Thermopile-based flow sensing device
阅读说明：本技术 基于热电堆的流量感测设备 (Thermopile-based flow sensing device ) 是由 罗伯特·西嘉石 斯科特·爱德华·贝克 王勇发 伊恩·本特利 比尔·胡佛 于 2020-04-20 设计创作，主要内容包括：本发明题为“基于热电堆的流量感测设备”。本文公开了使用基于热电堆的流量感测设备感测流体的流量的示例系统、装置和方法。示例装置包括流量感测设备,该流量感测设备包括具有中心线的加热结构。流量感测设备可以进一步包括热电堆。热电堆的至少一部分可以设置在加热结构上。热电堆可以包括第一热电偶,该第一热电偶具有设置在加热结构的中心线上游的第一热电偶结。热电堆可以进一步包括第二热电偶,该第二热电偶具有设置在加热结构的中心线下游的第二热电偶结。(The invention provides a thermopile-based flow sensing device. Example systems, apparatus, and methods of sensing a flow of a fluid using a thermopile-based flow sensing device are disclosed herein. An example apparatus includes a flow sensing device including a heating structure having a centerline. The flow sensing device may further comprise a thermopile. At least a portion of the thermopile may be disposed on the heating structure. The thermopile may include a first thermocouple having a first thermocouple junction disposed upstream of a centerline of the heating structure. The thermopile may further include a second thermocouple having a second thermocouple junction disposed downstream of the centerline of the heating structure.)
1. An apparatus for sensing fluid flow, the apparatus comprising:
a flow sensing device, the flow sensing device comprising:
a heating structure having a centerline; and
a thermopile, wherein at least a portion of the thermopile is disposed on the heating structure, and wherein the thermopile comprises
A first thermocouple having a first thermocouple junction disposed upstream of the centerline, and
a second thermocouple having a second thermocouple junction disposed downstream of the centerline.
2. The apparatus of claim 1, further comprising a substrate defining a microbridge structure, wherein a portion of the heating structure is disposed on the microbridge structure.
3. The apparatus of claim 1, further comprising a substrate defining a film structure, wherein a portion of the heating structure is disposed on the film structure.
4. The apparatus of claim 1, wherein the first thermocouple junction is disposed on the heating structure, and wherein the second thermocouple junction is disposed on the heating structure.
5. The apparatus of claim 1, wherein the first thermocouple junction is not disposed on the heating structure, and wherein the second thermocouple junction is not disposed on the heating structure.
6. The device of claim 1, wherein a maximum temperature differential is defined by a minimum temperature differential at a first location upstream of the centerline and a maximum temperature differential at a second location downstream of the centerline, wherein the first thermocouple junction is disposed near the first location, and wherein the second thermocouple junction is disposed near the second location.
7. The device of claim 1, wherein the thermopile comprises:
a first plurality of thermocouples having a first plurality of thermocouple junctions disposed upstream of the centerline; and
a second plurality of thermocouples having a second plurality of thermocouple junctions disposed downstream of the centerline, wherein the first and second plurality of thermocouple junctions are disposed near a plurality of locations on a maximum temperature differential contour.
8. The apparatus of claim 1, wherein the first thermocouple junction comprises an interface between a first thermocouple material and a second thermocouple material.
9. The device of claim 8, wherein the first thermocouple material comprises at least one of: nickel-iron alloy, chromium nitride, polysilicon, n-type polysilicon, p-type polysilicon, and copper.
10. The device of claim 8, wherein the second thermocouple material comprises at least one of: chromium, chromium disilicide, rhenium disilicide, copper, aluminum, p-type polycrystalline silicon, n-type polycrystalline silicon, and copper-nickel alloys.
Technical Field
Example embodiments of the present disclosure relate generally to sensors, and more particularly to flow sensors.
Background
Industrial and commercial applications increasingly use flow sensors to measure and control the mass flow of gases and liquids. Conventional flow sensor designs typically exhibit drift characteristics that reduce their measurement sensitivity.
Applicants have discovered a number of drawbacks and problems associated with conventional flow sensors. Many of these identified problems have been addressed by efforts, wisdom, and innovations through development solutions included in embodiments of the present disclosure, many examples of which are described in detail herein.
Disclosure of Invention
Systems, apparatus, methods, and computer program products are disclosed herein for providing a thermopile-based flow sensing device having low or no drift characteristics, in some cases, compatible with Complementary Metal Oxide Semiconductor (CMOS) processing.
In one exemplary embodiment, an apparatus for sensing fluid flow is provided. The apparatus may include a flow sensing device including a heating structure having a centerline. The flow sensing device may further comprise a thermopile. At least a portion of the thermopile may be disposed on the heating structure. The thermopile may include a first thermocouple having a first thermocouple junction disposed upstream of a centerline of the heating structure. The thermopile may further include a second thermocouple having a second thermocouple junction disposed downstream of the centerline of the heating structure.
In another example embodiment, a method for manufacturing a device for sensing fluid flow is provided. The method may include providing a heating structure having a centerline. The method may further include disposing at least a portion of the thermopile on the heating structure. The thermopile may include a first thermocouple having a first thermocouple junction disposed upstream of a centerline of the heating structure. The thermopile may further include a second thermocouple having a second thermocouple junction disposed downstream of the centerline of the heating structure.
In yet another example embodiment, an apparatus for sensing fluid flow. The apparatus may include a flow sensing device including a heating structure having a centerline. The flow sensing device may further include a first thermopile including a first plurality of thermocouples disposed upstream of the centerline of the heating structure. The first plurality of thermocouples may include a first subset of the first plurality of thermocouples aligned substantially parallel to a centerline of the heating structure. The first plurality of thermocouples may further include a second subset of the first plurality of thermocouples aligned substantially perpendicular to a centerline of the heating structure. The flow sensing device may further include a second thermopile including a second plurality of thermocouples disposed downstream of the centerline of the heating structure. The second plurality of thermocouples can include a third subset of the second plurality of thermocouples aligned substantially parallel to a centerline of the heating structure. The second plurality of thermocouples may further include a fourth subset of the second plurality of thermocouples aligned substantially perpendicular to the centerline of the heating structure.
In yet another example embodiment, a method for manufacturing a device for sensing fluid flow is provided. The method may include providing a heating structure having a centerline. The method may further include disposing the first thermopile upstream of a centerline of the heating structure. The first thermopile may include a first plurality of thermocouples disposed upstream of a centerline of the heating structure. The first plurality of thermocouples may include a first subset of the first plurality of thermocouples aligned substantially parallel to a centerline of the heating structure. The first plurality of thermocouples may further include a second subset of the first plurality of thermocouples aligned substantially perpendicular to a centerline of the heating structure. The method may further comprise disposing a second thermopile downstream of the centerline of the heating structure. The second thermopile may include a second plurality of thermocouples disposed downstream of the centerline of the heating structure. The second plurality of thermocouples can include a third subset of the second plurality of thermocouples aligned substantially parallel to a centerline of the heating structure. The second plurality of thermocouples may further include a fourth subset of the second plurality of thermocouples aligned substantially perpendicular to the centerline of the heating structure.
The above summary is provided merely for purposes of summarizing some example embodiments so as to provide a basic understanding of some aspects of the disclosure. Accordingly, it should be understood that the above-described embodiments are merely examples and should not be construed to narrow the scope or spirit of the disclosure in any way. It should be understood that the scope of the present disclosure encompasses many possible embodiments, some of which are further described below, in addition to those summarized herein.
Drawings
Having thus described certain example embodiments of the present disclosure in general terms, reference will now be made to the accompanying drawings, which illustrate example embodiments and features of the present disclosure and which are not necessarily drawn to scale. It should be understood that the components and structures shown in the figures may or may not be present in the various embodiments of the present disclosure described herein. Thus, some embodiments or features of the disclosure may include fewer or more components or structures than those shown in the figures without departing from the scope of the disclosure.
Fig. 1 illustrates an example layout of an example thermopile-based flow sensing apparatus, according to some example embodiments described herein.
Fig. 2A and 2B illustrate example temperature contours of an example thermopile-based flow sensing apparatus, according to some example embodiments described herein.
Fig. 3 illustrates another example layout of an example thermopile-based flow sensing apparatus, according to some example embodiments described herein.
Fig. 4 illustrates another example layout of an example thermopile-based flow sensing apparatus, according to some example embodiments described herein.
Fig. 5 illustrates another example layout of an example thermopile-based flow sensing apparatus, according to some example embodiments described herein.
Fig. 6 illustrates another example layout of an example thermopile-based flow sensing apparatus, according to some example embodiments described herein.
Fig. 7 illustrates another example layout of an example thermopile-based flow sensing apparatus, according to some example embodiments described herein.
Fig. 8 illustrates another example layout of an example thermopile-based flow sensing apparatus, according to some example embodiments described herein.
Fig. 9A, 9B, 9C, 9D, 9E, 9F, 9G, 9H, 9I, 9J, 9K, 9L, 9M, 9N, 9O, 9P, 9Q, 9R, 9S, and 9T illustrate example process flows for manufacturing an example thermopile-based flow sensing apparatus according to some example embodiments described herein.
Fig. 10 illustrates another example layout of an example thermopile-based flow sensing apparatus, according to some example embodiments described herein.
Fig. 11 illustrates an example table of thermocouple materials for use in an example thermopile-based flow sensing apparatus, according to some example embodiments described herein.
Fig. 12 illustrates an example flow diagram illustrating an example method according to some example embodiments described herein.
Fig. 13 illustrates an example flow diagram illustrating another example method according to some example embodiments described herein.
Detailed Description
The following description should be read with reference to the drawings, in which like reference numerals indicate like elements throughout the several views. The detailed description and drawings show several embodiments, which are intended to be illustrative of the disclosure. It will be understood that any numbering (e.g., first, second, etc.) of the disclosed features and/or directional terminology used with the disclosed features (e.g., front, back, bottom, etc.) is a relative term denoting an illustrative relationship between the related features. The word "example" as used herein is intended to mean "serving as an example, instance, or illustration. Any embodiment described herein as "exemplary" is not necessarily preferred or advantageous over other embodiments.
It should be understood at the outset that although illustrative embodiments of one or more aspects are illustrated below, the disclosed components, systems, and methods may be implemented using a variety of techniques. The present disclosure should in no way be limited to the exemplary embodiments, drawings, and techniques illustrated below, but may be modified within the scope of the appended claims along with their full scope of equivalents. Although dimensional values for various elements are disclosed, the drawings may not be to scale.
Typically, the hot wire anemometer flow sensor die output will drift when powered. In these hot wire anemometer flow sensors, which typically use platinum as the resistor material, drift in the sensor is due to stress relaxation in the platinum layer and changes in the stress in the silicon nitride layer around the platinum forming the air bridge, in part because platinum has piezoresistive properties that change with its resistive stress. In other words, drift in these hot-wire anemometer flow sensors is typically due to stress relaxation in the platinum layer and is affected by residual stresses in the air bridge (also referred to as microbridge). For example, drift has been directly related to stress in Plasma Enhanced Chemical Vapor Deposition (PECVD) silicon nitride layers on the surface of the microbridge. Such stress in the PECVD silicon nitride layer can change over time as the air bridge is continuously heated by the resistive heater, which is an integral part of the flow sensor. Experimentally, this drift value is up to 40uV per day at air flow. Therefore, 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 that reduce or eliminate drift experienced by conventional flow sensors by providing various arrangements for thermopile-based flow sensing devices. In some embodiments, the signal generated by the thermopile-based flow sensing devices disclosed herein is a voltage source and response to membrane resistance is minimal, by using a thermocouple or thermopile. Without the membrane resistance sensitivity, other sensitivities (such as stress or magnetoresistance change) are negligible. Additional thermocouples can provide additional voltage, signal, and sensitivity that conventional resistive flow sensors do not have. In some cases, the thermopile structure may be fabricated on a microbridge structure or a membrane structure. In some embodiments, the membrane structures disclosed herein can provide the same thermopile structure as the microbridge and other structures that the microbridge may not provide.
In some embodiments, a general flow for manufacturing a thermopile flow sensor is as follows:
1. thermal silicon dioxide is grown.
2. Bottom silicon nitride is deposited. In some embodiments, all silicon nitride dielectrics may be replaced with silicon dioxide, such as PECVD, Tetraethoxysilane (TEOS), or sputter deposition, to reduce thermal conductivity.
3. A resistive heater structure is deposited and patterned. The heater structure may be made of the following materials, etc.: silicon (including polysilicon); platinum; a nickel-chromium alloy; permalloy; PtSi and other silicides; w; TiN; AlN; WN; any other suitable material; or any combination thereof.
4. An inter-silicon nitride dielectric is deposited.
5. A first thermocouple material is deposited and patterned. Various thermocouple materials that may be used for the first thermocouple are discussed in more detail with reference to fig. 11.
6. An interlayer dielectric is deposited. In some cases, this step may be optional, depending on the materials used, but may result in higher yields. In some cases, if an interlayer dielectric is used, it must be patterned to open vias through the underlying thermocouple material.
7. A second thermocouple material is deposited and patterned. Various thermocouple materials that may be used for the second thermocouple are discussed in more detail with reference to fig. 11.
8. Interlayer dielectrics, patterns and open vias are deposited to the heater and thermopile connections.
9. A metal (such as Al/1% Cu) is deposited and patterned to form the lead lines and bond pads.
10. A silicon nitride overcoat is deposited and patterned to open the bond pad area.
11. The wafer backside is patterned and Deep Reactive Ion Etching (DRIE) is used to create a cavity under the thermopile structure.
In some embodiments, as discussed with reference to fig. 1, 2, 3, 4, 5, 6, 9, 10, and 12, 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 are not located on the silicon die. Instead, the thermocouple is suspended over the cavity or resides on the 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 membrane) with opposing thermocouples (e.g., cold junctions, hot junctions) oriented such that one set of junctions is upstream and the other set of junctions is downstream of the heating element centerline.
In some embodiments, as discussed with reference to fig. 7, 8, and 13, the heater structure may be located between two sets of thermocouples (e.g., two thermopiles), where one set of thermocouples is located upstream of the heater structure and another set of thermocouples is located downstream of the heater structure. In these arrangements, there are parasitic effects and each group of thermocouples has one side on the bulk silicon die that floats in temperature.
In some embodiments, the following formula may be used to characterize
The thermopile-based flow sensing apparatus disclosed herein:
ΔV＝nΔS(ΔT)
wherein Δ V is the potential difference; n is the number of thermocouples; s-seebeck coefficient (also known as thermal power, thermoelectric power (TE), or thermoelectric sensitivity); Δ S — TE1-TE2 (thermoelectric power of first thermoelectric material-thermoelectric power of second thermoelectric material); t-temperature; and Δ T ═ T1-Tref. (measured temperature at thermoelectric junction(s) — (temperature at reference thermoelectric junction (s)). In some cases, such asShown in FIG. 7, T1The downstream thermocouple junction 712 may be used for measurements on the membrane structure 716 and the downstream thermocouple junction 713 may be used for measurements on bulk silicon. In other cases, such as shown in fig. 6, the relative temperature difference Δ Τ may be measured on the membrane structure 716 using the
Embodiments disclosed herein have many advantages, such as: (1) providing a low-drift or no-drift device (e.g., as discussed with reference to fig. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, and 13); (2) potential compatibility with CMOS processing is provided by the unique combination of thermocouple materials (e.g., as discussed with reference to fig. 11).
Although the present disclosure describes features of the thermopile-based flow sensing devices disclosed herein with reference to flow sensors, the thermopile-based flow sensing devices disclosed herein may be used in testing or use of any suitable sensor, detector, gauge, instrument, application utilizing precision heating or temperature detection, or other needs.
Fig. 1 illustrates an example layout of an example thermopile-based
In some embodiments, the
In some embodiments, the thermopile-based example
In some embodiments, each of the plurality of upstream thermocouple junctions 108, the plurality of
In some embodiments, as shown in fig. 1, an example thermopile-based
In other embodiments (not shown in fig. 1 for simplicity), the example thermopile-based
Fig. 2A illustrates an example temperature contour 220 (e.g., including but not limited to temperature contour 220A, maximum temperature differential contour 220B (extending through the temperature contour near the location where the maximum temperature differential occurs), and temperature contour 220C) for a thermopile-based example flow sensing device 200 according to some example embodiments described herein.
In some embodiments, as shown in fig. 2A and 2B, a thermopile-based example flow sensing device 200 may be provided for sensing a flow of a fluid 201 (e.g., a flow of a gas or a liquid). In some embodiments, the example thermopile-based flow sensing device 200 may include a heating structure 202 having a centerline 204 and an axis 205 arranged perpendicular to the centerline 204. In some embodiments, the example thermopile-based flow sensing device 200 may further include a thermopile. In some embodiments, at least a portion of the thermopile may be disposed on the heating structure 202.
In some embodiments, as shown in fig. 2A and 2B, the thermopile may include 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 208 (e.g., seventeen upstream thermocouple junctions) disposed upstream of the centerline 204 of the heating structure 202. In some embodiments, the plurality of thermocouples may have a plurality of downstream thermocouple junctions 210 (e.g., seventeen downstream thermocouple junctions) disposed downstream from the centerline 204 of the heating structure 202. In some embodiments, the number of upstream thermocouple junctions 208 and the number of downstream thermocouple junctions 210 may be the same. In some embodiments, the number of upstream thermocouple junctions 208 and the number of downstream thermocouple junctions 210 may depend on (e.g., may be a function of) the seebeck coefficient of the thermocouple material in the thermocouple and the desired output voltage.
In some embodiments, as shown in fig. 2A and 2B, each of the plurality of upstream thermocouple junctions 208 and the plurality of downstream thermocouple junctions 210 can be generated along a maximum temperature difference contour 220B (e.g., extending through a temperature contour near a minimum temperature difference location 222 and a maximum temperature difference location 224), wherein a furthest upstream thermocouple junction of the plurality of upstream thermocouple junctions 208 occurs near the minimum temperature difference location 222, and wherein a furthest downstream thermocouple junction of the plurality of downstream thermocouple junctions 210 occurs near the maximum temperature difference location 224. For example, the maximum temperature differential may be defined by a minimum temperature differential location 222 upstream of the centerline 204 and a maximum temperature differential location 224 downstream of the centerline 204. A plurality of upstream thermocouple junctions 208 may be disposed near a plurality of locations on the maximum temperature difference contour 220B. In other words, a plurality of upstream thermocouple junctions 208 may be disposed upstream of the centerline 204 near a first plurality of points on an upstream portion of the maximum temperature difference contour 220B extending through the minimum temperature difference location 222. A plurality of downstream thermocouple junctions 210 may be disposed downstream of the centerline 204 near a second plurality of points on a downstream portion of the maximum temperature difference contour 220B extending through the maximum temperature difference location 224. In some embodiments, the plurality of upstream thermocouple junctions 208 and the plurality of downstream thermocouple junctions 210 may not be disposed on the heating structure 202.
FIG. 2B shows an example minimum temperature contour 223 disposed around the location of minimum temperature difference 222. FIG. 2B further illustrates an example maximum temperature contour 225 disposed about the location of maximum temperature difference 224.
In some embodiments, as shown in fig. 2A and 2B, the minimum temperature differential location 222 may be located about 135 microns upstream of the centerline 204. In some embodiments, as shown in fig. 2A and 2B, the location of maximum temperature differential 224 may be about 137 microns downstream of the centerline 204. The locations of the minimum temperature differential location 222 and the maximum temperature differential location 224 may vary with changes in the membrane structure 216 (e.g., shape, thickness), the heating structure 202 (e.g., shape, thickness, material (s)), the voltage applied to the heating structure 202, and other structures.
In some embodiments, each of the plurality of upstream thermocouple junctions 208 and the plurality of downstream thermocouple junctions 210 may include a respective interface between the first thermocouple material and the second thermocouple material, as described in more detail with reference to fig. 11.
In some embodiments, as shown in fig. 2A and 2B, an example thermopile-based flow sensing device 200 may include a substrate defining a membrane structure 216. In some embodiments, a portion of the heating structure 202 may be disposed on the membrane structure 216. In some embodiments, a thermopile, a plurality of thermocouples, a plurality of upstream thermocouple junctions 208, a plurality of downstream thermocouple junctions 210, one or more portions thereof, or a combination thereof may be disposed on the membrane structure 216. In some embodiments, the film structure 216 may provide thermal isolation from a bulk (e.g., silicon) die that may have high thermal conductivity. In some embodiments, the shape of the membrane structure 216 may be rectangular, square, circular, oval, or any other suitable shape or combination thereof.
In other embodiments (not shown in fig. 2A or 2B for simplicity), the example thermopile-based flow sensing device 200 may include a substrate defining a microbridge structure. In some embodiments, a portion of the heating structure 202 may be disposed on the microbridge structure. In some embodiments, a thermopile, a plurality of thermocouples, a plurality of upstream thermocouple junctions 208, a plurality of downstream thermocouple junctions 210, one or more portions thereof, or a combination thereof may be disposed on the microbridge structure.
Fig. 3 illustrates an example layout of an example thermopile-based flow sensing apparatus 300, according to some example embodiments described herein. In some embodiments, a thermopile-based example flow sensing device 300 may be provided for sensing a flow of a fluid 301 (e.g., a flow of a gas or a liquid). In some embodiments, the thermopile-based example flow sensing device 300 may include a heating structure 302 having a centerline 304. In some embodiments, the example thermopile-based flow sensing device 300 may further include a thermopile 306. In some embodiments, at least a portion of thermopile 306 may be disposed on heating structure 302.
In some embodiments, the thermopile 306 may include 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 308 (e.g., nineteen upstream thermocouple junctions) disposed upstream of the centerline 304 of the heating structure 302. In some embodiments, the plurality of thermocouples may have a plurality of downstream thermocouple junctions 310 (e.g., nineteen downstream thermocouple junctions) disposed downstream from the centerline 304 of the heating structure 302. In some embodiments, a plurality of upstream thermocouple junctions 308 and a plurality of downstream thermocouple junctions 310 may be disposed on the heating structure 302. In some embodiments, the number of upstream thermocouple junctions 308 and the number of downstream thermocouple junctions 310 may be the same. In some embodiments, the number of upstream thermocouple junctions 308 and the number of downstream thermocouple junctions 310 may depend on (e.g., may be a function of) the seebeck coefficient of the thermocouple material in the thermocouple and the desired output voltage.
In some embodiments, the thermopile-based example flow sensing apparatus 300 may further include a plurality of upstream sample temperature sensing thermocouple junctions 312 (e.g., two upstream sample temperature sensing thermocouple junctions) disposed upstream of the centerline 304 of the heating structure 302. In some embodiments, the thermopile-based example flow sensing apparatus 300 may further include a plurality of downstream sample temperature sensing thermocouple junctions 314 (e.g., two downstream sample temperature sensing thermocouple junctions) disposed downstream of the centerline 304 of the heating structure 302. In some embodiments, a plurality of upstream sample temperature sensing thermocouple junctions 312 and a plurality of downstream sample temperature sensing thermocouple junctions 314 may be disposed on the heating structure 302.
In some embodiments, each of the plurality of upstream thermocouple junctions 308, the plurality of downstream thermocouple junctions 310, the plurality of upstream sample temperature sensing thermocouple junctions 312, and the plurality of downstream sample temperature sensing thermocouple junctions 314 may include a respective interface between the first thermocouple material and the second thermocouple material, as described in more detail with reference to fig. 11.
In some embodiments, as shown in fig. 3, an example thermopile-based flow sensing device 300 may include a substrate defining a membrane structure 316. In some embodiments, a portion of the heating structure 302 may be disposed on the membrane structure 316. In some embodiments, a thermopile 306, a plurality of thermocouples, a plurality of upstream thermocouple junctions 308, a plurality of downstream thermocouple junctions 310, a plurality of upstream sample temperature sensing thermocouple junctions 312, a plurality of downstream sample temperature sensing thermocouple junctions 314, one or more portions thereof, or a combination thereof may be disposed on the membrane structure 316. In some embodiments, the film structure 316 may provide thermal isolation from a bulk (e.g., silicon) die that may have high thermal conductivity. In some embodiments, the shape of the membrane structure 316 may be rectangular, square, circular, oval, or any other suitable shape or combination thereof.
In other embodiments (not shown in fig. 3 for simplicity), the example thermopile-based flow sensing device 300 may include a substrate defining a microbridge structure. In some embodiments, a portion of the heating structure 302 may be disposed on the microbridge structure. In some embodiments, a thermopile 306, a plurality of thermocouples, a plurality of upstream thermocouple junctions 308, a plurality of downstream thermocouple junctions 310, a plurality of upstream sample temperature sensing thermocouple junctions 312, a plurality of downstream sample temperature sensing thermocouple junctions 314, one or more portions thereof, or a combination thereof may be disposed on the microbridge structure.
Fig. 1 illustrates an example layout of an example thermopile-based
In some embodiments,
In some embodiments, the thermopile-based example
In some embodiments, each of the plurality of
In some embodiments, as shown in fig. 4, an example thermopile-based
In other embodiments (not shown in fig. 4 for simplicity), the example thermopile-based
Fig. 5 illustrates an example layout of an example thermopile-based flow sensing device 500, according to some example embodiments described herein. In some embodiments, a thermopile-based example flow sensing device 500 may be provided for sensing a flow of a fluid 501 (e.g., a flow of a gas or a liquid). In some embodiments, the thermopile-based example flow sensing device 500 may include a heating structure 502 having a centerline 504. In some embodiments, the example thermopile-based flow sensing device 500 may further include a thermopile 506. In some embodiments, at least a portion of thermopile 506 may be disposed on heating structure 502.
In some embodiments, thermopile 506 may include 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 508 (e.g., nineteen upstream thermocouple junctions) disposed upstream of the centerline 504 of the heating structure 502. In some embodiments, the plurality of thermocouples may have a plurality of downstream thermocouple junctions 510 (e.g., nineteen downstream thermocouple junctions) disposed downstream from the centerline 504 of the heating structure 502. In some embodiments, the number of upstream thermocouple junctions 508 and the number of downstream thermocouple junctions 510 may be the same. In some embodiments, the number of upstream thermocouple junctions 508 and the number of downstream thermocouple junctions 510 may depend on (e.g., may be a function of) the seebeck coefficient of the thermocouple material in the thermocouple and the desired output voltage.
In some embodiments, each of the plurality of upstream thermocouple junctions 508 and the plurality of downstream thermocouple junctions 510 may be aligned parallel to the centerline 504 and occur along an upstream vertical line passing near a minimum temperature differential location (e.g., the minimum temperature differential location 222 shown in fig. 2A and 2B) and a downstream vertical line passing through a maximum temperature differential location (e.g., the maximum temperature differential location 224 shown in fig. 2A and 2B). For example, the maximum temperature differential may be defined by a minimum temperature differential at a first location upstream of the centerline 504 (e.g., the minimum temperature differential location 222 shown in fig. 2A and 2B) and a maximum temperature differential at a second location downstream of the centerline 504 (e.g., the maximum temperature differential location 224 shown in fig. 2A and 2B); a plurality of upstream thermocouple junctions 508 may be disposed upstream of the centerline 504 near a first plurality of points on a first line extending through the vicinity of the first location and aligned substantially parallel to the centerline 504; and a plurality of downstream thermocouple junctions 510 may be disposed downstream of the centerline 504 near a second plurality of points extending through a second line near the second location and aligned substantially parallel to the centerline 504. In some embodiments, the plurality of upstream thermocouple junctions 508 and the plurality of downstream thermocouple junctions 510 may not be disposed on the heating structure 502.
In some embodiments, the thermopile-based example flow sensing device 500 may further include a plurality of upstream sample temperature sensing thermocouple junctions 512 (e.g., two upstream sample temperature sensing thermocouple junctions) disposed upstream of the centerline 504 of the heating structure 502. In some embodiments, the thermopile-based example flow sensing device 500 may further include a plurality of downstream sample temperature sensing thermocouple junctions 514 (e.g., two downstream sample temperature sensing thermocouple junctions) disposed downstream from the centerline 504 of the heating structure 502. In some embodiments, a plurality of upstream sample temperature sensing thermocouple junctions 512 and a plurality of downstream sample temperature sensing thermocouple junctions 514 may be disposed on heating structure 502.
In some embodiments, each of the plurality of upstream thermocouple junctions 508, the plurality of downstream thermocouple junctions 510, the plurality of upstream sample temperature sensing thermocouple junctions 512, and the plurality of downstream sample temperature sensing thermocouple junctions 514 may include a respective interface between the first thermocouple material and the second thermocouple material, as described in more detail with reference to fig. 11.
In some embodiments, as shown in fig. 5, an example thermopile-based flow sensing device 500 may include a substrate defining a membrane structure 516. In some embodiments, a portion of the heating structure 502 may be disposed on the film structure 516. In some embodiments, thermopile 506, multiple thermocouples, multiple upstream thermocouple junctions 508, multiple downstream thermocouple junctions 510, multiple upstream sample temperature sensing thermocouple junctions 512, multiple downstream sample temperature sensing thermocouple junctions 514, one or more portions thereof, or a combination thereof may be disposed on membrane structure 516. In some embodiments, the film structure 516 may provide thermal isolation from a bulk (e.g., silicon) die that may have high thermal conductivity. In some embodiments, the shape of the membrane structure 516 may be rectangular, square, circular, oval, or any other suitable shape or combination thereof.
In other embodiments (not shown in fig. 5 for simplicity), the example thermopile-based flow sensing device 500 may include a substrate defining a microbridge structure. In some embodiments, a portion of the heating structure 502 may be disposed on the microbridge structure. In some embodiments, thermopile 506, multiple thermocouples, multiple upstream thermocouple junctions 508, multiple downstream thermocouple junctions 510, multiple upstream sample temperature sensing thermocouple junctions 512, multiple downstream sample temperature sensing thermocouple junctions 514, one or more portions thereof, or combinations thereof may be disposed on the microbridge structure.
Fig. 6 illustrates an example layout of an example thermopile-based
In some embodiments,
In some embodiments, each of the plurality of
In some embodiments, the thermopile-based example
In some embodiments, each of the plurality of
In some embodiments, as shown in fig. 6, an example thermopile-based
In other embodiments (not shown in fig. 6 for simplicity), the example thermopile-based
Fig. 7 illustrates an example layout of an example thermopile-based flow sensing apparatus 700, according to some example embodiments described herein. In some embodiments, a thermopile-based example flow sensing device 700 may be provided for sensing a flow of fluid 701 (e.g., a flow of gas or liquid). In some embodiments, the thermopile-based example flow sensing device 700 may include a heating structure 702 having a centerline 704. In some embodiments, the example thermopile-based flow sensing device 700 may further include a first thermopile 706 and a second thermopile 710.
In some embodiments, the first thermopile 706 may include a plurality of upstream thermocouples having a first plurality of upstream thermocouple junctions 708 (e.g., nineteen upstream thermocouple junctions) disposed upstream of the centerline 704 of the heating structure 702 and a second plurality of upstream thermocouple junctions 709 (e.g., nineteen upstream thermocouple junctions) disposed further upstream of the centerline 704 of the heating structure 702. In some embodiments, the number of first plurality of upstream thermocouple junctions 708 and the number of second plurality of upstream thermocouple junctions 709 may be the same. In some embodiments, the number of first plurality of upstream thermocouple junctions 708 and the number of second plurality of upstream thermocouple junctions 709 may depend on (e.g., may be a function of) the seebeck coefficient of the thermocouple material in the thermocouple and the desired output voltage.
In some embodiments, the first plurality of upstream thermocouple junctions 708 and the second plurality of upstream thermocouple junctions 709 may not be disposed on the heating structure 702. For example, the maximum temperature differential may be defined by a minimum temperature differential at a first location upstream of the centerline 704 (e.g., the minimum temperature differential location 222 shown in fig. 2A and 2B) and a maximum temperature differential at a second location downstream of the centerline 704 (e.g., the maximum temperature differential location 224 shown in fig. 2A and 2B); a first plurality of upstream thermocouple junctions 708 may be disposed upstream of the centerline 704 near a first plurality of points on a first line extending through the vicinity of the first location and aligned substantially parallel to the centerline 704; and a second plurality of upstream thermocouple junctions 709 may be disposed further upstream of the centerline 704 near a second plurality of points of the second line aligned substantially parallel to the centerline 704.
In some embodiments, the second thermopile 710 may include a plurality of downstream thermocouples having a first plurality of downstream thermocouple junctions 712 (e.g., nineteen downstream thermocouple junctions) disposed downstream from the centerline 704 of the heating structure 702 and a second plurality of downstream thermocouple junctions 713 (e.g., nineteen downstream thermocouple junctions) disposed further downstream from the centerline 704 of the heating structure 702. In some embodiments, the number of first plurality of downstream thermocouple junctions 712 and the number of second plurality of downstream thermocouple junctions 713 may be the same. In some embodiments, the number of first plurality of downstream thermocouple junctions 712 and the number of second plurality of downstream thermocouple junctions 713 may depend on (e.g., may be a function of) the seebeck coefficient of the thermocouple material in the thermocouple and the desired output voltage.
In some embodiments, each of the first plurality of upstream thermocouple junctions 708 and the first plurality of downstream thermocouple junctions 712 may be aligned parallel to the centerline 704 and occur along an upstream vertical line passing near a minimum temperature differential location (e.g., the minimum temperature differential location 222 shown in fig. 2A and 2B) and a downstream vertical line passing near a maximum temperature differential location (e.g., the maximum temperature differential location 224 shown in fig. 2A and 2B). For example, the maximum temperature differential may be defined by a minimum temperature differential at a first location upstream of the centerline 704 (e.g., the minimum temperature differential location 222 shown in fig. 2A and 2B) and a maximum temperature differential at a second location downstream of the centerline 704 (e.g., the maximum temperature differential location 224 shown in fig. 2A and 2B); a first plurality of downstream thermocouple junctions 712 may be disposed downstream of the centerline 704 near a third plurality of points on a third line extending through the second location and aligned substantially parallel to the centerline 704; and the second plurality of downstream thermocouple junctions may be disposed further downstream of the centerline 704 near a fourth plurality of points of a fourth line aligned substantially parallel to the centerline 704. In some embodiments, the first plurality of downstream thermocouple junctions 712 and the second plurality of downstream thermocouple junctions may not be disposed on the heating structure 702.
In some embodiments, each of the first plurality of upstream thermocouple junctions 708, the second plurality of upstream thermocouple junctions 709, the first plurality of downstream thermocouple junctions 712, the second plurality of downstream thermocouple junctions 713, the plurality of upstream sample temperature sensing thermocouple junctions, and the plurality of downstream sample temperature sensing thermocouple junctions may include a respective interface between the first thermocouple material and the second thermocouple material, as described in more detail with reference to fig. 11.
In some embodiments, as shown in fig. 7, an example thermopile-based flow sensing device 700 may include a substrate defining a membrane structure 716. In some embodiments, a portion of the
Fig. 8 illustrates an example layout of an example thermopile-based
In some embodiments, the
In some embodiments, the
In some embodiments, each of second plurality of
In some embodiments, each of the first plurality of
In some embodiments, as shown in fig. 8, an example thermopile-based
Fig. 9A, 9B, 9C, 9D, 9E, 9F, 9G, 9H, 9I, 9J, 9K, 9L, 9M, 9N, 9O, 9P, 9Q, 9R, 9S, and 9T illustrate example process flows for manufacturing an example thermopile-based flow sensing apparatus according to some example embodiments described herein.
As shown in fig. 9A, at
As shown in fig. 9B, at
As shown in fig. 9C, at
FIG. 9D illustrates an example layout of an example thermopile-based flow sensing device 905 fabricated at
As shown in fig. 9E, at step 906, the process flow may continue with fabricating (e.g., by depositing, such as by sputtering) a
As shown in fig. 9F, at step 908, the process flow may continue with fabricating (e.g., by depositing and patterning) a first thermocouple material layer 946 (e.g., 60:40NiFe, 80:20NiFe) on the top surface of the
FIG. 9G shows an example layout of an example thermopile-based flow sensing device 909 fabricated at step 908.
As shown in fig. 9H, at
FIG. 9I shows an example layout of an example thermopile-based
As shown in fig. 9J, at step 908, the process flow may continue with fabricating (e.g., by depositing and patterning) a second thermocouple material layer 948 (e.g., Cr) on the top surface of the first
Fig. 9K shows an example layout of an example thermopile-based
In some embodiments,
In some embodiments, each of plurality of
In some embodiments, the thermopile-based example
In some embodiments, each of the plurality of
As shown in fig. 9L, at
FIG. 9M shows an example layout of an example thermopile-based flow sensing device 915 fabricated at
As shown in fig. 9N, at step 916, the process flow may continue to fabricate (e.g., by depositing and patterning) an electrical contact layer 960 (e.g., TiW/Al, TiW/2% Al-Cu) on the top surface of the second
FIG. 9O illustrates an example layout of an example thermopile-based
As shown in fig. 9P, at step 918, the process flow may continue by fabricating (e.g., by Plasma Enhanced Chemical Vapor Deposition (PECVD)) a silicon nitride overcoat 962 (e.g., Si) on the top surface of
Fig. 9Q shows an example layout of an example thermopile-based
As shown in fig. 9R, at step 920, the process flow may continue to fabricate the film structure by forming (e.g., by DRIE) a cavity 964 through the
FIG. 9S shows an example layout of an example thermopile-based flow sensing device 921 fabricated at step 920. In some embodiments, the thermopile-based example flow sensing device 921 may include a substrate defining a membrane structure 968. In some embodiments, a portion of the
In other embodiments (not shown in fig. 9 for simplicity), the example thermopile-based flow sensing device 921 may include a substrate defining a microbridge structure. In some embodiments, a portion of
Fig. 9T shows a legend for the various example layers described with reference to fig. 9A, 9B, 9C, 9E, 9F, 9H, 9J, 9L, 9N, 9P, and 9R.
Fig. 10 illustrates an example layout of an example thermopile-based
In some embodiments, the
In some embodiments, the thermopile example-based
In some embodiments, each of the plurality of
In some embodiments, as shown in fig. 10, an example thermopile-based
In other embodiments (not shown in fig. 10 for simplicity), the example thermopile-based
Fig. 11 illustrates an example table 1100 of thermocouple materials for use in an example thermopile-based flow sensing apparatus, according to some example embodiments described herein. For example, the thermocouple materials shown in the example table 1100 may be used to provide a thermocouple junction that includes an interface between a first thermocouple material and a second thermocouple material. In some embodiments, the number of thermocouple junctions in the thermopile of the thermopile-based example flow sensing devices disclosed herein may depend on (e.g., may be a function of) the seebeck coefficient of the thermocouple material in the thermocouples and the desired output voltage. The term "dS" refers to the difference between the seebeck coefficients of the thermocouple materials in the thermocouple.
In some embodiments, the first thermocouple material may include polysilicon and the second thermocouple material may include aluminum. In some embodiments, the first thermocouple material and the second thermocouple material may include differently doped polysilicon (e.g., n-type and p-type polysilicon). For example, the first thermocouple material may include n-type polysilicon (npo Si) and the second thermocouple material may include p-type polysilicon (ppo Si). In another example, the first thermocouple material may include p-type polysilicon (pPoly Si) and the second thermocouple material may include n-type polysilicon (nPoly Si).
In some embodiments, the first thermocouple material may include a nickel-iron alloy (e.g., 60:40NiFe, 80:20NiFe) and the second thermocouple material may include chromium (Cr), where dS is about 65uV/C for 60:40NiFe and Cr or about 53uV/C for 80:20NiFe and Cr. In some embodiments, the first thermocouple material may include a nickel-iron alloy (e.g., 60:40NiFe, 80:20NiFe) and the second thermocouple material may include chromium disilicide (CrSi2), wherein dS is about 105uV/C for 60:40NiFe and CrSi2 or about 93uV/C for 80:20NiFe and CrSi 2. In some embodiments, the first thermocouple material may include a nickel-iron alloy (e.g., 60:40NiFe, 80:20NiFe), and the second thermocouple material may include rhenium disilicide (ReSi 2).
In some embodiments, the first thermocouple material may include chromium nitride (e.g., CrN) and the second thermocouple material may include copper (Cu), where dS is about 146uV/C for CrN and Cu. In some embodiments, the first thermocouple material may include chromium nitride (e.g., CrN) and the second thermocouple material may include aluminum (Al), wherein dS is about 138uV/C for CrN and Al. In some embodiments, the first thermocouple material may include chromium nitride (e.g., CrN) and the second thermocouple material may include p-type polysilicon (ppy Si), where dS is about 270uV/C for CrN and ppy Si.
In some embodiments, the first thermocouple material may include copper (Cu), and the second thermocouple material may include a copper-nickel alloy (e.g., constantan).
In some embodiments, the thermopile-based flow sensing devices disclosed herein may include any combination of the components, structures, and features discussed with reference to the thermopile-based example
Having described specific components of the example devices involved in the present disclosure, an example process for providing a thermopile-based flow sensing device is described below in connection with fig. 12 and 13.
Fig. 12 illustrates an example flow diagram 1200 that encompasses example operations for manufacturing or otherwise providing an apparatus (e.g., the
As shown in
As shown in
In some embodiments,
Fig. 13 illustrates an example flow diagram 1300 that encompasses example operations for manufacturing or otherwise providing an apparatus (e.g., apparatus 700, 800) for sensing fluid flow in accordance with some example embodiments described herein.
As shown in operation 1302, the example flowchart 1300 may begin by providing a heating structure (e.g., the heating structures 702, 802) having a centerline (e.g., the centerlines 704, 804).
The example flowchart 1300 may continue with disposing a first thermopile (e.g., thermopiles 706, 806) upstream of the centerline of the heating structure, as illustrated by operation 1304. The first thermopile may include a first plurality of thermocouples disposed upstream of a centerline of the heating structure. In some embodiments, the first plurality of thermocouples may include a first subset of the first plurality of thermocouples aligned substantially parallel to a centerline of the heating structure (e.g., upstream
As shown in operation 1306, the example flowchart 1300 may proceed to position a second thermopile (e.g., thermopiles 710, 826) downstream of the centerline of the heating structure. The second thermopile may include a second plurality of thermocouples disposed downstream of the centerline of the heating structure. In some embodiments, the second plurality of thermocouples can include a third subset of the second plurality of thermocouples aligned substantially parallel to the centerline of the heating structure (e.g., downstream
In some implementations, operations 1302, 1304, and 1306 may not necessarily occur in the order depicted in fig. 13. In some embodiments, one or more of the operations depicted in fig. 13 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. 13.
Accordingly, fig. 12 and 13 illustrate example flowcharts describing operations performed in accordance with example embodiments of the present disclosure. It will be understood that each block of the flowchart, and combinations of blocks in the flowchart, can be implemented by various means, such as hardware, firmware, one or more processors, and/or circuitry associated with execution of software including 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 above-described processes may be performed by a material handling apparatus (e.g., robotic arm, servo motor, motion controller, etc.) and computer program instructions residing on a non-transitory computer readable storage memory. In this regard, program code instructions that when executed result in performing the processes described above may be stored by a non-transitory computer-readable storage medium (e.g., memory) of a computing device and executed by a processor of the computing device. In this regard, the computer program instructions which embody the procedures described above may be stored by a memory of an apparatus employing embodiments of the present disclosure and executed by a processor of the apparatus. It will be understood that 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 embodiments of the functions specified in
The flowchart operations described with reference to fig. 12 and 13 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, can be implemented by special purpose hardware-based computer systems which perform the specified functions, or combinations of special purpose hardware and computer instructions.
In some example embodiments, some of the operations herein may be modified or further amplified as described below. Furthermore, in some embodiments, additional optional operations may also be included. It is to be understood that each of the modifications, optional additions or amplifications described herein may be included in the operations herein, either alone or in combination with any other of the features described herein.
The foregoing method descriptions and process flow diagrams are provided merely as illustrative examples and are not intended to require or imply that the steps of the various embodiments must be performed in the order presented. As will be appreciated by those skilled in the art, the order of steps in the above embodiments may be performed in any order. Words such as "after," "then," "next," and the like 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. Furthermore, for example, any reference to claim elements in the singular using the articles "a," "an," or "the" should not be construed as limiting the element to the singular and in some cases, can be construed in the plural.
As described above, and as will be appreciated based on the present disclosure, embodiments of the present disclosure may be configured as a system, an apparatus, a method, a mobile device, a backend network device, a computer program product, other suitable device, and combinations thereof. Thus, embodiments may comprise various means including entirely of hardware, or any combination of software and 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 memories, optical storage devices, or magnetic storage devices. It will be appreciated that any of the computer program instructions and/or other types of code described herein can be loaded onto the circuitry of a computer, processor, or other programmable apparatus to produce a machine, such that the computer, processor, or other programmable apparatus that executes the code on the machine form means for implementing the various functions, including those described herein. In some embodiments, features of the present disclosure may include or be communicatively coupled to an Application Specific Integrated Circuit (ASIC) configured to convert differential output voltages from one or more thermopiles (e.g., 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 can be made by one skilled in the art without departing from the teachings of the disclosure. The embodiments described herein are merely representative and are not intended to be limiting. Many variations, combinations, and modifications are possible and are within the scope of the disclosure. Alternative embodiments resulting from the incorporation, integration, and/or omission of features of one or more embodiments are also within the scope of the present disclosure. Accordingly, the scope of protection is not limited by the description set out above, but is instead defined by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each claim is incorporated into the specification as a further disclosure, and the claims are embodiments of the present disclosure. Moreover, any of the above advantages and features may be related to particular embodiments, but the application of such issued claims should not be limited to methods and structures accomplishing any or all of the above advantages or having any or all of the above features.
Further, the section headings used herein are for consistency with the recommendations of 37c.f.r. § 1.77 or to provide organizational cues. These headings should not limit or characterize the disclosure as set forth in any claims that may issue from this disclosure. For example, a description of a technology in the "background" should not be read as an admission that certain technology is prior art to any disclosure in this disclosure. Neither should the "summary" be considered a limiting characterization of the disclosure set forth in the published claims. Furthermore, any reference in this disclosure to "disclosure" or "embodiments" in the singular should not be used to prove that there is only one point of novelty in this disclosure. Embodiments of the disclosure may be set forth according to the limitations of the various claims issuing from this disclosure, and such claims accordingly define the disclosure protected thereby, and equivalents thereof. In all cases, the scope of these claims should be considered in light of the present disclosure in light of the advantages of the claims themselves, and should not be limited by the headings set forth herein.
Moreover, systems, subsystems, devices, 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 that are shown or discussed as being coupled or communicating 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.
Many modifications and other embodiments of the disclosure set forth herein will come to mind to one skilled in the art to which these embodiments pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Although the drawings show only certain components of the devices and systems described herein, various other components may be used in conjunction with the components and structures disclosed herein. Therefore, it is to be understood that the disclosure is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. For example, various elements or components may be combined, rearranged or integrated into another system, or certain features may be omitted, or not implemented. Further, the steps of any of the methods described above may not necessarily occur in the order depicted in the figures, and in some cases, one or more of the depicted steps may occur substantially simultaneously, or additional steps may be involved. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
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