microelements may according to embodiments be micro-openings with dimensions and distances in the respectively provided transmission wavelength range. According to embodiments, the microelements may comprise so-called split-ring resonators with dimensions and distances in the respective predetermined transmission range.

According to a further exemplary embodiment of the present invention, a single sensor element is formed from an optoelectronic sensor and a metal structure covering the optoelectronic sensor, for example one or more structured metal layers which are structured in such a way that for a predetermined wavelength range or a predetermined wavelength can form a plasmon-polariton resonance effect. Due to a sub-wavelength opening in the patterned metal layer may be due to the predetermined wavelength of the plasmon-polariton resonance effect in the vicinity of the opto-electronic sensor form an electromagnetic field concentration, which can then be detected by the opto-electronic sensor.

The plasmon-polariton resonance effect leads to a so-called extraordinary optical transmission, which can take place through slots or holes in metals which are smaller than a wavelength of the predefined wavelength range or the predefined resonance wavelength.

This phenomenon results from so-called surface plasmon resonance. A surface plasmon is a density sway of charge carriers at the boundary of semiconductors or metals to dielectric media and is one of many interactions between light and a metallic surface, for example.

According to exemplary embodiments, the distance between the optoelectronic sensor and the layer structure is less than 20 μm and preferably less than 8 μm. For 0.18 μm CMOS processes, the distance between the optoelectronic sensor and the layer structure is less than 2 μm. In order to detect an e ventricular field, the distance between the opto-electronic sensor and the layer structure is preferably within the range of the electromagnetic near field.

According to preferred embodiments, the means for holding together with the integrated sensor element is integrated together on the semiconductor substrate. By way of example, the means for holding may comprise a frame structure on the surface of the integrated sensor element, such that a receptacle results, for example, for a liquid to be analyzed. The frame structure can be formed by the passivation of the chip, so that the passivation with frame a kind of analysis basin for Liquids is formed, in which to be examined fluids can be given.

Furthermore, the device for determining the refractive index is designed as evaluation electronics, which is integrated according to preferred embodiments, together with the opto-electronic sensor and the layer structure on the semiconductor substrate is integrated into a single chip.

A refractometer system according to the invention thus requires no further optical components except for external illumination. In preferred embodiments, a refractometer system may even be fully integrated into a single chip. For this purpose, an optoelectronic component is additionally provided on the substrate as an exposure source, such as e.g. an LED or a laser, so that no external components are necessary at all.

The integrated sensor of the refractometer system is based on three-dimensional sub-wavelength structured metal and / or dielectric layers and photodiodes that are part of the integrated circuit sensor element. The sensor chip may e.g. be manufactured within a CMOS process and requires no adjustment. A measuring device and electronics for signal processing are integrated according to embodiments in a circuit.

Precise matching of mechanical and optical elements compared to conventional refractometers, where the critical angle of total reflection is accurately measured and the tolerances of each mechanical and optical component play a crucial role, is not necessary in embodiments of the present invention. In a refractometer system according to the invention, manufacturing process tolerances, eg CMOS process tolerances, can be calibrated out. If a plurality of similar sensor elements arranged in an array, a measurement of the refractive index with multiple measuring points is possible, each sensor element can determine a refractive index of a respective associated measuring point. A number of sensor elements per measuring surface can be freely defined in an IC design. An XY measuring table is not required.

According to embodiments, one or more temperature sensors are integrated in the sensor element and are therefore located in the vicinity of the test object to be examined (typically 3-4 μm away). The temperature sensors can therefore provide accurate values of the temperature of the liquid to be tested.

Embodiments of the present invention further enable simultaneous measurement with multiple monochromatic light sources. In this case, a plurality of sensor elements can be used whose layer structures are adapted to the respective wavelength. The number of wavelengths or measuring points can be freely defined in a system design.

According to embodiments, the light source and the sensor chip are fixed to each other, i. a position between the illumination and the measuring chip does not change. Angular errors between the light source and the measuring chip can thus always be calibrated out.

According to exemplary embodiments, the optoelectronic sensor or the photodiode is arranged very close to the test object to be examined (a few μm away). As a result, transmission losses of evanescent fields can be significantly reduced, which can lead to a considerable increase in a signal-to-noise ratio compared to near-field microscopy. Thus, increased measurement accuracy is achievable and allows use of a weaker light source. The integrated sensor element or the integrated sensor chip can be produced for example with a CMOS technology. Such a technology has a high accuracy and repeatability and is ideally suited for mass production. Thus, relatively low prices for end products can be achieved, whereby one-way refractometers can be realized. The integrated sensor chip integrates well into a manufacturing process, so that its surface always has an optical contact with a liquid. Thus, embodiments of the present invention provide a means for dynamic analysis of refractive index changes.

Preferred embodiments of the present invention will be explained in more detail below with reference to the accompanying drawings. Show it:

Fig. 1 is a schematic representation of a conventional refractometer;

FIG. 2 shows an illustration of a system for determining a refractive index of a test object according to an exemplary embodiment of the present invention; FIG.

3 shows a side view of a layer stack of optoelectronic sensor, metal layers and dielectric layers produced by CMOS technology according to one exemplary embodiment of the present invention;

4 shows a schematic perspective view of a sensor element with a receiving frame for liquid according to an exemplary embodiment of the present invention;

5a, 5b representations of an integrated sensor element to illustrate an evanescent field propagation in the integrated sensor chip according to embodiments of the present invention; FIG. 6 shows transmission curves of light through a layer structure according to exemplary embodiments of the present invention as a function of a desired refractive index; FIG.

7 shows a schematic illustration of an integrated sensor chip with integrated temperature sensor according to an exemplary embodiment of the present invention;

8 shows a plan view of a structured metal layer with split-ring resonators according to an exemplary embodiment of the present invention;

9 shows a schematic representation of a plurality of integrated sensor elements, adapted to different wavelengths of light, according to an exemplary embodiment of the present invention;

10 shows a schematic structure of a refractometer according to an exemplary embodiment of the present invention;

11 is a perspective view of a structured metal layer according to an embodiment of the present invention;

12 shows a perspective view of a structured metal layer according to a further exemplary embodiment of the present invention;

Fig. 13 is a schematic view of a metal layer having a two-dimensionally periodic arrangement of sub-wavelength openings; and

14 shows a side view of a layer stack made of opto-electronic sensor and layers of metal and polycrystalline semiconductor material produced by CMOS technology according to a further exemplary embodiment of the present invention. With regard to the following description, it should be noted that in the different embodiments, the same or functionally equivalent functional elements have the same reference numerals and thus the descriptions of these functional elements in the various embodiments shown below are interchangeable.

2 schematically shows a system 30 for determining a refractive index n (object) of a measuring object 31, according to an embodiment of the present invention.

The system 30 includes a light source 32 for emitting preferably monochromatic light 33 of a predefined wavelength. Further, an optic 34 may be provided to diffuse the light 33. The optic 34 may be, for example, a telescopic lens. Furthermore, the system 30 has an integrated sensor element 35 with an optoelectronic sensor 36 and a layer structure 37 with at least one structured layer of metal or polycrystalline semiconductor material, wherein the optoelectronic sensor 36 and the layer structure 37 are integrated together on a semiconductor substrate 38 , A device 39 serves to hold the measurement object 31 between the integrated sensor element 35 and the light source 33, so that the layer structure 37 is arranged between the measurement object 31 and the opto-electronic sensor 36, and so that an output signal of the opto-electronic sensor 36 depending on the refractive index n (object) of the measuring object 31 changes. The optoelectronic sensor 36 is coupled to a device 40 for determining the refractive index n (object) of the measuring object 31 based on the output signal of the optoelectronic sensor 36.

As will be discussed below, the (metal) layer structure may be designed such that the measuring device output signal of the sensor 36 depends on the refractive index of the measurement object 31 according to a plasmon-polariton effect, for example according to a dependence as described in the publication "Defracted evanescent wave model for enhanced and suppressed optical transmission through subwavelength hole arrays", describing a transmission function measured by a numerical aperture lens NA can be calculated by multiplying a first surface modulation function Ai (λ), an intrinsic transmission function D _H (λ) by a micro-aperture, a second surface modulation function A ₂ (A) and a function f _c (λ) representing a part of the transmitted power through the layer structure, The transmission function D _c (λ) can then be written as

TC (λ) = AKλ; n (object); Pl; d \) TH (λ; r7 _H; d; t) A2 (λ n2; P2; d2) fC (λ, NA; P2; d2);

Pl and P2 give lattice constants or repeat distances of structures around an aperture or nano-opening, dl and d2 lateral dimensions of the nano-openings, NA the numerical aperture, t the layer thickness of the metal layer, n _H the refractive index of the medium within the nano-openings. n, the refractive index in front of the metal layer, ie the refractive index n (object) of the specimen or of the object or the known refractive index n (reference) of a reference object, such as air, and n _{2 is} the refractive index of the medium behind the metal layer , and λ the wavelength. TC is in turn proportional or at least uniquely dependent on the sensor output of the sensor. Based on two measurements, one for a reference object with known refractive index (TC _Ref ) and another for the sample with refractive index (TCobject) ι, it is now according to TC _Ref / TC _object = Al (λ, n (reference), Pl, dl) / Al (λ, n (object), Pl, dl) and resolving to n (object) possible to calculate n (object). It can for a certain in the above publication also described Nanoöffnung in the form of a sub-wavelength slit (see Fig. 12) Al can be given as wherein α, the amplitude of CDEW (composite diffracted EVA nescent wave), that is, the composite broken EVA neszenten shaft, n _eff indicates the effective refractive index, the CDEW learns and P indicates the Widerholabstand the 2N grooves which surround the slot ,

As has already been described above, the layer structure 37 according to embodiments may be at least one metal layer having subwavelength structures, e.g. Micro or nano-openings, act. Such subwavelength structures allow passage of an electromagnetic field, e.g. in the form of an evanescent field, towards the optoelectronic sensor 36.

Furthermore, the layer structure 37 may be a three-dimensional photonic crystal or a periodic arrangement of a plurality of three-dimensional photonic crystals, the layer structure 37 or each of the three-dimensional photonic crystals being formed from a layer stack of dielectric layers and structured metal layers , which will be discussed in more detail below.

At this point, it will be explained with reference to FIG. 8, which represents a schematic plan view of the layer structure 37, which is to be understood below as a photonic crystal or an array of photonic crystals.

In exemplary embodiments, the layer structure 37 with the at least one photonic crystal 82 for electromagnetic radiation 33 arriving on a side remote from the opto-electronic sensor 36 effects a spectral selection or a spectral filtering of electromagnetic radiation. For this reason, an electromagnetic field concentration predominates near a side of the layer structure 37 facing the optoelectronic sensor or near the optoelectronic sensor 36 for the predefined wavelength range, which is detected by the optoelectronic sensor can. In the case of exemplary embodiments, the optoelectronic sensor 36 is a component which can convert electromagnetic radiation, in particular light, into an electrical output signal, such as, for example, a PN junction sensor, which can be designed as a photodiode.

In further exemplary embodiments, the layer structure 37 causes a plasmon-polariton resonance effect to form for the predetermined wavelength range or the predetermined wavelength. By means of a sub-wavelength opening in the layer structure 37, an electromagnetic field concentration can form for the predetermined wavelength due to the plasmon-polariton resonance effect in the vicinity of the optoelectronic sensor 36, which can then be detected by the optoelectronic sensor 36.

For this purpose, as shown in FIG. 11, the layered structure 37 has a sub-wavelength dimension opening 118. In order for the impinging electromagnetic radiation 33 to cause surface plasmons, the sub-wavelength opening 118 according to exemplary embodiments is surrounded by rotationally symmetrical periodically arranged grooves 142 around the opening. With proper sizing of the opening 118 and the grooves 142, a resonant interaction of the electromagnetic radiation and the surface plasmons of the layered structure 37 may result in the above-mentioned enhanced extraordinary transmission in the predetermined wavelength range. A structure element 140 of the layer structure 37 according to exemplary embodiments comprises a region of a metal layer which has a periodically structured surface of the period A with depressions 142 and elevations 144 and a sub-wavelength opening 118 which lies in the center of the structure 140. For a predetermined resonant wavelength λ _{res of} an incident on the structure 140 e- lektromagnetischen radiation 33, the plasmon-polariton resonance effect. This effect causes for the resonant wavelength λ _res through the sub-wavelength opening 118, for example, more than 15% of the incident electromagnetic radiation, although an area ratio of the opening 118 to the surface of the entire element 140 is very small. For other wavelengths than the resonant wavelength λ _res , on the other hand, there is no resonance and thus almost no transmission of electromagnetic radiation of the other wavelengths through the opening 118. This means that the transmission for a predetermined wavelength λ _res through the structural element 140 is of the area ratio the area of the opening 118 depends on the area of the entire element 140, as well as the period A of the structured surface or elevations 144 and depressions 142.

The period A which allows the highest transmission depends inter alia on the thickness (t + h) of the structured metal layer. For example, for a resonant wavelength λ "_res" of 650 nm, the width or diameter b of the aperture 118 could be chosen to be 110 nm, the area ratio of the area of the aperture 118 to the area of the entire element 340 could be 0.01 and A could be to 90 nm and t to 20 nm. At this point, it should be emphasized that these values represent only example values to give an idea of possible magnitudes. According to embodiments, A is in a range of 10 nm to 2110 nm. The thickness (t + h) of the metal layer is in embodiments in a range of 30 nm to 2500 nm, preferably in one range from 350 nm to 550 nm. The height h of the recess is of course smaller than the thickness (t + h) of the metal layer and in embodiments is in a range above (t + h) / 2. The area ratio of the area of the opening 118 to the area of the entire element 140 is less than 0.3 in embodiments.

Furthermore, non-rotationally symmetric surface structures of the layer structure 37 are also conceivable, which can cause the plasmon-polariton resonance effect, such as a slot-shaped opening with grooves arranged parallel thereto (FIG. 12) or a matrix-like arrangement of sub-wavelength openings, as shown in FIG 13 is shown.

The layer structure 37 thus has, for example, according to exemplary embodiments, a structured metal layer with an opening 118 with sub-wavelength dimensions, hereinafter also referred to as sub-wavelength opening, and rotationally symmetrical or parallel grooves or corresponding projections or elevations arranged periodically around the sub-wavelength opening are embedded in a dielectric in order to generate the surface plasmon-polariton resonance effect for the predetermined wavelength range in the layer structure 37. In this case, a sub-wavelength opening is a circular or slot-shaped opening having a width or a diameter smaller than the predefined wavelength of the light or the electromagnetic radiation 33.

Integrated components based on photonic crystals can be realized with CMOS processes, such as a CMOS opto process, without the need for additional process steps or further processing.

A method for manufacturing an integrated sensor element on a substrate according to embodiments comprises a step of generating the opto-electronic Sensor 36 on a substrate surface of the substrate 38 and applying a filter or layer structure 37 with at least one photonic crystal on the optoelectronic sensor 36, so that the opto-electronic sensor 36 at a distance d less than 3 microns, preferably less than 2μm, of which at least one photonic crystal is located and completely covered by it, the generating and depositing being part of a CMOS process.

According to exemplary embodiments, the application of the at least one photonic crystal 82 comprises depositing a layer stack of dielectric layers and metal layers, the metal layers each having microstructures 84 having dimensions and spacings between two adjacent microstructures 84 that transmit electromagnetic radiation of the predefined wavelength range through the at least one photonic crystal 82 allow.

An intermediate product of an integrated sensor element 35 of a refractometer system according to exemplary embodiments is shown schematically in FIG. 3.

The integrated sensor 41, which is not yet completely manufactured, shown in FIG. 3, comprises a substrate 38, in particular a semiconductor substrate, in which an optoelectronic sensor 36 is introduced. In this case, the opto-electronic sensor 36 is arranged in a plane 42, a type of focal plane known from classical optics.

The unfinished optical structure 41 has a layer stack of metallic layers 44 and dielectric layers 46. 3 merely exemplarily shows four metallic layers 44-1 to 44-4 and three dielectric layers 46-1 to 46-3. Depending on the embodiment, the number of layers may differ from the example shown in FIG. 3. In current CMOS processes, it is possible to pattern the metal layers 44 such that resulting microstructures or microelements 84 are arranged periodically and have dimensions and spacings which are smaller than the wavelength of the light 33 of the light source 32. This makes it possible to produce three-dimensional periodic structures with properties of photonic crystals directly on a chip. As already described above, in embodiments, the individual microelements or microstructures 84 are smaller than 1/10 of the predetermined optical wavelength, so that a three-dimensional photonic crystal is formed.

According to embodiments, the opto-electronic sensor 36 is preferably placed very close to the last metal layer 44-1 of the layer structure 37, the distance d being dependent on the manufacturing process. The distance d from the last metal layer 44-1 of the filter structure 37 can be adjusted by dimensions and spacings of patterns of the metal layers 44. For an integrated sensor, the distance d is chosen to be less than 20 μm and preferably less than 8 μm. For 0.18 μm CMOS processes, the distance between the opto-electronic sensor 36 and the layer structure 37 or the last metal layer 44-1 is less than 2 μm.

The metal layers 44-1 to 44-4 shown by way of example in FIG. 3 are suitably structured in a CMOS process in order to obtain a photonic crystal or a layer structure for the plasmon-polariton effect.

An integrated sensor element 35 according to exemplary embodiments can thus be realized by utilizing existing metallic and dielectric layers 44, 46. The opto-electronic sensor 36 of the integrated sensor element 35 is preferably in accordance with embodiments of the structured metal layers 44 completely covered.

If a measuring object 31 is applied to a surface of the integrated sensor element 35, which is formed, for example, by a passivation layer 48 over the uppermost structured metal layer 44-4, then an optical transmission through the layer structure 37 changes as a function of the dielectric constant of FIG Surface of the measured object 31.

An output signal of the opto-electronic sensor 36, e.g. a photocurrent of a photodiode, is dependent on the optical transmission of the overlying layer stack 37 of sub-wavelength-structured metal and / or dielectric layers 44, 46. The transmission of the layer stack 37 is in turn dependent on the refractive index n (object) of the measurement object 31, which is arranged above the layer stack 37. The test object 31 to be examined, for example, rests on a transparent passivation layer of the integrated sensor element 35, so that it optically with the underlying layer structure

37 is coupled. For holding the measurement object 31, a device 39 for holding in accordance with preferred exemplary embodiments together with the integrated sensor element 36 and the layer stack 37 is jointly applied to the semiconductor substrate

38 integrated.

As shown schematically in FIG. 4, the means 39 for holding may, for example, comprise a frame structure 49 on the surface of the integrated sensor element 35, so that a receptacle, for example for a liquid to be analyzed, results as the measurement object 31. The frame structure 49 can be formed by the passivation 39 of the chip, so that the passivation with frame forms a kind of analysis basin for liquids into which liquids to be examined can be added. The frame structure 49 is not mandatory. For the For example, other measures could be taken, such as laying a slide on the sample so that the sample forms a monolayer on the passivation of the chip.

The change in transmission as a function of the desired refractive index n (object) can be determined by certain properties of the optical microstructures or nanostructures 84 of the layer structure 37. In this case, for example, an evanescent field or a resonance change is determined by the optoelectronic sensor 36 and then calculated back to the refractive index n (object) of the test object 31.

As in the publications "The Optical Properties of Metal Nanoparticles: The Influence of Size, Shape, and Di- lectric Environment" by K. Lance Kelly, Eduardo Coronado, Lin Lin Zhao, and George C. Schatz, and in "Light transmis- is described by Juuso Olkkonen and Kari Kataja, the transmission of sub-wavelength-structured metal and / or dielectric layers is dependent on the dielectric constant G of the environment Layer structure 37.

For a calibration of the refractometer system 30 (FIG. 3), for example, a measurement object 31 (eg, liquid) having a known refractive index can be applied to the integrated sensor element 35. Calibration without a specific calibration measurement object, ie calibration with air as the calibration measurement object, is also conceivable. It is essential that during calibration the refractive index of the medium 31 located above the layer structure 37 is known. If a measurement is started, the photodiode 36, which is arranged in the immediate vicinity of the last metal layer 44-1, receives a light field transmitted through the measurement object 31 and the layer structure 37. From the current of the photodiode 36, one obtains a value dependent on a change in transmission with respect to the calibration transmission, which corresponds to the refractive index changes between the calibration medium and the test object 31 to be examined. For a calibration, for example, a special calibration sensor element may be provided on a chip, which is constructed similarly to sensor elements actually used for refractive index measurements. In this case, above the calibration sensor element, as described above, there is a calibration measurement object with a known refractive index, or simply not just the measurement object but, for example, air or vacuum.

According to embodiments, a temperature sensor 47 is additionally integrated in the integrated sensor element 35. With this additionally integrated temperature sensor 47 can be accurately determine which temperature the measurement object 31 has to make a corresponding correction of the determined refractive index n (object) depending on the temperature detected by the temperature sensor 47. The above-mentioned calibration procedure only needs to be carried out once for a specific height h of the measurement object 31.

There are several effects which cause the said transmission changes of the layer structure 37 as a function of the refractive index n (object) of the surroundings of the surface of the integrated sensor element 35. In the following, two of the effects are considered as examples.

From near-field microscopy with optical nanoprobes, it is known that an evanescent field arising after a sub-wavelength structure is dependent on the dielectric constant of the environment surrounding the sub-wavelength structure. This effect will be described below with reference to Figs. 5a, 5b.

In the arrangement shown in Fig. 5a monochromatic light 33 falls almost vertically from above through a glass plate 39 to the test object to be examined 31 and radiates this. The light 33 that has passed through the measurement object 31 strikes sub-wavelength structures 84 of the layer structure 37, as a result of which an evanescent field 52 arises in the vicinity of the sub-wavelength structures 84. This is similar to the situation where an object is scanned with a fiber probe having a corresponding nano-aperture. The amplitude of the evanescent field 52 is dependent on the wavelength of the incident light 33 and the refractive indices of the two media involved in the transition. The distance between the photoreceptor 36 and the location where the evanescent field 52 is formed is only a few microns or less according to embodiments. The smallest possible distance between the optoelectronic sensor 36 and the layer structure 37 is very important for the dimensioning of the integrated sensor element 35, wherein the intensity of the evanescent field 52 decreases exponentially with increasing distance from the interface. In comparison to near-field microscopy, where a signal-to-noise ratio is very poor, because a distance between the interface and a photomultiplier in the centimeter range, in embodiments of the present invention, measurement results are much more accurate, because here Distance between the photodiode 36 and the medium to be examined 31 is only in the micron range.

A second possibility, which is shown in FIG. 5b, is to measure the evanescent field which arises when the object to be examined 31 is illuminated obliquely such that at a boundary 54 between a glass plate 39 (holder) for fixing the object object to be examined 31 and the object 31, a total reflection is formed, as indicated in Fig. 5b. The "classical optics" implies that in such a case the whole energy of the electromagnetic radiation is reflected, in reality an evanescent field 52 is created at the boundary between the object to be examined 31 and the glass plate 39. In embodiments of the present invention Invention, this evanescent field 52 is transmitted to the photodiode 36 through the layer structure 37, which has sub-wavelength-structured metal and / or dielectric layers.

In the two cases shown in FIGS. 5a, 5b, the output signal or the photocurrent of the photodiode 36 is ultimately dependent on the refractive index n (object) of the test object 31.

A second physical effect that can be used for constructing a refractometer system 30 according to the invention is utilization of resonance wavelengths of the transmission spectrum of the layer structure 37 of the integrated sensor element 35. Resonance wavelengths of a light field passing through the layer structure 37 are dependent on the dielectric constant of the environment Layer Structure 37. From the literature "The Optical Properties of Metal Nanoparticles: The Influence of Size, Shape, and Dielectric Environment" by K. Lance Kelly, Eduardo Coronado, Lin Lin Zhao, and George C. Schatz, and in "Light transmission through a high index dielectric hole in a metal film surrounded by surface corrugations" by Juuso 01kkonen and Kari Kataja, it follows that the transmission spectrum of sub-wavelength-structured metal layers in dielectric environment has one or more strong resonance wavelengths are shown by way of example in FIG.

A first resonance curve 61 describes a resonance behavior at a first refractive index n (b) of a first test object to be examined (eg calibration object). A second resonance curve 62 results when the first measurement object is replaced by a second measurement object with a refractive index n (unb). In this case, resonance wavelengths λ (1) and λ (2) shift. FIG. 7 shows another possible structure of an integrated sensor element 35 according to an embodiment of the present invention. In the embodiment shown in FIG. 7, the integrated sensor element 35 has a structured metal layer 44 above the photodetector 36, wherein the metal of the structured metal layer 44 has a refractive index n (Me). Within micro-openings, a dielectric material having a refractive index n (D) is arranged. The refractive index of the measuring object 31 arranged above the structured metal layer 44 is n (unb). The structured metal layer 44 allows, for example, a plasmon-polariton effect, as has already been described above. The resonance wavelengths of a resulting transmission spectrum depend on the refractive index of the measurement object n (unb), the refractive index of the metal n (Me), the metal layer thickness d and the refractive index n (D) of the dielectric material in the openings.

For a given integrated sensor element 35, n (Me), n (D) and the metal layer thickness d are given and are constant. Only the refractive index n (unb) of the environment or the measuring object 31 is variable. If the refractive index n (b) of a reference measurement object changes to n (unb), then the transmission curve shifts, as shown in FIG. In the case shown here, this means that in monochromatic illumination with a predefined wavelength of light, e.g. λ (l), the resulting transmission T (λ) becomes smaller.

When calibrating the refractometer system, the photocurrent of the photodiode 36 can first be measured with a reference measurement object having a known refractive index n (b) and corresponding illumination with a monochromatic wavelength λ (l). Subsequently, the measurement is made with a test object 31 to be examined with refractive index n (unb). The difference of the photocurrent can be converted into the desired refractive index n (unb). According to the above-cited publication "Defective evanescent wave model for enhanced and suppressed optical transmission through subwavelength hole arrays", a transmission function measured by a lens with numerical aperture NA can be calculated by multiplying a first surface modulation function Ai (λ), an intrinsic transmission function D _H (λ) by a micro-aperture, a second surface modulation function λ ₂ (λ) and a function f _c (λ) representing a portion of the transmitted power through the layer structure The transmission function D _c (λ) can then be written as

TC (λ) = A \ (λ; nϊ; P \, d \) TH (λ; nH; d; t) A2 (λ n2; P2; d2) fC (λ, NA; P2; d2);

wherein, as described above, two measurements, once for known refractive index nl and once for unknown refractive index nl, allows the calculation of the unknown refractive index.

The simplest form of sub-wavelength structure 84 is a circular opening. However, to achieve a greater resonant effect, it is also possible to use other shapes for a microstructure 84, such as e.g. so-called split-ring resonators, as they are shown by way of example in a plan view of a structured metal layer in FIG. 8.

In CMOS technology, multiple photodiodes 36 can be placed on a chip and covered in a process with subwavelength structures that can have different shapes. As already mentioned, the geometry of the microstructures 84 of the structured metal layers has a very strong influence on the resulting resonance wavelengths. 9 shows an exemplary embodiment of an integrated sensor chip 90 which has a plurality of sensor elements 35-i (i = 1,..., N). Each of the sensor elements 35-i (i = 1,..., N) is adapted to a different exposure wavelength λ (i) (i = 1,..., N). That is, each photodiode 36-i (i = 1, ..., n) is associated with its own layer structure 37-i (i = 1, ..., n), each for a wavelength λ (i) (i = l, ..., n) is optimized. With the integrated sensor 90, it is possible to simultaneously measure the refractive index sought at several wavelengths λ (i) (i = l, ..., n). In the sensor design, it can be freely defined how large the number n of the measuring points and the covered spectral ranges should be exactly.

In CMOS technology, such a measuring chip can be mass-produced very inexpensively, even with the necessary electronics 40 for the signal processing, which is located in the device for determining the refractive index of the test object. For some biological applications in which a sterilization is necessary, such a sensor chip can for example be installed in a plug-in socket, so that it can be easily replaced after a measurement against a new sensor chip.

FIG. 10 shows a schematic structure of a refractometer system based on the sensor chip 90 shown in FIG. 9.

Light 33 from one or more monochromatic light sources 32 reaches the chip 90, which has at least one sensor element 35 with opto-electronic sensor 36 and sub-wavelength-structured metal layers 44. After amplification of an output signal of the optoelectronic sensor, signal processing takes place, which can also be integrated in the sensor chip itself by evaluation electronics 40. As a result, a desired refractive index n (object) can be determined.

For the structure shown in FIG. 10, no additional optical elements, such as a prism or micro-wave, are used. needed in conventional refractometers. The structure shown in Fig. 10 also has no mechanical moving elements. The light source 32 may also be integrated into the sensor chip 90 according to embodiments, so that external illumination is no longer necessary. There are already LEDs that can be manufactured within the framework of a CMOS-compatible process - simultaneously with the opto-electronic sensor 36 and the evaluation electronics 40. The refractive index of solids can be determined with the inventive concept, if the surface of the solid is well polished, so that between the material to be examined 31 and the measuring chip 35 is a good optical contact.

An integrated sensor element or an integrated sensor chip 35, 90 can be produced for example with a CMOS technology. Such technology has high accuracy and repeatability and is well suited for mass production. Thus, relatively low prices for end products can be achieved, whereby disposable refractometers can be realized. The integrated sensor chip can be easily integrated into a manufacturing process, so that its surface always has an optical contact with a measured object. Therefore, embodiments of the present invention also provide a means for dynamically analyzing refractive index changes.

Finally, it should be pointed out that it is not absolutely necessary for metal layers to be used to define the layer structure, regardless of whether the layer structure according to the above exemplary embodiments is a photonic crystal or a plasmon-polariton structure , Rather, instead of or in addition to the structured metal layers shown there, a structured polysilicon layer can also be used. FIG. 14 shows, like FIG. 3, an exemplary embodiment of an integrated device produced in CMOS technology. ruled sensor element. As can be seen, the same layers as in FIG. 3 exist according to this CMOS technique. However, a polysilicon layer 700 is arranged between the lowermost metal layer 44-1 and the semiconductor substrate 38. According to one exemplary embodiment of the present invention, it is now also possible to form an integrated sensor element by combining the optoelectronic sensor 36 with a layer structure which is obtained not only by the metal layers but also by structuring of the polysilicon layer 700, ie in combination with a structuring of one or more of the metal layers 44-1 to 44-4. Of course, according to alternative embodiments, a combination of multiple polysilicon layers would also be possible if such layers are present in the technology used. As can be seen, the polysilicon layer 700 rests directly on the substrate 38. Of course there are alternatives for this. As with the metal layers 44, the polysilicon layer 700 could also be farther from the semiconductor substrate 38, if allowed by a respective CMOS process. It would also be possible to form a filter structure by structuring only one polysilicon layer. Furthermore, instead of the use of polysilicon, it would also be possible to use other polycrystalline semiconductor material. The patterning of layer 700 to obtain a suitable refractive index determining effect as shown above may be performed in the same manner and shapes as described above with respect to the metal layers.

Finally, it should be mentioned that the above-described CMOS metal layers, such as, for example, the CMOS metal layer, can have electrical connections or interconnects in addition to the openings for forming the layer structures, the electrical connections between circuit elements (eg transistors) of the manufacture integrated sensor element. This also applies to the post shown above. silicon layer. Also, the laterally spaced apart from the actual opto-electronic sensors can be used to form interconnects or components.

Finally, it should be understood that the present invention is not limited to the particular components described or the illustrative procedures, as these components and methods may vary. The terms used herein are intended only to describe particular embodiments and are not intended to be limiting. When the singular or indefinite articles are used in the specification and claims, these also refer to the majority of these elements unless the context as a whole clearly indicates otherwise. The same applies in the opposite direction.

Claims

claims

A system (30) for determining a refractive index (n (object)) of a measuring object (31), having the following features:

a light source (32) for emitting light (33) of a predefined wavelength;

an integrated sensor element (35) with

an opto-electronic sensor (36), and

a layer structure (37) having at least one structured layer (44; 700) of metal or polycrystalline semiconductor material,

wherein the opto-electronic sensor (36) and the layer structure (37) are integrated together on a semiconductor substrate (38);

a device (39) for holding the measurement object (31) between the integrated sensor element (35) and the light source (32), so that the layer structure (37) is arranged between the measurement object (31) and the optoelectronic sensor (36) and in that an output signal of the opto-electronic sensor (36) changes to the light (33) having the predefined wavelength as a function of the refractive index (n (object)) of the measurement object (31); and

a device (40) for determining the refractive index (n (object)) of the measurement object (31) based on the output signal of the optoelectronic sensor (36).

A system according to claim 1, wherein the means (39) for holding is disposed on a surface of the integrated sensor element (35).

A system according to claim 1 or 2, wherein the means (39) for holding together with the integrated sensor element (36) is integrated on the semiconductor substrate (38).

A system according to any one of the preceding claims, wherein the means (39) for holding comprises a frame (49) for holding a liquid as a measurement object (31) on a surface of the integrated sensor element (35).

A system according to any preceding claim, wherein at least one metal structured layer (44) has a subwavelength aperture (118), the aperture (118) being surrounded by periodically arranged grooves around the aperture, the dimensions and distances from each other which are suitable for generating a plasmon-polariton resonance effect for the predetermined wavelength range in the at least one structured metal layer.

6. System according to claim 5, wherein the opening (118) and the grooves are each rotationally symmetrical.

7. A system according to claim 5, wherein the opening (118) is formed in a line shape and has a width smaller than the predefined wavelength, and in which the grooves extend at least approximately parallel to the opening.

8. A system according to any one of claims 1 to 4, wherein the at least one patterned layer (44/700) of metal or polycrystalline semiconductor material has a two-dimensional periodic array of sub-wavelength apertures (118).

9. System according to one of the preceding claims, wherein the opto-electronic sensor (36) in a Ab- Stand (d) of the layer structure (37) is arranged, which is smaller than the predefined wavelength.

A system according to any one of claims 1 to 4, wherein the layered structure (37) comprises at least one photonic crystal (82).

11. The system according to claim 10, wherein the layer structure (37) consists of an array of photonic

Crystals is formed around a layer structure facing surface of the opto-electronic sensor

(36) to be fully covered.

12. The system of claim 10, wherein the at least one photonic crystal is formed from a layer stack of dielectric layers and structured layers of metal and / or polycrystalline semiconductor material.

A system according to any one of claims 10 to 12, wherein the patterned layers (44; 700) of metal and / or polycrystalline semiconductor material of the layer stack comprise microelements (84) whose pitches and dimensions are of the order of magnitude near the opto electronic sensor (36) to effect a spectral selection.

The system of claim 13, wherein the dimensions and spacings of the microelements (84) are of the order of magnitude less than the predefined wavelength.

The system of claim 14, wherein the magnitude of the dimensions and spacing of the microelements (84) is in a range between 0.05 and 5 times the predefined wavelength.

16. System according to any one of claims 13 to 15, wherein the microelements are designed as split-ring resonators.

The system of any one of claims 10 to 16, wherein the patterned layers (44; 700) of metal and / or polycrystalline semiconductor material of the photonic crystal (82) are connected to metal vias to obtain three-dimensional microelements of the photonic crystal.

18. System according to one of the preceding claims, wherein the opto-electronic sensor is a PN junction sensor.

19. System according to one of the preceding claims, wherein the opto-electronic sensor is a photodiode.

20. System according to any one of the preceding claims, wherein the means (40) for determining the refractive index comprises an evaluation, which is integrated together with the integrated sensor element (35) on the semiconductor substrate (38).

21. System according to one of the preceding claims, wherein the 'integrated sensor element (35) is manufactured in CMOS technology.

22. A method for determining a refractive index of a measuring object (31), comprising the following steps:

Emitting light (33) of a predefined wavelength;

Coupling the test object (31) with an integrated sensor element (35) with an opto-electronic sensor (36), and a layer structure (37) with fewer at least one structured layer (44; 700) of metal and / or polycrystalline semiconductor material, so that the layer structure (37) is arranged between and the measurement object (31) and the optoelectronic sensor (36), and so that a Output of the optoelectronic sensor (36) due to the light (33) with the predefined wavelength depending on the refractive index (n (object)) of the measuring object (31) changes; and

Determining the refractive index (n (object)) of the measurement object (31) based on the output signal of the optoelectronic sensor (36).