Pyroelectric infrared sensor

Abstract

One or more separately arranged elevation(s) (2.1) having bearing surfaces for a sensor element (1) is / are present on a carrier element (2). The sensor element (1) is coated with a layer (1.1) of a pyroelectric material, which is coated with a thin electrically conductive layer, and the layers form a front electrode (2) and a rear electrode (3), and overlapping regions of the layers, which form the front electrode (2) and the rear electrode (3), form a sensitive region (1.4). The front electrode (2) and the rear electrode (3) are electrically contacted and electrical connection contacts (2a, 3a) are arranged. A base surface (2.2) is formed in a first plane and bearing surface(s) of the elevation(s) (2.1) are formed in a second plane on the carrier element (2). A constant distance having a maximum permissible deviation of 30% with respect to an average value is maintained between the surface of the base surface (2.2) and the rear electrode (1.3). The base surface (2.2) corresponds to at least 90% of the area of the sensitive region (1.4).

Description

[0001] InfraTec GmbH

[0002] P150402PC00

[0003] Pyroelectric infrared sensor

[0004] The invention relates to a pyroelectric infrared sensor that achieves high sensitivity and a high signal-to-noise ratio (SNR) at high irradiance, exhibits good linearity, and in particular a uniform, i.e., homogeneous, sensitivity distribution for signal frequencies in the range of 100 Hz to 2000 Hz. The sensor should therefore be particularly suitable for use as a receiver in FTIR spectrometers. It can be arranged within a housing containing a window element through which electromagnetic radiation can reach the sensor from the outside, and connected to an electronic evaluation unit, as is already common practice.

[0005] Pyroelectric sensors are widely used as radiation receivers in infrared optical measuring systems and spectrometers. They belong to the class of thermal sensors and should exhibit broadband spectral sensitivity. They are also robust, inexpensive, and can be operated without cooling.

[0006] The two-stage conversion principle can be briefly described as follows: The incident electromagnetic radiation is first absorbed by a flat, thin sensor element, causing a temperature increase. The plate-shaped sensor element consists of a pyroelectric material coated on its front and back sides with an electrode each (front and back electrodes, FE and RE), thus forming a plate capacitor.

[0007] A temperature change caused by incident electromagnetic radiation leads to a change in polarization within the pyroelectric material due to the pyroelectric effect. This charges the electrodes, resulting in an electric current flow that can be converted into an electrical voltage signal (sensor signal) for further processing and evaluation. A key characteristic of this conversion principle is that only temperature changes produce a signal. Pyroelectric sensors are therefore only sensitive to modulated electromagnetic radiation and not to continuous wave (CW) light, where there is no sufficient change in the intensity of the incident electromagnetic radiation. This can be exploited as an advantage in many applications.

[0008] To maximize radiation absorption, the sensor element is often equipped with an additional thin absorbing layer (absorber) onto which electromagnetic radiation can strike. The sensor's sensitivity is further maximized by making the sensor element particularly thin, resulting in low heat capacity. The sensor element should also be mounted or electrically contacted with as much thermal insulation as possible. The mounting method or the surrounding gas (typically air or nitrogen) dissipates the absorbed heat into a housing or the environment. This can be simplified by a thermal contact resistance R. th describe. Together with the heat capacity of the sensor element C th This results in a thermal low-pass filter behavior with the thermal time constant T. th = R th ■ C th or the thermal corner frequency / ^ = 1 / (2TT ■ T thIn the case of CW irradiation or for low modulation frequencies below the thermal cutoff frequency, the sensor element experiences the maximum temperature change (amplitude), which is determined solely by R. th is determined. The heat capacity of the sensor element C th is crucial in determining how quickly its temperature can change; the smaller it is, the faster a change can occur.

[0009] In the most common embodiment of pyroelectric sensors, the sensor element is completely coated with electrodes on both sides and, as a whole, constitutes the radiation-sensitive receiver area (the sensitive region) of the sensor. Good thermal insulation (large thermal time constant) is desired, with the sensor element being mounted and electrically contacted only at specific points. However, this results in an inhomogeneous temperature and sensitivity distribution, because heat dissipates more efficiently in the immediate vicinity of the mounting points than in areas with good thermal insulation.

[0010] One important application area for pyroelectric sensors is Fourier-transform infrared (FTIR) spectrometers.

[0011] Pyroelectric sensors are the preferred receivers for FTIR spectrometers for several reasons, including the fact that they respond only to the modulated radiation components, while the DC component does not generate a signal. Another important reason is that, despite the thermal conversion principle, they possess sufficiently high sensitivity and low noise in the specified frequency range, ensuring a high signal-to-noise ratio (SNR). DLaTGS is particularly preferred as a pyroelectric material for FTIR sensors because it offers the best SNR of all known materials. The pronounced temperature sensitivity of this material and its low Curie temperature are accepted in exchange for a high SNR. In special cases, Li-TaO3 can also be used as a pyroelectric material for FTIR spectrometers.

[0012] The aforementioned CW component of the incident electromagnetic radiation provides no information and does not generate a signal at a pyroelectric sensor; however, it does cause the sensor to heat up. This heat must be dissipated reliably and in a highly controlled manner. In the previously mentioned classic design of pyroelectric sensors with a large time constant, the temperature rise can be several tens of Kelvin. In the case of the pyroelectric material DLaTGS, this would very quickly lead to exceeding the Curie temperature, causing the sensor to lose its sensitivity. Even if the Curie temperature is not exceeded, at least a strongly nonlinear sensor behavior can be expected.

[0013] Sensors for FTIR spectrometers are therefore constructed differently. The sensor element is mounted in such a way that heat is dissipated more quickly and temperature changes due to irradiation are limited. The front and back electrodes are not solid but structured. This creates a sensitive area only in the overlap region of the electrodes, making it suitable for use in spectrometers.

[0014] In a typical embodiment of sensors for FTIR spectrometers, a very thin air layer is formed beneath the sensor element. Mechanical fixation and electrical contact are achieved via a single point-like contact in the center. In another embodiment used to date, the sensor element is bonded around its outer edges. Heat dissipation here occurs primarily through lateral conduction within the sensor, from the irradiated area in the center to the outer edges. Electrical contact with the back electrode is achieved via a bonded wire embedded within the sensitive sensor area.The known embodiments of pyroelectric sensors according to the prior art all share a common flaw: the function-determining aspects of the mounting, the mechanical fixing, the thermal insulation, and the electrical contacting are so intertwined that they cannot be optimized independently of one another. For this reason, they do not possess optimal and homogeneous heat dissipation, homogeneous sensitivity, and consequently, poor linearity or at least a large variation in sensor properties due to manufacturing tolerances.

[0015] The object of the invention is therefore to provide pyroelectric sensors that achieve high sensitivity or a high signal-to-noise ratio (SNR) even at high irradiance levels, while exhibiting good linearity and, in particular, a uniform, i.e., homogeneous, sensitivity distribution within the sensitive area of ​​a sensor element for signal frequencies in the range of 100 Hz to 2000 Hz. They are intended to be particularly suitable for use as receivers in FTIR spectrometers.

[0016] According to the invention, this problem is solved with pyroelectric sensors having the features of claim 1. Advantageous embodiments and further developments of the invention can be realized with features specified in dependent claims.

[0017] In the pyroelectric infrared sensor according to the invention, a support element has at least one planar, flat base surface and an annular projection, or at least two projections arranged at a distance from each other, forming one or more separately arranged pedestals. On the distal end face(s) of the pedestal(s), bearing surfaces are formed on which a planar sensor element rests.

[0018] The sensor element consists of a flat, planar layer of a pyroelectric material. It is coated with a thin, electrically conductive layer on both a surface facing the support element and on the opposite surface. These layers form a front electrode and a back electrode. Within this area, where the layers forming the front and back electrodes overlap, a sensitive region is created. The front and back electrodes are electrically contacted in areas outside this sensitive region, and electrical connection contacts are located there.

[0019] The term "flat" should in particular be understood to mean that the corresponding layer is uniformly flat or generally has a smooth surface.

[0020] In another alternative, which may be present alone or additionally, the flat planar base surface is formed in a first plane and the bearing surface(s) of the elevation(s) are formed in a second plane on the support element, such that a constant distance is maintained between the surface of the base surface and the surface of the back electrode arranged towards the base surface, with a maximum permissible deviation of 30%, preferably a maximum of 10%, in relation to a mean value of all distances between the surface of the back electrode in the area of ​​the sensitive region and the base surface of the support element.

[0021] Furthermore, the size of the base area corresponds to at least 90%, preferably at least 95%, of the area of ​​the sensitive region of the sensor element resting on the elevation(s). The base area may be slightly smaller than the area of ​​the sensitive region. Advantageously, it is at least the same size.

[0022] A flat, planar sensor element rests on the support surface(s) of the elevation(s) and can be fixed there. The fixing can be made directly to at least one elevation or to the support element.

[0023] A cavity is formed between the protrusion(s) due to the distance between them and the distance between the support element surface and a sensor element. With multiple protrusions arranged at intervals, cavities are also present on the sides between the protrusions. The protrusions can have different cross-sectional geometries, so the contact surfaces can also have corresponding geometries, such as circular, polygonal, or oval shapes. However, it is always important that the design, and in particular the position of the plane in which the contact surfaces are arranged, meets the conditions of claim 1 regarding the distance to the base surface.

[0024] Several protrusions should be arranged at equal angular intervals around the outer edge of the sensor element's sensitive area. For two protrusions, this would be an angle of 180°, for four protrusions 90°, and so on. A ring-shaped protrusion can form a circular platform or a platform with a polygonal contour. An analogous ring shape can also be chosen for an arrangement of multiple platforms, where there are gaps between the individual protrusions forming these platforms.

[0025] The sensitive area of ​​the sensor element is used for the actual measurement signal acquisition. Therefore, it does not necessarily have to be formed entirely by the two electrically conductive layers. The sensitive area typically represents a subset of the two electrically conductive layers that form the front and back electrodes. In other words, it can also be understood as a projection of the intersection of the two electrode surfaces.

[0026] The front and back electrodes are designed and dimensioned such that at least one of these two electrodes does not cover the entire respective surface of the flat, planar layer of pyroelectric material, meaning that only a portion of the total surface area of ​​the pyroelectric layer constitutes the sensitive area. An outer edge area uncoated with electrode material is therefore not part of the sensitive region of the sensor element.

[0027] The front electrode and the back electrode are electrically contacted in areas located outside the sensitive area. Electrical connection contacts are located there, through which signals can be transmitted to an electronic evaluation unit. The sensor element rests directly on the contact surfaces of the protrusion(s) only with surface areas arranged radially outside the sensitive area of ​​the sensor element, i.e., without an intermediate layer.

[0028] The base surface is understood to be the surface of the support element that is located below the sensitive area of ​​the sensor element when the latter rests on the elevation(s).

[0029] The deflection of the sensor element and the planarity of the surface of the back electrode facing the support element, as well as the surface of the base on the support element, must be maintained accordingly. Furthermore, the height at which the bearing surface(s) of the protrusion(s) are positioned above the plane in which the base is located is of considerable importance for meeting this criterion. This is significant and must be considered during the manufacturing of the protrusion(s) on the support element. Therefore, this will be discussed in more detail later.

[0030] At least one surface area can be formed on the support element and / or arranged on the elevation(s) at the outer edge of the base surface, the surface of which has a distance that differs from the distance of the surface of the base surface towards the back electrode, preferably a larger distance (see Figure 2a).

[0031] The base should be positioned centrally within one or more elevations and / or

[0032] The central or centroidal centers of the sensitive area and the base area should be aligned along a common axis. The base area and the sensitive area would thus be positioned directly above one another and parallel to each other.

[0033] On the surface of the carrier element facing the sensor element, at least one further surface area can be formed within an annular protrusion or within an arrangement of several discretely arranged protrusions next to the base surface. This surface area is / are arranged in one or more different planes at intervals from one another (see also Figure 2a). The pyroelectric layer of the sensor element according to the invention consists of a single-crystal pyroelectric material, e.g., LiTaO3 or DLaTGS (including TGS and DTGS or other variants based on TGS, e.g., also in the form of various dopings), or a comparable material, which is thinned to a correspondingly small and as homogeneous a target thickness as possible by suitable processing techniques (e.g., lapping and polishing). The preferred thickness range is 5 pm to 30 pm, with the range of 5 pm to 15 pm being particularly preferred.

[0034] The area where the layers forming the front electrode and the back electrode overlap constitutes the sensitive region in a central area of ​​the sensor element. It therefore does not necessarily have to be completely covered by the two electrically conductive layers.

[0035] The sensitive area is preferably circular or polygonal and should have a size in the range of 0.05 mm. 2 - 10 mm 2 The sensor element is characterized by circular sensitive areas with diameters between 1 mm and 3 mm. The edge regions of the sensor element are either uncoated or only partially or one-sidedly coated with electrode material, so that these areas do not belong to the sensitive region of the sensor element and do not contribute to the measurement result.

[0036] The front and back electrodes each have at least one contact pad for electrical contact, extending from the sensitive area to the edge of the sensor element. The electrical contact pads of the front and back electrodes should be arranged so that they do not overlap and are located, for example, on opposite sides of the sensitive area. They are offset from each other on different sides of the sensor element, preferably diametrically or at right angles to each other, but at least at an angle of at least 45° to each other on one sensor element. The front and back electrodes each consist of an electrically conductive layer of constant thickness made of, for example, chromium, gold, titanium, nickel, or other suitable metals, or of a multilayer system of these materials.

[0037] The electrode layers can be deposited, for example, by sputtering or vapor deposition. Structuring can be achieved, for example, by using shadow masks during the coating process. Alternatively, subsequent lithographic structuring using a resist mask and etching processes, or even by lift-off technology, is also possible.

[0038] The support element of the sensor according to the invention has a stepped surface profile, i.e. it has different areas with flat planar surfaces that are parallel to each other but have different heights.

[0039] The support element has at least one flat, planar contact surface on which the sensor element rests over part of its rear surface. All other areas of the support element, located below the contact sensor element, are recessed relative to the contact surface(s).

[0040] The contact surface(s) can be a single, continuous surface or comprise two or more sub-surfaces of equal height. These sub-surfaces are arranged on the surface of a raised area facing the sensor element, opposite the areas directly adjacent to them, and the raised area(s) can therefore also be referred to as a pedestal.

[0041] A pedestal is understood to be a body that forms part of the supporting element, i.e., typically as a single piece or integral part of the supporting element, and which is formed as at least one straight or oblique, widening, cross-sectionally constant, or tapering extrusion of a polygon, circle, annulus, or ellipse. Thus, several connected extrusions of different surfaces can also form one and the same pedestal.

[0042] The support element has at least one base surface which is lowered by a defined amount relative to the contact surface(s) and is parallel to it. The base surface extends at least over the central area of ​​the support element, which overlaps with the sensitive area of ​​the resting sensor element (in the projection).

[0043] The elevation(s) with their base(s) should be arranged essentially in a circular or ring shape around the central area and should not protrude into the central area of ​​the sensitive area.

[0044] In this case, a constant distance with a maximum permissible deviation of 30%, preferably 10%, is maintained between the at least entire surface of the sensitive area of ​​the sensor element pointing towards the support element and the surface (base surface) of the support element pointing towards the sensor element between the contact surfaces of the elevation(s), with a maximum permissible deviation of 30%, preferably 10%, in relation to a mean value of all distances between the surface of the back electrode in the area of ​​the sensitive area and the base surface of the support element.

[0045] In this way, a homogeneous gas layer can be present in the central area below the sensitive region, enabling uniform heat dissipation of the radiation absorbed on the sensor element.

[0046] The depth of this first recessed area, or the distance between the corresponding surface of the back electrode and the base surface of the support element in this area, can be precisely adjusted during manufacturing, depending on the application and desired heat dissipation. Values ​​in the range of 3 pm to 30 pm are preferred.

[0047] In this way, it can be ensured that the electromagnetic radiation or thermal energy irradiated onto the sensor element is essentially dissipated through this gas layer, particularly uniformly within the insensitive area of ​​the sensor element, towards the support element and the rest of the environment. This results in a homogeneous temperature and sensitivity distribution on the sensor element, even under high irradiation, at least in its surface region that constitutes the sensitive area.

[0048] The deflection of the sensor element and the planarity of the back electrode's surface facing the support element, as well as the surface of the base on the support element, must be maintained accordingly. Furthermore, the height at which the bearing surfaces of the raised area(s) are positioned above the plane in which the base is located is of considerable importance for meeting this criterion. This is significant and must be considered during the manufacturing of the raised area(s) on the support element. Therefore, this will be discussed in more detail later.

[0049] A cavity is formed between the protrusion(s) due to the distance between them and the distance between the support element surface and a sensor element. With multiple protrusions arranged at intervals, cavities are also present on the sides between the protrusions.

[0050] The support element may also have at least one mounting surface, the surface of which is arranged at a defined distance from the first plane in which the base surface is located, and may be aligned parallel to the support surface(s) by a defined dimension.

[0051] This difference in spacing can be dimensioned independently according to the requirements of its function. A spacing difference in the range of 20 pm to 50 pm is preferred. In this case, the support element has a height profile of at least two stages, i.e., it has at least three different height levels on its surface areas.

[0052] The mounting surface need not be a continuous surface; it can also be subdivided into discretely arranged sub-areas. The area in which a mounting surface is formed will also be referred to as the mounting gap. In a specific embodiment, the dimensions of the drop (height differences, distance differences) of the base surface and the mounting surface relative to the bearing surface(s) are equal, resulting in a single-level height profile, i.e., at least two different height levels of the parallel surface areas of the support element are formed. In other words, the areas of the base surface and the mounting surface are at the same height level in this embodiment, and both surfaces have the same distance to the back electrode.

[0053] The mounting surface(s) should be located in areas of the support element that do not overlap with the sensitive area of ​​the mounted sensor element (in projection) and in which no protrusion(s) are present. They are situated below the edge areas of the mounted sensor element that do not belong to the sensitive area but also do not rest on the contact surfaces of a protrusion. Within this area of ​​a mounting surface, the mounting gap, the sensor element can be mechanically fixed and electrically connected.

[0054] The carrier element may have at least one metallization as a connection contact surface (conductor pull / pad) in at least one area within the mounting surface, which, in conjunction with the sensor element placed on the support surface(s), overlaps with the electrical connection contact surface of the back electrode (in the projection) and can be used for electrical contacting of the back electrode.

[0055] The mechanical fixation and electrical contacting of the sensor element on the carrier element can be achieved using adhesives, which are first applied in a suitable quantity to predefined positions on a mounting surface. At least at the metallization point, a known electrically conductive adhesive (e.g., silver-filled) can be used. At other positions, a non-conductive mounting adhesive can be used. However, these connections are always located outside the sensitive area of ​​the sensor element. Adhesives that exhibit high flexibility in their cured or cross-linked state and thus a certain degree of elastic or plastic deformability (e.g., silicones) are particularly preferred.Following the application of the adhesive, the sensor element can be placed and pressed down until it lies flat on the corresponding surfaces of the mounting surface(s) of the raised area(s), directly and without any intermediate layer. It should be precisely aligned so that the central area of ​​the base surface of the carrier element aligns with the sensitive area of ​​the sensor element, as well as with the electrical contact surfaces of the back electrode and the metallization on the carrier element, as described above.

[0056] The adhesives are then cured or cross-linked. This allows for the mechanical fixation of the sensor element to the carrier element and simultaneously establishes the electrical contact between the back electrode and the metallization on the carrier element.

[0057] The metallization on the carrier element can also be connected to an amplifier circuit or the terminals of the sensor housing, and thus also to the back electrode of the sensor element; this can be achieved, for example, by a bond wire for electrical contacting.

[0058] Subsequently, the electrical contact of the front electrode can be established, for example, by conductively gluing a bond wire to the corresponding connection contact surface, the other end of which is connected to an integrated amplifier circuit or to the terminals of a sensor housing in which the sensor according to the invention can be arranged.

[0059] The resulting constant conditions in the sensitive area of ​​the sensor element advantageously influence heat dissipation and allow for the maintenance of nearly constant, undisturbed conditions during measurement. This prevents influences that could distort the measurement result. Heat dissipation from the sensor element can only occur via the contact surfaces of the raised area(s) and the gas surrounding the sensor element. Since the distance between the sensitive area of ​​the sensor element and the base surface is constant across the entire area, uniform conditions prevail there as well.

[0060] Interference from electrical connection contacts can also be largely avoided, as these can be located outside the sensitive area and therefore at a sufficiently large distance from it. This also applies to means for fixing the sensor element to the carrier element, which likewise operate outside the sensitive area.

[0061] In this way, the altered thermal connection or heat dissipation resulting from the electrical contact does not play a major role in the actual sensor behavior, since these areas do not contribute to signal generation.

[0062] In summary, it can be stated that by designing the pyroelectric sensor element and by mounting it on a suitable structured carrier element, which may have been manufactured using microtechnology, a consistent decoupling of the mechanical fixing, the thermal insulation or heat dissipation and the electrical contacting can be achieved, thus enabling independent optimization of these three function-determining aspects.

[0063] Figures a1a and b1b show exemplary embodiments of the sensor element with a circular and a square sensitive area, in which the electrical connection contact surfaces are arranged accordingly.

[0064] According to the invention, the sensor element is placed on a support element such that it has a clearly defined and precisely manufactured height profile, at least in the area where the sensor element, and in particular the sensitive area, is located. Firstly, the height profile creates flat / planar contact surface(s) of the protrusion(s) on which the sensor element rests substantially over its entire surface (ideally in direct contact). Within the entire surface of the support element, the contact surface(s) of the protrusion(s) are arranged with the greatest difference in their distance to the surface of the base on the support element.

[0065] It is assumed here that the sensor element itself is essentially flat, or that any existing warping has only a very minor influence. A further requirement is that no additional material (e.g., an adhesive layer) is present between the sensor element and the contact surfaces of the protrusion(s), as well as the base surface, that would create a significant gap or difference in distance and alter the height and distance between the base surface of the carrier element, in which the contact surface(s) are arranged, and the surface of the sensor element's back electrode facing in this direction in an undefined or poorly controllable manner. This distance is constant, i.e., uniform, across the entire sensitive area of ​​the sensor element.

[0066] However, it is also possible to apply a thin layer of adhesive between the contact surface(s) of the raised area(s), which can also be used to fix the sensor element. This thin layer of adhesive must then also meet the condition that a constant distance, as defined in claim 1, is maintained between the opposing surfaces of the sensor element and the support element in the sensitive area of ​​the sensor element.

[0067] Only in the area of ​​the contact surface(s) of the elevation(s) is there a strong thermal coupling of the sensor element to the support element, i.e. the heat flows away better in these areas and the temperature change of the sensor element as a result of irradiation with electromagnetic radiation is only lower there than in the considerably larger area of ​​the sensitive area of ​​the sensor element.

[0068] The lateral geometry or the position of the elevation(s) of the support element is / are therefore designed and arranged in such a way that they do not overlap with the sensitive area of ​​the sensor element and thus no influence on the temperature or sensitivity distribution of the sensor occurs.

[0069] Particularly preferred is the embodiment such that the contact surface(s) of the protrusion(s) have a minimum lateral distance to the area of ​​the sensitive region on the corresponding surface of the back electrode. This distance should be a multiple of the thickness of the sensor element and preferably in the range of 10 pm to 100 pm.

[0070] A support element that can be used in the invention can be manufactured in different ways. This can be a subtractive, an additive approach, or a combination of these approaches.

[0071] Subtractive manufacturing can be used, as in the production of microelectromechanical systems, employing silicon as the substrate material and utilizing commonly used etching technologies (e.g., with etch stop layers and / or adherence to specific, predetermined etching times with known chemical compounds used for etching). This ensures, in particular, that the desired constant distance between the contact surface(s) of the protrusions and the surface of the substrate's base can be maintained.

[0072] As a carrier element material, in addition to silicon, any other material can be used that has sufficient thermal conductivity and can be structured in the desired shape, e.g. ceramic or glass.

[0073] It is also possible to locally define material removal on a semi-finished product for a support element by means of laser irradiation in order to obtain a suitable height profile with the elevation(s) and the base surface.

[0074] In additive manufacturing, a support element can be produced layer by layer, for example, using suitable printing processes (e.g., screen printing) and, if necessary, subsequent thermal treatment. Following this, regardless of whether the manufacturing process up to that point was subtractive and / or additive, fine-tuning can be carried out, at least on the surfaces of the contact areas of the raised area(s). This can involve lapping or brushing to precisely maintain the desired distance relative to the surface of the base and ensure its flatness, thus guaranteeing a consistent distance to the sensor element when the sensor element is in contact with it.

[0075] A carrier element can accommodate other functional elements. It can also be designed as a wiring carrier. Functional elements can be, for example, a heating element, a temperature sensor, resistors, capacitors, transistors, or operational amplifiers. Functional elements can be interconnected or arranged discretely.

[0076] A carrier element may, for example, contain functional and / or contact elements for an electronic evaluation unit.

[0077] A sensor according to the invention can be housed within a casing with a window element, similar to conventional sensors, and connected to an electronic evaluation unit. A gas atmosphere, and not a vacuum, should be present around the sensor element, even within a casing.

[0078] The invention will now be explained in more detail and in a more understandable way using an example.

[0079] This shows:

[0080] Figures aa and bb each show an example of a sensor element that can be used in the invention in top and side view;

[0081] Figures 2a and 2b each show an example of a support element in top and side view in a state before assembly, and Figure 3 shows an example of a mounted sensor in top and side view.

[0082] Figures 1a and 1b show examples of a sensor element 1 that can be used in the invention, one with a circular and one with a square sensitive area 1.4, which are shown here with a radially outer boundary shown in dashed lines and correspondingly designed electrodes 1.2 and 1.3.

[0083] A planar layer 1.1 of pyroelectric material is coated on its two opposing surfaces with a similarly planar layer of an electrically conductive material. These layers form the front electrode 1.2 and the back electrode 1.3, each of which has an electrical contact surface 1.2a and 1.3a. As shown, the electrical contact surfaces 1.2a and 1.3a are located outside the sensitive region 1.4 and offset from each other, so that they do not interfere with each other or with heat conduction from the area of ​​the sensitive region 1.4.

[0084] In the example according to figure 1a, the electrical connection contact surfaces 1.2a and 1.3a are diametrically opposite each other on the sensitive area 1.4 and in figure 1b are arranged at an angle of 90° to each other.

[0085] The side views clearly show that the front electrode 1.2 and the back electrode 1.3 only partially overlap, and that there are areas of each of the electrodes 1.2 and 1.3 that do not belong to the sensitive area 4.

[0086] The examples shown in Figures 2a and 2b differ from each other in the height profile and in the manufacturing process for the surfaces of the support element 2 facing the sensor element 1.

[0087] Eight protrusions 2.1 are arranged at angular intervals of 45° to each other on the surface of the support element 2. Between these eight protrusions 2.1, a flat, planar base surface 2.2 is formed, which is aligned parallel to the bearing surfaces on the end faces of the protrusions 2.1. In a form not shown, a ring-shaped protrusion could also form a closed ring, so that only one protrusion 2.1 is present, within whose inner region the base surface 2.2 and above it the sensitive area 1.4 of the sensor element 1 would be arranged. A mounted sensor element 1 is then geometrically designed and dimensioned such that its sensitive area 1.4 can be positioned precisely above the base surface 2.2 and at a constant distance across the entire surface.

[0088] Between the eight elevations 2.1 there are gaps that are not visible here, through which gas can circulate into the environment and in the gap between sensor element 1 and base surface 2.2 or a mounting surface 2.3.

[0089] On the surface of the carrier element 2 facing the sensor element 1, a metallization 2.3a for an electrical contact connection is provided in the area of ​​the mounting surface 2.3, i.e., also at a distance from the sensitive area 1.4, which can be connected to the electrical connection contact surface 1.3a of the back electrode 1.3.

[0090] In the examples shown, a two-stage height profile is present on the surface of the support element 2, so that a mounting gap is formed between sensor element 1 and the surface of the support element 2 outside the area of ​​the sensitive area 1.4 of the sensor element 1, with a greater distance from sensor element 1 to the surface of the support element 2 than below the sensitive area 1.4 in the area of ​​a mounting surface 2.3.

[0091] At least in the side view of Figure 3, one can see how an example of a sensor according to the invention can be designed. It is clearly visible that a constant distance is maintained across the entire area between the sensitive area 1.4 of the sensor element 1 and the base surface 2.2 of the support element 2, and that no additional material is present between the sensor element 1 and the contact surfaces of the projections 2.1.

[0092] Between the surface of layer 1.1 facing the carrier element 2 and the surface of the carrier element 2, a simple mounting adhesive 3 is present below the electrical connection contact surface 1.2a of the front electrode 1.2, serving to fix the sensor element 1 to the carrier element 2, and an electrically conductive adhesive 4 is present on the opposite side of the sensitive area 1.4, which also serves to fix the sensor element 1 to the carrier element 2 and to provide an electrically conductive connection between the electrical connection contact surface 1.3a of the back electrode 1.3 and the metallization 2.3a.

[0093] As can also be seen in Figure 3, conventional bond wires can (also) be used for the further electrical connection of the electrical connection contact surfaces of the front electrode 1.2a and the metallization 2.3a of the carrier element 2 to the (not shown) evaluation unit.

[0094] Figures 2a and 3 also show the possibility in which at least one surface area can be formed on the support element 2 at the outer edge of the base surface and / or arranged on the projections 2.1, the surface of which has a greater distance from the surface of the base surface 2.2 towards the back electrode 1.3 than the surface of the base surface 2.2. One or more such surface areas can be arranged within an annular projection 2.1 or within an arrangement of several discretely arranged projections 2.1 next to the base surface 2.2. Reference numerals:

[0095] 1. Sensor element

[0096] 1. Planar layer of pyroelectric material

[0097] 2. Front electrode

[0098] 1.2a Connection contact surface of the front electrode

[0099] 3. Back electrode

[0100] 1.3a Connection contact surface of the back electrode

[0101] 4. Sensitive area

[0102] 2. Support element

[0103] 1. Elevation(s) with bearing surfaces

[0104] 2. Base area

[0105] 3. Mounting surface

[0106] 2.3a Metallization (connection contact surface, conductor track)

[0107] 3. Flexible mounting adhesive

[0108] 4. Electrically conductive adhesive

Images