Gas detection device

Abstract

The present invention relates to gas detection devices, and more particularly to volatile substance sensors, such as breath alcohol 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, the compound semiconductor including at least one light-emitting layer and a light-propagating layer. The optical waveguide resonator is formed in the light-propagating layer and is largely separated from the remainder of the light-propagating layer. The laser structure is positioned adjacent to a portion of the optical waveguide resonator and is arranged to transmit electromagnetic radiation at a specific wavelength band to the optical waveguide resonator, which is arranged to resonate at the specific wavelength band.

Description

Technical Field

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

[0002] In particular, the present invention relates to miniaturized semiconductor sensors and systems where small physical size, durability, 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 very high sensitivity with reliability and, preferably, short measurement and analysis times. Furthermore, it is desirable to provide such detection devices in large quantities to promote widespread use. Therefore, affordable solutions are highly sought after.

[0004] One example of the use of gas detection devices in which all of the above requirements exist is in the field of breath alcohol testing. In this field, evidential breathalyzers are used to provide legal evidence of illegal concentrations of alcohol in a person's blood (and breath); vehicle-based breathalyzers and fixed workplace breathalyzers 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 devices to control their level of intoxication. Evidential breathalyzers are typically based on spectrophotometer technology and are typically large, expensive, and consume a relatively large amount 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-use breathalyzers use platinum fuel cell sensors. These also require recalibration, but less frequently than semiconductor devices, typically once a year.

[0006] One type of spectral sensor that has been commercialized for use in vehicle-mounted and stationary breathalyzers is the multi-reflection spectral absorption cell. The term "multi-reflection" refers to the process of causing electromagnetic radiation to reflect within the measurement cell, preferably multiple times, to increase the optical path length and thereby improve the sensitivity of the sensor or measurement system of which the cell is a part. A particularly useful implementation of a multi-reflection cell is the so-called White cell, proposed by John U. White as early as 1942 (Journal of the Optical Society of America, 1942) and used ever since. White cell-based breathalyzers offer significant improvements in size and cost over other spectrophotometer-based sensors, as well as significant improvements in accuracy and reliability over silicon oxide sensors and other consumer products. However, this technology is difficult to miniaturize further, and the optical arrangement generally makes these sensors more expensive than sensors based purely on semiconductor technology. These issues are not limited to detectors used for alcohol detection. Rather, similar requirements can be found in all fields where the concentration of specific volatile substances (usually very small concentrations) needs to be determined, such as environmental monitoring, medical diagnostics and patient monitoring, and vehicle monitoring. Summary of the Invention

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

[0008] According to a first aspect, a semiconductor gas sensor device for determining the concentration of volatile substances in a gas flow is provided. 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 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 disposed on the substrate, wherein the plurality of epitaxially grown semiconductor single crystal layers include at least one light emitting layer and one light propagating layer. The light emitting layer is present at least in the laser structure and is configured to emit electromagnetic radiation within a specific wavelength band. The optical waveguide resonator is at least partially composed of a portion of the light propagating layer, and a majority of the portion is separated from the remaining portion of the light propagating layer, such that it can be optically viewed as a freely suspended element. The optical waveguide resonator is configured to resonate within the specific wavelength band. The laser structure is disposed adjacent to a portion of the optical waveguide resonator, thereby providing a device for transmitting electromagnetic radiation within the specific wavelength band generated in the light emitting layer of the laser structure to the optical waveguide resonator.

[0009] Therefore, the position and width of the specific wavelength 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 drive voltage. In each case, both the position and width of the specific wavelength band match the peak wavelength and width, or quality factor, of the absorption peak of the target substance.

[0010] 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.

[0011] 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 at a specific wavelength band, and the optical waveguide resonator is arranged to resonate at the specific wavelength band associated with a peak in absorbance of the specific substance.

[0012] 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.

[0013] According to one embodiment, the material of the light propagating layer is selected to be highly transmissive in a specific wavelength band.

[0014] According to one embodiment, the optical waveguide resonator is dimensioned such that its perimeter C r will be exactly equal to an integer N times the desired resonance wavelength λr corresponding to the absorption peak wavelength of the substance to be detected.

[0015] According to one embodiment, the optical waveguide resonator is a closed-loop structure. The closed-loop structure may be, for example, annular.

[0016] According to one embodiment, the optical waveguide resonator is a linear structure and includes a first reflector and a second reflector arranged at respective ends of the optical waveguide resonator.

[0017] According to one embodiment, the optical waveguide resonator is ring-shaped.

[0018] According to one embodiment, the optical waveguide resonator is provided with at least one straight portion positioned 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.

[0019] 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.

[0020] 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.

[0021] According to one embodiment, the optical waveguide resonator is partially freely suspended above the etched 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 bridges preferably have a width less than the shortest wavelength in a particular wavelength band, and preferably less than 1 μm.

[0022] 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.

[0023] According to one embodiment, a laser structure is used to measure the concentration of a volatile substance, and the semiconductor gas sensor device further comprises means for monitoring and controlling the current and voltage of the laser structure during use. The laser structure may be implemented as, for example, a double heterostructure laser or a quantum cascade laser.

[0024] According to one embodiment, the semiconductor gas sensor device further comprises a MEMS modulator formed at least partially in the light propagation layer and arranged to control the position of a specific wavelength band, hereinafter referred to as wavelength modulation.

[0025] According to one embodiment, the semiconductor gas sensor device further comprises an optical feedback grating formed at least partially in the light propagation layer.

[0026] According to one embodiment, the semiconductor gas sensor device further includes a photodiode formed at least partially from the plurality of epitaxial crystal growth layers.

[0027] According to one embodiment, the semiconductor gas sensor device further includes a temperature sensor formed at least in part from the plurality of epitaxial crystal growth layers.

[0028] According to one aspect of the present invention, a gas detection system comprises the semiconductor gas sensor device described above and an electronics unit electrically connected to at least the laser structure of the gas sensor device and controlling the gas sensor device. The electronics unit can be arranged to supply a modulation voltage superimposed on a DC drive voltage to the laser structure, thereby providing electronic modulation of the electromagnetic wave in the optical waveguide resonator, and thereby modulating a specific wavelength band of the electromagnetic wave in the waveguide resonator, in addition to or as an alternative to the MEMS modulation described above. Thus, two different wavelength modulation options are provided, namely, lateral shifting of the wavelength band across the absorption peak of the substance.

[0029] 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.

[0030] According to one aspect of the present invention, a method for determining the concentration of volatile substances in an air flow using the above-mentioned gas detection system is provided. The method comprises the following steps:

[0031] -Provide gas detection system;

[0032] - providing a gas flow to the immediate vicinity of the semiconductor gas sensor device of the gas detection system;

[0033] - supplying a drive voltage to the laser structure of the semiconductor gas sensor device; and

[0034] - recording the output from the device for detection, which is related to the optical power dissipation of the electromagnetic wave propagating in the optical waveguide resonator, this optical power dissipation being affected by the volatile substances in the air flow.

[0035] According to one embodiment, a laser structure is used not only to generate electromagnetic radiation but also to detect optical power dissipation caused by interaction with a volatile substance by monitoring and controlling the current and voltage of the laser structure and determining the concentration of the volatile substance based on how the current-voltage characteristics of the laser structure are affected by the volatile substance in the gas flow. Alternatively, the method includes monitoring and analyzing the output of a photodiode that detects optical power dissipation in an optical waveguide resonator.

[0036] The present invention can provide a gas sensor device based on a semiconductor gas sensor device arranged on a single chip. This offers significant advantages in terms of miniaturization, production costs, sensitivity, power consumption, and reliability. Compared to prior art semiconductor devices utilizing optical waveguides, the present invention provides more reliable and efficient optical coupling between a light source (e.g., a laser structure) and an optical waveguide resonator because both structures are formed within the same semiconductor multilayer structure.

[0037] Numerous additional benefits and advantages of the present invention will be readily apparent to those skilled in the art from the following detailed description and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention will now be described in more detail with reference to the accompanying drawings, in which:

[0039] Figures 1a to 1h A semiconductor gas sensor device according to the present invention is schematically shown, wherein a) is a cross-sectional view, b) is a top view, c) is a cross-sectional view of one embodiment, d) is a bottom 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 showing the reflection characteristics of the reflector according to one embodiment of the present invention;

[0040] Figure 2 is a graph showing the function of the semiconductor gas sensor device according to the present invention;

[0041] Figures 3a to 3c It shows In 1-x Ga x A graph of the properties of As;

[0042] Figures 4a to 4c Schematically illustrates an embodiment of the present invention, including a double heterostructure laser structure (a and b) and a quantum cascade laser structure (c), wherein a) is a bottom view of the double heterostructure laser structure, b) is a schematic diagram of the laser energy bands, and c) is a schematic diagram of the quantum cascade energy bands;

[0043] Figure 5 is a graph showing the current / voltage characteristics of the laser structure;

[0044] Figure 6 Schematically shows a sensor system configuration according to the present invention;

[0045] Figure 7 is a flow chart illustrating a method according to the present invention.

[0046] All figures are schematic, not necessarily 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 numeral appearing in more than one figure refers to the same object or feature throughout the figures. DETAILED DESCRIPTION

[0047] Terms such as "top," "bottom," "upper," "lower," "below," "above," and the like are used solely with reference to the geometry of embodiments of the invention as shown in the accompanying drawings and / or during normal operation or installation of one or more devices and are not intended to limit the invention in any way.

[0048] According to one aspect of the present invention, a device for determining the presence and concentration of volatile substances in the air is provided. According to the present 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 costs, and compatibility with other semiconductor devices. By integrating key components on a single chip, manufacturing steps requiring high precision and accuracy are performed in a process sequence known as surface micromachining, in which thousands of sensor devices on a single wafer can be processed in parallel. The desired manufacturing precision is managed using batch processing of semiconductor wafers, exposing the wafer surface to deposition or etching through tightly controlled two-dimensional patterns based on photolithography techniques with nearly atomic resolution.

[0049] According to an embodiment of the present invention, a single-mode laser is integrated with an optical waveguide, and devices for light modulation and detection are 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 Group IV and Group III-V compound semiconductors exhibit intrinsic properties that allow the design of sources and detectors of electromagnetic radiation in the IR range within the emission wavelength range between 0.5 μm and 10 μm. By alloying Group IV (e.g., C, Si, Ge) or Group III-V compounds (e.g., Al, Ga, In, P, As, Sb) using epitaxial crystal growth, complex structures with precisely controlled functions can be achieved. These properties of Group IV and Group III-V compound semiconductors and the mature technology for producing components using these materials make them good candidates for building materials for semiconductor gas sensor devices for determining the presence and concentration of volatile substances in air according to the present invention.

[0050] Table 1 provides three examples of volatile substances: water, carbon dioxide, and ethanol (EtOH), which include peak wavelength λ [μm] absorbance ε [ppm -1 m -1 ] and figures for the quality factor Q [dimensionless] and the dynamic concentration range [minimum…maximum ppm].

[0051] Infrared absorption by volatile substances is based on molecular vibrational transitions according to quantum mechanical transition rules. In the case of H2O and CO2, 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 vibrational stretching of the C-H bond, resulting in a peak surrounded by a continuous background of mixed vibrational and rotational transitions. Essentially, the same characteristic of unusually sharp absorption peaks is found in most organic compounds with C-H bonds.

[0052] Table 1. Main absorption peaks of H2O, CO2 and EtOH.

[0053]

[0054] Credit: Pacific Northwest National Laboratory (PNNL).

[0055] Note from Table 1 that all three substances exhibit singular absorption peaks within the outlined spectral range. The wavelength, absorbance, and quality factor vary between substances, but in most environments, including automotive applications, the peaks are clearly distinguishable from the background. The dynamic concentration range is estimated based on data from automotive applications and human exhalation over a temperature range of -40°C to +85°C. The minimum number corresponds to the resolution requirement, and the maximum number represents the highest expected concentration.

[0056] Figure 1a and Figure 1b Schematically shows a semiconductor gas sensor device 100 according to the present invention, 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 and electrically active portions of the device, and Figure 1bis a top view. The semiconductor gas sensor device 100 includes a single crystal substrate 101 (typically and preferably a III-V semiconductor) and a multilayer structure 125 disposed on top of the single crystal substrate 101. The multilayer structure 125 may be grown epitaxially and may also be partially removed at certain locations by selective etching using photolithography. The layers include, but are not limited to, a bottom layer 102 that acts as a buffer layer, for example, to mediate differences in crystalline properties between the substrate 101 and subsequent layers, a light emitting layer 103, and a light propagation layer 104. Conductive electrodes 105a and 105b supply current to the light emitting layer 103 in predetermined locations to induce reverse population of charge carriers and thereby stimulate coherent emission of IR radiation through lasing. The region between the electrodes 105a and 105b defines a laser structure 112. An optical waveguide resonator 106 is provided, in which the light propagation layer 104 resides. The optical waveguide resonator 106 is disposed as a free-standing structure at a distance above the substrate 101 as its primary portion. The optical waveguide resonator 106 may be suspended, for example, by a narrow bridge portion in the light propagating layer 104, by a vertical post supporting the optical waveguide resonator 106 from below, or by another support structure sized to interfere as little as possible with the optical properties of the optical waveguide resonator 106. Thus, a substantially empty space 106 c surrounds the optical waveguide resonator 106. Figure 1a , the structure of the optical waveguide resonator 106 is shown. The optical waveguide resonator 106 has a left portion 106a and a right portion 106b. Figure 1a The cross section passes through the laser structure 112 .

[0057] A portion of the optical waveguide resonator 106 is positioned 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 ¼ the wavelength, where "wavelength" refers to the shortest wavelength in the wavelength band intended for use with the semiconductor gas sensor device. Typically, this corresponds to a distance of 1 μm or less. As a result, the laser structure 112 is optically coupled to the optical waveguide resonator 106, and radiation originating from the emitting layer 103 within the laser structure 112 is transmitted into the optical waveguide resonator 106. The optical waveguide resonator 106 allows the light waves to propagate 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 beyond its physical boundaries into the immediate air environment in the empty space 106c as evanescent light fields 107a, 107b. The imaged area should not be considered quantitative, but rather indicates its presence and approximate extension. The evanescent optical fields 107a and 107b also extend to portions of the light propagation layer 104 that are not part of the optical waveguide resonator 106, and may also extend to the light emitting layer 103, which is part of the laser structure 112. The optical waveguide resonator 106 constitutes an optical resonator having a high quality factor, which is optically coupled to the laser structure 112, and whose emission wavelength band is determined by the resonant frequency and quality factor of the waveguide resonator.

[0058] 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 coupling the waveguide resonator 106 with the laser structure 112, which also comprises a waveguide, perpendicular to the waveguide. Figure 1a 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 overlaps, thereby providing efficient optical coupling.

[0059] according to Figure 1a 、 Figure 1b and Figure 1e In the embodiment of the present invention schematically shown in FIG, the waveguide resonator 106 is a closed loop structure and is preferably designed so that its circumference is exactly equal to the total number or integer multiples of the desired resonant wavelength corresponding to the absorption peak of the substance to be detected. The resonant light is coupled to the laser structure 112 to control its emission peak wavelength λ r Specifically, the perimeter C r =N×λ r / n eff , effective refractive index n eff= 1.7 is inserted to account for the fact that light propagation occurs as an evanescent field in the bulk waveguide 106 and in air, and N is an integer. As previously described, resonant light is coupled to the laser structure 112, controlling its emission peak wavelength.

[0060] Due to the close proximity of the laser structure 112 to the optical waveguide resonator 106, and as described with respect to Figure 1a ) is coupled from the laser structure to the optical waveguide resonator. The physical distance between the laser structure 112 and the optical waveguide resonator 106 is typically 1 μm, significantly less than the IR wavelength. As a result, optical power or intensity is 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 perimeter, but the majority of it is generally free-hanging, allowing single-mode propagation of IR radiation along its perimeter with low optical loss.

[0061] The light propagation layer 104, and therefore the optical waveguide resonator 106, is formed from a single crystal III-V semiconductor material epitaxially grown on the substrate 101, with a composition that makes it highly transparent to the IR radiation generated by the laser structure 112. A sacrificial layer has been etched away beneath the light propagation layer 104 of the optical waveguide resonator 106 to form an empty space 106c. The optical waveguide resonator 106 can typically have a rectangular cross-section with a width / thickness of approximately 2.0 / 0.2 μm, or preferably 2.0±0.5 / 0.2±0.1 μm. The gap defined by the sacrificial layer can typically be approximately 2 μm, or preferably 2.0±0.5 μm. Typically, during use, the IR radiation propagates twenty or more revolutions around the circumference before being completely scattered or absorbed.

[0062] 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 an air inlet 108a and an air outlet 108b for respectively introducing and withdrawing air into and from the measurement chamber 108c.

[0063] 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, with the other half constituting an evanescent wave propagating in the air, adjacent to the solid-state waveguide. This dimensionless ratio will be denoted as the external confinement factor Γ, depending on the size of the empty space 106c and other factors. A comprehensive description of the technical details of the waveguide implementation is provided in F. Ottonello Briano, Mid-Infrared Photonic Devices for On-Chip Optical Gas Sensing, PhD thesis, Royal Institute of Technology, Stockholm, Sweden, 2019.

[0064] According to one embodiment, the optical waveguide resonator 106 has an almost circular geometry and constitutes a high-Q optical resonator with a quality factor Q exceeding 10 4 This is achieved by minimizing light losses due to waveguide bending and scattering caused by surface defects. Its circumference is typically 1.2mm.

[0065] According to one embodiment, the optical waveguide resonator 106 comprises Figure 1b ) and linear sectors. Thus, efficient optical coupling to the laser structure 112 and modulator 114 (if used) can be achieved while maintaining low light bending losses in the curved sectors.

[0066] refer to Figure 1a to Figure 1b , the optical waveguide resonator 106 is depicted 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, connected from one end to the other. Figure 1e ) is not the waveguide Figure 1b ) is an S-shape, which allows the optical path of a single turn to be greater than that of a ring structure occupying a similar area. On the other hand, the S-shape inevitably means a smaller radius of curvature, which leads to 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 in close proximity.

[0067] During use, air flowing between the inlet 108a and the outlet 108b close to 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 air flow includes a concentration of c m The volatile material has an absorption peak that coincides with the emission wavelength of the laser structure 112. The interaction of the volatile material will cause optical power dissipation of the electromagnetic wave propagating in the optical waveguide resonator 106, and according to the present invention, this can be detected by the laser structure 112 itself or by additional detection devices representing different embodiments of the present invention.

[0068] According to one embodiment, the semiconductor gas sensor device 100 is arranged to utilize the current-voltage characteristic of the laser structure 112 as a device for detecting the interaction with the volatile material (i.e., the optical power dissipation in the optical waveguide resonator 106). According to the schematic equation, the power absorption of the laser structure 112 will affect the current-voltage characteristic of the laser as an additional power load.

[0069] i=i0-Δi(c m ) (1)

[0070] Where i0 is the current at the power supply voltage u0, which is not affected by the absorption of volatile substances, and △i(c m ) is the change in current due to the additional power load, which is the concentration of the species c m A monotonic function of . Figure 1a Schematically shown in FIG. 1 are a source 109 of a constant voltage u0 connected to the laser electrodes 105a, 105b and an ammeter 110 for measuring the current i.

[0071] Figure 1b The sensor chip shown in the top view may have a size of 0.5×0.5 mm 2 Typical surface dimensions and thickness are 0.3 mm. 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.

[0072] 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 a laser optical waveguide 113, one or more photodetectors, typically photodiodes 116, and one or more temperature sensors 117. Through strict temperature control, the position of a specific wavelength band can be adjusted to a position close to the absorption peak of the material, thereby defining the wavelength range of the modulation. This can be used in setup and calibration procedures to ensure the proper function of each individual sensor 100 according to the present invention.

[0073] 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 photodetectors can also be implemented as photoresistors, phototransistors, or as a combination and / or array of such detectors. Contact pads or terminals 118 are provided for electrical communication between the elements and external electronic circuitry. Terminals 118 are preferably arranged in a single row to facilitate connection to other components by, for example, wire bonding.

[0074] Laser structure 112 is arranged to emit single-mode infrared radiation along the surface of substrate 101 in the plane of the device. According to one embodiment, laser structure 112 is combined with optical feedback gratings 115a, 115b. Optical feedback gratings 115a, 115b comprise a repeating pattern with a continuously variable refractive index, thereby generating constructive reflections at different wavelengths of light defined by the repeating pattern of a continuous layer grown on or etched from substrate 101. This represents an optical resonator designed for a quality factor of approximately 300.

[0075] Feedback lines 115a, 115b and waveguide 113 provided in embodiments of the present invention are preferably formed in light propagation layer 104, constituting optical resonant elements that control laser emission. Therefore, single-mode emission from laser 112 is controlled by precise dimensions of its key parameters, such as the length, width, and thickness of the waveguide, its refractive index, and the length, depth, width, and repetition rate of the continuous steps of feedback lines 115a, 115b.

[0076] According to one embodiment, a MEMS (micro-electromechanical structure) modulator 114 is provided and, like the optical waveguide resonator 106, is constructed from a thin, partially suspended, partially free-hanging element formed at least partially within the light propagation layer 104. The MEMS modulator includes a fixed element 114a and flexible wires 114b, 114c, and 114d. Applying a voltage between the interdigitated "fingers" of elements 114a and 114b causes bending of elements 114c and 114d, which in turn causes a slight horizontal movement of 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.

[0077] Preferably, the modulator 114 is 3 Hz to 10 4 The invention relates to a novel optical multi-electromechanical ...

[0078] According to one embodiment, a photodiode 116 is disposed adjacent to the optical waveguide resonator 106 at another location along its perimeter. The distance between the photodiode 116 and the optical waveguide resonator 106 may preferably be 3 μm to 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 band gap are suitable for absorbing incident IR radiation. The photocurrent generated in the pn junction represents the total optical power propagated by the waveguide. The small portion of the 100 nm absorbed by the photodiode 116 is -5 or less is suitable for not affecting the quality factor of the optical waveguide resonator 106 to a large extent.

[0079] According to one embodiment, one or more temperature sensors 117 are disposed within the compound semiconductor 120. According to one embodiment, the temperature sensor 117 is positioned near the laser structure 112 to monitor the laser's operating temperature. The temperature sensor 117 is preferably a pn junction of a III-V material composition with a bandgap greater than the energy of the transmitted IR radiation. The open-circuit voltage of the pn junction is a reliable measure of temperature and depends primarily on its bandgap, which in turn is reproducible depending on temperature. Additional temperature sensors 117 may be positioned to measure the temperature of the gas within the measurement chamber 108c.

[0080] During operation, the compound semiconductor 120 should preferably be maintained within a controlled temperature range, 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.

[0081] As will be understood by those skilled in the art, the above structure 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, thereby allowing close control of the composition, crystal quality and thickness. The removal of one or several layers on specific areas can be achieved by etching, 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, which preferably has the same composition as the active waveguide layer 104, acts as a stop layer when the sacrificial layer 134 is etched away, allowing the optical waveguide resonator 106 to hang freely at the cross-sectional location, leaving space for the evanescent light field 107 in its vicinity.

[0082] The etching technique used to generate 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 dopant 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 inGaAs-AlGaAs, Sensors and Actuators 4, 1983, pp. 341-348, L Tenerz, B Micromachining of Three-Dimensional Structures Using Photo-Electrochemical Etching, Electronics Letters, 21, 1985, pp. 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, pp. 67 to 82.

[0083] Figure 1d ) shows a portion of the optical waveguide resonator 106, wherein it is mechanically attached to the substrate 101. Figure 1a ), an optical waveguide resonator 106 is constructed by depositing several layers 102, 103, and 104 on a semiconductor substrate 101. As previously described, the partial sacrificial nature of layer 103 is controlled by photolithography and selective etching. The optical waveguide resonator 106 consists of a portion of layer 104 that is freely suspended along nearly its entire perimeter, except for a location supported by a bridge 141 that passes through the optical waveguide resonator 106 and is attached to the substrate 101 by the remaining portions 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.

[0084] Figure 1e ) schematically shows the Figure 1b) , but with an alternative design for an optical waveguide resonator 106′, representing one embodiment, which, compared to a circular shape, includes several turns before connecting one end to the other. However, it still has a closed-loop structure, and its total length will be significantly longer than the circumference of a circle occupying the same surface. Optical path length is a key parameter for the sensitivity of sensors according to the present invention, but is offset by optical power losses caused by waveguide bending. Therefore, the choice between an optical waveguide resonator having a circular waveguide 106 or its more dense alternative 106′ is a question related to the technical performance requirements of various applications.

[0085] Figure 1f An embodiment of a gas sensing device 100 including an open optical waveguide resonator 106" is schematically shown. Here, open should be interpreted as not being in a closed-loop arrangement, and the optical waveguide resonator 106" according to this embodiment can be described as linear, such as but not limited to a straight line. The open optical waveguide resonator 106" is arranged adjacent to the laser structure 112 similar to the arrangement of the closed-loop optical waveguide resonator 106 described above, and can also be arranged to interact with the MEMS modulator 114 and / or the photodiode 116. The open optical waveguide resonator 106" can 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 provided at each end of the open optical waveguide resonator 106". The first reflector 106:1 and the second reflector 106:2 provide for increasing the optical path length of the open optical waveguide resonator 106". The first reflector 106:1 and the second reflector 106:2 can be provided as a periodic perturbation, for example, as a periodic variation of the refractive index or as a grating. Figure 1g to Figure 1h ) is a graph showing the function of a wavelength-specific reflector operating along the length x of a waveguide. By introducing periodic perturbations n1, n2 with respect to the refractive index n of the waveguide, the maximum optical reflectivity R will occur at the position given by the relation λ r =2n e Λ gives the specific wavelength λ r , which is the periodicity of the refractive index change, and n e is the effective refractive index, typically a weighted average of n1, 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, its spatial resolution accuracy and fine structure. In the present invention, the effect of wavelength-specific reflectors can be used to provide a resonator function as Figure 1a )and Figure 1b ) as an alternative to the ring waveguide 106 in ), or providing feedback lines 115a, 115b.

[0086] exist Figure 2 In Figure 1, the functional operation of the semiconductor gas sensor device 100 according to the present invention is summarized by a graph with wavelength as the horizontal axis and normalized light intensity or power as the vertical axis. An exemplary embodiment of the present invention is an EtOH sensor, which operates with a quality factor of about 1500 near the absorption peak 202 at 3.345 μm. Other implementations of H2O or CO2 sensors at their corresponding peak wavelengths can draw very similar graphs. Due to molecular rotational transitions that constitute the continuous absorption background at normal operating temperatures, the EtOH peak 202 extends above the continuous absorption "floor". However, this fact is not important here because the operation of the sensor is concentrated on a small wavelength interval of typically ±1 nm (0.001 μm), close to the EtOH peak 202 at 3.345 μm, and is controlled by the modulation depth of the modulator 114 or by controllably modulating the voltage feed circuit 109.

[0087] 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 shown by the peak 201 partially overlaps with the substance absorption peak 202. Figure 1b ) of the optical waveguide resonator 106 occurs at a spacing 205 of approximately 5 μm, corresponding to its free spectral range FSR = λ r 2 / n e L0, where λ r =3.345μm is the operating wavelength, n e =1.7 is the effective refractive index, and L0=1.2 is the waveguide circumference.

[0088] 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 only the central peak 201 exceeds the threshold 204 for laser operation, thereby maintaining the single-mode light emission at the peak 201. Therefore, Figure 2 The side peaks shown in are not emitted from the laser structure 112. As described above, by careful temperature control, the position of a specific wavelength band, as shown by the central peak 201, can be adjusted to be close to the absorption peak 202 of EtOH.

[0089] As described above, the modulation signals of the modulators 114a, 114b or the modulation signals applied to the voltage feed circuit 109 are controlling 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 2In FIG, the wavelength modulation of a specific wavelength band 201 is shown as interval 207. Graph 206a shows the position of the specific wavelength band 201 as a function of time, and graph 206b shows the resulting signal S=S0sin2ω m t. This signal will be described in more detail below. Preferably, as previously described, it is a sinusoidal angular frequency ω determined by the mechanical resonant frequency of the MEMS resonators 114a, 114b. m The modulation is performed by electronic modulation of the voltage feed circuit 109, or alternatively, by electronic modulation of the voltage feed circuit 109. The modulation amplitude M0 is preferably determined by the wavelength range suitable for the quality factor of the substance peak. Twice during each modulation cycle, when the EtOH substance is present near the optical waveguide resonator 106, the absorption of optical power will reach a peak. Therefore, in the presence of the substance, a signal representing power consumption at twice the modulation frequency will appear, synchronous with the modulation. Therefore, the presence and amplitude of the synchronous detection signal at twice the modulation frequency will carry information about the presence and concentration of the EtOH substance near the optical waveguide resonator 106.

[0090] 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 Group III and Group V of the periodic table include aluminum (Al), gallium (Ga), indium (In) (Group III) on the one hand, and phosphorus (P), arsenic (As), and antimony (Sb) (Group V) on the other. Similar structures can be fabricated using Group IV semiconductor compounds by alloying varying concentrations of carbon (C), silicon (Si), and germanium (Ge).

[0091] 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 ), Figure 3b )and Figure 3c ) shows the compound InIn 1-x Al x As, where x is the mole fraction of aluminum to indium (1-x) in the compound. These three properties are continuous and nearly linear functions of the mole fraction x, allowing the design of optoelectronic devices with specific and well-controlled properties. By doping III-V compounds with p-dopants or n-dopants belonging to Group II, IV, or VI of the periodic table, pn junctions can be introduced for various purposes.

[0092] Two embodiments of the laser structure 112 will be described by way of example with respect to FIG. 4 , wherein: Figure 4a )and Figure 4b ) describes the basic function of double heterostructure (DH) lasers, while Figure 4c) shows a quantum cascade laser. In both cases, an EtOH sensor operating at 3.345 μm is used as an example. It should be noted that other volatile substances (including H2O and CO2) can also be selected for equally effective examples. The only difference is the numerical value of the parameter. The semiconductor gas sensor device according to the present invention can be designed for any such substance.

[0093] Figure 4a The general DH laser structure of FIG depicts a multilayer structure grown by epitaxy on top of an n-doped indium arsenide (n-InAs) substrate 401. The active layer 403, where lasing 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 μm. Figure 3a ) is shown in Figure 2, which is obtained by pure InAs with a small molar fraction x1 = 0.022 and a band gap of 0.353 eV. 1-x1 Ga x1 An active layer 403 of As is surrounded by layers 402 and 404 which are transmissive to laser emission, wherein the molar fraction of gallium is x2 = 0.1.

[0094] The active layer 403 is intrinsic and lacks 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 exists across the active layer 403. On 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 such as Figure 4a ) is a metal layer at the bottom of the substrate 401, but it can also be as shown in FIG. Figure 1b ) is depicted from the surface arrangement.

[0095] 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 valence band spanning structure are drawn with solid lines. Due to its high gallium concentration, the band gap E of the active layer is g1 With 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 to the Fermi level E F .

[0096] When a voltage is applied across the anode-cathode junction in the forward direction, charge carriers, electrons and holes, are injected across the pn junction so that they recombine in the active region while emitting a charge with a charge close to E g1According to basic laser theory, at a certain threshold current, the carrier population becomes inverted, and spontaneous and uncorrelated photon emission will be overturned by stimulated coherent emission.

[0097] Figure 4c ) shows an energy band diagram of another laser structure (a quantum cascade laser, representing a laser structure 112 according to one embodiment of the present invention). For the sake of clarity, the figure shows only a small portion of the light emitting layer. The structure is constructed by a superlattice of semiconductor layers 411a to 411d and 412a to 412c that are equidistant and extremely thin in the horizontal direction of the diagram. Layers 411a to 411d constitute quantum wells, while layers 412a to 412c become energy barriers due to differences in composition. The superlattice can include hundreds of layers, only a few of which are in the Figure 4c ). The thickness of each layer is typically a few nanometers, which is comparable to the de Broglie wavelength of the electron. As a result, the electrons are confined to occupy discrete energy levels 413a to 413d in the band diagram as depicted by the dashed lines.

[0098] When the electron e - from Figure 4c ) is injected into the structure from the left side, some of which will pass through the thin barriers 412a to 412c and occasionally emit the energy The photons correspond to the difference between the discrete energy levels 413a to 413d. In the expression for E, h=6.63×10 -34 Js is Planck's constant, and ω is the angular frequency of the emitted IR radiation.Lasing action driven by population inversion will eventually constitute a coherent photon cascade due to the injection of high-energy electrons combined with non-radiative scattering from the lowest energy levels.

[0099] 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. As previously discussed, the current magnitude is small before reaching the threshold corresponding to the transition from spontaneous emission to stimulated emission. The threshold voltage u th and emission wavelength The relationship is u th =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 the voltage u is exceeded for the case of EtOH with λ0 = 3.345 μm th= 0.371V threshold, the current will increase with a linear slope with respect to the voltage. The slope or differential conductance will depend on the power dissipation across the various system components. In the absence of volatile substances, the losses within the optical waveguide depend on its quality factor Q wg =10 4 This situation corresponds to Figure 5 In the presence of a substance, the solid line corresponds to Figure 5 The slope of the current-voltage characteristic will decrease due to absorption losses. 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, as shown in FIG. Figure 2 Schematically depicted. Its amplitude will be proportional to the concentration of the substance. When used as an alternative or in addition to the MEMS modulator 114, the operating voltage from the voltage source 109 is modulated at a constant angle frequency ω m A similar situation occurs when modulation is performed by periodic variation of the modulation voltage. The modulation voltage will cause a small modulation of the temperature of the active layer and a corresponding synchronous wavelength shift of a specific wavelength band generated within the active laser structure 112. Typically, the modulation frequency f m =ω m / 2π is in the range of 10…1000 Hz, depending on the signal bandwidth requirements.

[0100] Therefore, two different options, namely the modulation of the MEMS modulator 114 and the voltage source 109, can be used to obtain the necessary wavelength modulation as defined in the present invention, such as Figure 2 The depicted wavelength band spans the lateral shift of the absorbing material peak, along with the synchronous detection of the power loss amplitude at twice the modulation frequency.

[0101] Figure 6 An exemplary embodiment of a sensor system 600 according to the present invention is schematically shown. A semiconductor gas sensor device 601 (also referred to as an on-chip sensor unit) is connected to a semiconductor gas sensor device 601 via its terminals or contact pads (e.g. Figure 1a ) are shown as items 105a, 105b and Figure 1b) is connected to an electronics unit 602. The four sensor elements—a laser structure 603, an optical modulator 604, a photodiode 605, and a temperature sensor 606—are connected to electronic buffer circuit elements 607, 608, 609, and 610, which provide analog-to-digital conversion (or vice versa) and other interface functions. An electronic control unit 613, typically a programmable general-purpose arithmetic and logic processor (including memory elements for permanent and temporary data storage), controls the operation of the sensor unit 601 and its wired or wireless communication 614 with external circuitry. Clearly, an on-chip sensor unit 601 comprising fewer elements will have fewer contact devices and correspondingly fewer buffer circuit elements.

[0102] In one embodiment of the sensor system according to the invention, the electronic modulation is performed by the electronic unit 602 instead of the light modulator 604, corresponding to Figure 1b ) 114a to 114d. In this embodiment, the modulation voltage (eg, a sinusoidally varying modulation voltage M=M0sinω) 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 at the terminals 105a, 105b indicates that a double modulation frequency S = S0sin 2ω will be detected. m t signal, and its amplitude S0 will be as about Figure 5 Concentration c of the substance being described m In this embodiment, the linear function of 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.

[0103] The interface circuit 611 may also include means for controlling temperature, for example, via a Peltier element 612, 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 remote from a local heat source. The Peltier element 612 preferably has a significantly greater thermal capacity than the sensor substrate 101.

[0104] The electronic unit 602 preferably comprises a single crystal silicon chip with an integrated circuit, a dedicated application specific integrated circuit ASIC, which is specifically designed for determining the concentration of volatile substances. Several such devices can be combined to measure or monitor multiple substances.

[0105] 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, instruments for medical diagnostics and patient monitoring, vehicle monitoring devices and systems, industrial processing equipment and household appliances.

[0106] In particular, gas sensor systems may be particularly useful in implementations where small physical size, durability, low production cost, and low power consumption are important.

[0107] Will refer to Figure 7 The flowchart of FIG. 6 illustrates a method for determining the concentration of volatile substances in an air flow using a gas detection system 600 including a gas sensor device 601 as described above. The method for determining the concentration of volatile substances in an air flow using the above gas detection system includes the following steps:

[0108] 705: Providing a gas detection system 600;

[0109] 710 : Providing a gas flow to the immediate vicinity of the semiconductor gas sensor device 100 of the gas detection system 600 ;

[0110] 715: Supplying a driving voltage to the laser structure 112 of the semiconductor gas sensor device 100; and

[0111] 720: Recording the output from the device for detection 112; 116, which is related to the optical power dissipation of the electromagnetic wave propagating in the optical waveguide resonator 106, which is affected by the volatile substances in the air flow.

[0112] The steps of providing airflow 710, applying drive voltage 715, and recording the output are repeated for each determination of volatile species in the airflow.A determination may also include recording multiple measurements and using a statistical average of, for example, the concentration measurements.

[0113] 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 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.

[0114] Alternatively, the method includes monitoring and analyzing the output from a light detector, such as a photodiode 116, which detects optical power dissipation in the optical waveguide resonator 106. The light detector may require a drive voltage / current to be supplied using suitable known devices.

[0115] The method may further comprise a step 716 of activating and controlling the wavelength modulator 604 , which is operated by the MEMS modulator 114 or by modulating the voltage source 109 , and thereby controlling and fine-tuning the optical resonance frequency of the optical waveguide resonator 106 .

[0116] The method may further comprise a 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.

[0117] Example

[0118] In the following examples, EtOH is used as an example substance to be detected. Other numerical parameters can be used to perform corresponding calculations on other substances (such as H2O and CO2). In the following, calculations are provided to describe the basic performance limitations on signal resolution, which represent the basic limitations of applicability. Parameter values ​​are based on data from commercial products (Nanoplus GmbH, Germany) and published experimental data (Mid-Infrared Photonic Devices for On-ChipOptical Gas Sensing by F.Ottonello Briano, PhD thesis, Royal Institute of Technology, Stockholm, Sweden, 2019). Data relate to devices not fully comparable to the present invention, but indicate the current state of the art.

[0119] The calculation is performed through the following various detection steps. Laser emission light power P e =QE×P0=1.5×10 -2 W, where P0 = 3.0 × 10 -2 W is the total power consumption, and QE=0.5 is the laser quantum efficiency. s (Assuming 20μm 2 ) and solid angle Ω s (0.01sr) is emitted to A with corresponding properties wg 、(10μm 2 ),Ω wg (0.01sr) in the waveguide. The misalignment MA = 0.7 is the cause of the additional loss. The total loss factor LF1 before the optical power enters the waveguide resonator can be calculated by the following equation

[0120]

[0121] According to equation (2), the loss factor LF1 = 0.35 and the coupling power P into the waveguide are obtained. wg =5.3×10 - 3 W. These values ​​are then inserted into the Lambert-Beer equation (3) to obtain the m The light power ΔP absorbed by EtOH corresponds to the desired detection limit of 0.2 ppm according to Table 1, and the expression includes the extinction coefficient Δε = 0.9 × 10 -4 pp-1 m -1 The effective length L of absorption in the evanescent field of the waveguide is given by equation (4), where the parameter λ p =3.345μm, Q wg =10 4 , and the effective refractive index n eff =1.7.

[0122] ΔP / P wg ≈Γ×Δε×c m ×L (3)

[0123]

[0124] According to equations (3) and (4), the absorbed power ΔP = 9.5 × 10 -10 W. Two detection options will be considered; (i) using a photodiode 116 to measure changes in optical power from the waveguide due to absorption; (ii) using the voltage fed circuits 109, 110 of the laser structure 112 to measure changes in current drawn from a constant voltage source.

[0125] Using the photodiode detectivity D from the waveguide to the photodiode ph =5.4A / W and optical coupling factor LF2=10 -5 , calculate the total photocurrent i from the photodiode 116 according to equations (5) and (6) ph And due to the absorption of △i ph The value of LF2 is selected so that it does not significantly affect Q wg .

[0126] i ph =D ph ×LF2×P wg (5)

[0127] Δi ph =D ph ×LF2×ΔP (6)

[0128] Using the results of the previous equations plugged into equations (5) and (6) provides the following results: i ph =2.9×10 -7 A, and △i ph =5.1×10 -14 A. According to equation (6), this number may be related to the fundamental shot noise current i nsh where ∆f is the effective bandwidth, assumed to be 10 Hz:

[0129]

[0130] The current noise i is calculated using equation (7) nsh =0.96×10 -12 A, and calculate the signal-to-noise ratio SNR = △i ph / i nsh = 0.053, it can be concluded that for very low species concentrations, there is a resolution gap in the photocurrent detection option.

[0131] Equations (8) and (9) can be used to calculate the corresponding values ​​using the second detection option of measuring the current, which varies due to the modulated drive voltage of the laser. The relative current change Δi / i0 due to the absorbed optical power ΔP / P0 is given by equation (8):

[0132]

[0133] Assuming a constant operating voltage u0 = 0.4 V, which is slightly higher than the laser threshold voltage of 0.371 V, the calculation result is: i0 = P0 / u0 = 3×10 -2 / 0.4=7.5×10 -2 A, △i=2.4×10 -9 A,i nsh =4.9×10 -10 , SNR=△i / i nsh =4.9.

[0134] Corresponding to the noise expressions in each detection case (i) and (ii) of equations (7) and (9), the shot noise is dominated by (4kTG△f / e) 1 / 2 The thermal noise is given by, where k = 1.38 × 10 -23 J / K, and G is the effective conductive load.

[0135] Therefore, when using the modulated voltage source 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, meeting the resolution limit of 0.2 ppm with a good margin.

[0136] The above embodiments should be understood as illustrative examples of the systems and methods of the present invention. It will be understood that those skilled in the art may make various modifications, combinations, and changes to the embodiments, including the above examples. In particular, where technically possible, different component solutions in different embodiments may be combined in other configurations.

Claims

1. A semiconductor gas sensor device (100) for determining the concentration of a volatile substance in an air 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 a device (112; 116) for detecting optical power dissipation of an electromagnetic wave propagating in the optical waveguide resonator (106), the compound semiconductor (120) comprising a single crystal substrate (101) and a plurality of epitaxially grown semiconductor single crystal layers (125) disposed 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 within 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 the 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), thereby providing means for transmitting electromagnetic radiation within the specific wavelength band generated in the light emitting layer (103) of the laser structure (112) to the optical waveguide resonator (106), The semiconductor gas sensor device (100) includes a MEMS modulator (114a, 114b) at least partially formed in the light propagation layer (104) and arranged to control the position of the specific wavelength band.

2. The semiconductor gas sensor device (100) according to claim 1, 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).

3. The semiconductor gas sensor device (100) according to claim 1 or 2, wherein: The semiconductor gas sensor device (100) is arranged to determine the concentration of a specific substance in the air, the laser structure (112) is arranged to emit electromagnetic radiation at the specific wavelength band, and the optical waveguide resonator (106) is arranged to resonate at the specific wavelength band associated with a peak in the absorbance of the substance.

4. The semiconductor gas sensor device (100) according to claim 1, wherein The laser structure (112) is arranged adjacent to a portion of the optical waveguide resonator (106) with a gap therebetween, the gap not exceeding ½ a wavelength in the specific wavelength band.

5. The semiconductor gas sensor device (100) according to claim 1, wherein The material of the light propagation layer (104) is selected to be highly transmissive in the specific wavelength band.

6. The semiconductor gas sensor device (100) according to claim 1, wherein The size of the optical waveguide resonator (106) is designed so that the circumference Cr will be exactly equal to an integer N times the desired resonance wavelength λr corresponding to the absorption peak wavelength of the substance to be detected.

7. The semiconductor gas sensor device (100) according to claim 1, wherein The optical waveguide resonator (106) is a closed loop structure.

8. The semiconductor gas sensor device (100) according to claim 7, wherein: The optical waveguide resonator (106) is ring-shaped.

9. The semiconductor gas sensor device (100) according to claim 1, 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).

10. The semiconductor gas sensor device (100) according to claim 1, 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).

11. The semiconductor gas sensor device (100) according to claim 1, 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).

12. The semiconductor gas sensor device (100) according to claim 1, 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).

13. The semiconductor gas sensor device (100) according to claim 1, 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 (106).

14. The semiconductor gas sensor device (100) according to claim 13, wherein: Each of the bridges (616) has a width smaller than the shortest wavelength in the particular wavelength band.

15. The semiconductor gas sensor device (100) according to claim 1, wherein: The optical waveguide resonator (106) has a rectangular cross section with a width / thickness of 2.0±0.5 / 0.2±0.1 μm.

16. The semiconductor gas sensor device (100) according to claim 1, wherein: Means for detecting optical power dissipation of electromagnetic waves propagating in the optical waveguide resonator (106) are provided by the laser structure (112), which also includes means for monitoring and controlling current and voltage of the laser structure (112) during use.

17. The semiconductor gas sensor device (100) according to claim 1, wherein The device for detecting optical power dissipation of electromagnetic waves propagating in the optical waveguide resonator (106) is a photodiode (116) at least partially composed of a plurality of epitaxial crystal growth layers (125).

18. The semiconductor gas sensor device (100) according to claim 1, wherein: The laser structure (112) is a double heterostructure laser.

19. The semiconductor gas sensor device (100) according to claim 1, wherein: The laser structure (112) is a quantum cascade laser.

20. The semiconductor gas sensor device (100) of claim 1, further comprising an optical feedback grating (115a, 115b) formed at least partially in the light propagation layer (104).

21. The semiconductor gas sensor device (100) of claim 1, further comprising a temperature sensor (117) formed at least in part from the plurality of epitaxial crystal growth layers (125).

22. The semiconductor gas sensor device (100) according to claim 1, configured such that the specific wavelength band at least partially overlaps with the position and width of an absorption peak of a substance.

23. The semiconductor gas sensor device (100) according to claim 4, wherein The gap does not exceed 1 / 4 of the wavelength in the specific wavelength band.

24. The semiconductor gas sensor device (100) according to claim 14, wherein Each of the bridges (616) has a width of less than 1 μm.

25. A method of determining the concentration of a volatile substance in a gas stream, comprising: - (705): Providing a semiconductor gas sensor device (100) according to any one of the preceding claims; - (710): providing a gas flow to the immediate vicinity of the semiconductor gas sensor device (100); - (715): supplying a driving voltage to the laser structure (112) of the semiconductor gas sensor device (100); and - (720): recording an output from a device for detecting (112; 116), said output being related to the optical power dissipation of an electromagnetic wave propagating in an optical waveguide resonator (106), said optical power dissipation being affected by the volatile substance in the air flow.

26. The method according to claim 25, wherein The step of recording the output from the device 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 flow.

27. The method according to claim 25, wherein The step of recording the output from the means for detecting (116) includes monitoring and analyzing the output from a photodiode (116) that detects the optical power dissipation in the optical waveguide resonator (106).

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