Sensor element for the detection of fluids and production method

p0001The invention relates to a sensor element for the detection of liquid, gaseous or fluid substances with a sensing layer formed on a substrate and a manufacturing method of such a sensor element. The sensor layer is the layer at which the substance to be measured is converted into a measurable sensor signal. The sensor layer may consist of a continuous layer of a suitable material, such as tin oxide, or include Interdigital capacitor structures, gate regions of field effect transistors, Hall structures etc..

p0002Such a sensor element and such a manufacturing method are known from practice.

p0003The electrical contacting of the sensor element results in a number of difficulties. The sensor layer must be connected to the recording of measured values ​​of the sensor element to external electrical contacts. This compound is usually carried out by means of bonding wires. For this purpose, bonding pads are arranged in a spatially very small distance to the sensor surface. This usually leads to the fact that bonding pads and bonding wires during the measurement come into contact with the substance to be detected. The reliability of the bonds will be significantly affected. On the other hand, it is technically very complex, the sensor element be designed so that the bonds do not come into contact with the substance to be detected. Further, surface of the sensor layer is formed by the bonding pads additionally required since. At the point at which the bonding wire is attached, a reaction of the sensor layer is prevented due to the substance to be detected

p0004In the case of sensor elements for which a heater is required would be reduced by the heating, the reliability of the bonding connection. Further, the measurement accuracy of the sensor element may be affected, that part of the substance to be detected which does not contribute to the reaction with the sensor surface, resulting in reactions with the bonding wire, which significantly limit accuracy. Also, it is complicated to connect the sensor element with devices by means of which the substance to be detected is supplied, as with pumps, valves, etc. The production of such sensing elements is also costly, since the sensor elements must be attached to special chip carriers (leadframe), and since mounting technology is complicated because for performing various process steps individual sensor elements have to be handled.

p0005The invention is based is to provide a reliable, simple and inexpensive generic sensor element the task.

p0006This object is achieved by a generic sensor element in which a signal line device for conducting a sensor signal is disposed in the substrate such that it connects the facing the substrate back side of the sensor layer with the substrate rear side or at least one side of the substrate surface.

p0007Furthermore, the object is solved by a manufacturing method in which in the substrate, a signal line device for conducting a sensor signal is arranged such that it connects the facing the substrate back side of the sensor layer with the substrate backside or substrate side face.

p0008Due to the inventive arrangement of the signal conduit means of the sensor layer, to which the substance to be measured is applied, no electrical contacts in the form of bonding pads and bonding wires are required on the front side. This is an impairment of the measuring accuracy of the sensor element as can be formed by the above-mentioned bonds, completely excluded. The sensor layer and thus also the sensor element can be made smaller, because no additional space for the application of bonding pads is required. This contributes in particular if an expensive material is used for the substrate, considerably cost reduction. Moreover, ever-smaller sensors are also desirable for many applications, since this space can be saved. The reliability of the signal conduit means is not impaired even by a heater of the sensor since the heating in a different place can be mounted in the substrate. In addition, such a sensor is also characterized cheaper that no additional chip carrier is necessary because the contact directly to the substrate backside or / the substrate side surfaces can be carried out. Also, an interaction of the substance to be measured is connected to the signal conduit means reliably prevented, since this runs in the substrate.

p0009According to an advantageous development of the sensor element, the signal line means comprises line shaped cavities for receiving signal lines that extend from the back of the sensor layer to the substrate backside or / the substrate side surface / s. The cavities may be filled with a metal. Thus, a simple, reliable, electrical connection between the sensor surface and external electrical contacts is possible.

p0010The sensor element can be further simplified, that directly contact pins are inserted into the metal in the cavities with which the sensor element can be used for example in a circuit board. The voids are particularly easy to produce, as they extend in a line from the back of the sensor layer to the substrate backside.

p0011According to an advantageous embodiment of the invention, a side surface of the substrate delimits, on the sensor layer protruding protection device is formed. This is the area in which the substance to be detected can spread spatially limited. The substance is prevented from passing to the out of the substrate contacts. Conveniently, the protective device to the substance is sealingly formed on the side surfaces. This ensures that the entire substance used remains on the surface of the substrate. Even small amount are prevented from passing on the side surface or the back of the substrate and thus to the electrical contacts. It is thereby a lesser part of the substance is required.

p0012According to an advantageous development of the invention, the sensing layer extends substantially over the entire cross section of the substrate. The upper end of the protective device may be provided with a connecting device. It is then particularly easy target supply the substance. The substance can be fed without any losses. It may further also a discharge device for the proportion of the substance are arranged in the terminal device, which is not used for the detection and to the reaction on the sensor surface.

p0013According to a preferred embodiment, the substrate is a semiconductor substrate. According to another embodiment, the substrate is a glass substrate.

p0014In the following the invention will be explained in more detail with reference to FIG.

p0015Fig. 1 shows an inventive sensor element in cross section.

p0016The sensor element 1 includes a substrate 2, on its front side a sensor layer 3 is applied. The sensor layer 3 covers the entire cross section of the substrate 1. In the substrate 2, two signal lines 4 are arranged so as to connect the substrate 1 facing the rear side of the sensor layer 3 with the substrate backside. 5 The signal lines 4 are in line-shaped, cylindrical here, cavities 6 and consist of a metal with which the cavities are filled 6. Of the substrate rear side 5 contact pins 7 are inserted into the cavities 6 and rigidly connected to the present in the cavities 6 metal. The substrate 2 and the sensor layer 3 are surrounded by a protection device 8 which is preferably sealingly to the substance, formed on the substrate side surfaces. The protective device 8 projects beyond the surface of the sensor layer 3rd The length of the projecting part 9 of the protector 8 over the sensor layer 3 is selected depending on the substance to be measured. It is essential that prevents the substance to be measured passes to the back of the sensor element 1, where the electrical contacts, the contact here Styles 7 are located. The protruding part 9 of the protection device 8 can be provided with a connection device, to the device for supplying or discharging the substance to be measured, such as pumps, valves, etc., can be connected.

p0017For the manufacture of the sensor element according to the invention, the sensing layer 3 is applied on the substrate 2 in a conventional manner. For very small sensor elements, in particular in semiconductor technology, it is often customary to produce a plurality of sensor elements 1 in one body. By conventional methods, when this is necessary, the thinned rear side of the body and further suitable processing steps performed. Then, the cavities 6 are formed in the sensor elements 1 and filled with a suitable metal. The Kontaktstife 7 are attached to the signal lines 4, for example by soldering, welding, gluing, etc.. Then, the sensor elements 1 are separated from each other. Thereafter, the protective device 8 is applied on the side surfaces of the individually present sensor elements. The protection device 8 can be for example a shrink tube, which is fastened by heat treatment on the side surfaces of the substrate 2 sealingly against the substance. The protection device 8 can be produced for example by an interference fit of a metal.