WO2004102140A1

WO2004102140A1 - Infrared sensor with optimised surface utilisation

Info

Publication number: WO2004102140A1
Application number: PCT/DE2004/000970
Authority: WO
Inventors: Marion Simon; Wilhelm Leneke; Mischa Schulze; Karlheinz Storck; Jörg SCHIEFERDECKER
Original assignee: Heimann Sensor Gmbh
Priority date: 2003-05-13
Filing date: 2004-05-13
Publication date: 2004-11-25
Also published as: JP5001007B2; DE10321639A1; JP2007501404A

Abstract

The invention relates to a radiation sensor, for example, for non-contact temperature measurement, or infra-red spectroscopy, with a detector element, comprising an absorber element (13, 14, 15, 16, 51, 52), which absorbs radiation and thus heats up and a support body (2) with a support body surface, for housing the absorber element (13, 14, 15, 16, 51, 52). The support body surface has a recess and the absorber element (13, 14, 15, 16, 51, 52) is arranged on the support body surface and over the recess such that at least a section of the absorber element (13, 14, 15, 16, 51, 52) is not in contact with the support body (2). According to the invention, a radiation sensor of the above type may be provided, which generates an amplified signal on the smallest possible chip surface, which permits a small measurement point and which may be produced by conventional standardised technology, whereby the recess has a size corresponding to at least 45 % of the support body surface.

Description

Infrared sensor with optimized use of space

The present invention relates to a radiation sensor, e.g. for non-contact temperature measurement or infrared gas spectroscopy.

A large number of techniques for measuring temperatures are known which take advantage of a large number of effects in measurement, in which physical or chemical substance properties show a temperature dependence. Almost all processes are based on heat transfer to the sensor or sensor. In the case of the so-called contact thermometers, this heat transport takes place by conduction and convection, in the case of the contactless thermometers (radiation thermometers) by heat radiation.

Even though the contact thermometers generally work very reliably and are usually simple and inexpensive to manufacture, their area of use is nevertheless restricted. For example, due to the material properties of the sensor, there is an upper temperature limit above which the sensor can no longer be operated. In addition, the touch thermometers are unsuitable for measuring the temperature of quickly moving or difficult to access objects.

For this reason, non-contact measurement methods based on thermal radiation are used in many areas of application. Every surface with a temperature T> 0 K emits electromagnetic radiation, the so-called temperature radiation. If radiation emanating from one surface strikes another surface, it is partially reflected, absorbed or transmitted. Therefore, absorption elements are used in radiation thermometers, which ideally have an absorption capacity that is independent of the wavelength and which heat up when the radiation (infrared radiation) strikes it, so that the heating of the absorption element can serve as evidence of the infrared radiation emitted.

Radiation thermometers or so-called radiation pyrometers generally have optics, a detector element with an absorption element and a housing which mechanically and thermally protects the optics and detector. With these sensors, the infrared radiation emitted by the measurement object is imaged onto an absorbing surface by suitable windows or optical components, this surface experiencing a temperature increase due to the absorption. It goes without saying that the radiation thermometer can also be used to measure temperatures which are below the intrinsic temperature of the thermometer. In this case, the absorbent surface emits more radiation than it absorbs, so that the absorbent surface cools overall. This temperature increase (or decrease) can then be measured in different ways. With thermistor bolometers, the change in electrical resistance is measured, with thermocouples, the voltage at the contact point of two metal wires, with pyroelectric detectors, a charge shift that occurs when the temperature of special insulator crystals changes.

The thermocouples use the so-called Seebeck effect to detect the elevated temperature. The connection point of a thermocouple made of two different thermoelectric materials is brought into contact with the absorber area, while the reference contacts are generally at the temperature of the sensor housing. Since the sensor output voltages of such thermocouples are very low, many such thermocouples are often connected in series. Such a series connection of a large number of thermocouples is also referred to as a thermopile or thermopile.

In recent years, great efforts have been made in many technological fields to miniaturize electrical and electronic components, whereby they should be inexpensive to manufacture using known, standardizable processes wherever possible. which in turn leads to a lower signal and thus to a reduced resolution.

It is therefore particularly important for the miniaturized radiation sensors to achieve the highest possible absorption of the infrared radiation in the absorber system and to isolate the absorber surface thermally as well as possible from the surroundings in order to generate the greatest possible temperature increase and thus a large sensor output signal.

Infrared sensors are already known which have a detector element, the detector element having an absorber element which absorbs radiation and is heated thereby, and a support body with a support body surface for receiving the absorber element, the support body surface having a recess and the absorber element in this way on the support body surface and is arranged above the recess that a portion of the absorber element does not touch the support body. Usually a membrane with very low thermal conductivity is arranged above the recess, on which in turn the absorber element is arranged. This ensures extensive thermal decoupling between the absorber element on the one hand and the support body serving as a heat sink on the other hand, which in turn leads to a high temperature difference between the absorber element and support body and thus to a high signal strength. Such a sensor has already been described in DE 42 21 037. This sensor is manufactured using micro-mechanical technology. The detector here has a supporting body made of silicon, which is connected to a base plate of the sensor housing.

The sensor shown in DE 42 21 037 is produced in a so-called wet etching technology (KOH), but this has the consequence that the recess has sloping side walls. In other words, the webs of the supporting body, which surround the recess, are designed to taper. However, this means that the webs are made quite wide on their side facing the absorber element, which either leads to poor thermal insulation or to a smaller usable area for the absorber element.

In almost all known infrared sensors, the size of the absorber element is relatively small compared to the overall size of the detector, for example, a chip, which leads to a low signal yield.

DE 100 09 593 already describes a support body serving as a heat sink, in which the walls which surround the recess are substantially perpendicular to a base plate. In this embodiment, however, a relatively large distance between the edge of the absorber element and the silicon heat sink is achieved. Only a thermally poorly conductive membrane is arranged in this area, which has only a low absorption for infrared radiation compared to the absorber element. Therefore, the infrared radiation impinging on the membrane is used insufficiently for signal generation, so that the size of the measurement spot is increased by the detector chip area, which is particularly disadvantageous for pyrometric applications. In addition, the edge of the support body in the embodiment shown in DE 100 09 593 is very large, so that the effective size of the absorber element is small compared to the overall size of the detector element.

In the known infrared sensors there is also a relatively large distance between the edge of the absorber element and the silicon heat sink. In addition, the absorber area is relatively small compared to the total detector area.

Starting from this prior art, it is therefore an object of the present invention to provide a radiation sensor of the type mentioned at the outset, which generates an amplified signal on the smallest possible chip area. In addition, it is an object of the invention to provide an infrared sensor which allows a small measuring spot and can be produced using known standardized technologies. According to the invention, this object is achieved in that the recess, at least on its side facing the absorber element, has an area dimension which corresponds to at least 45% of the area of the supporting body. In other words, at least 45% of the surface of the carrier body is removed by introducing the recess into the carrier body. The remaining rest of the support body surface surrounding the recess thus has a total surface extension of at most 55% of the total support body surface. As a result, the total sensor area can be reduced while the signal strength remains the same, which leads to a reduction in the production costs. The support body is advantageously produced using a dry etching process.

In a particularly preferred embodiment, the recess has an extent that makes up between 45 and 75%, preferably between 50 and 70% and particularly preferably about 65% of the support body area. It has been shown that a particularly good signal yield can be achieved by the dimensioning of the recess and at the same time a sufficient stability of the support body is ensured.

In a particularly expedient embodiment, the recess has side walls which form an angle between 80 and 100 °, preferably between 85 and 95 ° and particularly preferably about 90 °, with the surface of the support body or the top of the support body. This measure can also be used to increase the ratio of the area of the absorber element to the entire detector area or support body area.

It has been shown that the recess is preferably designed such that it extends through the entire support body. In other words, the support body, which can be mounted on a base plate of the sensor, has a continuous opening. As a result, the greatest possible distance between the absorber element and the support body or base plate of the sensor is achieved, which in turn reduces the signal reduction which is caused by the thermal conductivity of the gas located between the absorber element or membrane and the base or bottom of the recess.

The support body is preferably produced using silicon technology. Furthermore, the absorber element is advantageously designed such that it has at least one CMOS-compatible cover layer. In an expedient embodiment, this CMOS-compatible cover layer is arranged on at least one radiation-sensitive functional layer.

It has been shown that the cover layer advantageously takes up an area of at least 30%, preferably between 35 and 70%, particularly preferably between 40 and 60% of the entire surface of the support body. At this point it should be emphasized again that the entire surface of the support body is understood to mean the surface of the support body including the recess. It goes without saying that the absorber elements described here do not necessarily have to be used in combination with thermocouples or thermopiles, but can also be used, for example, in combination with pyroelectric elements or bolometers.

Tests have also shown that the signal yield can be further increased if at least the bottom or the bottom of the recess consists of a material that reflects infrared radiation. This can be achieved, for example, by applying a metal layer, for example a gold layer, the layer preferably having a thickness of less than 1 μm.

Furthermore, it is provided in a particularly preferred embodiment that the sensor has a housing which consists of a base plate and a cap connected to it, the detector element or the support body being arranged on the base plate. The base plate is advantageously designed such that it does not reflect infrared radiation, at least in the areas surrounding the support body. This can be achieved, for example, in that the base plate is made of a corresponding non-reflective material. As an alternative to this, the base plate can be coated with a non-reflective material, preferably a lacquer or a photoresist, in the regions surrounding the support body.

Further particularly preferred embodiments implement the features of the subclaims.

Further advantages, features and possible uses of the present invention will become clear from the following description of preferred embodiments and the accompanying figures. Show it:

FIGS. 1a and 1b show two schematic representations of the structure of infrared sensors, FIGS. 2a and 2b show a sectional and top view of a thermopile sensor on a non-metallic support,

FIG. 3 shows the schematic structure of a sensor according to the invention,

FIG. 4 shows a schematic representation of the contacts on the sensor,

FIGS. 5a and 5b show two different embodiments with the absorber system according to the invention, FIGS. 6a and 6b show two different embodiments of sensor housings,

Figures 7a, 7b and 7c three different embodiments of sensor caps with imaging optics and Figures 8a and 8b two further embodiments of sensor caps with integrated imaging optics.

FIGS. 1a and 1b show two different basic structures of the infrared sensors according to the invention, as are at least partially already known from the prior art. A detector element 2 and a reference element 3 for measuring the ambient temperature with good thermal contact to the base plate 1 are attached to a base plate 1.

Alternatively, the reference element can also be integrated in a silicon circuit 11, as shown in the embodiment of FIG. 1b. This can be done, for example, together with the first stages for signal conditioning and ambient temperature compensation.

The mechanical connection between reference element 3 and base plate 1 is preferably made by means of a conductive epoxy resin, e.g. an epoxy resin filled with silver. Of course, other processes are also possible, such as soldering with low-melting solder is possible.

The detector element 2 and the reference element 3 or the silicon circuit 11 are connected to connection pins 5 or connection contact surfaces 6 to the base plate 1 via wires 4, which can be embodied, for example, as thin bond wires.

As will be explained in detail below, the detector element 2 has a recess 40. The bottom of the recess 40 is covered with a very well reflective metallic layer 7, e.g. with a thickness of less than one micrometer.

The regions of the base plate 1 surrounding the detector element 2 can, as is the case in the embodiment shown, be covered with a non-reflective layer 8. This layer can e.g. a varnish or a photoresist. During production, the coating is advantageously carried out over the entire surface, with the exception of the contact points for the detector element 2, the reference element 3 or the silicon circuit. The infrared sensor additionally has a metallic cap 9, which can be made of steel, nickel, brass or copper, for example. The metallic cap 9 is connected to the base plate 1 in a sealing manner. The sealing of the cap 9 with respect to the base plate 1 can e.g. by welding, soldering or gluing. In the metallic cap 9, an opening is provided above the detector element, into which a filter 10 that is transparent to infrared radiation is inserted.

As already mentioned and shown in FIG. 1b, the temperature reference 3 can also be used as a silicon circuit 11, for example in the form of an application-specific integrated circuit, a so-called called ASIC, with an integrated temperature reference and optionally with amplifier and compensation circuits.

The base plate 1 can, for example, as shown in Figure 1a, made of metal or a metal alloy, such as e.g. used in standard transistor packages. Examples of preferred materials are steel, nickel, cobalt or similar materials. Alternatively, as shown in Figure 1b, the base plate 1 can be made of a ceramic or an organic material, e.g. the printed circuit board material FR4.

FIGS. 2a and 2b show a preferred embodiment of a sensor structure on a non-metallic carrier substrate, such as e.g. made of a standard circuit board material (FR3, FR4 or ceramic). Figure 2a is a sectional view taken along line A-A of Figure 2b, showing a top view of the sensor assembly. The detector element 2 and the temperature reference 3 or a signal preprocessing component (ASIC) 11 are mounted on the circuit board. A metal layer 41, which preferably has a thickness between 20 and 100 μm, is applied to the non-metallic printed circuit board. This metal layer can be formed, for example, by the copper layer that is often present in commercially available printed circuit boards. The metal layer 41 runs below the detector element, the temperature reference or the ASIC up to the contact surface of the cap 9.

This metal layer 41 serves to ensure a good thermal connection between cap 9 with filter 10 on the one hand and detector element 2 and temperature reference 3 on the other. The metallic layer 41 is particularly preferably carried out continuously on the base plate 1, individual islands 42 being excluded for receiving the contacts 48 and bushings 44.

The cap 9 can be attached to the base plate 1, for example by soldering, gluing or welding. Depending on the application, an electrical contact between the cap 9 and the metal layer 41 or an electrically insulated assembly can be advantageous.

In the embodiment shown, the metallic layer 41 is in the area under the detector element, i.e. provide an additional highly reflective and preferably easily bondable layer 7 at the point at which the detector element or the supporting body has a continuous recess and in the immediate vicinity of the connection contacts 48. This layer 7 can be a thin gold layer, for example.

In the embodiment shown, around the detector element 2 and around the contact areas are the metallic layers 7, 41 with an absorbent layer 43, for example with a Resist resist, covered. The absorbing layer 43 serves to avoid reflections from incident light rays, which could otherwise have an undesirable effect on the measurement result.

The through holes 44, which are often also called vias, can also be seen, which provide contact with the underside of the base plate. The through holes 44 are metallized on their inner walls and are closed as gas-tight as possible from the bottom after completion of the assembly. This can be done, for example, with a drop of adhesive or a solder seal 45. This closure is used to seal the sensor housing against external influences, e.g. Moisture, but also aggressive gases are required. In some applications, it can be advantageous if the closure is carried out under a defined gas atmosphere, e.g. under dry nitrogen or under an inert gas, in order to establish a defined gas and humidity ratio within the sensor.

On the underside of the base plate 1, the metallic components of the contacts 44 are guided to the solder bumps 46 printed on them. These solder mounds can consist of tin solder, for example. By later melting the tin solders, the so-called reflow soldering can be used to automatically populate the sensor on standard circuit boards.

FIG. 3 shows the basic structure of an embodiment of a sensor according to the invention on the base plate. The mode of operation of the sensor is described below on the basis of these and the previous figures.

Infrared radiation 53, which originates from the object whose temperature is to be measured, passes through the filter arranged in the cap 9 and strikes the detector element 2, which has an absorber system.

The heat radiation is essentially completely absorbed in the absorber system 19, which leads to a temperature difference between the absorber region 19 and the edge of the support body 12 of the detector element 2 above the silicon carrier. A series of thermocouples are arranged on the absorber system in such a way that one of their connections lies in the region of the absorber system that is exposed to infrared radiation, while the other connection is fastened to the edge of the detector element. Due to the thermoelectric effect, there is a voltage difference in each thermocouple. This voltage difference is proportional to the temperature difference between the area of the absorber system which is exposed to infrared radiation and the edge of the detector element. The thermal voltage is usually very low and is a few microvolts. In order to increase the signal voltage, a whole series of thermocouples are therefore connected in series to form a so-called thermopile. This can typically be ge ten, but also over a hundred thermocouples. The two ends of the thermocouples linked in this way are connected to the bonding pads 21. From the bonding pads 21, the bonding wires 4 lead the signal to the outside of the connecting wires or contacts.

The detector element 2 with the sensitive element or the absorber element is applied to the base plate 1, which preferably has good thermal conductivity. In the embodiment shown, the detector element 2 consists of a support body 12 made of silicon between about 250 and 650 μm, preferably about 400 μm thick, and the membrane and thin layers 13, 14, 15, 16 lying above it. The thermally insulating, about 0.3 Up to 1 μm thin membrane layer 13, 14 consists of dielectric layers (preferably silicon nitrite and silicon oxide or silicon oxynitrite).

The membrane layer has a sandwich structure with at least two layers. The bottom layer 14, which is also referred to as the base layer 14, is advantageously made from silicon oxide and has a thickness of between 50 and 30 nm. Silicon dioxide has been selected because it forms a type of etch stop layer, since it has only a very low etch rate for the later reactive silicon etching process. A membrane layer 13 is applied over the base layer, on which the thermoelectrically active layers 15, 16 are applied. For this purpose, polycrystalline silicon with p-line (hole line) and polycrystalline silicon with n-line (electron line) are preferably used together. Both materials have a high thermoelectric coefficient with opposite sign and are easily available in standard CMOS processes.

The individual thermocouples each have a leg made of n-type polysilicon and one made of p-type poly-silicon. These two legs are preferably arranged one above the other and are each connected at the ends to the previous or the following thermocouple. This creates so-called "warm" contacts 18 in the center of the membrane, since this area is acted upon by infrared radiation, and so-called "cold" contacts 17 on the edge of the chip 2 via the silicon carrier 2, which acts as a heat sink. The contact can be made via one or more contact windows with aluminum or an aluminum alloy.

The insulation between the two stacked polysilicon legs is in the preferred embodiment using a standard CMOS method, e.g. using a thin layer of silicon dioxide or silicon nitride.

An absorber structure 19 is applied above the warm contacts 18. This at least one, but possibly also multi-layer cover layer must have the lowest possible reflection and high absorption for the infrared radiation to be measured (for example between 3 and 15 μm). overall together with the thin membrane layers 13, 14, 15, 16 and the reflector layer 20, they form the absorber system according to the invention.

The sensor chip according to the invention can be produced in a composite on a silicon wafer of usually 100 to 200 mm in diameter. Typically, 2,000 to 20,000 chips can be arranged on a wafer. The sensitive layers are located on the top of the wafer. For this purpose, dielectric layers 13, preferably silicon nitride and silicon oxide or silicon oxynitrite, are deposited on the silicon with the aid of CVD processes standardized in CMOS technology. As a result, a sandwich structure that has several layers is obtained. The layer thicknesses are chosen so that the mechanical stresses which arise due to the different thermal expansion coefficients due to the cooling of the chip after the deposition at elevated temperature to room temperature are compensated for as far as possible. For example, silicon nitrite is under tensile stress after cooling, while silicon oxide is under pressure stress after cooling. The layer thicknesses should advantageously be chosen such that the entire layer stress is approximately canceled out after cooling to room temperature or a slight tensile stress remains, if appropriate.

FIG. 4 shows a further illustration of the sensor 2 including the membrane, the absorber and the contacts, by means of which the size relationships according to the invention are clear.

It can be clearly seen that the support body 12, which is constructed here from a silicon layer, has a recess 40, so that it essentially consists of only four walls of thickness D arranged approximately at right angles to one another. The thickness D of the remaining frame of the support body is preferably a maximum of 18%, particularly preferably between 8 and 12% of the entire side length S of the chip 2. This increases the radiation yield of the thermal sensor. Furthermore, the distance A1 between the edge of the absorber structure 19 and the membrane takes up less than 6%, preferably between 2 and 5%, of the total side length of the chip. It goes without saying that for very small detector elements, for example with side lengths of approximately 1 mm or less, the values of D and A1 are at the upper specified limit, while the lower values are advantageous for detector elements with side lengths of> 2 mm.

The width or length A2 of the absorber element is preferably, based on the side length of the chip, at least 52%, in particular for detector sizes of less than approximately 1 mm, and preferably between 65 and 80%, in particular for detector sizes with a side length of more than 1.5 mm.

The size ratios given in the following table have proven themselves in tests.

The configuration of the chip geometry according to the invention ensures that the signal voltage that can be achieved with respect to the detector surface is significantly increased compared to the known sensors. In experiments, signal voltages were measured that were between 1, 4 and 2 times larger than the signal voltages of known sensor chips with the same detector area.

In addition, the edge of the support body, which is greatly reduced in comparison to the sensors of the prior art, reduces the probability of reflections which can lead to an undesired expansion of the measurement spot. As a result, the measurement accuracy of the infrared radiation thermometer according to the invention for the measurement of spatially limited objects to be measured is significantly increased.

It has been shown that the cold contacts 17 are advantageously arranged on the edge of the membrane near the edge of the silicon substrate 12, while the warm contacts are arranged as far as possible under the absorber 19, so that the entire area of the absorber surface is used. As a result, some contacts, for example every second or third contact, are arranged near the edge of the absorber, while the others are distributed between the edge of the absorber and the center of the absorber 19.

The structure of the absorber system according to the invention is shown in FIGS. 5a and 5b. The entire sensor including the housing bottom surface is designed in such a way that all elements contribute to absorption. The infrared radiation falling on the detector element 2 through the infrared filter 10 first reaches the absorber cover layer 52. This cover layer, which can preferably be produced by CMOS-compatible processes, has the lowest possible reflection coefficient and a high self-absorption in the spectral range of, for example, 3 to 14 μm. Since CMOS and cleanroom-compatible layers generally only have an absorption of at most about 50-70%, part of the infrared radiation inevitably passes through the cover layer 52 and strikes a passivation layer 51 arranged below the cover layer 52 and the thermoelectric layer located below the passivation layer 51 Layers 15, 16 and the membrane layers 13, 14. These layers also show a certain absorption in the infrared range. The total absorption of the layered structure depends both on the wavelength of the infrared radiation and the thickness of the dielectric layers used. It is therefore possible that part of the incident infrared radiation penetrates the layer structure and reaches the base plate 1. However, as already explained, a highly reflective layer 7 is arranged on the base plate 1 in the region of the recess, which layer shows almost no self-absorption and no transmission, but rather reflects the radiation component back to the membrane. Since the membrane layer 14 may also reflect some of the radiation reflected by the layer 7, multiple reflections can occur until the radiation portion almost completely penetrates the membrane layers from below again. Most of the residual radiation, ie the radiation that first penetrated the absorber layer, is then absorbed in the second passage through the layer system with the layers 13, 14, 15, 16, 51 and 52.

As an alternative to this, it is also possible to introduce a reflection layer within the sequence of dielectric layers of the absorption layers, so that the multiple reflections only take place in part of the layer system. Furthermore, it can be advantageous for some applications to optimize the thicknesses of the dielectric layers with regard to interference effects in order to achieve the most complete absorption possible of the incident light in the absorption layer.

For example, a 0.5 to 1 μm thick dielectric layer, for example made of silicon oxide, can be applied over the additional reflection layer. In the case of quite broadband sensors, it can be advantageous to increase the total thickness of the dielectric layers up to 1.5 to 2.5 μm.

According to the invention, in order to absorb the incident radiation as completely as possible, the thermoelectric layers are arranged essentially on the entire membrane. In addition, the absorber cover layer advantageously fills the self-supporting membrane surface, i.e. the area of the membrane that is not in contact with the support body is at least 70 to 85%.

The layer system consists of the base oxide layer 14, which can consist, for example, of thermal silicon oxide or CVD oxide, and the membrane sandwich 13, which consists, for example, of silicon nitrite, silicon oxide or silicon oxynitrite. The thermoelectric layers 15 and 16, which consist for example of n- and p-type polycrystalline silicon or of silicon or germanium, can also be produced by CVD deposition. A passivation layer made of silicon oxide or silicon nitride with a thickness of approximately 100 to 1,500 nm is located above the thermoelectric layers 15 and 16.

The absorber cover layer 52 can be made in one or more layers. Experiments have shown that two variants are particularly advantageous. In the first variant, a thin reflection-reducing metal layer, which consists for example of titanium nitride, is deposited on the passivation layer 51. The deposition can take place, for example, by sputtering or evaporation. Although the use of such a reflection-reducing thin layer is known in principle, in the known layers the layer resistance and thus the absorption properties are changed in the course of time by oxidation or aging processes. According to the invention, it is therefore proposed to apply a passivation layer made of silicon oxide or silicon nitrite to the reflection-reducing layer, which preferably has a thickness between 10 and 50 nm. This layer can be produced, for example, by plasma-induced CVD deposition at temperatures below approx. 350 to 400 ° C. Such a very thin passivation layer only insignificantly deteriorates the reflection properties of the metal layer, but does provide high long-term stability of the reflection-reducing thin layer,

In the second variant, a polymer layer is used as the absorber cover layer. The thickness of the polymer layer is approximately 2 to 10 μm. The polymer layer used is preferably photoimide or other polymers, such as e.g. Polyimide, for use.

In addition, the two variants described can also be combined to increase the absorption. Then the reflection-reducing metal layer is deposited over the polymer layer.

In order to further limit the measurement spot, the silicon carrier body of the detector element 2 used according to the invention has a very small width, so that the usable absorber area is very high compared to the total detector element area. If parts of the infrared radiation 26 nevertheless fall on the edge of the detector element 2, they can be prevented from further reflections at the edge 25 by an absorber layer generated on the membrane at the same time as the absorber. The absorber layer 25 can cover the entire edge of the supporting body above the silicon carrier, the area necessary for the connection of the wires being excluded. Because of the high thermal conductivity of silicon and the good thermal connection of the absorber layer to the silicon carrier and the silicon carrier to the housing, the absorption of the radiation impinging on the edge region does not lead to a significant increase in the temperature of the cold contacts 17.

If parts of the infrared radiation 24 strike the base plate 1 next to the detector element 2, these can be absorbed by an additional absorber layer 43. This prevents this radiation component 24 from possibly being caused by multiple reflections on the base plate, Cap wall and cap cover are led back to the absorber. Otherwise this would lead to a deterioration in the imaging behavior of the optics.

Figure 6 shows two embodiments with improved cap geometry according to the invention. The accuracy of measurement is to be increased by the special cap geometries shown, in particular when the so-called "thermal shock effect" occurs. The so-called thermal shock effect is based on the fact that a sudden gradient in the ambient temperature can lead to a temperature gradient between the cap and the base plate. This temperature difference inevitably leads to a false signal, which cannot be corrected by the temperature reference 3 applied to the base plate. The false signal only disappears after the cap and base plate have exactly the same temperature again. This effect is particularly pronounced if the absorber system of the detector element or chip 2 has the filter adhesive 27, which is generally used for fastening the filter 10 on the cap 9, in the “field of view”. The reason for this is the often very high self-absorption and emission of the filter adhesive used in comparison to the metallic cap 9. This causes temperature differences between the base body and cap 9 or between the base body and the adhesive 27 used to form detector element 2 via infrared radiation emitted by the adhesive 27 used transfer. This leads to measurement errors if the cap 9 has a different temperature than the detector element 2.

In the embodiment shown in Figure 6a, an additional aperture 28, which can be made of metal or plastic, for example, is therefore mounted in the cap 9 above the detector element 2 such that an aperture 28 allows the radiation from the filter 10 to the absorber and that from keeps the radiation components arriving from the outer cap wall away from the detector element 2. This diaphragm 28 can advantageously be designed to be reflective on both sides, but particularly preferably at least the top side facing the infrared filter 10 is coated with an absorbent coating.

In the second embodiment of a cap geometry shown in FIG. 6b, the filter 10 is mounted on the top of the cap 9 in a recess. This depression is designed such that the filter adhesive 27 is not in the "field of view" of the detector element 2. The depth of the depression is preferably designed such that it is somewhat larger than the filter thickness, so that the filter does not protrude above the top of the cap.

FIGS. 7a and 7b show further preferred cap geometries with the aid of which the spatial resolution of the thermopile sensor is further increased.

Thus, in the cap 29 shown in FIG. 7a, a rotationally symmetrical mirror 30 is introduced, which can consist, for example, of metal or of a reflectively coated plastic part. The upper part of the mirror 30 is shaped so that the rays passing through the infrared filter 10 are focused on the absorber surface of the detector element 2. This can be achieved, for example, by designing the upper part of the mirror 30 as a paraboloid or as a so-called Winston cone.

The lower end 32 of the mirror, however, is shaped so that the wall area of the cap 29 is not in the field of view of the sensor absorber. A metallic reflective layer on the inside of the mirror 31, 33, which consists for example of a thin gold, silver or aluminum layer with a passivating cover layer, e.g. silicon oxide or a polymeric material, prevents additional measurement errors by heating the mirror or the cap. The underside 32 of the mirror can be both curved, as shown in FIG. 7a, and also flat, for example running essentially parallel to the base plate.

Another embodiment with optical focusing is shown in FIG. 7b. The cap 29 has an inserted lens 34, which can consist, for example, of silicon, germanium, calcium fluoride or the like. In certain applications, the transmission range of the lens 34 can be correspondingly restricted by known anti-reflection filter layers on the lens surface. A rotationally symmetrical aperture or opening body 36, which is preferably made of plastic, is arranged in the cap in order to prevent reflections on the cap wall. Therefore, the inner surface 35 of the opening body 36 is made absorbent. The underside of the aperture body 36 can be both curved and parallel to the base plate 1 and can optionally be reflective.

It goes without saying that more than one detector element 2, for example a line or an array of sensor elements, each with an absorber system according to the invention, can be integrated on the detector element 2. The signal preprocessing of the individual signals can then be carried out both monolithically in the detector element 2 and on the application-specific silicon circuit 11 next to the detector element 2 on the base plate 1.

A further embodiment of the absorber system according to the invention is shown in FIG. 7c. In principle, the chip structure and the layer sequence of this embodiment correspond to the embodiments described in connection with FIGS. 2, 3 and 5. Even with multi-element arrangements, a highly reflective layer 7 is arranged in the area under the membrane. The absorber structure 19 is arranged above the membrane layer 13, 14 and also fills the major part of the element area between the remaining walls 54 of the silicon carrier 12. In contrast to the one-element solution, a lens 34 must be used and the size of the aperture opening of the aperture body 30 must be adapted to the size of the sensor elements located on the outside. It is understood that the aperture body 36 and the mirror 30 can be designed as part of the cap 29. Corresponding embodiments are shown in FIGS. 8a and 8b.

The cap 29, which can be, for example, a deep-drawn part made of metal or an injection molded part made of plastic, has a recess 37 at the upper end for receiving the filter 10. The mirror surface 30 is connected to the recess with a reflective coating 31. The mirror surface 31 and the cap 29 are thus formed from a single part, as a result of which a particularly good thermal connection of the mirror, cap and filter or lens to the base plate can be achieved. In addition, the assembly costs are reduced by this embodiment, because no separate gluing in of the mirror and its corresponding adjustment is required. In the embodiment shown, the inner part of the mirror 30 with its reflective coating 31 is shaped such that it has a focusing effect on the radiation passing through the infrared filter 10. The radiation is thereby imaged on the absorber surface of the detector element 2. For this purpose, the mirror preferably has the shape of a paraboloid or a so-called Winston cone.

With the embodiment shown in FIG. 8a, particularly reproducible optical imaging properties can be achieved, since the distance between the mirror and the detector element 2 is well defined due to the design of the cap 29 as a deep-drawing tool or as an injection molding tool. In a particularly preferred embodiment, at least the entire inside of the cap is coated with a reflective coating.

In addition, it can be advantageous if the outside of the cap is additionally coated with a reflective coating, in order to prevent the cap 29 from heating up undesirably relative to the base plate 1.

The embodiment shown in FIG. 8b has a lens 34, for example made of silicon, germanium, calcium fluoride or the like, which is inserted into the cap 29. The cap 29 is also formed here as a deep-drawn part made of metal or as an injection molded part made of plastic and has a recess 37 at the upper end, into which the lens 34 is inserted. Furthermore, the recess 37 has a circumferential groove 38. The circumferential groove 38, which could also be used in the embodiment shown in FIG. 8a, prevents the adhesive for attaching filter 10 or lens 34 from penetrating down to the filter, mirror or lens surface visible by the sensor. In this embodiment, too, the depression is directly adjoined by the aperture surface 30 with an absorbent coating 35. An additional aperture 28, which is preferably formed as a metal deep-drawn part or can consist of a re reflective coated plastic, is arranged above the chip 2 in such a way that the aperture 28 allows the radiation from the filter to the absorber to pass and the radiation portions arriving from the outer cap wall from Keeps detector element away. If the cap 29 is made of plastic, then the pinhole 28 is preferably made of metal and the lower end <39 is extended to the base plate 1 and connected to it in such a way that good thermal contact is produced. The pinhole 28 is used to improve the optical ratios and to reduce the so-called thermal shock effect. Again, the entire inside and outside of the cap 29 is preferably coated with a reflective coating.

LIST OF REFERENCE NUMBERS

1 base plate

2 detector element 3 temperature reference element

4 connecting wire

5 pins

6 contact surface

7 reflective layer 8 absorbent layer

9 cap

10 filters

11 signal processing circuit

12 support body 13 membrane layer

14 base layer / lower membrane layer

15.16 thermoelectric layers

17 cold contacts

18 warm contacts 19 absorber structure

20 reflective layer

21 bond island

24 part of infrared radiation

25 edge regions of the absorber layer 26 part of the infrared radiation

27 filter adhesive

28 aperture

29 cap

30 mirror 31 mirror layer

32 bottom of the mirror

33 reflective layer

34 lens

35 surface 36 aperture body

37 deepening

38 groove

39 lower end of the bezel

40 recess 41 metal layer

42 islands

43 absorbent layer

44 executions

45 solder lock 46 solder bump

48 contacts

51 passivation layer

52 absorber top layer

53 infrared radiation 54 walls of the silicon supporting body

A1 Distance between the edge of the absorber and the membrane

A2 length of the absorber element

D thickness of the supporting frame S side length of the detector element

Claims

PATENT CLAIMS

1. radiation sensor, e.g. B. for non-contact temperature measurement or infrared spectroscopy, with a detector element, the detector element being an absorber element (13, 14, 15, 16, 51, 52) that absorbs radiation and is thereby heated, and one

Has support body (2) with a support body surface for receiving the absorber element (13, 14, 15, 16, 51, 52), wherein the support body surface has a recess and the absorber element (13, 14, 15, 16, 51, 52) in such a way is arranged on the support body surface and above the recess such that at least a portion of the absorber element (13, 14, 15, 16, 51, 52) does not touch the support body (2), characterized in that the recess has an extension which is at least 45% corresponds to the area of the supporting body.

2. Sensor according to claim 1, characterized in that the recess at least on its side facing the absorber element (13, 14, 15, 16, 51, 52) has a cross section which is between 45 and 75%, preferably between 50 and 70% and particularly preferably occupies about 65% of the surface of the support body.

3. Sensor according to claim 1 or 2, characterized in that the recess has side walls (2) which form an angle between 80 and 100 °, preferably between 85 and 95 ° and particularly preferably about 90 ° with the top of the support body.

4. Sensor according to one of claims 1 to 3, characterized in that the recess extends perpendicular to the support plane through the entire support body (2).

5. Sensor according to one of claims 1 to 4, characterized in that the support body (2) is made by means of silicon technology.

6. Sensor according to one of claims 1 to 5, characterized in that a base plate (1) is provided on which the support body is attached.

7. Sensor according to one of claims 1 to 6, characterized in that the absorber element (13, 14, 15, 16, 51, 52) has at least one CMOS-compatible cover layer (52).

8. Sensor according to claim 7, characterized in that the absorber element (13, 14, 15, 16, 51, 52) is multi-layered, the CMOS-compatible cover layer (52) on at least one radiation-sensitive or temperature-sensitive functional layer (13, 14th , 15, 16) is arranged.

9. Sensor according to claim 7 or 8, characterized in that the cover layer (52) occupies an area of at least 30%, preferably between 35 and 70%, particularly preferably between 40 and 60% of the surface of the support body.

10. Sensor according to one of claims 1 to 9, characterized in that at least the bottom surface or the bottom of the recess consists of an infrared radiation reflecting material, preferably a metal layer (7), particularly preferably a gold layer, the layer (7) preferably has a thickness of less than 1 μm.

11. Sensor according to one of claims 6 to 10, characterized in that the base plate (1) is made of an infrared radiation non-reflective material or at least on the areas (43) surrounding the support body (43) with an infrared radiation non-reflective material, preferably a varnish or photoresist.

12. Sensor according to one of claims 1 to 11, characterized in that a membrane (13) is provided which carries the absorber element (13, 14, 15, 16, 51, 52), the membrane (13) at least two layers having.

13. Sensor according to claim 12, characterized in that the layers of the membrane (13) are constructed from silicon dioxide, silicon nitride or silicon carbide.

14. Sensor according to one of claims 1 to 13, characterized in that the absorber element (13, 14, 15, 16, 51, 52) is constructed in several layers.

15. Sensor according to claim 14, characterized in that the absorber element (13, 14, 15, 16, 51, 52) has a cover layer (19, 52) which is designed as a, preferably CMOS-compatible, metal absorption layer.

16. Sensor according to claim 15, characterized in that the cover layer (19, 52) has a thickness of less than 50 nm.

17. Sensor according to claim 15 or 16, characterized in that the cover layer (19, 52) consists of titanium nitride.

18. Sensor according to one of claims 15 to 17, characterized in that the cover layer (19, 52) has a sheet resistance between about 180 and 400 ohms.

19. Sensor according to one of claims 15 to 18, characterized in that a passivation layer is arranged on the cover layer (19, 52), the passivation layer preferably consisting of silicon oxide or silicon nitride.

20. Sensor according to claim 15 or 16, characterized in that the cover layer (19, 52) is formed by a polymer layer with a thickness of preferably between 2 and 10 microns.

21. Sensor according to claim 15 or 16, characterized in that the cover layer (19) from a preferably between 2 and 10 microns thick polymer layer, a preferably less than 50 nm thick metal absorption layer arranged above the polymer layer and a passivation layer arranged above the metal absorption layer with a Thickness of preferably between 10 and 50 nm.

22. Sensor according to one of claims 15 to 21, characterized in that at least one of the layers forming the cover layer (19, 52) extends at least partially to the upper edge surface of the support body (2) which surrounds the recess.

23. Sensor according to one of claims 1 to 22, characterized in that a device for measuring the temperature of the absorber element is provided.

24. Sensor according to claim 23, characterized in that the temperature measuring device has at least one thermocouple, preferably a thermopile.

25. Sensor according to claim 24, characterized in that the at least one thermocouple or the thermopile are formed from two layers of polycrystalline silicon, one layer being n-type and the other p-type and the two layers by an insulation layer, which are preferably formed by a silicon oxide or silicon nitride layer, are separated from one another.

26. Sensor according to one of claims 1 to 25, characterized in that the absorber element (13, 14, 15, 16, 51, 52) has a reflection layer which reflects radiation.

27. Sensor according to claim 26, characterized in that a dielectric layer with a preferred thickness between 0.5 and 2.5 microns is provided on the reflection layer.

28. Sensor according to claim 27, characterized in that the dielectric layer is composed of polysilicon and silicon dioxide or silicon nitride, preferably of silicon dioxide.

29. Sensor according to one of claims 23 to 28, characterized in that a plurality of thermopile elements are provided in a row or matrix arrangement, preferably each thermopile element being assigned to a separate absorber element.

30. Sensor according to claim 29, characterized in that the carrier element has a plurality of recesses and a plurality of absorber elements, each absorber element being arranged above a recess.

31. Sensor according to one of claims 24 to 30, characterized in that in each case a connection, the so-called warm contact, of the thermocouples of the thermopile is arranged under the absorber element, the warm contact preferably being every second or third thermocouple up to a central region of the absorber element, while the warm contact of the other thermocouples extends only into an edge region of the absorber element.

32. Sensor according to one of claims 24 to 31, characterized in that a connection, the so-called cold contact, of the thermocouples of the thermopile is connected to the edge of the support body surrounding the recess, the connection point of the cold contact with the support body preferably in Area of the inner edge of the frame of the support body surrounding the recess lies.