DE10321639A1 - Infrared sensor with optimized use of space - Google Patents

Abstract

The present invention relates to a 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) which absorbs radiation and is thereby heated, and a supporting body (2) a supporting body surface for receiving the absorber element (13, 14, 15, 16, 51, 52), the supporting body surface having a recess and the absorber element (13, 14, 15, 16, 51, 52) in this way on the supporting body surface and above the Is arranged recess that at least a portion of the absorber element (13, 14, 15, 16, 51, 52) does not touch the support body (2). In order to provide a radiation sensor of the type mentioned at the outset, which generates an amplified signal on the smallest possible chip area and which allows a small measuring spot and can be produced using known standardized technologies, it is proposed according to the invention that the recess has an extent which is at least 45 % of the supporting body area corresponds.

Description

The present invention relates to a radiation sensor, e.g. for the contactless Temperature measurement or infrared gas spectroscopy.

It a variety of techniques for measuring temperatures are known, which is a big one Number of effects by measurement take advantage of physical or chemical properties a temperature dependency demonstrate. Almost all processes are based on heat transfer to the sensor or Sensor. With the so-called touch thermometers this heat transfer takes place through heat conduction and convection, for the non-contact Thermometers (radiation thermometers) through thermal radiation.

Also when the touch thermometer generally very reliable work and are usually simple and inexpensive to manufacture their area of application is nevertheless restricted. For example, there are conditions an upper temperature limit due to the material properties of the sensor, above which the sensor is not can be operated more. About that beyond are the touch thermometers unsuitable, the temperature of quickly moving or difficult to access To measure objects.

Therefore non-contact measurement methods are used in many areas of application to use, which are based on the temperature radiation. Any surface with a temperature T> 0 K emits electromagnetic radiation, the so-called temperature radiation. Strikes one from a surface outgoing radiation on another surface, so it becomes partial reflected, absorbed or transmitted. Therefore, with radiation thermometers Absorption elements are used, which ideally have an absorption capacity that is independent of the wavelength and which change when the radiation strikes (infrared radiation) heat, So that the warming of the absorption element as proof of the emitted infrared radiation can serve.

radiation thermometer or so-called radiation pyrometers generally have optics, a detector element with an absorption element and a housing, that mechanically and thermally protects the optics and detector. at These sensors receive the infrared radiation emitted by the measurement object through suitable windows or optical components onto an absorbent area mapped, this area due to the absorption experiences a temperature increase. It is understood that the radiation thermometer too for measuring temperatures below the intrinsic temperature of the thermometer can be used. In this case shines the absorbent surface emits more radiation than it absorbs, so that the absorbing surface itself cools down overall.

This temperature increase (or lowering) can then be done in different ways be measured. The change is measured for the thermistor bolometers of electrical resistance, for thermocouples the voltage at the contact point of two metal wires, the pyroelectric Detectors a charge shift that occurs when the temperature changes special isolator crystals are created.

The Thermocouples use the so-called Seebeck effect for detection the elevated Temperature off. The connection point of a thermocouple made of two different thermoelectric materials in contact brought with the absorber area while the reference contacts generally located at the temperature of the sensor housing. Because the sensor output voltages Such thermocouples are often very small such thermocouples connected in series. Such a series connection a large number of thermocouples is also used as a thermopile or Called thermopile.

In Great efforts have been made in many technological fields in recent years undertaken to miniaturize electrical and electronic components, where possible inexpensive to manufacture with known standardizable processes should be. The increasing miniaturization leads to radiation sensors to a smaller absorber area and thus to a lower temperature increase, which in turn leads to a lower signal and thus leads to a reduced resolution.

Therefore it’s especially important for miniaturized radiation sensors, one if possible To achieve high absorption of infrared radiation in the absorber system and the absorber surface preferably good thermal insulation from the environment, in order to make one as possible size temperature increase and therefore a big one Generate sensor output signal.

Infrared sensors are already known which have a detector element, the detector element ment an absorber element, which absorbs radiation and heats up, and has a support body with a support body surface for receiving the absorber element, the support body surface having a recess and the absorber element is arranged on the support body surface and above the recess such that a portion of the absorber element Carrier not touched. 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 is already in the DE 42 21 037 have been described. This sensor is manufactured using micromechanical technology. The detector here has a supporting body made of silicon, which is connected to a base plate of the sensor housing.

The Indian DE 42 21 037 The sensor shown is manufactured in a so-called wet etching technology (KOH), which however 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.

at almost all known infrared sensors have the size of the absorber element compared to the overall size of the for example Detector designed as a chip is relatively small, resulting in a low Signal yield leads.

In the DE 100 09 593 a supporting body serving as a heat sink has already been described, in which the walls surrounding the recess are essentially perpendicular to a base plate. However, in this embodiment, 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 at the in the DE 100 09 593 Embodiment shown very large, so that there is a small effective size of the absorber element compared to the overall size of the detector element.

at the known infrared sensors also have a relatively large distance between the edge of the absorber element and the silicon heat sink. About that is also the absorber surface relatively small compared to the total detector area.

outgoing from this prior art it is therefore the task of the present Invention, a radiation sensor of the type mentioned disposal to ask which on as possible small chip area a reinforced one Signal generated. About that it is also an object of the invention to provide an infrared sensor make a small measurement spot allowed and manufactured with known standardized technologies can be.

According to the invention Task solved by that the Recess at least on its side facing the absorber element an area extension has at least 45% of the area of the supporting body. With others Words is at least through the introduction of the recess in the support body 45% of the supporting body surface removed. The remaining rest of the support body surface surrounding the recess has thus an entire area of a maximum of 55% of the total support area. As a result, the total sensor area at constant signal strength to be downsized, resulting in a reduction in manufacturing costs leads. The supporting body is advantageous with a dry etching process manufactured.

In a particularly preferred embodiment the recess has an extension that is between 45 and 75%, preferably accounts for between 50 and 70% and particularly preferably about 65% of the support body area. It has been shown that through the dimensioning of the recess has a particularly good signal yield can be achieved while ensuring sufficient stability of the support body is.

In a particularly useful embodiment the recess has side walls with the surface of the supporting body or the top of the support body an angle between 80 and 100 °, preferably between 85 and 95 ° and particularly preferably include about 90 °. Also through this measure can be achieved that relationship the area of the absorber element is enlarged to the entire detector surface or support body surface.

It has been shown to be preferred the recess executed in this way is, that you through the entire supporting body extends through. In other words, the support body has the can be mounted on a base plate of the sensor, a continuous opening. This will make one as possible greater Distance between the absorber element and the supporting body or base plate of the sensor achieved what in turn the signal reduction due to the thermal conductivity between the absorber element or membrane and the floor or Due to the recess of the gas that is produced, reduced.

The supporting body is preferably manufactured using silicon technology. Farther the absorber element is advantageously designed such that it at least has a CMOS-compatible cover layer. This makes it CMOS compatible Top layer in an expedient embodiment arranged on at least one radiation-sensitive functional layer.

It has been shown that with Advantage the top layer is a surface of at least 30%, preferably between 35 and 70%, particularly preferably occupies between 40 and 60% of the total support surface. It was on this Again emphasize that under the entire surface of the supporting body surface of the supporting body including the recess is understood.

It it is understood that the Absorber elements described here are not necessarily in combination must be used with thermocouples or thermopiles, but for example in combination with pyroelectric elements or bolometers can be used.

Farther could be demonstrated in experiments that the signal yield continues reinforced can be if at least the bottom or the bottom of the recess consists of a material that reflects infrared radiation. This can for example by applying a metal layer, for example a gold layer, the layer being preferred a thickness of less than 1 μm having.

Farther is provided in a particularly preferred embodiment that the sensor a housing has, which consists of a base plate and a connected to this Cap exists, with the detector element or the support body the bottom plate is arranged. The bottom plate is an advantage is designed so that it at least to the supporting body surrounding areas not reflecting infrared radiation. This can be realized, for example, in that the base plate from one corresponding non-reflective material is made. Alternatively can the base plate with the areas surrounding the support body a non-reflective material, preferably a paint or a photoresist.

Further particularly preferred embodiments realize the features of the subclaims.

Further Advantages, features and possible uses of the present Invention will become more preferred from the following description embodiments as well as the accompanying figures. Show it:

1a and 1b two schematic representations of the structure of infrared sensors,

2a and 2 B a sectional and top view of a thermopile sensor on a non-metallic carrier,

3 the schematic structure of a sensor according to the invention,

4 a schematic representation of the contacts on the sensor,

5a and 5b two different embodiments with the absorber system according to the invention,

6a and 6b two different embodiments of sensor housings,

7a . 7b and 7c three different embodiments of sensor caps with imaging optics and

8a and 8b two further embodiments of sensor caps with integrated imaging optics.

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

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

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

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

The detector element 2 has, as will be explained in detail below, a recess 40 on. The bottom of the recess 40 is with a very well reflective metallic layer 7 , for example with a thickness of less than a micrometer.

The the detector element 2 surrounding areas of the floor slab 1 can, as is the case in the embodiment shown, with a non-reflective layer 8th be covered. This layer can be a varnish or a photoresist, for example. 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 also has a metallic cap 9 on, which can be made of steel, nickel, brass or copper, for example. The metallic cap 9 becomes as tight as possible with the base plate 1 connected. Sealing the cap 9 opposite the base plate 1 can be done for example by welding, soldering or gluing. In the metallic cap 9 an opening is provided above the detector element into which a filter that is permeable to infrared radiation can be found 10 is inserted.

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

The bottom plate 1 can, for example, like this in 1a is shown, made of metal or a metal alloy, such as is used for example in standard transistor housings. Examples of preferred materials are steel, nickel, cobalt or similar materials. Alternatively, like this in 1b the base plate is shown 1 consist of a ceramic or an organic material, such as, for example, the circuit board material FR4.

In the 2a and 2 B is a preferred embodiment of a sensor structure on a non-metallic carrier substrate, such as shown, for example, from a standard printed circuit board material (FR3, FR4 or ceramic). 2a Fig. 3 is a sectional view taken along line AA of Fig 2 B , which shows a top view of the sensor structure. The detector element 2 and the temperature reference 3 or a signal preprocessing component (ASIC) 11 are mounted on the circuit board. There is a metal layer on the non-metallic circuit board 41 applied, which preferably has a thickness between 20 and 100 microns. 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 ver runs below the detector element, the temperature reference or the ASIC up to the contact surface of the cap 9 ,

This layer of metal 41 serves to establish a good thermal connection between the cap 9 with the filter 10 on the one hand and detector element 2 and temperature reference 3 on the other hand to ensure. The metallic layer is particularly preferred 41 continuously on the base plate 1 running, with individual islands 42 for establishing contacts 48 and bushings 44 with exception of.

The attachment of the cap 9 on the bottom plate 1 can be done for example by soldering, gluing or welding. Depending on the application, there may be electrical contact between the cap 9 and the metal layer 41 or an electrically insulated assembly may be advantageous.

In the embodiment shown, the metallic layer 41 in the area under the detector element, ie at the point where the detector element or the support body has a continuous recess, and in the immediate vicinity of the connection contacts 48 with an additional highly reflective and preferably well bondable layer 7 Mistake. This layer 7 can be a thin layer of gold, for example.

All around the detector element 2 and around the contact surfaces are the metallic layers in the embodiment shown 7 . 41 with an absorbent layer 43 , for example covered with a solder resist. The absorbent layer 43 is used to avoid reflections from incident light rays that could otherwise affect the measurement result in an undesirable manner.

The through holes can still be seen 44 , which are often called vias, which provide contact to the underside of the base plate. The through holes 44 are metallized on their inner walls and are sealed as gas-tight as possible from the bottom after installation is complete. This can be done, for example, with a drop of glue or a solder seal 45 respectively. This seal is required to seal the sensor housing against external influences, such as moisture, but also aggressive gases. In some applications, it can be advantageous if the sealing takes place under a defined gas atmosphere, such as, for example, under dry nitrogen or under an inert gas, in order to establish a defined gas and moisture ratio within the sensor.

At the bottom of the base plate 1 become the metallic components of the contacts 44 to the printed solder bumps 46 guided. These solder mounds can be made 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.

In 3 the basic structure of an embodiment of a sensor according to the invention is shown 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 that comes from the object whose temperature is to be measured passes through that in the cap 9 arranged filter and strikes the detector element 2 which has an absorber system.

In the absorber system 19 the heat radiation is essentially completely absorbed, resulting in a temperature difference between the absorber area 19 and the edge of the support body 12 of the detector element 2 leads 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 a few tens, but also over a hundred thermocouples. The two ends of the thermocouples linked in this way are connected to the bonding pads 21 connected. From the bond islands 21 lead the bond wires 4 the signal to the connecting wires or connecting contacts to the outside.

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

The membrane layer has a sandwich structure with at least two layers. Here is the bottom layer 14 that also act as a base layer 14 is advantageously made of silicon oxide and has a thickness 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. There is a membrane layer over the base layer 13 applied to the etching process. There is a membrane layer over the base layer 13 applied on which the thermoelectrically active layers 15 . 16 are upset. Polycrystalline silicon with p-line (hole line) and polycrystalline silicon with n-line (electron line) are preferably used for this purpose. 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 connected at the ends to the previous or the following thermocouple. This creates so-called "warm" contacts in the center of the membrane 18 , because this area is exposed to infrared radiation, and on the edge of the chip 2 over the silicon carrier acting as a heat sink 2 so-called "cold" contacts 17 , Contacting can take place via one or more contact windows with aluminum or an aluminum alloy.

The Isolation between the two superimposed Poly-silicon legs are used in the preferred embodiment using a standard CMOS method, e.g. using a thin layer made of silicon dioxide or silicon nitrite.

Above the warm contacts 18 is an absorber structure 19 applied. 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). Together with the membrane thin 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 are placed on the silicon 13 , preferably silicon nitride and silicon oxide or silicon oxynitrite, deposited using CVD processes standardized in CMOS technology. As a result, a sandwich structure having multiple 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 are advantageously chosen so that the entire layer stress is approximately canceled after cooling to room temperature or a slight tensile stress remains.

In the 4 is another illustration of the sensor 2 including the membrane, the absorber and the contacts shown, by means of which the proportions of the invention are clear.

It can be clearly seen that the supporting body 12 , which is constructed here from a silicon layer, a recess 40 has, 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 at most 18%, particularly preferably between 8 and 12% of the total side length S of the chip 2 , This increases the beam output of the thermal sensor. The distance A1 between the edge of the absorber structure also increases 19 and the membrane 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 preferably, based on the side length of the chip, at least 52%, especially with detector sizes of less than about 1 mm, and preferably between 65 and 80%, in particular with detector sizes with one side length of more than 1.5 mm.

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

By the configuration according to the invention The chip geometry ensures that the achievable in relation to the detector area Signal voltage opposite the known sensors is significantly increased. So have been in trials Signal voltages measured that are between 1.4 and 2 times greater than the signal voltages of known sensor chips were of the same detector area.

In addition, by the strong compared to the sensors of the prior art reduced edge of the supporting body the likelihood of reflections leading to an unwanted Extension of the measuring spot to lead can, reduced. This makes the measurement accuracy of the Invention infrared radiation thermometer for the Spatial measurement limited measuring objects clearly increased.

It has been shown that the cold contacts are advantageous 17 at the edge of the membrane near the edge of the silicon substrate 12 be arranged while the warm contacts are placed under the absorber if possible 19 be arranged 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 rest are located between the edge of the absorber and the center of the absorber 19 are distributed.

In the 5a and 5b the structure of the absorber system according to the invention is shown. The entire sensor including the housing bottom surface is designed in such a way that all elements contribute to absorption. That through the infrared filter 10 on the detector element 2 falling infrared radiation first reaches the absorber top 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 clean room 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 through and meets one below the top layer 52 arranged passivation layer 51 as well as the one under the passivation layer 51 lying thermoelectric 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 on the thickness of the dielectric layers used. It is therefore possible that part of the incident infrared radiation penetrates the layer structure and to the base plate 1 arrives. On the bottom plate 1 is, however, as already mentioned, a highly reflective layer in the area of the recess 7 arranged, which shows almost no self-absorption and no transmission, but reflects the radiation portion back to the membrane. Since also the membrane layer 14 possibly part of that from the shift 7 reflected radiation, multiple reflections can occur until the radiation portion almost completely re-penetrates the membrane layers from below. The majority of the residual radiation, ie the radiation that first penetrated the absorber layer, is then in the second passage through the layer system with the layers 13 . 14 . 15 . 16 . 51 and 52 absorbed.

alternative it is also possible within the sequence of dielectric layers of the absorption layers to introduce a reflective layer so that the multiple reflections only take place in part of the layer system. Furthermore, it can for some use cases be advantageous in terms of the thicknesses of the dielectric layers to optimize for interference effects in order to achieve the most complete absorption possible to reach the incident light in the absorption layer.

So can for example about the additional Reflection layer a 0.5 to 1 μm thick dielectric layer, for example made of silicon oxide, applied become. With quite broadband sensors it can be an advantage the total thickness of the dielectric layers up to 1.5 to 2.5 μm too increase.

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, ie the surface of the membrane that does not have a con clock to the support body has 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 nitride, silicon oxide or silicon oxynitrite. The thermoelectric layers 15 and 16 For example, which consist of n- and p-type polycrystalline silicon or of silicon or germanium, can also be produced by CVD deposition. Over the thermoelectric layers 15 and 16 there is a passivation layer made of silicon oxide or silicon nitrite with a thickness of approx. 100 to 1,500 nm.

The absorber top layer 52 can be carried out 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 applied to the passivation layer 51 deposited. 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 over 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 approximately 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 uses a polymer layer as an absorber cover layer used. The thickness of the polymer layer is approximately 2 to 10 μm. As a polymer layer come preferably photoimide or other polymers, e.g. polyimide, for use.

Furthermore can the two variants described to increase absorption are also combined become. Then the reflection-reducing metal layer over the Polymer layer deposited.

In order to further limit the measurement spot, the silicon carrier body used has the detector element 2 According to the invention a very small width, so that the usable absorber area is very high compared to the total detector element area. Nevertheless, parts of the infrared radiation fall 26 on the edge of the detector element 2 , they can be created by an absorber layer on the edge of the membrane that is generated simultaneously with the absorber 25 be prevented from further reflections. The absorber layer 25 can cover the entire edge of the supporting body over the silicon carrier, except for the area necessary for the connection of the wires. 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 next to the detector element 2 on the base plate 1 can hit them by an additional absorber layer 43 be absorbed. This prevents these radiation components 24 possibly led back to the absorber via multiple reflections on the base plate, cap wall and cap ceiling. Otherwise this would lead to a deterioration in the imaging behavior of the optics.

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 that is not due to the temperature reference applied to the base plate 3 can be corrected. The false signal only disappears after the cap and base plate have exactly the same temperature again. This effect is particularly pronounced when the absorber system of the detector element or chip 2 the filter adhesive 27 which is generally used to attach the filter 10 on the cap 9 is used 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 , As a result, temperature differences between the base body and cap 9 or between the base body and the adhesive used 27 over from the glue used 27 emitted infrared beam tion to the detector element 2 transfer. This leads to measurement errors when the cap 9 a different temperature than the detector element 2 Has.

At the in 6a shown embodiment is therefore an additional aperture 28 which can be made of metal or plastic, for example, in the cap 9 over the detector element 2 mounted so that a pinhole 28 the radiation from the filter 10 to the absorber and the radiation components arriving from the outer cap wall from the detector element 2 keeps. This aperture 28 can advantageously be designed to be reflective on both sides, but particularly preferably at least to the infrared filter 10 pointing top is coated absorbent.

At the in 6b shown second embodiment of a cap geometry is the filter 10 on top of the cap 9 mounted in a recess. This depression is designed such that the filter adhesive 27 not in the "field of view" of the detector element 2 lies. 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.

In the 7a and 7b further preferred cap geometries are shown, with the aid of which the spatial resolution of the thermopile sensor is further increased.

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

The bottom end 32 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 can consist, for example, of a thin gold, silver or aluminum layer with a passivating cover layer, for example made of silicon oxide or a polymeric material, prevents additional measurement errors by heating up the mirror or the cap. The bottom 32 the mirror can be both curved as in 7a is shown, as well as flat, for example running essentially parallel to the base plate.

Another embodiment with optical focusing is shown in 7b shown. The cap 29 has an inserted lens 34 , which can consist of silicon, germanium, calcium fluoride or similar. In certain applications, the transmission range of the lens 34 be correspondingly restricted by known antireflection 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 to prevent reflections on the cap wall. That is why the inner surface 35 of the opening body 36 made absorbent. The bottom of the aperture body 36 can be curved as well as parallel to the base plate 1 be designed to be continuous and can optionally be reflective.

It goes without saying that more than one detector element 2 , for example a row or an array of sensor elements, each with an absorber system according to the invention on the detector element 2 can be integrated. The signal preprocessing of the individual signals can then be monolithic in the detector element 2 as well as on the application-specific silicon circuit 11 next to the detector element 2 on the bottom plate 1 be made.

In 7c Another embodiment of the absorber system according to the invention is shown. In principle, the chip structure and the layer sequence of this embodiment correspond to those in connection with the 2 . 3 and 5 described embodiments. Even with multi-element arrangements there is a highly reflective layer in the area under the membrane 7 arranged. The absorber structure 19 is over the membrane layer 13 . 14 arranged and fills the largest part of the element area between the remaining walls 54 of the silicon carrier 12 out. In contrast to the one-element solution, a lens 34 are used and the size of the aperture of the aperture body 30 must be adapted to the size of the outside sensor elements.

It is understood that the aperture body 36 as well as the mirror 30 as part of the cap 29 can be executed. Corresponding embodiments are in the 8a and 8b shown.

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 depression at the upper end 37 to hold the filter 10 , The mirror surface connects to the recess 30 with a reflective coating 31 on. The mirror surface 31 and the cap 29 are thus formed from a single part, which enables a particularly good thermal connection of the mirror, cap and filter or lens to the base plate. 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 shaped so that it has a focusing effect for that through the infrared filter 10 penetrating radiation shows. As a result, the radiation is applied to the absorber surface of the detector element 2 from formed. For this purpose, the mirror preferably has the shape of a paraboloid or a so-called Winston cone.

With the in 8a shown embodiment, particularly reproducible optical imaging properties can be achieved because of the design of the cap 29 the distance between the mirror and the detector element as a deep-drawing tool or as an injection molding tool 2 is well defined. 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 from heating up undesirably 29 opposite the base plate 1 to prevent.

In the 8b shown embodiment has a lens 34 , for example made of silicon, germanium, calcium fluoride or the like, on the cap 29 is used. The cap 29 is also designed as a deep-drawn part made of metal or as an injection molded part made of plastic and has a recess at the upper end 37 into which the lens 34 is inserted. Furthermore, the depression points 37 a circumferential groove 38 on. The circumferential groove 38 which, incidentally, also in the 8a shown embodiment could be used, prevents the adhesive for attaching filters 10 or lens 34 penetrates to the filter, mirror or lens surface visible by the sensor. In this embodiment too, the aperture surface is directly connected to the depression 30 with an absorbent coating 35 on.

An additional aperture 28 , which can preferably be formed as a metal deep-drawn part or consist of a reflectively coated plastic, is placed above the chip in this way 2 arranged that the aperture 28 lets the radiation pass from the filter to the absorber and keeps the radiation components arriving from the outer cap wall away from the detector element. If the cap 29 is made of plastic, then there is the pinhole 28 preferably made of metal and the lower end 39 is going to the bottom plate 1 lengthened and connected to it in such a way that good thermal contact arises. The pinhole 28 serves to improve the optical imaging conditions and to reduce the so-called thermal shock effect. Again, the entire inside and outside of the cap 29 preferably coated reflective.

1

baseplate

2

detector element

3

Temperature reference element

4

connecting wire

5

pins

6

contact area

7

reflective layer

8th

absorbing layer

9

cap

10

filter

11

Signal processing circuit

12

supporting body

13

membrane layer

14

Base layer / lower membrane layer

15 16

thermoelectric layers

17

cold contacts

18

warmth contacts

19

absorber structure

20

reflective layer

21

Bond island

24

part of infrared radiation

25

border areas the absorber layer

26

part of infrared radiation

27

filter glue

28

cover

29

cap

30

mirror

31

mirror layer

32

bottom of the mirror

33

reflective layer

34

lens

35

surface

36

Aperturkörper

37

deepening

38

groove

39

lower End of aperture

40

recess

41

metal layer

42

Islands

43

absorbing layer

44

bushings

45

Lotverschluß

46

solder bumps

48

contacts

51

passivation

52

absorber top layer

53

infrared radiation

54

Walls of the Silicon support body

A1

distance between the edge of the absorber and the membrane

A2

Length of absorber element

D

thickness of the support frame

S

Side length of the detector element

Claims (32)

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 ), which absorbs radiation and thereby heats up, and a supporting body ( 2 ) with a supporting 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 ) is arranged on the supporting body surface and above the recess such that at least a section of the absorber element ( 13 . 14 . 15 . 16 . 51 . 52 ) the supporting body ( 2 ) not touched, characterized in that the recess has an extent which corresponds to at least 45% of the support body area. Sensor according to claim 1, characterized in that the recess at least on the absorber element ( 13 . 14 . 15 . 16 . 51 . 52 ) facing side has a cross section that occupies between 45 and 75%, preferably between 50 and 70% and particularly preferably about 65% of the surface of the support body. Sensor according to claim 1 or 2, characterized in that the recess 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. 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 ) extends through. Sensor according to one of claims 1 to 4, characterized in that the supporting body ( 2 ) is manufactured using silicon technology. Sensor according to one of claims 1 to 5, characterized in that a base plate ( 1 ) vorese hen is on which the support body is attached. Sensor according to one of claims 1 to 6, characterized in that the absorber element ( 13 . 14 . 15 . 16 . 51 . 52 ) at least one CMOS-compatible cover layer ( 52 ) having. 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 . 14 . 15 . 16 ) is arranged. 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. Sensor according to one of claims 1 to 9, characterized in that at least the bottom surface or the bottom of the recess made 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. Sensor according to one of claims 6 to 10, characterized in that the base plate ( 1 ) is made of a material that does not reflect infrared radiation or at least on the support body ( 2 ) surrounding areas ( 43 ) is coated with a material that does not reflect infrared radiation, preferably a lacquer or photoresist. Sensor according to one of claims 1 to 11, characterized in that a membrane ( 13 ) is provided, which the absorber element ( 13 . 14 . 15 . 16 . 51 . 52 ), the membrane ( 13 ) has at least two layers. Sensor according to claim 12, characterized in that the layers of the membrane ( 13 ) are made up of silicon dioxide, silicon nitride or silicon carbide. Sensor according to one of claims 1 to 13, characterized in that the absorber element ( 13 . 14 . 15 . 16 . 51 . 52 ) has a multilayer structure. Sensor according to claim 14, characterized in that the absorber element ( 13 . 14 . 15 . 16 . 51 . 52 ) a top layer ( 19 . 52 ), which is designed as a, preferably CMOS-compatible, metal absorption layer. Sensor according to claim 15, characterized in that the cover layer ( 19 . 52 ) has a thickness of less than 50 nm. Sensor according to claim 15 or 16, characterized in that the cover layer ( 19 . 52 ) consists of titanium nitride. Sensor according to one of claims 15 to 17, characterized in that the cover layer ( 19 . 52 ) has a sheet resistance between approximately 180 and 400 ohms. Sensor according to one of claims 15 to 18, characterized in that on the cover layer ( 19 . 52 ) a passivation layer is arranged, the passivation layer preferably consisting of silicon oxide or silicon nitride. 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 μm. Sensor according to claim 15 or 16, characterized in that the cover layer ( 19 ) consists of 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. Sensor according to one of claims 15 to 21, characterized in that at least one of the cover layers ( 19 . 52 ) forming layers at least partially up to the upper edge surface of the support body pers ( 2 ) that surrounds the recess. Sensor according to one of claims 1 to 22, characterized in that that a Device for measuring the temperature of the absorber element is provided is. Sensor according to claim 23, characterized in that the temperature measurement has at least one thermocouple, preferably a thermopile. Sensor according to claim 24, characterized in that this at least one thermocouple or the thermopile from two layers be formed from polycrystalline silicon, the one layer is n-type and the other is p-type and the two layers through an insulation layer, which is preferably made of a silicon oxide or silicon nitride layer is formed, are separated from each other. Sensor according to one of claims 1 to 25, characterized in that the absorber element ( 13 . 14 . 15 . 16 . 51 . 52 ) has a reflective layer that reflects radiation. Sensor according to claim 26, characterized in that on the reflection layer is a dielectric layer with a preferred one Thickness between 0.5 and 2.5 μm is provided. Sensor according to claim 27, characterized in that the dielectric layer made of polysilicon and silicon dioxide or silicon nitride, preferably composed of silicon dioxide. Sensor according to one of claims 23 to 28, characterized in that that several Thermopile elements are provided in a row or matrix arrangement, each thermopile element preferably having a separate absorber element assigned. Sensor according to claim 29, characterized in that this support element a plurality of recesses and a plurality of absorber elements has, each absorber element above a recess is arranged. Sensor according to one of claims 24 to 30, characterized in that that each a connection, the so-called warm contact, the thermocouple of the thermopile is arranged under the absorber element, preferably being the warm contact of every second or third thermocouple to extends into a central region of the absorber element while the warm contact of the other thermocouples only to an edge area extends of the absorber element. Sensor according to one of claims 24 to 31, characterized in that that each a connection, the so-called cold contact, the thermocouple of the thermopile is connected to the edge of the support body surrounding the recess, wherein the connection point of the cold contact with the support body preferably in the area of the inner edge of the frame surrounding the recess of the supporting body.