WO2009124875A1

WO2009124875A1 - Flow-rate sensor and method for manufacturing thereof

Info

Publication number: WO2009124875A1
Application number: PCT/EP2009/053940
Authority: WO
Inventors: Noa Schmid; Helmut Knapp; Mark Fretz; Janko Auerswald
Original assignee: Csem Centre Suisse D'electronique Et De Microtechnique Sa - Recherche Et Developpement
Priority date: 2008-04-09
Filing date: 2009-04-02
Publication date: 2009-10-15
Also published as: CH700906B1

Abstract

The present invention discloses a flow-rate sensor adapted to measure the differential pressure between an inlet and an outlet of a main channel. In embodiments, the flow-rate sensor comprises a sensor channel, wherein the sensor channel comprises an upstream channel, a downstream channel and a sensor die employing a pressure-sensitive membrane having an upstream side and downstream face communicating with the upstream channel and the downstream channel of said sensor channel. In embodiments, thes main channel comprises an inlet channel, a flow-restriction channel and an outlet channel which are operatively connected to each other in series. The sensor channel is operatively connected in parallel to the main channel at an upstream junction and downstream junction such that the pressure-sensitive membrane is subjected to differential pressure between an upstream location and a downstream location with respect to the flow-restriction channel. Additional and alternative embodiments are disclosed and claimed.

Description

FLOW-RATE SENSOR AND METHOD FOR MANUFACTURING THEREOF

FIELD OF THE INVENTION

[0001] The present invention relates to the field of flow-rate measurement and more specifically, to the field of flow-rate sensors that are operational based on the measurement of differential pressure.

BACKGROUND OF THE INVENTION

[0002] Commercially available flow-rate sensor to measure very low fluid flow- rates of, e.g., below 100μI/s, may be based on thermal dispersion mass flow measurement as used employed in hot wire anemometer or other thermal flow- rate sensors; on differential pressure; or on the concept of inertia as employed in association with a mass flow meter or coriolis flow meter. [0003] Fully integrated thermal flow-rate sensors are offered by various companies as exemplified and listed below: [0004] Bronkhorst: http://www.bronkhorst.com/en/products/liquid flow meters & controllers/ http://www.bronkhorst.com/files/published articles/thermal.pdf [0005] Honeywell: http://sensing.honevwell.com/index.cfm7ci id=140301&la id=1&pr id=106049 [0006] Upchurch: http://www.upchurch.com/Products/specsheet.asp?vSpecSheet=799&vFrom=L [0007] Sierra Instruments: http^/www.sierrainstruments.com/products/diciital.html [0008] Sensirion: http://www.sensirion.com/en/02 liquid flow sensors/00 liquid flow sensor.htm [0009] HSG-IMIT: http://www.hsg- imit.de/fileadmin/qfx/pdfs/0801 AB 24 Thermische Stroemungssensoren d e.

[0010] Further, coriolis flow sensors are offered by Bronkhorst and Honeywell: http://www.bronkhorst.com/en/products/liquid flow meters & controllers/cori- flow/ http://hpsweb.honeywell.com/Cultures/en-

US/Products/lnstrumentation/flow/coriolis/default.htm

[0011] Flow-rate sensors that are based on the measurement of differential pressure (hereinafter: differential flow-rate sensor) are offered by Cole Parmer and Seyonic http://www.coleparmer.co.uk/catalog/product index.asp?cls=1766 http://www.seyonic.com/prodflowsensor.php

[0012] Differential flow-rate sensors have a significantly faster response time than thermal flow-rate sensors and Coriolis flow-rate sensors. On the other hand differential flow-rate sensors measure volume flow instead of mass flow.

Examples of differential flow-sensors are outlined herein below.

[0013] US patent δ'945'605 to Francis et al. discloses a non-invasive sensor assembly device that includes a pedestal mounted sensor die for stress isolation of the sensor die from external stresses, a substrate and die porting configuration to limit exposure of the sensor assembly to only the interior of the sensor die and a connecting tube to provide significant isolation of the sensor assembly and its constituent parts from the fluid stream, and an inert coating conformally deposited on the inside surfaces of the die, pedestal, and connecting tube that are in contact with the fluid media to thereby provide complete isolation of the sensor assembly from the media. The pedestal is fabricated on the substrate by screening multiple layers of conductive ink on the substrate, flashing off the solvents, and firing the substrate to burn off the binders to provide a boss of sufficient height such that the sensor die, once mounted on the boss, is substantially isolated from the substrate and, therefore, from included stresses that might otherwise have been transferred to the die from the substrate. The contact area of the boss with the die is optimally selected to provide maximum stress isolation and sufficient mounting strength. A through hole in the substrate and through the longitudinal center of the boss is in cooperative coaxial alignment with a fluid entry port in the die to permit measurement of the physical characteristic of interest within the interior of the die.

[0013] US patent 6'150'681 to Allen discloses a monolithic, integrated circuit sensor combining both a differential pressure sensor and a flow sensor on the same silicon chip. The integrated circuit has a diaphragm with a number of piezo-resistive elements placed on it in the normal manner for a pressure sensor. In addition, a channel is provided between the spaces on the two sides of the diaphragm. The channel has a cross-section which is a fraction of the size of the diaphragm. In one embodiment, the channel is a hole in the diaphragm. In another embodiment, the channel is an etched groove in the frame supporting the diaphragm.

[0014] US patent 5'959'213 to lkeda et al. discloses a semiconductor differential pressure measuring device comprising two measurement diaphragms and two detection sensors provided in a semiconductor substrate using micromachining techniques, and a computing circuit which computes the differences between the two sensor outputs, wherein a communicating hole is provided for applying pressure to each diaphragm so that the diaphragms operate in opposite phases by differential pressure, and two detecting sensors are provided on each diaphragm for detecting displacement or strain of each diaphragm caused by the differential pressure applied to the respective diaphragm, whereby detecting the differences in displacement or strain cancels the static pressure error and temperature error so that the invention has excellent temperature and static pressure characteristics, and whereby the computing circuit comprises a bridge using the two detecting sensors, which substantially reduces the cost of the device.

[0015] US patent 4'565'096 to Knecht et al. discloses a transducer having a first and second sensing diaphragm configured such that a first pressure P1 is applied to the first diaphragm and a second pressure P2 is applied to the second diaphragm and wherein both diaphragms are formed on the same substantially flat face of a diaphragm wafer. The transducer is configured such that each diaphragm responsive to P1 or P2 respectively also affects a fluid in a closed common fluid cavity such that the deflection of the diaphragm is representative of the pressure differential (P1-P2).

[0016] US patent 5'969'591 to Fung discloses a single-sided differential pressure sensing chip having a cavity formed in the top surface of a substrate, a deformable diaphragm spanning the cavity, and a pressure passage connecting the top surface of the substrate with the cavity, and a method of making the same. A first fluid pressure applied to the top surface of the substrate in the vicinity of the diaphragm exerts a force on the top surface of the diaphragm, and a second fluid pressure applied to the top surface of the substrate near the pressure passage exerts a force on the bottom surface of the diaphragm. The diaphragm deflects in response to the forces exerted upon it, and a sensing element detects the flexing of the diaphragm. The pressure sensing chip can be contained within a housing structure formed of a carrier and a cap. The housing structure forms a first pressure chamber that communicates with the top surface of the diaphragm and a second pressure chamber that communicates with the bottom surface of the diaphragm through the pressure passage. The cap can include a first opening for connecting a first fluid pressure with the first chamber, and a second opening for connecting a second fluid pressure with the second chamber.

[0017] US patent δ'898'981 to Boillat e al. discloses a device for measuring pressure in two points of a fluid flow, comprising: a frame consisting of two plates comprising each two planar surfaces, one outer and the other inner and wherein one of the plates is perforated with recess closed by the other plate to form an assembly of two chambers comprising two planar walls parallel to the surfaces of the frame and a side wall forming its periphery and a fluidic restriction channel connecting the two chambers with each other, and means for supplying a measurement of the pressure in each of the chambers. In order to improve the accuracy of the measurement, the side wall of the chambers is perpendicular to its two planar walls and is configured such that the chambers are spindle-shaped.

DESCRIPTION OF THE FIGURES

[0018] These and further features and advantages of the invention will become more clearly understood in the light of the ensuing description of a some embodiments thereof, given by way of example only, with reference to the accompanying figures (FIGs), wherein:

[0019] FIG. 1 is a schematic channel layout illustration of a flow-rate sensor, according to an embodiment of the invention;

[0020] FIG. 2 is a schematic cross-sectional front view illustration of the flow- rate sensor, according to the embodiment of FIG. 1;

[0021] FIG. 3 is a schematic cross-sectional side view illustration of the flow-rate sensor, according to the embodiment of FIG. 1 ;

[0022] FIG. 4 is a schematic top view illustration of a base substrate, according to the embodiment of FIG. 1;

[0023] FIG. 5 is a schematic top view illustration of an intermediate substrate, according to the embodiment of FIG. 1 ;

[0024] FIG. 6 is a schematic isometric illustration of the flow-rate sensor, according to an embodiment of the invention;

[0025] FIG. 7 is a schematic detailed isometric cross-sectional illustration of a sensor die of the flow-rate sensor, according to the embodiment of FIG. 6; [0026] FIG. 8 is a schematic detailed top view illustration of the courses of a flow-restriction channel, an upstream channel and a downstream channel, according to the embodiment of FIG. 6;

[0027] FIG. 9 is a schematic channel-layout illustration of a flow-rate sensor, according to an alternative embodiment of the invention; [0028] FIG. 10 is a schematic detailed isometric illustration of the courses of a flow-restriction channel, an upstream channel and a downstream channel, according to an embodiment of the invention; [0029] FlG. 11 is a schematic isometric detailed cross-sectional illustration of a sensor die, according to the embodiment of FIG. 10;

[003O] FIG. 12 is a schematic detailed top view illustration of the courses of a flow-restriction channel, an upstream channel and a downstream channel, according to the embodiment of FIG. 10;

[0031] FIG. 13 is a schematic channel-layout illustration indicating gas traps in the flow-rate sensor of FIG. 6;

[0032] FIG. 14 is a schematic channel-layout illustration of a flow-rate sensor employing a plurality of sensor dies in parallel, according to an embodiment of the invention;

[0033] FIG. 15A is a schematic top view illustration of base substrate, according to the embodiment of FIG. 14; and

[0034] FIG. 15B is a schematic top view illustration of an intermediate substrate, according to the embodiment of FIG. 14.

DESCRIPTION OF THE INVENTION

[0035] Positional terms such as "upper", "lower" "right", "left", "bottom", "below", "lowered", "low", "top", "above", "elevated", "high", "vertical" and "horizontal" as well as grammatical variations thereof as may be used herein do not necessarily indicate that, for example, a "bottom" component is below a "top" component, or that a component that is "below" is indeed "below" another component or that a component that is "above" is indeed "above" another component as such directions, components or both may be flipped, rotated, moved in space, placed in a diagonal orientation or position, placed horizontally or vertically, or similarly modified. Accordingly, it will be appreciated that the terms "bottom", "below", "top" and "above" may be used herein for exemplary purposes only, to illustrate the relative positioning or placement of certain components, to indicate a first and a second component or to do both.

[0036] It should further be noted that the term "vertically" and "horizontally" as used herein also encompass the meaning of the terms "at least approximately vertically" and "at least approximately horizontally", respectively. [0037] Summary of the invention:

[0038] Embodiments of the present invention disclose a flow-rate sensor comprising a sensor channel and a main channel. Sensor channel comprises a sensor die configured, e.g., as known in the art, employing a pressure-sensitive membrane having an upstream side and downstream face communicating with an upstream channel and a downstream channel of the sensor channel. The pressure-sensitive membrane comprises piezo-resistive material and is thus be electrically responsive to mechanical deflections. More specifically, mechanical deflections of the piezo-resistive membrane may result in a corresponding change in the electrical resistance.

[0039] The main channel comprises an inlet channel, a flow-restriction channel and an outlet channel, which are operatively connected to each other in series. The cross-sectional area of the flow-restriction channel is smaller compared to the cross-sectional area of inlet channel and outlet channel. The cross- sectional area of inlet channel may be at least approximately equal ot the cross- sectional area of the outlet channel. The sensor channel is operatively connected in parallel to the main channel at an upstream junction and downstream junction, wherein the upstream junction is located upstream of the fluid-restriction channel, and the downstream junction is located downstream of the fluid-restriction channel.

[0040] The sensor die is configured such that when being operatively coupled in parallel with a flow-restriction channel, the upstream face is subjected to pressure which is present at a location upstream (hereinafter: upstream location) of the flow-restriction channel, whilst the downstream face is subjected to pressure which is present at a location downstream (hereinafter: downstream location) of the flow-restriction channel. A potential deflection of the pressure- resistive membrane thus corresponds to the differences in absolute pressure P1 and P2 (hereinafter: differential pressure) between an upstream location and a downstream location. It should be noted that the differential pressure (P1-P2) to which the pressure-sensitive membrane may be subjected to may be significantly lower than the system pressure to which two membranes may be subjected to for measuring the differential pressure based on the deflection of each of the two membranes. [0041] The flow-rate sensor comprises at least one substrate comprising at least some of the sensor channel and the main channel.

[0042] The flow-rate sensor according to embodiments of the invention may be adapted to measure differential pressure ranging, for example, from 1 mbar to 100 mbar, and thus the corresponding flow-rate.

[0043] The response time to changes in the flow rate of the flow-rate sensor according to embodiments of the invention may be, for example, maximal 1 ms, and for example have a value of 0.5 ms.

[0044] According to embodiments of the invention, the flow-rate sensor comprises electric conductors such that an electronic readout module is mechanically and operatively coupleable with the electric conductors for readout of the electrical resistance change due to the deflection of the pressure- sensitive membrane.

[0045] According to embodiments of the invention, the flow-rate sensor is configured such that the pressure-sensitive membrane remains unaffected to sudden changes in absolute pressure, but is only affected by the changes in the differential pressure, which is proportional to the flow rate through the flow- restriction channel according to the law of Hagen-Poiseuille. [0046] Detailed description of the invention

[0047] Reference is now made to FIG. 1A and to FIG. 1B. According to embodiments of the invention, flow-rate sensor 1000 comprises an inlet 1211 to an inlet channel 1210 leading to a flow-restriction channel 1230, which leads to an outlet channel 1220 having an outlet 1221. Both inlet channel 1210 and outlet channel 1220 have as cross-sectional area being larger than the cross- sectional area of flow-restriction channel 1230. Accordingly, flow-restriction channel 1230 constitutes a narrowing section between inlet 1211 and outlet 1221 causing a pressure drop of fluid (not shown) flowing from inlet 1211 to outlet 1221 from P1 to P2, wherein P1 is the pressure of the fluid upstream of fluid-restriction channel 1230 and P2 is the pressure of the fluid downstream of fluid-restriction channel 1230. The drop in the pressure (P2-P1) is at least approximately proportional to the fluid's volume flow or flow-rate. The proportionality may be expressed by the Hagen-Poisseuilles law. [0048] Flow-rate sensor 1000 further comprises a sensor channel 1100 which communicates in parallel with flow-restriction channel 1230 via inlet channel 1210 and outlet channel 1220 such to share inlet 1211 and outlet 1221. More specifically, sensor channel 1100 comprises an upstream channel 1240 which communicates upstream of flow-restriction channel 1230, at an upstream junction 1241, with inlet channel 1210. Further, sensor channel 1100 comprises a downstream channel 1250 which communicates with outlet channel 1220 at a downstream junction 1251. It should be noted that to simplify the discussion that follows, a possible drop in pressure of fluid in inlet channel 1210, outlet channel 1220, upstream channel 1240 and downstream channel 1250 may be considered as negligible, at least in comparison to the drop in pressure of fluid between upstream channel 1210 and downstream channel 1220 caused by flow-restriction channel 1230.

[0049] Sensor channel 1100 additionally includes a sensor die 1500, e.g., as known in the art, comprising a pressure-sensitive membrane 1115, which may be U-shaped such to have a diaphragm 1118 connected to legs 1119, which are coupled to a membrane substrate 1111 comprising a fluid opening 1112. Upstream channel 1240 operatively communicates via an upstream outlet 1260 with an upstream face 1113 of pressure-sensitive membrane 1115. Similarly, downstream channel 1250 operatively communicates via a downstream outlet 1270 with a downstream face 1114 of pressure-sensitive membrane 1115. [0050] According to embodiments of the invention, flow-restriction channel 1230, upstream channel 1240 and downstream channel 1250 are manufactured in at least one substrate layer, as outlined herein below in greater detail. [0051] Further reference is now made to FlG. 2 and FIG. 3. According to embodiments of the invention, flow-rate sensor 1000 comprises a base substrate 2100, whereon an intermediate substrate 2200 is provided. In embodiments of the invention, flow-rate sensor 1000 moreover may comprise a circuit substrate 2300 including or constituting a circuit board having an electrical circuit and/or comprising electric connections and/or electric components such as, for example, an amplifier or amplifier circuit. According to embodiments of the invention, circuit substrate 2300 may for example comprise electric vias 2355 terminating in electric connections. Intermediate substrate 2200 may be sandwiched between circuit substrate 2300 and base substrate 2100. To simplify the discussion that follows, circuit substrate 2300 comprising or constituting the circuit board is hereinafter referred to as "circuit board 2300". Circuit board 2300 may have a concavity 2310 adapted to house therein in a sealed manner sensor die 1500 and may be mechanically coupled, e.g., adhesively, with intermediate substrate 2200. Accordingly, circuit board 2300 may constitute a part of a housing of flow-rate sensor 1000. [0052] The course of inlet channel 1210, outlet channel 1220, flow-restriction channel 1230, upstream channel 1240 and downstream channel 1250 in flow- rate sensor 1000 is outlined hereinafter. It should however be noted that the described course is for exemplary purposes only and that it may be vary in respective embodiments of the invention.

[0054] According to embodiments of the invention, inlet channel 1210 may first run horizontally from its inlet 1211 and then vertically in circuit board 2300 via intermediate substrate 2200 to base substrate 2100. In base substrate 2100, inlet channel 1210 may run horizontally such to pass upstream junction 1241 and to lead into flow-restriction 1230. Flow restriction 1230 may run horizontally in base substrate 2100 and lead into outlet channel 1220 prior to passing downstream junction 1251. Outlet channel 1220, after passing downstream junction 1251 may further run horizontally in base substrate 2100 and then vertically from base substrate 2200 via intermediate substrate 2200 to circuit board 2300. In circuit board 2300, outlet channel 1220 may run horizontally and terminate in its outlet 1221.

[0055] Additional reference is now made to FIG. 4. According to embodiments of the invention, upstream channel 1240 may depart horizontally from upstream junction 1241 and run within base substrate 2100 until it vertically emerges into intermediate substrate 2200 to terminate in concavity 2310 such to communicate with upstream face 1113 of pressure-sensitive membrane 1115. Similarly, downstream channel 1250 may depart horizontally from downstream junction 1251 and run within base substrate 2100 until downstream channel 1250 vertically emerges out of intermediate substrate 2200 such to communicate with downstream face 1114 of pressure sensitive membrane 1115.

[0056] According to some embodiments of the invention, a flow-rate sensor such as, for example, flow-rate sensor 1000 may be designed to prevent or at least to reduce the risk of contamination and/or clogging flow in flow-restriction channel 1230, since any change in the geometry of flow-restriction channel 1230 may cause a corresponding change of the pressure drop between an upstream location and a downstream location such as, for example, upstream junction 1241 and downstream junction 1251. As a consequence, the flow-rate and thus the corresponding measurement thereof may be altered. Further, performed calibration of flow-rate sensor 1000 may be distorted. Therefore, according to some embodiments of the invention, the section of inlet channel 1210 and outlet channel 1220 integrated in intermediate substrate 2200 may comprise a plurality of parallel channels 1231 which may act as a backup to one another to reduce the risk that particles enter flow-restriction channel 1230 and clog within the latter the flow of fluid. Additionally or alternatively, a filter structure (not shown) may be included, e.g., in base substrate 2100, wherein the filter structured may be employed such to reduce the risk of clogging of flow- restriction channel 1230.

[0057] According to some embodiments of the invention, circuit board 2300 may comprise fluidic connections. For example, at least some of the horizontal portion of inlet channel 1210 and outlet channel 1220 in circuit board 2300 may be embodied by fluidic connections such as, for example, an inlet tube 2361 and an outlet tube 2362, respectively, and/or by any other suitable fluidic connection such as, for example, threaded holes.

[0058] Additional reference is now made to FIG. 5. According to embodiments of the invention, flow-rate sensor 1000 comprises a plurality of membrane connections 2351 and circuit connections 2352 provided between intermediate substrate 2200 and circuit board 2300. More specifically, membrane connections 2351 are provided between pressure-sensitive membrane 1115 and intermediate substrate 2200, and further to make a seal between concavity 2310 and intermediate substrate 2200 to guide fluid to upstream face 1113 of pressure-sensitive membrane 1115.

[0058] According to embodiments of the invention, pressure-sensitive membrane 1115 is flipped such that its diaphragm 1118 is electrically coupled to membrane connections 2351. Thusly configured, flow-rate sensor 1000 obviates the need of employing wirebonds that would otherwise be required for electrically coupling pressure-sensitive membrane 1115 with electric vias 2355. [0059] According to embodiments of the invention, circuit connections 2352 may be aligned with and positioned between respective electrical vias 2355 of circuit board 2300 and intermediate substrate 2200. As is schematically illustrated in FIG. 5, circuit connections 2352 are electrically coupled via electric conducts 2356 with respective membrane connections 2351. Consequently, electric vias 2355 are electrically coupled with pressure-sensitive membrane 1115. [0060] According to some embodiments of the invention, electric vias 2355 may electrically communicate with integrated circuitry, and/or electronic components such as, for example, transistors, electric conducts and/or interconnections provided and/or embedded in circuit board 2300.

[0061] According to embodiments of the invention, the number of electric conducts 2356 employed connecting between membrane connections 2351 and circuit connections 2352 enables for example the connection to a Wheatstone bridge which may be implemented on sensor die 1500.

[0062] According to embodiments of the invention, flow-rate sensor 1000 may comprise additional conductive connections and/or conducts (not shown) to enable the implementation of an integrated temperature sensor such as, for example, thermocouples, thermistors, resistance temperature detectors (RTDs) etc. Membrane connections 2351 and/or circuit connections 2352 may have a relatively low modulus of elasticity of, e.g. < 10 MPa.

[0063] According to embodiments of the invention, flow-rate sensor 1000 may further include seals 2360 between intermediate substrate 2200 and circuit board 2300 to make a seal between intermediate substrate 2200 and concavity 2310. Similar to membrane connections 2351 and/or circuit connections 2352, seals 2360 may be made of a material having a relatively low modulus of elasticity of, e.g., < 10 MPa. The relatively low modulus of elasticity of seals 2360 and/or membrane connections 2351 and/or circuit connections 2352 are chosen such to limit the mechanical stress between intermediate substrate 2200 and circuit board 2300 that might develop due to their possible difference in coefficient of thermal expansion.

[0064] According to embodiments of the invention, flow-rate sensor 1000 may include an electronic readout 2400 adapted to measure a change in electrical resistance due to the deflection of pressure-sensitive membrane 1115. Electronic readout 2400 may be electrically coupleable with pressure-sensitive membrane 1115, e.g., by placing electronic readout 2400 on circuit board 2300 such that electronic readout 2400 operatively communicates with electrical vias 2355. Electronic readout 2400 may be adapted, for example, to amplify signals corresponding to change in electrical resistance in response to the mechanical deflections of pressure-sensitive membrane 1115, and/or to perform analog-to- digital conversion and/or to calibrate flow-rate sensor 1000 based on the measured differential pressure and temperature. Electronic readout 2400 may be mechanically coupled e.g., soldered, with circuit board 2300. [0065] It should be noted that in some embodiments of the invention, at least some of the functions that may be performed by electronic readout 2400 may additionally or alternatively performed by elements of circuit board 2300. For example, amplification may be performed by elements embedded in circuit board 2300. As a consequence, in some embodiments of the invention, flow- rate sensor 1000 may be operational without the employment of electronic readout 2400.

[0066] According to some embodiments of the invention, flow-rate sensor 1000 may be circuit board-less, i.e., flow-rate sensor 1000 may not include circuit board 2300. Instead, a change in the resistance of pressure-sensitive membrane 1115 may be measured simply by applying a voltage between circuit connections 2352, e.g., with or without performing amplification of the measured change in resistance. Further, a tube or hose (not shown) may be operatively coupled with fluid opening 1112 and thus with upstream face 1113 of pressure- sensitive membrane 1115.

[0067] Referring to FIG. 6, a schematic isometric illustration of flow-rate sensor 1000 is depicted; referring to FIG. 7 a schematic isometric detailed cross- sectional illustration of sensor die 1500 is depicted; and referring to FIG. 8, a schematic top view illustration of courses of flow-restriction channel 1230, upstream channel 1240 and downstream channel 1250 is depicted. [0068] According to embodiments of the invention, the length of a first course of fluid flow measured from a location upstream of upstream junction 1241 until upstream face 1113 as well as the length of a second course of fluid flow measured from said location to downstream face 1114 is at least approximately equal. As a consequence, changes in the absolute pressure at the upstream location are conveyed to upstream face 1113 and downstream face 1114 by an at least approximately equal delay. Therefore, upstream face 1113 and downstream face 1114 are subjected to changes in absolute pressure att least approximately at the same time, thus preventing deflections of pressure- sensitive membrane 1115 corresponding to changes in absolute pressure only at the upstream location or the downstream location. Correspondingly, pressure-sensitive membrane 1115 is unaffected by sudden changes in the absolute pressure that might occur at the upstream location and/or at the downstream location, but may thus only affected by the changes in the differential pressure between the upstream and downstream location and thus less prone to damage. More specifically, pressure-sensitive membrane 1115 may be subjected to at any given time to P1-P2 and not to P1 or P2 alone. It should be noted that the term "any given time" also encompasses the term "substantially at any given time".

[0069] As is schematically illustrated in FIG. 1 , FIG. 2, FIG. 3, FIG. 4, FIG. 5 and FIG. 6, upstream outlet 1260 and downstream outlet 1270 communicate with opposite sides of diaphragm 1118. However, as is outlined herein below, with reference to FIG. 9, FIG. 10, FIG. 11 and FIG. 12, a flow-rate sensor 9000 according to an embodiment of the invention may employ a single-sided differential pressure die, for example, as disclosed in US patent 5'969'591. For example, flow-rate sensor 9000 may employ a sensor die 9500 comprising a housing 1116 wherein upstream outlet 1260 (of an upstream channel 9240) and downstream outlet 1270 of a downstream channel 9250 terminate with respect to diaphragm 1118 at the same side. Sensor die 9500 further comprises a seal 1280, which diverts fluid exiting upstream outlet 1260 towards upstream face 1113 and fluid exiting downstream outlet 1270 towards downstream face 1114, thereby subjecting different sections of diaphragm 1118 at the same side with respective upstream pressure P1 and downstream pressure P2. Consequently, the deflection of diaphragm 1118 corresponds to the differential pressure P1- P2.

[0070] Reference is now made to FIG. 13. According to embodiments of the invention, flow-rate sensor 1000 may be adapted to measure the flow-rate of a fluid which may be, e.g., a liquid 1295. In that case, gas pockets 1290 may be trapped between sensor die 1500 and inlet channel 1210 and outlet channel 1220. The appearance of gas pockets 1290 may be utilized to protect sensor die 1500 from liquid 1295, which may be aggressive (e.g., highly acidic or basic) such to have the potential to damage sensor die 1500. Clearly, the phenomenon of gas pockets 1290 may be utilized when merely measuring pressure of liquid 1295, instead of measuring the flow-rate of the latter. [0071] According to embodiments of the invention, upstream channel 1240 and downstream channel 1250 may have a length such that borders 1293 between liquid 1295 and gas 1290 appear at locations that are between upstream junction 1241 and sensor die 1500, as well as between downstream junction 1251 and sensor die 1500, respectively.

[0072] According to embodiments of the invention, flow-rate sensor 1000 may be configured such that the volume of gas is such that still ensures a responsiveness of, e.g., maximal 1 ms. For example, the volume of the gas surrounding sensor die 1500 may be as small as possible. [0073] Reference is now made to FIG. 14, and FIG. 15A. According to embodiments of the invention, a plurality of sensor dies 1500 may be integrated into a flow-rate sensor 14000, which may be configured such that each one measures a corresponding differential pressure. More specifically, flow-rate sensor 14000 may comprise sensor dies 1500A and 1500B that are operatively connected to each other in parallel. Sensor die 1500A may communicate with upstream channel 14240A and with downstream channel 14250A and be connected in parallel to flow-restriction channel 14230 through inlet channel 14210 and outlet channel 14220. Sensor die 1500B communicates with downstream channel 14250B which is connected in parallel to upstream channel 14240A. In addition, sensor die 1500B communicates with inlet channel 14210B and outlet channel 14220B. Thusly configured, the system pressure to which sensor die 1500A is subjected to corresponds to P1-P2, wherein P1 may be the pressure upstream of flow-restriction channel 14230 and P2 the pressure downstream of flow-restriction channel 14230. The system pressure to which sensor die 1500B may be subjected to corresponds to P0-P1, wherein PO is the pressure in inlet channel 1421 OB. As a consequence, flow- rate sensor 14000 may be adapted to measure relative high absolute pressure of e.g., 10 bar, with sensor die 1500B; and a relative low differential pressure corresponding to a flow rate of, e.g., less than 100 μl/seconds,. [0074] It should be noted that the length of a first course of fluid flow measured from a location upstream of upstream junction 1241 until upstream face 14113, as well as the length of a second course of fluid flow measured from said location to downstream face 14114 may be at least approximately equal. [0075] Reference is now made to FIG. 15B. Flow-rate sensor 14000 includes membrane connectors 2351, readout connections 2352, electric conducts 2356 and electric vias (not shown) such to enable the readout of P0-P1 and P1-P2 by electronic readout 2400.

[0076] Manufacturing methods of a flow-rate sensor according to an embodiment of the invention such as, for example, flow-rate sensor 1000, may include the following steps: providing base substrate 2100; providing inlet channel 1210, providing outlet channel 1220 providing flow-restriction channel 1230, upstream channel 1240 and downstream channel 1250 in base substrate 2100. Further, the method may include providing intermediate substrate 2200; and providing therein inlet channel 1210, outlet channel 1220, upstream channel 1240 and downstream channel 1250. The method may additionally include providing membrane connections 2351 , circuit connections 2352; and seals 2360 on intermediate substrate 2200. The method may also include the step of providing intermediate substrate 2200 onto base substrate 2100 to provide a cover for base-sections of inlet channel 1210, outlet channel 1220, flow-restriction channel 1230; upstream channel 1240 and downstream channel 1250 and such that intermediate-sections of the channels communicate with base-sections of the channels, as is for example schematically illustrated in FIG. 2, FIG. 3 and FIG.4.

[0077] In addition, the method may include providing electric vias 2355, sensor die 1500 and circuit-board sections of flow-restriction channel 1230 into circuit board 2300; and providing circuit board 2300 on intermediate substrate 2200 such that intermediate-sections of the channels communicate with circuit-board sections of the channels and such that sensor die 1500 communicates with electric vias 2355.

[0078] According to embodiments of the invention, upstream channel 1240 and downstream channel 1250 may be provided into base substrate 2100 and/or intermediate substrate 2200, e.g., as known in the art, for example, by employing an etching process like, for example, wet etching and/or Deep Reactive Ion Etching (DRIE) and/or sand blasting; and/or by employing photostructurable glass, epoxy or polysiloxane and/or a structured tape between base substrate 2100 and intermediate substrate 2200. Structures provided in the photostructurable epoxy (SU-8), polysiloxane and/or the structured tape enables the direct manufacturing of upstream channel 1240 and downstream channel 1250 in an etching-less process, which is a process that obviates the need of employing any additional etching processes.

[0079] It should be noted that the sequence of the above-mentioned steps for manufacturing a flow-rate sensor according to an embodiment of the invention should not be construed as limiting and that the order of the steps may be interchanged and ordered in any others suitable way. It should further be noted that at least some of the above-mentioned steps may be performed in a plurality of steps or consolidated into a fewer steps, e.g., as known in the art. [0080] According to some embodiments of the invention, base substrate 2100 and/or intermediate substrate 2200 may be made for example, of silicon or glass, or any other suitable material. According to embodiments of the invention the piezo-sensitive material of pressure-sensitive membrane 1115 and the material of circuit board 2300 may be chosen such that the coefficient of thermal expansion is at least approximately equal. According to embodiments of the invention, circuit board 2300 may be made, of a material suitable for implementing a printed circuit board (PCB), (e.g. woven glass with epoxy), e.g., as known in the art.

Claims

1. A flow-rate sensor adapted to measure the differential pressure between an inlet and an outlet of a main channel, characterized by comprising a sensor channel, wherein said sensor channel comprises an upstream channel, a downstream channel and a sensor die employing a pressure-sensitive membrane having an upstream side and downstream face communicating with said upstream channel and said downstream channel of said sensor channel; wherein said main channel comprises an inlet channel, a flow-restriction channel and an outlet channel which are operatively connected to each other in series, and wherein said sensor channel is operatively connected in parallel to said main channel at an upstream junction and downstream junction such that said pressure-sensitive membrane is subjected to differential pressure between an upstream location and a downstream location with respect to said flow- restriction channel.

2. The flow-rate sensor of claim 1 , wherein said flow-restriction channel has a cross-sectional area that is smaller compared to the cross-sectional area of said inlet channel and said outlet channel.

3. The flow-rate sensor according to any of the preceding claims, wherein said inlet channel and said outlet channel have an at least approximately equal cross-sectional area.

4. The flow-rate sensor according to any of the preceding claims comprising at least one substrate integrating at least some of said sensor channel and said main channel.

5. The flow-rate sensor of according to any of the preceding claims, characterized in that the length of a first course of fluid flow measured from a location upstream of said upstream junction until upstream face as well as the length of a second course of fluid flow measured from said location is at least approximately equal such that changes in the absolute pressure at said location are conveyed to said upstream face and said downstream face by an at least approximately equal delay.

6. The flow-rate sensor according to any of the preceding claims, characterized in that said upstream face and said downstream face are on opposite sides of the diaphgram of said pressure-sensitive membrane.

7. The flow-rate sensor according to any of the preceding claims, characterized in that said upstream face and said downstream face are on the same side of the diaphgram of said pressure-sensitive membrane.

8. The flow-rate sensor according to any of the preceding claims characterized by comprising an electronic readout which is electrically coupled with said pressure-sensitive membrane.

9. The flow-rate sensor according to any of the preceding claims, characterized by comprising electrical conductors, membrane connections and electronic readout connections that are operative with said pressure-sensitive membrane.

10. The flow-rate sensor according to any of the preceding claims, characterized in that said base substrate and said intermediate substrate are made of material consisting of the following group: silicon, and glass

11.A manufacturing method for manufacturing the flow-rate sensor according to any of the preceding claims characterized by: providing said sensor channel and said main channel in said at least one substrate; providing seals, membrane connections, circuit connections and electric conducts on an intermediate substrate of said at least one substrate.

12. The manufacturing method according to claim 11 , characterized in that providing said upstream channel and said downstream channel is accomplished by at least one of the following methods: etching, sand blasting, by photostructurable glass, polysiloxane or epoxy (SU-8); and by a structured tape.