GB2588397A

GB2588397A - Flow sensor assembly

Info

Publication number: GB2588397A
Application number: GB1915211.5A
Authority: GB
Inventors: De Luca Andrea; Gardner Ethan; Zeeshan Ali Syed; Udrea Florin
Original assignee: Flusso Ltd
Current assignee: Flusso Ltd
Priority date: 2019-10-21
Filing date: 2019-10-21
Publication date: 2021-04-28
Also published as: GB201915211D0

Abstract

A flow sensor assembly is disclosed comprising flow sensing channel regions with different cross-sectional areas for optimum performance with different flow ranges. The flow sensor assembly comprises a flow inlet channel 1; a flow outlet channel 2; a flow sensing channel 3a, 3b, 3c through the flow sensor assembly located between the flow inlet channel 1 and the flow outlet channel 2; one or more substrates; and one or more dielectric layers each located on a first side of a substrate. The flow sensing channel comprises at least two flow sensing channel regions 3a, 3b, 3c. A first flow sensing channel region 3a has a first cross-sectional area and a second flow sensing region 3b has a second cross-sectional area different from the first cross-sectional area. The flow sensor assembly has at least two flow sensing elements 4a, 4b, 4c each located on or embedded within a dielectric layer. A first flow sensing element 4a is configured to sense fluid flow in the first flow sensing channel region 3a and a second flow sensing element 4b is configured to sense a fluid flow property in the second flow sensing channel region 3b. The sensor assembly may be a MEMS thermal flow sensor. The sensing elements may be resistive hot wires. The flow channel regions may be in series fig. 1 or parallel fig. 3.

Description

Flow Sensor Assembly

Field

The present disclosure relates to flow sensor packaging, particularly but not exclusively, to MEMS based thermal flow sensors, that are integrated into assembly level packaging.

Background

Micro-machined sensors are used in an eclectic range of applications including industrial, medical, automotive, aeronautical, space, military and others. Namely, flow sensors can be used to measure the flow rate of a fluid. It is due to the ongoing market demand that there is a need for constant miniaturisation of flow sensors, which comes with inherent problems not seen with macro-scale sensor implementation.

Reviews of fluid flow sensors have been previously published in (B. Van Oudheusden, "Silicon flow sensors," in Control Theory and Applications, IEE Proceedings D, 1988, pp. 373-380; B. Van Oudheusden, "Silicon thermal flow sensors," Sensors and Actuators A: Physical, vol. 30, pp. 5-26, 1992; N. Nguyen, "Micromachined flow sensors-A review," Flow measurement and Instrumentation, vol. 8, pp. 7-16, 1997; Y.-H. Wang et at, "MEMS-based gas flow sensors," Microfluidics and nanofluidics, vol. 6, pp. 333-346, 2009; J. T. Kuo et at, "Micromachined Thermal Flow Sensors-A Review," Micromachines, vol. 3, pp. 550-573, 2012). One issue in miniaturising flow sensors is the packaging.

Typically, the packaging is concentrated on protecting the flow sensor from being damaged or contaminated by the flowing media and/or mechanical loads of the module. Examples of this are given in US2017/0184433, US4548078, U55404753 and US9003877. Many other reports of fluid flow packaging concentrate on methods that promote laminarising the flow, such as US2018/0172493 and U52016/0161314. Improving flow channel design has also been used to control the flow and thereby increase the sensitivity measured by the sensor. Some examples are US6813944 and U57793410. US8418549 and US9091577 are related to changing the measurable flow range with use of a bypass channel.

Summary

Aspects and preferred features are set out in the accompanying claims.

According to a first aspect of the present disclosure, there is provided a flow sensor assembly comprising: a flow inlet channel; a flow outlet channel; a flow sensing channel through the flow sensor assembly located between the flow inlet channel and the flow outlet channel, and wherein the flow sensing channel comprises at least two flow sensing channel regions, wherein a first flow sensing channel region has a first cross-sectional area and a second flow sensing region has a second cross-sectional area different from the first cross-sectional area; one or more semiconductor substrates; one or more dielectric layers, each located on a first side of a semiconductor substrate of the one or more semiconductor substrates; and at least two flow sensing elements each located on or within a dielectric layer wherein a first flow sensing element is configured to sense a fluid flow property in the first flow sensing channel region and a second flow sensing element is configured to sense a fluid flow property in the second flow sensing channel region.

At least one semiconductor substrate may comprise an etched portion. At least one dielectric layer may comprise at least one dielectric membrane located over the etched portion of the semiconductor substrate. Generally speaking, a dielectric membrane region may be located immediately adjacent to the etched portion of the substrate. The dielectric membrane region corresponds to the area of the dielectric region above the etched cavity portion of the substrate. Each dielectric membrane region may be over a single etched portion of the semiconductor substrate.

The flow sensing elements may be formed on or within the at least one dielectric membrane.

The flow sensor assembly may comprise: A flow sensor chip or flow sensor, comprising of at least one semiconductor substrate and a dielectric membrane on the front side of the semiconductor substrate, which is also the front side of the chip. The semiconductor substrate may have at least one etched portion, and the part of the dielectric adjacent to the etched portion may be referred to as a membrane.

A housing defining at least part of the inlet port (or flow inlet channel) and at least part of the outlet port (or flow outlet channel), and defining the flow channel (or flow sensing channel) within. The flow channel defined includes an inhomogeneous cross-section of at least two different sizes between the inlet port and the outlet port.

At least two flow sensors may be integrated into the assembly in at least two parts of the flow channel with different cross-sections, each measuring the fluid flow rate through their relative section. The at least said two flow sensors may be placed such that they are exposed to the fluid flow in the said flow channel in at least two of the cross-sectional regions (or flow sensing channel regions), each measuring the fluid flow rate through their relative section.

An array of flow sensors may have a common semiconductor substrate (as part of the same chip) or manufactured as part of the wafer.

Such an assembly forces a range of fluid velocities through one system, allowing multiple optimum channel cross-sections for a variety of flow-ranges. This will create a system with an increased flow rate range in addition to increasing sensitivity or accuracy across this large range. For example, when the flow rate is low, the sensor in the region of the large cross-section will not see much effect and have low sensitivity or accuracy, whilst the sensor in the region of the small cross-section will see a greater effect due to higher fluid velocity. Conversely, when the flow rate is high, the sensor in the region of the small cross-section may not be able to measure it as it might be beyond its sensing range, or where the signal saturates at high flow velocities, but will be measurable by the sensor in the region of the larger cross-section.

The flow sensor housing may comprise of more than one channel, with multiple or an array of flow sensors, and one or more channels having varying cross-sections throughout their length. The horizontal widths, vertical heights of each channel can be varied to allow measurement in different flow ranges.

The array of flow sensors may be integrated on the same chip, or could be manufactured as part of the same semiconductor wafer in which case the membranes, heaters or any thermal sensors can be done at the same time during the fabrication process The substrate on the flow sensor chip can have the cavity with sloping sidewalls (formed by KOH (Potassium Hydroxide) or TMAH (Tetramethylammonium hydroxide) etching), or with vertical sidewalls (formed by Deep Reactive Ion Etching (DRIE)). The cavity in the semiconductor substrate may be etched from the backside of the chip (the side opposite the dielectric) -and may etch all the way up to the dielectric or be etched partway. The dielectric region adjacent to the cavity may be referred to as a membrane, and the membrane may or may not have holes. The membrane can be circular, rectangular or rectangular with rounded corners. The substrate may be made from any semiconductor material, such as Silicon, Germanium, Gallium Nitride or Silicon Carbide.

The flow sensor design and geometry may be altered to create a sensor best suited for the range of flow it is intended to measure.

The sensor can be used for any fluid, such as liquids and gases.

The at least one dielectric membrane may comprise at least one recessed region (holes) between one of the flow sensing elements and an edge of the dielectric membrane.

An edge of the dielectric membrane may refer to a perimeter edge of the dielectric membrane, in other words, the area where the dielectric membrane meets or joins the semiconductor substrate. The area of the dielectric layer or region above the semiconductor substrate may refer to the area of the dielectric layer outside the dielectric membrane.

The at least one recessed region may comprise one or more discontinuous regions where the thickness of the dielectric membrane is discontinuous or varies from an average or most common dielectric membrane thickness. The at least one recessed region or discontinuity in the dielectric membrane provide an interruption (or partial interruption) in the thermal conduction path through the solid of the dielectric membrane. This in turn will mean that the heat path will occur more through the fluid above the recess (via conduction and convention) or through the cavity space formed as a result of the recess (mainly through fluid conduction). In both cases (heat above the cavity space or within the cavity space), the heat dissipation will depend on the thermal conductivity of the fluid.

The at least one recessed region may comprises one or more holes. The holes may refer to apertures, perforations or slots extending through an entire height or depth or thickness of the dielectric membrane. This would be advantageous, as the thermal conduction path through the solid of the dielectric membrane will be impeded and this will mean that the thermal conduction will occur through the holes (mainly via conduction) or above the holes (via both conduction and convection), thus facilitating the measurement of the composition of the fluid based on the different thermal conductivity of each of the components of the fluid flow.

The at least one of the one or more holes may comprise an elongate slot extending towards opposite edges of the dielectric membrane. The elongate slot may not extend completely to the edges of the dielectric membrane. This increases thermal isolation across a width of the dielectric membrane of the device. Optionally the elongate slot may be extending in a same direction as one or more heating elements and/or sensing elements. The elongate slots may be, for example, rectangular, square, or semicircle.

The one or more holes may comprise an array of perforations. The perforations may comprise individual holes significantly smaller than a width of the dielectric membrane of the device. The array of perforations may can extend substantially across a width of the device.

The at least one recessed region may comprise a partial recess within the dielectric membrane. The partial recess or trench may extend from a top surface of the dielectric membrane or may extend from a bottom surface of the dielectric membrane. The partial recess may extend partially through a height or depth or thickness of the dielectric membrane.

The first flow sensing element may be formed on or within a first dielectric membrane and the second flow sensing element may be formed on or within a second dielectric membrane. The first dielectric membrane may have a different area to the second dielectric membrane. The flow sensor assembly may have has different die, dielectric membrane and/or resistor size for each cross-sectional area or flow sensing channel region.

The at least one flow sensing element may comprise at least one heating element. The heating element may be a resistive hotwire. The change in the resistance of the heating elements is associated with the flow rate, speed, volume or mass flow rates.

The heating element could be maintained in a constant temperature or constant resistance mode by modifying the power supplied to the heater element. In this case, one can measure the change in the power due to the flow rate, velocity, volume or mass flow rates.

The flow sensor may work on anemometric, calorimetric or time of flight principle. In the anemometric principle the membrane includes a single heater, and the flow of fluid increases the power consumption on the heater. The heater may be operated in either constant temperature, constant power, constant current or constant voltage mode. In a calorimetric principle, the membrane includes at least one heater and at least one (typically two) temperature sensor. The heater may be operated in constant temperature mode, while the reading from the temperature sensor, or sensors may vary the fluid flow. In time of flight principle, a heater and temperature sensor are present. The power applied to the heater is varied, and the time taken for the signal to reach the temperature sensor determines the rate of fluid flow.

The heater can be a resistive heater made of a CMOS material, such as aluminium, polysilicon, tungsten, titanium or single crystal silicon. Alternately the heater can be a diode or a transistor. The heater can also be a non-CMOS material, such as platinum.

The at least one heater may be embedded within the membrane.

The at least one flow sensing element may comprise at least one temperature sensing element comprising any of a resistor, a diode, a thermocouple, or a thermopile. The temperature sensor may be a resistive temperature sensor, made of platinum, tungsten, aluminium, polysilicon, titanium or single crystal silicon. Alternatively it can be a thermocouple, or a thermopile made with a combination of metal, polysilicon or single crystal silicon.

The at least one flow sensing element may comprise at least one piezo-resistor. The piezo-resistor may be formed on or within the membrane.

The flow sensor assembly may comprise at least two flow outlet channels. The first flow sensing channel region and the second flow sensing channel region may be arranged in parallel. The flow inlet channel may be connected to both the first sensing region and the second sensing region and the first sensing region may be connected to a first flow outlet channel and the second sensing region may be connected to a second outlet channel. The fluid flow through the flow inlet channel may be split into the two separate flow sensing channel regions, rather than flowing through both sensing channel regions sequentially. This allows measurements to be taken from both flow sensing channel regions simultaneously. In parallel here refers to parallel analysis, and the topology of the sensing channel regions. This does not require the flow sensing channel regions to be parallel to each other geometrically.

Alternatively, the flow sensor assembly may comprise one flow outlet channel. The first flow sensing channel region and the second flow sensing channel region may be arranged in series. The flow inlet channel may be connected to the first flow sensing region and the first flow sensing region may be connected to the second flow sensing region, and the second flow sensing region may be connected to the flow outlet channel. A single inlet channel may feed through to a single outlet channel.

The etched portion of the semiconductor substrate may define the at least two flow sensing channel regions. The flow sensing channel regions may be defined by the back of the sensor chips (the etching of the semiconductor substrate). The etched portion of the semiconductor substrate may define the flow sensing channel regions and one or more connecting channels. The flow sensing channel regions may be fluidly connected to each other by the connecting channels.

The inhomogeneous flow channels (or flow sensing channel regions) may be defined by the etched portion at the backside of the sensor chip of the sensor assembly. The flow sensor chip may include a semiconductor substrate and a dielectric layer. The semiconductor substrate may have multiple cavities that are formed by etching of the semiconductor. Multiple etched portions may be used as the flow sensing channel regions. There may be a sensor corresponding to each of the etched portions of the semiconductor substrate. Another substrate or moulded plastic section may be attached to the other side of the flow sensor chip and may be designed such that the other substrate and the cavities in the semiconductor substrate form the flow channels for the fluid flow. The substrate may be designed such that the height or width of the channel above each sensor is different. The second substrate may be made of any semiconductor material or another appropriate material such as moulded plastic, glass, sapphire and metal.

The dielectric region may comprise at least two dielectric membranes corresponding to the flow sensing channel regions. The dielectric region may comprises a plurality of sensing elements, each of the plurality of sensing elements may be formed within a separate dielectric membrane. The flow sensing channel formed through sensor assembly may flow through past each sensing element in the dielectric region. In other words, the sensing channel may flow past a plurality of dielectric membranes, where each dielectric membrane is operating as a separate flow sensor, and therefore one or more sensing elements are formed within each dielectric membrane. This does not limit the dielectric membranes to contain only one sensing element, but there may multiple dielectric membranes each with one or more sensing elements and therefore each dielectric membrane is operating as a flow sensor.

The flow sensor assembly may further comprise a lid formed over a second side of the semiconductor substrate. The lid may define at least two apertures, and at least one of the flow inlet channel or flow outlet channel may comprises a channel through an aperture defined by the lid. The lid may comprise an additional substrate, and may be one substrate or two separate substrates forming the lid. The additional substrate of the lid may be etched such that the height of each flow sensing channel region is different.

The semiconductor substrate and the lid may cooperate to define the flow inlet channel and the flow outlet channel. In other words, the flow inlet channel and the flow outlet channel may be defined by the cooperation of the shapes of the semiconductor substrate and the lid, and/or defined as a region between semiconductor substrate and the lid.

The etched portion of the semiconductor substrate may extend partially through a thickness of the semiconductor substrate, and the flow inlet channel and the flow outlet channel may comprise apertures defined by the dielectric membrane. In this configuration, the flow sensor assembly may be formed on a single flow sensor chip.

Alternatively, the flow sensor assembly may further comprise an assembly housing defining the flow sensing channel. The housing may define at least two apertures, and at least one of the flow inlet channel or flow outlet channel may comprise a channel through an aperture defined by the housing. Each sensing element may be formed on a separate dielectric membrane on separate semiconductor substrates. These may form separate sensors formed inside the flow sensing channel regions defined by the assembly housing.

The flow sensing channel may be defined by two or more separate sections of the flow sensor assembly that are joined.

The flow sensor assembly may comprises of a housing that defines a flow channel which has regions of different cross-sectional area, and each region may embed at least one flow sensor or flow sensor chip. The flow sensor chip may comprise of a silicon substrate and a dielectric comprising of silicon oxide and silicon nitride. The silicon substrate may have at least one etched portion, and the region of the dielectric adjacent to the substrate cavity may be called a membrane, which may be of any shape such as rectangular, circular and rectangular with rounded corners. Each flow sensor may have at least one membrane. In the case of a thermal flow sensor, a heater may be embedded within the membrane. Further heaters and/or thermal sensors may also be present. For flow sensors based on other principles, such as ultrasonic, pressure, other components may be present such as one or more piezo resistors. The assembly will form the varying cross-sections for enhanced flow-range capabilities. The different channel cross-sections can be achieved by varying either the channel width or the channel height, or both.

The housing may be fabricated from any material, such as metal, plastic or glass and the inlet and outlet may be a straight connection, a barbed connection or an opening in the packaging with no protrusion.

There may also be multiple inlets and/or outlets of any shape to best fit external system/application. Additionally, a protective material may be applied to the walls of the channel for additional protection.

The inhomogeneous flow channel housing may be comprised of multiple moulded sections. The different sections may be connected by any method, including glue, clamping, screws and o-rings. The different cross-sectional areas may be designed in a vertical or horizontal direction.

At least one outer surface of the sensor assembly may be substantially flat such that at least one of the flow inlet channel and the flow outlet channel terminates on the at least one outer surface of the sensor assembly. The inlet and outlet ports may have a flat connection. The outer surface may be a top surface and may be defined as the exterior surface of the housing or lid that extends in a lateral direction, substantially parallel to the flow sensing channel. The apertures or openings defining the flow inlet channel and the flow outlet channel may be flat.

Alternatively, at least one outer surface of the sensor assembly may comprise a plurality of protrusions, and at least one of the flow inlet channel and the flow outlet channel may extend through one or more of the plurality of protrusions. The protrusions may extend away from the flow sensing channel.

The protrusions may be perpendicular to the sensing channel, and the flow inlet channel and flow outlet channel may then be perpendicular to the flow sensing channel. In this embodiment, fluid enters and exits the flow sensor in opposite directions.

The protrusions may be parallel to the flow sensing channel, and the flow inlet channel and flow outlet channel may then be parallel to the flow sensing channel. In this embodiment, fluid enters and exits the flow sensor in the same direction.

The plurality of protrusions may be configured to enable the sensor to be coupled with another device. At least one of the plurality of protrusions may have a barbed connection.

In use, the flow inlet channel or flow outlet channel may be perpendicular to a direction of flow through the flow sensor assembly. The inlet and outlet ports may be perpendicular to the direction of flow.

In use, the flow inlet channel or flow outlet channel may be parallel to a direction of flow through the flow sensor assembly. The inlet and outlet ports may be parallel to the direction of flow.

The flow inlet channel and the flow outlet channel may be defined on opposite surfaces of the flow sensor. In other words the flow inlet channel and flow outlet channel may be on opposite sides of the flow sensor such that fluid travels in one direction through the sensor. Fluid enters in same direction as it leaves, and therefore the sensor can be used in a continuous flow.

The flow sensor assembly may comprise a flow restrictor located within the flow sensing channel. The cross-sectional areas may incorporate a restrictor. The size, shape, and location of the restrictors may be chosen to best control the flow. The restrictor helps mitigate against the tolerance in manufacturing and connection variability, whilst also controlling the flow.

The sensing channel may comprise a protective coating. The sensing channel may be coated with a protective coating. This may also be present on the flow inlet channel and/or the flow outlet channel. There may be a protective material on the walls of the flow channel. Additionally or alternatively, the dielectric layer may have one or more protective coatings. Such a coating could be used to improve resistance to corrosion and also to make the sensor biocompatible for a range of fluids used. This may comprise of polymers, such as parylene.

The flow sensor assembly may further comprise integrated circuitry connected to the flow sensing elements. There may be circuitry on the flow sensor chip, or another chip within the same housing. The integrated circuitry may be an application specific integrated circuit (ASIC). The flow sensor may have on-chip circuitry, which may be on the same chip as the flow sensor, or may be integrated on another chip within the package.

According to a further aspect of the disclosure there is provided a method of manufacturing a flow sensor assembly, the method comprising: forming a flow inlet channel; forming a flow outlet channel; forming a flow sensing channel through the flow sensor assembly located between the flow inlet channel and the flow outlet channel, and wherein the flow sensing channel comprises at least two flow sensing channel regions, wherein a first flow sensing channel region has a first cross-sectional area and a second flow sensing region has a second cross-sectional area different from the first cross-sectional area; forming one or more semiconductor substrates; forming one or more dielectric layers, each located on a first side of a semiconductor substrate of the one or more semiconductor substrates; and forming at least two flow sensing elements each located on or within a dielectric layer wherein a first flow sensing element is configured to sense a fluid flow property in the first flow sensing channel region and a second flow sensing element is configured to sense a fluid flow property in the second flow sensing channel region.

Brief Description of the Figures

Some embodiments of the disclosure will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 shows a 3D schematic of the flow sensor housing or a flow sensor assembly,

according to an embodiment of the disclosure;

Figure 2 shows a 2D cross section of the flow sensor housing shown in Figure 1; Figure 3 shows a 3D schematic of a flow sensor housing with separated flow sensing channels in parallel, according to an embodiment of the disclosure; Figure 4 shows a flow sensor housing with a vertical variation of flow sensing channel region cross-section area; Figure 5 shows a cross section of a flow sensor assembly in which the backside etched portion of the flow sensor chip forms the flow channel; Figure 6 shows a cross section of an alternative flow sensor assembly with a multiple attached substrates for varying the cross-section of the flow sensing channel regions; Figure 7 shows packaging flow sensor assembly formed of two moulded sections that come together to form the housing; Figure 8 shows a cross-section of a vertical configuration of the housing of a flow sensor assembly; Figure 9 shows a cross-section of a vertical configuration with flow channel restrictions; and Figure 10 shows a cross section of a flow sensor that could be used in a flow sensor assembly according to an embodiment of the disclosure.

Detailed Description the Preferred Embodiments

Some examples of the disclosed device are given in the accompanying figures.

Figure 1 shows a 3D wireframe schematic of the flow sensor packaging (or housing). This housing includes an inlet (or flow inlet channel) 1 and outlet (or flow outlet channel) 2. The inlet and outlet are formed of apertures through the housing. The flow channel (or flow sensing channel) includes three regions (or flow sensing channel regions) of different cross-sectional area 3a, 3b, 3c, achieved by varying the width of the channel. It is designed such that each cross-sectional area will target a specific flow range. Each sensor may be optimised to have the highest sensitivity for the desired flow range in their channel region.

The housing can be made from a range of materials, including metal, ceramic, glass and moulded plastic. It can be designed such that it controls the flow through multiple regions of varying cross-sections. The example here shows one design, but many channel shapes and sizes are possible. The variation in cross-section can also be achieved by varying the channel height instead of the channel width.

Figure 2 shows a 2D cross-section of the flow sensor packaging presented in Figure 1.

This housing includes an inlet 1 and outlet 2. There are three cross-sections of different cross-sectional area 3a, 3b, 3b with an example of where each of the sensors would sit 4a, 4b, 4c. The picture shows a particular location for the position of the flow sensors, but it is possible to place it in other locations along each of the channels.

Figure 3 shows a 3D wireframe schematic of a flow sensor packaging whereby a single inlet 1 feeds into three separated flow channels 3a, 3b, 3b, of different cross-sectional area, that are independent from one another and arranged in parallel to each other. The flow sensor assembly includes three flow outlet channels, each connected to one flow sensing channel regions. The position where the sensors would be included in each channel is shown 4a, 4b, 4c.

Figure 4 shows a 3D schematic of the flow sensor housing whereby the fluid flow is through two-cross-sectional areas that vary in the vertical direction, and are arranged in series. A single inlet 1 feeds through to a single outlet 2. The channel changes into two sections with different cross-sectional areas 3a, 3b that run-in series. An array of sensors 4 a, 4b can be located along the top to measure the different sections.

Figure 5 shows a fluid sensor assembly where the inhomogeneous flow channels are defined by the backside of the sensor chip. The flow sensor chip includes a semiconductor substrate 5, and a dielectric layer 6. The semiconductor substrate has multiple cavities formed by etching of the semiconductor 3a, 3b, 3c. The dielectric layer has three dielectric membranes, each located over an etched cavity of the semiconductor substrate. There is a sensor corresponding to each of the etched portions of the semiconductor substrate 3a, 3b, 3c.

Another substrate 7 or lid is attached to the other side of the flow sensor chip and is designed such that the substrate 7 and the cavities in the semiconductor substrate 3a, 3, 3c form the flow channels for the fluid flow. The substrate 7 is designed such that the height of the channel above each sensor is different. This allows measurement of different ranges of flows rates.

The flow inlet channel 1 and the flow outlet channel 2 are formed through protrusions on an outer surface of the substrate 7. The protrusions have a barbed connected to enable the sensor assembly to be coupled with another device Figure 6 shows a further fluid sensor assembly where the inhomogeneous flow channels are defined by the backside of the sensor chips. It is similar to Figure 5, except that the variation in channel cross-section is achieved by changing the channel width as opposed to the channel height. Figure 6 shows a second substrate 7 which defines the inlet 1 and outlet 2, and another substrate 8 which is attached to the first semiconductor substrate 5 and is used to achieve the variation in cross-sectional width. The two additional substrates 7, 8 form a lid of the flow sensor assembly. The substrate 7 in this design can be achieved by using other semiconductor materials, moulded plastic and other materials such as glass, sapphire or metal.

Figure 7 shows a 3D schematic of a flow sensor assembly where the flow channel is created by connecting two separately fabricated sections of the housing. In this design the inlet 1 and outlet 2 are defined by a first section whilst the flow sensing channels 3a, 3b, 3c are defined by the second section. The flow sensors or sensing elements 4a, 4b, 4c are situated in the top section and will become exposed to the flow as the channel roof when the two sections become joined.

In embodiments, the first section may be the dielectric layer and the second section may be the substrate, with sensing elements in the flow sensing channels.

Alternatively, the first section and the second section may be a housing with flow sensors, each including a dielectric layer and one or more substrates, located within the flow sensing channel.

Figure 8 shows a vertical configuration of the inhomogeneous cross-sections 3a, 3b, 3c of the flow sensor package where the inlet 1 and outlet 2 are parallel to the direction of flow.

Figure 9 shows a 3D schematic of the vertical configuration flow sensor package, as shown in Figure 8, where restrictors or restrictions are added to the flow channels 3a, 3b, 3c. The picture shows a particular size and location for the restrictors, but it is possible to change the size and shape of the restrictors in order to best control the flow.

Figure 10 shows a flow sensor or flow sensor chip or die that could be used in a flow sensor assembly according to an embodiment of the disclosure. The flow sensor includes a semiconductor substrate 5 with an etched portion, a dielectric layer 6 on top of the substrate, and a heater 9 embedded within the dielectric membrane. The dielectric membrane is the portion of the dielectric layer 6 adjacent to the etched portion of the semiconductor substrate.

The skilled person will understand that in the preceding description and appended claims, positional terms such as 'above', 'overlap', 'under', 'lateral', etc. are made with reference to conceptual illustrations of an device, such as those showing standard cross-sectional perspectives and those shown in the appended drawings. These terms are used for ease of reference but are not intended to be of limiting nature. These terms are therefore to be understood as referring to a device when in an orientation as shown in the accompanying drawings.

Although the disclosure has been described in terms of preferred embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in the disclosure, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.

Claims

CLAIMS: 1 A flow sensor assembly comprising: a flow inlet channel; a flow outlet channel; a flow sensing channel through the flow sensor assembly located between the flow inlet channel and the flow outlet channel, and wherein the flow sensing channel comprises at least two flow sensing channel regions, wherein a first flow sensing channel region has a first cross-sectional area and a second flow sensing region has a second cross-sectional area different from the first cross-sectional area; one or more substrates; one or more dielectric layers, each located on a first side of a substrate of the one or more substrates; and at least two flow sensing elements each located on or within a dielectric layer of the one or more dielectric layers wherein a first flow sensing element is configured to sense a fluid flow property in the first flow sensing channel region and a second flow sensing element is configured to sense a fluid flow property in the second flow sensing channel region.
2 A flow sensor assembly according to claim 1, wherein at least one substrate comprises an etched portion, and wherein at least one dielectric layer comprises at least one dielectric membrane located over the etched portion of the substrate.
3. A flow sensor assembly according to claim 2, wherein the flow sensing elements are formed on or within the at least one dielectric membrane.
4 A flow sensor assembly according to claim 3, wherein the at least one dielectric membrane comprises at least one recessed region between one of the flow sensing elements and an edge of the dielectric membrane.
A flow sensor assembly according to any of claim 3 or 4, wherein the first flow sensing element is formed on or within a first dielectric membrane and the second flow sensing element is formed on or within a second dielectric membrane, and wherein the first dielectric membrane has a different area to the second dielectric membrane.
6. A flow sensor assembly according to any preceding claim, wherein the at least one flow sensing element comprises at least one heating element.
7 A flow sensor assembly according to any preceding claim, wherein the at least one flow sensing element comprises at least one temperature sensing element comprising any of a resistor, a diode, a thermocouple, or a thermopile.
8. A flow sensor assembly according to any preceding claim, where the at least one flow sensing element comprises at least one piezo-resistor.
9 A flow sensor assembly according to any preceding claim, comprising at least two flow outlet channels, and wherein the first flow sensing channel region and the second flow sensing channel regions are arranged in parallel, and wherein the flow inlet channel is connected to both the first sensing region and the second sensing region and wherein the first sensing region is connected to a first flow outlet channel and the second sensing region is connected to a second outlet channel
10. A flow sensor assembly according to any of claims 2 to 9, wherein the etched portion of the substrate defines the at least two flow sensing channel regions.
11. A flow sensor assembly according to claim 10, further comprising a lid formed over a second side of the substrate, wherein the lid defines at least two apertures, and wherein at least one of the flow inlet channel or flow outlet channel comprises a channel through an aperture defined by the lid.
12. A flow sensor assembly according to any of claims 2 to 10, wherein the etched portion of the substrate extends partially through a thickness of the substrate, and wherein the flow inlet channel and the flow outlet channel comprise apertures defined by the dielectric membrane.
13 A flow sensor assembly according to any preceding claim, further comprising an assembly housing defining the flow sensing channel, wherein the housing defines at least two apertures, and wherein at least one of the flow inlet channel or flow outlet channel comprises a channel through an aperture defined by the housing.
14. A flow sensor assembly according to any preceding claim, wherein at least one outer surface of the sensor assembly is substantially flat such that at least one of the flow inlet channel and the flow outlet channel terminate on the at least one outer surface of the sensor assembly.
15. A flow sensor assembly according to any preceding claim, wherein the at least one outer surface of the sensor assembly comprises a plurality of protrusions, and wherein at least one of the flow inlet channel and the flow outlet channel extend through one or more of the plurality of protrusions.
16. A flow sensor assembly according to claim 15, wherein the plurality of protrusions are configured to enable the sensor assembly to be coupled with another device, and/or wherein a least one of the plurality of protrusions has a barbed connection.
17. A flow sensor assembly according to any preceding claim, wherein, in use, the flow inlet channel or flow outlet channel are perpendicular to a direction of flow through the flow sensor assembly.
18. A flow sensor assembly according to any preceding claim, wherein, in use, the flow inlet channel or flow outlet channel are parallel to a direction of flow through the flow sensor assembly.
19. A flow sensor assembly according to any preceding claim, further comprising a flow restrictor located within the flow sensing channel.
20. A flow sensor assembly according to any preceding claim, wherein the flow sensing channel comprises a protective coating.
21. A flow sensor assembly according to any preceding claim, further comprising integrated circuitry connected to the flow sensing elements.
22 A method of manufacturing a flow sensor assembly, the method comprising: forming a flow inlet channel; forming a flow outlet channel; forming a flow sensing channel through the flow sensor assembly located between the flow inlet channel and the flow outlet channel, and wherein the flow sensing channel comprises at least two flow sensing channel regions, wherein a first flow sensing channel region has a first cross-sectional area and a second flow sensing region has a second cross-sectional area different to the first cross-sectional area; forming one or more substrates; forming one or more dielectric layers, each located on a first side of a substrate of the one or more substrates; and forming at least two flow sensing elements each located on or within a dielectric layer wherein a first flow sensing element is configured to sense a fluid flow property in the first flow sensing channel region and a second flow sensing element is configured to sense a fluid flow property in the second flow sensing channel region.