Patent Application
20110252882
The disclosure relates generally to sensors, and more particularly, to robust sensors that are configured to sense a property of a fluid.
Sensors are commonly used to sense one or more properties of a fluid. For example, flow sensors and pressure sensors are used in a wide variant of applications such as in industrial process control, medical devices, engines, and so on. Flow sensors are often used to measure flow rates of fluids, and provide flow signals for instrumentation and/or control. Likewise, pressure sensors are often used to measure pressure of fluids, and provide pressure signals for instrumentation and/or control. These are just a few examples of sensors that can be used to sense one or more properties of a fluid. Some sensors may be vulnerable when exposed to the fluid that is to be sensed. For example, a sensor may be vulnerable or sensitive to moisture, particulate matter, corrosive properties or other conditions of a fluid to be sensed. In some cases, the accuracy and/or reliability of the sensor may be affected. Thus, a need exists for robust sensors.
The disclosure relates generally to sensors, and more particularly, to sensors that are configured to sense a property of a fluid. In one illustrative embodiment, a flow sensor assembly for providing a measure of fluid flow from an inlet to an outlet includes one or more flow sensor components secured relative to a membrane, and a substrate for supporting the membrane. In some cases, the one or more flow sensor components may be substantially thermally isolated from the substrate by the membrane. One or more wire bond pads may be situated adjacent to a first side of the substrate and may be provided for communicating signals relative to the one or more flow sensor components. A top cap may be situated adjacent to the first side of the substrate and secured relative to the substrate. The top cap may define at least part of the inlet and/or the outlet of the flow sensor assembly and may at least partially define a flow channel that extends from the inlet, past at least one of the one or more flow sensor components, and out the outlet of the flow sensor assembly. The top cap may be structured and attached relative to the first side of the substrate such that the one or more wire bond pads are not exposed to the fluid in the flow channel, but are accessible for electrical connection to an external device. While a flow sensor is used as an example, it is contemplated that any suitable sensor may be used, as desired.
The above summary is not intended to describe each and every disclosed illustrative example or every implementation of the disclosure. The Description that follows more particularly exemplifies various illustrative embodiments.
The following description should be read with reference to the drawings. The drawings, which are not necessarily to scale, depict selected illustrative embodiments and are not intended to limit the scope of the disclosure. The disclosure may be more completely understood in consideration of the following description of various illustrative embodiments in connection with the accompanying drawings, in which:
The following description should be read with reference to the drawings, in which like elements in different drawings are numbered in like fashion. The drawings, which are not necessarily to scale, depict selected illustrative embodiments and are not intended to limit the scope of the disclosure. Although examples of construction, dimensions, and materials are illustrated for the various elements, those skilled in the art will recognize that many of the examples provided have suitable alternatives that may be utilized.
In some cases, thin film layers 104 may form a membrane 106 supported by substrate 102. Membrane border 108 may demark the area of thin film layers 104 that form the membrane. A void 110 (see
One or more flow sensor components may be secured relative to membrane 106. In the example shown, a heater 112 and sense resistors 114 and 116 are provided in or on the thin film layers 104 as flow sensor components. Heater 112 and sense resistors 114, 116 (sensor elements) may be components of a Wheatstone bridge flow sensor, for example as described in U.S. Pat. No. 7,278,309, “INTERDIGITATED, FULL WHEATSTONE BRIDGE FLOW SENSOR TRANSDUCER,” Dmytriw et al., which is hereby incorporated by reference in its entirety. The illustrative flow sensor die 100 may include other flow sensor components not disposed in or on the membrane 106, such as a temperature resistor 118. All of, or a subset of, flow sensor components may be referred-to more generally as a “flow sensor.”
In the example provided, flow sensor components may be formed in or on the thin film layers 104 with any suitable methods. For example, resistive components may be deposited and defined on top of lower membrane thin film layer(s). A variety of thin film resistor materials are available, including platinum, doped polysilicon, doped crystalline silicon, Permalloy, SiCr, tantalum, tantalum nitride, chromalloy, nichrome, and/or any other suitable material or material combination. After resistor definition, a thin film protective layer such as silicon nitride may be deposited over the resistors. Etching of the void 110 may be performed after deposition of the resistors and thin film layers. Any suitable etching technique may be used, such as wet etching with anisotropic etchants (e.g., KOH, TMAH, or EDP) or dry, deep reactive ion etching.
In a flow sensor incorporating flow sensor die 100, fluid may be directed to flow past flow sensor components secured to and/or disposed in or on membrane 106. In the example shown, fluid flow may flow in the direction denoted by directional arrows 120. Heater 112 may dissipate electrical energy as heat, warming the fluid in its proximity. The resistor 114 is shown positioned downstream of the heater 112, and resistor 116 is shown positioned upstream (or visa-versa). A temperature differential between the sense resistors 114 and 116 may result, depending on the fluid flow rate.
Performance of the flow sensor may be dependent on heat transferred to the sense resistors 114 and 116 from the fluid, and not through other heat conduction paths. In the embodiment shown, membrane 106 may substantially thermally isolate the heater 112 and sense resistors 114, 116, and/or other flow sensor components if any, from the substrate. Without such thermal isolation, heat may be conducted to/from the flow sensor components from/to the substrate, which may reduce the sensitivity and/or performance of the sensor. Material selection may provide an additional or alternative way to thermally isolate flow sensor components, which may be used in flow sensors with or without thermally-isolating membranes. For example, low thermal conductivity substrate materials that may be used, such as fused silica, fused quartz, and/or borosilicate glass. Additionally or alternatively, thermal isolation may be achieved on a substrate with low thermal conductivity thin films such as oxidized porous silicon, aerogels, or any other suitable materials.
In the example shown, flow sensor die 100 may include one or more wire bond pads 122 situated adjacent or on substrate 102. In some illustrative embodiments, the wire bond pads are situated along one side of the substrate, as in
Other flow sensor die configurations are contemplated.
In an illustrative embodiment, flow sensor dies such as dies 100 and 200 may be combined with a top cap to form a flow sensor assembly for providing a measure of fluid flow.
Top cap 552 may at least partially define a flow channel that extends from the inlet 556, past at least one of the one or more flow sensor components 512, 514, 516, and out the outlet 558 of the illustrative flow sensor assembly 500. The flow channel may be at least partially defined by at least one interior surface of the top cap, such as surface 566. The flow sensor die 550 and/or flow sensor die substrate 555 may at least partially define another part of the flow channel, as shown.
Top cap 552 may be structured and attached relative to the side of the substrate 555 that is facing the one or more wire bond pads 554 such that the one or more wire bond pads are not exposed to the flow channel, but are accessible for electrical connection to an external device. The top cap 552 may be considered to fluidly isolate the one or more wire bond pads 554 from the flow channel. In each of
Top cap 552, or any other top cap of the present disclosure, may be formed of any suitable material or materials. Top caps may be formed substantially of glass, and may be substantially optically transparent, if desired. Fabrication of glass top caps may be accomplished with micro abrasive jet machining (also referred to as precision micro sandblasting, swarm sandblasting, or power blasting), ultrasonic drilling, laser micromachining, etching, or any other suitable method. Possible cap materials include borosilicate glass, fused silica, quartz, or any other suitable material. A cap material with a low thermal conductivity may be employed, which may help reduce the transfer of heat from the fluid steam. In some cases, cap materials with thermal conductivities of less than about 2, 1.5, 1.4, 1.3, 1.2, 1.1, or 1 W/m·° K. may be used. A cap material with a coefficient of thermal expansion (CTE) close to that of a substrate material (e.g., silicon) of the flow sensor die, may be used. Matching or substantially matching CTEs for caps and substrates may result in increased thermal robustness for flow sensor assemblies. In some cases, materials are used for caps and substrates with values for CTEs within 50, 40, 30, 20, or 10% of each other. Any suitable method may be used to attach and seal the caps to the flow sensor dies to form flow sensor assemblies. For a glass cap, glass frit bonding may be used, if desired. With some glasses, anodic bonding may be used. In some instances, transparent caps may allow optical methods of alignment when the caps are attached to flow sensor dies to form the flow sensor assemblies.
It is contemplated that plastic caps may also be used, and such caps may be micro-molded, machined or formed in any other suitable manner. Adhesives may be used to attach such plastic caps (or glass caps). Epoxy, silicone, or other adhesives may be used for attachment, as desired.
Other cap configurations are also contemplated. For example,
The disclosure should not be considered limited to the particular examples described above. Various modifications, equivalent processes, as well as numerous structures to which the disclosure can be applicable will be readily apparent to those of skill in the art upon review of the instant specification.
