Integrated photoacoustic gas sensor and method for manufacturing the same

Abstract

The present disclosure relates to a photoacoustic gas sensor for detecting the presence or absence of gas using the interaction of a laser beam and gas molecules. The integrated photoacoustic gas sensor according to an embodiment includes a light output unit; a lens unit configured to concentrate a laser beam output from the light output unit; and a photoacoustic sensing unit having a quartz tuning fork aligned on the lens unit and configured to convert a vibration, generated when the laser beam passing through the lens unit interacts with gas molecules, into an electric signal.

Claims

1. An integrated photoacoustic gas sensor, comprising: a light output unit; a lens unit disposed on the light output unit and configured to concentrate a laser beam output from the light output unit; and a photoacoustic sensing unit disposed on the light output unit and configured to convert a vibration, generated when the laser beam passing through the lens unit interacts with gas molecules, into an electric signal; wherein the lens unit and the photoacoustic sensing unit are aligned vertically and integrated in a single semiconductor chip.

2. The integrated photoacoustic gas sensor according to claim 1, wherein the light output unit is aligned vertically with the lens unit and the photoacoustic sensing unit in the single semiconductor chip.

3. The integrated photoacoustic gas sensor according to claim 2, wherein the single semiconductor chip has a surface area of several cm.sup.2 or less.

4. The integrated photoacoustic gas sensor according to claim 1, wherein the light output unit includes: a substrate; a laser active layer formed on the substrate; and a cladding layer formed on the laser active layer.

5. The integrated photoacoustic gas sensor according to claim 4, wherein the light output unit further includes a reflection unit configured to adjust a travel direction of a laser beam emitted from the laser active layer to a vertical upward direction.

6. The integrated photoacoustic gas sensor according to claim 1, wherein the photoacoustic sensing unit includes a U-shaped quartz tuning fork aligned on the lens unit and having an opening, wherein gas molecules existing around the quartz tuning fork absorb the laser beam passing through the opening to generate a photoacoustic wave, and wherein the photoacoustic sensing unit is configured to convert a vibration by the photoacoustic wave into an electric signal by using a piezoelectric element.

7. The integrated photoacoustic gas sensor according to claim 6, wherein the photoacoustic sensing unit further includes an acoustic resonator configured to amplify the photoacoustic wave.

8. The integrated photoacoustic gas sensor according to claim 1, wherein the light output unit includes a vertical cavity surface emitting laser.

9. An integrated photoacoustic gas sensor, comprising: a lens unit configured to concentrate a laser beam output from an external light source; and a photoacoustic sensing unit having a quartz tuning fork aligned on the lens unit and configured to convert a vibration, generated when the laser beam passing through the lens unit interacts with gas molecules, into an electric signal; wherein the lens unit and the photoacoustic sensing unit are aligned vertically and integrated in a single semiconductor chip.

10. The integrated photoacoustic gas sensor according to claim 9, wherein the single semiconductor chip has a surface area of several cm.sup.2 or less.

11. The integrated photoacoustic gas sensor according to claim 9, wherein the photoacoustic sensing unit comprises a U-shaped quartz tuning fork aligned on the lens unit and having an opening, wherein gas molecules existing around the quartz tuning fork absorb the laser beam passing through the opening to generate a photoacoustic wave, and wherein the photoacoustic sensing unit is configured to convert the vibration by the photoacoustic wave into the electric signal by using a piezoelectric element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a sectional view showing a structure of a photoacoustic gas sensor according to an embodiment.

(2) FIG. 2 shows that a laser beam passing through a quartz tuning fork (QTF) interacts with gas molecules in the photoacoustic gas sensor according to an embodiment.

(3) FIG. 3 is a plan view showing the photoacoustic gas sensor according to an embodiment.

(4) FIGS. 4A and 4B are a sectional view and a plan view showing a photoacoustic gas sensor according to another embodiment.

(5) FIGS. 5A to 5F are sectional views of each step for illustrating a method for manufacturing the photoacoustic gas sensor according to an embodiment.

DETAILED DESCRIPTION

(6) The terms used in this specification are selected as currently widely used general terms as possible while considering their functions, but may vary depending on the intention or custom of a person skilled in the art or the emergence of new technology. In addition, in a specific case, there is a term arbitrarily selected by the applicant, and in this case, its meaning will be described in this specification. Therefore, it should be understood that the terms used in this specification should be interpreted based on the actual meaning of the terms and the contents of the entire specification, rather than simple names of the terms.

(7) Hereinafter, embodiments will be described in detail with reference to the accompanying drawings and the contents described in the accompanying drawings, but the scope of the claims is not limited or defined by the embodiments.

(8) FIG. 1 is a sectional view showing a structure of a photoacoustic gas sensor according to an embodiment.

(9) Referring to FIG. 1, the photoacoustic gas sensor according to an embodiment includes a light output unit 10, a lens unit 20 disposed on the light output unit 10, and a photoacoustic sensing unit 30 disposed on the light output unit 10. The components of the photoacoustic gas sensor are vertically disposed on a single semiconductor chip 40.

(10) The light output unit 10 is a component for outputting a laser light irradiated toward the photoacoustic sensing unit 30 through the lens unit 20. According to an embodiment, the light output unit 10 includes a stacked structure composed of a substrate 110, a laser active layer 120 and a cladding layer 130, and a reflection unit 140 attached to an etched side of the structure.

(11) For example, if the principle of a general semiconductor laser is used, when a current flows through a semiconductor, which is a gain medium, a pumping action occurs, and electrons and holes meet to generate light while returning to a stable state. The material or structure of the semiconductor laser changes according to the wavelength at which the absorption spectrum of a gas molecule to be detected exists. Wavelength bands of ultraviolet (UV), visible (VIS), and infrared (IR) may be used, and accordingly, semiconductor laser diodes or quantum cascade lasers may be used.

(12) The light generated in this way travels along a waveguide in the laser active layer 120 and arrives at the reflection unit 140 attached to the edge surface of the pre-etched structure. The edge surface to which the reflection unit 140 is attached has an appropriate inclination (e.g., 45°) to change a travel path of the light, and the laser beam reflected by the reflection unit 140 travels vertically upward (i.e., a direction perpendicular to the surface of the substrate).

(13) The lens unit 20 is disposed on a portion of the light output unit 10 to be aligned with a laser beam output terminal, and includes, for example, a convex lens or a planar lens capable of refracting the laser beam output from the light output unit 10 so that the laser beam travels straight without spreading. As the beam is concentrated more on a quartz tuning fork, explained later, it is possible to detect gas molecules with higher sensitivity.

(14) The photoacoustic sensing unit 30 is disposed on the light output unit 10 and is a component for converting the vibration, generated when the laser beam passing through the lens unit 20 interacts with gas molecules, into an electric signal. The photoacoustic sensing unit 30 includes a quartz tuning fork 310 aligned on the lens unit 20, The quartz tuning fork 310 may be, for example, a U-shape (a form having an opening at one side) commonly used in a photoacoustic sensor as shown in FIG. 2. The quartz tuning fork has a high Q value, and as the Q value increases, the amount of change in electric energy according to the concentration of gas molecules increases, thereby securing higher sensitivity. The quartz tuning fork may be, for example, several millimeters in size similar to the size of a laser/photonic circuit chip, and since the laser beam is aligned according to a concentrated position, the sensor unit may be integrated on one chip.

(15) FIG. 2 shows that a laser beam passing through a quartz tuning fork (QTF″) interacts with gas molecules in the photoacoustic gas sensor according to an embodiment. As shown in FIG. 2, a laser beam L output from the light output unit 10 and concentrated by the lens unit 20 passes through an opening (a perforated portion) of the quartz tuning fork 310. At this time, a gas molecule G absorbs the laser beam L to generate a photoacoustic wave, and the photoacoustic sensing unit converts the vibration caused by the photoacoustic wave into an electric signal by using a piezoelectric element. A processor connected to the gas sensor processes the electric signal to obtain related information such as type and density of the gas.

(16) According to an embodiment, the photoacoustic sensing unit 30 may further include an acoustic resonator that amplifies the photoacoustic wave.

(17) FIG. 3 is a plan view showing the photoacoustic gas sensor according to an embodiment.

(18) As described above, the laser light generated by the light output unit 10 travels along a waveguide and is reflected by the reflection unit to be output in a vertical upward direction. The output laser beam is concentrated by the lens unit 20 and passes through the quartz tuning fork 310 to detect the presence or absence of gas by processing the electric signal generated by the piezoelectric effect.

(19) According to this structure, since components such as the light output unit, the lens unit and the photoacoustic sensing unit are vertically aligned on a single semiconductor chip, the components occupy a much smaller volume, compared to a conventional structure in which components are horizontally arranged on a semiconductor chip. Preferably, since the surface area of the semiconductor chip on which the integrated gas sensor is aligned according to the embodiment is several cm.sup.2 or less, it is possible to provide a gas sensor that is portable and highly useful.

(20) In addition, unlike the existing QEPAS structure using a large number of optical components that must be aligned from time to time, in the present disclosure, realignment is not required once the components are aligned in the manufacturing stage, and the number of components may also be drastically reduced, thereby greatly reducing the product cost.

(21) Hereinafter, a structure of a photoacoustic gas sensor according to another embodiment, different from the structure according to the former embodiment, will be described.

(22) FIGS. 4A and 4B are a sectional view and a plan view showing a photoacoustic gas sensor according to another embodiment. The structure shown in FIGS. 4A and 4B uses a vertical cavity surface emitting laser device instead of the stack-type semiconductor laser device and the mirror reflection unit described above. That is, the light output unit 11 does not require a separate structure such as a reflection mirror, a waveguide and a condensing lens because it outputs a laser in a vertical upward direction according to power supply. The other structures detect the presence or absence of gas based on the interaction between the laser beam and gas molecules existing in the opening of the quartz tuning fork 310 by the photoacoustic sensing unit 30 disposed on the substrate 110, similar to in the former embodiment.

(23) According to still another embodiment of the present disclosure, the integrated photoacoustic gas sensor may include only a lens unit and a photoacoustic sensing unit except for the light output unit. In this case, gas is detected using a laser beam output from an external light source. According to the structure that does not include the light output unit as described above, the overall size of the system including the external light source may be increased, but there is an advantage that several types of gas molecules may be detected using one sensor.

(24) Hereinafter, a method for manufacturing a photoacoustic gas sensor will be described with reference to the drawings.

(25) FIGS. 5A to 5F are sectional views of each step for illustrating a method for manufacturing the photoacoustic gas sensor according to an embodiment.

(26) Referring to FIG. 5A, a light output unit 10 in which a first the substrate 110, a laser active layer 120 and a cladding layer 130 are stacked is formed. The substrate 110 may be made of, for example, silicon, glass, III-V compound semiconductors, or a combination thereof, but is not limited thereto. The laser active layer 120 is a layer that generates light when an electric current is supplied, and includes a waveguide core that is a path through which light travels.

(27) Subsequently, a portion of the light output unit 10 is etched as shown in FIG. 5B. The inclination of the etched surface is preferably 45°, but may vary depending on the location or arrangement of the components.

(28) Subsequently, as shown in FIG. 50, a reflection unit 140 for reflecting a laser beam is formed on the etched portion. The reflection unit 140 may adjust the travel direction of the laser beam traveling along the waveguide of the laser active layer into a direction perpendicular to the substrate.

(29) Subsequently, as shown in FIG. 5D, the light output unit 10 to which the reflection surface is attached is turned over and disposed on the semiconductor chip 40. Since the surface area of the semiconductor chip 40 is preferably several cm.sup.2 or less as described above, it is possible to manufacture an integrated gas sensor having a much smaller volume than that of a conventional structure.

(30) Subsequently, the lens unit 20 is placed on the inverted light output unit 10 as shown in FIG. 5E. The lens unit 20 is arranged to align with the laser beam output terminal, and helps the laser beam to travel straight without spreading.

(31) Finally, the photoacoustic sensing unit 30 is disposed on the light output unit 10 as shown in FIG. 5F. The photoacoustic sensing unit 30 has a U-shaped quartz tuning fork 310 aligned on the lens unit 20. According to an embodiment, the quartz tuning fork 310 may have a U-shape having an opening used in a general photoacoustic sensor. The quartz tuning fork may be, for example, several millimeters in size similar to the size of a laser/photonic circuit chip, and since the laser beam is aligned according to a concentrated position, the sensor unit may be integrated on one chip.

(32) As described above, the light output unit 10, the lens unit 20 and the photoacoustic sensing unit 30 are vertically aligned and integrated on a single semiconductor chip 40. According to this structure, the components occupy a much smaller volume compared to the conventional QEPAS structure in which components are individually disposed on a semiconductor chip. In addition, the existing QEPAS uses a large number of optical components and has a disadvantage that components must be aligned from time to time, but according to the structure of this embodiment, realignment is not required after the components are once aligned ire the manufacturing stage, and the number of components may also be significantly reduced, thereby greatly reducing the product cost.

(33) Although the present disclosure has been described above with reference to the embodiments, it should be understood that the present disclosure can be changed and modified by those skilled in the art in various ways without departing from the idea and scope of the present disclosure defined in the appended claims.