SMD-COMPLIANT THERMOPILE INFRARED SENSOR

Description

[0001] The invention relates to an SMD-capable thermopile infrared sensor for contactless temperature measurement, as a hot spot or for gesture detection, with at least one miniaturized thermopile pixel on a monolithically integrated sensor chip, which is accommodated in a hermetically sealed housing consisting of at least partially non-metallic housing substrate and a housing cover, wherein a gas or gas mixture is located in the housing.

[0002] Non-contact temperature measurement, gesture control, and the detection of hot and cold objects are becoming increasingly interesting, especially for mobile devices such as smartphones, tablets, and other small wearable devices. Due to the limited space available and the ever-decreasing thickness of devices, particularly small dimensions of the SMD components to be mounted are essential. Because even more distant or spatially restricted measurement objects need to be detected, a narrow viewing angle for the sensor(s) is required.

[0003] Likewise, the infrared sensor must be "calibrated" before installation in one of the aforementioned devices, i.e., it must enable the output of a reproducible object temperature. A preferred application, for example, is using a smartphone for contactless fever measurement, which in turn requires very high measurement accuracy.

[0004] Typical requirements for the dimensions of smartphone housings include, in particular, that the Z-axis (i.e., in the measurement direction) is no more than 3 mm, and preferably only 2 mm, so that the infrared sensor can be positioned, for example, next to a CMOS camera on the circuit board or in a very tight space on the front of the smartphone. Furthermore, the lateral dimensions in the x- and y-directions of the infrared sensor should also be less than 5 mm, and preferably less than 3-4 mm in at least one axis.

[0005] A large number of thermal infrared sensors manufactured using Si micromechanics technology are known. Examples include pyroelectric sensors, bolometers, and thermopiles. To achieve high absolute accuracy in temperature measurement, pyroelectric sensors require a modulator (chopper). Bolometers also require offset adjustment, at least temporarily, using a mechanical shutter to achieve high accuracy.

[0006] As mechanically moving parts of the sensor, both the chopper and the shutter require sufficient reliability over the lifetime of the device and must be installed in the optical channel of the IR sensor (i.e., in front of the sensor in the viewing direction). Therefore, the dimension in the "z-direction" would increase by approximately 1 mm, since the chopper or shutter must be installed in the optical channel. Since, in addition to the additional chopper / shutter assembly, the focusing optics, the sensor chip, and the housing also require space, it is not possible with the current state of the art to build such a small IR sensor with a z-axis of < 3 mm or even < 2 mm (so-called optical track) using pyroelectric sensors or bolometer sensors.

[0007] Without a chopper / shutter, the required measurement accuracy, especially for fever measurements with bolometers or pyroelectric sensors, cannot be achieved. However, even without a built-in shutter, the smallest currently known bolometer-based infrared array sensor with built-in optics and signal processing for temperature measurement, the "Lepton" from FLIR Systems, has a housing height of 5.9 mm (see data sheet "FLIR Lepton," FLIR Systems, Goleta, CA, USA). This is far from the permissible housing dimensions for modern smartphones. This precludes the use of pyroelectric sensors and bolometers in modern, slim smartphones given the current state of the art.

[0008] Thermopile infrared sensors are also used in large quantities for high-accuracy consumer measuring devices (e.g., clinical thermometers). These typically use a transistor package (TO package). The smallest TO sensors for such measuring purposes have a package height of approximately 3 mm, but they lack focusing optics, resulting in a much too large viewing angle of over 100 degrees, and they also lack any signal processing (see data sheet 10TP583T-0154, data sheet from Semitek Ishizuka Electronics, Japan).

[0009] Heimann Sensor has developed a thermopile sensor with focusing optics, also housed in a TO package. The HMS M21 L3.0 F5.5 model (see data sheet from Heimann Sensor GmbH, Dresden 2012) allows a viewing angle of < 30 degrees, but its 5.2 mm housing height is far too high for use in mobile devices, and it lacks signal processing for temperature measurements.

[0010] All of the above-mentioned thermopile solutions in TO packages also have in common that the wire pin connections on the underside of the packages make mounting on a printed circuit board impossible. Surface mountability on printed circuit boards (SMD capability) is, however, required.

[0011] Further solutions for miniaturized thermopile sensors can be found in the following publications: For example, EP 1 296 122 B1 describes a thermopile sensor chip with vertical walls and the largest possible membrane to maximize the measurement signal. Information on miniaturizing the package shape, SMD capability, and restricting the aperture angle is missing.

[0012] Another sensor for non-contact temperature measurement is described in US Pat. No. 8,592,765 B2, which describes a thermopile sensor pixel with a thin membrane, also mentioning an integrated signal processing circuit that is not described in detail. However, there is no indication of SMD capability or even of very small dimensions along the optical axis (z-axis), as the package types described are all large, leaded TO packages.

[0013] DE 103 21 640 B2 presents an SMD-capable thermopile, but it doesn't allow for a small package size and doesn't propose monolithic integration of the signal processing. It also lacks a focusing lens optic, which allows for a narrow viewing angle for pixels with a small package height. Even without focusing lens optics, the package height exceeds 3 mm.

[0014] Furthermore, EP 2 887 033 A1 and EP 2 916 118 A1 propose thermopile pixels in a wafer-level package, which are provided with an aperture in front of the thermopile pixel. However, a focusing lens and an SMD-capable solution that achieves the required small dimensions in the z-axis are missing.

[0015] EP 2 940 442 A1 relates to a wafer-level package for a thermopile pixel constructed using the flip-chip process, with a pinhole or aperture diaphragm located in front of the sensor pixel. However, there is no mention of SMD capability or focusing optics. However, unlike focusing lens optics, such pinhole diaphragms have the disadvantage that the signal decreases with the square of the f-number D / f, where D is the diameter of the pinhole or aperture diaphragm and f is the focal length or the distance between the pinhole or aperture diaphragm and the sensitive absorber surface.

[0016] This effect can be clearly estimated using the example of a 15-degree viewing angle, where a focusing lens can even achieve f-numbers D / f greater than one, and D / F = 1 is a typical f-number for single-lens IR optics (f / 1 optics). The signal reaching the sensor pixel is equal to the square of the f-number. A pinhole lens with a 15-degree viewing angle would reduce the signal by approximately fourteen times compared to a focusing lens, significantly impairing the resolution and measurement accuracy of such a sensor with pinhole optics.

[0017] EP 2 975 371 A1 presents an infrared sensor with temperature compensation in a wafer level package solution, in which one or two sensor pixels are housed in a wafer housing and a different number of thermocouples can be switched on or off at the pixels via switches in order to calibrate the thermopile.

[0018] Furthermore, EP 3 026 406 A1 also describes a sensor pixel housed in a wafer-level package with adjacent compensation pixels and a cavity above and below each pixel. An internal layer is apparently applied to the cavity above the compensation pixel, which has either a reflective or absorbent effect and blocks external radiation, but still allows it to reach the adjacent pixel.

[0019] Here, too, no possibility for surface mountability is specified, nor is there a focusing lens for a small viewing angle of the pixel, nor a signal processing unit.

[0020] EP 3 035 015 A1 also presents a wafer level package housing with two pixels, in which one pixel is shielded from external radiation by an infrared blocking layer located on the wafer edge above it, with heating coils additionally connected to both pixels in order to bring the pixels to a different temperature if necessary.

[0021] What all these solutions have in common is that one or more measuring pixels are provided, but no focusing optics are provided to enable the sensor to have a small viewing angle for measuring the temperature of distant objects despite the low installation height, or the achievable signals would be so attenuated that the measuring task cannot be fulfilled.

[0022] Furthermore, US 2014 / 117201 A1 discloses an optical sensor element with integrated data processing, which, however, is not suitable for SMD applications.

[0023] The sensor element comprises an optical sensor element, various peripheral circuits, and an external connection. The interior is either filled with an inert gas or evacuated to facilitate light transmission from the radiation transmission window to the sensor element. Furthermore, the sensor element is mounted on a PCB, comprising an ASIC and a thermopile array as separate components, as well as capacitors inside the sensor element, and a microcontroller and a capacitor on the back of the PCB on the outside, which are encapsulated by a potting compound. The housing tapers gradually upwards and is provided with a flange for accommodating a lens.

[0024] US 2014 / 0041214 A1 describes an SMD-capable sensor package 100 consisting of an enclosure and a base part as a substrate with through-holes on the rear. The substrate can be a PCB or a fiberglass plate. A sensor is located centrally on the substrate, with an electronic component, e.g., an ASIC, next to it. A lens is located centrally above the sensor. A vacuum or near-vacuum exists inside the sensor package. Due to its design, the sensor package 100 has a high structure, which is also due to the wire bridges, severely limiting its application possibilities.

[0025] Furthermore, KR 101 661 920 B1 describes a sensor package with a base substrate in the form of a flat printed circuit board (PCB) and a sensor chip, with an ASIC next to it on the PCB. This arrangement is enclosed in a housing that is tightly connected to the PCB using silver solder. For this purpose, the PCB is masked with a metal coating at the edges. A lens is located above the sensor chip, which also closes an opening in the housing. This sensor package also has a disadvantageous high structure, which precludes its use in flat mobile devices.

[0026] US 2016 / 0305829 A1 relates to a sensor arrangement consisting of a frame-like housing made of a ceramic material, silicon, metal, a metal alloy, or a polymer-based material, and a substrate that seals the frame-like housing at the bottom and on which two thermopiles and a thermal reference sensor are located as individual components. The frame-like housing is closed by a cover that is provided on at least one side with a metal layer as a light absorber, with an opening in the metal layer above one of the thermopiles. With such a sensor arrangement, a particularly low installation height cannot be achieved, and there is no focusing optics.

[0027] US 2011 / 174978 A1 relates to a thermal infrared sensor in a housing with optics and a chip with thermocouples on a membrane that is mounted over a frame-shaped support body with good heat conduction, the support body having vertical or nearly vertical walls. The thermopile infrared sensor is designed using monolithic silicon micromechanics, which, despite its small chip size, offers high thermal resolution, a high fill ratio, and a fast response time. This infrared sensor uses a standardized TO housing with contact pins extending downwards for mounting on printed circuit boards. This housing design is unsuitable for particularly flat applications, especially SMD applications.

[0028] US 2016 / 149105 A1 describes a chip for radiation measurement, comprising a first and a second sensor. The chip is further provided with a first and a second recess with sloped walls. A radiation-permeable substrate with recesses above the first and second sensors is located above the sensors for hermetic sealing. Furthermore, an internal layer is provided on the inside of the second recess, which prevents radiation from reaching the second sensor.

[0029] None of the described prior art solutions, except for DE 103 21 640 B2, specify surface mount (SMD) options and there is no reference to a signal processing unit that calculates, for example, temperature values.

[0030] The object underlying the invention is to provide a miniaturized surface-mountable thermopile infrared sensor for contactless temperature measurement, as a hot spot or for gesture detection, as well as with integrated signal processing, which has such a low installation height, particularly in the z-direction, that it can be easily installed in mobile devices such as smartphones.

[0031] The object underlying the invention is achieved by an SMD-capable thermopile infrared sensor for non-contact temperature measurement having the features of claim 1. Advantageous modifications are defined in the dependent claims.

[0032] The thermopile infrared sensor according to the invention is characterized by a particularly small design, particularly along the optical axis, and represents an SMD-capable construction, with at least one sensor pixel having an absorber area of ​​<0.5 mm, preferably <0.3 mm. Furthermore, the housing substrate is provided with an integrated focusing lens to focus only infrared radiation from a small viewing angle or even from distant objects onto the sensor pixel.

[0033] On each individual chip, a monolithic signal processing unit and a storage medium (e.g. EEPROM) monolithically housed on the chip are provided to store correction values ​​for measured sensitivities, offset values, etc. and to make these available for later accurate measurement of the object temperature and corresponding error and ambient temperature drift corrections inside or outside the chip.

[0034] The essential features of the invention consist in a surface-mountable SMD-capable infrared sensor on a monolithically integrated sensor chip, which is housed in a housing consisting of an at least partially non-metallic housing base and a housing cover, for example in the form of a metallic deep-drawn part, and is provided with a gas or gas mixture and is hermetically sealed.

[0035] The monolithic sensor chip is located on the housing substrate (base plate) and is hermetically sealed by the housing cover, with an opening in the housing cover that is closed with an imaging lens that images the radiation from objects onto the sensor pixel(s).

[0036] The gas or gas mixture contained in the hermetically sealed housing should have a thermal conductivity that is significantly lower than that of air or nitrogen at normal pressure.

[0037] Furthermore, the size of the sensor elements that see through the lens is smaller than 500 µm, but preferably smaller than 300 µm.

[0038] The dimensions of the housing, consisting of the housing substrate and the housing cover, should be no more than 5 mm in length and width, but preferably less than 3 mm.

[0039] Furthermore, the thickness of the housing substrate, ie the base plate, should be less than 0.5 mm, preferably less than 0.3 mm.

[0040] Finally, the miniaturized focusing lens is manufactured in a mass process (e.g. on Si wafers) with a focal length of at most 1.9 mm, but preferably of at most 0.5 mm.

[0041] A special version of the thermopile infrared sensor according to the invention consists in that at the other end of the sensor chip there is another sensor pixel for compensation purposes, which does not look through the lens, but rather preferentially at the metallic housing cover located above it.

[0042] In order to enable gesture recognition or to detect temperature distribution, several sensor pixels are arranged in a horizontal multiple arrangement, e.g. matrix-like, on the sensor chip.

[0043] The invention is explained in more detail below using exemplary embodiments. The accompanying drawing figures show: Fig. 1: the basic structure of a single-element thermopile infrared sensor as a sectional view in an SMD package with a single chip, built-in lens optics and monolithically integrated signal processing; Fig. 1a: a section A from Fig. 1 with some details highlighted; Fig. 1b: a modification of the miniaturized SMD sensor with a particularly low overall height; Fig. 2: a top view of a single-element thermopile infrared sensor in an SMD housing; Fig. 3: an embodiment of the SMD sensor with an additional reference pixel for compensation purposes; Fig. 3a: an embodiment of the miniaturized SMD sensor according to the invention with a reference pixel with a different cover height above the signal and reference pixels; Fig. 3b: a further embodiment of the miniaturized SMD sensor with a lens mounted externally on the housing cover; Fig. 4: a top view of the thermopile infrared sensor in the SMD housing with reference pixel; and Fig. 5: a further embodiment of the SMD thermopile infrared sensor according to the invention with multiple sensor pixels and monolithically integrated signal processing.

[0044] Fig. 1 und 1a show the basic structure of an SMD-capable miniaturized thermopile infrared sensor, in which a monolithic sensor chip 2 is arranged in a sensor housing consisting of a base plate / housing substrate 1 provided with a recess 30 and side walls 31 and a housing cover 3. The housing substrate 1 consists of an insulator, such as ceramic. The sensor chip 2 is provided with a membrane 6 (sensor pixel) and an absorber layer for infrared radiation located thereon, beneath which there is a cavity 5 with vertical walls, i.e. the sensor chip surrounds the cavity like a frame, which also serves as a heat sink for the thermopile, as will be explained later. The membrane 6 is suspended above the cavity 5 with the aid of beams 23, wherein the beams 23 connect the membrane 6 to the sensor chip 2. For thermal insulation, there are slits between the beams 23 and the membrane 6 or the sensor chip 2.The cavity 5 also limits the area of ​​the pixel 29 (. Fig. 1b ). In addition to the membrane 6, a signal processing unit 12 is located on the sensor chip 2.

[0045] On the sides of the base plate 1, there are metallic connections 9 from the front to the back of the base plate 1 ( Fig. 1 ). On the inside of the base substrate 1, the metallic connection 9 ends in a contact surface 8 on the inside of the side wall 31 in the form of a metallization as a connecting surface for a bonding wire 7 for the electrical connection of a contact pad 25 on the sensor chip 2 and the contact surface 8 on the base substrate 1 ( Fig. 1a ). On the back of the housing substrate 1, ie at the bottom as shown in the drawing, the metallic connections 9 each end in a contact area 10 for surface mounting, e.g. on a printed circuit board or a substrate. In Fig. 1 On the right and left sides, a metallic connection 9 with a bonding wire 7 is shown as representative of further adjacent metallic connections 9 which extend into the depth of the figure.

[0046] The housing substrate 1 is covered with a housing cover 3, the outwardly angled side edge 32 of which rests hermetically on the side wall 31 of the housing substrate 1 ( Fig. 1 ). Inside, i.e. between the housing cover 3 and the housing substrate 1, there is a gas or gas medium 11 with special properties to be described later.

[0047] In the housing cover 3 there is also an aperture opening 26, in front of which a focusing lens 4 is arranged on the inside of the housing cover 3 ( Fig. 1a ). Alternatively, the lens 4 can also be mounted from the outside on the housing cover 3, as shown in Fig. 3b It is essential for the function that the central axis of the aperture opening 26 or the focusing lens 3 coincides with the axis of symmetry of the membrane 6.

[0048] The lens 4 focuses the infrared radiation from a measuring object located in front of the aperture opening 26 from a field of view FOV 24 onto the sensor pixel with the absorber surface on the membrane 6 or the thin carrier membrane 22 of the pixel.

[0049] The housing cover 3 is a metallic deep-drawn part to ensure good thermal conductivity, which is glued, soldered, or welded to a contact point 18 of the housing substrate 1. Alternatively, the housing cover 3 can also be a metallic or non-metallic injection-molded or die-cast part, which preferably has good thermal conductivity and has prepared coatings at the contact points to the housing substrate 1 for a hermetic adhesive, soldered, or welded seal to the side edge 31 of the housing substrate 1.

[0050] In the case of soldering or welding, the weldable or solderable metallic contact point 18 on the housing substrate 1 must be placed over an insulation layer 19 on the metallic connection 9 ( Fig. 1a ) to prevent a short circuit between the metal conductor tracks 9 on the side wall 31 of the housing substrate 1. The required hermetic housing closure is ensured by means of a circumferential solder or adhesive joint 20.

[0051] The housing substrate 1, which comprises a central, flat base plate with surrounding side walls 31, consists primarily of a non-metallic material (e.g., ceramic) onto which metallic conductive traces 9 are applied. These conductive traces 9 terminate on the top side with inner contact pads 8 and on the bottom side with outer contact surfaces 10 for surface mounting. The contact surfaces 10 contain a solderable or weldable coating for mechanical and electrical mounting on underlying printed circuit boards (not shown) or other wiring carriers.

[0052] The housing substrate 1 can be provided on the top side under the sensor pixel, ie in the recess 30 with a reflective metal layer 21 (e.g. gold, silver, aluminum) ( Fig. 1a ) to increase the signal sensitivity of the sensor pixel by reflecting transmitted radiation.

[0053] The absorber surface on the membrane 6 covers the so-called "hot" contacts of the thermopile sensor, which are arranged on the thin membrane 22, which may be made of silicon oxide or silicon nitride, or other insulating materials. The membrane with the absorber layer 6 is suspended above the recess 5 in the monolithic sensor chip 2 (Si substrate). In the solution according to Fig. 1 The recess 5 has vertical or nearly vertical walls and is driven into the sensor chip 2 from the back of the wafer, for example, by reactive ion etching (a so-called RIE process). Alternatively, the cavity under the sensor pixel can also be (as in Fig. 3 shown) are driven from the front side into the sensor chip 2 (Si wafer). Instead of reactive ion etching, a known wet-chemical etching process is used, in which a sacrificial layer (e.g. porous silicon) or parts of the silicon substrate are dissolved and etched through known slits between the membrane 6 and the beams 23, or between the beams 23 and the side wall of the recess 5. An example of this are the inclined walls 13, 14 of the recesses 5 in Fig. 3 .

[0054] The thermocouples of the thermopile structure are manufactured from known thermoelectric materials of different thermoelectric polarities. These can be semiconductor materials deposited in a CMOS process, such as n-type and p-type polysilicon, (doped) amorphous silicon, germanium, or a hybrid of silicon and germanium, or deposited thin thermoelectric metal layers (such as bismuth, antimony, or similar) with a thickness of less than 1 µm.

[0055] While the "hot" contacts of the thermocouples are located on the thin membrane 22 below the absorber layer, the "cold" contacts are arranged on the edge of the silicon substrate 2, so that the largest possible temperature difference is achieved between the two contacts. Particularly preferably, the small pixels have long, known beams 23, which are insulated from the Si substrate of the sensor chip 2 and the absorber region by slits etched into the membrane from the front side. Since such highly sensitive thermopile pixels are well known in the art, further details (such as the design of the beams and the insulating slits) are not shown in the drawings.

[0056] The signal processing unit 12 integrated into the sensor chip 2 contains, for example, known temperature and voltage references, signal amplifiers, possibly low-pass filters, analog / digital converters, a microprocessor unit with data memory (e.g., EEPROM), and an interface for communication with the external electronics of the mobile device (e.g., smartphone). The temperature reference integrated on the sensor chip 2 (e.g., a so-called PTAT (Proportional To Ambient Temperature) circuit) measures the temperature of the sensor chip and thus of the "cold" contacts.

[0057] The preamplifiers contained in the signal processing unit 12 amplify the very low signal voltages of the thermopile sensor pixel(s) and compare them with the voltage and ambient temperature references. All these analog signals are converted into digital values ​​in the analog / digital converter, which in turn are used in the microprocessor unit, together with the correction values ​​stored in the data memory (e.g., EEPROM), to calculate the object temperature.

[0058] The lens optics / focusing lens 4 mounted in the housing cover 3 has focusing lens surfaces on the bottom, top, or both sides. Mounting is typically performed such that the distance to the sensor pixel corresponds exactly to the focal length (or the so-called "back focal length") of the lens 4. The lens is manufactured using a conventional mass process (e.g., pressing, molding) or, more preferably, using a wafer-level process, e.g., on silicon wafers, in which many thousands of lenses are simultaneously manufactured on a wafer and provided with infrared filter layers. Such wafer lenses have the additional advantage that, when mounting the lenses in the housing cover 3, they can be "picked" from the silicon wafer and mounted using the same automated handling systems (so-called pick & place or die bonders) as normal semiconductor chips.Both refractive lenses (with usual spherical or aspherical curvature of the active surface) and diffractive lenses (e.g. Fresnel lenses) can be used.

[0059] The lens 4 can be mounted in the housing cover 3, for example, by gluing, soldering, or welding. The edge of the lens is coated with a metallization layer (not shown) for soldering or welding. The lens 4 and housing substrate 1 are usually mounted to the cover 3 by gluing if the gas or gas mixture to be enclosed is to be at atmospheric pressure. If the pressure of the gas medium 11 in the housing is to be significantly lower than atmospheric pressure, a soldering or welding process is preferred for assembly.

[0060] The viewing angle of a sensor pixel should be < 40 degrees for the application, if possible, and preferably < 15 degrees. The easiest way to estimate the viewing angle FOV 24 is to use a formula that relates the pixel size to the focal length. The ARCTAN of the ratio of half the pixel size to the focal length yields half the viewing angle (FOV / 2). This means, for example, that a lens focal length of 1 mm and a pixel size of 0.5 mm results in a viewing angle of 30 degrees. A pixel size of 0.26 mm results in a viewing angle of approximately 12 degrees. With a longer lens focal length, the viewing angle decreases, but even with a lens focal length of 1.5 mm and the typical thicknesses of the lens (e.g. 0.26 mm), sensor chip (0.4 mm), cover, and base plate (each 0.2 mm), depending on the lens design, housing heights of 2.6 to 3 mm already result - too much for most smartphones.

[0061] Fig. 1b shows a modification of the miniaturized SMD sensor with a particularly low overall height. The housing cover 3 is provided with an upward bulge 33, which approximately corresponds to the lens curvature. The curved (convex) side of the focusing lens 4 points upwards, so that the apex of the lens 4 corresponds approximately to the maximum height of the cover 3 and thus determines the overall housing height. In this way, the overall height of the housing can be reduced compared to the arrangement according to Fig. 1a be reduced by approximately the thickness of the lid.

[0062] Alternatively, the housing cover 3 can also have an additional elevation 28, which merges into a recess 34 for receiving the lens 4 and encloses its outer circumference. In this case, the lens 4 is inserted into the recess 34 with the curved side facing downwards ( Fig. 3b ). The aperture opening 26 here forms the inner edge of the recess 34, which also supports the focusing lens 4.

[0063] The medium 11 enclosed in the housing is a gas or gas mixture whose thermal conductivity is significantly lower than air or nitrogen at normal pressure. Preferably, the gas medium 11 is a gas with a high molar mass (e.g., xenon, krypton, or argon) or a gas with a significantly reduced internal pressure compared to normal pressure. The housing must be sealed so that no gas exchange with the environment occurs.

[0064] Fig. 2 shows a top view of a surface-mounted IR single-element sensor according to Fig. 1 with further details.

[0065] The lens 4 is located here exactly symmetrically above the sensor pixel 6, with several connection contacts 9 establishing an electrical connection from the sensor chip 2 inside the housing to the connection contacts 10 for SMD assembly on the underside of the housing.

[0066] A further embodiment of the miniaturizable SMD thermopile sensor according to the invention shows Fig. 3 , in which, in addition to the active sensor pixel 6, another pixel is provided as a reference pixel 15, which is arranged at the far end of the sensor chip 2. This reference pixel 15 does not receive infrared radiation from the measurement object itself, but rather "looks" at an emitting surface 16 that is applied or mounted on the inside of the cover. This makes it possible to compensate for measurement errors caused by temperature gradients in the sensor housing, for example, by the so-called "heat shock" effect. This emitting layer 16 is preferably created by printing, spraying, or vapor deposition using interchangeable masks. Alternatively, an additional part with high emission can be glued to the inner surface of the cover or otherwise mounted with good thermal contact to the housing cover 3.

[0067] When executed in Fig. 3 The thermopile pixels are manufactured using surface micromechanics, i.e., by etching the cavities 5 beneath the membranes 6 and 15 from the front through slits in the self-supporting membranes. Both pixels 6 and 15 can also be manufactured, like the sensor pixels according to Fig. 1 or Fig. 3a have a cavity with vertical walls 5, which have been driven into the sensor chip 2 from the back by DRIE.

[0068] Fig. 3a shows an inventive embodiment of the miniaturized SMD sensor with a reference pixel 15. In this arrangement, the housing cover for the lens has an additional elevation 28 to achieve the distance (so-called "back focal length") between the lens 4 and the absorber 6 on the membrane necessary for sharp imaging, while the cover 3 with the absorbing layer 16 above the reference pixel is designed to be particularly flat. This effectively allows the reference pixel with the absorber 15 to move closer to the sensor pixel with the absorber 6 while still not receiving any radiation from the object via the lens.The special elevation 28 can also be designed in a form-fitting manner so that the lens 4 is mounted exactly symmetrically above the absorber 6 of the sensor pixel during assembly in order to avoid optical imaging errors, such as "squinting", when the optical axis of the lens lies exactly perpendicularly above the absorber center.

[0069] Fig. 4 shows the top view of an inventive design of the miniaturized SMD sensor according to Fig. 3 und 3a . This shows that the active sensor pixel 6 sees outward through the lens optics 4 of the aperture opening, while the reference pixel 15, on the other hand, sees the absorbing layer 16 located behind the cover and thereby measures the housing temperature. In principle, square or nearly square housing shapes can also be achieved, depending on the space requirements in the terminal device. With the design in Fig. 3a It is easier to make the entire housing approximately square because the distance between absorbers 6 and 16 can be significantly reduced.

[0070] With the additional reference pixel 15, both the chip temperature and thus the temperature of the "cold" thermopile contacts via an integrated PTAT reference, as well as the housing temperature of the cover 3 with the absorber layer 16, are available for compensation purposes for slow and rapid ambient temperature changes. This allows for effective compensation of the short-term temperature changes that occur in mobile devices (e.g., smartphones), e.g., after switching on, when taking the device out of the pocket, when holding it to the face or ear, or when moving from the temperature-controlled interior to the outside, where significantly higher or lower temperature changes can suddenly occur.

[0071] A very interesting extension of the invention for mobile devices is the design of the active pixel as a multiple pixel. A corresponding solution is Fig. 5 Here, instead of a single pixel, several pixels 17 (e.g., 2x2, 4x4, 8x8, 16x16) are arranged under the lens to capture the spatial temperature distribution of the object or to facilitate gesture recognition. Again, the recesses beneath the pixels with the slotted membranes can be driven into the sensor chip 2 from the top or bottom.

[0072] The sensor chip 2 according to the invention Fig. 5 contains several individual cells 17 with a slotted membrane and a known beam structure on which the thermocouples (not shown in detail) are accommodated.

[0073] The signals of the individual pixels are processed in the signal processing unit 12, at whose output (interface) digital signal information from the individual pixels is output along with the correction values ​​for measuring the temperature distribution or, for example, for gesture control. The lens optics are designed so that the distant measurement objects are sharply imaged on the sensor pixels. Bezugszeichenliste

[0074] 1Packaging substrate (base plate) 2Monolithic sensor chip 3Packaging cover 4Focusing lens 5Hollow under pixel 6Membrane with absorber layer 7Bond wire 8Contact surface (metallization) on package substrate 9Metallic connection 10Contact surface on package back 11Gas medium in the hermetically sealed package 12Signal processing unit 13Hollow under active pixel 14Hollow under reference pixel 15Membrane with absorber layer of the reference pixel 16Absorbing layer 17Sensor pixel in matrix form 18Metallized, solderable connection surface on package substrate 19Insulation layer 20Solder or adhesive joint 21Reflecting metal layer 22Thin carrier membrane of the pixel 23Beam 24External beam path 25Connection contact 26Aperture opening 27Viewing angle of the Reference pixel 28Elevation of the housing cover above sensor pixel 29Thermopile pixel 30Recess 31Side wall 32Side wall 33Bump 34Indentation

Claims

1. SMD-enabled infrared thermopile sensor for contactless temperature measurement, as a hot spot or for gesture detection, with at least one miniaturized thermopile pixel (29) on a monolithically integrated sensor chip (2), which is arranged in a hermetically sealed housing consisting of an at least partially non-metallic housing substrate (1) and a housing cover (3), wherein a gas or gas mixture is contained in the housing, and wherein an aperture opening (26) is introduced in the housing cover (3) opposite the at least one thermopile pixel (29), which is closed with a focusing lens (4) which focuses the radiation from objects onto the at least one thermopile pixel (29) on the housing substrate (1), wherein the housing substrate (1) consists of a ceramic material, and is provided with a recess (30) with a central flat base plate and side walls (31) for receiving the sensor chip (2), wherein the distance between the focusing lens / lens optics (4) and the at least one thermopile pixel (29) corresponds to its focal length, wherein the housing cover (3) has an additional form-fitting elevation (28) for the focusing lens (4) for symmetrical mounting of the focusing lens (4) above the at least one thermopile pixel (29) in order to achieve the distance between the focusing lens (4) and the absorber (6) on the membrane that is necessary for a sharp image, wherein a reference pixel (15) is arranged next to the at least one thermopile pixel (29), which is directed toward an absorbing layer (16) on the inside of the cover (3) and is in thermal contact with the housing cover (3), and wherein the distance between the housing cover (3) and the reference pixel (15) is less than the distance between the lens (4) and the at least one thermopile pixel (29) in order to avoid optical imaging errors.

2. SMD-enabled infrared thermopile sensor according to claim 1, characterized in that the housing cover (3) is a heat-conductive metal deep-drawn part or a metal or non-metal injection-molded or die-cast part.

3. SMD-enabled infrared thermopile sensor according to claim 1, characterized in that the focusing lens (4) is diffractive or refractive and has both aspherical and spherical surfaces.

4. SMD-enabled infrared thermopile sensor according to claim 1, characterized in that the focusing lens (4) has a focal length between 0.5 mm and 1.9 mm.

5. SMD-enabled infrared thermopile sensor according to claim 1, characterized in that a reflective metal layer (21) is located under the at least one sensor pixel (2).