Spectrometer

Abstract

According to an example aspect of the present invention, there is provided a spectrometer comprising a bulk inorganic semiconductor substrate and a dielectric layer directly on the semiconductor substrate, a two-dimensional semimetal layer partly directly on the semiconductor substrate and partly directly on the dielectric layer, a first electrode electrically coupled to the two-dimensional semimetal layer and a second electrode coupled to the semiconductor substrate, and a tuneable voltage source arranged to provide a selectable voltage between the first electrode and the second electrode, and readout circuitry configured to measure a physical response of the spectrometer to incident radiation.

Description

SPECTROMETERFIELD

[0001] The present disclosure relates to the field of spectrometry.BACKGROUND

[0002] A spectrometer is a device used to determine a spectrum of radiation, usually electromagnetic radiation, or at least certain features of this spectrum. For example, it may be of interest to discover, if the spectrum comprises emission lines associated with certain chemical compounds or elements which are of interest.

[0003] Spectrometers typically require dispersive optical components, such as prisms or gratings, and other movable components, which make these spectrometers bulky and expensive.SUMMARY

[0004] According to some aspects, there is provided the subject-matter of the independent claims. Some embodiments are defined in the dependent claims..

[0005] According to a first aspect of the present disclosure, there is provided a spectrometer comprising a bulk inorganic semiconductor substrate and a dielectric layer directly on the semiconductor substrate, a two-dimensional semimetal layer partly directly on the semiconductor substrate and partly directly on the dielectric layer, a first electrode electrically coupled to the two-dimensional semimetal layer and a second electrode coupled to the semiconductor substrate, and a tuneable voltage source arranged to provide a selectable voltage between the first electrode and the second electrode, and readout circuitry configured to measure a physical response of the spectrometer to incident radiation.

[0006] According to a second aspect of the present disclosure, there is provided an integrated circuit comprising a spectrometer according to the first aspect, wherein the semiconductor substrate is a substrate of the integrated circuit, the integrated circuit comprising at least one further device in addition to the spectrometer.

[0007] According to a third aspect of the present disclosure, there is provided a spectrometer comprising a sensing element the sensing element having a voltage- controllable photoresponse which is further dependent on one or more wavelength of incident radiation. Some embodiments of this aspect further comprise a readout circuitry configured to measure a photoresponse of the sensing element to incident radiation, and at least one tuneable voltage source arranged to provide at least one selectable voltage between electrodes of the sensing element.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIGURE 1A illustrates an example system in accordance with at least some embodiments of the present invention;

[0009] FIGURE IB illustrates a process in accordance with at least some embodiments of the present invention;

[0010] FIGURE 2A illustrates a spectrometer in accordance with at least some embodiments of the present invention;

[0011] FIGURE 2B illustrates a spectrometer in accordance with at least some embodiments of the present invention;

[0012] FIGURE 2C illustrates a spectrometer in accordance with at least some embodiments of the present invention;

[0013] FIGURE 2D illustrates a spectrometer in accordance with at least some embodiments of the present invention, and

[0014] FIGURE 3 illustrates an example apparatus capable of supporting at least some embodiments of the present invention.EMBODIMENTS

[0015] Herein is described a tuneable spectrometer which may be manufactured using complementary metal-oxide semiconductor, CMOS, processes. A mixed-dimension heterostructure junction, combining a two-dimensional semimetal layer with a three- dimensional bulk semiconductor material, is set to a selectable voltage and a physical response of the device, in the form of a photocurrent, is measured using readout circuitry electrically coupled to the heterostructure materials. A spectrum of incident radiation may be obtained by using plural values of the selectable voltage and a spectral responsivity matrix, which associates selected voltage and photocurrent values with incident-radiation wavelengths.

[0016] FIGURE 1A illustrates an example system in accordance with at least some embodiments of the present invention. Here a spectrometer 101 is configured with selectable voltages by setting potential differences between each of the electrodes Vg and Vd and the electrical ground. Then incident radiation 110 causes a photocurrent Iph in a heterostructure of spectrometer 101.

[0017] A spectral responsivity matrix R may be defined for spectrometer 101, such that the spectral responsivity matrix describes the photocurrent Iph responsivity of the spectrometer to monochromatic light of unit power spectral density when the selected voltage(s) and wavelength X of incident radiation are provided as inputs. In practice, spectral responsivity matrix R may be a matrix, where the photocurrent Iph response is a value of a matrix element and wavelength X and voltage values are indices of the matrix. Alternatively, spectral responsivity matrix R may be approximated using an experimentally defined function, which takes as inputs the wavelength X and voltage values and produces the photocurrent Iph response as output. For example, the spectral responsivity matrix R may be determined prior to the use of spectrometer 101, in a calibration process using selectable wavelengths X, such as monochromatic incident radiation of selectable wavelength, with different selected voltage values to measure the response of the spectrometer under different operating conditions. In detail, the matrix element values of spectral responsivity matrix R may be measured by going through each combination of selected voltage and incidentradiation wavelength. Once the responsivity of spectrometer 101 is known, it may be used using a known voltage value, and a measured photocurrent Iph response to determine, based on the spectral responsivity matrix R, the spectral content of incident radiation 110. In some embodiments, the measuring of spectral responsivity matrix R may be performed once for a spectrometer type and applied to spectrometers of the same type as an initial calibration.

[0018] Alternatively to the system of FIGURE 1A, an example system in accordance with at least some embodiments of the present invention has, instead of two voltage inputs Vg and Vd, three voltage inputs Vg, Vg’ and Vd. These enable provision of three selectable voltage controls to a sensing element of spectrometer 101, while the two voltage inputs of FIGURE 1A provide two selectable voltage controls to a sensing element of spectrometer 101.

[0019] FIGURE IB illustrates a process in accordance with at least some embodiments of the present invention. The process begins in phase 120. In phase 120, in a calibration process, a photocurrent Iph response of the spectrometer is measured, using incident radiation of known wavelength X and known power, and applying known selected voltage values Vd and Vg, or Vg, Vg’, and Vd. Once the photocurrent has been measured, processing advances to phase 125, where it is determined, if the photocurrent has been measured for all planned wavelength X and voltage value combinations, in other words, if spectral responsivity matrix R has been determined. If not, processing advances to phase 130, where either the incident wavelength, or voltage value, is modified, and processing advances back to phase 120 where the photocurrent Iph response of the spectrometer is measured for the new combination of wavelength X and voltage value.

[0020] Once it is determined in phase 125 that the photocurrent has been measured for all planned known wavelength X and voltage value combinations, calibration of the spectrometer is complete, and its spectral responsivity matrix R is known. Processing then advances to phase 140 where the spectrometer is used in a live setting with incident radiation of unknown spectral content. The photocurrent Iph is measured in this phase using known selected voltages, and the result is used in phase 150 along with the calibration information established during phases 120, 125 and 130 to deduce what the spectral content of the incident radiation is. The calibration information corresponds to spectral responsivity matrixR discussed herein above. In some cases, phase 140 comprises measuring the photocurrent Iph with plural selected voltage values, for example the same set of voltage values as were used in determining spectral responsivity matrix R, to obtain a set of measured photocurrent values. In other words, to determine features of a spectrum of incident radiation, a sweep of selected voltage values may be made to obtain the photocurrent Iph at several values of the voltage, enabling determination of the spectrum of incident radiation, or at least features of the spectrum.

[0021] It is of note, that there may be a significant elapsed time between phase 125 and phase 140, for example, the calibration process of phases 120, 125 and 130 may be performed at manufacture and / or at infrequent intervals, such as annually.

[0022] The operation principle of the herein described spectrometer uses a tuneable heterojunction, which exhibits a highly controllable wavelength-dependent optoelectronic response. Some embodiments further use a reconstructive algorithm to reconstruct the spectrum from the measured photocurrent data, while some embodiments use machinelearning based computational techniques to directly extract relevant spectral information (e.g., the present or absence of particular features in the spectrum of the incident light). This differs from previously demonstrated spectrometers, which mainly rely on dispersive components, such as bulky diffraction gratings. Thus, the herein described miniaturized spectrometers offer an extensively simplified and cost-effective approach for on-chip spectroscopy, by being significantly smaller in dimensions and substantially better in performance than current state-of-the-art spectrometers.

[0023] Spectrometers are widely used radiation characterization tools. Spectroscopic analyses provide fundamental and necessary information to identify and quantify samples and materials for various industrial and research applications, for example. A typical state- of-the-art spectrometer based on existing designs uses several mechanical and optical components, such as diffraction gratings and mirrors to resolve light into its constituent colours for spectroscopic analysis, such as determination of a spectrum of the radiation incident on the spectrometer. Therefore, traditional spectrometers tend to be bulky, thus limiting their usage for portable and on-site analyses, for example. Furthermore, the need for dispersive optical elements makes it challenging to integrate these traditional designs with CMOS technologies to realize cost-effective on-chip miniaturized spectrometers. CMOS compatible miniaturization of spectrometers is of interest for emerging applications, as itwould not only provide high performance and small size, but it could also enable integration of spectroscopic tools with existing on-chip technologies to uncover new functionalities in all scientific and industrial areas.

[0024] A chip as herein discussed is an integrated circuit, which comprises a semiconductor substrate and one or more devices integrated thereon. For example, an integrated circuit may comprise a spectrometer and a computing device, such as a processing core and memory accessible to the processing core, configured to perform the determining of the spectrum of the incident radiation.

[0025] Towards this goal, herein is described a class of miniaturized spectrometers based on CMOS compatible materials by combining a 2D semimetal, such as graphene, with semiconductors such as silicon, germanium, or III-V semiconductors to form a heterostructure.

[0026] Here, CMOS-compatible materials and designs are selected for seamless integration with semiconductor industry fabrication processes and technologies to realize mass manufacturing at a low cost. The herein disclosed spectrometer is a CMOS manufacturing compatible on-chip miniaturized spectrometer with high performance and low complexity, and as such has the potential to expand the scope of spectroscopic applications, with potential application in portable smart devices, personalized health trackers, handheld food and environmental monitoring for better well-being, for example.

[0027] Based on spectral responsivity matrix R constructed during the calibration process and use of a reconstruction algorithm, the spectral content of incident light with an unknown spectral information measured during the testing process can be computationally obtained from the photocurrent data, even when the spectrum is a continuous, rather than a set of distinct spectral lines.

[0028] A reconstruction algorithm may be used to obtain the unknown spectrum of the incident light on the spectrometer heterojunction based on the spectral responsivity matrix and the measured physical responsivity data in measuring phase 140. In a reconstruction process, the measured physical responsivity data is the photocurrent dataset through the integration of an unknown spectrum function and the spectral responsivity matrix over the wavelength range. To extract the unknown spectrum, a set of wavelengthindependent weight coefficients may be determined for a linear expansion of the spectrumwith simple basis functions. The Gaussian function may be selected as the basis function for the linear expansion of the spectrum, for example. Discretization of the integral formula that combines the unknown spectrum function, spectral responsivity matrix, and photocurrent data allows the expression of the integral formula in the form of a system of linear equations. In the given matrix form, the residual norm, that being the squared error, is minimized by solving the non-negative least-square problem, for example.

[0029] A direct minimization of the residual norm may lead to instabilities in the solution due to high-frequency noise signals. To address this issue, Tikhonov regularization may be used to stabilize the minimization procedure. In this approach, an auxiliary term, termed a damping coefficient and defined by the regularization factor, may be added to the residual norm. This regularization factor should be chosen properly to satisfy conditions of robustness and reflect the signal noise level. The generalized cross-validation adaptive method may be used to find the optimal value of the regularization factor. A vector of coefficients that provides a global minimum of the modified residual norm enables the reconstruction of an unknown spectrum with substitution of it in the initial expansion in basis functions. Spectra reconstructed with the spectrometer and measured with a standard spectrometer may be normalized with maximum intensities.

[0030] FIGURE 2A illustrates a spectrometer in accordance with at least some embodiments of the present invention. A semiconductor substrate 210 comprises a three- dimensional, 3D, semiconductor, such as a bulk inorganic semiconductor substrate, for example. This substrate may comprise silicon, germanium or III-V semiconductors, for example. A dielectric layer 220 is disposed directly on substrate 210. The dielectric layer may comprise, for example, silicon dioxide, silicon nitride, aluminum oxide, hafnium oxide or zirconium oxide. By being disposed directly on substrate 210 it is herein meant, that no functional layer is present between dielectric layer 220 and substrate 210, but manufacturing impurities may be present between the two surfaces.

[0031] A two-dimensional, 2D, semimetal layer 230 is partly directly on the semiconductor substrate and partly on dielectric layer 220. For example, the 2D semimetal layer may be a graphene layer. Where 2D semimetal layer 230 is directly on 3D substrate 210, a mixed-dimension heterostructure is formed between these layers. A thickness of 2D semimetal layer 230 may be 0.3 to 10 nm or 0.3 to 5 nm, for example.

[0032] A first electrode 240 is electrically coupled to 2D semimetal layer 230 and a second electrode 250 is coupled to the semiconductor substrate 210. Further, a tuneable voltage source 260 is arranged to provide the selectable voltage between the first electrode and the second electrode.

[0033] The mixed-dimension heterostructure interface between 2D semimetal layer 230 and 3D substrate 210 is a Schottky barrier, in other words, it has a potential energy barrier for electrons. A Schottky barrier height denotes an energy barrier an electron needs to overcome, in order to cross to another side of the mixed-dimension heterostructure interface. The height of the barrier may be effectively modulated by tuning, by setting the selectable voltage between first and second electrodes 240, 250. The selectable voltage also creates a bias over this interface, such that incident radiation may prompt electrons to overcome the Schottky barrier and create the photocurrent Iph. The working principle of the spectrometer is embodied in its wavelength-selective response when modulating the interfacial heterostructure barrier with the applied electrical field.

[0034] FIGURE 2B illustrates a spectrometer in accordance with at least some embodiments of the present invention. Like numbering denotes like structure as in FIGURE 2A, here second electrode 250 is on another side of substrate 210, than in the spectrometer of FIGURE 2A. The functioning of the device is similar to that of FIGURE 2A.

[0035] FIGURE 2C illustrates a spectrometer in accordance with at least some embodiments of the present invention. The device of FIGURE 2C resembles those of FIGURES 2A and 2B, and indeed like numbering denotes like structure as in those figures. The spectrometer of FIGURE 2C comprises, in addition to the structure of FIGURE 2A, further a gate dielectric layer 235, with a third electrode 255 thereon, and a second tuneable voltage source 270. Gate dielectric layer 235 may be comprised of silicon dioxide, silicon nitride, aluminum oxide, hafnium oxide, or zirconium oxide, for example.

[0036] In the embodiments of FIGURE 2C, both voltages put into tuneable voltage sources 260 and 270 may be independently selected in phases 130 and 140. An advantage from the separate gate dielectric layer 235 is that it physically separates the gate electrode 255 from the semimetal 230 and substrate 210. Additionally, it serves as a capacitive layer for the top gate 255.

[0037] FIGURE 2D illustrates a spectrometer in accordance with at least some embodiments of the present invention. Like numbering denotes like structure as in FIGURE 2C, here second electrode 250 is on another side of substrate 210, than in the spectrometer of FIGURE 2C. The functioning of the device is similar to that of FIGURE 2C.

[0038] The spectrometers of FIGURES 2A, 2B, 2C and 2D further comprise readout circuitry, which is configured to determine the photocurrent response of the heterostructure. Further, suitable control is provided to configure the tuneable voltage source(s) to enable sweeping a voltage range to determine a spectrum of the incident radiation 110.

[0039] FIGURE 3 illustrates an example apparatus capable of supporting at least some embodiments of the present invention. Illustrated is device 300, which may comprise, for example, a spectrometer data processor device, such as a controller of a spectrometer. The controller may be integrated on a same integrated circuit as the spectrometer of FIGURES 2A, 2B, 2C or 2D, for example. Comprised in device 300 is processor 310, which may comprise, for example, a single- or multi-core processor wherein a single-core processor comprises one processing core and a multi-core processor comprises more than one processing core. Processor 310 may comprise, in general, a control device. Processor 310 may comprise more than one processor. A processing core may comprise, for example, a Cortex-A8 processing core manufactured by ARM Holdings or a Zen processing core designed by Advanced Micro Devices Corporation. Processor 310 may comprise at least one application-specific integrated circuit, ASIC. Processor 310 may comprise at least one field- programmable gate array, FPGA. Processor 310 may be configured, at least in part by computer instructions, to perform actions. In particular, processor 310 may be configured to obtain a wavelength of incident radiation, or a spectrum of incident radiation, by using spectral responsivity matrix R. Likewise processor 310 may be configured to configure tuneable voltage source(s) 260, 270 for performing a measurement by the spectrometer. Processor 310 may further be configured to receive photocurrent values measured by the readout circuitry.

[0040] Device 300 may comprise memory 320. Memory 320 may comprise randomaccess memory and / or permanent memory. Memory 320 may comprise at least one RAM chip. Memory 320 may be a computer readable medium. Memory 320 may comprise solid- state, magnetic, optical and / or holographic memory, for example. Memory 320 may be at least in part accessible to processor 310. Memory 320 may be at least in part comprised inprocessor 310. Memory 320 may be meant for storing information, such as spectral responsivity matrix R. Memory 320 may comprise computer instructions that processor 310 is configured to execute. When computer instructions configured to cause processor 310 to perform certain actions are stored in memory 320, and device 300 overall is configured to run under the direction of processor 310 using computer instructions from memory 320, processor 310 and / or its at least one processing core may be considered to be configured to perform said certain actions.

[0041] Device 300 may comprise user interface, UI, 360. UI 360 may comprise at least one of a display, a keyboard, a touchscreen, a vibrator arranged to signal to a user by causing device 300 to vibrate, a speaker or a microphone. A user may be able to operate device 300 via UI 360, for example to configure the spectrometer to perform a measurement of incident radiation.

[0042] Processor 310 may be furnished with a transmitter arranged to output information from processor 310, via electrical leads internal to device 300, to other devices comprised in device 300. Such a transmitter may comprise a serial bus transmitter arranged to, for example, output information via at least one electrical lead to memory 320 for storage therein. Alternatively, to a serial bus, the transmitter may comprise a parallel bus transmitter. Likewise, processor 310 may comprise a receiver arranged to receive information in processor 310, via electrical leads internal to device 300, from other devices comprised in device 300. Such a receiver may comprise a serial bus receiver arranged to, for example, receive information via at least one electrical lead from receiver 340 for processing in processor 310. Alternatively, to a serial bus, the receiver may comprise a parallel bus receiver.

[0043] Processor 310, memory 320, and UI 360 may be interconnected by electrical leads internal to device 300 in a multitude of different ways. For example, each of the aforementioned devices may be separately connected to a master bus internal to device 300, to allow for the devices to exchange information. However, as the skilled person will appreciate, this is only one example and depending on the embodiment various ways of interconnecting at least two of the aforementioned devices may be selected without departing from the scope of the present invention.

[0044] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but areextended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0045] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0046] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another but are to be considered as separate and autonomous representations of the present invention.

[0047] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the preceding description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0048] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principlesand concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0049] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality.

[0050] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.INDUSTRIAL APPLICABILITY

[0051] At least some embodiments of the present invention find industrial application in the field of spectroscopy.ACRONYMS LIST2D two dimensional3D three dimensionalCMOS complementary metal-oxide semiconductorREFERENCE SIGNS LIST

Claims

CLAIMS:

1. A spectrometer comprising:- a bulk inorganic semiconductor substrate and a dielectric layer directly on the semiconductor substrate;- a two-dimensional semimetal layer partly directly on the semiconductor substrate and partly directly on the dielectric layer;- a first electrode electrically coupled to the two-dimensional semimetal layer and a second electrode coupled to the semiconductor substrate, and a tuneable voltage source arranged to provide a selectable voltage between the first electrode and the second electrode, and- readout circuitry configured to measure a physical response of the spectrometer to incident radiation.

2. The spectrometer according to claim 1, wherein the bulk inorganic semiconductor substrate comprises one of silicon, germanium and a III - V semiconductor.

3. The spectrometer according to claim 1 or 2, wherein the two-dimensional semimetal layer is a graphene layer.

4. The spectrometer according to any of claims 1 - 3, configured to determine a wavelength of the incident radiation based on a spectral responsivity matrix and a value of the selectable voltage.

5. The spectrometer according to any of claims 1 - 3, configured to determine a spectrum of the incident radiation based on a spectral responsivity matrix and a plurality of the physical responses, the plurality of physical responses obtained using a plurality of values of the selectable voltage.

6. The spectrometer according to any of claims 1 - 5, wherein the spectrometer does not comprise a photodetector array or a filter array.

7. The spectrometer according to any of claims 1 - 6 wherein the physical response is a photocurrent.

8. The spectrometer according to any of claims 1 - 7, wherein the selectable voltage between the first electrode and the second electrode causes a voltage between the two-dimensional semimetal layer and the bulk inorganic semiconductor substrate.

9. The spectrometer according to any of claims 1 - 8, wherein the spectrometer comprises a complementary metal-oxide semiconductor, CMOS, structure.

10. The spectrometer according to any of claims 1 - 9, further comprising a second dielectric layer directly on the semiconductor substrate and on the two-dimensional semimetal layer.

11. An integrated circuit comprising a spectrometer according to at least one of claims 1 - 10, wherein the semiconductor substrate is a substrate of the integrated circuit, the integrated circuit comprising at least one further device in addition to the spectrometer.

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