Distance measuring sensor

Abstract

To provide a range sensor capable of being reduced in size.SOLUTION: A range sensor according to the present invention comprises a light-receiving element and light-emitting elements. The plurality of light-emitting elements are insularly disposed on the light-receiving element. It is configured that the light-receiving element receives reflected light that has passed through portions between the light-emitting elements, the reflected light of light having been emitted by the light-emitting elements. Consequently, the light-emitting elements and the light-receiving element can be stacked, and a size of the range sensor can be reduced.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a distance measuring sensor, and more particularly to a light detection type distance measuring sensor.

Background Art

[0002] In systems such as an advanced driver assistance system (ADAS) or an autonomous driving system, it is necessary to obtain information on the environment in which the vehicle travels. One such sensor is a light detection type distance measuring sensor.

[0003] A light detection type distance measuring sensor detects reflected light in which the irradiated laser light is reflected by an object in the surrounding environment, and detects the distance to the object in the environment from the time delay between the irradiated laser light and the reflected light.

[0004] Currently, the scanning method of this light detection type distance measuring sensor is mainly a mechanical scanning method using movable parts. However, this mechanical scanning method is difficult to miniaturize the distance measuring sensor and is also vulnerable to vibration, so it is difficult to use for autonomous vehicles and the like.

[0005] Patent Document 1 discloses a distance measuring sensor that can be scanned without using a mechanical mechanism by using an optical phased array (OPA) that changes the phase of light to change the irradiation angle of light.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, the distance measuring sensor described in Patent Document 1 has an optical transmitter and an optical receiver having an optical phased array integrated circuit, which are arranged side by side on a printed circuit board. Since the optical transmitter and the optical receiver are separate components, further miniaturization is difficult.

[0008] This invention has been made in view of the problems of the prior art, and its objective is to provide a distance measuring sensor that can be further miniaturized. [Means for solving the problem]

[0009] As a result of diligent research to achieve the above objective, the inventors have discovered that by arranging light-emitting elements in an island-like manner and allowing reflected light to pass through the spaces between the light-emitting elements, it becomes possible to stack light-emitting elements and light-receiving elements, thereby achieving the above objective, and thus completing the present invention.

[0010] In other words, the distance measuring sensor of the present invention comprises a light-receiving element and a light-emitting element. Furthermore, multiple light-emitting elements are arranged in an island-like manner on the light-receiving element. The above-mentioned light-receiving element is characterized by receiving reflected light from the light-emitting elements that has passed through the space between the light-emitting elements. [Effects of the Invention]

[0011] According to the present invention, by arranging multiple light-emitting elements in an island-like configuration and allowing reflected light to pass through the gaps between the light-emitting elements, the light-emitting elements and the light-receiving elements can be stacked, thereby providing a distance measuring sensor that can be further miniaturized. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram showing an example of the distance measuring sensor of the present invention. [Figure 2] This is a schematic diagram showing another example of the distance measuring sensor of the present invention. [Figure 3] This is a schematic diagram showing an example of a distance measuring sensor equipped with the phase modulator of the present invention. [Figure 4] This is a process diagram illustrating an example of the manufacturing process for the distance measuring sensor of the present invention. [Modes for carrying out the invention]

[0013] The distance measuring sensor of the present invention will be described in detail. As shown in Figure 1, the distance measuring sensor of the present invention comprises a light-receiving element and a light-emitting element, with a plurality of light-emitting elements arranged in an island-like configuration on the light-receiving element. Each light-emitting element then emits coherent light in the stacking direction between the light-receiving element and the light-emitting element (upward direction in Figure 1). The reflected light, which is reflected by objects in the environment and returns, passes through the spaces between the light-emitting elements, and the light-receiving element receives this reflected light to detect the distance to the object.

[0014] In this way, by arranging multiple light-emitting elements in an island-like configuration, reflected light from objects in the environment passes through the spaces between the light-emitting elements. Therefore, even if the light-emitting elements are placed on a light-receiving element, the light-receiving element can receive the reflected light that returns. This eliminates the need to arrange the light-emitting elements and light-receiving elements side by side, enabling miniaturization. Note that Figures 1 and 2 omit the transparent oxide film provided between the light-emitting elements.

[0015] The above-mentioned light-emitting element and light-receiving element are formed from semiconductor elements where a P-type semiconductor and an N-type semiconductor are joined in a PN junction. The light-emitting element emits light when a voltage is applied, and the light-receiving element is a diode that generates a voltage when it receives light.

[0016] Specifically, the light-emitting element described above is a vertical cavity surface-emitting laser (VCSEL) with a structure in which a light-emitting layer, made by stacking multiple P-type, N-type semiconductors or undoped semiconductors of different compositions, is sandwiched between a lower electrode and an upper transparent electrode. The photodetector, on the other hand, has a structure in which a P-type semiconductor and an N-type semiconductor are joined together, and electrodes are provided on both the P-type and N-type semiconductors to extract the current generated by light detection.

[0017] As the semiconductor material constituting the diode, for example, known semiconductor materials conventionally used in diodes such as aluminum gallium arsenide (AlGaAs), gallium arsenide phosphide (GaAsP), indium gallium nitride (InGaN), aluminum gallium nitride (AlGaN), etc. can be used. However, indium gallium arsenide (InGaAs) and indium gallium arsenide phosphide (InGaAsP) can be preferably used because they emit eye-safe laser light with a wavelength of 1.4 μm or more.

[0018] Note that the P-type semiconductor is a semiconductor in which a dopant that supplies holes with few electrons in the outermost shell is added to the above semiconductor material, and the N-type semiconductor is a semiconductor in which a dopant that supplies electrons with many electrons in the outermost shell is added to the above semiconductor material.

[0019] In addition, as the lower electrode of the light-emitting element, a material obtained by heavily doping the above semiconductor material with an N-type dopant to increase the conductivity and making it metallic can be used. With such a material, when forming a distance measurement sensor using molecular beam epitaxy or metalorganic chemical vapor deposition (MOCVD), the light-emitting element and the light-receiving element can be continuously formed by changing the type and amount of the dopant. As the upper transparent electrode, indium tin oxide (ITO) or the like can be used.

[0020] In the region where the above light-emitting elements exist in an island shape, one light-receiving element may be continuously formed in the in-plane direction of the distance measurement sensor, or a plurality of light-receiving elements may be arranged in a matrix in the in-plane direction of the distance measurement sensor.

[0021] By continuously forming one large light-receiving element in the in-plane direction of the distance measurement sensor, the current generated when receiving light is averaged in the plane, so the noise sensitivity can be reduced and the signal-to-noise ratio can be increased. Also, by arranging a plurality of light-receiving elements in a matrix, it is possible to measure the light-receiving level for each divided portion.

[0022] The region in which the above-mentioned light-receiving element is formed may be the same as the region in which the island-shaped light-emitting elements are located, or it may be formed outside the region in addition to the region in which the light-emitting elements are located.

[0023] By making the region where the light-receiving element is formed the same as the region where the light-emitting element is located, it is possible to miniaturize the size of the distance measuring sensor to match the region where the light-emitting element is located. Furthermore, if the region where the light-receiving element is formed is larger than the region where the light-emitting element is located, and light-receiving elements are also formed outside this region, the light-receiving area increases, resulting in a greater amount of light received and thus improving the distance measuring accuracy.

[0024] The above-mentioned light-receiving element may be formed by stacking an N-type semiconductor and a P-type semiconductor on an insulating substrate, as shown in Figure 1. In this case, electrodes are provided at the edges of the P-type semiconductor layer and the N-type semiconductor layer, respectively.

[0025] The product resistivity is 10 7 By using an insulating substrate with an insulating strength of Ωcm or more, circuits with other functions, such as circuits for controlling the photodetector and light-emitting element, can be formed on the same substrate as the photodetector and light-emitting element.

[0026] As the above-mentioned insulator, in addition to materials conventionally used as circuit boards, an insulator containing the above-mentioned semiconductor material can be used.

[0027] Furthermore, as shown in Figure 2, the above-mentioned photodetector may be formed by partially doping a P-type semiconductor in a grid pattern onto the surface of an N-type semiconductor substrate, and the substrate may also serve as the photodetector. Note that the N-type and P-type semiconductors can be reversed.

[0028] By using an N-type semiconductor with a volume resistivity of 1 to 10 Ωcm for the substrate of the distance measuring sensor, electrodes can be provided on unprocessed areas such as the back surface of the substrate. Specifically, back-side electrodes can be provided on the back side of the N-type semiconductor substrate, and the upper P-type semiconductor can be routed to the edge of the area where the light-emitting element is located, with electrodes provided at that edge. This reduces the number of processing steps and enables miniaturization of the distance measuring sensor.

[0029] Examples of semiconductors that can be used in the above-mentioned substrate include N-GaAs and P-GaAs.

[0030] As shown in Figure 3, each of the above-mentioned light-emitting elements can have a phase modulator. The phase modulator allows the light emitted by the light-emitting elements to be deflected in the stacking direction, thereby changing the direction of illumination and enabling scanning of the environment.

[0031] The phase modulator has a structure in which a modulation section with a changing refractive index is sandwiched from above and below by two transparent electrodes, and light-shielding walls are provided on the sides of the modulation section to prevent light leakage in the lateral direction. The transparent electrodes may, for example, have an upper electrode for Y-axis scanning and a lower electrode for X-axis scanning. Note that in Figure 3, the photodetector is shown in the area where the Y-axis scanning electrodes and X-axis scanning electrodes of the phase modulator are not located; however, in reality, a transparent oxide film is formed on the photodetector.

[0032] The above-described phase modulator operates as an optical phased array. By changing the refractive index of the modulation section, it modulates the phase of the light emitted in the stacking direction of the light-emitting elements, and controls the shape and direction of the emitted light without any mechanical moving parts through light diffraction and interference.

[0033] Specifically, the above-mentioned light-emitting elements are arranged in a matrix at equal intervals, and a phase modulator is provided on each of these light-emitting elements to form an optical phased array. Different voltages are applied to each phase modulator to change the refractive index of the modulation section.

[0034] Each phase modulator is separated by a light-shielding wall, so the light emitted from each light-emitting element does not interfere with each other until it passes through the phase modulator. The coherent light emitted from the light-emitting element passes through the phase modulator and is modulated to a phase corresponding to its respective voltage.

[0035] The emitted light modulated by each phase modulator is combined after passing through the phase modulator. This combined emitted light is diffracted and deflected at an angle corresponding to the phase difference, thus changing the shape and direction of the emitted light.

[0036] Since a phased optical array can be deflected at a higher angle the narrower the array pitch, it is preferable that the spacing between adjacent light-emitting elements is less than or equal to the wavelength of the light emitted by the light-emitting elements, so that the emitted light interferes sufficiently with each other.

[0037] Examples of materials that constitute the modulation section and whose refractive index changes depending on the applied voltage include electro-optic polymers (EO polymers), organic nonlinear optical crystals (DAST), LiNbO3, and LiTaO3.

[0038] In particular, EO polymers have a low dielectric constant, and because they can be constructed by placing transparent electrodes above and below the EO polymer, sandwiching the EO polymer between the transparent electrodes, they can be driven at low voltages, are easy to process, and can easily prevent lateral light leakage by providing light-shielding walls, making them a preferred choice.

[0039] The above-mentioned light-blocking wall can be made of an opaque material, such as chromium or nickel-molybdenum.

[0040] Next, a description of the manufacturing method for the distance measuring sensor will be provided. The method for manufacturing the distance measuring sensor of the present invention will be explained using the case where the semiconductor is GaInAs as an example.

[0041] As shown in Figure 4(a), an N-GaInAs thin film and a P-GaInAs thin film are stacked on an insulating substrate by molecular beam epitaxy or metal-organic vapor deposition to form a pn junction and fabricate a photodetector.

[0042] Next, a buffer layer is formed on the photodetector by growing GaInAs in an amount that can be epitaxially grown, and then a large amount of N-type dopant is doped to form metallic n+GaInAs. This portion is used as the lower electrode, and a light-emitting layer is formed on top of it to fabricate a light-emitting element. Furthermore, the light-receiving element and the light-emitting layer can be formed continuously by changing the dopant.

[0043] On this light-emitting layer, indium tin oxide (ITO) is deposited over the entire surface using electron beam deposition or sputtering to form a transparent electrode.

[0044] Then, as shown in Figure 4(b), the area is masked in an island shape, and the portion above the lower electrode is removed in an island shape by dry etching to create gaps between the light-emitting elements. An oxide film such as silicon dioxide, alumina, or zirconia is then deposited over the entire surface to fill these gaps.

[0045] When a phase modulator is provided, as shown in Figure 4(c), an indium tin oxide (ITO) film is deposited, patterned with a mask material to form the shape of the phase modulator, and then dry-etched to form an X-axis scanning electrode that extends in the X-axis direction on the light-emitting element. Island-shaped modulation sections are then formed on these X-axis scanning electrodes. The modulation sections can be formed by depositing an organic EO polymer film, patterning it into an island shape with a mask material, and then dry-etching it.

[0046] Next, as shown in Figure 4(d), an oxide film is formed on the top surface, sides, and all areas between the modulation sections so as to cover the modulation section. Furthermore, as shown in Figure 4(e), a light-shielding wall is similarly formed using an opaque material such as chromium.

[0047] Then, as shown in Figure 4(f), the modulation section is masked, and the areas between the modulation sections where no modulation section exists are etched away in island-like shapes above the X-axis scanning electrode by dry etching to create gaps between the light-emitting elements, and the entire surface is covered with an oxide film to fill these gaps.

[0048] Contact holes are formed in this oxide film to make contact with the modulation section, and indium tin oxide (ITO) is placed there to form a Y-axis scanning electrode that extends in the Y-axis direction.

[0049] Finally, as shown in Figure 4(g), contact holes are formed to create contact points with each electrode layer, and the electrode material is deposited into these holes to fabricate a distance measuring sensor.

[0050] As described above, by fabricating a distance measuring sensor by stacking light-emitting elements on a light-receiving element, not only can the distance measuring sensor be miniaturized, but productivity is improved because precise positioning of the light-receiving element and the light-emitting element is not required, and the distance measuring accuracy is improved because the problem of misalignment between the light-receiving element and the light-emitting element is eliminated. [Explanation of Symbols]

[0051] 1. Distance measuring sensor 2. Light-receiving element 21 N-type semiconductor 22 P-type semiconductor 23 electrodes 24 N-type semiconductor substrate 25 Backside electrode 3 Light-emitting elements 31 Lower electrode (buffer layer) 32. Emitting layer 33 Transparent electrode 4 Phase modulator 41 X-axis scanning electrode 42 Modulation section 43 Y-axis scanning electrode 44 Light-blocking wall 5. Oxide film 6 circuit boards

Claims

1. A distance measuring sensor comprising a light-receiving element and a light-emitting element, Multiple of the above-mentioned light-emitting elements are arranged in an island-like manner on the above-mentioned light-receiving element. A distance measuring sensor characterized in that the light-receiving element receives reflected light emitted by the light-emitting elements that has passed through the space between the light-emitting elements.

2. The above-mentioned light-emitting elements are arranged in a matrix at equal intervals, Furthermore, the above-mentioned light-emitting element has a phase modulator, The distance measuring sensor according to claim 1, characterized in that the phase modulator modulates the phase of light emitted by the light-emitting element and changes the direction of light irradiation by diffraction and interference of light.

3. The distance measuring sensor according to claim 2, characterized in that the spacing between adjacent light-emitting elements is less than or equal to the wavelength of light emitted by the light-emitting elements.

4. A distance measuring sensor according to any one of claims 1 to 3, characterized in that one light-receiving element is formed continuously in the in-plane direction.

5. A distance measuring sensor according to any one of claims 1 to 3, characterized in that a plurality of light-receiving elements are arranged in a matrix in the in-plane direction.

6. The distance measuring sensor according to any one of claims 1 to 5, characterized in that the region where the light-receiving element is formed is the same as the region where the light-emitting element is present.

7. The distance measuring sensor according to any one of claims 1 to 5, characterized in that the region where the light-receiving element is formed is larger than the region where the light-emitting element exists.

8. The above light-receiving elements are stacked on a substrate, The volume resistivity of the above substrate is 10 ７ A distance measuring sensor according to any one of claims 1 to 7, characterized in that it is Ωcm or greater.

9. The above-mentioned light-receiving element is formed by partially doping a P-type semiconductor in a grid pattern onto the surface of a substrate made of an N-type semiconductor. The distance measuring sensor according to any one of claims 1 to 7, characterized in that the volume resistivity of the above substrate is 1 to 10 Ωcm.

10. The distance measuring sensor according to any one of claims 1 to 9, characterized in that the light-emitting layer of the above-mentioned light-emitting element is made of a semiconductor material containing indium gallium arsenide (InGaAs).

11. The distance measuring sensor according to any one of claims 1 to 10, characterized in that the light-receiving layer of the above-mentioned light-receiving element is made of a semiconductor material containing indium gallium arsenide (InGaAs).

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