Patent Description:
Industrial and commercial applications are increasingly utilizing flow sensors to measure and control the mass flow rates of gases and liquids. However, conventional flow sensor designs often exhibit drift characteristics that decrease their measurement sensitivities.

Applicant has identified a number of deficiencies and problems associated with conventional flow sensors. Through applied effort, ingenuity, and innovation, many of these identified problems have been solved by developing solutions that are included in embodiments of the present disclosure, many examples of which are described in detail herein. <CIT> discloses a thermal flowmeter with two thermocouples parallel to a centerline and partly disposed over a diaphragm. The junctions are disposed upstream and downstream of the heater, following a temperature isoline.

Reference will now be made to the accompanying drawings, which illustrate example embodiments and features of the present disclosure and are not necessarily drawn to scale. It will be understood that the components and structures illustrated in the drawings may or may not be present in various embodiments of the disclosure described herein. Accordingly, some embodiments or features of the present disclosure may include fewer or more components or structures than those shown in the drawings while not departing from the scope of the disclosure.

The following description should be read with reference to the drawings wherein like reference numerals indicate like elements throughout the several views. The detailed description and drawings show several embodiments which are meant to be illustrative of the disclosure. It should be understood that any numbering of disclosed features (e.g., first, second, etc.) and/or directional terms used in conjunction with disclosed features (e.g., front, back, under, above, etc.) are relative terms indicating illustrative relationships between the pertinent features. The word "example," when used herein, is intended to mean "serving as an example, instance, or illustration. " Any implementation described herein as an "example" is not necessarily preferred or advantageous over other implementations.

It should be understood at the outset that although illustrative implementations of one or more aspects are illustrated below, the disclosed assemblies, systems, and methods may be implemented using any number of techniques. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, but may be modified within the scope of the appended claims along with their full scope of equivalents. While values for dimensions of various elements are disclosed, the drawings may not be to scale.

Typically, hot wire anemometer flow sensor die outputs drift while powered. In these hot wire anemometer flow sensors, which typically use platinum as the resistor material, the drift in the sensor is due to stress relaxation in the platinum layer and changes in stress in the silicon nitride layers around the platinum which form the air bridge, in part because platinum has piezo-resistive properties whose resistance changes with stress. In other words, the drift in these hot wire anemometer flow sensors often is due to stress relaxation in the platinum layer and is impacted by the residual stress in the air bridge (also known as the microbridge). For example, drift has been directly correlated to the stress in the plasma enhanced chemical vapor deposition (PECVD) silicon nitride layer on the surface of the microbridge. This stress in the PECVD silicon nitride layer can change over time since the air bridge is constantly heated by a resistive heater, which is an integral part of the flow sensor. Experimentally, this drift has been measured at values up to about <NUM> uV per day at null flow. Accordingly, there is a need for a flow sensor that can be used with gases and liquids that exhibits low drift characteristics.

Example embodiments described herein provide systems, apparatuses, and methods for reducing or eliminating the drift experienced by conventional flow sensors by providing various arrangements for a thermopile-based flow sensing device. In some embodiments, by using a thermocouple or thermopile, the signal generated by the thermopile-based flow sensing device disclosed herein is a voltage source and is minimally responsive to film resistance. Without film resistance sensitivity, other sensitivities such as stress or magnetic resistance changes are negligible. Additional thermocouples give additional voltage, signal, and sensitivity, whereas a conventional resistive flow sensor does not have this advantage for sensitivity. In some instances, the thermopile structures may be fabricated on either a microbridge structure or a membrane structure. In some embodiments, the membrane structures disclosed herein may provide for the same thermopile structures as a microbridge plus additional structures not possible with a microbridge.

In some embodiments, the general flow for fabricating a thermopile flow sensor is as follows:.

In some embodiments, not part of the claimed invention, as discussed with reference to <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>, the heater structure may be located below a single set of thermocouples (e.g., one thermopile) with one side located upstream of the heater structure and the other side located downstream of the heater structure. In these arrangements, the thermocouples do not sit on the silicon die. Rather, the thermocouples are suspended over a cavity or reside on a membrane structure. In some embodiments, the set of thermocouples may be collectively referred to as a thermopile. In some embodiments, the thermopile may be placed on a thermally isolated structure, such as a bridge or a membrane, with the opposing thermocouples (e.g., cold junction, hot junction) oriented such that one set of junctions are upstream and the other set of junctions is downstream of the centerline of a heating element.

In some embodiments, as discussed with reference to <FIG>, <FIG>, and <FIG> the heater structure may be located between two sets of thermocouples (e.g., two thermopiles), with one set of thermocouples located upstream of the heater structure and the other set of thermocouples located downstream of the heater structure. In these arrangements, there are parasitics and each set of thermocouples has one side on the bulk silicon die, which can float in temperature.

In some embodiments, the following equation may be used to characterize the thermopile-based flow sensing devices disclosed herein: <MAT> where ΔV = potential difference; n = the number of thermocouples; S = Seebeck coefficient (also referred to as thermopower, thermoelectric power (TE), or thermoelectric sensitivity); ΔS = TE1 - TE2 (the thermoelectric power of the first thermoelectric material - the thermoelectric power of the second thermoelectric material); T = temperature; and ΔT = T<NUM> - Tref. (the temperature at the measured thermoelectric junction(s) - the temperature at the reference thermoelectric junction(s)). In some instances, such as is shown in <FIG>, T<NUM> may be measured on the membrane structure <NUM> using the downstream thermocouple junctions <NUM>, and may be measured on the bulk silicon using the downstream thermocouple junctions <NUM>. In other instances, such as is shown in <FIG>, the relative temperature difference ΔT may be measured on the membrane structure <NUM> using the upstream thermocouple junctions <NUM> and the downstream thermocouple junctions <NUM> without the use of a reference temperature.

There are many advantages of the embodiments disclosed herein, such as: (<NUM>) providing low drift or no drift devices (e.g., as discussed with reference to <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>); (<NUM>) providing potential compatibility with CMOS processing via unique combinations of thermocouple materials (e.g., as discussed with reference to <FIG>).

Although the disclosure describes the features of the thermopile-based flow sensing device disclosed herein with reference to a flow sensor, the thermopile-based flow sensing device disclosed herein may be used to test in any suitable sensor, detector, gauge, instrument, or application where precision heating or temperature detection is utilized, utilizable, or otherwise desirable.

<FIG> illustrates an example layout for an example thermopile-based flow sensing device <NUM> in accordance with some example embodiments described herein, not being part of the claimed invention. In some embodiments, the example thermopile-based flow sensing device <NUM> may be provided for sensing a flow of fluid <NUM> (e.g., a flow of a gas or liquid). In some embodiments, the example thermopile-based flow sensing device <NUM> may comprise a heating structure <NUM> having a centerline <NUM>. In some embodiments, the example thermopile-based flow sensing device <NUM> may further comprise a thermopile <NUM>. In some embodiments, at least a portion of the thermopile <NUM> may be disposed over the heating structure <NUM>.

In some embodiments, the thermopile <NUM> may comprise a plurality of thermocouples having a plurality of thermocouple junctions. In some embodiments, the plurality of thermocouples may have a plurality of upstream thermocouple junctions <NUM> (e.g., nineteen upstream thermocouple junctions) disposed upstream of the centerline <NUM> of the heating structure <NUM>. In some embodiments, the plurality of thermocouples may have a plurality of downstream thermocouple junctions <NUM> (e.g., nineteen downstream thermocouple junctions) disposed downstream of the centerline <NUM> of the heating structure <NUM>. In some embodiments, the plurality of upstream thermocouple junctions <NUM> and the plurality of downstream thermocouple junctions <NUM> may be disposed over the heating structure <NUM>. In some embodiments, the number of upstream thermocouple junctions <NUM> and the number of downstream thermocouple junctions <NUM> may be the same. In some embodiments, the number of upstream thermocouple junctions <NUM> and the number of downstream thermocouple junctions <NUM> may depend (e.g., may be a function of) the Seebeck coefficients of the thermocouple materials in the thermocouples and the desired output voltage.

In some embodiments, the example thermopile-based flow sensing device <NUM> may further comprise a plurality of upstream sample temperature sensing thermocouple junctions <NUM> (e.g., two upstream sample temperature sensing thermocouple junctions) disposed upstream of the centerline <NUM> of the heating structure <NUM>. In some embodiments, the example thermopile-based flow sensing device <NUM> may further comprise a plurality of downstream sample temperature sensing thermocouple junctions <NUM> (e.g., two downstream sample temperature sensing thermocouple junctions) disposed downstream of the centerline <NUM> of the heating structure <NUM>. In some embodiments, the plurality of upstream sample temperature sensing thermocouple junctions <NUM> and the plurality of downstream sample temperature sensing thermocouple junctions <NUM> may be disposed over the heating structure <NUM>.

In some embodiments, each of the plurality of upstream thermocouple junctions <NUM>, the plurality of downstream thermocouple junctions <NUM>, the plurality of upstream sample temperature sensing thermocouple junctions <NUM>, and the plurality of downstream sample temperature sensing thermocouple junctions <NUM> may comprise a respective interface between a first thermocouple material and a second thermocouple material as described in greater detail with reference to <FIG>.

In some embodiments, as shown in <FIG>, the example thermopile-based flow sensing device <NUM> may comprise a substrate defining a membrane structure <NUM>. In some embodiments, a portion of the heating structure <NUM> may be disposed over the membrane structure <NUM>. In some embodiments, the thermopile <NUM>, the plurality of thermocouples, the plurality of upstream thermocouple junctions <NUM>, the plurality of downstream thermocouple junctions <NUM>, the plurality of upstream sample temperature sensing thermocouple junctions <NUM>, the plurality of downstream sample temperature sensing thermocouple junctions <NUM>, one or more portions thereof, or a combination thereof may be disposed over the membrane structure <NUM>. In some embodiments, the membrane structure <NUM> may provide thermal isolation from the bulk (e.g., silicon) die, which may have a high thermal conductivity. In some embodiments, the shape of the membrane structure <NUM> may be rectangular, square, circular, oval, or any other suitable shape or combination thereof.

In other embodiments (not shown in <FIG> for the sake of brevity), the example thermopile-based flow sensing device <NUM> may comprise a substrate defining a microbridge structure. In some embodiments, a portion of the heating structure <NUM> may be disposed over the microbridge structure. In some embodiments, the thermopile <NUM>, the plurality of thermocouples, the plurality of upstream thermocouple junctions <NUM>, the plurality of downstream thermocouple junctions <NUM>, the plurality of upstream sample temperature sensing thermocouple junctions <NUM>, the plurality of downstream sample temperature sensing thermocouple junctions <NUM>, one or more portions thereof, or a combination thereof may be disposed over the microbridge structure.

<FIG> illustrates example temperature isolines <NUM> (e.g., including, but not limited to, temperature isoline 220A, maximum temperature difference isoline 220B (the temperature isoline that extends through about the locations where the maximum temperature difference occurs), and temperature isoline 220C) for an example thermopile-based flow sensing device <NUM> in accordance with some example embodiments described herein, not being part of the claimed invention.

In some embodiments, as shown in <FIG> and <FIG>, the example thermopile-based flow sensing device <NUM> may be provided for sensing a flow of fluid <NUM> (e.g., a flow of a gas or liquid). In some embodiments, the example thermopile-based flow sensing device <NUM> may comprise a heating structure <NUM> having a centerline <NUM> and an axis <NUM> arranged perpendicular to the centerline <NUM>. In some embodiments, the example thermopile-based flow sensing device <NUM> may further comprise a thermopile. In some embodiments, at least a portion of the thermopile may be disposed over the heating structure <NUM>.

In some embodiments, as shown in <FIG> and <FIG>, the thermopile may comprise a plurality of thermocouples having a plurality of thermocouple junctions. In some embodiments, the plurality of thermocouples may have a plurality of upstream thermocouple junctions <NUM> (e.g., seventeen upstream thermocouple junctions) disposed upstream of the centerline <NUM> of the heating structure <NUM>. In some embodiments, the plurality of thermocouples may have a plurality of downstream thermocouple junctions <NUM> (e.g., seventeen downstream thermocouple junctions) disposed downstream of the centerline <NUM> of the heating structure <NUM>. In some embodiments, the number of upstream thermocouple junctions <NUM> and the number of downstream thermocouple junctions <NUM> may be the same. In some embodiments, the number of upstream thermocouple junctions <NUM> and the number of downstream thermocouple junctions <NUM> may depend (e.g., may be a function of) the Seebeck coefficients of the thermocouple materials in the thermocouples and the desired output voltage.

In some embodiments, as shown in <FIG> and <FIG>, each of the plurality of upstream thermocouple junctions <NUM> and the plurality of downstream thermocouple junctions <NUM> may occur along a maximum temperature difference isoline 220B (e.g., the temperature isoline that extends through about the minimum temperature difference location <NUM> and the maximum temperature difference location <NUM>), where the farthest upstream thermocouple junction of the plurality of upstream thermocouple junctions <NUM> occurs at about a minimum temperature difference location <NUM>, and where the farthest downstream thermocouple junction of the plurality of downstream thermocouple junctions <NUM> occurs at about a maximum temperature difference location <NUM>, respectively. For example, a maximum temperature difference may be defined by a minimum temperature difference location <NUM> upstream of the centerline <NUM> and a maximum temperature difference located at a maximum temperature difference location <NUM> downstream of the centerline <NUM>. The plurality of upstream thermocouple junctions <NUM> may be disposed at about a plurality of locations on the maximum temperature difference isoline 220B. In other words, the plurality of upstream thermocouple junctions <NUM> may be disposed upstream of the centerline <NUM> at about a first plurality of points on an upstream portion of the maximum temperature difference isoline 220B that extends through the minimum temperature difference location <NUM>. The plurality of downstream thermocouple junctions <NUM> may be disposed downstream of the centerline <NUM> at about a second plurality of points on a downstream portion of the maximum temperature difference isoline 220B that extends through the maximum temperature difference location <NUM>. In some embodiments, the plurality of upstream thermocouple junctions <NUM> and the plurality of downstream thermocouple junctions <NUM> may not be disposed over the heating structure <NUM>.

<FIG> illustrates example minimum temperature isolines <NUM> disposed around the minimum temperature difference location <NUM>. <FIG> further illustrates example maximum temperature isolines <NUM> disposed around the maximum temperature difference location <NUM>.

In some embodiments, as shown in <FIG> and <FIG>, the minimum temperature difference location <NUM> may be located about <NUM> micrometers upstream of the centerline <NUM>. In some embodiments, as shown in <FIG> and <FIG>, the maximum temperature difference location <NUM> may be about <NUM> micrometers downstream of the centerline <NUM>. The locations of the minimum temperature difference location <NUM> and the maximum temperature difference location <NUM> may change with changes in the membrane structure <NUM> (e.g., shape, thickness), heating structure <NUM> (e.g., shape, thickness, material(s)), voltage applied to the heating structure <NUM>, and other structures.

In some embodiments, each of the plurality of upstream thermocouple junctions <NUM> and the plurality of downstream thermocouple junctions <NUM> may comprise a respective interface between a first thermocouple material and a second thermocouple material as described in greater detail with reference to <FIG>.

In some embodiments, as shown in <FIG> and <FIG>, the example thermopile-based flow sensing device <NUM> may comprise a substrate defining a membrane structure <NUM>. In some embodiments, a portion of the heating structure <NUM> may be disposed over the membrane structure <NUM>. In some embodiments, the thermopile, the plurality of thermocouples, the plurality of upstream thermocouple junctions <NUM>, the plurality of downstream thermocouple junctions <NUM>, one or more portions thereof, or a combination thereof may be disposed over the membrane structure <NUM>. In some embodiments, the membrane structure <NUM> may provide thermal isolation from the bulk (e.g., silicon) die, which may have a high thermal conductivity. In some embodiments, the shape of the membrane structure <NUM> may be rectangular, square, circular, oval, or any other suitable shape or combination thereof.

In other embodiments (not shown in <FIG> or <FIG> for the sake of brevity), the example thermopile-based flow sensing device <NUM> may comprise a substrate defining a microbridge structure. In some embodiments, a portion of the heating structure <NUM> may be disposed over the microbridge structure. In some embodiments, the thermopile, the plurality of thermocouples, the plurality of upstream thermocouple junctions <NUM>, the plurality of downstream thermocouple junctions <NUM>, one or more portions thereof, or a combination thereof may be disposed over the microbridge structure.

In some embodiments, the thermopile <NUM> may comprise a plurality of thermocouples having a plurality of thermocouple junctions. In some embodiments, the plurality of thermocouples may have a plurality of upstream thermocouple junctions <NUM> (e.g., nineteen upstream thermocouple junctions) disposed upstream of the centerline <NUM> of the heating structure <NUM>. In some embodiments, the plurality of thermocouples may have a plurality of downstream thermocouple junctions <NUM> (e.g., nineteen downstream thermocouple junctions) disposed downstream of the centerline <NUM> of the heating structure <NUM>. In some embodiments, the plurality of upstream thermocouple junctions <NUM> and the plurality of downstream thermocouple junctions <NUM> may not be disposed over the heating structure <NUM>. In some embodiments, the number of upstream thermocouple junctions <NUM> and the number of downstream thermocouple junctions <NUM> may be the same. In some embodiments, the number of upstream thermocouple junctions <NUM> and the number of downstream thermocouple junctions <NUM> may depend (e.g., may be a function of) the Seebeck coefficients of the thermocouple materials in the thermocouples and the desired output voltage.

In some embodiments, the example thermopile-based flow sensing device <NUM> may further comprise a plurality of upstream sample temperature sensing thermocouple junctions <NUM> (e.g., two upstream sample temperature sensing thermocouple junctions) disposed upstream of the centerline <NUM> of the heating structure <NUM>. In some embodiments, the example thermopile-based flow sensing device <NUM> may further comprise a plurality of downstream sample temperature sensing thermocouple junctions <NUM> (e.g., two downstream sample temperature sensing thermocouple junctions) disposed downstream of the centerline <NUM> of the heating structure <NUM>. In some embodiments, the plurality of upstream sample temperature sensing thermocouple junctions <NUM> and the plurality of downstream sample temperature sensing thermocouple junctions <NUM> may not be disposed over the heating structure <NUM>.

In some embodiments, the thermopile <NUM> may comprise a plurality of thermocouples having a plurality of thermocouple junctions. In some embodiments, the plurality of thermocouples may have a plurality of upstream thermocouple junctions <NUM> (e.g., nineteen upstream thermocouple junctions) disposed upstream of the centerline <NUM> of the heating structure <NUM>. In some embodiments, the plurality of thermocouples may have a plurality of downstream thermocouple junctions <NUM> (e.g., nineteen downstream thermocouple junctions) disposed downstream of the centerline <NUM> of the heating structure <NUM>. In some embodiments, the number of upstream thermocouple junctions <NUM> and the number of downstream thermocouple junctions <NUM> may be the same. In some embodiments, the number of upstream thermocouple junctions <NUM> and the number of downstream thermocouple junctions <NUM> may depend (e.g., may be a function of) the Seebeck coefficients of the thermocouple materials in the thermocouples and the desired output voltage.

In some embodiments, each of the plurality of upstream thermocouple junctions <NUM> and the plurality of downstream thermocouple junctions <NUM> may be aligned parallel to centerline <NUM> and occur along an upstream vertical line through about a minimum temperature difference location (e.g., minimum temperature difference location <NUM> shown in <FIG> and <FIG>) and a downstream vertical line through about a maximum temperature difference location (e.g., maximum temperature difference location <NUM> shown in <FIG> and <FIG>), respectively. For example, a maximum temperature difference may be defined by a minimum temperature difference located at a first location (e.g., minimum temperature difference location <NUM> shown in <FIG> and <FIG>) upstream of the centerline <NUM> and a maximum temperature difference located at a second location (e.g., maximum temperature difference location <NUM> shown in <FIG> and <FIG>) downstream of the centerline <NUM>; the plurality of upstream thermocouple junctions <NUM> may be disposed upstream of the centerline <NUM> at about a first plurality of points on a first line that extends through about the first location and is aligned substantially parallel to the centerline <NUM>; and the plurality of downstream thermocouple junctions <NUM> may be disposed downstream of the centerline <NUM> at about a second plurality of points on a second line that extends through about the second location and is aligned substantially parallel to the centerline <NUM>. In some embodiments, the plurality of upstream thermocouple junctions <NUM> and the plurality of downstream thermocouple junctions <NUM> may not be disposed over the heating structure <NUM>.

In some embodiments, each of the plurality of upstream thermocouple junctions <NUM> and the plurality of downstream thermocouple junctions <NUM> may occur along a maximum temperature difference isoline (e.g., maximum temperature difference isoline 220B shown in <FIG> and <FIG>), where the farthest upstream thermocouple junction of the plurality of upstream thermocouple junctions <NUM> occurs at about a minimum temperature difference location (e.g., minimum temperature difference location <NUM> shown in <FIG> and <FIG>), and where the farthest downstream thermocouple junction of the plurality of downstream thermocouple junctions <NUM> occurs at about a maximum temperature difference location (e.g., maximum temperature difference location <NUM> shown in <FIG> and <FIG>), respectively. For example, a maximum temperature difference may be defined by a minimum temperature difference located at a first location (e.g., minimum temperature difference location <NUM> shown in <FIG> and <FIG>) upstream of the centerline <NUM> and a maximum temperature difference located at a second location (e.g., maximum temperature difference location <NUM> shown in <FIG> and <FIG>) downstream of the centerline <NUM>; and the plurality of upstream thermocouple junctions <NUM> may be disposed at about a plurality of locations on a maximum temperature difference isoline (e.g., maximum temperature difference isoline 220B shown in <FIG> and <FIG>). In other words, the plurality of upstream thermocouple junctions <NUM> may be disposed upstream of the centerline <NUM> at about a first plurality of points on a first portion (e.g., an upstream portion) of a maximum temperature difference isoline that extends through the first location; and the plurality of downstream thermocouple junctions <NUM> may be disposed downstream of the centerline <NUM> at about a second plurality of points on a second portion (e.g., a downstream portion) of the maximum temperature difference isoline that extends through the second location. In some embodiments, the plurality of upstream thermocouple junctions <NUM> and the plurality of downstream thermocouple junctions <NUM> may not be disposed over the heating structure <NUM>.

<FIG> illustrates an example layout for an example thermopile-based flow sensing device <NUM> in accordance with some example embodiments described herein, according to the claimed invention. According to the invention, the example thermopile-based flow sensing device <NUM> is provided for sensing a flow of fluid <NUM> (e.g., a flow of a gas or liquid). According to the invention, the example thermopile-based flow sensing device <NUM> has to comprise a heating structure <NUM> having a centerline <NUM>. According to the invention, the example thermopile-based flow sensing device <NUM> has to further comprise a first thermopile <NUM> and a second thermopile <NUM>.

According to the invention, the first thermopile <NUM> has to comprise a plurality of upstream thermocouples having a first plurality of upstream thermocouple junctions <NUM> (e.g., nineteen upstream thermocouple junctions) disposed upstream of the centerline <NUM> of the heating structure <NUM> and a second plurality of upstream thermocouple junctions <NUM> (e.g., nineteen upstream thermocouple junctions) disposed further upstream of the centerline <NUM> of the heating structure <NUM>. In some embodiments, the number of the first plurality of upstream thermocouple junctions <NUM> and the number of the second plurality of upstream thermocouple junctions <NUM> may be the same. In some embodiments, the number of the first plurality of upstream thermocouple junctions <NUM> and the number of the second plurality of upstream thermocouple junctions <NUM> may depend (e.g., may be a function of) the Seebeck coefficients of the thermocouple materials in the thermocouples and the desired output voltage.

In some embodiments, the first plurality of upstream thermocouple junctions <NUM> and the second plurality of upstream thermocouple junctions <NUM> may not be disposed over the heating structure <NUM>. For example, a maximum temperature difference may be defined by a minimum temperature difference located at a first location (e.g., minimum temperature difference location <NUM> shown in <FIG> and <FIG>) upstream of the centerline <NUM> and a maximum temperature difference located at a second location (e.g., maximum temperature difference location <NUM> shown in <FIG> and <FIG>) downstream of the centerline <NUM>; the first plurality of upstream thermocouple junctions <NUM> has to be disposed upstream of the centerline <NUM> at about a first plurality of points on a first line that extends through about the first location and is aligned substantially parallel to the centerline <NUM>; and the second plurality of upstream thermocouple junctions <NUM> has to be disposed further upstream of the centerline <NUM> at about a second plurality of points on a second line that is aligned substantially parallel to the centerline <NUM>.

According to the invention, the second thermopile <NUM> has to comprise a plurality of downstream thermocouples having a first plurality of downstream thermocouple junctions <NUM> (e.g., nineteen downstream thermocouple junctions) disposed downstream of the centerline <NUM> of the heating structure <NUM> and a second plurality of downstream thermocouple junctions <NUM> (e.g., nineteen downstream thermocouple junctions) disposed further downstream of the centerline <NUM> of the heating structure <NUM>. In some embodiments, the number of the first plurality of downstream thermocouple junctions <NUM> and the number of the second plurality of downstream thermocouple junctions <NUM> may be the same. In some embodiments, the number of the first plurality of downstream thermocouple junctions <NUM> and the number of the second plurality of downstream thermocouple junctions <NUM> may depend (e.g., may be a function of) the Seebeck coefficients of the thermocouple materials in the thermocouples and the desired output voltage.

According to the invention, each of the first plurality of upstream thermocouple junctions <NUM> and the first plurality of downstream thermocouple junctions <NUM> has to be aligned parallel to centerline <NUM> and occur along an upstream vertical line through about a minimum temperature difference location (e.g., minimum temperature difference location <NUM> shown in <FIG> and <FIG>) and a downstream vertical line through about a maximum temperature difference location (e.g., maximum temperature difference location <NUM> shown in <FIG> and <FIG>), respectively. According to the invention, a maximum temperature difference has to be defined by a minimum temperature difference located at a first location (e.g., minimum temperature difference location <NUM> shown in <FIG> and <FIG>) upstream of the centerline <NUM> and a maximum temperature difference located at a second location (e.g., maximum temperature difference location <NUM> shown in <FIG> and <FIG>) downstream of the centerline <NUM>; the first plurality of downstream thermocouple junctions <NUM> may be disposed downstream of the centerline <NUM> at about a third plurality of points on a third line that extends through about the second location and is aligned substantially parallel to the centerline <NUM>; and the second plurality of downstream thermocouple junctions may be disposed further downstream of the centerline <NUM> at about a fourth plurality of points on a fourth line that is aligned substantially parallel to the centerline <NUM>. In some embodiments, the first plurality of downstream thermocouple junctions <NUM> and the second plurality of downstream thermocouple junctions may not be disposed over the heating structure <NUM>.

In some embodiments, each of the first plurality of upstream thermocouple junctions <NUM>, the second plurality of upstream thermocouple junctions <NUM>, the first plurality of downstream thermocouple junctions <NUM>, the second plurality of downstream thermocouple junctions <NUM>, the plurality of upstream sample temperature sensing thermocouple junctions, and the plurality of downstream sample temperature sensing thermocouple junctions may comprise a respective interface between a first thermocouple material and a second thermocouple material as described in greater detail with reference to <FIG>.

According to the invention, as shown in <FIG>, the example thermopile-based flow sensing device <NUM> has to comprise a substrate defining a membrane structure <NUM>. In some embodiments, a portion of the heating structure <NUM> may be disposed over the membrane structure <NUM>. In some embodiments, the first thermopile <NUM>, the plurality of upstream thermocouples, the first plurality of upstream thermocouple junctions <NUM>, the second plurality of upstream thermocouple junctions <NUM>, the second thermopile <NUM>, the plurality of downstream thermocouples, the first plurality of downstream thermocouple junctions <NUM>, the second plurality of downstream thermocouple junctions <NUM>, the plurality of upstream sample temperature sensing thermocouple junctions, the plurality of downstream sample temperature sensing thermocouple junctions, one or more portions thereof, or a combination thereof may be disposed over the membrane structure <NUM>. According to the invention, as shown in <FIG>, a portion of the first thermopile <NUM> has to be disposed over the membrane structure <NUM> such that the first plurality of upstream thermocouple junctions <NUM> is disposed over the membrane structure <NUM> and the second plurality of upstream thermocouple junctions <NUM> is not disposed over the membrane structure <NUM>. According to the invention, as shown in <FIG>, a portion of the second thermopile <NUM> has to be disposed over the membrane structure <NUM> such that the first plurality of downstream thermocouple junctions <NUM> is disposed over the membrane structure <NUM> and the second plurality of downstream thermocouple junctions <NUM> is not disposed over the membrane structure <NUM>. In some embodiments, the membrane structure <NUM> may provide thermal isolation from the bulk (e.g., silicon) die, which may have a high thermal conductivity. In some embodiments, the shape of the membrane structure <NUM> may be rectangular, square, circular, oval, or any other suitable shape or combination thereof.

<FIG> illustrates an example layout for an example thermopile-based flow sensing device <NUM> in accordance with some example embodiments described herein, according to the invention. In some embodiments, the example thermopile-based flow sensing device <NUM> may be provided for sensing a flow of fluid <NUM> (e.g., a flow of a gas or liquid). In some embodiments, the example thermopile-based flow sensing device <NUM> may comprise a heating structure <NUM> having a centerline <NUM> and an axis <NUM> arranged perpendicular to the centerline <NUM>. According to the invention, the example thermopile-based flow sensing device <NUM> has to further comprise a first thermopile <NUM> and a second thermopile <NUM>.

According to the invention, the first thermopile <NUM> has to comprise a plurality of upstream thermocouples disposed upstream of the centerline <NUM> of the heating structure <NUM>. In some embodiments, the plurality of upstream thermocouples may comprise a first subset of the plurality of upstream thermocouples aligned substantially parallel to the centerline <NUM> of the heating structure <NUM>, such as a first plurality of upstream parallel thermocouples <NUM> having a first plurality of upstream thermocouple junctions <NUM> (e.g., six thermocouple junctions) and a second plurality of upstream thermocouple junctions <NUM> (e.g., seven thermocouple junctions). According to the invention, the plurality of upstream thermocouples has to further comprise a second subset of the plurality of upstream thermocouples aligned substantially perpendicular to the centerline <NUM> of the heating structure <NUM>, such as a plurality of upstream perpendicular thermocouples <NUM> having a third plurality of upstream thermocouple junctions <NUM> (e.g., eleven thermocouple junctions) and a fourth plurality of upstream thermocouple junctions <NUM> (e.g., twelve thermocouple junctions). In some embodiments, the plurality of upstream thermocouples may comprise a third subset of the plurality of upstream thermocouples aligned substantially parallel to the centerline <NUM> of the heating structure <NUM>, such as a second plurality of upstream parallel thermocouples <NUM> having a fifth plurality of upstream thermocouple junctions <NUM> (e.g., six thermocouple junctions) and a sixth plurality of upstream thermocouple junctions <NUM> (e.g., six thermocouple junctions). In some embodiments, the first thermopile <NUM> may not be disposed over the heating structure <NUM>. In some embodiments, the number of the first plurality of upstream thermocouple junctions <NUM>, the number of the second plurality of upstream thermocouple junctions <NUM>, the number of the third plurality of upstream thermocouple junctions <NUM>, the number of the fourth plurality of upstream thermocouple junctions <NUM>, the number of the fifth plurality of upstream thermocouple junctions <NUM>, and the number of the sixth plurality of upstream thermocouple junctions <NUM> may depend (e.g., may be a function of) the Seebeck coefficients of the thermocouple materials in the thermocouples and the desired output voltage.

According to the invention, the second thermopile <NUM> has to comprise a plurality of downstream thermocouples disposed downstream of the centerline <NUM> of the heating structure <NUM>. In some embodiments, the plurality of downstream thermocouples may comprise a first subset of the plurality of downstream thermocouples aligned substantially parallel to the centerline <NUM> of the heating structure <NUM>, such as a first plurality of downstream parallel thermocouples <NUM> having a first plurality of downstream thermocouple junctions <NUM> (e.g., six thermocouple junctions) and a second plurality of downstream thermocouple junctions <NUM> (e.g., seven thermocouple junctions). According to the invention, the plurality of downstream thermocouples has to further comprise a second subset of the plurality of downstream thermocouples aligned substantially perpendicular to the centerline <NUM> of the heating structure <NUM>, such as a plurality of downstream perpendicular thermocouples <NUM> having a third plurality of downstream thermocouple junctions <NUM> (e.g., eleven thermocouple junctions) and a fourth plurality of downstream thermocouple junctions <NUM> (e.g., twelve thermocouple junctions). In some embodiments, the plurality of downstream thermocouples may comprise a third subset of the plurality of downstream thermocouples aligned substantially parallel to the centerline <NUM> of the heating structure <NUM>, such as a second plurality of downstream parallel thermocouples <NUM> having a fifth plurality of downstream thermocouple junctions <NUM> (e.g., six thermocouple junctions) and a sixth plurality of downstream thermocouple junctions <NUM> (e.g., six thermocouple junctions). In some embodiments, the second thermopile <NUM> may not be disposed over the heating structure <NUM>. In some embodiments, the number of the first plurality of downstream thermocouple junctions <NUM>, the number of the second plurality of downstream thermocouple junctions <NUM>, the number of the third plurality of downstream thermocouple junctions <NUM>, the number of the fourth plurality of downstream thermocouple junctions <NUM>, the number of the fifth plurality of downstream thermocouple junctions <NUM>, and the number of the sixth plurality of downstream thermocouple junctions <NUM> may depend (e.g., may be a function of) the Seebeck coefficients of the thermocouple materials in the thermocouples and the desired output voltage.

In some embodiments, each of the second plurality of upstream thermocouple junctions <NUM>, the fourth plurality of upstream thermocouple junctions <NUM>, the sixth plurality of upstream thermocouple junctions <NUM>, the second plurality of downstream thermocouple junctions <NUM>, the fourth plurality of downstream thermocouple junctions <NUM>, and the sixth plurality of downstream thermocouple junctions <NUM> may be disposed above the bulk substrate (e.g., bulk silicon) and may be at the same temperature and thus serve as a reference for measurements.

In some embodiments, each of the first plurality of upstream thermocouple junctions <NUM>, the second plurality of upstream thermocouple junctions <NUM>, the third plurality of upstream thermocouple junctions <NUM>, the fourth plurality of upstream thermocouple junctions <NUM>, the fifth plurality of upstream thermocouple junctions <NUM>, the sixth plurality of upstream thermocouple junctions <NUM>, the first plurality of downstream thermocouple junctions <NUM>, the second plurality of downstream thermocouple junctions <NUM>, the third plurality of downstream thermocouple junctions <NUM>, the fourth plurality of downstream thermocouple junctions <NUM>, the fifth plurality of downstream thermocouple junctions <NUM>, and the sixth plurality of downstream thermocouple junctions <NUM> may comprise a respective interface between a first thermocouple material and a second thermocouple material as described in greater detail with reference to <FIG>.

According to the invention, as shown in <FIG>, the example thermopile-based flow sensing device <NUM> has to comprise a substrate defining a membrane structure <NUM>. In some embodiments, a portion of the heating structure <NUM> may be disposed over the membrane structure <NUM>. In some embodiments, the plurality of upstream thermocouples, the first subset of the plurality of upstream thermocouples, the first plurality of upstream parallel thermocouples <NUM>, the first plurality of upstream thermocouple junctions <NUM>, the second plurality of upstream thermocouple junctions <NUM>, the second subset of the plurality of upstream thermocouples, the plurality of upstream perpendicular thermocouples <NUM>, the third plurality of upstream thermocouple junctions <NUM>, the fourth plurality of upstream thermocouple junctions <NUM>, the third subset of the plurality of upstream thermocouples, the second plurality of upstream parallel thermocouples <NUM>, the fifth plurality of upstream thermocouple junctions <NUM>, the sixth plurality of upstream thermocouple junctions <NUM>, the second thermopile <NUM>, the plurality of downstream thermocouples, the first subset of the plurality of downstream thermocouples, the first plurality of downstream parallel thermocouples <NUM>, the first plurality of downstream thermocouple junctions <NUM>, the second plurality of downstream thermocouple junctions <NUM>, the second subset of the plurality of downstream thermocouples, the downstream perpendicular thermocouples <NUM>, the third plurality of downstream thermocouple junctions <NUM>, the fourth plurality of downstream thermocouple junctions <NUM>, the third subset of the plurality of downstream thermocouples, the second plurality of downstream parallel thermocouples <NUM>, the fifth plurality of downstream thermocouple junctions <NUM>, the sixth plurality of downstream thermocouple junctions <NUM>, one or more portions thereof, or a combination thereof may be disposed over the membrane structure <NUM>. For example, as shown in <FIG>, a portion of the first thermopile <NUM> may be disposed over the membrane structure <NUM> such that: the first plurality of upstream thermocouple junctions <NUM> may be disposed over the membrane structure <NUM>, and the second plurality of upstream thermocouple junctions <NUM> may not be disposed over the membrane structure <NUM>; the third plurality of upstream thermocouple junctions <NUM> has to be disposed over the membrane structure <NUM>, and the fourth plurality of upstream thermocouple junctions <NUM> has to not be disposed over the membrane structure <NUM>; and the fifth plurality of upstream thermocouple junctions <NUM> may be disposed over the membrane structure <NUM>, and the sixth plurality of upstream thermocouple junctions <NUM> may not be disposed over the membrane structure <NUM>. In another example, as shown in <FIG>, a portion of the second thermopile <NUM> may be disposed over the membrane structure <NUM> such that: the first plurality of downstream thermocouple junctions <NUM> may be disposed over the membrane structure <NUM>, and the second plurality of downstream thermocouple junctions <NUM> may not be disposed over the membrane structure <NUM>; the third plurality of downstream thermocouple junctions <NUM> has to be disposed over the membrane structure <NUM>, and the fourth plurality of downstream thermocouple junctions <NUM> has to not be disposed over the membrane structure <NUM>; and the fifth plurality of downstream thermocouple junctions <NUM> may be disposed over the membrane structure <NUM>, and the sixth plurality of downstream thermocouple junctions <NUM> may not be disposed over the membrane structure <NUM>. In some embodiments, the membrane structure <NUM> may provide thermal isolation from the bulk (e.g., silicon) die, which may have a high thermal conductivity. In some embodiments, the shape of the membrane structure <NUM> may be rectangular, square, circular, oval, or any other suitable shape or combination thereof.

<FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, and <FIG> illustrate an example process flow for fabricating an example thermopile-based flow sensing device in accordance with some example embodiments described herein, not being part of the claimed invention.

As shown in <FIG>, at step <NUM> the process flow may begin with fabricating (e.g., by thermal oxidation) a silicon dioxide (SiO2) layer 932A on the top surface of a substrate <NUM> (e.g., a silicon die or wafer) and a silicon dioxide layer 932B on the bottom surface of the substrate <NUM>.

As shown in <FIG>, at step <NUM> the process flow may continue to fabricating (e.g., by deposition, such as by sputtering) a silicon nitride layer <NUM> (e.g., Si3N4) on the top surface of the silicon dioxide layer 932A.

As shown in <FIG>, at step <NUM> the process flow may continue to fabricating (e.g., by deposition and patterning) a heater layer (e.g., TaN/NiFe/TaN) defining a heating structure <NUM> on the top surface of the silicon nitride layer <NUM>.

<FIG> illustrates an example layout for the example thermopile-based flow sensing device <NUM> fabricated at step <NUM>. In some embodiments, the example thermopile-based flow sensing device <NUM> may be provided for sensing a flow of fluid <NUM> (e.g., a flow of a gas or liquid). In some embodiments, the example thermopile-based flow sensing device <NUM> may comprise a heating structure <NUM> having a centerline <NUM>.

As shown in <FIG>, at step <NUM> the process flow may continue to fabricating (e.g., by deposition, such as by sputtering) a silicon nitride layer 944A (e.g., Si3N4) on the top surface of the silicon nitride layer <NUM> and the heater layer defining the heating structure <NUM>.

As shown in <FIG>, at step <NUM> the process flow may continue to fabricating (e.g., by deposition and patterning) a first thermocouple material layer <NUM> (e.g., <NUM>:<NUM> NiFe, <NUM>:<NUM> NiFe) on the top surface of the silicon nitride layer 944A.

<FIG> illustrates an example layout for the example thermopile-based flow sensing device <NUM> fabricated at step <NUM>.

As shown in <FIG>, at step <NUM> the process flow may continue to fabricating (e.g., by deposition, such as by sputtering, and patterning) a silicon nitride layer 944B (e.g., Si3N4) on the top surface of the silicon nitride layer 944A and the first thermocouple material layer <NUM> and opening contact vias in the silicon nitride layer 944B to provide access to the top surface of the first thermocouple material layer <NUM>.

As shown in <FIG>, at step <NUM> the process flow may continue to fabricating (e.g., by deposition and patterning) a second thermocouple material layer <NUM> (e.g., Cr) on the top surface of the first thermocouple material layer <NUM> through contact windows opened in the silicon nitride layer 944B.

<FIG> illustrates an example layout for the example thermopile-based flow sensing device <NUM> fabricated at step <NUM>. In some embodiments, the example thermopile-based flow sensing device <NUM> may be provided for sensing a flow of fluid <NUM> (e.g., a flow of a gas or liquid). In some embodiments, the example thermopile-based flow sensing device <NUM> may comprise a heating structure <NUM> having a centerline <NUM>. In some embodiments, the example thermopile-based flow sensing device <NUM> may further comprise a thermopile <NUM>. In some embodiments, at least a portion of the thermopile <NUM> may be disposed over the heating structure <NUM>.

In some embodiments, the thermopile <NUM> may comprise a plurality of thermocouples having a plurality of thermocouple junctions. In some embodiments, the plurality of thermocouples may have a plurality of upstream thermocouple junctions <NUM> (e.g., nineteen upstream thermocouple junctions) disposed upstream of the centerline <NUM> of the heating structure <NUM>. In some embodiments, the plurality of thermocouples may have a plurality of downstream thermocouple junctions <NUM> (e.g., nineteen downstream thermocouple junctions) disposed downstream of the centerline <NUM> of the heating structure <NUM>. In some embodiments, the number of upstream thermocouple junctions <NUM> and the number of downstream thermocouple junctions <NUM> may be the same. In some embodiments, the number of upstream thermocouple junctions <NUM> and the number of downstream thermocouple junctions <NUM> may depend (e.g., may be a function of) the Seebeck coefficient of the first thermocouple material layer <NUM>, the Seebeck coefficient of the second thermocouple material layer <NUM>, and the desired output voltage.

In some embodiments, each of the plurality of upstream thermocouple junctions <NUM> and the plurality of downstream thermocouple junctions <NUM> may be aligned parallel to centerline <NUM> and occur along an upstream vertical line through about a minimum temperature difference location (e.g., minimum temperature difference location <NUM> shown in <FIG> and <FIG>) and a downstream vertical line through about a maximum temperature difference location (e.g., maximum temperature difference location <NUM> shown in <FIG> and <FIG>), respectively. For example, a maximum temperature difference may be defined by a minimum temperature difference located at a first location (e.g., minimum temperature difference location <NUM> <FIG> and <FIG>) upstream of the centerline <NUM> and a maximum temperature difference located at a second location (e.g., maximum temperature difference location <NUM> shown in <FIG> and <FIG>) downstream of the centerline <NUM>; the plurality of upstream thermocouple junctions <NUM> may be disposed upstream of the centerline <NUM> at about a first plurality of points on a first line that extends through about the first location and is aligned substantially parallel to the centerline <NUM>; and the plurality of downstream thermocouple junctions <NUM> may be disposed downstream of the centerline <NUM> at about a second plurality of points on a second line that extends through about the second location and is aligned substantially parallel to the centerline <NUM>. In some embodiments, the plurality of upstream thermocouple junctions <NUM> and the plurality of downstream thermocouple junctions <NUM> may not be disposed over the heating structure <NUM>.

In some embodiments, each of the plurality of upstream thermocouple junctions <NUM>, the plurality of downstream thermocouple junctions <NUM>, the plurality of upstream sample temperature sensing thermocouple junctions <NUM>, and the plurality of downstream sample temperature sensing thermocouple junctions <NUM> may comprise a respective interface between a first thermocouple material and a second thermocouple material as described in greater detail with reference to <FIG> and <FIG>.

As shown in <FIG>, at step <NUM> the process flow may continue to fabricating (e.g., by deposition, such as by sputtering, and patterning) a silicon nitride layer 944C (e.g., Si3N4) on the top surface of the silicon nitride layer 944B and the second thermocouple material layer <NUM> and opening contact vias in the silicon nitride layer 944C to provide access to the top surface of the second thermocouple material layer <NUM>.

As shown in <FIG>, at step <NUM> the process flow may continue to fabricating (e.g., by deposition and patterning) an electrical contact layer <NUM> (e.g., TiW / Al, TiW / <NUM>% Al-Cu) on the top surface of the second thermocouple material layer <NUM> through the contact vias opened in the silicon nitride layer 944C.

As shown in <FIG>, at step <NUM> the process flow may continue to fabricating (e.g., by plasma enhanced chemical vapor deposition (PECVD)) a silicon nitride overcoat layer <NUM> (e.g., SixNy-H) on the top surface of the silicon nitride layer 944C and the electrical contact layer <NUM> and opening contact vias in the silicon nitride overcoat layer <NUM> to provide access to the top surface of the electrical contact layer <NUM>.

As shown in <FIG>, at step <NUM> the process flow may continue to fabricating a membrane structure by forming (e.g., by DRIE) a cavity <NUM> through the silicon dioxide layer 932B and the substrate <NUM> until reaching the bottom surface of the silicon dioxide layer 932A. At step <NUM> the process flow may include forming (e.g., by DRIE) one or more side cavities <NUM> through the silicon dioxide layer 932B and a portion of the substrate <NUM> (e.g., through <NUM>% of the thickness of the substrate <NUM>).

<FIG> illustrates an example layout for the example thermopile-based flow sensing device <NUM> fabricated at step <NUM>. In some embodiments, the example thermopile-based flow sensing device <NUM> may comprise a substrate defining a membrane structure <NUM>. In some embodiments, a portion of the heating structure <NUM> may be disposed over the membrane structure <NUM>. In some embodiments, the thermopile <NUM>, the plurality of thermocouples, the plurality of upstream thermocouple junctions <NUM>, the plurality of downstream thermocouple junctions <NUM>, the plurality of upstream sample temperature sensing thermocouple junctions <NUM>, the plurality of downstream sample temperature sensing thermocouple junctions <NUM>, one or more portions thereof, or a combination thereof may be disposed over the membrane structure <NUM>. In some embodiments, the membrane structure <NUM> may provide thermal isolation from the substrate <NUM>, which may have a high thermal conductivity. In some embodiments, the shape of the membrane structure <NUM> may be rectangular, square, circular, oval, or any other suitable shape or combination thereof.

<FIG> illustrates a legend for the various example layers described with reference to <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>.

<FIG> illustrates an example table <NUM> of thermocouple materials for use in an example thermopile-based flow sensing device in accordance with some example embodiments described herein, not being part of the claimed invention. For example, the thermocouple materials shown in example table <NUM> may be used to provide a thermocouple junction comprising an interface between a first thermocouple material and a second thermocouple material. In some embodiments, the number of thermocouple junctions in the thermopile of an example thermopile-based flow sensing device disclosed herein may depend (e.g., may be a function of) the Seebeck coefficients of the thermocouple materials in the thermocouples of the thermopile and the desired output voltage. The term "dS" refers to the difference between the Seebeck coefficients of the thermocouple materials in a thermocouple.

In some embodiments, the first thermocouple material may comprise polysilicon, and the second thermocouple material may comprise aluminum. In some embodiments, the first thermocouple material and the second thermocouple material may comprise differently doped polysilicon (e.g., n-type and p-type polysilicon). For example, the first thermocouple material may comprise n-type polysilicon (nPoly Si), and the second thermocouple material may comprise p-type polysilicon (pPoly Si). In another example, the first thermocouple material may comprise p-type polysilicon (pPoly Si), and the second thermocouple material may comprise n-type polysilicon (nPoly Si).

In some embodiments, the first thermocouple material may comprise a nickel-iron alloy (e.g., <NUM>:<NUM> NiFe, <NUM>:<NUM> NiFe), and the second thermocouple material may comprise chromium (Cr), where dS is about <NUM> uV/C for <NUM>:<NUM> NiFe and Cr or about <NUM> uV/C for <NUM>:<NUM> NiFe and Cr. In some embodiments, the first thermocouple material may comprise a nickel-iron alloy (e.g., <NUM>:<NUM> NiFe, <NUM>:<NUM> NiFe), and the second thermocouple material may comprise chromium disilicide (CrSi2), where dS is about <NUM> uV/C for <NUM>:<NUM> NiFe and CrSi2 or about <NUM> uV/C for <NUM>:<NUM> NiFe and CrSi2. In some embodiments, the first thermocouple material may comprise a nickel-iron alloy (e.g., <NUM>:<NUM> NiFe, <NUM>:<NUM> NiFe), and the second thermocouple material may comprise rhenium disilicide (ReSi2).

In some embodiments, the first thermocouple material may comprise chromium nitride (e.g., CrN), and the second thermocouple material may comprise copper (Cu), where dS is about <NUM> uV/C for CrN and Cu. In some embodiments, the first thermocouple material may comprise chromium nitride (e.g., CrN), and the second thermocouple material may comprise aluminum (Al), where dS is about <NUM> uV/C for CrN and Al. In some embodiments, the first thermocouple material may comprise a chromium nitride (e.g., CrN), and the second thermocouple material may comprise p-type polysilicon (pPoly Si), where dS is about <NUM> uV/C for CrN and pPoly Si.

In some embodiments, the first thermocouple material may comprise copper (Cu), and the second thermocouple material may comprise a copper-nickel alloy (e.g., Constantan).

In some embodiments, the thermopile-based flow sensing device disclosed herein may comprise any combination of components, structures, and features discussed with reference to example thermopile-based flow sensing devices <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, and any of the example thermopile-based flow sensing devices described with reference to <FIG> (e.g., example thermopile-based flow sensing devices <NUM>, <NUM>, <NUM>, <NUM>, <NUM>), including the addition or omission of components, structures, and features.

Having described specific components of example devices involved in the present disclosure, example procedures for providing a thermopile-based flow sensing device are described below in connection with <FIG> and <FIG>.

<FIG> illustrates an example flowchart <NUM> that contains example operations for manufacturing or otherwise providing an apparatus (e.g., apparatus <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) for sensing a flow of fluid according to some example embodiments described herein, not being part of the claimed invention.

As shown by operation <NUM>, the example flowchart <NUM> may begin by providing a heating structure (e.g., heating structure <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) having a centerline (e.g., centerline <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>).

As shown by operation <NUM>, the example flowchart <NUM> may proceed to disposing at least a portion of a thermopile (e.g., thermopile <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) over the heating structure. The thermopile may comprise a first thermocouple having a first thermocouple junction (e.g., one of the one or more upstream thermocouple junctions <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) disposed upstream of the centerline of the heating structure. The thermopile may further comprise a second thermocouple having a second thermocouple junction (e.g., one of the one or more downstream thermocouple junctions <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) disposed downstream of the centerline of the heating structure. In some embodiments, the number of upstream thermocouple junctions and the number of downstream thermocouple junctions in the thermopile may depend (e.g., may be a function of) the Seebeck coefficients of the thermocouple materials in the thermocouples and the desired output voltage.

In some embodiments, operations <NUM> and <NUM> may not necessarily occur in the order depicted in <FIG>. In some embodiments, one or more of the operations depicted in <FIG> may occur substantially simultaneously. In some embodiments, one or more additional operations may be involved before, after, or between any of the operations shown in <FIG>.

<FIG> illustrates an example flowchart <NUM> that contains example operations for manufacturing or otherwise providing an apparatus (e.g., apparatus <NUM>, <NUM>) for sensing a flow of fluid according to some example embodiments described herein, being part of the claimed invention.

As shown by operation <NUM>, the example flowchart <NUM> has to begin by providing a heating structure (e.g., heating structure <NUM>, <NUM>) having a centerline (e.g., centerline <NUM>, <NUM>).

As shown by operation <NUM>, the example flowchart <NUM> has to proceed to disposing a first thermopile (e.g., thermopile <NUM>, <NUM>) upstream of the centerline of the heating structure. The first thermopile has to comprise a first plurality of thermocouples disposed upstream of the centerline of the heating structure. In some embodiments, the first plurality of thermocouples may comprise a first subset of the first plurality of thermocouples (e.g., upstream parallel thermocouples <NUM>, <NUM>) aligned substantially parallel to the centerline of the heating structure. In some embodiments, the first plurality of thermocouples may further comprise a second subset of the first plurality of thermocouples (e.g., upstream perpendicular thermocouples <NUM>) aligned substantially perpendicular to the centerline of the heating structure. In some instances, the first thermopile may be disposed above the heating structure, such as in a layer above the heating structure but not over the heating structure.

As shown by operation <NUM>, the example flowchart <NUM> has to proceed to disposing a second thermopile (e.g., thermopile <NUM>, <NUM>) downstream of the centerline of the heating structure. The second thermopile has to comprise a second plurality of thermocouples disposed downstream of the centerline of the heating structure. In some embodiments, the second plurality of thermocouples may comprise a third subset of the second plurality of thermocouples (e.g., downstream parallel thermocouples <NUM>, <NUM>) aligned substantially parallel to the centerline of the heating structure. In some embodiments, the second plurality of thermocouples may further comprise a fourth subset of the second plurality of thermocouples (e.g., downstream perpendicular thermocouples <NUM>) aligned substantially perpendicular to the centerline of the heating structure. In some instances, the second thermopile may be disposed above the heating structure, such as in a layer above the heating structure but not over the heating structure.

In some embodiments, operations <NUM>, <NUM>, and <NUM> may not necessarily occur in the order depicted in <FIG>. In some embodiments, one or more of the operations depicted in <FIG> may occur substantially simultaneously. In some embodiments, one or more additional operations may be involved before, after, or between any of the operations shown in <FIG>.

<FIG> and <FIG> thus illustrate example flowcharts describing operations performed in accordance with example embodiments of the present disclosure. It will be understood that each operation of the flowcharts, and combinations of operations in the flowcharts, may be implemented by various means, such as devices comprising hardware, firmware, one or more processors, and/or circuitry associated with execution of software comprising one or more computer program instructions. In some embodiments, one or more of the procedures described above may be performed by execution of program code instructions. For example, one or more of the procedures described above may be performed by material handling equipment (e.g., a robotic arm, servo motor, motion controllers, and the like) and computer program instructions residing on a non-transitory computer-readable storage memory. In this regard, the program code instructions that, when executed, cause performance of the procedures described above may be stored by a non-transitory computer-readable storage medium (e.g., memory) of a computing apparatus and executed by a processor of the computing apparatus. In this regard, the computer program instructions which embody the procedures described above may be stored by a memory of an apparatus employing an embodiment of the present disclosure and executed by a processor of the apparatus. As will be appreciated, any such computer program instructions may be loaded onto a computer or other programmable apparatus (e.g., hardware) to produce a machine, such that the resulting computer or other programmable apparatus provides for implementation of the functions specified in the flowcharts <NUM> and <NUM>. When executed, the instructions stored in the computer-readable storage memory produce an article of manufacture configured to implement the various functions specified in the flowcharts <NUM> and <NUM>. The program code instructions may also be loaded onto a computer or other programmable apparatus to cause a series of operations to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions executed on the computer or other programmable apparatus provide operations for implementing the functions specified in the operations of flowcharts <NUM> and <NUM>. Moreover, execution of a computer or other processing circuitry to perform various functions converts the computer or other processing circuitry into a particular machine configured to perform an example embodiment of the present disclosure.

The flowchart operations described with reference to <FIG> and <FIG> support combinations of means for performing the specified functions and combinations of operations for performing the specified functions. It will be understood that one or more operations of the flowcharts, and combinations of operations in the flowcharts, may be implemented by special purpose hardware-based computer systems which perform the specified functions, or combinations of special purpose hardware and computer instructions.

Words such as "thereafter," "then," "next," and similar words are not intended to limit the order of the steps; these words are simply used to guide the reader through the description of the methods. Further, any reference to claim elements in the singular, for example, using the articles "a," "an" or "the," is not to be construed as limiting the element to the singular and may, in some instances, be construed in the plural.

As described above and as will be appreciated based on this disclosure, embodiments of the present disclosure may be configured as systems, apparatuses, methods, mobile devices, backend network devices, computer program products, other suitable devices, and combinations thereof. Accordingly, embodiments may comprise various means including entirely of hardware or any combination of software with hardware. Furthermore, embodiments may take the form of a computer program product on at least one non-transitory computer-readable storage medium having computer-readable program instructions (e.g., computer software) embodied in the storage medium. Any suitable computer-readable storage medium may be utilized including non-transitory hard disks, CD-ROMs, flash memory, optical storage devices, or magnetic storage devices. As will be appreciated, any computer program instructions and/or other type of code described herein may be loaded onto a computer, processor or other programmable apparatus's circuitry to produce a machine, such that the computer, processor, or other programmable circuitry that executes the code on the machine creates the means for implementing various functions, including those described herein. In some embodiments, features of the present disclosure may comprise, or be communicatively coupled to, an application specific integrated circuit (ASIC) configured to convert the differential output voltage from the thermopile or thermopiles (e.g., either in a single chip or two-chip configuration).

While various embodiments in accordance with the principles disclosed herein have been shown and described above, modifications thereof may be made by one skilled in the art without departing from the teachings of the disclosure. The embodiments described herein are representative only and are not intended to be limiting. Many variations, and modifications are possible and are within the scope of the disclosure Accordingly, the scope of protection is not limited by the description set out above, but is defined by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present disclosure. Furthermore, any advantages and features described above may relate to specific embodiments, but shall not limit the application of such issued claims to processes and structures accomplishing any or all of the above advantages or having any or all of the above features.

Also, systems, subsystems, apparatuses, techniques, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other devices or components shown or discussed as coupled to, or in communication with, each other may be indirectly coupled through some intermediate device or component, whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the scope disclosed herein.

Claim 1:
An apparatus for sensing a flow of fluid (<NUM>), the apparatus comprising:
a flow sensing device (<NUM>) comprising:
a heating structure (<NUM>) having a centerline (<NUM>) that defines upstream and downstream sections of the flow sensing device (<NUM>);
a membrane structure (<NUM>);
a first thermopile (<NUM>), wherein at least a portion of the first thermopile (<NUM>) is disposed over the membrane structure (<NUM>), and wherein the first thermopile (<NUM>) comprises:
a first plurality of upstream thermocouple junctions (<NUM>) disposed over the membrane structure (<NUM>), and
a second plurality of upstream thermocouple junctions (<NUM>) offset from the membrane structure (<NUM>); and
a second thermopile (<NUM>), wherein at least a portion of the second thermopile (<NUM>) is disposed over the membrane structure (<NUM>), and wherein the second thermopile (<NUM>) comprises:
a first plurality of downstream thermocouple junctions (<NUM>) disposed over the membrane structure (<NUM>), and
a second plurality of downstream thermocouple junctions (<NUM>) not disposed over the membrane structure (<NUM>),
characterised in that
a maximum temperature difference is defined by a minimum temperature difference location located upstream of the centerline (<NUM>) and a maximum temperature difference location located downstream of the centerline (<NUM>);
wherein the first plurality of upstream thermocouple junctions (<NUM>) is aligned substantially parallel to the centerline (<NUM>) along an upstream vertical line through about the minimum temperature difference location, and
wherein the first plurality of downstream thermocouple junctions (<NUM>) is aligned substantially parallel to the centerline (<NUM>) along a downstream vertical line through about the maximum temperature difference location.