Gas detection system

Abstract

The present invention relates to gas detection devices, and in particular to volatile substance sensors, such as respiratory alcohol device sensors. A semiconductor gas sensor device according to the present invention includes a laser structure and an optical waveguide resonator formed in the same compound semiconductor including at least one light emission layer and one light propagation layer. The optical waveguide resonator is formed in the light propagating layer, and a majority thereof is separated from a remainder of the light propagating layer. The laser structure is disposed adjacent a portion of the optical waveguide resonator and is arranged to transmit electromagnetic radiation of a particular wavelength band to the optical waveguide resonator arranged to resonate at the particular wavelength band.

Description

Technical Field

[0001] The present invention relates to gas detection systems, and in particular to volatile substance sensors, such as breath alcohol devices, handheld devices for mobile use, fixed or mobile environmental monitoring devices, medical diagnostic and patient monitoring instruments, vehicle monitoring devices and systems, industrial process equipment, and household appliances.

[0002] In particular, the present invention relates to systems including miniature semiconductor sensors, and systems where small physical size, ruggedness, low production cost, and low power consumption are important. Background Art

[0003] Gas detection devices for detecting volatile substances in air or breath samples need to combine extremely high sensitivity and reliability, and preferably short measurement and analysis times. In addition, it is desirable to provide a large number of such detection devices to promote widespread use. Therefore, an economical and affordable solution is urgently needed.

[0004] An example of a gas detection device that meets all of the above requirements is in the field of breath alcohol testing. In this field, witness breathalyzers are used to provide legal proof of illegal primary alcohol concentrations in a person's blood (and breath); vehicle-mounted testers and fixed workplace testers are used to prohibit people who are, for example, under the influence of alcohol from driving and / or entering hazardous workplaces; and individuals use cheaper consumer testing units to control their level of intoxication. Witness breathalyzers are typically based on spectrophotometer technology and are typically large, expensive, and consume relatively large amounts of power during operation. Such devices provide very high accuracy, but the technology is not suitable for consumer products such as handheld or vehicle-mounted products.

[0005] Many handheld breathalyzers sold to consumers use semiconductor metal oxide sensors to determine blood alcohol concentration. These sensors are susceptible to contamination and interference from substances other than breath alcohol. The sensors need to be recalibrated or replaced every six months. High-end personal breathalyzers and professional breathalyzers use platinum fuel cell sensors. These also need to be recalibrated, but less frequently than semiconductor devices, typically once a year.

[0006] A spectral sensor has been commercialized as a vehicle-mounted breath analyzer and a fixed breath analyzer, a multi-channel spectral absorption unit. The term "multi-channel" refers to allowing electromagnetic radiation to reflect in a measuring cell, preferably multiple reflections, to increase the optical path, and thereby increase the sensitivity of the sensor or measurement system, the cell being a part of the sensor or measurement system. A particularly useful implementation of a multi-channel cell is the so-called White-cell, which was proposed by John U White as early as 1942 (Journal of the Optical Society of America, 1942) and has been used since then. Compared with other spectrophotometer-based sensors, White-cell-based breath analyzers have significant improvements in size and cost, and compared with silicon oxide sensors and other consumer products, their accuracy and reliability have also been significantly improved. However, the technology is difficult to further miniaturize, and the optical arrangement will always make these sensors more expensive than sensors based purely on semiconductor technology. These problems are not limited to detectors for alcohol testing. Rather, similar requirements can be found in all areas where the concentrations of specific volatile substances are determined (usually in very small concentrations), for example in the fields of environmental monitoring, medical diagnostics and patient monitoring and vehicle monitoring. Summary of the invention

[0007] It is an object of the present invention to overcome the disadvantages associated with prior art gas sensor devices. This is achieved by a semiconductor gas sensor device as defined in the independent claims.

[0008] According to a first aspect, a gas detection system is described. The gas detection system includes a semiconductor gas sensor for determining the concentration of volatile substances in a gas flow. The semiconductor gas sensor device includes a laser structure and an optical waveguide resonator formed in the same compound semiconductor, and a device for detecting the optical power dissipation of electromagnetic waves propagating in the optical waveguide resonator. The compound semiconductor includes a single crystal substrate and a plurality of epitaxially grown semiconductor single crystal layers arranged on the substrate, wherein the plurality of epitaxially grown semiconductor single crystal layers include at least one light emitting layer and a light propagation layer. The light emitting layer is present at least in the laser structure and is arranged to emit electromagnetic radiation in a specific wavelength band. The optical waveguide resonator is at least partially composed of a portion of the light propagation layer, and its main portion is separated from the remaining portion of the light propagation layer so that it can be optically regarded as a free-hanging unit. The optical waveguide resonator is arranged to resonate in a specific wavelength band. The laser structure is arranged adjacent to a portion of the optical waveguide resonator, thereby providing a device for transmitting electromagnetic radiation in a specific wavelength band generated in the light emitting layer of the laser structure to the optical waveguide resonator. The gas detection system further comprises an electronic unit arranged in electrical connection with the gas sensor device, wherein the electronic unit is arranged to output a wavelength modulated signal for a specific wavelength band.

[0009] Therefore, the position and width of a specific band are determined by the specific properties of both the emitting layer and the waveguide resonator, which are related to the optical feedback and the driving voltage. In each case, both the position and width of a specific band match the peak wavelength and width or quality factor of the absorption peak of the target substance.

[0010] By having an electronic unit arranged to be electrically connected to the gas sensor device and outputting a signal for wavelength modulation of a specific wavelength band, the position of the specific wavelength band near the absorption peak of the volatile substance can be modulated.

[0011] According to one embodiment, the gas detection system can be configured so that the specific wavelength band at least partially overlaps with the position and width of the absorption peak of the substance. This can be achieved in different ways as described below.

[0012] According to one embodiment, the electronic unit is arranged in electrical connection with at least the laser structure of the gas sensor device, and the signal for wavelength modulation is a modulation voltage superimposed on the DC drive voltage of the laser structure, thereby providing electronic modulation of the electromagnetic waves in the optical waveguide resonator and thereby providing wavelength modulation of a specific wavelength band. This is a first alternative solution how to achieve modulation of a specific wavelength band.

[0013] According to one embodiment, the semiconductor gas sensor device may include a MEMS modulator formed at least partially in the light propagation layer, wherein the signal for wavelength modulation is configured to control the MEMS modulator and thereby arranged to control the position of a specific wavelength band, hereinafter referred to as wavelength modulation. This is how the second alternative of modulation of a specific wavelength band is achieved.

[0014] Thus, two different options are provided for wavelength modulation across the absorption peak of a substance. The alternatives can also be combined.

[0015] According to one embodiment, the laser structure comprises a laser waveguide at least partially formed in or otherwise optically coupled to the light propagating layer, and wherein, during use, the laser waveguide is optically coupled to the optical waveguide resonator.

[0016] According to one embodiment, the semiconductor gas sensor device is arranged to determine the concentration of a substance in the air, and the laser structure is arranged to emit electromagnetic radiation in a specific band, and the optical waveguide resonator is arranged to resonate in the specific band so that the specific band can be modulated across the absorption peak of the substance. In other words, the specific band is arranged close to the absorption peak of the substance. This enables the modulation to shift the specific band across the absorption peak.

[0017] According to one embodiment, the laser structure is arranged adjacent to a portion of the optical waveguide resonator with a gap of no more than 1 / 2 of the wavelength in the specific wavelength band, preferably no more than 1 / 4 of the wavelength in the specific wavelength band.

[0018] According to one embodiment, the material of the light propagating layer is selected to be highly transparent in a specific wavelength band.

[0019] According to one embodiment, the dimensions of the optical waveguide resonator are designed such that its circumference C r will be exactly equal to the expected resonant wavelength λ corresponding to the absorption peak wavelength of the substance to be detected r An integer N times of .

[0020] According to one embodiment, the optical waveguide resonator is a closed loop structure. For example, the closed loop structure may be annular.

[0021] According to one embodiment, the optical waveguide resonator is a linear structure and includes a first reflector and a second reflector arranged at each end of the optical waveguide resonator.

[0022] According to one embodiment, the optical waveguide resonator is ring-shaped.

[0023] According to one embodiment, the optical waveguide resonator is provided with at least one straight portion located adjacent to the laser structure, and the length of the straight portion is at least as long as the extension length of the laser structure in the plane of the compound semiconductor, in order to minimize optical losses while maximizing the optical coupling efficiency between the laser structure and the waveguide resonator.

[0024] According to one embodiment, the plurality of layers includes at least one intermediate layer arranged between the substrate and the light propagation layer, the intermediate layer being present below the light propagation layer in the laser structure and the intermediate layer being at least partially absent below the light propagation layer forming the optical waveguide resonator.

[0025] According to one embodiment, the optical waveguide resonator is partially freely suspended above the etched away portion of the intermediate layer and is partially supported by the remaining structure of the intermediate layer.

[0026] According to one embodiment, the optical waveguide resonator is partially freely suspended above the etched away portion of the intermediate layer and is partially supported by a plurality of bridges provided in the light propagation layer and extending from the base structure to the optical waveguide resonator. The width of the bridge is preferably less than the shortest wavelength in a particular wavelength band, and preferably less than 1 μm.

[0027] According to one embodiment, the optical waveguide resonator (106) has a substantially rectangular cross-section with a width / thickness of approximately 2.0±0.5 / 0.2±0.1 μm.

[0028] According to one embodiment, the laser structure is used to determine the concentration of volatile substances, and the semiconductor gas sensor device further comprises means for monitoring and controlling the current and voltage of the laser structure during use. For example, the laser structure may be implemented as a double heterostructure laser or a quantum cascade laser.

[0029] According to one embodiment, the semiconductor gas sensor device further comprises an optical feedback grating formed at least partially in the light propagation layer.

[0030] According to one embodiment, the semiconductor gas sensor device further includes a photodiode formed at least in part from the plurality of epitaxially grown crystalline layers.

[0031] According to one embodiment, the semiconductor gas sensor device further comprises a temperature sensor formed at least in part from the plurality of epitaxially grown crystalline layers.

[0032] According to one embodiment, the electronics unit is arranged in electrical connection with at least the laser structure and the photodiode of the gas sensor device.

[0033] According to one aspect of the present invention, a method for determining the concentration of volatile substances in an airflow using the above-mentioned gas detection system is provided. The method comprises the following steps:

[0034] -Provide gas detection system;

[0035] -providing a gas flow to the surroundings of a semiconductor gas sensor device of a gas detection system;

[0036] - supplying a driving voltage to a laser structure of the semiconductor gas sensor device so that electromagnetic radiation of a specific wavelength band is emitted;

[0037] - supplying a signal for wavelength modulation so that a specific wavelength band is modulated across the absorption peak of the substance; and - recording an output from the device for detection related to the optical power dissipation of an electromagnetic wave propagating in an optical waveguide resonator affected by the volatile substance in the gas flow.

[0038] According to one embodiment, the laser structure is used not only to generate electromagnetic radiation, but also to detect optical power dissipation caused by interaction with the volatile material, by monitoring and controlling the current and voltage of the laser structure, and determining the concentration of the volatile material based on how the current-voltage characteristics of the laser structure are affected by the volatile material in the gas flow. Alternatively, the method includes monitoring and analyzing the output from a photodiode that detects the optical power dissipation in the optical waveguide resonator.

[0039] Due to the present invention, a gas sensor device based on a semiconductor gas sensor device arranged on one chip can be provided. This has great advantages in terms of miniaturization, production cost, sensitivity, power consumption and reliability. Compared with prior art semiconductor devices using optical waveguides, the present invention provides a more reliable and more efficient optical coupling between a light source (e.g., a laser structure) and an optical waveguide resonator, because both structures are formed in the same semiconductor multilayer structure.

[0040] Numerous additional benefits and advantages of the present invention will be readily appreciated by those skilled in the art from the following detailed description and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The present invention will now be described in more detail with reference to the accompanying drawings, in which:

[0042] Figure 1a to Figure 1h Schematically showing a semiconductor gas sensor device according to the present invention, wherein a) is a cross-sectional view, b) is a top view, c) is a cross-sectional view of one embodiment, d) is a front view of one embodiment, and e) is a top view of one embodiment of the present invention, f) is a top view of one embodiment of the present invention using a linear optical waveguide, g) is a graph showing the structure of a reflector according to one embodiment of the present invention, and h) is a graph of reflectivity characteristics of a reflector according to one embodiment of the present invention;

[0043] Figure 2 is a graph showing the functionality of a semiconductor gas sensor device according to the present invention;

[0044] Figure 3a to Figure 3c In 1-x Ga x A graph of the properties of As;

[0045] Figures 4a to 4c Schematically illustrates an embodiment of the present invention comprising a double heterostructure laser structure (a and b) and a quantum cascade laser structure (c), wherein a) is a front view of the double heterostructure laser structure, b) is a laser band diagram, and c) is a quantum cascade band diagram;

[0046] Figure 5 is a graph showing the current / voltage characteristics of the laser structure;

[0047] Figure 6 A sensor system configuration according to the invention is schematically shown.

[0048] Figure 7 is a flow chart illustrating a method according to the present invention.

[0049] All figures are schematic, not necessarily drawn to scale, and generally show only parts necessary to illustrate the respective embodiments, while other parts may be omitted or merely suggested. Unless otherwise indicated, any reference number appearing in multiple figures refers to the same object or feature throughout the figures. DETAILED DESCRIPTION

[0050] Terms such as "top", "bottom", "upper", "lower", "below", "above", etc. refer solely to the geometry of embodiments of the invention shown in the accompanying drawings and / or are used during normal operation or installation of a device / devices, and are not intended to limit the invention in any way.

[0051] According to one aspect of the invention, there is provided a device for determining the presence and concentration of volatile substances in the air. According to the invention, at least the electromagnetic radiation source and the optical waveguide and optionally the detector are integrated on a compound semiconductor chip. Obvious advantages are small size, low production cost and compatibility with other semiconductor devices. By integrating the key components on a single chip, the manufacturing steps requiring high precision and accuracy are carried out in a process sequence called surface micromachining, in which thousands of sensor devices on a single wafer can be processed in parallel. The required manufacturing precision is managed using batch processing of semiconductor wafers, exposing the wafer surface to deposition or etching through precisely controlled two-dimensional patterns based on lithography with almost atomic resolution.

[0052] According to an embodiment of the present invention, a single-mode laser is integrated with an optical waveguide, and a device for light modulation and detection is provided on a compound semiconductor substrate. It is a well-known fact that many volatile substances exhibit sharp absorption peaks in the mid-infrared (IR) wavelength range. In addition, several IV and III-V compound semiconductors exhibit inherent properties that allow electromagnetic radiation sources and detectors in the IR range to be designed within an emission wavelength range between 0.5 μm and 10 μm. Complex structures with precisely controlled functions can be achieved by alloying IV (e.g., C, Si, Ge) or III-V compounds (e.g., Al, Ga, In, P, As, Sb) using epitaxial crystal growth. These properties of IV and III-V compound semiconductors and the mature technology of producing components with these materials make them good candidates for the construction materials of semiconductor gas sensor devices for determining the presence and concentration of volatile substances in the air according to the present invention.

[0053] Table 1 provides three examples of volatile substances: water, carbon dioxide, and ethanol (EtOH), where the peak wavelength λ [μm], absorbance ε [ppm], -1 m -1 ], the quality factor Q [dimensionless], and the numerical value of the dynamic concentration range [min...max ppm].

[0054] The infrared absorption of volatile substances is based on molecular vibration transitions according to quantum mechanical transition rules. 2 O and CO 2 In the case of EtOH, the peaks in Table 1 were selected based on size and sharpness (quality factor, Q). The EtOH peak represents a non-rotational transition corresponding to the vibrational stretching of the C-H bond, resulting in a peak surrounded by a continuous background of mixed vibrational and rotational transitions. Basically, the same single sharp absorption peak characteristic is found in most organic compounds with C-H bonds.

[0055] Table 1.H 2 O、CO 2 The main absorption peaks of EtOH

[0056]

[0057] Credit: Pacific Northwest National Laboratory (PNNL).

[0058] As can be seen in Table 1, all three substances exhibit a single absorption peak in the spectral range outlined. Wavelength, absorbance and quality factor vary from substance to substance, but in most environments, including automotive applications, the peak is clearly distinguishable from the background. The dynamic concentration range is estimated based on in-vehicle application data and human exhaled concentrations over the temperature range of -40...+85°C. The minimum number corresponds to the resolution requirement and the maximum number is the highest expected concentration.

[0059] Figure 1a and Figure 1b A semiconductor gas sensor device 100 according to the present invention is schematically shown and illustrates the basic principle and main functional elements of the detection device according to the present invention. Figure 1a is a cross-sectional view of a compound semiconductor 120 that provides the optically active and electrically active portions of the device, and Figure 1b1 is a top view. The semiconductor gas sensor device 100 includes a single crystal substrate 101 (usually and preferably a III-V semiconductor) and a multilayer structure 125 disposed on top of the single crystal substrate 101. The multilayer structure 125 can be grown by epitaxy and can also be partially removed at certain locations by selective etching by photolithography. These layers include, but are not limited to, a bottom layer 102 acting as a buffer layer (e.g., for coordinating the difference in crystal properties between the substrate 101 and subsequent layers), a light emitting layer 103, and a light propagation layer 104. At predetermined positions, conductive electrodes 105a, 105b supply current to the light emitting layer 103 to cause reverse population of charge carriers and, thus, stimulate coherent emission of IR radiation by laser action. The region between the electrodes 105a, 105b defines a laser structure 112. An optical waveguide resonator 106 is provided, in which a light propagation layer 104 is present. The optical waveguide resonator 106 is provided as its main part with a free-hanging structure at a distance above the substrate 101. For example, the optical waveguide resonator 106 may be suspended by a narrow bridge portion in the light propagation layer 104, by a vertical column supporting the optical waveguide resonator 106 from below, or by other support structures whose dimensions interfere as little as possible with the optical properties of the optical waveguide resonator 106. Thus, substantially the empty space 106c surrounds the optical waveguide resonator 106. The structure of the optical waveguide resonator 106 is Figure 1a 1 and 2. An optical waveguide resonator 106 is shown in FIG. 1 as having a left portion 106a and a right portion 106b. Figure 1a A cross section passes through the laser structure 112 .

[0060] A portion of the optical waveguide resonator 106 is arranged adjacent to and in close proximity to the laser structure 112. Preferably, the distance between the optical waveguide resonator 106 and the laser structure 112 is less than or equal to the wavelength, more preferably less than half the wavelength and even less than 1 / 4 of the wavelength, where "wavelength" refers to the shortest wavelength in the band in which the semiconductor gas sensor device is intended to be used. Typically, this corresponds to a distance of 1 μm or less. Therefore, the laser structure 112 will be optically coupled to the optical waveguide resonator 106, and the radiation originating from the emission layer 103 within the laser structure 112 is transmitted to the optical waveguide resonator 106. The optical waveguide resonator 106 allows the light waves to propagate through several turns in the waveguide direction with low loss. The light field is only partially confined to the solid waveguide material 106, but also extends across its physical boundaries into the surrounding air environment in the empty space 106c, forming an attenuated light field 107a, 107b, the imaging area of ​​which should not be regarded as quantitative, but as an indication of existence and approximate extension. The attenuated optical fields 107a, 107b also extend to a portion of the light propagation layer 104 that is not part of the optical waveguide resonator 106, and may also extend to the light emitting layer 103 that is part of the laser structure 112. The optical waveguide resonator 106 constitutes an optical resonator with a high quality factor that is optically coupled to the laser structure 112, and its emission band is determined by the resonant frequency and the quality factor of the waveguide resonator.

[0061] According to one embodiment of the present invention, the laser structure 112 comprises a waveguide disposed on top of the light emitting layer 103. The waveguide of the laser structure may be provided at least in part by the light propagating layer 104. The optical coupling between the waveguide resonator 106 and the laser structure 112, which also comprises a waveguide, is achieved by their being arranged perpendicular to the waveguide. Figure 1a The parallel extension in the direction of ) provides an overlap of the evanescent field 107a between the emission layer 103 of the laser structure 112 and the light propagation layer 104 of the waveguide resonator 106, thereby providing efficient optical coupling.

[0062] According to an embodiment of the present invention, Figure 1a , Figure 1b and Figure 1e As shown schematically, the waveguide resonator 106 is a closed loop structure and should preferably be designed so that its circumference will be exactly equal to an integer multiple of the desired resonant wavelength corresponding to the absorption peak of the substance to be detected. The resonant is optically coupled to the laser structure 112 to control its emission peak wavelength λ r Specifically, the perimeter C r =N×λ r / n eff , substituting the effective refractive index n eff= 1.7 to account for the fact that light propagation occurs both in the bulk waveguide 106 and in the attenuation field in air, and N is an integer. As previously described, the resonance is optically coupled to the laser structure 112, controlling its emission peak wavelength.

[0063] The optical radiation is caused by the laser structure 112 and the optical waveguide resonator 106 being close to the sides and as described above. Figure 1a ) is coupled from the laser structure 112 to the optical waveguide resonator 106 by the attenuation field described by ). The physical distance between the laser structure 112 and the optical waveguide resonator 106 is typically 1 μm, which is significantly smaller than the IR wavelength. Therefore, optical power or intensity will be coupled from the laser structure 112 to the optical waveguide resonator 106, and vice versa. The optical waveguide resonator 106 is suspended from the substrate 101 at several points along its circumference, but the majority of it is typically free-hanging, allowing the IR radiation to propagate in single mode along its circumference with low optical losses.

[0064] The light propagation layer 104 and hence the optical waveguide resonator 106 is formed of a single crystal III-V semiconductor material epitaxially grown on the substrate 101, the composition of which makes it highly transparent to the IR radiation generated by the laser structure 112. A sacrificial layer is etched away below the light propagation layer 104 of the optical waveguide resonator 106 to form an empty space 106c. The optical waveguide resonator 106 may typically have a rectangular cross-section with a width / thickness of about 2.0 / 0.2 μm or preferably 2.0±0.5 / 0.2+0.1 μm. The gap defined by the sacrificial layer may typically be of the order of about 2 μm or preferably 2.0±0.5 μm. Typically, during use, the IR radiation propagates around the circumference for twenty turns or more before being completely scattered or absorbed.

[0065] The semiconductor gas sensor device 100 may further include a housing 108 providing a measurement chamber 108c accommodating the compound semiconductor 120. The housing 108 is provided with a gas inlet 108a and a gas outlet 108b respectively leading to the measurement chamber 108c.

[0066] Without being bound by theory, it can be estimated that approximately half of the radiated power associated with the propagating electromagnetic wave propagates within the optical waveguide resonator 106, and the other half constitutes an evanescent wave propagating in the air, close to the solid waveguide. This dimensionless ratio will be denoted as the external confinement factor Γ below, depending on the size of the empty space 106c and other factors. The technical details of the waveguide implementation are fully described in F. Ottonello Briano, Mid-Infrared Photonic Devices for On-Chip Optical Gas Sensing, Doctoral Thesis, The Royal Institute of Technology, Stockholm, Sweden, 2019.

[0067] According to one embodiment, the optical waveguide resonator 106 has an almost circular geometry and has a quality factor Q exceeding 10. 4 This is achieved by minimizing light losses due to waveguide bending and scattering due to surface defects. Its circumference is typically 1.2 mm.

[0068] According to one embodiment, the optical waveguide resonator 106 includes Figure 1b ) and the linear sector. Thus, efficient optical coupling with the laser structure 112 and the modulator 114 (if used) can be achieved while maintaining low optical bending losses in the curved sector.

[0069] See also Figure 1a to Figure 1b , the optical waveguide resonator 106 is described as being generally annular. In some cases, finer geometries may be advantageous, and Figure 1e An embodiment of the invention is shown in which the waveguide resonator 106' is a closed loop, in the sense that light propagation can pass through several turns of the structure, with one end meeting the other. Figure 1b ) is different from the ring, Figure 1e ) has an S-shape, which allows the optical path of a single turn to be larger than that of a ring structure occupying a similar area. On the other hand, the S-shape inevitably means a smaller radius of curvature, resulting in higher bending losses. Figure 1b ), the optical coupling between the waveguide structure 106' and the laser waveguide 113 is achieved by running them in parallel and closely adjacent to each other.

[0070] In use, air flowing between the air inlet 108a and the air outlet 108b near the sensor substrate 101 will interact with the optical waveguide resonator 106 and optionally also with the laser waveguide of the laser structure 112, and if the airflow itself includes a concentration of cm If the volatile material is present, the absorption peak of the volatile material is consistent with the emission wavelength of the laser structure 112. The interaction of the volatile material will cause the optical power of the electromagnet propagating in the optical waveguide resonator 106 to be dissipated, and according to the present invention, it can be detected by the laser structure 112 itself or an additional detection device, which represents different embodiments of the present invention.

[0071] According to one embodiment, the semiconductor gas sensor device 100 is arranged to utilize the current-voltage characteristics of the laser structure 112 as a means of detecting the interaction with the volatile substance, i.e. the optical power dissipation in the optical waveguide resonator 106. According to the schematic formula, the power absorption of the laser structure 112 will affect the current-voltage characteristics of the laser as an additional power load:

[0072] i=i 0 -Δi(c m ) (1)

[0073] Among them, i 0 is the supply voltage u that is not affected by the absorption of volatile substances 0 The current under the condition, and Δi(c m ) is the change in current due to the additional power load, which is the concentration of the substance c m A monotonic function of . Figure 1a The constant voltage u connected to the laser electrodes 105a, 105b is schematically shown. 0 A power supply 109 and an ammeter 110 for measuring a current i.

[0074] Figure 1b The typical surface size of the sensor chip shown in the top view may be 0.5×0.5 mm 2 , and the thickness is 0.3mm. Figure 1a In addition to the components described, Figure 1b ) also includes other elements, which can increase the performance and applicability of the sensor according to the present invention and represent different embodiments of the present invention.

[0075] According to an embodiment of the present invention, in addition to the laser structure 112 and the optical waveguide resonator 106, the compound semiconductor 120 further includes one or a combination of the following elements: MEMS modulators 114a, 114b, optical feedback gratings 115a, 115b, and laser optical waveguides 113, one or more photodetectors (usually photodiodes 116), and one or more temperature sensors 117. Through strict temperature control, the position of a specific band can be adjusted to a portion close to the absorption peak of the substance, thereby defining the wavelength range of the modulation. This can be used for setting and calibration procedures to ensure the normal operation of each individual sensor 100 according to the present invention.

[0076] All elements 112, 106, 113, 114a, 114b, 115a, 115b, 116, 117 are formed by a combination of epitaxial growth and other additive deposition or subtractive steps (such as etching). The photodetector can also be implemented as a photoresistor, a phototransistor, or a combination and / or array of such detectors. Contact pads or terminals 118 are provided for electrical communication between the elements and external electronic circuits. Terminals 118 are preferably arranged in a single row to facilitate connection to other components, such as by wire bonding.

[0077] The laser structure 112 is arranged to emit single-mode infrared radiation along the surface of the substrate 101 in the plane of the device. According to one embodiment, the laser structure 112 is combined with an optical feedback grating 115a, 115b. The optical feedback grating 115a, 115b comprises a repeating pattern with a continuously variable refractive index, resulting in a constructive reflectivity at different optical wavelengths, which is defined by the repeating pattern of a continuous layer grown on or etched from the substrate 101. It represents an optical resonator designed for a quality factor of about 300.

[0078] The feedback lines 115a, 115b and the waveguide 113 provided in the embodiments of the present invention are preferably formed in the light propagation layer 104, constituting an optical resonance element for controlling the laser emission. Therefore, the single-mode emission of the laser 112 is controlled by the precise dimensions of its key parameters such as the length, width and thickness of the waveguide, the refractive index, and the length, depth, width and repetition rate of the successive steps of the feedback lines 115a, 115b.

[0079] According to one embodiment, a microelectromechanical structure (MEMS) modulator 114 is provided and, similar to the optical waveguide resonator 106, is composed of a partially suspended, partially free-suspended thin element at least partially formed in the light propagation layer 104. The MEMS modulator includes a fixed element 114a and flexible wires 114b, 114c and 114d. By applying a voltage between the interdigitated "fingers" of the elements 114a and 114b, bending of the elements 114c and 114d will be induced, which in turn will cause a slight horizontal movement of the wire 114b. By its proximity to the optical waveguide resonator 106, the optical resonant frequency of the optical waveguide resonator 106 can be modulated in a controlled manner.

[0080] Preferably, the modulator 114 is 3 Hz-10 4The invention relates to a novel method for operating a waveguide 103 at a mechanical resonant frequency in the Hz range, which is determined by the mass of the movable wire 114b parallel to the waveguide 103 and the effective spring constants of the flexible members 114c and 114d. Technical details can be found in C. Errando-Herranz et al, IEEE Journal of Selected Topics in Quantum Electronics vol. 26, (2020) and P. Edinger et al, Conference on Lasers and Electro-Optics (2020), paper SM3J.2.

[0081] According to one embodiment, the photodiode 116 is disposed at another location along the circumference of the optical waveguide resonator 106 adjacent to the photodiode 116. The distance between the photodiode 116 and the optical waveguide resonator 106 may preferably be 3 μm-10 μm and is selected so that the Q value of the optical waveguide resonator 106 is not adversely affected. The photodiode 116 is essentially a pn junction whose composition and energy bandgap are suitable for absorbing incident IR radiation. The photocurrent generated in the pn junction represents the total optical power propagated by the waveguide. The 10 μm absorbed by the photodiode 116 is -5 A small portion or less is not suitable to affect the quality factor of the optical waveguide resonator 106 to a great extent.

[0082] According to one embodiment, one or several temperature sensors 117 are arranged in the compound semiconductor 120. According to one embodiment, the temperature sensor 117 is positioned close to the laser structure 112 in order to monitor the operating laser temperature. The temperature sensor 117 is preferably a pn junction of III-V material composition, whose energy band gap is higher than the energy of the propagated IR radiation. The open circuit voltage of the pn junction is a reliable measure of the temperature which depends mainly on its energy band gap, which in turn can be reproduced depending on the temperature. Further temperature sensors 117 can be positioned to measure the gas temperature in the measurement chamber 108c.

[0083] During operation, the compound semiconductor 120 should preferably be kept within a controlled temperature interval, typically 40+1°C. According to one embodiment, this is achieved by mounting the compound semiconductor 120 and its associated components on top of a Peltier element (not shown). With this arrangement, the sensor according to the present invention can accommodate an external operating temperature range of -40°C to +85°C or higher.

[0084] As will be appreciated by those skilled in the art, the above structures may include additional layers, and for example, the light emitting layer 103 and the light propagating layer 104 may include sub-layers. Figure 1c) schematically shows an illustrative but non-limiting example. According to an embodiment, several single crystal III-V semiconductor layers 131, 132, 103, 133, 134, 104 are deposited on the substrate 101 by molecular beam epitaxy, allowing strict control of composition, crystal quality and thickness. One or several layers on specific areas can be removed by etching, and the etching is controlled by a temporarily deposited mask to cover the areas to be protected from etching. The layers 131, 132 surrounding the light emitting layer 103 are used to define the laser structure 112 (not shown). The layer 133 preferably has the same composition as the active waveguide layer 104, acting as a stop layer when etching the sacrificial layer 134, allowing the optical waveguide resonator 106 to hang freely at the cross-sectional position, leaving space for the attenuated optical field 107 in its vicinity.

[0085] The etching technique used to produce the steep vertical walls is called anisotropic chemical etching or reactive ion beam etching (RIE). The sacrificial layer can preferably be etched away using composition-based selectivity, photoelectrochemical etching, or doping selective etching (DSE), typically using the same composition as the stop layer and the free-hanging structure. For more technical details, see B C Ovrén, E Gustafsson Batch Fabrication of Micromechanical Elements in GaAs-AlGaAs, Sensors and Actuators 4, 1983, 341-348, L Tenerz, B Micromachining of Three-Dimensional Structures Using Photo-Electrochemical Etching, Electronics Letters, 21, 1985, 1207-1208 and Y Lindén, L Tenerz, J Tirén, B Fabrication of Three-Dimensional Silicon Structures By Means of Doping-Selective Etching (DSE), Sensors and Actuators 16, 1989, 67-82.

[0086] Figure 1d ) shows a portion of an optical waveguide resonator 106, wherein the optical waveguide resonator is mechanically attached to the substrate 101. Figure 1a), an optical waveguide resonator 106 is built by depositing several layers 102, 103, 104 on a semiconductor substrate 101. Layer 103 is partially sacrificed, as previously described, controlled by photolithography and selective etching. The optical waveguide resonator 106 consists of portions of layer 104 that are freely suspended over almost their entire circumference, except for locations supported by a bridge 141 spanning the optical waveguide resonator 106 and attached to the substrate 101 by the remainder of layers 103 and 102. The width of the bridge 141 is typically 1 μm to minimize interference with light propagating through the optical waveguide resonator 106.

[0087] Figure 1e ) schematically shows the Figure 1b ) the same element, but with an alternative design, represents an embodiment of an optical waveguide resonator 106' which, compared to a circular shape, comprises several turns before connecting one end to the other. However, the optical waveguide resonator 106' still has a closed loop structure and its total length will be much longer than the circumference of a circle occupying the same surface. The optical path length is a key parameter for the sensitivity of the sensor according to the invention, but is offset by the optical power losses due to the bending of the waveguide. Therefore, choosing between an optical waveguide resonator with a circular waveguide 106 or its more dense alternative 106' is a question related to the technical performance requirements in various applications.

[0088] Figure 1f One embodiment of a gas sensing device 100 is schematically shown, which includes an open optical waveguide resonator 106". Here, open should be interpreted as not being in a closed loop arrangement and the optical waveguide resonator 106" according to this embodiment may be described as linear, for example but not limited to a straight line. Similar to the arrangement with a closed loop optical waveguide resonator 106 described above, the open optical waveguide resonator 106" is arranged to be adjacent to the laser structure 112 and may also be arranged to interact with the MEMS modulator 114 and / or with the photodiode 116. The open optical waveguide resonator 106" may preferably be provided with at least one mirror or reflector. According to one embodiment, a first reflector 106:1 and a second reflector 106:2 are arranged at each end of the open optical waveguide resonator 106". The first reflector 106:1 and the second reflector 106:2 are used to increase the optical path of the open optical waveguide resonator 106". The first reflector 106:1 and the second reflector 106:2 may be provided as a periodic perturbation, eg a periodic variation of the refractive index or a grating. Figure 1g to Figure 1h ) is a graph showing the function of the wavelength specific reflector operating along the length x of the waveguide. By introducing a change n relative to the refractive index n of the waveguide 1 、n 2 The maximum light reflectance R will occur at a specific wavelength λ rThe wavelength is given by the relation λ r =2n e Λ is given by, which is the periodicity of the refractive index variation, and n e is the effective refractive index, usually n 1 The weighted average of n2 and the ambient refractive index (close to 1). Periodic variations in the refractive index can be introduced by doping the waveguide material through a photolithographic mask. Figure 1h The sharpness of the peak reflectivity shown in the graph of can be controlled by the amount of perturbation, the precision of its spatial resolution and the fine structure. In the present invention, the effect of a wavelength-specific reflector can be used to provide a resonator function as Figure 1a ) and 1b) as an alternative to the ring waveguide 106, or providing feedback lines 115a, 115b.

[0089] exist Figure 2 , the functional operation of the semiconductor gas sensor device 100 according to the present invention is summarized by a graph with wavelength as the abscissa and normalized light intensity or power as the ordinate. An exemplary embodiment of the present invention is an EtOH sensor operating near the absorption peak 202 at 3.345 μm with a quality factor of about 1500. Other implementations (e.g., H 2 O or CO 2 The EtOH peak 202 extends above the continuous absorption "floor" due to molecular rotational transitions, which constitute the continuous absorption background at normal operating temperatures. However, this fact is not important here because the operation of the sensor is focused on a small wavelength interval, typically ±1nm (0.001μm), close to the absorption peak 202 at 3.345μm, and is controlled by the modulation depth of the modulator 114 or by controllably modulating the voltage feed circuit 109.

[0090] The laser structure 112 combined with the optical waveguide resonator 106 operates at a sharp peak 201 with a quality factor of approximately 10 4 , which is basically determined by the optical waveguide resonator 106. The specific wavelength band indicated by the peak 201 partially overlaps with the material absorption peak 202. Figure 1b The additional resonance of the optical waveguide resonator 106 occurs when the spacing 205 is about 5 μm, corresponding to its free spectral range FSR = λ r 2 / n e L 0 , where λ r =3.345 is the operating wavelength, n e =1.7 is the effective refractive index, and L 0 =1.2mm is the waveguide circumference.

[0091] The peak 203 with Q≈300 originates from the optical feedback gratings 115a, 115b. They suppress the influence of the side peaks on the peak 201, so that the threshold 204 for laser operation only exceeds the central peak 201, thus maintaining single-mode light emission at the peak 201. Therefore, Figure 2 The side peaks shown in are not emitted from the laser structure 112. By strict temperature control as described above, the position of the specific wavelength band shown by the central peak 201 can be adjusted to be close to the absorption peak 202 of EtOH.

[0092] As described above, the modulation signal of the modulator 114a, 114b or the modulation signal applied to the voltage feeding circuit 109 controls the exact position of the waveguide resonance peak within the short wavelength interval, or in other words, the position of a specific wavelength band. Figure 2 , the wavelength modulation of a particular wavelength band 201 is shown as interval 207. Graph 206a shows the change in position of a particular wavelength band 201 over time, and graph 206b shows the resulting signal S=S 0 sin 2ω m t. This signal will be described in more detail below. Preferably, the modulation is a sinusoidal angular frequency ω determined by the mechanical resonant frequency of the MEMS resonators 114a, 114b. m is performed as described above, or correspondingly with electronic modulation of the voltage feed circuit 109. The modulation amplitude M 0 Preferably, it is determined by the wavelength range adapted to the quality factor of the substance peak. In each modulation period, when the EtOH substance is present near the optical waveguide resonator 106, the absorption of optical power will peak twice. Therefore, in the presence of the substance, a signal representing the power consumption synchronized with the modulation will appear, which has twice the modulation frequency. Therefore, the appearance and amplitude of the synchronous detection signal at twice the modulation frequency will carry information about the presence and concentration of the EtOH substance close to the optical waveguide resonator 106.

[0093] Single crystal III-V semiconductors provide a unique technology platform for designing complex integrated structures such as the present invention. Various combinations of elements from Groups III and V of the periodic table include aluminum (Al), gallium (Ga), indium (In) on the one hand (Group III), and phosphorus (P), arsenic (As) and antimony (Sb) on the other hand (Group V). Similar structures can be made using Group IV semiconductor compounds by alloying carbon (C), silicon (Si) and germanium (Ge) in various concentrations.

[0094] By alloying Group IV or Group III and Group V elements, specific properties such as band gap, lattice constant and refractive index can be matched. Figure 3a ), 3b) and 3c) for compound In 1-x Al xAs is illustrated, where x is the mole fraction of aluminum compared to indium (1-x) in the compound. These three properties are continuous and almost linear functions of the mole fraction x, allowing the design of optoelectronic devices with specific and controllable properties. By doping III-V compounds with p or n dopants belonging to Groups II, IV or VI of the periodic table, pn junctions can be combined for various applications.

[0095] Two embodiments of the laser structure 112 will be described with reference to FIG. 4 , where 4a) and 4b) describe the basic functionality of a double heterostructure (DH) laser, and 4c) shows a quantum cascade laser. Both cases are exemplified by an EtOH sensor operating at 3.345 μm. It should be noted that other volatile substances (including H 2 O and CO 2 ) are equally valid examples. The only difference is the number of parameter values. The semiconductor gas sensor device according to the present invention can be designed for any such substance.

[0096] Figure 4a ) shows a multilayer structure epitaxially grown on top of an n-doped indium arsenide (n-InAs) substrate 401. The active layer 403, where laser emission occurs, has a small concentration of gallium to obtain a nominal band gap of 0.371 eV, corresponding to the desired emission wavelength of 3.345 μμm. Figure 3a ), which is obtained by a smaller molar fraction x1 = 0.022, and the band gap of pure InAs is 0.353 eV. 1-x1 Ga x1 The active layer 403 of As is surrounded by the layers 402 and 404 which are transparent to laser emission, in which the molar fraction of gallium is x2=0.1.

[0097] The active layer 403 is intrinsic and has no dopants, while the layer 402 closest to the substrate 401 is doped with n-doped In 1-x2 Ga x2 As, and the top layer is p-doped. Therefore, a pn junction is commonly present on the active layer 403. The top of the laser structure is a metal layer 405, preferably gold or other highly conductive metal, which constitutes the anode connection of the laser structure. The cathode connection 406 can be a metal layer at the bottom of the substrate 401, such as Figure 4a ), but it can also be Figure 1b ) is shown in the surface arrangement.

[0098] Figure 4b ) shows the energy diagram of the laser structure in equilibrium (i.e. no voltage is applied between the anode and cathode connections). The conduction band and the valence band are plotted on the structure as solid lines, where the band gap E of the active layer g1is having a higher band gap E g2 According to basic semiconductor theory, the doping of the layers positions the energy bands relative to each other and the Fermi level EF.

[0099] When a voltage is applied in the forward direction across the anode-cathode connection, charge carriers, electrons and holes, are injected into the pn junction, causing them to recombine in the active region with an emission energy close to E g1 At some threshold current, the population of the carriers is reversed and, according to basic laser theory, the spontaneous and uncorrelated photon emission will be flipped by the stimulated coherent emission.

[0100] Figure 4c ) shows an energy band diagram of another laser structure (quantum cascade laser), which represents a laser structure 112 according to one embodiment of the present invention. For the sake of clarity, the figure shows only a small part of the light emitting layer. The structure is composed of a superlattice of semiconductor layers 411a-411d and 412a-412c that are equidistant and very thin in the horizontal direction of the figure. Layers 411a-411d constitute quantum wells, while layers 412a-412c become energy barriers due to the difference in composition. The superlattice may include hundreds of layers, only a few of which are in Figure 4c ) is shown in FIG. The thickness of each layer is typically a few nanometers, which is equivalent to the de Broglie wavelength of the electron. As a result, the electrons are confined to occupy discrete energy levels 413a-413d shown by the dashed lines in the energy band diagram.

[0101] When the electron - from Figure 4c ), some of the electrons will tunnel through the thin barriers 412a-412c and occasionally emit electrons with energy The energy of a photon corresponds to the difference between the discrete energy levels 413a-413d. In the expression for E, h=6.63×1 0 - 34 Js is Planck's constant and ω is the angular frequency of the emitted IR radiation. Laser action driven by population inversion ultimately results in a stream of coherent photons due to the injection of high-energy electrons combined with non-radiative scattering of the lowest energy levels.

[0102] Figure 5 The typical current-voltage characteristics of the laser structure according to the present invention are shown. The basic signal characteristics of both DH structure lasers and quantum cascade lasers are similar. The current intensity is small before reaching a threshold value, which corresponds to the transition from spontaneous to excited radiation as described above. The threshold voltage u th With emission wavelength λ 0 The relationship is ut h =hc / eλ0 , where h = 6.6 × 10 -34 Js is Planck's constant, c = 3 × 10 8 m / s is the speed of light, and e = 1.6 × 10 -19 As is the electron charge. When for EtOH (λ 0 =3.345μm) exceeds the voltage u th = 0.371V threshold, the current will increase with a linear slope relative to the voltage. The slope or differential conductance will depend on the power dissipated across the various system components. In the absence of volatile materials, the losses within the optical waveguide depend on its quality factor Q wg =10 4 This situation is similar to Figure 5 In the presence of a substance, Figure 5 The dotted line in FIG. 1 corresponds to the slope of the current-voltage characteristic due to absorption loss. When the laser wavelength is modulated across the material absorption peak by the MEMS modulator 114, the current measurement at a constant voltage will produce a signal with twice the modulation frequency, such as Figure 2 As shown. Its amplitude will be proportional to the concentration of the substance. When used as an alternative or supplement to the MEMS modulator 114, by modulating the frequency ω at a constant angle m A similar situation occurs when modulation is performed by periodically changing the operating voltage from the voltage feed circuit 109. The modulation voltage will cause a small modulation of the temperature of the active layer and cause a corresponding, synchronized wavelength shift of a specific wavelength band generated within the active laser structure 112. Typically, the modulation frequency f is 1 / 200 MHz, depending on the signal bandwidth requirements. m =ω m / 2π in the range of 10...1000Hz.

[0103] Therefore, two different options, namely the modulation of the MEMS modulator 114 and the voltage feed circuit 109, can be used to obtain the necessary wavelength modulation, Figure 2 The lateral shift of the peak across the absorbing material for a specific band is shown, along with the synchronous detection of the power consumption amplitude at twice the modulation frequency.

[0104] Figure 6 An exemplary embodiment of a sensor system 600 according to the invention is schematically shown. A semiconductor gas sensor device 601 (which may also be referred to as an on-chip sensor unit) is connected to an electronic unit 602 via its terminals or contact pads, as already described in Figure 1a ) shown in the objects 105a, 105b and Figure 1b) is shown as item 118. The four sensor elements: laser structure 603, light modulator 604, photodiode 605 and temperature sensor 606 are connected to electronic buffer circuit elements 607, 608, 609, 610, providing analog / digital conversion, or vice versa, and other interface functions. An electronic control unit 613 (usually a programmable general purpose arithmetic and logic processor including memory units for permanent and temporary data storage) is used to control the operation of the sensor unit 601 and its wired or wireless communication 614 with external circuits. Obviously, an on-chip sensor unit 601 comprising fewer elements will have fewer contact devices and correspondingly fewer buffer circuit elements.

[0105] In one embodiment of the sensor system according to the invention, the electronic modulation is performed by the electronic unit 602 instead of by the optical modulator 604, Figure 1b In this embodiment, the modulation voltage (eg, the modulation voltage M=M 0 sinω m t) is superimposed on the DC drive voltage and applied to Figure 1a ) of the laser structure terminals 105a, 105b. In the presence of the substance to be detected, the current to the terminals 105a, 105b (representing a double modulation frequency S = S 0 sin 2ω m t signal) will be detected, and its amplitude S 0 will be the concentration of the substance c m A linear function of Figure 5 In this embodiment, Figure 6 An electronic control unit 613 mediated by a buffer unit 607 connected to the laser structure 606 provides the required modulation and demodulation operations.

[0106] The interface circuit 611 may also include means for controlling temperature, for example, by means of a Peltier element 612, which is also managed by the processor 613. Preferably, the heating and cooling capabilities of the Peltier element 612 are controlled by more than one temperature, including at least one point away from local heat sources. The thermal capacity of the Peltier element 612 is preferably much greater than that of the sensor substrate 101.

[0107] The electronics unit 602 preferably comprises a single crystal silicon chip with integrated circuits, an application specific integrated circuit (ASIC), specifically designed for determining the concentration of volatile substances. A plurality of such devices may be combined to measure or monitor a variety of substances.

[0108] The gas sensor system 600 according to the present invention can be used, for example, in breath alcohol devices, handheld devices for mobile use, fixed or mobile environmental monitoring devices, medical diagnostic and patient monitoring instruments, vehicle monitoring devices and systems, industrial processing equipment, and household appliances.

[0109] In particular, gas sensor systems are particularly useful in implementations where small physical size, ruggedness, low production cost, and low power consumption are important.

[0110] Reference Figure 7 The flowchart of FIG. 6 depicts a method for determining the concentration of volatile substances in an airflow using a gas detection system 600 including the above-mentioned gas sensor device 601. The method for determining the concentration of volatile substances in an airflow using the above-mentioned gas detection system comprises the following steps:

[0111] 705: Provide a gas detection system 600;

[0112] 710: Providing a gas flow to the surrounding environment of the semiconductor gas sensor device 100 of the gas detection system 600;

[0113] 715: supplying a driving voltage to the laser structure 112 of the semiconductor gas sensor device 100; and

[0114] 720: Recording the output from the means for detecting 112, 116 relating to the optical power dissipation of electromagnetic waves propagating in the optical waveguide resonator 106 as affected by the volatile substance in the gas stream.

[0115] The steps of providing the gas flow 710, supplying the drive voltage 715 and recording the output are repeated each time the volatile species in the gas flow are determined. A determination may also include recording multiple measurements and using, for example, a statistical average of the concentration measurements.

[0116] According to one embodiment, the laser structure is used not only to generate electromagnetic radiation, but also to detect the optical power dissipation caused by the interaction with the volatile material, by monitoring and controlling the current and voltage of the laser structure 112, and determining the concentration of the volatile material based on how the current-voltage characteristics of the laser structure 112 are affected by the volatile material in the gas flow.

[0117] Alternatively, the method includes monitoring and analyzing the output from a photodetector (eg, photodiode 116) which detects optical power dissipation in the optical waveguide resonator 106. The photodetector may require a drive voltage / current which would be provided by suitable known means.

[0118] The method may further include step 716 of activating and controlling the wavelength modulator 604 by the MEMS modulator 114 or by the modulation voltage feeding circuit 109 , thereby controlling and fine-tuning the optical resonance frequency of the optical waveguide resonator 106 .

[0119] The method may further comprise step 717 of measuring and controlling the temperature of the gas sensor device 601, for example comprising controlling the current supplied to the Peltier element 612 thermally connected to the gas sensor device 601. The method may further comprise measuring the temperature in the gas flow.

[0120] Example

[0121] In the following examples, EtOH is used as an exemplary substance to be detected. Other numerical parameters can be used for other substances (such as H 2 O and CO 2 ) to perform the corresponding calculations. In the following, calculations are provided to describe the basic performance limitations with respect to signal resolution, which represent the basic limitations of applicability. The parameter values ​​are based on data from commercial products (Nanoplus GmbH, Germany) and published experimental data (F. Ottonello Briano, Mid-Infrared Photonic Devices for On-Chip Optical Gas Sensing, Doctoral Thesis, The Royal Institute of Technology, Stockholm, Sweden, 2019). These data relate to devices that are not completely comparable to the present invention, but are indicative of the state of the art.

[0122] The calculation is performed through the following various detection steps. The laser is emitting light power P e =QE×P 0 =1.5×10 - 2 W, where P 0 =3.0×10 -2 W is the total power consumption, and QE=0.5 is the laser quantum efficiency. The optical power is from the region As (assuming 20 μm 2 ) and solid angle Ω s (0.01sr) is emitted to the corresponding attribute A wg (10μm 2 ),Ω wg (0.01sr) waveguide. Misalignment MA = 0.7 results in additional losses. The total loss factor LF1 before the optical power enters the waveguide resonator can be calculated from the following formula:

[0123]

[0124] According to formula (2), the loss factor LF1 = 0.35 is obtained, and the coupling power P entering the waveguide is obtained wg =5.3×10 -3 W. These values ​​are then substituted into the Beer-Lambert equation (3) to obtain m The light power AP absorbed by EtOH corresponds to the expected detection limit of 0.2 ppm according to Table 1, and the expression also includes the extinction coefficient Δε = 0.9 × 10 -4 pp - 1 m -1 The effective length L of absorption in the waveguide attenuation field is given by the following formula (4), where the parameter λ p =3.345μm, Q wg =10 4 , and the effective refractive index n eff =1.7.

[0125] ΔP / P wg ≈Γ×Δε×c m ×L (3)

[0126]

[0127] According to formulas (3) and (4), the absorbed power AP = 9.5 × 10 -10 W. Two detection options will be considered: (i) using a photodiode 116 to measure the change in waveguide optical power due to absorption, (ii) using the voltage feed circuits 109, 110 of the laser structure 112 to measure the change in current drawn from a constant voltage source.

[0128] The total photocurrent i from the photodiode 116 ph and its change Δi due to absorption ph The photodiode detection rate D can be used from the waveguide to the photodiode ph =5.4A / W and optical coupling factor LF2 = 10 -5 Calculated according to equations (5) and (6). The value of LF2 is chosen so as not to significantly affect Q wg .

[0129] i ph =D ph ×LF2×P wg (5)

[0130] Δi ph =D ph ×LF2×ΔP (6)

[0131] Substituting the results from the previous formulas into equations (5) and (6) provides the following results: ph =2.9×10 -7 A, and Δi ph =5.1μ10 -14 A. According to formula (6), this number may be related to the fundamental shot noise current i nsh where Δf is the effective bandwidth assumed to be 10 Hz.

[0132]

[0133] Use formula (7) to calculate the current noise i nsh =0.96×10 -12 A, and calculate the signal-to-noise ratio SNR = Δi ph / i nsh = 0.053, it can be concluded that for very low species concentrations, the photocurrent detection option has a resolution gap.

[0134] Formulas (8) and (9) can be used to calculate the corresponding values ​​using the second detection option of measuring the current, where the current varies due to the modulated drive voltage of the laser. Formula (8) gives the absorbed optical power AP / P 0 The relative current change Δi / i caused by 0 :

[0135]

[0136] Assuming a constant operating voltage u 0 =0.4V, which is slightly higher than the laser threshold voltage of 0.371V, the calculation result is: i 0 =P 0 / u 0 =3Δ10 -2 / 0.4=7.5×10 -2 A, Δi=2.4×10 -9 A,i nsh =4.9×10 -10 , and SNR = Δi / i nsh =4.9.

[0137] The noise expression for each of the detection cases (i) and (ii) corresponding to equations (7) and (9) is given by (4kTGΔf / e) 1 / 2 The thermal noise is more dominant, where k = 1.38 × 10 -23 J / K, and G is the effective conductive load.

[0138] Therefore, when using the modulated voltage feeding circuit 109, the detection principle of current measurement results in a signal-to-noise ratio that is almost two orders of magnitude higher than the photocurrent option, thereby meeting the 0.2 ppm resolution limit with a good margin.

[0139] The above embodiments should be understood as illustrative examples of the system and method of the present invention. It should be understood that those skilled in the art can make various modifications, combinations and changes to the embodiments that also include the above examples. Specifically, different partial solutions in different embodiments can be combined in other configurations that are technically possible.

Claims

1. A gas detection system (600) comprising a semiconductor gas sensor device (100) for determining the concentration of a volatile substance in a gas flow, the semiconductor gas sensor device (100) comprising a laser structure (112) and an optical waveguide resonator (106) formed in the same compound semiconductor (120), and means for detecting optical power dissipation of electromagnetic waves (112, 116) propagating in the optical waveguide resonator, the compound semiconductor (120) comprising a single crystal substrate (101) and a plurality of epitaxially grown semiconductor single crystal layers (125) arranged on the substrate (101), wherein: The plurality of epitaxially grown semiconductor single crystal layers (125) include at least one light emitting layer (103) and one light propagating layer (104), and wherein: - the light emitting layer (103) is present at least in the laser structure (112) and is arranged to emit electromagnetic radiation in a specific wavelength band; - the optical waveguide resonator (106, 106', 106") is at least partially constituted by a portion of the light propagation layer (104), and a main portion of the optical waveguide resonator (106, 106', 106") is separated from a remaining portion of the light propagation layer (104) and is arranged to resonate in the specific wavelength band; and - the laser structure (112) is arranged adjacent to a portion of the optical waveguide resonator (106) so as to provide means for transmitting electromagnetic radiation of the specific wavelength band generated in the light emitting layer (103) of the laser structure (112) to the optical waveguide resonator (106), wherein the gas detection system (600) further comprises an electronic unit (602) arranged to be electrically connected to the gas sensor device (601), and wherein the electronic unit (602) is arranged to output a wavelength modulated signal for the specific wavelength band.

2. The gas detection system (600) according to claim 1, wherein the gas detection system is configured so that the specific wavelength band at least partially overlaps with the position and width of the absorption peak of the substance.

3. The gas detection system (600) according to claim 1 or 2, wherein: The electronic unit (602) is arranged to be electrically connected to at least the laser structure (112) of the gas sensor device (601), and wherein the signal for wavelength modulation is a modulation voltage superimposed on a DC driving voltage of the laser structure (112), thereby providing electronic modulation of the electromagnetic wave in the optical waveguide resonator (106) and thereby providing wavelength modulation of the specific wavelength band.

4. A gas detection system (600) according to claim 1, 2 or 3, wherein: The semiconductor gas sensor device (100) includes a MEMS modulator (114a, 114b) at least partially formed in the light propagation layer (104), wherein the signal for wavelength modulation is configured to control the MEMS modulator (114a, 114b).

5. A gas detection system (600) according to any one of the preceding claims, wherein: The laser structure (112) comprises a laser waveguide (113) at least partially formed in or optically coupled to the light propagation layer (104), and wherein, during use, the laser waveguide (113) is optically coupled to the optical waveguide resonator (106).

6. A gas detection system (600) according to any one of the preceding claims, wherein: The semiconductor gas sensor device (100) is arranged to determine the concentration of a substance in the air, and the laser structure (112) is arranged to emit electromagnetic radiation in the specific wavelength band, and the optical waveguide resonator (106) is arranged to resonate in the specific wavelength band so that the specific wavelength band can be modulated across the absorption peak of the substance.

7. A gas detection system (600) according to any one of the preceding claims, wherein: The laser structure (112) is arranged adjacent to a portion of the optical waveguide resonator (106) with a gap of no more than 1 / 2 of a wavelength in the specific wavelength band, preferably no more than 1 / 4 of a wavelength in the specific wavelength band.

8. The gas detection system (600) according to any one of claims 1 to 6, wherein: The material of the light propagation layer (104) is selected to be highly transparent in the specific wavelength band.

9. The gas detection system (600) according to any one of claims 1 to 7, wherein: The size of the optical waveguide resonator (106) is designed so that the circumference C of the optical waveguide resonator r will be exactly equal to the expected resonant wavelength λ corresponding to the absorption peak wavelength of the substance to be detected r An integer N times of .

10. The gas detection system (600) according to any one of claims 1 to 4, wherein: The optical waveguide resonator (106) is a closed loop structure.

11. The gas detection system (600) according to claim 7, wherein: The optical waveguide resonator (106) is ring-shaped.

12. The gas detection system (600) according to any one of claims 1 to 8, wherein: The optical waveguide resonator (106) is a linear structure and includes a first reflector (106:1) and a second reflector (106:2) arranged at respective ends of the optical waveguide resonator (106).

13. The gas detection system (600) according to any one of claims 1 to 11, wherein: The optical waveguide resonator (106) is provided with at least one straight portion located adjacent to the laser structure (112), and the length of the straight portion is at least as long as the extension length of the laser structure (112) in the plane of the compound semiconductor (120).

14. The gas detection system (600) according to any one of claims 1 to 12, wherein: The plurality of layers (125) include at least one intermediate layer (103 / 102) arranged between the substrate (101) and the light propagation layer (104), the intermediate layer (103 / 102) existing below the light propagation layer (104) in the laser structure (112), and the intermediate layer (103 / 102) at least partially not existing below the light propagation layer (104) forming the optical waveguide resonator (106).

15. The gas detection system (600) according to any one of claims 1 to 13, wherein: The optical waveguide resonator (106) is partially freely suspended above the etched away portion of the intermediate layer (102, 103) and is partially supported by the remaining structure of the intermediate layer (102, 103).

16. The gas detection system (600) according to any one of claims 1 to 13, wherein: The optical waveguide resonator is partially freely suspended above the etched away portions of the intermediate layers (102, 103) and is partially supported by a plurality of bridges (616) disposed in the light propagation layer (104) and extending from a base structure (111) to the optical waveguide resonator (113).

17. The gas detection system (600) according to any one of claims 1 to 15, wherein: The width of each of the bridges (616) is smaller than the shortest wavelength in the particular wavelength band, and preferably smaller than 1 μm.

18. The gas detection system (600) according to any one of claims 1 to 16, wherein: The optical waveguide resonator (106) has a substantially rectangular cross-section with a width / thickness of approximately 2.0±0.5 / 0.2±0.1 μm.

19. The gas detection system (600) according to any one of claims 1 to 16, wherein: The means for detecting optical power dissipation of electromagnetic waves propagating in the optical waveguide resonator (106) is provided by the laser structure (112), which also includes means for monitoring and controlling current and voltage of the laser structure (112) during use.

20. The gas detection system (600) according to any one of claims 1 to 16, wherein: The means for detecting optical power dissipation of an electromagnetic wave propagating in the optical waveguide resonator (106) is a photodiode (116) constructed at least in part from a plurality of epitaxially grown crystalline layers (125).

21. The gas detection system (600) according to any one of claims 1 to 19, wherein: The laser structure (112) is a double heterostructure laser.

22. The gas detection system (600) according to any one of claims 1 to 19, wherein: The laser structure (112) is a quantum cascade laser.

23. The gas detection system (600) according to any one of claims 1 to 21, further comprising an optical feedback grating (115a, 115b) at least partially formed in the light propagation layer (104).

24. The gas detection system (600) of any one of claims 1-22, further comprising a temperature sensor (117) formed at least in part from a plurality of epitaxially grown crystalline layers (125).

25. The gas detection system (600) of claim 19, wherein: The electronic unit (602) is arranged to be also electrically connected to the photodiode (116) of the gas sensor device (601).

26. A method for determining the concentration of a volatile substance in a gas stream, comprising: -(705): Providing a gas detection system (600) according to any one of claims 1 to 24; - (710): providing a gas flow to the surrounding environment of the semiconductor gas sensor device (100) of the gas detection system (600); -(715): supplying a driving voltage to the laser structure (112) of the semiconductor gas sensor device (100) so as to emit electromagnetic radiation in a specific wavelength band; - supplying a signal for wavelength modulation so that the specific wavelength band is modulated across the absorption peak of the substance; and - (720): recording an output from said means for detecting (112, 116), said output being related to the optical power dissipation of an electromagnetic wave propagating in said optical waveguide resonator (106), said optical waveguide resonator being affected by said volatile substance in said gas flow.

27. The method according to claim 26, wherein: The step of recording the output from the means for detecting (112) includes monitoring and controlling the current and voltage of the laser structure (112) and determining the concentration of the volatile material based on how the current-voltage characteristics of the laser structure (112) are affected by the volatile material in the gas stream.

28. The method according to claim 26, wherein: The step of recording the output from the means for detecting (116) includes monitoring and analyzing the output from a photodiode (116) which detects the optical power dissipated in the optical waveguide resonator (106).

Images