Integrated particulate matter sensor with cavity

Abstract

A particulate matter (PM) sensor comprises: a substrate forming a cavity (5), the substrate comprising a semiconductor chip (4); and a light source (1) arranged in the cavity (5). The light source (1) is adapted to emit a light beam (7). The light beam (7) forms a detection volume (8) for particulate matter (9) outside the cavity (5). Optionally, the particulate matter sensor comprises an optical element (2) delimiting the cavity (5) at one end. The optical element (2) is configured to shape the light beam (7). Furthermore, the particulate matter sensor comprises at least one photodetector (3) integrated into a surface of the semiconductor chip (4). The surface into which the at least one photodetector (3) is integrated faces the detection volume (8). The at least one photodetector (3) is adapted to detect light (10) scattered by particulate matter (9) in the detection volume (8).

Description

Technical Field

[0001] The present invention relates to a particulate matter sensor and a particulate matter sensor module including the particulate matter sensor. Background Art

[0002] Particulate matter (PM) refers to solid particles and / or liquid droplets in fluids. PM can pose health risks, for example, when inhaled, or can contribute to the poor visibility known as smog. Typical types of PM are PM10 and PM2.5, particles with diameters of 10 μm and 2.5 μm, respectively, as well as smaller particles.

[0003] Conventional PM sensor modules include a light source that emits light into a detection volume and a light detector that detects light scattered by particulate matter in the detection volume. Conventional PM sensor modules are constructed from discrete components, including a light source assembly with a laser diode, optical elements, a photodetector, a printed circuit board (PCB), a discrete amplifier, a microprocessor, and a housing. A fan or, alternatively, a heater element is used to generate the airflow for particulate sampling. An example is disclosed, for example, in WO2018100209A2.

[0004] Such PM sensor modules are of macroscopic scale, ie have dimensions of the order of a few centimeters.The form factor and size of conventional PM sensor modules is due to the discrete nature of the used optoelectronic components, ie laser diodes, optics, mounting aids and photodetectors.

[0005] US20150153275A1 discloses a PM sensor comprising a light source and a light detector disposed adjacent to each other in a main body. The light source emits light toward air introduced into the main body. An optical lens disposed on the light source focuses the emitted light. The light detector detects scattered light.

[0006] US20160025628A1 discloses a mobile device configured to sense particulate matter. The sensor in the mobile device includes a light emitter and a light receiver arranged at a certain angle.

[0007] CN106483051B discloses a mobile device for measuring the concentration of particulate matter. Light is emitted by a flash lamp of the mobile device. The backscattered light is collected by a collection lens and filtered and detected by a light detector.

[0008] A problem addressed by embodiments of the present invention is to provide a compact PM sensor which produces, inter alia, reliable high-quality measurements. Summary of the Invention

[0009] This problem is solved by a particulate matter (PM) sensor according to claim 1. Advantageous embodiments are provided in the dependent claims.

[0010] Therefore, there is provided a particulate matter sensor comprising:

[0011] - a substrate comprising a semiconductor chip, said substrate forming a cavity, at least a portion of said cavity being formed in the semiconductor chip;

[0012] - at least one photodetector integrated into the surface of the semiconductor chip; and

[0013] a light source arranged in the cavity, the light source being adapted to emit a light beam towards one end of the cavity (hereinafter referred to as the "first" end), the light beam defining a detection volume for particulate matter outside the cavity,

[0014] wherein the surface of the semiconductor chip on which the at least one photodetector is integrated faces the detection volume, and

[0015] Therein, at least one photodetector is adapted to detect light scattered by particulate matter in the detection volume.

[0016] By providing a cavity that is at least partially formed in the very same semiconductor chip in which the at least one photodetector is integrated and arranging the light source in the cavity, a very compact PM sensor can be obtained.

[0017] The detection volume comprises a portion of the light beam where the intensity is sufficiently high to enable detection of light scattered from PM in the beam by at least one photodetector. Specifically, the detection volume can be defined as the volume in which the presence of PM induces a clear (i.e., statistically significant) signal above the noise level in the PM sensor. Thus, the detection volume depends on various factors, such as the size of the PM, the optical power of the light source, and the geometry of the light beam.

[0018] In some embodiments, the semiconductor chip includes a CMOS layer stack. One or more layers in the CMOS layer stack may then form a membrane that spans the cavity at its first end. The membrane may have a thickness of less than 20 μm, particularly less than 10 μm. Thus, the membrane may protect the light source. In particular, the cavity may be completely enclosed by the membrane at its first end, such that the cavity is fluid-tight at its first end.

[0019] In some embodiments, a particulate matter sensor may include an optical element defining a cavity at a first end, the optical element being configured to shape a light beam to form a detection volume. In other embodiments, the optical element may be omitted. For example, the light source itself may be configured to produce a sufficiently collimated or focused light beam so that the light beam has sufficient intensity outside the cavity to form a detection volume. In some embodiments, the optical element includes a film formed from one or more layers in a CMOS layer stack. In other embodiments, the cavity is open at a first end, and the optical element is disposed on the open first end of the cavity.

[0020] The cavity is preferably open at a second end opposite the first end.The light source is preferably arranged in the cavity at the second end of the cavity.

[0021] In some embodiments, the substrate may be formed entirely of the semiconductor chip, ie, the substrate may include only the semiconductor chip. In other embodiments, the substrate may include a spacer to which the semiconductor chip is bonded, as described in further detail below.

[0022] If the substrate includes only a semiconductor chip, and if optical elements are present, the particulate matter sensor may have the following features:

[0023] - a semiconductor chip, said semiconductor chip forming a cavity;

[0024] - at least one photodetector integrated into the surface of the semiconductor chip;

[0025] - a light source arranged in the cavity, said light source being adapted to emit a light beam,

[0026] - an optical element defining the cavity at one end (the "first" end);

[0027] wherein the light source is arranged to direct a light beam onto the optical element,

[0028] wherein the optical element is configured to shape the light beam so that the light beam forms a detection volume for particulate matter outside the cavity,

[0029] wherein the surface of the semiconductor chip on which the at least one photodetector is integrated faces the detection volume, and

[0030] Therein, at least one photodetector is adapted to detect light scattered by particulate matter in the detection volume.

[0031] Advantageous embodiments of a PM sensor are described below. A PM sensor generally includes the following elements:

[0032] - Cavity-forming substrate: The substrate includes or consists of a semiconductor chip, advantageously comprising a complementary metal oxide semiconductor (CMOS) layer stack. Thus, the PM sensor functionality is preferably integrated into the semiconductor chip. The cavity has sidewalls formed by the substrate. At least a portion of each sidewall is formed by the semiconductor chip. The cavity can have a substantially cubic shape, for example, with an edge length ranging from 0.3 mm to 1 mm, or a cylindrical shape, for example, with a diameter ranging from 0.3 mm to 1 mm. In other embodiments, the cavity can have the shape of a truncated cone or a truncated pyramid. More generally, each sidewall of the cavity can have at least one inclined portion that is tilted relative to the optical axis or relative to an axis of symmetry of the cavity. At least a portion of the cavity can be fabricated, for example, by etching the semiconductor chip, preferably from the bottom side of the substrate, or by alternative processing techniques. In some embodiments, the cavity can extend through the entire thickness of the semiconductor chip, while in other embodiments, the cavity may not extend through the entire thickness of the semiconductor chip, but may instead take the form of a recess defined by the remainder of the semiconductor chip, typically by a membrane formed from one or more layers in the CMOS layer stack.

[0033] - a light source suitable for emitting a light beam. The light source is arranged in the cavity. In an advantageous embodiment, the light source is a laser diode, such as a vertical cavity surface emitting laser (VCSEL). The term "light" is not limited to visible light, but also includes at least ultraviolet light and infrared light. Typically, the wavelength of the emitted light is in the range of 500nm to 1100nm, in particular between 640nm and 950nm. The light source emits a light beam towards the first end of the cavity. The light source can be arranged at the second end of the cavity.

[0034] Optionally, an optical element defining a cavity at a first end: Typically, the optical element is disposed at the end of the cavity opposite the light source. The light source is disposed in the cavity to direct a light beam through at least a portion of the cavity onto the optical element. The optical element is adapted to shape the light beam, thereby forming a detection volume. In advantageous embodiments, the optical element focuses the light beam, as described in further detail below.

[0035] - At least one photodetector integrated in the substrate: At least one photodetector is integrated into the surface of the semiconductor chip. The at least one photodetector may comprise at least one photodiode. It may be formed in the semiconductor chip by a CMOS process. The at least one photodetector faces the detection volume and is suitable for detecting light scattered by PM in the detection volume. In particular, the at least one photodetector is arranged at a distance of at most 2 mm from the optical element (measured from edge to edge), and more in particular adjacent to the optical element. Furthermore, it is advantageous if the optical element is arranged within a tolerance of +1 mm / -0.1 mm in a plane defining the at least one photodetector, more precisely in a plane defined by the surface of the semiconductor chip in which the at least one photodetector is integrated, as described in further detail below.

[0036] Such a PM sensor can be constructed with a small form factor, i.e., less than 7 mm × 7 mm × 2 mm, and particularly less than 5 mm × 5 mm × 1.6 mm. Such a PM sensor can also be integrated into a PM sensor module or a portable electronic device, such as a smartphone or an Internet of Things (IoT) device. Furthermore, such a PM sensor has the advantage of low current consumption, which again makes it well-suited for integration into battery-powered devices.

[0037] In some advantageous embodiments, the PM sensor further comprises:

[0038] - A control unit electrically connected to the at least one photodetector: the control unit is adapted to receive a signal from the at least one photodetector caused by light scattered by PM in the detection volume. Furthermore, the control unit is adapted to evaluate the signal in dependence on a physical quantity related to the PM, i.e. to determine a physical quantity related to the particulate matter based on the signal. In particular, the physical quantity may comprise at least one of the number concentration, size and size distribution of the PM. Advantageously, at least a part of the control unit can be integrated into a semiconductor chip. In particular, at least a part of the control unit can be formed in a CMOS layer stack. More particularly, at least a part of the control unit can be an ASIC formed in a CMOS layer stack. The control unit can be implemented completely in the semiconductor chip or a part of the control unit can be implemented separately from the semiconductor chip, for example in a separate signal processor or computing unit.

[0039] Further advantageous technical features will become apparent from the following description. For a skilled person, it will be apparent that these features can be combined in various ways to form embodiments of the present invention.

[0040] light source

[0041] The amount of light scattered by PM in the detection volume and received by the at least one photodetector depends, among other things, on the optical power of the light source. Therefore, it is useful to quantify the optical power. The following embodiments are particularly advantageous if the light source comprises a VCSEL, since the optical power of a VCSEL is typically not controlled, as the exact optical power is irrelevant for applications such as time-of-flight (TOF) measurements.

[0042] In order to quantify the optical power of the light source, the PM sensor may include a photosensitive auxiliary detector, which is arranged to receive light emitted from the light source and not scattered by the PM. The auxiliary detector may be integrated into a semiconductor chip. The auxiliary detector may be manufactured using the same technology as the at least one photodetector used to detect light scattered from the PM. In particular, the auxiliary detector may be a photodiode, in particular a photodiode manufactured using a CMOS process. The surface area of the auxiliary detector in the photodetector plane may be significantly smaller than the total surface area of the photodetector used to detect light scattered from the PM, for example not exceeding 1% of the surface area of the latter, thereby ensuring that the signal from the auxiliary detector is not significantly affected by light scattered by the PM and minimizing sensitivity to ambient light.

[0043] If the auxiliary detector is integrated into a semiconductor chip, which includes a CMOS layer stack, there are at least three different possible light paths between the light source and the auxiliary detector. The first light path extends through the semiconductor chip. Although light can be strongly attenuated by semiconductors such as silicon, the penetration depth of light is generally not small enough to be ignored. If the auxiliary detector is arranged in the semiconductor chip close enough to the wall of the cavity (for example, at a lateral distance of not more than 200 μm), a sufficient amount of light can reach the auxiliary detector through the semiconductor chip. The second light path extends through the CMOS layer stack, which can act as a light guide. Stray light can be guided laterally to the auxiliary detector in this way. The third light path extends through the optical element (if present). Stray light that has been scattered inside the optical element or on its surface can reach the auxiliary detector in this way. Depending on the design, one or more of these light paths can be active.

[0044] Therefore, in a first embodiment, an auxiliary detector, particularly a photodiode, is positioned adjacent to the optical element. In this way, the auxiliary detector can receive stray light from the optical element. The auxiliary detector can be positioned within the cavity, for example, on a cavity wall facing the optical element. By integrating the auxiliary detector into a semiconductor chip, the manufacturing process is simplified, for example, the auxiliary photosensitive detector can be formed during conventional CMOS processing.

[0045] The auxiliary detector is adapted to measure stray light from the optical element, i.e., light that does not exit the optical element toward the detection volume but is instead reflected or scattered in other directions, such as backwards. It has been found that the amount of stray light is particularly proportional to the optical power of the light source. Therefore, the control unit is also electrically connected to the auxiliary detector and adapted to determine the optical power of the light source based on the stray light and to evaluate a physical quantity related to PM based on the determined optical power. Alternatively or additionally, the control unit is adapted to control the light source based on the determined optical power.

[0046] In a second embodiment, an auxiliary detector, in particular a photodiode, is arranged in the cavity or adjacent to the cavity and is suitable for measuring the spontaneous emission of the light source. This can be particularly relevant if the light source is a VCSEL. It has been found that VCSELs exhibit spontaneous emission of light on one or more side walls, i.e. one or more walls other than the main emission surface of the VCSEL. Furthermore, it has been found that the amount of spontaneous emission is also indicative, in particular proportional to the optical power of the light source. Therefore, the control unit is also electrically connected to the photodiode and is suitable for determining the optical power of the light source based on the measured spontaneous emission and for evaluating a physical quantity related to PM based on the determined optical power. Alternatively or additionally, the control unit is suitable for controlling the light source based on the determined optical power. Furthermore, the photodiode is advantageously integrated in the substrate.

[0047] The described embodiments facilitate more accurate measurement of PM-related quantities, particularly where the optical power of the light source is otherwise unknown, such as is the case with VCSELs.

[0048] Optical components

[0049] Typically, the described PM sensors are optimized for large detection volumes, since the PM count is proportional to the detection volume as defined above. As explained above, the PM particles need to generate enough scattered light in the direction of at least one photodetector so that the signal from the scattered light detected by the at least one photodetector is above the noise level, such as dark current noise. The volume that meets this condition is called the detection volume. The light scattered from the PM can be approximately described by the Mie theory. To illustrate the optimization of the detection volume, a further approximation may be helpful: Obviously, the detection volume is limited, among other things, by geometric effects, such as the diffusion of light emitted by a point source or scattered by particles. This diffusion causes the intensity of the light to decrease with the distance d from the point source or, respectively, the scattering particle to 1 / d^2, which corresponds to the growth surface of the outgoing spherical wave. This has implications for the design of PM sensors in general and for the design of optical elements in particular.

[0050] The optical element typically defines an optical axis. The optical axis is preferably perpendicular to the surface of the semiconductor chip on which the at least one photodetector is integrated. In advantageous embodiments, the optical element focuses the light beam, for example, at a focal point or focal region. Consequently, the intensity of the light beam increases along the optical axis as the distance I from the optical element to the focal point increases by I^2, corresponding to the decreasing surface area of the conical light beam. It can be seen that this effect of increasing the light intensity within the detection volume counteracts and, to a certain extent, balances the diffusion effect of light scattered by PM particles, as described above. In this way, the detection volume is maximized for a given light source and a given photodetector.

[0051] In particular, the detection volume extends from the optical element at least to the focal point of the light beam. The distance I0 between the optical element and the focal point can be at least 1 mm. Typically, the optimal focal length depends on the threshold of at least one photodetector used to distinguish between particle scattered light and noise, the optical power of the light source, and the numerical aperture of the optical element. Depending on the size of the PM particles, the detection volume can even extend beyond the focal point, for example to 1.2 or 1.5 times I0 for large particles. In this way, the PM sensor is suitable for detecting PM at least 1.5 mm away from the optical element.

[0052] As an alternative to focusing, the optical element can be adapted to collimate the beam—that is, to shape it so that the different rays within it are essentially parallel outside the cavity. In this case, assuming no scattering and no attenuation, the light intensity theoretically remains constant along the beam. Furthermore, such a setup with collimating optics instead of focusing optics can yield a large detection volume, for example, up to 3 cm from the optical element.

[0053] Likewise, taking into account the maximum size of the detection volume, it is advantageous if the optical element is located in the same plane as the at least one photodetector (i.e. in the same plane as the surface of the semiconductor chip in which the at least one photodetector is integrated) or, as previously described, only slightly above or below this plane. Thus, in one embodiment, the optical element may protrude from the plane of the at least one photodetector or, in another embodiment, only slightly, for example a maximum of 0.6 mm. It is also advantageous if the thickness of the optical element perpendicular to the light beam is small, i.e. below 2 mm, in particular below 1 mm. In this way, shadowing of the at least one photodetector by the optical element from light scattered by PM particles in the vicinity of the optical element can be prevented. In other words, the detection volume can increase towards the optical element or, optimally, up to the optical element.

[0054] At the same time, it is advantageous if the cavity height, i.e., the distance between the light source and the optical element, is at least 0.25 mm, particularly at least 0.45 mm. This makes the PM sensor more robust against manufacturing errors, such as minor deviations from the optimal dimensions. Combined with the aforementioned considerations regarding shading, this leads to the conclusion that the thickness of the optical element should advantageously be small.

[0055] In some embodiments, the substrate is disposed on top of a base substrate, which can be, for example, a carrier made of glass, semiconductor, ceramic, etc. In such embodiments, the cavity can be bounded at one (first) end by the optical element and at the other (second) end by the base substrate. A light source can be disposed on the base substrate and emit light in a direction toward the optical element.

[0056] In general, the optical element can be a refractive optical element, particularly a lens, or a diffractive optical element. Refractive optical elements shape a light beam by refraction, while diffractive optical elements shape a light beam by diffraction. These principles can also be combined. In some embodiments, the optical element comprises an embossed polymer lens or an injection molded lens.

[0057] In some embodiments, the optical element may include a glass carrier substrate and an optical structure, particularly a polymer lens, formed on the glass carrier substrate. The optical structure may be formed, for example, by stamping a UV-curable polymer with a stamp and then UV curing it, or the optical structure may be formed by photolithography.

[0058] During the embossed lens manufacturing process, a polymer lens is formed on a glass carrier substrate. Specifically, multiple polymer lenses can be formed on the glass carrier substrate. The glass carrier substrate is then cut to form individual lens units. The polymer lens and the glass carrier substrate are then placed over the cavity.

[0059] In an embodiment, the glass carrier substrate has a thickness of less than 1000 μm, such as 800 μm, in particular less than 750 μm or less than 600 μm.

[0060] In other embodiments, the optical element comprises a film formed from one or more layers in a CMOS layer stack. Optical structures can be provided on the film to form the optical element. Additionally or alternatively, the film itself can comprise at least one structured CMOS layer to form the optical element. The film thus acts as a diffractive optical element (DOE). In particular, the film can act as a metamaterial transparent for a light beam, the metamaterial comprising structures that effectively shape the light beam. To generate such a DOE, the film is manufactured from a substrate, for example in the form of a thin layer and, for example, by etching the substrate from the bottom side almost through the entire thickness of the substrate, so that the film remains on the front side of the substrate covering the cavity. The structures for shaping the light beam can be generated in a previous step during the processing of the CMOS layer stack, or they can be generated in a subsequent step, for example by structuring the film, for example by etching, or by applying structures to the film. Advantageously, the thickness of the film or metamaterial is less than 20 μm, in particular less than 10 μm.

[0061] Generally, thin optical elements, as proposed in the above-described embodiments, can minimize shadowing from scattered light, thereby providing a large detection volume. In other words, thin optical elements facilitate the minimum required distance between the optical element and the at least one photodetector while preventing shadowing. Furthermore, they facilitate a small overall form factor for the PM sensor.

[0062] Another aspect related to the optical element is stray light, which leaves the optical element in a direction other than the desired light beam, for example to the side, particularly toward the at least one photodetector. If such stray light reaches the at least one photodetector, it significantly increases the noise level and thus reduces the signal-to-noise ratio of the PM sensor, effectively reducing the detection volume.

[0063] In order to prevent stray light from the optical element, in particular in the direction towards the at least one photodetector, the PM sensor advantageously comprises a light barrier between the optical element and the at least one photodetector.

[0064] In some embodiments, the light barrier comprises a blackened or silvered portion of the sidewall of the optical element facing the at least one photodetector. Specifically, the blackened or silvered portion can comprise a selective coating that reacts only with the carrier glass layer and not with the aforementioned polymer lens. A prime example is the application of a mirror layer using the well-known silver nitrate process. The term "silvered portion" should be understood as a reflective coating that acts as a light barrier but is not necessarily composed of silver. Other materials that block light transmission may also be used.

[0065] In some embodiments, the light barrier includes an aperture formed by a coating on the optical element, the aperture defining an aperture for the light beam. The aperture can be formed, for example, by a chrome coating on a glass carrier substrate. In particular, for an embossed polymer lens on a glass carrier substrate, the aperture with the aperture can advantageously be positioned on at least one of the top or bottom sides of the glass carrier substrate.

[0066] Such a light barrier allows stray light to be blocked from reaching the at least one photodetector. At the same time, the light beam passes unimpeded through the optical beam. Furthermore, stray light exiting the optical element toward the cavity remains largely unaffected, making the aforementioned method for quantifying the optical power of the light source still feasible for such an embodiment.

[0067] The present invention also provides an optical element having a light barrier as described herein, regardless of whether the optical element is integrated into a PM sensor or not.

[0068] Photodetectors

[0069] The following disclosure relating to one or more photodetectors should be considered as disclosed in conjunction with a PM sensor, but also outside the application of such a PM sensor, i.e. independently of the PM sensor, as a photodetector device comprising a photodetector integrated into a semiconductor chip, which may include a dielectric layer and a CMOS metallization portion on top of the semiconductor chip.

[0070] While the at least one photodetector can be of any type, it is advantageously a silicon-based photodetector. Such photodetectors can preferably be manufactured in the same process steps as the control unit, which is represented by electronic circuitry integrated into a preferred silicon substrate, for example, a CMOS process. Compared to other semiconductor photodetectors, such photodetectors are easier to handle and less expensive to manufacture. Therefore, they are well-suited for manufacturing large quantities of PM sensors, such as those used in IoT devices.

[0071] In an advantageous embodiment, the particulate matter sensor comprises a plurality of photodetectors integrated into the same surface of a semiconductor chip. The photodetectors may be arranged in an array, i.e. a plurality of photodetectors may be arranged in a regular pattern. This is useful because it is desirable for at least one photodetector to cover a large area while minimizing the distance to the first end of the cavity, in particular to the optical element (if present). The photodetectors may be arranged at different positions around the cavity or optical element, preferably on diametrically opposite sides of the cavity or optical element, more preferably distributed at a plurality of positions along the perimeter of the cavity or optical element. In particular, if the photodetectors are arranged in one or more arrays, the one or more arrays may be distributed around the cavity or optical element. As an example, four photodetectors may be distributed in the same plane as the optical element.

[0072] Each photodetector may form a pixel. Preferably, the photodetector pixels each have a size of less than 1 x 1 mm 2 , preferably less than 0.5×0.5mm 2 , even more preferably less than 0.3×0.3 mm 2 The same square metric applies to the case of non-square pixels, such as circular pixels.

[0073] In this way, the yield of light scattered by the PMs in the detection volume and hitting the photodetector is maximized.

[0074] Furthermore, the above-mentioned geometric considerations apply here: the at least one photodetector should advantageously be as close as possible to the cavity or optical element. In this way, the optical path length from the scattering particles in the detection volume to the at least one photodetector is minimized, thus maximizing the signal-to-noise ratio.

[0075] Optionally, the PM sensor includes an optical filter on at least one photodetector. This means that the optical filter covers the surface of the at least one photodetector opposite the substrate. The optical filter can be disposed on the surface of the semiconductor chip on which the at least one photodetector is integrated. Advantageously, the optical filter filters out light and radiation outside the main wavelength band of the light source. In this way, background suppression is achieved because spurious light or radiation events do not reach the at least one photodetector. The optical filter can be an interference filter, which includes multiple layers with different refractive indices to cause destructive interference outside the desired wavelength band.

[0076] In an advantageous embodiment, the photodetectors are separated by a conductive material, for example in the form of a grid, wherein the photodetectors are arranged in the gaps of the grid, for example in the form of tiles or pixels already arranged thereon. In particular, the photodetectors can be separated by a metallization of the substrate. In this way, the conductive material can be integrated into the conventional processing of the semiconductor chip, wherein the topmost metallization of the CMOS layer stack is manufactured so that it, in particular its dividing boundaries, serves as the conductive material separating the photodetectors. This conductive material between the photodetectors can be grounded and thus act as a Faraday cage and can be exposed toward the measurement volume. To ground the conductive material, the conductive material can be connected to a ground connector of the sensor device. In particular, the conductive material is suitable for protecting the photodetectors from electromagnetic interference, for example from other electronic devices in the environment of the PM sensor. Therefore, the above-mentioned range of pixel sizes defines the distance between the metallizations and promotes shielding against electromagnetic interference.

[0077] In order to further reduce electromagnetic interference, it is advantageous if the at least one photodetector is divided into a first partition facing the detection volume and a second partition which is shielded with respect to light scattered by PM in the detection volume. For example, the at least one photodetector in the second partition may be covered by an opaque layer, which is opaque at least in a wavelength range comprising the main wavelength of the light source. The opaque layer is preferably electrically insulating to ensure that both partitions are exposed to the same level of electromagnetic interference. For example, the opaque layer can be produced by inkjet printing. The two separated partitions can be used to detect and eliminate signals in the photodetector which are only due to unwanted electromagnetic interference and not to light scattered by PM in the detection volume. To this end, the control unit is adapted to perform a differential measurement of the first partition and the second partition. In particular, parasitic effects of electromagnetic interference on the first partition and the second partition of the at least one photodetector are thereby eliminated.

[0078] Further aspects

[0079] As mentioned above, the substrate can include spacers. The semiconductor chip can be bonded to the spacers, particularly at the back surface of the semiconductor chip, which faces away from the surface on which the photodetector is integrated. The cavity can be formed in both the spacer and the semiconductor chip. By using spacers, the distance between the light source and the optical element can be increased. Increasing the distance between the light source and the optical element enables the use of optical elements with a larger focal length. This can have several beneficial effects, particularly on the size of the detection volume and sensitivity to production tolerances.

[0080] As already mentioned, the PM sensor may include a base substrate. The light source may be mounted on the base substrate. The substrate may also be arranged on the base substrate such that the light source is arranged in the cavity. If the substrate includes a semiconductor chip, the semiconductor chip may be directly connected to the base substrate. If the substrate includes a spacer, the spacer may be arranged between the base substrate and the semiconductor chip. The base substrate preferably extends in a plane parallel to the surface of the semiconductor chip on which the photodetectors are integrated. The base substrate may form or include a land grid array.

[0081] To reduce the amount of light from the light source that reaches the at least one photodetector through the sidewalls of the cavity, an opaque coating can be applied to the sidewalls of the cavity. Similarly, to reduce the effects of ambient light, an opaque coating can be applied to the back surface of the substrate or semiconductor chip, which is away from the surface on which the at least one photodetector is integrated. If the substrate includes a semiconductor chip and a spacer, the opaque coating can be applied to the back surface of the spacer, the back surface of the semiconductor chip, or both. The opaque coating can include a metallization and / or a coating applied by an inkjet process.

[0082] The cavity may have an axis of symmetry. In particular, the cavity may have discrete or continuous rotational symmetry about the axis of symmetry. The axis of symmetry is preferably perpendicular to the surface of the semiconductor chip on which the photodetector is integrated. The axis of symmetry is preferably parallel to the optical axis defined by the optical element. It may coincide with the optical axis.

[0083] The PM sensor may further include a light-blocking element arranged on the surface of the semiconductor chip on which the photodetectors are integrated, such that the light-blocking element selectively shields a portion of one or more of the photodetectors from light scattered from particulate matter particles in the detection volume, the portion depending on the distance of the particles from the surface of the semiconductor chip on which the at least one photodetector is integrated, while one or more other photodetectors are not shielded by the light-blocking element. The light-blocking element may be formed by an asymmetric extension of the optical element. The control unit may be configured to determine a measure of the distance of the particles from the surface of the semiconductor chip on which the at least one photodetector is integrated by comparing signals from the photodetectors partially shielded by the light-blocking element with signals from photodetectors not shielded by the light-blocking element. The control unit may also be configured to take the determined distance into account when determining a physical quantity related to the particulate matter. In particular, taking the distance into account may allow for a more reliable determination of a PM size parameter.

[0084] In order to mechanically protect the substrate, the PM sensor may include a housing laterally surrounding the substrate, the housing being made of a molded material.

[0085] According to another aspect of the present invention, a PM sensor module includes a housing and a flow passage disposed in the housing. Furthermore, the PM sensor module includes a fan or heater disposed in the housing and adapted to move air through the flow passage, and a PM sensor as described in any one of the above or one of the following embodiments. The PM sensor is disposed within the housing such that a portion of the flow passage overlaps with a detection volume.

[0086] According to another aspect, the present invention provides a method for determining a physical amount of particulate matter using a particulate matter sensor as described herein. The method comprises:

[0087] operating a light source to emit a light beam;

[0088] operating at least one photodetector to detect light that has been scattered by particulate matter that intersects the light beam; and

[0089] A signal from the at least one photodetector is analyzed to determine at least one parameter indicative of a physical quantity of the particulate matter.

[0090] As explained above, the determination of the at least one parameter may involve determining the optical power of the light source and / or determining the distance of the particle from the surface of the semiconductor chip in which the at least one photodetector is integrated and / or performing a differential measurement of the signals from the shielded partition and the unshielded partition.

[0091] According to another aspect, the present invention provides a method of manufacturing a particulate matter sensor as described herein, the method comprising the steps of:

[0092] a) forming at least one photodetector in a surface of a semiconductor chip;

[0093] b) etching the semiconductor chip in a direction perpendicular to the surface to form at least a portion of the cavity;

[0094] c) optionally, bonding the semiconductor chip to a spacer, the spacer forming another part of the cavity;

[0095] d) disposing a light source in the cavity, the light source being configured to emit a light beam toward the first end of the cavity;

[0096] e) Optionally, an optical element is provided on the semiconductor chip, the optical element delimiting the cavity at the first end, the optical element being configured to shape the light beam.

[0097] Step b) is typically performed after step a), but may also be performed before step a). Step c), if present, is typically performed after steps a) and b). Step d), typically performed after steps a) and b) and after step c), if present. Step e), may be performed simultaneously with steps a) and b), such as in the case of a DOE integrated into a film formed from layers of a CMOS layer stack, or may be performed after any of steps b) to d).

[0098] The method may involve further steps, for example, forming at least a portion of a control unit, i.e., an ASIC, in a semiconductor chip as described herein, providing an optical filter on a semiconductor chip as described herein, applying a coating to the cavity walls and / or to the back side of the semiconductor chip and / or spacer as described herein, forming an optical element by any of the methods described herein, arranging a light source and a substrate on a base substrate, forming wire bonds between the ASIC and the base substrate and / or between the light source and the base substrate, enclosing the substrate in a housing made of a molding material, and integrating the PM sensor in a PM sensor module as described herein.

[0099] Further advantageous embodiments are listed in the dependent claims and in the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0100] The present invention will be better understood and objects other than those set forth above will become apparent from the following detailed description thereof. Such description refers to the accompanying drawings, in which:

[0101] Figure 1 shows a schematic longitudinal section through a PM sensor according to an embodiment of the invention;

[0102] Figure 2 Shown Figure 1 A perspective view of a PM sensor;

[0103] Figures 3 to 6 Shown Figure 1 Different aspects of PM sensors;

[0104] Figures 7 to 9 shows a schematic longitudinal section through a PM sensor with different optical elements according to an embodiment of the invention;

[0105] Figure 10 shows a schematic longitudinal section through a PM sensor according to another embodiment of the present invention;

[0106] Figure 11A A schematic longitudinal section through a PM sensor according to an embodiment of the present invention is shown, thereby Figures 1 to 10 The PM sensor is shown in greater detail than;

[0107] Figure 11B Shown Figure 11A Schematic functional diagram of the PM sensor in FIG;

[0108] Figure 12 shows a schematic longitudinal section through a PM sensor according to a further embodiment of the present invention;

[0109] Figure 13A and Figure 13B Shown is shown for the Figure 12 Schematic diagram of signal processing of PM sensor;

[0110] Figures 14 to 26 shows a schematic longitudinal section through a PM sensor according to an embodiment of the invention;

[0111] Figure 27 shows a perspective view of a PM sensor having two partitions of a photodetector;

[0112] Figure 28 shows a schematic longitudinal section through a sensor module according to a first embodiment; and

[0113] Figure 29A schematic longitudinal section through a sensor module according to a second embodiment is shown. DETAILED DESCRIPTION

[0114] Throughout this specification and claims, the terms "particularly", "preferably" and "optionally" should be understood to convey that the corresponding subject matter is optional.

[0115] General setup of PM sensor ( Figure 1 and Figure 2 )

[0116] Figure 1 shows a schematic cross-sectional view through a PM sensor according to an embodiment, and Figure 2 A perspective view of a PM sensor is shown. On a base substrate 6, a cavity 5 is formed in the substrate, which in this example is formed by a semiconductor chip 4. Alternatively, the base substrate 6 can also be part of the semiconductor chip 4. The cavity is delimited by side walls 26 formed by the substrate. The cavity 5 is preferably formed from the bottom side (back side) of the substrate, so that inclined side walls as indicated by the dotted lines can also be shown. In the cavity 5, a light source 1 is arranged at the bottom end of the cavity, i.e. the end facing the base substrate 6. An example of the light source 1 is a laser diode, in particular a vertical cavity surface emitting laser (VCSEL). At the upper end of the cavity 5, i.e. the end opposite to the bottom end, an optional optical element 2 is arranged, thereby closing the cavity 5. The optical element 2 defines an optical axis 20. In addition, a photodetector 3, such as a photodiode, is integrated into the semiconductor chip 4 on two or more sides of the optical element 2.

[0117] like Figure 1 As depicted in FIG, the photodetector 3 is integrated onto the upper surface of the semiconductor chip 4, facing away from the base substrate 6. This surface defines a plane, which will be referred to below as the "photodetector plane". The photodetector plane extends perpendicular to the optical axis 20. Figure 1 In the embodiment of the invention, the optical element 2 is arranged substantially in the photodetector plane. In particular, the optical element 2 should not protrude more than 1 mm beyond the photodetector plane. The reasons for this have been discussed above and in Figure 9 It is shown in FIG. 1 that the protruding lens 15 causes a shadow, so that scattered light pulses 10 scattered by PM particles that are closer to the lens 15 than the particles 9 do not reach the photodetector 3 and are therefore not detected.

[0118] like Figure 2As depicted in , the upper surface of the semiconductor chip 4 may include an array of photodetectors 3, for example an array of four photodetector pixels. Metallizations 18 are provided between or around the individual photodetector pixels. The metallizations 18 may be made of any electrically conductive material. Advantageously, they are formed during conventional processing of the CMOS layer stack of the semiconductor chip 4 by exposing one of the metal layers on the surface. The metallizations 18 act as a Faraday cage when grounded and shield the photodetectors 3 from electromagnetic interference and thus from spurious signals. In particular, some of the metallization layers of the CMOS layer stack may form connections for reading out the photodetectors, while at least one of the metallization layers (preferably the topmost layer) may be grounded to act as a Faraday cage. Ground contacts may be formed on the semiconductor chip for connecting the respective layer to ground. Preferably, the photodetector pixels 3 each have a diameter of less than 1x1 mm 2 Planar dimensions, preferably less than 0.5x0.5mm 2 Planar dimensions, even more preferably less than 0.3x0.3mm 2 The same squareness metric applies to non-square shaped pixels, such as circular pixels.

[0119] exist Figure 2 In the embodiment shown, the optical element 2 is not shown. In fact, in some embodiments, for example, when the light source 1 itself already generates a light beam with a sufficiently small divergence, the optical element 2 can be omitted.

[0120] Operation of PM sensor ( Figures 3 to 6 )

[0121] Figures 3 to 6 Shown Figure 1 Various aspects of the PM sensor. The light source 1 is switched on, emitting light towards the optical element 2. The optical element 2 shapes the light beam 7 and in particular focuses the light beam 7 at the focal point 21. In the measurement setup, as Figure 4 As shown in FIG, PM particles 9 approach the light beam 7. This can be achieved, for example, by placing the PM sensor on the wall of a flow channel through which the air laden with PM is blown by a fan or alternatively a heater (see below). Figure 28 and Figure 29 discussion).

[0122] Figures 4 to 6 A portion of the light beam 7 is depicted with different profile lines: this is the detection volume 8, which defines the PM particles 9 present in the detection volume 8 generating scattered light pulses 10 that are large enough to be detected by at least one of the photodetectors 3, meaning that the resulting signal in the photodetector 3 exceeds the noise level, such as dark current noise.

[0123] The proposed arrangement with focusing optical element 2 and photodetector 3 in the same plane has the advantage that detection volume 8 extends at least up to focal point 21 of optical element 2. The geometric reasons for this have been discussed above. Especially for large PM particles 9, detection volume 8 can even extend beyond focal point 21, meaning that scattered particle height 11 can be greater than the focal length of optical element 2 while still being detected.

[0124] Typically, the size and shape of the detection volume 8 can be optimized and adjusted to a specific application by changing one or more parameters such as the optical power of the light source 1, the focal length of the optical element 2, the distance between the light source 1 and the optical element 2, the distance between the optical element 2 and the photodetector 3, the sensitivity of the photodetector 3, and the electromagnetic shielding to reduce the noise level.

[0125] Design of optical components

[0126] Figures 7 to 9 Shown as Figure 1 A similar embodiment of the PM sensor of , however, with a different optical element 2. Figure 7 In the embodiment of the present invention, the optical element is a conventional optical lens 12 made of, for example, glass or polymer. Depending on the optical index of the lens material, the conventional optical lens 12 needs to have a certain thickness in order to exhibit a desired focal length caused by the law of refraction.

[0127] Figure 8 , an alternative optical element is shown: for example, a diffractive optical element (DOE) 13 arranged on a film 22 can be structured with a smaller thickness for the same focal length. The film 22 for the DOE 13 can be exposed from the CMOS layer stack of the semiconductor chip 4 during manufacturing. In a particular embodiment, the DOE 13 can be a metamaterial, for example, in which the surface of the film has been structured so that it effectively acts as an optical lens.

[0128] Figure 9 A further optical element is shown: a lens is provided on a carrier substrate, for example a polymer lens 15 provided as described above on a glass carrier substrate 23. Such a lens 15 on a glass carrier substrate 23 can be manufactured as an embossed polymer lens on a glass carrier substrate 23 and then mounted on a semiconductor chip 4, for example, with the aid of an adhesive. Since the thermal expansion coefficients of the glass carrier substrate 23 and the semiconductor chip 4 match or are at least similar, the strain in the adhesive is reduced during temperature cycling.

[0129] Figure 9Also shown are geometrical considerations related to the propagation of the spherical wavefront of scattered light as described above: the distance 14 of the photodetector 3 from the optical axis 20 and thus from the optical element is advantageously minimized. This results in a large detection volume 8, or in other words, a high PM count.

[0130] Figure 9 and Figure 10 Another advantageous feature of embodiments of the present invention is depicted. In the case of a glass carrier substrate 23 carrying lens 15, the sidewalls of optical element 2 are provided with a light barrier 19, for example, a blackened or silvered portion. This prevents stray light from the optical element from directly reaching photodetector 3, which would significantly increase the noise level and reduce the PM sensor's ability to detect PM particles, i.e., significantly reduce detection volume 8. The blackening or silvering can be achieved by applying a selective coating to the glass carrier substrate 23, for example, using a chemical that binds to the glass carrier substrate 23 rather than the glass of polymer lens 15 and blackens or silvers it. Furthermore, such a coating is inherently thin and therefore does not contribute to the lateral thickness of the optical element in terms of material, and thus does not exacerbate the aforementioned shadowing.

[0131] Figure 10 A schematic cross-section through a PM sensor according to another embodiment is shown. Figure 1 The PM sensor of FIG1 shares most features with FIG2 . However, this PM sensor has a photodetector 3 only on one side of the optical element, which in the embodiment shown is again a lens 15 on a carrier substrate 23. On the opposite side, the optical element is supported by a support 16, which can be, for example, a dummy substrate spacer formed by the substrate or a mold frame. Figure 10 The PM sensor can obviously have a Figures 1 to 9 However, current PM sensors can be constructed using even smaller form factors, making them well-suited for miniaturized applications.

[0132] PM sensor details ( Figure 11A )

[0133] Figure 11A shows a PM sensor similar to Figure 9 In an embodiment of the embodiment, the sensor shown is Figures 1 to 10 More details.

[0134] In this embodiment, semiconductor chip 4 is a silicon chip that carries a CMOS layer stack 24. Photodetectors 3 are formed in the semiconductor material using a CMOS process. For example, each photodetector 3 can be a photodiode formed by creating a negatively doped well in a positively doped portion of the silicon chip. To allow light to reach the photodiode, the CMOS layer stack above the photodiode is removed by etching. The anode and cathode of the photodiode are connected to the metallization layers of the CMOS layer stack 24.

[0135] The analog and digital electronic circuitry is formed in the CMOS layer stack 24. The electronic circuitry forms an application specific integrated circuit (ASIC). The ASIC serves in particular as a control unit 27, as will be described below with reference to Figure 11B Explanatory.

[0136] An auxiliary photosensitive detector 25 is formed in semiconductor chip 4 for determining the optical power of light source 1. This detector can also be referred to as a "feedback detector" because it can provide feedback to adjust the output of light source 1 in a closed loop. Auxiliary detector 25 can be of the same type as main photodetector 3. Preferably, auxiliary detector 25 is a photodiode. Auxiliary detector 25 can be formed in semiconductor chip 4 in the same manner as main photodetector 3. Auxiliary detector 25 is preferably arranged very close to the surface of sidewall 26 that bounds cavity 5. The auxiliary detector preferably has a very small surface area compared to the total surface area of main photodetector 3. For example, the auxiliary detector can cover a surface area of less than 100 μm x 100 μm, for example 50 μm x 50 μm. In this manner, auxiliary detector 25 is relatively insensitive to light that has been scattered by PM in detection volume 8. However, auxiliary detector 25 is sensitive to light that may reach auxiliary detector 25 via other optical paths.

[0137] The light received by the auxiliary detector 25 can have at least two different sources. On the one hand, the auxiliary detector 25 can receive light that has been emitted by the light source 1 approximately along its main emission direction, i.e., approximately along the direction of the light beam 7, and that has been scattered away from this direction before the light has left the optical element. Such scattering may occur, for example, at the surface of the optical element or within the optical element. In the present disclosure, this type of light is designated as "stray light". On the other hand, the auxiliary detector 25 can receive light that has been emitted by the light source along directions other than its main emission direction. For example, if the light source is a VCSEL, the light source has a main emission surface at which the light beam 7 is emitted, and the light source has lateral sidewalls. The main emission surface faces the direction of the light beam. VCSELs typically also generate a certain amount of light at their lateral sidewalls by spontaneous emission. This light can also propagate to the auxiliary detector 25.

[0138] exist Figure 11AIn the example of FIG, there are at least three possible light paths from the light source 1 to the auxiliary detector 25:

[0139] - The first light path extends through the semiconductor chip 4. The penetration depth of light into silicon depends on the wavelength. At a typical IR wavelength of 940 nm, the light intensity decreases to approximately 10% (1 / e ) after approximately 100 μm. 2 ). This optical path is particularly relevant for light generated by spontaneous emission. If it is desired to monitor the optical power of the light source 1 by monitoring the intensity of the light generated by spontaneous emission, the auxiliary detector 25 should therefore be arranged as close as possible to the surface of the side wall 26 that delimits the cavity 5, and the surface of the side wall 26 should not be covered by an opaque material. In addition, the top surface of the auxiliary detector 25 may be covered by at least some of the layers of the CMOS layer stack to prevent light from impinging from above the auxiliary detector 25.

[0140] - The second optical path extends through the CMOS layer stack 24. The CMOS layer stack can act as a light guide perpendicular to the optical axis of the optical element, i.e. in the plane of the photodetector or parallel to the photodetector plane. Light entering the CMOS layer stack will thus be guided to the auxiliary detector 25. In some embodiments, stray light and / or light from spontaneous emission can enter the CMOS layer stack at the cavity wall 26, e.g. Figure 11A However, in practice, this mechanism may often be overlooked. In other embodiments, the membrane 22 is formed by one or more layers of a CMOS layer stack (as in Figure 8 ), and stray light can originate from scattering events within the membrane 22 and / or at its boundaries, resulting in stray light being generated directly within the CMOS layer stack. This optical path is active even in the presence of an opaque layer on the surface of the sidewalls 26 of the cavity 5.

[0141] A third optical path extends through an optical element. In the example of FIG11 a , the optical element is a polymer-embossed lens 15 on a glass carrier substrate 23. The glass carrier substrate 23 is capable of directing stray light to a portion of its bottom surface, positioned directly above the auxiliary detector 25. Light exiting this portion of the glass carrier substrate 23 can strike the auxiliary detector 25 from above. Similar considerations apply to other types of optical elements. Similarly, this optical path is active even in the presence of an opaque layer on the surface of the sidewall 26 of the cavity 5.

[0142] Depending on the arrangement of the auxiliary detector 25 relative to the cavity 5 (in particular, its lateral distance from the cavity wall), the presence or absence, type and arrangement of optical elements (e.g., whether an optical element is present, whether the optical element comprises a membrane made of a CMOS layer stack, whether there is a direct light path from the optical element to the top of the auxiliary detector, whether the auxiliary detector is covered by one or more opaque layers of the CMOS layer stack), and other measures such as adding an opaque layer on the surface of the cavity sidewall, the light received by the auxiliary detector 25 may be dominated by stray light or by light from spontaneous emission. Therefore, the control unit 27 may determine the optical power of the light source based on stray light, based on spontaneous emission, or based on a combination of the two.

[0143] An optical filter 28 is disposed on the top surface of semiconductor chip 4, covering both photodetector 3 and auxiliary detector 25. Optical filter 28 is an optical bandpass filter that only allows light within a wavelength range that includes the wavelength of light source 1 to pass through. Optical filter 28 is an interference filter applied using a wafer-level process in which several layers of different refractive indices are stacked on top of each other. The thickness of each layer can be within the range of approximately one-quarter wavelength of the main wavelength of the light source. This results in destructive interference for all wavelengths except the desired wavelength band. For the main photodetector 3, optical filter 28 helps avoid elevated noise levels and DC saturation caused by ambient light, thereby improving the signal-to-noise ratio of signal pulses originating from PM. For the auxiliary detector 25, optical filter 28 reduces the contribution of ambient light to the output signal, making the auxiliary detector 25 relatively insensitive to ambient light.

[0144] The bonding and packaging of the PM sensor can be performed as follows: The base substrate 6 can be, for example, a land grid array (LGA). The light source 1 and controller 27 can be connected to the flat surfaces of the LGA via wire bonds 31. During the manufacture of the PM sensor, the light source 1 can initially be mounted on the LGA and wire bonded to the appropriate flat surfaces of the LGA. In some embodiments, the LGA with the light source bonded thereto can be provided as a pre-assembled unit. For example, VCSELs are sometimes provided as pre-assembled units on an LGA. Thereafter, the semiconductor chip 4, its cavity 5, and the CMOS layer stack 24 can be mounted on the LGA (e.g., glued to the LGA) in such a manner that the light source 1 is arranged in the cavity 5. The circuitry in the CMOS layer stack 24 can then also be wire bonded to the LGA. The resulting assembly can then be partially encapsulated in a housing 32 via open-cavity molding, thereby providing access from above to the photodetector 3, auxiliary detector 25, and cavity 5. In some embodiments, optical elements are finally attached to the semiconductor chip 4 to cover the cavity 5. In other embodiments, the optical elements may have already been created or attached to the semiconductor chip in a previous production step.

[0145] exist Figure 11A In the embodiment of FIG. 2 , as in some other embodiments, the optical element is a polymer lens 15 on a glass carrier substrate 23. In particular, the lens can be a "wafer-level optical lens" or simply a "WLO lens." In wafer-level optics, the carrier substrate is provided in the form of a wafer, the optical structure is created on the wafer, and the wafer is subsequently diced. In particular, a polymer lens can be created on a wafer by coating the wafer with a UV-curable polymer, imprinting the uncured polymer using a wafer-sized stamp, and UV-curing the polymer. In the present disclosure, a polymer lens created in this manner is referred to as an imprinted polymer lens.

[0146] The sidewalls of the glass carrier substrate 23 may be provided with a light barrier 19, or an opaque coating, to prevent stray light from reaching the photodetector 3. The light barrier 19 may be a mirror-like silver coating that can be applied to the sidewalls of the glass carrier substrate 23 using a known silver nitrate mirroring process. To this end, after the polymer lens 15 is created on the glass wafer forming the glass carrier substrate, the wafer is mounted on a dicing foil and diced. The diced wafer is then processed using a silver nitrate mirroring process. Because the backside of the wafer is protected by the dicing foil and the polymer from which the lens is formed does not react with chemicals, only the diced sidewalls of the glass carrier substrate 23 are formed as mirrors.

[0147] In order to further reduce the risk of stray light problems, a further coating 29 forming an aperture defining the aperture may be provided on the top and / or bottom surface of the glass carrier substrate 23. The coating 29 may be, for example, a chromium coating. Figure 11A In the example shown, a chrome coating has been applied to the top surface of a glass carrier substrate 23. The coating forms an aperture defining an aperture, and the polymer lens 15 is disposed in the aperture. Instead of or in addition to forming an aperture on the top of the glass carrier substrate, an aperture defining an aperture can also be formed on the bottom of the glass carrier substrate.

[0148] Although the principles of wafer-level optics have been described using the example of a glass wafer forming a glass carrier substrate, the carrier substrate may also be formed of materials other than glass.

[0149] Control Unit ( Figure 11B )

[0150] Figure 11B yes Figure 11ASchematic functional diagram of a PM sensor. The control unit 27 receives signals both from the photodetector 3 and from the auxiliary photosensitive detector 25. The control unit 27 processes the signals from the photodetector 3 to detect signal pulses corresponding to light pulses of PM in the detection volume 8 originating from the light beam 7. The control unit 27 also analyses these signal pulses to derive at least one parameter indicative of a physical quantity of PM, such as a parameter indicative of PM concentration, at least one PM size parameter (such as an average size and / or at least one parameter characterizing a size distribution), and / or at least one PM velocity parameter. For example, the determination of the PM concentration parameter can be based on the number of pulses per unit time and a known, measured or estimated flow rate of the fluid flow passing through the PM sensor, as this is known per se. The determination of the PM size parameter can be based on the amplitude of the pulses, as this is also known per se. When calculating the PM parameters, the control unit 27 can take into account the light power of the light source 1 as represented by the signal from the auxiliary detector 25. The control unit 27 can also use the signal from the auxiliary detector 25 to control the light output power of the light source 1 by means of a closed-loop control algorithm. The control unit can also take into account the distance of the PM particles from the photodetector plane, as will be combined with Figure 12 More detailed description.

[0151] In summary, the control unit 27 has two main purposes: a) processing the signal from the photodetector 3 to derive at least one parameter indicative of a property of the PM; and b) monitoring and optionally controlling the output power of the light source 1 using the auxiliary detector 25 .

[0152] In some embodiments, the control unit 27 can be fully implemented "on-chip" in an ASIC formed by the CMOS layer stack 24. In other embodiments, part of the functionality of the control unit 27 can be implemented in the ASIC, while other functionality can be implemented "off-chip" in an external circuit system. The external circuit system can be connected to the ASIC, for example, via the base substrate 6. For example, some initial processing steps of the signals received from the main photodetector 3 and / or the auxiliary detector 25, such as signal amplification, analog-to-digital conversion, and filtering, can be performed on-chip by the ASIC formed by the CMOS layer stack 24, while subsequent processing steps, such as calculation steps for calculating parameters indicative of properties of the PM and / or calculation of control signals for controlling the light source 1, can be performed off-chip by the external circuit system. The external circuit system can include a general-purpose processor or a special-purpose processor that is configured to execute a computer program that causes the processor to perform one or more processing steps for determining the parameters.

[0153] Distance determination ( Figure 12 、 Figure 13A 、 Figure 13B )

[0154] Figure 12An embodiment of a PM sensor is shown which allows determining the distance from the photodetector plane where a detected particle intersects the light beam 7. To this end, the optical element can be supplemented by an asymmetric extension 41.

[0155] The asymmetric extension 41 selectively extends laterally toward one or more of the photodetectors, thereby partially shielding those photodetectors without shielding other photodetectors. Figure 12 In the example of FIG. 5 , the partially shielded photodetector is designated as photodetector 3 b and the non-shielded photodetector is designated as photodetector 3 a. The asymmetric extension 41 shields the affected photodetector 3 b from some of the light of PM particles that intersect the light beam 7 approaching the optical element. Figure 12 This example illustrates two PM particles 9 and 9' passing through the PM sensor at different distances from the photodetector plane. Particle 9 passes through the PM sensor at a relatively large distance. Asymmetric extension 41 does not prevent any light scattered from the particle from reaching photodetector 3b. Therefore, photodetectors 3a and 3b receive the same amount of scattered light. In contrast, particle 9' passes through the PM sensor at a relatively small distance from the photodetector plane. Because asymmetric extension 41 blocks some of the light scattered from particle 9', photodetectors 3a and 3b receive different amounts of scattered light.

[0156] Figure 13A The signal pulses recorded by photodetectors 3a and 3b, caused by scattered light received from particles 9 and 9', respectively, are shown schematically. At time t1, photodetectors 3a and 3b receive scattered light from particle 9. The resulting signal pulses have approximately the same amplitude. At time t2, photodetectors 3a and 3b receive scattered light from particle 9'. The resulting signal pulse from photodetector 3a is much larger than the pulse from photodetector 3b.

[0157] Figure 13B The resulting ratio of the signals from the photodetectors 3a and 3b is shown. This ratio is a direct measure of the distance of the particle from the photodetector plane when it intersects the light beam 7. In particular, the ratio exhibits the following behavior:

[0158] a) The closer this ratio is to 1 (equal signal levels), the further away the particle is from the photodetector plane when it intersects the light beam.

[0159] b) The closer this ratio is to 0 (no light at the photodetector 3b facing the asymmetric extension due to shadowing), the closer the particle is to the photodetector plane when it intersects the light beam.

[0160] c) The ratio between 0 and 1 corresponds to different distances of the particles from the photodetector plane.

[0161] This information can be used by control unit 27 to compensate for any unwanted effects that the distance may have on the signal level. For example, if the intensity distribution of light beam 7 along the optical axis is known, control unit 27 can correct the measured pulse amplitude for this known intensity distribution. Thus, a better estimate of the particle size can be obtained. Generally speaking, better sensor performance can be achieved.

[0162] And in Figure 12 In FIG. 4 , the effect of the asymmetric extension 41 of the optical element is illustrated using the example of a polymer lens 15 on a glass carrier substrate 23 , but the same concept can also be used for other types of optical elements.

[0163] More generally, asymmetric extension 41 is an example of a light-blocking element that is arranged on semiconductor chip 4 in such a manner that it selectively shields a portion of one or more photodetectors from light scattered by PM particles in light beam 7, the portion depending on the distance of the particles from the photodetector plane. The light-blocking element can be separate from the optical element. The light-blocking element can be arranged laterally adjacent to the optical element. It can even be provided if the optical element is completely absent.

[0164] Opaque coating on the side walls of the cavity ( Figure 14 and Figure 15 )

[0165] A "light blocker," i.e., a coating that is opaque to the primary emission wavelength of light source 1, is created on the sidewalls of the cavity and / or on the bottom side of semiconductor chip 4 facing base substrate 6. This prevents direct light from light source 1 and / or stray light from reaching the photodetector through the semiconductor chip. This prevents detector saturation and / or reduces (Schottky) noise. A lower noise level means a lower threshold for PM detection can be selected, which results in increased performance. In particular, smaller particles can be detected. This increases the statistics of the data evaluation, leading to better accuracy.

[0166] exist Figure 14 In an embodiment, such a coating is formed by the backside metallization 51 of the semiconductor chip 4. Such a metallization can be created, for example, by sputtering deposition. If the deposition process is performed after the cavity has been etched into the semiconductor chip, the cavity sidewalls will also automatically be covered by the metallization 51. Examples of suitable materials for the metallization are, but are not limited to, Al, Cu, Ag, Ti, and TiN. The sensible metallization thickness ranges from 50 nm to 1 μm or more.

[0167] However, such metallization process is different from Figure 8The product design including a film formed by one or more CMOS layers in the example of is not compatible because the metallization will make the film opaque. Therefore, other processes for creating an opaque coating on the chip surface should be used for such an embodiment.

[0168] Figure 15 , an embodiment in which the opaque coating 52 has been created by an alternative process is shown. In this embodiment, a membrane 22 formed from one or more layers of the CMOS layer stack 24 spans the cavity 5. The membrane can be part of an optical element, as will be described in more detail below, or the membrane can simply be provided to protect the light source from contamination. The opaque coating 52 can be created by wafer-level inkjet printing into the cavity 5. This process is very cost-effective. It is compatible with product designs that use the membrane 22 due to the small droplet size. To prevent the ink from overflowing towards the center of the membrane, which should remain transparent to allow the light beam to pass through, a flow stop structure 53 (e.g., a ring composed of an oxide in the membrane) can be designed into the membrane 22.

[0169] Note that the ink disposed on the membrane 22 radially outwardly of the flow stop structure 53 may be considered to represent another example of an aperture defining an aperture, as discussed above by way of the example of a chrome coating.

[0170] In both embodiments (metallization or inkjet coating), if the cavity sidewalls are formed by Figure 1 This is advantageous if the dotted line indicates an inclination towards the back side of the semiconductor chip 4 .

[0171] Spacer( Figure 16 )

[0172] Figure 16 An embodiment is shown in which a spacer 61 is arranged between the base substrate 6 and the semiconductor chip 4. The spacer 61 and the semiconductor chip 4 together form a substrate 60.

[0173] The spacer 61 is also preferably made of silicon. The spacer 61 has a central opening (through hole) extending from the bottom side of the spacer 61 facing the base substrate 6 to the top side of the spacer 61 facing the semiconductor chip 4. The central opening is arranged coaxially with the cavity in the semiconductor chip 4. The cavity in the semiconductor chip 4 and the central opening in the spacer 61 together form the cavity 5 in which the light source 1 is arranged.

[0174] exist Figure 16 In the embodiment of the present invention, the central opening in the spacer 61 has a lateral dimension that is slightly larger than the lateral dimension of the cavity in the semiconductor chip 4. However, in other embodiments, the lateral dimension of the opening in the spacer 61 can be the same as or smaller than the lateral dimension of the cavity in the semiconductor chip 4.

[0175] Spacer 61 increases the distance H between light source 1 and the optical element along optical axis 20. A larger distance H allows the use of optical elements with larger focal lengths. On the one hand, such optical elements may be easier to produce. On the other hand, the larger focal length of the optical element provides the possibility of increasing the distance between the optical element and the beam focus. It should be noted that this distance is not necessarily the same as the focal length of the optical element, as the position of the focal point generally depends on the emission characteristics of the light source (e.g., divergent vs. collimated), and in the case of divergent emission, on the distance H between the light source and the optical element. By increasing the distance between the optical element and the beam focus, the size of the detection volume 8 can be increased. A larger distance H between light source 1 and the optical element also reduces the sensitivity of the arrangement to variations in the manufacturing process and materials, in particular to variations in the thickness of semiconductor chip 4, thereby increasing production stability and reducing device-to-device variations in performance. This is particularly important if a collimated (cylindrical) beam is used instead of a focused beam, as collimation is particularly sensitive to tolerances in the distance between the light source and the optical element.

[0176] If spacers are not used, the distance H is limited by the maximum available thickness of the wafer from which the semiconductor chip 4 is produced. For example, the maximum thickness of a commercially available 8-inch silicon wafer is typically 720 μm. By using spacers also made from silicon wafers, the overall thickness of the substrate 60 can be easily doubled. If an even greater thickness is desired, two or more spacers can be stacked, or thicker spacers can be obtained by using larger wafers that can be used at greater thicknesses.

[0177] Therefore, the thickness of the semiconductor chip 4 in which the photodetector 3 is integrated becomes a freely adjustable design parameter. For example, it becomes possible to use a thin silicon wafer (typically around 300 μm) for manufacturing the photodetector 3 and the electronic circuit system, and to compensate for the remaining required distance between the light source 1 and the optical element by using a spacer 61 of the desired thickness.

[0178] The wafer with integrated photodetectors and the silicon spacer wafer can be connected before dicing using readily available bonding techniques, such as a "direct bonding" process in which two Si wafers are bonded to each other using van der Waals forces. Alternatively, "adhesive bonding" using structured foil as a bonding interface is also possible.

[0179] If desired, an opaque coating may be applied to the sidewalls of the central opening and / or the backside of the spacer, as described above with respect to the semiconductor chip in which the photodetector is integrated.

[0180] although Figure 16 An optical element in the form of a polymer lens 15 on a glass carrier substrate 23 is shown, but any optical element in combination with a spacer may be used.

[0181] Imprint on the membrane ( Figures 17 to 19 )

[0182] The optical element may be produced by depositing a structure acting as a refractive optical element (ROE) or a diffractive optical element (DOE) directly on a film formed from one or more layers of the CMOS layer stack. Figures 17 to 19 An example is shown in .

[0183] The membrane 22 is typically created by creating a CMOS layer stack on a silicon wafer and subsequently etching the wafer from the back side to create the cavity 5. The etch stop can be formed by the bottommost oxide layer in the layer stack. Further thinning of the membrane can be accomplished by further etching from within the cavity and / or from the top of the CMOS layer stack. In the region of the membrane, the CMOS layer stack should preferably only include SiO and / or SiN layers in order to make the membrane transparent to light.

[0184] The optical structure is then created directly on the membrane 22 by means of wafer-level optical processes. Wafer-level optical processes applied directly to the wafer from which the semiconductor chip 4 is formed have several advantages: Manufacturing tolerances will be reduced because the optical elements are created by wafer-level processes. The optical elements can be brought closer to the photodetector plane, in which the photodetectors are arranged. Shadows caused by the optical elements are minimized, thereby increasing the measurement volume. The flow over the sensor will become more laminar. Measurement accuracy is generally better in laminar flow. In addition, the sensor will be less prone to accumulation of dirt and, therefore, an increased lifetime can be achieved. The design is natively fluid-tight at the first end of the cavity and is therefore particularly suitable for applications like wearable devices, where a certain degree of water resistance is required.

[0185] exist Figure 17 In an embodiment, the polymer lens 71 is created directly on the film 22 by wafer-level imprinting. Figure 18 and Figure 19 As shown in FIG, the Fresnel lens 72 can also be embossed ( Figure 18 ) or diffractive optical element (DOE) pattern 73 ( Figure 19 ) for even flatter device topography.

[0186] The ROE or DOE pattern can also be created on the film 22 using related wafer-level techniques such as nanoimprint lithography or grayscale lithography. In grayscale lithography, a photoresist is applied to the wafer surface in a spin-coating process. Standard lithography equipment is used in conjunction with a grayscale mask to partially cure the photoresist. The uncured resist is removed, leaving the shape of the optical element on the wafer. Grayscale lithography can also be accomplished using direct laser writing, where the grayscale curing intensity is modulated by varying the laser power while scanning the photoresist surface on the wafer.

[0187] In all of these techniques, the optical polymer or photoresist should not cover the photodetector 3 or the pads used for wire bonding on the semiconductor chip 4. This can be achieved by selectively UV curing the optical polymer or photoresist through a partially transparent stamp. The uncured and still liquid polymer can be removed from the surface of the semiconductor chip 4 after the optical component is manufactured.

[0188] Dispensed or droplet microlenses ( Figure 20 )

[0189] In some embodiments, the optical element may include a dispensed or droplet microlens 74, such as Figure 20 As shown in [ 1 ], a dispensed or droplet microlens acquires its shape through the action of phenomena such as surface tension, wetting and dewetting, and gravity. The shape of a dispensed or droplet microlens is determined by several factors, including the film surface energy, the droplet volume, the structuring of the film surface, and the droplet surface tension. These parameters can be varied to some extent to influence the optical properties of the microlens. For example, the film surface energy can be altered through plasma processing. The droplet surface tension can also be varied by choosing different lens materials.

[0190] Liquid drop lenses can also be obtained using a melted photoresist process. In this process, polymer pillars are created on top of the membrane using (binary) photolithography. The polymer is then melted using a reflow process.

[0191] Optical elements on the bottom side of the film

[0192] like Figure 21 As shown in FIG, an optical structure 75 can also be provided on the bottom side of the membrane 22 facing the cavity 5. The same techniques as described above can be used to create the optical structure. To this end, the wafer can be flipped so that the cavity is open toward the top, and the optical structure can be created by imprinting and UV curing or by photolithography from above. The side walls of the cavity act as a native flow stop for the polymer or photoresist. In an alternative process, the wafer is not flipped, and the optical structure is created from below by a process in which a stamp is filled with an optical polymer and the wafer is pushed down onto the stamp from above.

[0193] DOE in membrane( Figure 22 )

[0194] Figure 22An embodiment is shown in which optical structure 76 is created directly within the CMOS membrane, i.e., within the membrane formed by the layers of CMOS layer stack 24. This can be achieved by manufacturing optical structure 76 using CMOS processes or by subsequent wafer-level processes applied to the top or bottom of the CMOS membrane. In this way, manufacturing tolerances can be further reduced, and costs can also be reduced. Flow over the sensor will be even more laminar, further reducing the accumulation of dirt on the optical elements. Again, such a design is inherently fluid-tight at the first end of the cavity.

[0195] If a film has been structured in this way, the film material can be considered to have been transformed into a metamaterial, ie a material that has been structured to have properties that were not found in the material before it had been structured.

[0196] The method of manufacturing DOE using CMOS process is disclosed in the following publication: Dai, Ching-Liang & Chen, Hunglin & Lee, Chi-Yuan & Chang, Pei-Zen, "Fabrication of diffractive optical elements using the CMOS process", Journal Of Micromechanics and Microengineering, 12(1): 22 (2001), DOI: 10.1088 / 0960-1317 / 12 / 1 / 304.

[0197] Another possible manufacturing method is as follows: the optical structure can be created on the wafer by imprinting photoresist or by photolithography. Subsequently, an etching process can be applied, which removes the photoresist while transferring the optical structure of the photoresist to the film topography. This can be done from either side of the film.

[0198] In these embodiments, stray light used to monitor the optical power of the light source 1 can directly pass through the CMOS layer of the film to reach the auxiliary detector 25. Therefore, the opaque coating can be safely applied to the sidewalls 26 of the cavity 5.

[0199] 2K molded lens( Figure 23 )

[0200] Figure 23 An embodiment is shown where the optical element is a 2K molded lens 77. A 2K molded lens comprises an injection molded lens frame where the lens itself is replicated by dispensing the lens material into a replication mold and UV curing.

[0201] and Figures 17 to 23The embodiment shown has a spacer 61, which can also be omitted. Figure 15 As noted, an opaque layer may be applied to the cavity sidewalls to reduce stray light at the photodetector.

[0202] The shape of the side wall of the cavity ( Figures 24 to 26 )

[0203] Figures 24 to 26 Some examples of possible shapes for the cavity sidewalls 26 are shown. Figure 24 In the embodiment, the side walls 26 are inclined towards the bottom, i.e. the transverse dimension of the cavity 5 increases towards the bottom. Such an embodiment is particularly advantageous if an opaque coating is to be applied to the cavity side walls 26. Figure 25 In the , the side walls slope towards the top. Figure 26 In the embodiment of the present invention, the sidewall has a top portion inclined toward the top and a bottom portion opened toward the bottom in a convex shape. As is well known in the art, different shapes can be easily created by appropriate etching methods.

[0204] In all of these embodiments, the cavity 5 has an axis of symmetry perpendicular to the plane of the photodetector. For example, in the case of a cavity with a square cross-section, the cavity may have a four-fold rotational symmetry about the axis of symmetry. In the case of a cavity with a circular cross-section, the cavity may be cylindrically symmetric. Preferably, the axis of symmetry coincides with the optical axis 20.

[0205] Photodetector classification ( Figure 27 )

[0206] Figure 27 An embodiment is shown in which some of the photodetectors are covered by an opaque layer, such as a black layer created by inkjet printing, that shields these photodetectors from light scattered by PM in the detection volume, while other photodetectors face the detection volume without being shielded. The unshielded photodetectors form a first sector 81, while the shielded photodetectors form a second sector 82. A control unit can receive signals from both the shielded and unshielded photodetectors and apply differential processing to cancel signals caused by electromagnetic interference. Sensor module (Fig. 28 and Figure 29 )

[0207] Figure 28 An embodiment of a complete PM sensor module 90 is shown. Sensor module 90 includes a PM sensor 91 according to any of the above-described embodiments. PM sensor 91 is housed in a housing 92, which defines a flow channel 97. A heater 93 creates a convective flow 98 in flow channel 97. The PM sensor transmits a light beam 7 into flow channel 97. In this embodiment, the direction of light beam 7 is perpendicular to the direction of convective flow 98. The light beam is deflected by a mirror 94 into a beam dump 95.

[0208] In the present example, the light beam 7 is a focused beam having a focus 21. The focus is arranged inside the flow channel 97. The detection volume is thus located inside the flow channel 97.

[0209] Figure 29 Another embodiment of a complete PM sensor module is shown. In this embodiment, there is no heater. Instead, flow 98 is created by a fan 99.

[0210] Reference Signs List

[0211] 1 Light source

[0212] 2 Optical elements

[0213] 3.3a, 3b Photodetectors

[0214] 4. Semiconductor Chips

[0215] 5-cavity

[0216] 6 Basic substrate

[0217] 7 Beam

[0218] 8 Detection volume

[0219] 9, 9' PM particles

[0220] 10, 10' scattered light pulse

[0221] 11 Scattering particle height

[0222] 12 Conventional optical lenses

[0223] 13 Diffractive Optical Element (DOE) on Film

[0224] 14 Distance between the photodetector and the optical axis

[0225] 15 Polymer lens on glass substrate

[0226] 16 Support

[0227] 17 Optical elements, such as glass windows

[0228] 18 Metallization

[0229] 19 Light Barrier

[0230] 20 optical axis

[0231] 21 Focus

[0232] 22 membrane

[0233] 23 Glass substrate

[0234] 24 CMOS layer stack

[0235] 25 Auxiliary detector / photodiode

[0236] 26 Cavity wall

[0237] 27 Control Unit

[0238] 28 Optical Filters

[0239] 29 Chrome coating

[0240] 30 aperture

[0241] 31 Wire Bonding

[0242] 32 shell

[0243] 41 Asymmetric extension

[0244] 51 Metallization

[0245] 52 Inkjet coating

[0246] 53 Inkjet flow stops

[0247] 60 substrates

[0248] 61 Spacer

[0249] 71 Wafer-level polymer imprinted lenses directly on film

[0250] 72 Wafer-level polymer imprinted Fresnel lenses directly on film

[0251] 73 Wafer-scale polymer imprinting patterns directly on membranes

[0252] 74 Wafer-scale droplet microlenses directly on membrane

[0253] 75 Wafer-scale polymer embossed pattern on the bottom side of the film

[0254] 76 Diffractive Optical Element (DOE) inside the membrane

[0255] 77 2K molded lens

[0256] 81 First Division

[0257] 82 Second Division

[0258] 90 PM sensor module

[0259] 91 PM sensor

[0260] 92 PCB

[0261] 93 Heater

[0262] 94 Mirror

[0263] 95 beam collector

[0264] 96 shell

[0265] 97 flow channels

[0266] 98 Flow

[0267] 99 Fan

Claims

1. A particulate matter sensor comprising: - a substrate comprising a semiconductor chip (4), said substrate forming a cavity (5), at least a portion of said cavity (5) being formed in said semiconductor chip (4); - at least one photodetector (3) integrated into the surface of the semiconductor chip (4); a light source (1) arranged in the cavity (5), the light source (1) being suitable for emitting a light beam (7) towards a first end of the cavity (5), the light beam defining a detection volume (8) for particulate matter (9) outside the cavity (5), wherein the surface of the semiconductor chip (4) on which the at least one photodetector (3) is integrated faces the detection volume (8), and Therein, the at least one photodetector (3) is adapted to detect light (10) scattered by particulate matter (9) in the detection volume (8).

2. The particulate matter sensor according to claim 1, in, The semiconductor chip (4) comprises a CMOS layer stack (24), and wherein one or more layers in the CMOS layer stack (24) form a membrane (22) spanning the cavity (5) at a first end of the cavity.

3. The particulate matter sensor according to claim 2, wherein: The thickness of the film (22) is less than 20 μm.

4. A particulate matter sensor according to claim 1, comprising an optical element (2) arranged at a first end of the cavity (5), the optical element (2) being configured to shape the light beam (7), whereby the light beam (7) forms the detection volume (8).

5. The particulate matter sensor according to claim 4, wherein: The optical element defines the cavity (5) at the first end.

6. The particulate matter sensor according to claim 4, wherein The optical element defines an optical axis (20) which is perpendicular to the surface of the semiconductor chip (4) on which the at least one photodetector (3) is integrated.

7. The particulate matter sensor according to claim 4, wherein: The optical element (2) is configured to focus the light beam (7).

8. The particulate matter sensor according to claim 4, wherein: The height of the cavity (5) between the light source (1) and the optical element (2) is at least 0.25 mm.

9. The particulate matter sensor according to claim 4, in, The optical element (2) is arranged in a plane defined by the surface of the semiconductor chip (4) in which the at least one photodetector (3) is integrated, and / or The optical element (2) protrudes from the surface of the semiconductor chip (4) on which the at least one photodetector (3) is integrated by no more than 1 mm.

10. The particulate matter sensor according to claim 4, in, The at least one photodetector (3) is arranged at a distance of at most 2 mm from the optical element (2).

11. The particulate matter sensor according to claim 4, wherein: The optical element (2) includes a refractive lens (12; 15; 71; 72; 74) or a diffractive optical element (13; 73; 75).

12. The particulate matter sensor according to claim 4, in, The optical element (2) comprises a glass carrier substrate (23) and an optical structure, wherein the optical structure is formed on the glass carrier substrate (23). Wherein, the thickness of the glass carrier substrate (23) is less than 1000 μm.

13. The particulate matter sensor according to claim 12, in, The optical structure is a polymer lens formed on the glass carrier substrate (23) by embossing.

14. The particulate matter sensor according to claim 4, in, The semiconductor chip (4) comprises a CMOS layer stack (24), and The optical element (2) comprises a film (22) formed from one or more layers of the CMOS layer stack (24).

15. The particulate matter sensor according to claim 14, wherein The thickness of the film is less than 20 μm.

16. The particulate matter sensor according to claim 14, in, An optical structure (71; 72; 73; 74; 75) is provided on the film (22) to form the optical element (2) together with the film (22).

17. The particulate matter sensor according to claim 14, wherein: The film (22) comprises at least one structured CMOS layer (76) to form the optical element (2).

18. The particulate matter sensor of claim 4, further comprising: - an aperture (29) formed by a coating on the optical element (2), the aperture (29) defining an aperture for the light beam (7); and / or - a light barrier (19) between the optical element (2) and the at least one photodetector (3).

19. The particulate matter sensor according to claim 4, wherein: The particulate matter sensor comprises a plurality of photodetectors (3) arranged in an array and / or disposed at different positions around the cavity (5).

20. The particulate matter sensor according to claim 19, in, On the surface of the semiconductor chip (4) on which the photodetectors (3) are integrated, the photodetectors (3) are separated by a conductive material (18).

21. A particulate matter sensor according to any preceding claim, wherein: An optical filter (28) is provided on the surface of the semiconductor chip (4) on which the at least one photodetector (3) is integrated, the optical filter (28) covering the at least one photodetector (3), and the optical filter (28) being configured to reject light having a wavelength outside a wavelength band including a main wavelength of the light source (1).

22. The particulate matter sensor according to any one of claims 1 to 20, further comprising: - a control unit (27) electrically connected to the at least one photodetector (3) and adapted to receive from the at least one photodetector (3) a signal caused by light (10) scattered by the particulate matter (9) in the detection volume (8) and to determine a physical quantity related to the particulate matter (9) based on the signal.

23. The particulate matter sensor according to claim 22, wherein: At least a part of the control unit (27) is integrated into the semiconductor chip (4).

24. The particulate matter sensor according to claim 22, wherein The physical quantity includes at least one of number concentration, size, and size distribution of particulate matter.

25. The particulate matter sensor according to claim 22, further comprising a light-sensitive auxiliary detector (25) integrated into the semiconductor chip (4) and configured to receive light that has been emitted from the light source (1) and has not been scattered by the particulate matter (9) in the detection volume (8), in, The control unit (27) is connected to the auxiliary detector (25) and is configured to determine the optical power of the light source (1) based on the signal of the auxiliary detector (25), and The control unit (27) is configured to take the determined light power into account when determining the physical quantity related to the particulate matter, or to control the light source (1) depending on the determined light power.

26. The particulate matter sensor according to claim 25, wherein The light-sensitive auxiliary detector is a photodiode.

27. The particulate matter sensor according to claim 25, in, The particulate matter sensor comprises an optical element (2) arranged at a first end of the cavity (5), the optical element (2) being configured to shape the light beam (7), and the auxiliary detector (25) being arranged adjacent to the optical element (2) and being adapted to measure stray light from the optical element (2).

28. The particulate matter sensor according to claim 22, in, The photodetector (3) is divided into a first partition (81) facing the detection volume (8) and a second partition (82) shielded from light (10) scattered by particulate matter (9) in the detection volume (8), and The control unit (27) is configured to perform a differential measurement of the first partition (81) and the second partition (82), thereby eliminating parasitic effects of electromagnetic interference on the at least one photodetector (3).

29. The particulate matter sensor according to any one of claims 1 to 20 further comprises a light blocking element (41), which is arranged above the surface of the semiconductor chip (4) in which the photodetector (3) is integrated in the following manner: the light blocking element (41) selectively shields a portion of one or more of the photodetectors (3b) relative to light scattered from particulate matter particles in the detection volume (8), the portion depending on the distance of the particles from the surface of the semiconductor chip (4) in which the at least one photodetector (3) is integrated, while one or more other photodetectors (3a) are not shielded by the light blocking element (41).

30. A particulate matter sensor according to claim 29, comprising an optical element (2) arranged at a first end of the cavity (5), the optical element (2) being configured to shape the light beam (7), wherein The light blocking element (41) is formed by an asymmetric extension of the optical element (2).

31. The particulate matter sensor according to claim 29, comprising a control unit (27) electrically connected to the at least one photodetector (3) and adapted to receive a signal from the at least one photodetector (3) caused by light (10) scattered by the particulate matter (9) in the detection volume (8) and to determine a physical quantity related to the particulate matter (9) based on the signal, in, The control unit (27) is configured to determine a measure of the distance of the particle from the surface of the semiconductor chip (4) in which the at least one photodetector (3) is integrated by comparing a signal from a photodetector (3b) partially shielded by the light-blocking element (41) with a signal from a photodetector (3a) not shielded by the light-blocking element (41), and Therein, the control unit (27) is configured to take the determined distance into account when determining the physical quantity related to the particulate matter.

32. The particulate matter sensor according to any one of claims 1 to 20, wherein: The substrate includes the semiconductor chip (4).

33. A particulate matter sensor according to any one of claims 1 to 20, in, The substrate (60) includes a spacer (61) to which the semiconductor chip (4) is bonded, and Wherein, the cavity (5) is formed in both the spacer (61) and the semiconductor chip (4).

34. A particulate matter sensor according to any one of claims 1 to 20, comprising a base substrate (6), wherein: The light source (1) is mounted on the base substrate (6), The substrate formed with the cavity (5) is arranged on the base substrate (6), and the cavity (5) opens toward the base substrate (6) at its second end.

35. The particulate matter sensor of claim 34, wherein: The base substrate (6) extends in a plane parallel to the surface of the semiconductor chip (4) on which the photodetector (3) is integrated.

36. A particulate matter sensor according to any one of claims 1 to 20, in, The cavity (5) is laterally delimited by side walls (26), the side walls (26) being formed by the substrate, at least a portion of the side walls (26) being formed by the semiconductor chip (4).

37. The particulate matter sensor according to any one of claims 1 to 20, wherein: The cavity (5) has an axis of symmetry, the cavity (5) has rotational symmetry about the axis of symmetry, and the axis of symmetry is perpendicular to the surface of the semiconductor chip (4) on which the photodetector (3) is integrated.

38. The particulate matter sensor according to any one of claims 1 to 20, further comprising: an opaque coating (51; 52), said opaque coating covering at least one side wall (26) of said cavity (5) to prevent light from said light source (1) from passing through said wall (26) to reach said at least one photodetector (3), and / or said opaque coating covering a back surface of said substrate or said semiconductor chip (4), said back surface facing away from a surface on which said at least one photodetector (3) is integrated, to prevent ambient light from passing through said back surface to reach said at least one photodetector (3).

39. The particulate matter sensor of claim 38, wherein: The opaque coating (51; 52) comprises a coating and / or a metallization which has been applied by an inkjet process.

40. The particulate matter sensor according to any one of claims 1 to 20, wherein The light source (1) is a laser diode.

41. The particulate matter sensor of claim 40, wherein: The light source (1) is a vertical cavity surface emitting laser (VCSEL).

42. The particulate matter sensor according to any one of claims 1 to 20, further comprising a housing (32) laterally surrounding the substrate, the housing (32) being made of a molded material.

43. A particulate matter sensor module comprising: - housing (92); - a flow channel (97) arranged in the housing (92); a fan (99) or a heater (93) disposed in the housing (92) and configured to move air through the flow channel (97); as well as - A particulate matter sensor according to any one of the preceding claims, arranged in the housing (92) such that the flow channel (97) includes at least a portion of the detection volume (8).

44. A method for determining a physical quantity of particulate matter using a particulate matter sensor according to any one of claims 1 to 42, the method comprising: operating the light source (1) to emit the light beam (7); operating the at least one photodetector (3) to detect light that has been scattered by particulate matter that intersects the light beam (7); as well as The signal from the at least one photodetector (3) is analyzed to obtain at least one parameter indicative of a physical quantity of the particulate matter.

45. A method for manufacturing a particulate matter sensor according to any one of claims 1 to 42, the method comprising the steps of: a) forming at least one photodetector (3) in a surface of a semiconductor chip (4); b) etching the semiconductor chip (4) along a direction perpendicular to the surface to form at least a portion of a cavity (5); d) arranging a light source (1) in the cavity (5), the light source being configured to emit a light beam (7) towards a first end of the cavity (5).

46. The method according to claim 45, comprising c) bonding the semiconductor chip (4) to a spacer (61), the spacer (61) forming a further part of the cavity (5).

47. The method according to claim 45, comprising e) Arranging an optical element (2) on the semiconductor chip (4), the optical element (2) delimiting the cavity (5) at the first end, the optical element (2) being configured to shape the light beam (7).

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