EP3039392A1

EP3039392A1 - Thermal sensor and method for producing a thermal sensor

Info

Publication number: EP3039392A1
Application number: EP14755094.1A
Authority: EP
Inventors: Ingo Herrmann; Fabian Utermoehlen
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2013-08-26
Filing date: 2014-08-25
Publication date: 2016-07-06
Also published as: WO2015028419A1; DE102013216909A1; CN105473989A; US20160231178A1; US9891113B2

Abstract

The present invention relates to a thermal sensor and a method for producing a thermal sensor of this type having a low signal-to-noise ratio at relatively high signal strengths. To this end, a thermoelectric generator is combined with a field effect transistor and a diode. Owing to its integrated diode and the barrier effect associated therewith, the thermal sensor is suitable for the economical and efficient design of imaging sensor arrays for converting thermal radiation into electrical signals.

Description

Description title

Thermal sensor and method for manufacturing a thermal sensor

The present invention relates to a thermal sensor, and a method for

Production of a thermal sensor. In particular, the present invention relates to a thermal sensor for providing a temperature dependent output between a first and a second output.

As sensor elements for detecting heat rays, thermodiodes or thermocouples are known, for example. For imaging detector systems, a two-dimensional array is used, in which such detectors for thermal radiation are arranged in a matrix of a plurality of rows and columns.

The document US 5,554,849 A discloses an array of thermodiodes for

two-dimensional detection of infrared radiation. Furthermore, US Pat. No. 4,558,342 A discloses a detector array which uses thermocouples as detector elements. To increase the detector voltage several Thermocouples are connected in succession to so-called thermopiles (thermopiles).

When using thermodiodes in the imaging arrays, it is possible to form a matrix in which individual pixels can be addressed by applying appropriate voltages to row or column lines. To evaluate the corresponding pixels and to detect the temperature across the diode, the diode must be actively energized. In numerous applications, several such thermodiodes per pixel are connected in series to increase the resolution.

Thermocouples, on the other hand, have the advantage that they are made from one through the

Heat radiation resulting temperature difference directly generate a voltage. In contrast to thermo-diodes is therefore an active energization of the individual

Sensor elements not required. For the evaluation of each pixel of a

However, for each pixel, sensor arrays must connect both terminals of the thermocouple to an evaluation circuit. There is therefore a need for a thermocouple that allows a cost-effective design of large sensor arrays. Further, there is a need for one

Thermocouple with an improved signal-to-noise ratio. There is also a need for a thermocouple that is inexpensive to manufacture.

Disclosure of the invention

According to a first aspect, the present invention provides a thermal sensor for providing a temperature dependent output signal between a first and a second output, comprising a field effect transistor having a gate terminal, a source terminal and a drain terminal; a diode connected at one connection point to the drain terminal of the field-effect transistor and connected at another connection point to the first output of the thermal sensor; and a thermoelectric generator configured to provide a temperature dependent voltage between a first and a second connection point, wherein the first connection point of the thermoelectric generator is connected to the gate terminal of the field effect transistor and the second

Connection point of the thermoelectric generator is connected to the source terminal of the field effect transistor and the second output of the thermal sensor.

In another aspect, the present invention provides a method of fabricating a thermal sensor that provides a temperature dependent output between a first and a second output, comprising the steps of providing a field effect transistor having a gate terminal, a source terminal, and a drain. Connection has; the provision of a diode; providing a thermoelectric generator configured to provide a temperature dependent voltage between a first and a second terminal of the thermoelectric generator; connecting a terminal of the diode to the drain of the field effect transistor; connecting a further connection point of the diode to the first output of the thermal sensor; connecting the first connection point of the thermoelectric generator to the gate terminal of the field effect transistor; and connecting the second one

Connection point of the thermoelectric generator with the source terminal of the field effect transistor and the second output of the thermal sensor. Advantages of the invention

The present invention is based on the idea of a thermal sensor from a combination of a thermoelectric generator, such as a

Thermocouple, as well as a field effect transistor and a diode to form. In this case, the gate potential of the field effect transistor is provided by the thermoelectric generator, whereby the field effect transistor amplifies the temperature-dependent output signal of the thermoelectric generator. The field effect transistor in turn is connected in series with a p-n diode, which allows electrical current to flow in one direction while blocking current flow in the opposite direction.

The amplification of the thermoelectric generator thermoelectric generator by the field effect transistor allows a significantly higher output signal, compared to the output signal, as would be achieved by a pure thermoelectric generator, or another temperature-dependent component without amplification.

By the series connection of the diode with the field effect transistor, the control of the thermal sensor is possible in a purely passive matrix. The individual thermal sensors in such a matrix can be addressed analogously to a sensor array of thermodiodes. Compared to arrays with thermodiodes can by the

Thermal sensor according to the invention an output signal with significantly improved signal-to-noise ratio can be generated.

Due to the possibility of individually addressing the individual thermal sensors in a matrix, the thermosensors according to the invention can furthermore be used to form a two-dimensional sensor array in an efficient, space-saving and hence cost-effective manner. In contrast to conventional thermocouples, it is not necessary for each of the two terminals of each individual sensor element to be separate from one another

Evaluation circuit to be contacted.

According to a further embodiment, the thermoelectric generator comprises a thermocouple with at least two tracks of materials with different Seebeck coefficients. A thermoelectric generator based on the Seebeck effect provides an efficient way to achieve the required potential for the

To provide control of the gate terminal of the field effect transistor. According to a specific embodiment, the thermoelectric generator comprises a thermopile with a plurality of thermocouples. By series connection of several thermocouples, the voltage signal of the thermoelectric

Generators are further increased and thus the field effect transistor are particularly well controlled.

In a further embodiment, at least the field effect transistor and the first and second connection point of the thermoelectric generator are arranged on a common substrate. The combination of the field effect transistor with the connection points of the thermoelectric generator on a common substrate allows a space-saving design of the thermal sensor.

In a further embodiment, the field effect transistor, the first and second connection point of the thermoelectric generator and the diode are on one

common substrate arranged. As a result, a particularly efficient production of the thermal sensor is possible.

The present invention further includes a sensor array having a plurality of

Thermal sensors, wherein the plurality of thermal sensors are arranged in a matrix of rows and columns, and each thermal sensor of the plurality of thermal sensors is individually addressable. Thus, a sensor array for thermal radiation can be realized, which takes advantage of the individual thermal sensors, in which the

Thermosensors of the matrix are individually addressable and provides in a small space an output signal with high dynamics and low signal-to-noise ratio.

Furthermore, the present invention comprises a camera with a previously mentioned sensor array. Such a camera can be used for example for thermography applications or in a night vision device. Further embodiments and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings. Brief description of the drawings

Show it

Figure 1 is a schematic representation of a circuit diagram of a thermal sensor according to an embodiment of the present invention;

FIG. 2 shows a schematic illustration of a top view of a thermal sensor according to a further embodiment of the present invention;

FIG. 3 shows a schematic representation of a sensor array according to FIG

Embodiment of the present invention; and FIG. 4 shows a schematic representation of a method for producing a

Thermosensors, as is another embodiment of the

present invention is based.

Embodiments of the invention

1 shows a circuit diagram of a possible embodiment of a thermal sensor 1. The thermal sensor 1 comprises a thermoelectric generator 10, a

Field effect transistor (FET) 20 and a diode 30. Further, the thermal sensor 1 comprises two outputs A and B. Between these two outputs A and B, the

Thermal sensor 1, a temperature-dependent output signal U_temp ready. For this purpose, the thermal sensor 1 is actively energized by an external source (not shown). The resulting voltage drop U_temp between the outputs A and B depends on the temperature difference that exists over the thermoelectric generator 10. The thermoelectric generator 10 is, for example, a

Component that outputs a voltage as a function of a temperature between two connection points. For example, the thermoelectric generator 10 may be a thermocouple (thermocouple). Such thermocouples can be made, for example, from two tracks of two materials with different Seebeck- coefficient. Suitable material combinations for this purpose, for example, aluminum and p-type silicon or n-type silicon and p-type silicon. Further Material combinations are also conceivable. Will be one

Thermocouple with at least two tracks of two materials with

different Seebeck coefficients led from a heat sink to a heat source, the result is a voltage difference between the two connection points of the thermocouple. This voltage difference can be used to drive the FET 20. In addition, all other types of thermoelectric generators are also possible, depending on a temperature or a

Temperature difference output a defined voltage. The FET 20 comprises a source terminal S, a drain terminal D and a gate terminal G. The thermoelectric generator 10 is provided with a

Terminal connected to the gate terminal G of the FET 20. Of this

Connection point leads from the thermoelectric generator 10 via a connection at the output B of the thermal sensor 1 on to the source terminal S of the FET 20. The drain terminal D of the FET 20 is further connected to a connection point of the diode 30. The other connection point of the diode 30 is connected to a connection point at the further output A of the thermal sensor 1.

The thermoelectric generator 10 now generates between the source terminal S and the gate terminal G of the FET 20, a voltage difference, which of the

Temperature difference between heat source and heat sink on the

thermoelectric generator 10 depends. In the example shown, this is approximately the temperature difference between the temperature at the FET 20 and the terminal B of the thermal sensor. To increase the voltage difference, it is also possible to realize so-called thermopile, in which several thermocouples

(Thermocouples) are connected in series. In this case, each thermocouple of the thermopile between the heat source and the heat sink must be arranged.

Figure 2 shows a plan view of a thermal sensor 1, according to the circuit diagram of Figure 1. The FET 20 and the diode 30 are on a common

Substrate 2 is arranged. It is also possible that FET 20 and diode 30 are arranged on different substrates, or at least one of the components is also designed as a discrete component. The substrate 2 may be

For example, act to a micromechanically isolated silicon island. This silicon island can be suspended via thin holding elements 13, 43. At the same time, via these holding elements 13 and 43, the electrical contacting of the substrate. 2 respectively. The thermoelectric generator 10 is realized in the illustrated case of a series of two conductor tracks 1 1 and 12 of materials with different Seebeck- coefficients. The first conductor 1 1 leads from the source terminal S of the FET 30 to the connection point at the output B of the thermal sensor 1. The second conductor 12 runs parallel to the first conductor 1 1 from the connection point at the output B of the thermal sensor 1 to the Gate terminal G of the FET 3. As already mentioned above, several thermocouples (thermocouples) can be connected in series to increase the voltage signal. A substrate 2 is, for example, a silicon island of epitaxially grown silicon. The dopants required for the FET 20 and also for the diode 30 are preferably doped into this silicon island. Alternatively, instead of the silicon island and SOI (silicon on insulator = silicon on a

Insulator layer) can be used. In this case, the dopants for the FET 20 and the diode 30 must be introduced into the functional silicon layer of the SOI. The one connection point of the diode 30 is connected via the feed line 40 to the first output A of the thermal sensor 1. The other terminal of the diode 30 is connected to the drain terminal D of the FET 20. Thus, with active energization between the two outputs A and B of the thermal sensor 1, an output signal L emp, whose size as a function of the temperature difference between the substrate 2 and the temperature at the opposite point of the thermoelectric generator 10, that in this case the second output B varies.

FIG. 3 shows a sensor array for converting heat radiation into an electrical signal. The sensor array comprises a plurality of thermal sensors 1, which are arranged in a matrix structure of a plurality of rows 61, 62 and 63 and a plurality of columns 51, 52 and 53. The restriction to three rows and columns is only for better visualization and does not limit the sensor array. Sensor arrays with more than three rows and / or more than three columns are possible. At each crossing point of a line 61, 62, 63 with a column 51, 52, 53 a thermosensor 1 is arranged in each case. An output of the thermal sensor 1 is with the respective control line of

corresponding column 51, 52 or 53 connected. The other output of the

Thermal sensor is connected to the respective control line of the corresponding line 61, 62 or 63. Thus, by driving the corresponding column 51, 52, or 53 through the column controller 50, a respective column may be selected. The row controller 60 also selects the corresponding row 61, 62 or 63 off. Thus, within the matrix of the sensor array, each individual thermal sensor 1 can be individually addressed. Since the diode 30 in the thermal sensor 1 allows current to flow only in one direction and blocking in the other direction, a flow of current from one row to another row, or from one column to another column through the thermal sensors 1 is not possible.

By selecting a column 51, 52 or 53 and simultaneously evaluating the signals in all lines 61, 62 and 63 by the line evaluating device 60, a simultaneous evaluation of all the output signals of the thermal sensors 1 of a complete column can take place. Alternatively, it is also conceivable to control one row by the row control device 60 and then all columns 51, 52 and 53 by the

Column control device 50 to evaluate simultaneously. In both cases, a particularly rapid and efficient evaluation of the complete sensor array is possible. Such a sensor array for converting thermal radiation into electrical signals can be used in numerous imaging systems. For example, such a sensor array is suitable as a two-dimensional sensor for thermographic applications in a thermal imaging camera or the like. Such thermal imaging cameras allow an assessment of building insulation or for monitoring processes in which the control of temperatures, in particular of temperature differences are important.

In addition, sensor arrays can also be used in camera systems for night vision devices. Such night vision devices allow the detection of the environment even in partial or complete darkness. In this way, for example, in a motor vehicle, a camera system can be realized in the dark due to temperature differences in the environment an additional evaluation of

Surrounding area allows and thus information for one or more

Driver assistance systems provides. Other use cases for the on or

Multidimensional detection of temperature differences is also possible.

FIG. 4 shows a schematic representation of a method 100 for producing a thermal sensor, which provides a temperature-dependent output signal between a first output A and a second output B. In a first step 110, a field-effect transistor 20 is provided. The FET 20 has a gate terminal G, a Source terminal S and a drain terminal D on. In a further step, a diode 30 is provided. This diode 30 is, for example, a pn diode with two terminals. Furthermore, in step 130, a thermoelectric

Generator 10 is provided, which is adapted to provide a temperature-dependent voltage between a first and a second connection point.

Subsequently, in step 140, a connection point of the diode 30 is connected to the drain terminal D of the field effect transistor 20. In step 150, another connection point of the diode 30 is connected to the connection point of the first output A of the thermal sensor 1. In step 160, the first terminal of the thermoelectric generator 10 is connected to the gate terminal G of the FET 10. Finally, in step 170, the connection point of the second output B of the thermoelectric generator 10 is connected to the source terminal S of the FET 20 and the connection point of the second output B of the thermal sensor 1.

Preferably, the provision of FET 20 and / or diode 30 is on a silicon substrate. For this purpose, to form the FET 20 and the diode 30th

corresponding dopants introduced into the silicon substrate. The provision of the thermoelectric generator 10 is preferably carried out by providing at least two interconnects of materials

different Seebeck coefficients. For example, an interconnect may be made of aluminum and another interconnect of a p-type silicon. Other

Material combinations such as n-type silicon and p-type silicon or the like are also possible.

In summary, the present invention relates to a thermal sensor and a method for producing such a thermal sensor with low signal-to-noise ratio at relatively high signal strength. For this purpose, a thermoelectric generator is combined with a field effect transistor and a diode. The thermosensor is suitable due to its integrated diode and the associated

Barrier effect for a cost-effective and efficient design of imaging sensor arrays for the conversion of heat radiation into electrical signals.

Claims

Thermal sensor (1) for providing a temperature-dependent

Output signal (U_temp) between a first and a second output (A, B), comprising: a field effect transistor (20) having a gate terminal (G), a source terminal (S) and a drain terminal (D) ; a diode (30) connected at one connection point to the drain terminal (D) of the field-effect transistor (20) and connected at a further connection point to the first output (A) of the thermal sensor (1); and a thermoelectric generator (10) adapted to provide a temperature dependent voltage between a first and a second connection point, the first connection point being connected to the gate terminal (G) of the field effect transistor (20) and the second connection point being connected to the Source terminal (S) of the field effect transistor (20) and the second output (B) of the thermal sensor (1) is connected.

Thermal sensor (1) according to claim 1, wherein the thermoelectric generator (10) comprises a thermocouple with at least two conductor tracks (11, 12) made of materials having different Seebeck coefficients.

A thermal sensor (1) according to claim 2, wherein the thermoelectric generator (10) comprises a thermopile having a plurality of thermocouples

Thermosensor (1) according to one of claims 1 to 3, wherein at least the field effect transistor (20) and the first and second connection point of

thermoelectric generator (10) on a common substrate (2) are arranged.

Thermal sensor (1) according to one of claims 1 to 4, wherein the

Field effect transistor (20), the first and second connection point of thermoelectric generator (10) and the diode (30) on a common substrate (2) are arranged.

Sensor array with a plurality of thermal sensors (1) according to one of

Claims 1 to 5, wherein the plurality of thermal sensors (1) are arranged in a matrix of rows and columns and each thermal sensor (1) of the plurality of thermal sensors (1) is individually addressable.

Camera with a sensor array according to claim 6.

Method (100) for producing a thermal sensor (1), comprising

Temperature-dependent output signal (U_temp) between a first and a second output (A, B) provides, with the steps:

Providing (1 10) a field effect transistor (20) having a gate terminal (G), a source terminal (S) and a drain terminal (D);

Providing (120) a diode (30);

Providing (130) a thermoelectric generator (10) which is adapted to connect between a first and a second connection point

to provide temperature-dependent voltage;

Connecting (140) a connection point of the diode to the drain terminal (D) of the field effect transistor (20);

Connecting (150) a further connection point of the diode (30) to the first output (A) of the thermal sensor (1);

Connecting (160) the first terminal of the thermoelectric generator (10) to the gate terminal (G) of the field effect transistor (10); and

Connecting (170) the second connection point of the thermoelectric generator (10) to the source terminal (S) of the field effect transistor and the second output (B) of the thermal sensor (1).