DE102020201119A1 - Detector element for a time-of-flight sensor - Google Patents

Abstract

Detector element (10a ... 10n) for a time-of-flight sensor (100), comprising: - at least one semiconductor layer (HL1, HL2), the at least one semiconductor layer (HL1, HL2) being formed, at least two wavelengths more electromagnetic To detect radiation using the wavelength-selective photoelectric effect, at least near-infrared and a visible wavelength being detectable by means of the at least one semiconductor layer (HL1, HL2); and - one electrode element (20a -... 20b) functionally connected to each semiconductor layer (HL1, HL2) for detecting an electrical signal generated from the detected electromagnetic radiation.

Description

The invention relates to a detector element for a time-of-flight sensor. The invention also relates to a method for operating a detector element for a time-of-flight sensor. The invention also relates to a computer program product.

State of the art

Is known, for example, from US 2016/0240579 A1 a combined SPAD / RGB (single photon avalanche diode) sensor system with separate detectors, where a “color-seeing” sensor system is proposed, in which RGB pixels are combined with SPAD pixels to form a unit. The RGB pixels and SPAD pixels are read out individually and separately and the data are only combined afterwards as part of signal processing.

WO 2011/041066 A2 discloses an imager for generating color and depth images with a dual mode that includes a light source configured to project structured lighting from which visible light can be filtered. The two-mode imager also includes a detector configured to detect both the structured lighting and visible light of the scene. A temporal or spatial filter is used to selectively block visible light from one or more parts of the detector while the structured illumination is directed to one or more parts of the detector.

Furthermore, for example, are off JP 2017-208651 A Video image converter with a common active surface for wavelengths in the visible range is known. In contrast to conventional CMOS / CCD imagers, the wavelength selectivity of the individual color channels (red, green and blue) is not based on a color filter array (also: "Color field array", e.g. Bayer filter, with a corresponding loss of real) in front of the intensity-measuring pixels Resolution of the sensor), but on a wavelength-selective absorption over the depth of the semiconductor material of the imager chip. The active area of the imager can be used for all three color channels simultaneously.

It is an object of the invention to provide an improved detector element for a time-of-flight sensor.

• - wenigstens eine Halbleiterschicht, wobei die wenigstens eine Halbleiterschicht ausgebildet ist, wenigstens zwei Wellenlängen elektromagnetischer Strahlung unter Ausnutzung des wellenlängenselektiven photoelektrischen Effekts zu detektieren, wobei mittels der wenigstens einen Halbleiterschicht wenigstens Nah-Infrarot und eine sichtbare Wellenlänge detektierbar ist; und
• - jeweils ein mit jeder Halbleiterschicht funktional verbundenes Elektrodenelement zum Erfassen eines aus der detektierten elektromagnetischen Strahlung generierten elektrischen Signals.

According to a first aspect, the invention creates a detector element for a time-of-flight sensor, comprising:

• At least one semiconductor layer, the at least one semiconductor layer being designed to detect at least two wavelengths of electromagnetic radiation using the wavelength-selective photoelectric effect, at least near-infrared and one visible wavelength being detectable by means of the at least one semiconductor layer; and
• an electrode element functionally connected to each semiconductor layer for detecting an electrical signal generated from the detected electromagnetic radiation.

With the proposed detector element, it is advantageously possible to selectively detect a plurality of electromagnetic wavelengths or to separate them from one another. As a result, only a single time-of-flight sensor is required to record color and distance information. As a result, a time-of-flight sensor implemented with a plurality of detector elements can be implemented in a very compact manner, for example as a camera or a lidar sensor for applications in motor vehicles.

According to a second aspect, the object is achieved with a time-of-flight sensor with a defined number of proposed detector elements and an evaluation device for evaluating the electrical signals of the detector elements.

• - Auswerten von elektrischen Signalen aus wenigstens einer Halbleiterschicht unter Ausnutzung des wellenlängenselektiven photoelektrischen Effekts; und
• - Erfassen eines entsprechenden elektrischen Signals aus der detektierten elektromagnetischen Strahlung.

According to a third aspect, the object is achieved with a method for operating a detector element for a time-of-flight sensor having the steps:

• Evaluation of electrical signals from at least one semiconductor layer using the wavelength-selective photoelectric effect; and
• - Acquisition of a corresponding electrical signal from the detected electromagnetic radiation.

According to a fourth aspect, the object is achieved with a computer program product with program code means, set up to carry out the proposed method for operating a detector element for a time-of-flight sensor when it runs on an electronic device or is stored on a computer-readable data carrier.

Preferred embodiments of the proposed detector element are the subject of the respective dependent claims.

An advantageous development of the detector element is characterized in that the at least one semiconductor layer is defined for Wavelengths is selective. In this way, a semiconductor material is advantageously selected which has properties with which the desired wavelengths can be detected. In this way, for example, the fact can be used that the higher the penetration depth of the radiation into the semiconductor material, the higher the wavelengths are detected.

Another advantageous development of the device provides that a single semiconductor layer is provided. In this way, a particularly compact detector element is made possible.

Another advantageous development of the device is characterized in that two semiconductor layers are provided. In this way, an even better selective detection of different electromagnetic radiation is supported.

A further advantageous development of the device provides that a semiconductor layer is provided with a filter device arranged in front of it. In this way, for example, a known Bayer filter can advantageously be combined with a detector element with a semiconductor material.

Another advantageous development of the device is characterized in that a gap is formed between two semiconductor layers. An electrical short circuit between the different semiconductor materials can thereby advantageously be avoided.

Another advantageous development of the detector element is characterized in that the gap is air or a transparent material. This provides different options for separating the two semiconductor materials.

The invention is described in detail below with further features and advantages on the basis of several figures. Identical or functionally identical components have the same reference numerals. The figures are intended in particular to clarify the principles essential to the invention and are not necessarily drawn to scale. For the sake of clarity, it can be provided that not all reference symbols are drawn in in all figures.

Disclosed device features result analogously from corresponding disclosed method features and vice versa. This means in particular that features, technical advantages and designs relating to the detector element for a time-of-flight sensor result in an analogous manner from corresponding designs, features and advantages of the method for operating a detector element for a time-of-flight sensor and vice versa.

• 1, 2 Verläufe einer Wellenlängenselektivität von Halbleitermaterialien, die für das vorgeschlagene Detektorelement verwendet werden können;
• 3 eine schematische Darstellung einer ersten Ausführungsform eines vorgeschlagenen Detektorelements;
• 4 eine schematische Darstellung einer zweiten Ausführungsform eines vorgeschlagenen Detektorelements;
• 5 ein Blockschaltbild eines vorgeschlagenen Time-of-Flight-Sensors mit mehreren vorgeschlagenen Detektorelementen; und
• 6 eine prinzipielle Darstellung des Ablaufs einer Ausführungsform eines Verfahrens zum Betreiben eines Detektorelements für einen Time-of-Flight-Sensor.

In the figures shows:

• 1 , 2 Characteristics of a wavelength selectivity of semiconductor materials which can be used for the proposed detector element;
• 3 a schematic representation of a first embodiment of a proposed detector element;
• 4th a schematic representation of a second embodiment of a proposed detector element;
• 5 a block diagram of a proposed time-of-flight sensor with several proposed detector elements; and
• 6th a basic illustration of the sequence of an embodiment of a method for operating a detector element for a time-of-flight sensor.

Description of embodiments

1 shows a basic profile of an absorption or penetration depth AT over the wavelength W for various materials or semiconductor materials (for example Al, Ge, Fe, Si, Cu, Cr). It can be seen that each semiconductor material can absorb different wavelengths of electromagnetic radiation to different degrees. It can be seen, for example, that the absorption depth AT is largely constant over the wavelength W for silicon.

2 shows a diagram of a dependence of a wavelength W on the sensitivity α or the photon energy PE for various semiconductor materials. It can be seen that with the material silicon, for example, it is not possible to detect radiation with a wavelength of 1.4 µm. It can also be seen that the semiconductor material germanium is particularly well suited for detection of a wavelength range between approximately 0.7 μm and approximately 1.5 μm. As a result, different sensitivities or penetration depths of different semiconductor materials can be achieved for a proposed detector element 10a ... 10n a time-of-flight sensor 100 can be used as described in more detail below.

Four different types of detector elements are proposed in a merely exemplary manner 10a ... 10n for a time-of-flight sensor 100 .

3 shows a first basic embodiment of a proposed detector element 10a . You can see in the left representation of 3 that photons P have different penetration depths into a semiconductor layer HL1 of the detector element 10a where, for example, visible blue radiation B has a low penetration depth and invisible infrared radiation IR a high penetration depth into the semiconductor layer HL1 of the detector element 10a . The penetration depth of visible green radiation G and visible red radiation R are arranged in between. Said detector element 10a thus represents a pixel of a sensor array. In this first variant, a layer made of a semiconductor material (for example Si or Ge) can be provided, for which purpose the natural wavelength-selective absorption in the semiconductor material is used.

By means of an electrode element (not shown) which is attached in a suitable manner to the detector element 10a are attached, an electrical signal generated from the detected radiation can be tapped and made available for further processing.

3 In the illustration on the right, shows a 4x4 pixel sensor for a proposed time-of-flight sensor 100 can be used. In this way, for example, an optical color-sensitive camera can be combined with an infrared-sensitive lidar sensor.

4th shows a further embodiment of a proposed detector element 10a . In this case, two different semiconductor layers HL1, HI2 are used, which are arranged one on top of the other, with a gap between the two semiconductor layers HL1, HL2 which can be filled, for example, with air or with another suitable material.

It is conceivable, for example, that Si is provided as the upper first semiconductor layer HL1 and Ge is provided as the lower second semiconductor layer HL2. This enables an even sharper separation and a more broadband variant of the detector element 10a will be realized.

In this further variant, two superimposed semiconductor layers HL1, HL2 made of two different semiconductor materials (e.g. Si and InGaAs) can be arranged so that two spectra below (Si) and above 1000 nm (InGaAs, or other semiconductor material with a corresponding absorption spectrum) are separated can be. For example, Si becomes increasingly transparent from approx. 1000 nm, whereas InGaAs is largely absorbed.

The wavelength-selective absorption of the semiconductor material is not required for this.

In the right section of 4th Figure 3 is a perspective view of a 4x4 pixel array 10a ... 10n shown, also for a time-of-flight sensor 100 can be used. In this way, a particularly high-quality and powerful time-of-flight sensor 100 will be realized.

By choosing suitable semiconductor materials, a sensing characteristic of the detector element 10a can be defined, for example, when using germanium, both 900nm and 1600nm can be measured.

As a result, a multispectral detector is provided in the manner described above for the simultaneous detection of depth and color information on the basis of the wavelength-selective photoelectric effect over the depth of the semiconductor material (e.g. near infrared and red-green-blue over the depth of the semiconductor material). The semiconductor material is preferably Si or Ge, for example.

For example, a multispectral detector for the simultaneous detection of two IR wavelengths (e.g. 800 nm and 900 nm or 900 nm and 1550 nm) can be implemented in the manner described, which has advantages e.g. in the environmental robustness of a LiDAR system with spectrally differentiable properties of weather influences , Background light, object reflectivities, etc. are realizable.

In a further embodiment of the proposed detector element not shown in the figures 10a ... 10n A multispectral detector can also be used for the simultaneous acquisition of the depth information (NIR) based on the wavelength-selective photoelectric effect and the color information (VIS) via a color filter array (here: RGB resolved via the color filter array, e.g. Bayer filter, so that a sharper separation can be achieved NIR). As a result, this means a combination of a conventional arrangement with a filter element array and a detector element provided with a semiconductor material 10a according to 3 .

5 shows a functional block diagram of a time-of-flight sensor 100 . A defined number of proposed detector devices 10a ... 10n , each of which is electrically conductive to an electrode element 20a ... 20b are switched on, the evaluations of the signals from the detector elements 10a ... 10n make. The electrical result signals from the electrodes are sent to an evaluation device 30th supplied, which carries out the evaluation.

The proposed detector element can advantageously be used to implement a combination of depth and color detection in a single Si semiconductor detector. This advantageously enables a combination of depth and color detection in one optical path, which can result in advantages, for example in terms of size. As a result, a combination of passive color video camera and LiDAR operation can advantageously be implemented in a single device, which can advantageously mean lower costs, a smaller size, no adjustment and calibration effort, etc.

In this way, SPAD / APD / CCD / CMOS-based LiDAR systems can advantageously be expanded to include the acquisition of color information. For the detection of object properties, three additional parameters are recorded with the RGB channels, so that, for example, machine learning algorithms for object recognition that are based on data from the proposed time-of-flight sensor 100 are fed, can be significantly improved. As a result, an efficient object recognition system can be implemented.

In this way, optimal time synchronization of color and depth information can advantageously be carried out. An expansion of the detection by an additional dimension (depth of the semiconductor material) is advantageously possible. This advantageously eliminates the need to use optical wavelength / color filters (e.g. made of organic dyes or as coated Bragg filter structures). There is advantageously no need for interpolation between the pixels to determine color / intensity / depth information that has not been recorded. As a result, a maximized real image resolution, no image artifacts, etc. can thereby be provided.

Advantageously, no bandpass filtering of the individual detection channels is required. Advantageously, no photons are lost between the transmission spectra of the color filter channels. An entire active area of the semiconductor material can advantageously be used for all wavelengths.

The proposed detector device can advantageously be used in backside illumination systems, with a degree of filling of approximately 100% and multispectral detection being implemented. Advantageously, no adjustment or calibration effort is required to assemble the individual channels.

As a result, an integrated, multispectral chip is possible that provides various options for semiconductor materials with spectral penetration depth.

This makes it particularly advantageous to use the proposed time-of-flight sensor 100 for multispectral LiDAR systems of different functional principles possible, such as flash LiDAR, macro scanners, microscanners, imaging LiDAR detectors (2D), single pixel detection (1D), etc.

6th shows a basic sequence of a method for operating a detector element 10a ... 10n for a time-of-flight sensor 100 .

In one step 200 evaluation of electrical signals from at least one semiconductor layer HL1, HL2 takes place using the wavelength-selective photoelectric effect.

In one step 210 a corresponding electrical signal is detected from the detected electromagnetic radiation.

The proposed method can advantageously be implemented as software, which supports easy adaptability and storability of the method.

The person skilled in the art will thus recognize that a large number of modifications of the invention are possible without departing from the essence of the invention.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 2016/0240579 A1 [0002]
• WO 2011/041066 A2 [0003]
• JP 2017208651 A [0004]

Claims (11)

Detector element (10a ... 10n) for a time-of-flight sensor (100), having: - At least one semiconductor layer (HL1, HL2), the at least one semiconductor layer (HL1, HL2) being designed to detect at least two wavelengths of electromagnetic radiation using the wavelength-selective photoelectric effect, at least near by means of the at least one semiconductor layer (HL1, HL2) -Infrared and a visible wavelength can be detected; and - one electrode element (20a -... 20b) functionally connected to each semiconductor layer (HL1, HL2) for detecting an electrical signal generated from the detected electromagnetic radiation. Detector element (10a ... 10n) Claim 1 , characterized in that the at least one semiconductor layer (HL1, HL2) is selective for defined wavelengths. Detector element (10a ... 10n) Claim 1 or 2 , characterized in that a single semiconductor layer is provided. Detector element (10a ... 10n) Claim 1 or 2 , characterized in that two semiconductor layers (HL1, HL2) are provided. Detector element (10a ... 10n), characterized in that a semiconductor layer is provided with a filter device arranged in front of it. Detector element (10a ... 10n) Claim 5 , characterized in that a gap is formed between two semiconductor layers. -> to avoid a short circuit of the materials Detector (10a ... 10n) Claim 6 , characterized in that the gap is air or a transparent material. Time-of-flight sensor (100), comprising: - a defined number of detector elements (10a ... 10n) according to one of the preceding claims; and - An evaluation device (30) for evaluating the electrical signals of the detector elements (10a ... 10n). Time-of-flight sensor (100) Claim 8 , wherein the time-of-flight sensor (100) is a camera or a lidar sensor. Method for operating a detector element (10a ... 10n) for a time-of-flight sensor (100), comprising the steps: - Evaluation of electrical signals from at least one semiconductor layer (HL1, HL2) using the wavelength-selective photoelectric effect; and - Acquisition of a corresponding electrical signal from the detected electromagnetic radiation. Computer program product with program code means set up to carry out the method according to Claim 10 if it runs on an electronic device or is stored on a computer-readable medium.

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