WO2001086723A1

WO2001086723A1 - Multiwavelength optical microsensor, digital spectrophotometer and polychromator

Info

Publication number: WO2001086723A1
Application number: PCT/CH2001/000295
Authority: WO
Inventors: Michel Martin-Bouyer; Jean-Michel Thenard; Thierry Aubry; Hervé MUGNIER; Claude Fachinger; Christophe Turnar
Original assignee: Eyetronic S.A.
Priority date: 2000-05-12
Filing date: 2001-05-14
Publication date: 2001-11-15
Also published as: AU5458101A

Abstract

The invention concerns a multiwavelength matrix optical microsensor comprising a set of sensing elements (1) and at least one signal conditioner (20). The sensing elements (11) comprise electronic junctions produced by assembling structures, said structures comprising doped materials. The microsensor further comprises at least two sub-sets (10) of sensing elements, each of the sub-sets having a specific spectral response. The specific spectral response is obtained by modifying the machining depth of the sensing elements when the device is being manufactured.

Description

MULTI-WAVELENGTH OPTICAL MICROSENSOR,

DIGITAL SPECTROPHOTOMETER AND POLYCHROMATOR

Technical area

The present invention relates to a multi-wavelength matrix optical microsensor comprising a set of detector elements and at least one signal conditioner, the detector elements comprising electronic junctions produced by assembling structures, said structures comprising doped materials, the microsensor comprising at least two subsets of detector elements, each of the subsets having a specific spectral response, the specific spectral response being obtained by modification of the intrinsic characteristics of the detector elements during the production of the device.

It also relates to a polychromator and in particular a polychromator with integrated electronics. It further relates to a corresponding digital spectrophotometer. It has applications in photonic spectral analysis and differential photonic detection.

Prior art

Conventional optical detectors are made up of elements used to convert a stream of photons into electric current and / or electric charge to produce a signal. The intensity of the current produced or of the charge generated depends on many parameters and mainly on the intrinsic characteristics of the photosensitive element and on the spectral content of the light flux. In order to characterize a type of detector or a particular detector, we mainly refer to its spectral response curve giving its characteristic response curve and / or its sensitivity as a function of the frequency of the incident light radiation. Optical vacuum detectors, of the electron photomultiplier type, generally do not allow a uniform response between the near ultraviolet (190 nanometers) and the near infrared (1.3 micrometer). It is however possible to remedy this drawback and to partially linearize the response curve of the electron photomultipliers by carrying out physicochemical processing of the photocathode and / or by performing downstream corrections during signal processing. These devices are mainly used in mechanical scroll monochromators.

More recently, solid detectors have appeared, making it possible to simply produce matrix structures comprising a multitude of individual detector elements of reduced size. These structures are generally one-dimensional (row), or two-dimensional (rows and columns). Along a line and / or a column are distributed a set of individual detector elements. These matrix structures are produced from a wafer of generally semiconductor material. By way of example, mention may be made of detectors of the photodiode on silicon type used in what is known as polychromators or optical imagers. In these applications, optical filtering is necessary between the light source and the detector in order to select and improve the spectral response of the detectors. This filtering can be obtained by a surface treatment of the detector making it possible to attenuate or suppress the response of a block of photosensitive elements for certain areas of the spectrum. This surface treatment, which generally affects a block of detector elements, leads to a significant attenuation in the bandwidth which limits the dynamic range of the detector.

An optical imager of this type is described in American patent application US-A-4,438,455. This imager comprises three layers each sensitive to a different wavelength range, for example located in green, red and blue. The layers are practically transparent to other wavelengths.

The international patent application WO 99-19912 describes a device similar to the previous one, using the properties of thin layers as a filter.

Detectors of the charge transfer type also make it possible to produce photosensitive matrix structures.

The signal generated by each detector element in a matrix structure must be conditioned in an electronic stage called "driver" or conditioner. In common applications, the output of the conditioner is connected to an analog / digital circuit which can be used in a computer device for further signal processing. Synchronization signals with the conditioner and the converter make it possible to correlate a measured value to a particular detector element of the matrix structure.

These devices produced from semiconductors include electronic junctions produced by assembling structures comprising doped materials. Doping makes it possible to produce structures conventionally called N or P depending on the dopant. Conventionally, silicon is used as a semiconductor and its oxides as an insulator. However, depending on the characteristics sought, other materials can be used, for example germanium or gallium arsenide.

These devices are however complex because the detectors, conditioners and analog / digital converters are generally distinct and separate structures. Consequently, the maximum frequency of use is limited by the propagation times and the signal is degraded during the transmission between the different circuits. In addition, the surface treatment for producing an optical surface filter does not make it possible to obtain reproducible devices and reduces the sensitivity by the attenuation which it provides in the passband.

Another disadvantage of these detectors comes from the fact that they must be made specifically for the application in which they are intended. Indeed, each layer has physical characteristics defined during manufacture and cannot be modified. In addition, the reading of each photodiode must be done in an order imposed by the driver. This order cannot be changed. This implies that it is not possible to modify the response of the sensor according to the input signal. Some wavelengths may not be detected because their intensity is too low compared to the intensity of other wavelengths.

Statement of the invention

The present invention proposes to resolve these drawbacks and to increase the precision of the results of the measurements in an optical microsensor consisting of a polychromator or a small imager in which the device of sensitive elements is integrated. To this end, the multiwavelength optical microsensor comprises a set of detector elements and at least one signal conditioner, the detector elements comprising electronic junctions produced by assembling structures comprising doped materials. It also proposes to produce a sensor which can be used in practically any application by making only modifications of software which manages the measurements carried out by the sensor.

The objects of the invention are achieved by a microsensor as defined in the preamble and characterized in that the modification of the intrinsic characteristics is obtained by modification of the junction depth. According to a preferred embodiment, at least one subset of detector elements is made up of "blind" detector elements by masking.

According to a first embodiment, the detector elements of the same sub-assembly are grouped in the same area of the microsensor.

According to a second embodiment, the detector elements of several sub-assemblies are distributed periodically in the microsensor.

According to an advantageous embodiment, the conditioner is arranged to allow to choose individually, which detector elements are used to carry out a measurement and which detector elements are not used. It can also be arranged to measure the intensity of the detector elements in any order, this order being able to be chosen by a user. Finally, it can be arranged to individually determine the measurement time for each detector element.

According to a particular embodiment of the invention, the conditioner is arranged to linearize the spectral response of the microsensor.

According to a preferred embodiment of the invention, the microsensor further comprises at least one analog / digital converter. It can also include digital computing means.

According to a particularly advantageous embodiment, the microsensor comprises at least two groups of detector elements, the calculation means being arranged to carry out operations on the basis of the results of the measurements of these groups of detector elements. These operations can be at least one of the following operations: addition, subtraction, multiplication, division, Fourier transform, use of a random or pseudo-random function. Advantageously, the detector elements, the conditioner and the calculation means are arranged on the same support.

The microsensor advantageously comprises a connector arranged to transmit signals to a data processing device.

This microsensor can be incorporated into a polychromator.

The object of the invention is also achieved by a polychromator characterized in that it comprises a microsensor according to the present invention, to form an electronic eye.

Finally, the object of the invention is also achieved by a polychromator as defined above, characterized in that it comprises a microcomputer having predetermined calculation functions discriminating for the recognition of colors.

According to the invention, the microsensor comprises at least two subsets of detector elements, each of the subsets having a specific spectral response, the specific spectral response being obtained by modification of the intrinsic characteristics of the detector elements during the production of the device.

The term "specific spectral response" means that the spectral responses of the various subsets are different from each other, certain specific spectral zones being able to overlap or not with equal sensitivity or not.

In various embodiments of the invention, the following means can be used alone or according to all their possible technical combinations, are used: the modification of the intrinsic characteristics is obtained by modification of the doping of the materials, the modification of the intrinsic characteristics is obtained by modification of the junction depth, - at least one subset consists of detector elements

"blind" obtained by masking, the matrix microsensor is one-dimensional, the matrix microsensor is produced by stacking layers of detector elements, - the matrix microsensor is therefore three-dimensional, the matrix microsensor comprises two subsets of elements detectors, the matrix microsensor comprises three subsets of detector elements, - the matrix microsensor comprises more than three subsets of detector elements, one subset has a spectral response limited to ultraviolet radiation, the spectral response limited to radiation ultraviolet is approximately between X and Y, a subset has a spectral response limited to visible radiation, the spectral response limited to visible radiation is approximately between X and Y, - a subset has a limited response to infrared , the spectral response limited to infrared is approximately between X and Y, a penny s-set has a spectral response limited to green, the spectral response limited to green is approximately between X and Y, a subset has a spectral response limited to red, the spectral response limited to red is approximately between X and Y, a subset has a spectral response limited to blue, the spectral response limited to blue is approximately between X and Y, the detector elements of the same subset are grouped together in the same area of the microsensor, the detector elements of several sub-assemblies are distributed in the microsensor, - the detector elements of several sub-assemblies are distributed periodically in the microsensor, the microsensor further comprises at least one analog / digital, the microsensor further comprises digital calculation means, - the digital calculation means are a microprocessor, the digital calculation means are a digital signal processing unit (DSP), the microsensor comprises a storage unit making it possible to store a signal processing program, the storage unit comprises at least one memory selected from read-only memories, saved live memories, electrically programmable memories that can be erased or not, the microsensor is incorporated in a polychromator.

The present invention also relates to a digital spectrometer. According to the invention, the digital spectrometer includes a microsensor according to one or more of the preceding characteristics, possibly combined.

Thus, unlike the state of the art in which filtering is carried out between the light source and the detector or on the surface of the detector, the present invention makes it possible to obtain specific spectral responses by modifying the intrinsic and therefore internal properties of the elements. detectors. The microsensor of the invention allows spectrophotometry devices to be produced simply. It can for example be used in fluorimeters, "tasters" of food products, drinks or fruits for example, "electronic eye" reflectometers for color recognition.

Brief description of the drawings

The present invention will be better understood on reading examples of implementation and with reference to the drawings in which:

FIG. 1 represents a distribution of sub-sets of detector elements by grouping;

- Figure 2 shows a first example of periodic distribution of the subsets of detector elements;

FIG. 3 represents a second example of periodic distribution of sub-assemblies of detector elements;

FIG. 4 represents a third example of periodic distribution of sub-assemblies of detector elements;

FIG. 5 schematically represents a microsensor comprising photosensitive elements, an analog / digital conversion arrangement and a digital calculation means;

Figure 6 is a schematic sectional view of the sensor element of Figure 1;

Figure 7 is a schematic sectional view of the sensor element of Figure 2; Figures 8 to 11 illustrate four embodiments of microsensors according to the invention.

Best Ways to Carry Out the Invention

In FIG. 1, a one-dimensional matrix detector 1 comprising a line of detector elements 10 is shown. A conditioner 20 makes it possible to condition and select a particular element, for example 11, of the detector from among all of the elements. The conditioner is a circuit comprising for example a serializing multiplexer. For reasons of simplification, we simply consider here four, S = 4, sub-sets of detector elements corresponding to a “blind” sub-set by masking and to three specific spectral bands and for example, infrared, visible and the ultraviolet. The first subset has L> 0 detector elements AL..AL. The second subset has M> 0 detector elements B1 ... BM. The third subset includes N> 0 detector elements C1 ... CN. The fourth subset has P> 0 detector elements D1 ... DP. In this distribution, the detector elements of the same sub-assembly are grouped together in the same area of the microsensor. The blind elements allow a measurement of the device's own noise. The elements are made "blind" by surface treatment producing a layer which does not allow the transmission of light waves.

In FIG. 2, a one-dimensional matrix detector comprising a line of detector elements is shown. For reasons of simplification, we simply consider here three subsets, S = 3, of detector elements corresponding to three specific spectral bands and for example red, blue, green. The distribution is periodic and for each elementary period, only one, n = 1, detector element per subset is produced. The number of elements per period is therefore nx S = 3. FIG. 3 represents a one-dimensional matrix detector comprising a line of detector elements. For reasons of simplification, we simply consider here three subsets, S = 3, of detector elements corresponding to three specific spectral bands and for example red, blue, green. The distribution is periodic and for each period, i> 0 detector elements of the first subset A, j> 0 detector elements of the second subset B, k> 0 detector elements of the third subset C, are produced. The number of elements per period is therefore i + j + k. The values of i, j, k can be any relative to one another, but in a preferred embodiment we will take i = j = k. However, in the case where the sensitivity of the detector elements of a first subset is lower than that of another subset, it is envisaged to increase the number of elements for this first subset in the period.

In the case of a microsensor comprising several lines in parallel and therefore forming a row x column matrix, the preceding arrangements may be combined according to all the technically possible possibilities. In a preferred embodiment, all the rows of a column row microsensor have the same distribution of the sub-assemblies. It is however envisaged to shift cyclically from one line to the next the sub-assemblies as represented by FIG. 4, where the line x column conditioner makes it possible to select the element.

FIG. 5 diagrammatically represents a microsensor 1 comprising an analog / digital converter 30 and a digital calculation means 40. The control orders and the results of the calculations are exchanged on an interface 41. The microsensor comprises its conditioner 20 which makes it possible to select from the row x column matrix 13 of all the detector elements, an element 10 Ci, j. The interface is connected to a computer, micro- computer or any other viewing device. However, it is envisaged that a network or modem type connection means will be interposed.

Figure 6 schematically illustrates the device of Figure 1. It comprises a support 50 of a semiconductor material such as silicon. The detector elements 10, which are photodiodes, are formed by holes in the support. These holes have substantially the shape of rectangular parallelepipeds. The surface of these holes, that is to say the product of their length and their width, determines the sensitivity of the photodiode. The depth determines the wavelength range to which the photodiode will be sensitive.

These holes are produced according to various methods well known to those skilled in the art, in particular by machining.

In the example illustrated in FIG. 6, a group of photodiode D1-DL is sensitive to a wavelength range, for example located in the infrared. Photodiodes B1-BL are sensitive to visible light and diodes A1-AL are sensitive to ultraviolet.

In the example illustrated in FIG. 7, the detector elements 10 are distributed in a similar manner to the distribution in FIG. 2.

FIG. 8 illustrates an embodiment in which the support 50 comprises a group of detector elements 10 produced in the form of a strip 51 of photodiodes and a conditioner 20.

As explained with reference to FIG. 4, the conditioner 20 can address any photodiode of the array 51, in any order. This is particularly important for various reasons. On the one hand, this makes it possible to select, among all the photodiodes available, those which are sensitive to the wavelengths which it is desired to detect. This allows the same detector to be used for practically any application, whether the wavelengths sought are in the ultraviolet, in the infrared or in any frequency.

This also makes it possible to select, in a light spectrum, the frequency range in which detection is desired, the photodiodes sensitive to other wavelengths not being activated.

On the other hand, for each photodiode, it is possible to carry out a measurement for a time determined individually. This makes it possible to process the signal in the detector in order to increase the intensity of the response in the areas of spectrum having a low emission intensity and to decrease the response in the areas with high emission intensity. This makes it possible to linearize the signal and thus optimize the sensitivity of the microsensor.

FIG. 9 illustrates an embodiment of a sensor containing two arrays 51 of photodiodes associated with the conditioner 20. The existence of the two arrays makes it possible to carry out differential measurements. This finds particular application during the analysis of a beam reflected on a network. The reflection creates harmonics which add to the original signal and distort the measurement. By making a differential measurement between the direct beam received by one of the photodiode bars and the beam reflected on the other photodiode bar, it is possible to eliminate second order harmonics. This significantly increases the rejection rate of the sensor.

FIG. 10 illustrates an embodiment in which the support 50 containing the two photodiode arrays 51 also contains an analog / digital converter 30. This makes it possible to connect the support, via an appropriate connector, to a computer such than a computer that can process the analyzed signals. The integration of different components allow a particularly simple implementation of the device.

FIG. 11 illustrates an alternative embodiment in which the support also contains a calculation means 40. This makes it possible to perform a certain number of operations on the signals coming from the two photodiode arrays 51. These operations are in particular addition, subtraction, division and multiplication. They can also be a Fourrier transform or a random or pseudo-random function. This is particularly interesting because such a function makes optical encryption extremely difficult to decode. Decoding can be carried out by means of a key which can be contained in a single sensor, or in several, which makes it possible to decode images transmitted for example in the form of an electronic file.

The examples given are merely illustrative and not limiting. Instead of a single dimension, row, and three or four subsets, a two-dimensional device row x column and two or more of four subsets can be made. The more energetic ultraviolet photon is absorbed by the deepest holes and the less energetic infrared photon by the shallow holes, producing the same response in the sensitive element object of this invention as a three-dimensional detector.

It is also envisaged that the modification of the intrinsic characteristics of the various detectors is substantially regular along a line or line x column in order to obtain a device making it possible to obtain a finer spectral resolution. For example, when the intrinsic characteristics are modified by action on doping, the dopant level can vary linearly or according to another curve, along the device and for example by tilting the silicon wafer relative to a source projecting a dopant. . In the event that the spectral responses partially overlap, further processing of the signal makes it possible to eliminate the overlapping zones step by step and to obtain values according to the fine spectral resolution. For example if a first subset is sensitive between 400 nm and 600 nm, a second between 400 nm and 500 nm, the differential processing of the two signals makes it possible to obtain a corrected value for the band between 500 nm and 600 nm.

Claims

1. Multi-wavelength matrix optical microsensor comprising a set of detector elements (1) and at least one signal conditioner (20), the detector elements (11) comprising electronic junctions produced by assembling structures, said structures comprising doped materials, the microsensor comprising at least two subsets (10) of detector elements, each of the subsets having a specific spectral response, the specific spectral response being obtained by modification of the intrinsic characteristics of the detector elements during the production of the device, characterized in that the modification of the intrinsic characteristics is obtained by modification of the junction depth.

2. A microsensor according to claim 1, characterized in that at least one sub-assembly (10) consists of “blind” detector elements by masking.

3. Microsensor according to any one of the preceding claims, characterized in that the detector elements (11) of the same subassembly are grouped in the same area of the microsensor (1).

4. Microsensor according to any one of the preceding claims, characterized in that the detector elements (11) of several subassemblies (10) are distributed periodically in the microsensor (1).

5. A microsensor according to claim 1, characterized in that the conditioner (20) is arranged to allow to choose individually, which detector elements (11) are used to carry out a measurement and which detector elements (11) are not used .

6. Microsensor according to claim 1, characterized in that the conditioner (20) is arranged to measure the intensity received by the detector elements (11) in any order, and in that this order can be chosen by a user.

7. A microsensor according to claim 1, characterized in that the conditioner (20) is arranged to individually determine the measurement time for each detector element (11).

8. Microsensor according to claims 5 to 7, characterized in that the conditioner (20) is arranged to linearize its spectral response.

9. Microsensor according to any one of the preceding claims, characterized in that it also comprises at least one analog / digital converter (30).

10. Microsensor according to claim 9, characterized in that it further comprises digital calculation means (40).

11. Microsensor according to claim 10, characterized in that it comprises at least two groups (51) of detector elements and in that the calculation means (40) are arranged to carry out operations on the basis of the results of the measurements of these groups (51) of detector elements.

12. A microsensor according to claim 11, characterized in that said operations are at least one of the following operations: addition, subtraction, multiplication, division, Fourier transform, use of a random or pseudo-random function.

13. A microsensor according to claim 10, characterized in that the detector elements (11), the conditioner (20) and the calculation means (40) are arranged on the same support (50).

14. The microsensor according to claim 1, characterized in that it comprises a connector arranged to transmit signals to a data processing device.

15. Microsensor according to any one of the preceding claims, characterized in that it is incorporated in a polychromator.

16. Polychromator characterized in that it comprises a microsensor (1) according to any one of the preceding claims to form an electronic eye.

17. Polychromator with integrated electronics characterized in that it comprises a microcomputer having predetermined calculation functions discriminating for color recognition.