Cryo-temperature sensor and cryo-temperature measuring arrangement for temperature measurement in the cryogenic temperature range

Abstract

The invention relates to a cryogenic temperature sensor (01) for temperature measurement in the cryogenic temperature range. The sensor comprises a microtechnologically manufactured primary measuring resistor (03) and a secondary semiconductor measuring resistor (04), which are arranged on a common sensor carrier (02) and whose temperature-dependent resistance values ​​can be determined by a measuring circuit. The semiconductor measuring resistor (04) has an extreme point in its resistance-temperature characteristic curve in the cryogenic operating range of the temperature sensor, which extreme point can be predetermined during the manufacturing process. This extreme point can be used as the sensor's own fixed point for in-situ calibration of the primary measuring resistor (03). The invention also relates to a cryogenic temperature measuring arrangement for temperature measurement in the cryogenic temperature range, which comprises such a cryogenic temperature sensor (01).

Description

[0001] The invention relates to a cryogenic temperature sensor for temperature measurement in the cryogenic temperature range and to a cryogenic temperature measuring arrangement using this sensor.

[0002] In recent times, there have been increasing numbers of technical applications that require very low ambient temperatures, which must be measured precisely.

[0003] Cryogens or cryogenic fluids are materials whose boiling points are at very low temperatures (helium 4.2 K; hydrogen 20.3 K; nitrogen 77.3 K; argon 87.1 K; oxygen 90.2 K). Solid cryogens also exist, such as frozen carbon dioxide, which has a sublimation point of 194.5 K. Cryogens are used, for example, to freeze organic materials, cool superconductors, or as fuel for rocket engines. Cryogenic fluids are used in research laboratories and technical devices to provide very low-temperature environments.

[0004] In the context of the present invention, a cryogenic temperature range is considered to be below 200 K, preferably below 100 K, particularly preferably below 70 K.

[0005] For precise temperature measurement, different sensors are used in the current state of the art, depending on the accuracy requirements and temperature range. Common temperature sensors are often based on platinum measuring resistors (platinum resistance thermometers), which, according to DIN 60751, can be used for temperature measurement down to approximately 73 K.

[0006] Below this temperature, the sensitivity of platinum measuring resistors is low, so that they are only of limited use for accurate, high-resolution temperature measurement.

[0007] An additional problem in the cryogenic temperature range is that platinum measuring resistors must be calibrated for accurate measurements in this range, but there are no readily available fixed points for such calibration. The standardized fixed points of the International Temperature Scale (ITS-90) are formed by phase transformation points of various metals. The "Provisional Low Temperature Scale" (PLTS-2000) serves as an extension of the ITS-90 into the low-temperature range and covers a range from 0.902 mK to 1 K. The PLTS-2000 uses the relationship between the melting pressure of the helium-3 isotope and temperature to represent it; this requires considerable technical effort and can therefore only be implemented in a laboratory environment. In the cryogenic temperature range, such fixed points are hardly available for industrial applications.

[0008] EP 3 566 033 B1 describes a device for determining and / or monitoring the temperature of a medium. The device comprises a temperature sensor, a reference element for in-situ calibration and / or validation of the temperature sensor, and an electronic unit. The reference element consists at least partially of a material that exhibits a phase transition at a predetermined phase transition temperature in the temperature range relevant for calibrating the temperature sensor.

[0009] RU 2 602 400 C1 shows a measuring device that can be used for cryogenic temperatures. The measuring device comprises a reference resistor and a current source connected to the current input of the reference resistor. The resistance is measured in a 4-wire circuit using a constant current.

[0010] DE 10 2014 225 897 B3 describes a low-hysteresis high-temperature sensor. A thin conductor layer is applied in a meandering pattern on a ceramic substrate. The conductor layer consists of two individual meander structures connected in parallel. At least two of these parallel individual meander structures are connected in series. The conductor layer is designed as a thin-film resistor and is made of platinum. The ceramic substrate is made of Al2O3.

[0011] Based on the prior art, one object of the invention is to provide an inexpensive, improved cryogenic temperature sensor that allows sufficiently accurate temperature measurement in the cryogenic temperature range in an industrial environment. Furthermore, a cryogenic temperature measurement system using this cryogenic temperature sensor is to be specified.

[0012] These objects are achieved by a cryogenic temperature sensor according to claim 1 or by a cryogenic temperature measuring arrangement according to claim 10.

[0013] The cryogenic temperature sensor is suitable for temperature measurement in the cryogenic temperature range, in particular at temperatures < 70 K. The invention is based, among other things, on the discovery that semiconductor measuring resistors are more sensitive in the temperature range < 60 K than metallic measuring resistors or other microtechnologically manufactured measuring resistors, in particular platinum measuring resistors, and that they also exhibit an extreme point in their characteristic curve in this temperature range. The characteristic curve of a semiconductor measuring resistor regularly shows two extreme points, a maximum and a minimum, in the temperature range from 4 K to 300 K. In the cryogenic temperature sensor according to the invention, preferably only one extreme point is used for the measurement; whether maximum or minimum depends on the dopant used in the semiconductor. For example, the maximum (high point) is suitable for p-doped, e.g. boron-doped semiconductor resistors.In contrast, the minimum (low point) would be used for n-doped, e.g., phosphorus-doped semiconductor resistors. The precise position of the extreme point can be easily adjusted to a desired temperature during the manufacturing process using variable parameters (e.g., doping, annealing, substrate). The invention takes advantage of the fact that such an adjustable extreme point can be used as an (individual) sensor-specific fixed point to which a calibration measurement can be coupled, for example, for in-situ calibration of a primary measuring resistor assigned to the sensor.

[0014] It has been shown that not all semiconductor resistors are suitable for measurement in the cryogenic temperature range. For example, boron-doped or other p-doped semiconductor resistors with an implantation dose of 5 10 13 cm -2not suitable as cryogenic temperature sensors, as they show an exponential growth of the resistance value below 90 K. However, it was surprisingly found that semiconductor resistors with an implantation dose of 10 15 cm -2 have a different characteristic curve and are therefore suitable for thermometry purposes in the range from 8 K to 200 K.

[0015] The cryogenic temperature sensor according to the invention comprises at least one primary measuring resistor and at least one secondary semiconductor measuring resistor, which are arranged on a common sensor carrier and whose temperature-dependent resistance values ​​can be determined by a measuring circuit.

[0016] For the purposes of the invention, the primary measuring resistor is a microtechnologically manufactured measuring resistor. In the field, a microtechnologically manufactured measuring resistor is understood to be a resistor manufactured using thin-film processes or semiconductor processes used in microsystem technology, whose RT characteristic allows it to be used as a temperature sensor. The spectrum of suitable primary measuring resistors ranges from metal resistors and semiconductor resistors to ruthenium oxide resistors and carbon resistors. The primary measuring resistor is preferably a metallic measuring resistor, in particular a platinum measuring resistor. Alternatively, the primary measuring resistor can also be another microtechnologically manufactured measuring resistor made of pure metal.The primary measuring resistor can also be formed by Kondo systems, for example, AuFe, CuFe, or RhFe as materials with deliberately introduced magnetic impurities. Furthermore, the primary resistor can be a ruthenium oxide resistor (RuO2). Such primary measuring resistors can be calibrated and utilized as components of the cryogenic temperature sensor according to the invention, even outside the specifications of DIN 60751.

[0017] The semiconductor shunt has at least one selected extreme point in its characteristic curve within the cryogenic operating range of the temperature sensor. This defined extreme point can be used as the sensor's own fixed point for calibrating the primary shunt (e.g., platinum shunt), provided that both shunts are at the same temperature, which is achieved by the structural coupling on the sensor carrier.

[0018] Preferably, the extreme point in the characteristic curve is determined during the manufacturing process by the appropriate selection of a doping of the semiconductor material. Alternatively, other parameters can be used to define the extreme point at a desired location in the resistance-temperature characteristic curve. In addition to the doping, the base substrate can be selected alternatively or cumulatively, for example, or annealing steps can be performed that affect the characteristic curve. Other adjustable parameters in the manufacture of semiconductor measuring resistors are known to those skilled in the art.

[0019] The properties of the semiconductor measuring resistor are determined, among other things, by the following parameters: the doping concentration and the substrate used. If one of these parameters is changed, the RT characteristic changes. The characteristic curve of the semiconductor measuring resistor to be set within the scope of the present invention must be suitable for sensor applications (sufficient sensitivity and unambiguousness in combination with the primary measuring resistor).

[0020] A key advantage of the cryogenic temperature sensor is that the integrated combination of platinum and semiconductor resistors allows the usable operating range of the platinum resistor to be extended to temperatures below 100 K, sometimes even into the single-digit Kelvin range. The semiconductor resistor provides a sensor-specific fixed point in this low temperature range, which complements and extends the technically much more complex provision of naturally occurring fixed points (phase inversion points). By selecting suitable parameters during the manufacturing process, in particular the selection of a suitable semiconductor doping, this sensor-specific fixed point can be placed precisely within the desired operating range of the cryogenic temperature sensor. These measures are technically simple to implement, thus keeping the manufacturing costs of the cryogenic temperature sensor low.

[0021] According to a preferred embodiment, the extreme point of the resistance-temperature characteristic curve of the semiconductor measuring resistor lies in the range from 4 K to 100 K, preferably in the range from 50 K to 70 K. Such resistance maxima occur with a suitable doping concentration or dose for numerous substrate-dopant combinations. Particularly preferred embodiments of the doped semiconductor measuring resistor are, for example, n-SiB, p-SiP, p-InSb, p-GaAs, or p-GaSb. By appropriate selection, the semiconductor measuring resistor can thus be given a resistance extremum at a predetermined temperature in the cryogenic temperature range. This extreme point is then used as a fixed point or individual reference point for calibrating the platinum measuring resistor.

[0022] According to an advantageous embodiment of the cryogenic temperature sensor, the two measuring resistors are mounted on a ceramic carrier, which forms the sensor carrier. This is preferably achieved by means of a material-to-material connection, in particular using glass solder or a chip adhesive, which, however, is less temperature-stable. In this embodiment, it is particularly advantageous if the semiconductor measuring resistor is mounted symmetrically to the primary measuring resistor.

[0023] In general, it is important to ensure good thermal conductivity between the measuring resistors. If a joining compound is used, air pockets should be avoided. This ensures that both measuring resistors measure virtually the same temperatures.

[0024] Furthermore, the choice of materials used in the cryogenic temperature sensor should ensure good overall temperature stability. Since the temperature sensor is used in the cryogenic temperature range, it is preferable to combine only a few different materials that have similar thermal expansion coefficients in this temperature range, so that temperature changes cause only minimal mechanical stresses within the sensor.

[0025] In the aforementioned embodiment, in which the measuring resistors are connected to one another or to the sensor carrier by joining material, these requirements can be met if the base material of the primary measuring resistor is, for example, an Al2O3 ceramic, on which a resistance track (e.g. platinum track) runs preferably in a meandering shape, with a predefined resistance value of preferably 1,000 ohms (at 0°C). The substrate material of the doped semiconductor measuring resistor is silicon. The cryogenic temperature sensor designed in this way therefore has a layer sequence from bottom to top as follows: ceramic (Al2O3); vapor-deposited platinum track as a Pt1000 platinum measuring resistor; potting compound; a glass solder applied to the ceramic for joining the measuring resistors; above this, a semiconductor substrate (silicon) in which an implantation is introduced.

[0026] According to a modified embodiment, the cryogenic temperature sensor can be constructed in an even more integrated manner, eliminating the need for a separate joining step. In this case, the sensor carrier is formed by a silicon chip, on one side of which is formed the doped semiconductor measuring resistor and on the other side the micro-manufacturable primary measuring resistor, preferably a platinum measuring resistor. This allows the temperature sensor to be easily manufactured using known semiconductor process technologies.

[0027] In this embodiment, for example, the following layer sequence results from bottom to top: implantation layer, substrate (Si) of the semiconductor measuring resistor as sensor carrier, oxide layer (SiO2) as insulation layer, if necessary an adhesive layer (e.g. titanium), a platinum track as platinum measuring resistor.

[0028] A further developed embodiment is characterized by the fact that several microtechnologically manufactured primary measuring resistors, preferably several platinum measuring resistors, and / or several semiconductor measuring resistors form the cryogenic temperature sensor. This is particularly easy to implement with the design in which the measuring resistors are mounted on opposite sides of a chip. This results, among other things, in redundancy in the sensor, thus providing greater reliability.

[0029] The cryogenic temperature sensor combines two different, temperature-dependent measuring resistors, namely at least one primary measuring resistor, preferably a platinum resistor, and at least one doped semiconductor measuring resistor. The system-related ambiguity near an extreme point of the resistance-temperature characteristic curve of the doped semiconductor resistor is compensated for by the measuring circuit by taking into account the uniqueness of the characteristic curve of the primary measuring resistor (platinum resistor). In this way, a measurement uncertainty in the range of ±0.4 K (k=1) can be achieved. Due to the decreasing sensitivity of the RT characteristic curve of the doped semiconductor resistor, the measurement uncertainty can be significantly greater than ±0.4 K (k=1) near the extreme point and between 200 K and 300 K.

[0030] It should be noted that the extreme point in the RT characteristic curve, which can be used as a fixed point for calibration, can be set not only by the doping of the substrate material of the semiconductor measuring resistor, but also by other parameters. Several sub-goals can be pursued when determining the extreme point. For example, it may be desirable for this temperature reference point to be reproducibly realizable within a tolerance of ±0.2 K (k=1) across a sample. During the manufacturing process, technological parameters such as doping concentration and profile, substrate material, crystal orientation, dopant, and external magnetic field are particularly variable in order to shift the position of the temperature reference point (extreme point) primarily to temperatures below 60 K, particularly preferably below 50 K.According to an advantageous embodiment, the extreme point in the RT characteristic of the semiconductor resistance is determined by setting the aforementioned parameters at or near the phase transition point of hydrogen (14.025 K).

[0031] The cryogenic temperature measuring arrangement according to the invention for temperature measurement in the cryogenic temperature range comprises the cryogenic temperature sensor in one of the previously described embodiments and further comprises a measuring circuit configured to supply the measuring resistors of the temperature sensor with a measuring current, to determine the measuring voltages at the measuring resistors, and to determine the temperature-dependent resistance values ​​therefrom. Calibration values ​​for the platinum measuring resistor, which were previously determined by an initial calibration measurement, are taken into account. The in-situ calibration measurement is carried out at an extreme point in the resistance-temperature characteristic curve of the semiconductor measuring resistor. This in-situ calibration can be repeated as required, for example, whenever the extreme point is detected.

[0032] To derive a temperature value, the measuring circuit determines the corresponding temperature value from a resistance value after storing a calibration curve or corresponding calibration values ​​in a dedicated memory. The measuring resistors are preferably operated in a 4-wire circuit, with a constant current of, for example, 100 µA, followed by a voltage measurement and calculation of the resistance using Ohm's law.

[0033] According to a preferred embodiment, a Howland current source is used to provide a constant measuring current for each measuring resistor. The control of the measuring array and the processing of the measured values ​​can be carried out, for example, using a microcontroller that is part of the measuring circuit.

[0034] Further advantages and details of the invention will become apparent from the following description of preferred embodiments, with reference to the drawings. Fig. 1 a plan view and a perspective view of a first embodiment of a cryogenic temperature sensor according to the invention; Fig. 2 a schematic diagram of a second embodiment of the cryogenic temperature sensor in several views; Fig. 3 a simplified block diagram of a measuring circuit of a cryogenic temperature measuring arrangement according to the invention.

[0035] Fig. Figure 1 shows a simplified top view and a perspective view of a cryogenic temperature sensor 01 according to a first embodiment. The cryogenic temperature sensor has a sensor carrier 02 made of ceramic. A platinum measuring resistor 03 is mounted on the sensor carrier 02, which can be passivated, for example, with glass solder. A semiconductor measuring resistor 04 is attached to the sensor carrier with joining material, for example, glass solder, so that the semiconductor measuring resistor 04 is in good thermal contact with the platinum measuring resistor 03.

[0036] Fig. 2 shows several views of the basic construction of a second embodiment of the cryogenic temperature sensor 01. In this case, the sensor carrier 02 is formed by a section of a wafer, in particular a silicon chip. In the illustration, the chip is shown divided along an axis of symmetry in order to make the two sides of the chip visible. In fact, the chip 02 is preferably designed in one piece. The platinum measuring resistor 03 is applied to the right-hand side of the chip (in the right-hand illustration). The doped semiconductor measuring resistor 04 is attached to the left-hand side of the chip 02 (in the right-hand illustration). In this embodiment, a redundant system is created by doubling the semiconductor measuring resistor 04 and the platinum measuring resistor 03, which increases reliability.

[0037] For the appropriate doping of the semiconductor measuring resistor, the person skilled in the art can initially resort to numerous known materials described in the literature (see, for example, LONG, D.; ZOOK, J.; CHAPMAN, P.; TUFTE, O.: Electrical Properties and Resonance Scattering in Heavily Doped Semiconductors, Solid State Communications, Vol. 2, pp. 191-195, Pergamon Press. 1964). The doping concentrations are then to be determined in the manner already described above. For example, for a boron-doped semiconductor measuring resistor in silicon, an implantation dose of 1 10 15 cm -2 which corresponds to a doping concentration of approximately 1.2·10 19 cm -3 corresponds (depending on the tempering).

[0038] The implantation dose significantly influences the characteristic curve of doped semiconductor measuring resistors. Changing the doping concentration through annealing or changing the implantation dose results in a different characteristic curve and thus also shifts the maximum (extreme point) in the characteristic curve. Another parameter in the characteristic curve is the track width, which has no influence on the characteristic curve shape but does influence the value of the measured resistance. The greater the track width, the smaller the resistance value. Furthermore, the characteristic curve can be influenced by the selected substrate material, the crystal orientation, the dopant used (n- or p-doped), or an external magnetic field applied during the process.

[0039] Fig.Figure 3 shows a simplified block diagram of a measuring circuit of an embodiment of a cryogenic temperature measuring system, symbolizing both the basic circuit units and important steps in performing a measurement. The measuring circuit comprises an analog block 10 and a digital block 20. The analog block 10 has a current source 11 that supplies a constant measuring current of, for example, 100 µA to a measuring resistor, at which a voltage drop thereby occurs. The voltage value is supplied to an amplifier stage 12. The digital block 20 contains an analog-to-digital converter 21 that digitizes the amplified voltage value. A microprocessor 22 calculates the resistance value R from the digitized values. PW of the platinum measuring resistor and the resistance value R HWof the semiconductor measuring resistor. Calibration values ​​or characteristic curve functions for the temperature range to be covered are stored in a memory, which were recorded during a previous calibration (e.g., an initial calibration). Since the values ​​of the semiconductor measuring resistor are not unique in the extreme range due to the characteristic curve, the resistance value R, which must be determined unambiguously in each case, serves as the reference value. PW of the platinum resistor to select the appropriate resistance values ​​R HW of the semiconductor resistance. In the next step, the exact temperature value can be calculated, taking the selected values ​​into account. The temperature value can then be output and / or recorded. The measurement steps are repeated at a specified interval to enable continuous temperature measurement. Reference symbol 01 Cryo temperature sensor 02 Sensor carrier 03 Platinum measuring resistor 04 Semiconductor measuring resistor 10 Analog block 11 Power source 12 amplifier stage 20 digital blocks 21 analog-to-digital converters 22 microprocessor QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] EP 3 566 033 B1

[0008] RU 2 602 400 C1

[0009] DE 10 2014 225 897 B3

[0010] Cited non-patent literature

[0000] LONG, D.; ZOOK, J.; CHAPMAN, P.; TUFTE, O.: Electrical Properties and Resonance Scattering in Heavily Doped Semiconductors, Solid State Communications, Vol. 2, pp. 191-195, Pergamon Press. 1964

[0037]

Claims

[1] Cryo-temperature sensor (01) for temperature measurement in the cryogenic temperature range, comprising a microtechnologically producible primary measuring resistor (03) and a secondary semiconductor measuring resistor (04), which are arranged on a common sensor carrier (02) and whose temperature-dependent resistance values ​​can be determined by a measuring circuit, wherein the semiconductor measuring resistor (04) has an extreme point in its resistance-temperature characteristic curve in the cryogenic working range of the temperature sensor, which extreme point can be predetermined in the manufacturing process and which can be used as a sensor-specific fixed point for in-situ calibration of the primary measuring resistor (03). [2] Cryo-temperature sensor according to claim 1, characterized by that the semiconductor measuring resistor (04) has a predetermined doping by which the extreme point in its resistance-temperature characteristic curve is defined. [3] Cryo-temperature sensor according to claim 2, characterized bythat the semiconductor measuring resistor (04) has an implantation dose of 10 15 cm -2 or more. [4] Cryo-temperature sensor according to one of claims 1 to 3, characterized by that the extreme point of the resistance-temperature characteristic of the semiconductor measuring resistor (04) lies in the range from 4 K to 100 K, preferably in the range from 50 to 70 K. [5] Cryo-temperature sensor according to one of claims 1 to 4, characterized by that the semiconductor measuring resistor (04) is formed by one of the following doped substrates: n-SiB, p-SiP, p-InSb, p-GaAs or p-GaSb. [6] Cryo-temperature sensor according to one of claims 1 to 5, characterized by that the sensor carrier (02) is formed by a ceramic carrier and that the primary measuring resistor (03) and the semiconductor measuring resistor (04) are fastened to the ceramic carrier by a material connection. [7] Cryo-temperature sensor according to one of claims 1 to 5, characterized bythat the sensor carrier (02) is formed by a dopable silicon chip, on one side of which the doped semiconductor measuring resistor (04) and on the other side of which the primary measuring resistor (03) are formed. [8] Cryo-temperature sensor according to one of claims 1 to 7, characterized by that the primary measuring resistor is selected from the following group of microtechnologically manufactured measuring resistors: - metallic measuring resistors, - Platinum measuring resistors (03), - Kondo system measuring resistors, - Ruthenium oxide measuring resistors. - Carbon resistors. [9] Cryo-temperature sensor according to one of claims 1 to 8, characterized by that it comprises several primary measuring resistors (03) and / or several semiconductor measuring resistors (04). [10] Cryo-temperature measuring arrangement for temperature measurement in the cryogenic temperature range, comprising a cryo-temperature sensor (01) according to one of claims 1 to 9 with at least one microtechnologically producible primary measuring resistor (03) and at least one secondary semiconductor measuring resistor (04), and further comprising a measuring circuit which is configured to supply the measuring resistors (03; 04) of the temperature sensor with a measuring current, to determine the measuring voltages at the measuring resistors and to determine the temperature-dependent resistance values ​​therefrom. [11] Cryo-temperature measuring arrangement according to claim 10, characterized by that the primary measuring resistor (03) and the semiconductor measuring resistor (04) are arranged in a 4-wire circuit, which is part of the measuring circuit. [12] Cryo-temperature measuring arrangement according to claim 10 or 11, characterized bythat the primary measuring resistor (03) and the semiconductor measuring resistor (04) are each connected to a Howland current source, which each supplies a constant measuring current to the measuring resistor (03; 04).

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