CN110940706A

CN110940706A - Gas sensitive Hall device

Info

Publication number: CN110940706A
Application number: CN201910025481.4A
Authority: CN
Inventors: W·布罗伊尔; M·艾克金格
Original assignee: Infineon Technologies AG
Current assignee: Infineon Technologies AG
Priority date: 2018-09-25
Filing date: 2019-01-11
Publication date: 2020-03-31
Also published as: DE102019214694A1

Abstract

Disclosed herein is a gas sensitive hall device. A chemically sensitive hall device having: a substrate; a chemically sensitive layer disposed on the substrate and configured to operatively interact with atoms or molecules of a gaseous or liquid fluid; a first electrode connected to the chemically sensitive layer and configured to feed a sensor current through the chemically sensitive layer along a first direction; and a second electrode connected to the chemically sensitive layer and configured to tap the hall voltage at the chemically sensitive layer along a second direction.

Description

Gas sensitive Hall device

Technical Field

The present invention relates to the field of gas sensors, and in particular to gas sensitive hall devices for detecting specific gases using the hall effect.

Background

The gas sensor may be used to measure the concentration of a target gas. In most gas sensors, the target gas is oxidized or reduced to an electrode, which results in a measurable sensor current. Integrated gas sensors utilize a gas-sensitive layer disposed on a semiconductor substrate. Many commercial chemical gas sensors utilize a gas-sensitive Metal Oxide (MOX) layer disposed on a semiconductor material. Such sensors can be produced at relatively low cost and exhibit high sensitivity. Among MOX materials, tin oxide is often used in solid state sensors.

Recently, graphene is used as a gas sensor material due to its unique electrical characteristics. The band structure of graphene makes it particularly sensitive to chemical doping. Even the withdrawal or donation of a small number of electrons causes the fermi level to deviate significantly from the dirac point and therefore even small changes in the number of charge carriers have a significant effect on the resistance of the graphene layer. In addition to its band structure, graphene has many other properties that make it particularly suitable for applications in gas sensors. Single layer graphene has every atom at the surface, with high metal conductivity even though there are very few charge carriers. In addition, it has few crystal defects, resulting in low johnson noise. A low noise level in the graphene device means that very small changes in resistivity (i.e. small sensor response) can be measured, resulting in a high sensitivity sensor. Graphene is also chemically very stable due to its strong bonds and lack of defects. The conductivity of graphene allows direct measurement of resistance, and the robustness of graphene allows layers of only one atom thickness to be processed into gas sensors.

Other gas sensors utilize a two-dimensional electron gas (2DEG) layer that is sensitive to the presence of a particular gas. For example, a two-dimensional electron gas (2DEG) formed at the interface of an AlGaN/GaN layer grown on a silicon substrate may be used to detect nitrogen oxides (NOx). The interaction of the oxynitride with the open gate region can reversibly change the conductivity of the 2DEG in the presence of humidity.

As mentioned above, the measurable effect in solid state gas sensors is typically a change in the conductivity (or resistivity) of the gas-sensitive layer. Recent studies have shown that gas-sensitive layers (or generally chemically sensitive layers) such as graphene layers can also be used to form hall bars. Measurable lateral voltages (e.g., hall voltages) caused by the hall effect also exhibit significant sensitivity to the presence of particular atoms or molecules of a gas or liquid fluid. It is therefore an object of the present invention to provide a sensor that utilizes the hall effect in a chemically sensitive layer.

Drawings

The invention may be better understood with reference to the following description and accompanying drawings. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. In the drawings:

fig. 1 is a cross-sectional view of a first exemplary embodiment of a gas sensitive hall element including a back gate for controlling the charge carrier density in the gas sensitive layer of the hall element.

Fig. 2 is a top view corresponding to the cross-sectional view of fig. 1.

Fig. 3 is a circuit diagram illustrating the use of the hall element of fig. 1 and 2.

Fig. 4 is a cross-sectional view of a second exemplary embodiment of a gas sensitive hall element including a heating coil for regenerating the gas sensitive layer of the hall element.

FIG. 5 is a cross-sectional view of a third exemplary embodiment of a gas sensitive Hall element including a permanent magnet for generating a magnetic field to magnetically bias the Hall element.

Fig. 6 shows a top view of a fourth exemplary embodiment of a gas sensitive hall element comprising a micro-heater (polysilicon resistor for heating).

Fig. 7A-7E show top views of different geometries that can be used to form the hall element.

Fig. 8 includes two graphs showing ohmic resistivity and hall resistivity with respect to a gate voltage applied to a back gate of the gas sensor according to fig. 1.

Fig. 9 shows an exemplary circuit for controlling the gate voltage applied to the back gate of the gas sensor according to fig. 1.

FIG. 10 is a cross-sectional view of a first exemplary embodiment of a gas sensitive Hall element formed on a silicon film.

FIG. 11 is a top view of an array of Hall elements that can be used to differentially measure or detect different gases.

Fig. 12 schematically illustrates another example of a hall element array that can be controlled using a multiplexer/demultiplexer circuit to select one or more particular hall elements in the array.

FIG. 13 shows a flow chart illustrating a method of operating the gas sensor described herein.

Fig. 14A to 14C show two exemplary adjustment schemes for adjusting the gate voltage applied to the back gate of the hall element by means of a block diagram and a timing diagram.

FIG. 15 is a cross-sectional view of a fifth exemplary embodiment of a gas sensitive Hall device.

FIG. 16 shows a flow chart of a method of operating the gas sensitive Hall device of FIG. 15.

Fig. 17A to 17B show rotation current pattern examples of the gas sensitive hall device of fig. 15.

Detailed Description

In the exemplary embodiments described below, graphene layers are used as one possible option for the gas-sensitive layer. However, other materials may be used as an alternative to graphene. The choice of material may depend on the actual application and in particular on the physical and chemical properties of the gas molecules to be detected.

Fig. 1 is a cross-sectional view of an exemplary solid-state gas sensor formed on a silicon substrate 1. Fig. 2 shows a corresponding top view. It should be noted that other substrate materials may be used as an alternative to silicon. The present illustration shows only the structure of the gas sensor. However, other components and circuits (e.g., control, driver and evaluation circuits) may be integrated in the same substrate and/or the same chip package as the gas sensor.

A conductive back gate region 10 is formed in the substrate 1, for example by depositing a metal layer (e.g. in a recess on the top surface of the substrate) or creating a doped semiconductor region by, for example, diffusion of dopants, ion implantation, etc. Alternatively, a polycrystalline silicon (polysilicon) layer may be deposited to form the back gate region 10. The isolation layer 2 is formed on the top surface of the substrate 1 such that the isolation layer 2 covers the back gate region 10 from the gas sensitive layer 15 formed on top of the isolation layer 2. In the case of using graphene as a gas-sensitive material for forming the gas-sensitive layer 15, the separation layer 2 may be made of hexagonal boron nitride (h-BN). Boron nitride is isoelectronic to graphene and the h-BN spacer can reduce the waviness of the graphene layer (compared to using a silicon oxide spacer) and the spatial non-uniformity of the charge carrier density in the graphene layer 15. As described above, the hall effect occurring in the gas sensitive layer 15 when exposed to the magnetic field B will be evaluated in order to detect gas molecules or measure gas concentration. Thus, the gas sensing layer 15 can be considered as a Hall plate (sometimes also referred to as a Hall bar). Alternatively, barrier layer 2 may be formed using molybdenum disulfide (MoS2) or an oxide or nitride of another material (e.g., silicon oxide). As described above, the gas sensing layer 15 may be formed using a layer forming a two-dimensional electron gas (2DEG) instead of graphene. The 2DEG layer may be present in III-V semiconductor heterostructures based on, for example, InAs, InSb, GaAs, GaN, etc. The purpose and function of the back gate will be described later with reference to fig. 8 and 9.

The gas-sensitive hall plate 15 is contacted by

force contact electrodes

11 and 12 and sensing contact electrodes 21 and 22 (see also the top view of fig. 2) contacting the top surface of the hall plate 15. The

force contact electrodes

11, 12 may be formed of metal (e.g., gold, aluminum, etc.) and arranged at opposite ends of the gas sensitive hall plate 15 along the longitudinal direction. The

sensing contact electrodes

21, 22 may also be formed of metal (e.g., gold, aluminum, etc.), but are arranged at opposite ends of the gas sensitive hall plate 15 along a transverse direction (which is perpendicular to the longitudinal direction). The

force contact electrodes

11, 12 serve for feeding the sensor current i_HPassing the sensor current i through the gas-sensitive Hall plate 15_HSubstantially in the longitudinal direction through the hall plate 15. Due to the hall effect, when exposed to a magnetic field B oriented perpendicular to the top surface of the hall plate 15, a voltage is generated laterally across the current carrying hall plate 15. This voltage is also referred to as "hall voltage" and can be tapped at the hall plate 15 via the

sensing contact electrodes

21, 22.

Fig. 3 shows the above-described situation by means of a circuit diagram. Thus, the current source Q_iGenerating a sensor current i_HThe sensor current i_HIs applied to the first force contact electrode 11 and is discharged from the second force contact electrode 12. When exposed to a magnetic field as shown in FIG. 1, a Hall voltage is generated between the sensing contact electrodes 21 and 22V_H. In fig. 3, the meter is connected to

sensing contact electrodes

21 and 22. It will be understood, however, that the meter is only representative for processing hall voltage V_HIn order to determine any circuit indicative of the desired output of the gas molecules 3 interacting with the gas sensitive hall plate 15 (see fig. 1).

Hall voltage V_HCan be calculated according to the following equation

V_H＝R_H·_HB/d (1)

Where d is the thickness of the gas-sensitive Hall plate (see FIG. 1). Scale factor R_HCommonly referred to as the hall constant, and has a cubic meter size per coulomb. It can be calculated as:

RH＝(n·q)^-1(2)

in equation 2, the parameter n represents the charge carrier density (e.g., number of electrons per cubic meter) and the parameter q represents the charge per charge carrier (e.g., the base charge-1602 · 10 in the case of electrons)^-19C) In that respect In the case of electron conduction (q ═ e), the hall constant can also be expressed as:

R_H＝ρ·μ＝μ/σ (3)

where ρ represents the specific resistance of the hall plate 15(σ represents the corresponding conductivity), and μ represents the electron mobility. In view of equations 2 and 3, the hall constant is substantially dependent on the conductivity (which is proportional to the charge carrier density) and the charge carrier mobility.

When molecules are adsorbed at the surface of the gas-sensitive layer 15, the gas molecules 3 can be detected (see fig. 1). Due to this interaction between the gas-sensitive layer 15 and the gas molecules 3, the charge carrier density or charge carrier mobility (or both) of the layer 15 changes, which results in a hall constant R_HAnd a corresponding change in the specific resistance p of the gas-sensitive layer 15. The changes in specific resistance mentioned in gas-sensitive resistive sensors are measured using ohm's law, resulting in a relatively small sensor signal. In contrast, the effect is significantly greater when the hall voltage is evaluated. The lower the charge carrier density, the higher the charge carrier mobility and the higher the hall constant. When the gas sensitive layer 15 (Hall plate) is thin (d is small) and the magnetic flux density B is high, the Hall plateThe effect can be further "amplified" by a factor B/d (see fig. 1). Therefore, by using a thin gas sensitive layer having a hall plate, a gas sensor of high sensitivity can be constructed.

Fig. 4 shows a cross-sectional view of a further exemplary embodiment of a gas-sensitive hall sensor. The example of fig. 4 is substantially the same as the previous example of fig. 1, except that an additional coil 18 is provided in the substrate 1. The coil may be integrated in the silicon substrate using any known technique. Similar techniques are used to produce coils for integrated coreless transformers and the like. The coil 18 can be used to generate a magnetic field B (during the measurement period) and/or to generate heat to heat the gas-sensitive layer for desorption of gas molecules from the gas-sensitive layer 15 (during regeneration). For heating purposes, a polysilicon (polycrystalline silicon) micro-heater may be used instead of the coil 18 (see description with reference to fig. 6). The components shown in fig. 4 are identical to those of fig. 1, except for the coil 18, and therefore the corresponding description is not repeated here.

Fig. 5 shows a cross-sectional view of a further exemplary embodiment of a gas-sensitive hall sensor. The example of fig. 5 is essentially the same as the previous fig. 4, but wherein an additional permanent magnet 4 is arranged below the semiconductor substrate 1. The permanent magnet 4 is perpendicularly magnetized to generate a vertically oriented magnetic field B (i.e., perpendicular to the surface of the hall plate 15), which is required for the operation of the gas sensor. In this case, the heating coil 18 is used for heating (regeneration) of the gas-sensitive layer 15. The components shown in fig. 5 are the same as those in fig. 4 except for the permanent magnet 4, and therefore, the corresponding description is not repeated here.

Fig. 6 is a top view showing substantially the same example as shown in fig. 2, but with an additional polysilicon micro-heater disposed around the gas sensitive hall plate 15 on the substrate 1. The micro-heater is formed of a strip line made of polysilicon. However, a material other than polysilicon (e.g., metal) may be used instead. The strip line forms a loop around the hall plate 15 on the substrate 1. However, the strip line may also be arranged below the hall plate 15 (below the isolation layer 2, see fig. 1), and may also have a different geometry (e.g. a meandering shape). When supplied with a current i_HEATTime, energy R_POLY2·i_HEATIs dissipated into the substrate and the local temperature of the substrate 1 and thus the hall plate 15 increases. Controllable current source Q_HIs representative of a current i configured to be provided to the microheater_HEATAny electronic circuit of (1). As described above, the micro-heater may be activated periodically to "refresh" the hall plate 15 (desorb gas atoms/molecules from the hall plate) in each measurement cycle. In case the back gate region 10 (not shown in top view, see cross-section of fig. 1) is formed of a polysilicon layer, the back gate region may additionally serve as a micro-heater, thus avoiding the need for a separate micro-heater.

In the example of fig. 1 to 6, the hall plate 15 has a rectangular plate shape. However, the hall plate 15 does not necessarily have to have a rectangular layout. Fig. 7 (fig. 7A to 7D) shows a top view of different possible layouts for the hall plate 15. Fig. 7A shows a rectangular shape as in the previous example. Fig. 7B shows a square layout. Fig. 7C is an octagonal layout, and fig. 7D shows a cross-shaped complex polygonal layout. Various other arrangements are possible. The exemplary layout shown in FIG. 7E allows measurement of the Hall voltage V_H(in the transverse direction) and due to the ohmic resistance R of the Hall plate 15_XXInduced voltage drop V_S(see also FIG. 8, top panel), where V_S＝R_XX·i_H。

As described above, the charge carrier density n (see the examples of fig. 1 to 5) in the gas sensitive layer 15 affects the hall constant R_H(see equation 2) and the charge carrier density n is influenced by the gas molecules 3 adsorbed at the surface of the gas-sensitive layer 15 (hall plate). Usually, the Hall constant R_HIncreasing with decreasing charge carrier density n. It is also possible to control the gate voltage V by varying the gate voltage_GIs applied to the back gate region 10 to control the charge carrier density n (see fig. 1, 4 and 5). The diagram of fig. 8 shows the voltage V_GHow to influence the (ohmic) resistance R of the gas-sensitive layer 15_XX(see top diagram of FIG. 8) and Hall constant R_H(see bottom view of FIG. 8). The solid line in the graph of fig. 8 indicates a case where the gas molecules 3 are not present, and the gas molecules 3 can be adsorbed at the gas sensitive layer 15. Characteristic curve (solid line) in existenceThe gas molecules 3 move to the right or to the left in the case of the same. Where the gas molecule is a donor (e.g. NH)₃) In the case of (1), the curve moves to the right (dotted line) and the gas molecule is the receptor (NO)₂) In the case of (2), the curve moves to the right (dashed line). In other words, the gate voltage V can be changed_GTo "calibrate" the hall plate. Furthermore, the back gate allows for applying an appropriate gate voltage V_GTo "switch" between electron conduction and hole conduction, with a Hall constant R_HPositive for hole conduction and negative in the case of electron conduction. When the holes and electrons are in equilibrium (at the so-called dirac point), the hall constant is zero.

Fig. 9 is a diagram showing a gate voltage V that can be used for driving a gas sensor and controlling the application to the back gate 10 of the gas sensor_GA circuit diagram of an exemplary circuit arrangement. In the present example, a sensor control unit 50 comprising a gate control circuit provides a constant sensor current i_HCurrent i_HAre fed through the gas-sensitive hall plate 15 (see fig. 1) via the

force contact electrodes

11 and 12. Before starting actual measurement, by appropriately adjusting the gate voltage V applied to the back gate 10 (see fig. 1) of the gas sensor_GThe obtained Hall voltage V can be used_H(see equation 1) to zero. This calibration (V)_H0) allows for highly sensitive detection/measurement of gas molecules or changes in the concentration of gas molecules in the surrounding atmosphere. Furthermore, it allows to differentiate the use as donor (e.g. NH)₃) Or receptors (e.g. NO)₂) The gas molecules of (1). Thus, the sensor may also be used in liquids to distinguish OH^-(hydroxide) and H3O⁺(oxonium) ion, i.e. for measuring pH. In this case, it should be noted that the embodiments described herein may also be used in a liquid atmosphere rather than in a gaseous atmosphere, depending on the material used for the hall plate 12. The term "chemically sensitive" is used as a generic term for both "gas sensitive" and "liquid sensitive".

In one exemplary embodiment, the Hall voltage V_HIs continuously adjusted to zero (for a constant magnetic field B). In this case, the gas sensor continues at the dirac pointOperate, and can use the Hall voltage V_HGate voltage V required for zero_GAs a sensor signal indicating the presence of gas molecules.

As described above with reference to fig. 4, a micro-heater may be provided to heat the gas sensitive hall plate 15 in order to reabsorb gas molecules previously adsorbed at the surface of the gas sensitive hall plate 15. Although in the previous example of fig. 4a heating coil was used to heat the substrate and thus the hall plate 15, current/heat is instead fed through the back gate region 10. Resistance of the back gate region 10 (represented by the resistor R in fig. 10)_BGRepresents) cause i_HEAT2·R_BGWhich heats the back gate region 10 and thus the gas sensitive hall plate 15 above. To achieve the desired temperature increase, the heat capacity of the heated material should be small. This is the case when the mass of the heated material is small; and this can be achieved by forming the gas-sensitive layer 15 on the film 1', as shown in the example of fig. 10. The cavity 1 ″ in the substrate 1 under the film 1' is effectively thermally isolated and is therefore surrounded by a current i in the back gate region 10_HEATMost of the generated heat is dissipated through the hall plate 15.

For repeated measurements, the gas-sensitive layer 15 can be cyclically regenerated by heating (see fig. 4, 5 and 10). After regeneration of the gas-sensitive layer 15, calibration (i.e. gate voltage V) can then be performed_GAdjustment of) as explained with reference to fig. 9.

Fig. 11 shows an array of

hall plates

15, 15', 15 ", 15'" which are connected in series such that they carry a current source Q_iThe same sensor current i is supplied_H(see FIG. 3). In the present case, the array consists of four hall plates 15. However, in different embodiments, only two hall plates may be provided (e.g., for differential measurement). Other embodiments may include three or more hall plates. Due to the series connection, the force contact electrode 12 of the first hall plate 15 and the force contact electrode 11 'of the second hall plate 15' may be formed as one body. The sensitivity to gas atoms or molecules may be different for

different hall plates

15, 15', 15 ", 15'". In this case, the Hall plates may be respectively arranged on the Hall plates15. Hall voltage V tapped at 15', 15 ", 15' ″_H、V_H'、V_H"and V_H"' is different and may indicate interaction of a gas or a particular gas component with the Hall plate. The array of

hall plates

15, 15', 15 ", 15'" may be formed on a single semiconductor chip. Alternatively, separate chips may be used for different hall plates, however, these different hall plates may be included in the same chip package. In the case of differential measurement, an array of two hall plates 15 and 15' can be used, with passivation on the hall plates so that it cannot interact with gas molecules in the environment. Both hall-plates 15 and 15' see the same sensor current i_HAnd the same magnetic field B, but only one hall plate is subjected to the gas. In this case, the Hall voltage V of the two Hall plates can be evaluated_HAnd V_H' Difference V_H-V_H' to detect gas atoms/molecules and/or to measure their concentration in the surrounding atmosphere.

Fig. 12 schematically illustrates another example of a hall element array that can be controlled using a multiplexer/demultiplexer circuit to select one or more particular hall elements in the array. By appropriate control of the multiplexer MUX and the demultiplexer DEMUX, one or more individual hall plates 15 in the array can be selected and used for a particular measurement. The hall plates 15 may be arranged in a matrix and distributed along rows and columns, as shown in fig. 12. However, alternative arrangements are possible. The control unit 50 may perform a similar function to the control circuit 50 shown in fig. 9. That is, the control unit 50 supplies the sensor current i to the selected hall element 15_HReceiving the Hall voltage V tapped at the selected Hall element 15_HAnd applying a gate voltage V to the selected Hall element 15_G. Depending on the actual implementation, the gate voltage V may be adjusted_GSo that the Hall voltage V_HHeld at the set point of zero volts. However, different adjustment schemes may be used. May be provided by selection signals SELROW and SELROW, respectively, supplied to a multiplexer MUX and a demultiplexer DEMUXSELCOL to select the hall element. The multiplexer MUX is configured to couple a signal (e.g., a gate voltage V)_GAnd/or sensor current i_HOr represents V_GOr i_HSignal for activating the micro-heater, etc.) to be directed by the select signal S_ROWAn identified hall element. The demultiplexer DEMUX is configured to be activated by a selection signal S_COLSignals tapped at identified Hall elements (e.g. Hall voltage V)_HOr represents V_HSignal(s) to the control circuit 50.

In the present example as described above, a specific hall element may be selected and then used for detecting gas atoms/molecules and/or for measuring the concentration of gas atoms/molecules in the surrounding atmosphere. Each hall element may be chemically functionalized differently to be sensitive to different gas atoms/molecules. By making a series of measurements and selecting different hall elements in sequence, different types of gases can be identified. Further, more than one hall element may be selected at a time. In this case, two or more hall elements may be connected in parallel to increase sensitivity (because the total chemically active area of the gas sensitive layer 15 is increased). In this case, "parallel connection" means the sensor output (here tapped hall voltage V)_H) Are connected in parallel. With respect to sensor current i_HThe Hall elements 15 are connected in series such that each Hall element 15 carries the same sensor current i_H。

FIG. 13 shows a flow chart illustrating a method of operating the gas sensor described herein. The method may be implemented, for example, by using a suitably configured control unit, such as the sensor control unit 50 in the example of fig. 9. At the start of the measurement, the gas sensitive hall plate is "refreshed" by heating the sensor. The heating results in desorption of gas molecules/atoms that have previously been adsorbed at the surface of the gas sensitive hall plate (see fig. 5). For this purpose, the micro-heaters comprised in the sensor may be activated for a defined period of time (and deactivated after this period of time, see fig. 13, step 121). During operation of the sensor, the hall voltage is continuously monitored (see fig. 9), and applied to the back gate of the sensorGate voltage V of region 10_G(see, e.g., fig. 5) is controlled such that the sensor operates at a defined operating point (see description with reference to fig. 8 and 9). The hall voltage may be processed (e.g., digitized) to obtain a desired form of measurement (see fig. 13, step 122). However, the desired information is already at the Hall voltage V_HAnd/or the back gate voltage V_GIn (1). Due to the gate voltage V_GWithout the need to continuously heat the sensor. Only when the gate voltage V is_GOnly when the predefined target range is left can the heater be activated again to refresh the hall plate and the measurement cycle starts again. Check the gate voltage V_GWhether or not it is still within the desired target range is labeled as step 123 in the example of fig. 13. As an alternative, the refreshing of the gas-sensitive hall plate can be time-triggered. In this case, the Hall plate will refresh when the predefined cycle time is over. When two sensors are used, the sensors may be operated in an alternating manner such that one sensor is refreshed (heater activated) while the other sensor is in a measurement mode (see fig. 13, step 122).

Fig. 14 shows, by means of a block diagram and a timing diagram, two exemplary regulation schemes for regulating the gate voltage applied to the back gate of a hall element. FIG. 14a shows a control loop that can be used to continuously adjust the gate voltage V of a particular Hall element 15_GSo that the Hall voltage V tapped at the Hall element 15_HRemains at a level of substantially zero volts. That is, the setpoint of the control loop is zero. In this case, the hall element 15 is operated continuously at the most sensitive operating point, i.e. the zero crossing of the curve in the bottom graph of fig. 8. In this regard, reference is made to the corresponding description of fig. 8 and 9. Since in this example the hall voltage V is_HSubstantially zero, the information on the concentration of gas atoms/molecules (or the information on whether gas atoms/molecules have been detected) is only at the gate voltage V applied to the back gate 10 of the hall element 15_GIn (1). If the gate voltage V is_GExceeding a predetermined value, a refresh of the hall element 15 may be triggered, for example by activating a micro-heater. In this examination, proportional/integral is used(PI) controller 501 to regulate the gate voltage V_GSo as to apply the Hall voltage V_HRemains at a zero level. However, other controller types may be used.

FIG. 14b shows a schematic diagram for regulating the gate voltage V_GAnother example of a control loop of (1). Unlike the previous example, the Hall voltage V_HInstead of being adjusted continuously to zero, at regular intervals or when the Hall voltage V is present_HExceeding a predefined threshold level V_HXThe time returns to zero. However, more complex schemes for zeroing the hall voltage may be used. In the present example, each time the Hall voltage reaches or exceeds the threshold level V_HXTime, Hall voltage V_HIs zeroed (by appropriate adjustment of the gate voltage V_G). This function is further illustrated by the timing diagram of fig. 14C. Hall voltage V at a time_HReaches the threshold value V_HXWhile regulating the gate voltage V_GTo apply a Hall voltage V_HIs set to zero. Then, the gate voltage is constant until the hall voltage V_HReaches the threshold value V again_HX. When the gate voltage V_GFrom a predetermined range (e.g. from-V)_GXTo V_GX) While the measurement may be suspended and the hall element may be refreshed, for example, by activating a micro-heater (see fig. 4-6).

FIG. 15 is a cross-sectional view of a fifth exemplary embodiment of a gas sensitive Hall device. The hall device is substantially the same as the example shown in fig. 1, except that the hall device does not comprise a back gate 10. Although the hall device and other hall devices are described as being gas sensitive, it should be understood that these devices are typically chemically sensitive.

Without the back gate 10, the specific gas molecule concentration is not detected. The gas sensitive hall plate 15 without the back gate 10 is quite sensitive to gas molecule types and detects the presence of gas molecule types (e.g., carbon monoxide, carbon dioxide, etc.) more simply than the specific gas concentration of such gas molecule types. If the presence of the gas molecule type is detected, safety measures may be taken, such as shutting down electrical equipment.

The components shown in fig. 15 are substantially the same as those of fig. 1 except for the back gate 10, and therefore, the description is not repeated here.

An array of the gas sensitive hall plates 15 of fig. 15 can be formed. The gas sensitive hall plates 15 are connected in series and chemically functionalized differently to provide sensitivity to different atoms or molecules. The array may be used to monitor a multi-phase gas composition or a multi-gas composition. Such an array is described in detail above, and for the sake of brevity, further description is not repeated here.

For example, the method may be implemented using a suitably configured control unit as described above with respect to fig. 9. At the start of the measurement, the gas sensitive hall plate 15 is "refreshed" by heating the sensor. As described above, the heating causes desorption of gas molecules/atoms that have been adsorbed before the heating at the surface of the gas sensitive hall plate 15. For this purpose, the micro-heater comprised in the sensor may be activated for a defined period of time and deactivated after this period of time (step 161) in order to achieve a desired heating of the gas sensitive hall-plate 15. During operation of the sensor, the hall voltage is continuously monitored (step 162). The hall voltage may be processed (e.g., digitized) to obtain a measurement of the qualitative concentration of the gas (step 163). As noted above, although the method is described as measuring gas, the present disclosure is more broadly directed to measuring chemicals.

The rotating current method results in a more accurate measurement by averaging the contributions of the defects of the gas sensitive hall plate 15 in order to reduce the offset. The force and sense electrodes are not fixed, but rather rotate. More specifically, in the rotating current mode, the electrodes feed the sensor current through the gas sensitive hall plate 15 in a first sequence of directions, and tap the hall voltage at the gas sensitive hall plate 15 in a second sequence of directions. The second sequence of directions may be perpendicular to the first sequence of directions. More specifically, the measurement direction is rotated according to predefined steps during the cycle, for example, by 90 ° at a certain clock frequency. The sensor current flows from one electrode to the facing electrode and the hall voltage is tapped at the transverse electrode, whereupon the measuring direction is rotated by 90 ° in the next cycle, i.e. in the next measuring phase. The hall voltages measured in the various measurement phases are evaluated by means of suitable correct signatures and weighted summation or subtraction. The offset voltages during rotation should substantially cancel each other out, thereby preserving the magnetic field dependent portion of the hall signal. In other words, by averaging the current rotation phase, the offset error is reduced while increasing the signal-to-noise ratio.

Fig. 17A shows a rotating current pattern example with four measurement phases rotating in a clockwise direction. In the first stage, the first diagonal has a Force1 electrode and a Force3 electrode, with the upper right corner being a Force1 electrode and the lower left corner being a Force3 electrode. On the other diagonal are the Sense4 electrode and the Sense2 electrode, the upper left corner is the Sense4 electrode and the lower right corner is the Sense2 electrode. Each of the electrodes is rotated clockwise 90 degrees in the second stage, another 90 degrees in the third stage, and another 90 degrees in the fourth stage. The stages following the fourth stage are the same as the first stage. In this example, there are four different stages, but there may be any number of suitable stages. Furthermore, there may be any number of rotations sufficient to obtain an average of the measured values to reduce the measurement offset to increase the measurement signal-to-noise ratio and thus increase the measurement accuracy.

Fig. 17B shows a rotating current pattern example with four measurement phases, which is similar to the example of fig. 17A, except that the rotation is in a counter-clockwise direction.

While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible that are within the scope of the invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents. In regard to the various functions performed by the above described components or structures (assemblies, devices, circuits, systems, etc.), the terms (including a reference to a "means") used to describe such components are intended to correspond, unless otherwise indicated, to any component or structure which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the invention.

Claims

1. A chemically sensitive hall device comprising:

a substrate;

a chemically sensitive layer disposed on the substrate and configured to operatively interact with atoms or molecules of a gaseous or liquid fluid;

a first electrode connected to the chemically sensitive layer and configured to feed a sensor current through the chemically sensitive layer; and

a second electrode connected to the chemically sensitive layer and configured to tap a Hall voltage at the chemically sensitive layer.

2. The chemically sensitive hall device of claim 1 further comprising:

a back gate disposed on or integrated in the substrate and isolated from the chemically sensitive layer by an isolation layer.

3. The chemically sensitive hall device of claim 1 wherein the hall device is a rotating current hall device.

4. The chemically sensitive hall device of claim 3 wherein the rotary current hall device is configured to cause the first and second electrodes to sequentially feed the sensor current through the chemically sensitive layer in a first direction and to tap the hall voltage at the chemically sensitive layer in a second direction.

5. A sensor array comprising at least two chemically sensitive hall devices according to claim 1, wherein the at least two chemically sensitive hall devices are integrated in one substrate or one sensor package.

6. The sensor array of claim 5, wherein at least two of the Hall devices have chemically sensitive layers that are chemically functionalized differently to provide sensitivity to different atoms or molecules.

7. The sensor array of claim 6, further comprising:

a control circuit coupled to the first electrode of the chemically sensitive Hall device and the second electrode of the chemically sensitive Hall device and configured to sequentially select the at least two Hall elements.

8. The sensor array of claim 6, further comprising:

a control circuit coupled to the first electrode of the chemically sensitive Hall device and the second electrode of the chemically sensitive Hall device and configured to select two or more Hall devices, and the selected Hall devices are connected in parallel.

9. The chemically sensitive hall device of claim 1 wherein a coil is integrated in the substrate below the chemically sensitive layer.

10. The chemically sensitive hall device of claim 9 wherein the coil is operable to supply current to generate a magnetic field having a field component perpendicular to the top surface of the chemically sensitive layer.

11. The chemically sensitive hall device of claim 10 wherein the coil is configured to operate as a heating coil to generate heat for heating the chemically sensitive layer.

12. The chemically sensitive hall device of claim 1 further comprising:

a permanent magnet configured to generate a magnetic field having a field component perpendicular to a top surface of the chemically sensitive layer.

13. The chemically sensitive hall device of claim 1 further comprising:

a heating circuit having a heat-generating element configured to heat the chemically sensitive layer to desorb atoms or molecules from the chemically sensitive layer.

14. The chemically sensitive hall device of claim 13 wherein the chemically sensitive layer functions as a heat-generating element and the sensor current is increased to heat the chemically sensitive layer.

15. The chemically sensitive hall device of claim 13 wherein the heating circuit is configured to cyclically heat the gas sensitive layer.

16. The chemically sensitive hall device of claim 1 wherein the chemically sensitive layer comprises a hall element.

17. A method for operating a sensor comprising a chemically sensitive hall element disposed on a substrate, the method comprising:

applying a sensor current to the chemically sensitive hall element such that the sensor current passes through the hall element in a first direction;

sensing a hall voltage at the hall element along a second direction; and

the hall voltage is monitored to obtain a qualitative concentration measurement of the chemical.

18. The method of claim 17, wherein the hall element is a rotating current hall element, and the applying and the sensing are performed according to a rotating current pattern.

19. The method of claim 17, wherein:

the hall element is a rotating current hall element,

the applying includes applying the sensor current to the chemically sensitive hall element such that the sensor current passes through the hall element in a first sequence of directions, an

The sensing includes sensing the hall voltage at the hall element along a second sequence of directions.

20. The method of claim 17, further comprising:

heating the chemically sensitive Hall element to desorb atoms or molecules from the chemically sensitive Hall element.