Polysilicon on sapphire oilless pressure sensor

Abstract

The pressure sensor assembly (110) includes a pressure sensor (112) having a support structure (220) and a sapphire insulating member (226) coupled to the support structure (220) and forming a region (230) between a first surface of the sapphire insulating member (226) and the support structure (220). A second surface of the sapphire insulating member (226) is positioned to interface with a fluid from or coupled to a process. An electrical lead (224) is coupled to a polysilicon strain gage pattern (232) disposed in the region (230) on the first surface of the sapphire insulating member (226), the polysilicon strain gage pattern (232) being configured to generate an electrical signal indicative of the pressure (P) of the fluid when the sapphire insulating member (226) deflects in response to pressure.

Description

[Technical field]

[0001] TECHNICAL FIELD Embodiments of the present disclosure relate to industrial process transmitters, and more particularly to pressure sensor assemblies for use in such transmitters. [Background technology]

[0002] Industrial process field devices, such as process transmitters, are used in industrial process control and monitoring systems to monitor industrial process variables and send measurements of the process variables back to a control room, for example in a chemical, oil, gas, pharmaceutical, or another fluid processing plant. The term "process variable" refers to the physical or chemical state of a substance or a transformation of energy. Examples of process variables include pressure, temperature, flow, conductivity, pH, and other properties.

[0003] Pressure transmitters, and other pressure sensing field devices or instruments, include a pressure sensor that senses pressure, such as the pressure of a process fluid. The pressure sensor provides an electrical output indicative of the sensed pressure. The sensed pressure may be processed by circuitry in the pressure transmitter and / or communicated to an external control unit.

[0004] Some pressure transmitters rely on a thin (0.001 to 0.002 in. (0.0254 to 0.0508 mm)) metal diaphragm to isolate the process fluid from the pressure sensor, and a factory-installed fill fluid transmits the pressure signal from the process to an electronic pressure sensor. These systems may be poorly suited for applications where the process is abrasive, or where the process (e.g., sanitary processes) cannot risk potential contamination of the process if the isolation diaphragm fails. These filled systems also run the risk of diffused gas and / or vacuum affecting the integrity of the fluid.

[0005] Some pressure transmitters address these issues with an "oil-free" (fill fluid-free) design that incorporates an alumina ceramic insulation with integrated capacitive sensing. These products use an alumina ceramic as a process isolating diaphragm, forming part of an integrated capacitance sensor. While offering "oil-free" functionality, these pressure transmitters may have drawbacks including reduced accuracy, range, stability, and overpressure capability when compared to similar metal-insulated fluid-filled devices. Some of these limitations are inherent to the alumina material, which is both the isolation element and the pressure sensor deflection element in the sensor system. Additionally, the insulation / sensor ceramic has a granular nature that makes it prone to impact / crack propagation failure. Also, when configured for gauge measurements, ambient atmosphere enters the capacitive sensing cavity in some of these types of pressure transmitters, which can lead to performance issues as the "air" dielectric can wet / condense and / or otherwise become contaminated, creating measurement errors. Summary of the Invention

[0006] The embodiments of the present disclosure generally relate to a pressure sensor assembly and a method of manufacturing the pressure sensor assembly. One embodiment of the pressure sensor assembly includes a header forming a cavity, the header providing a fluid path to the cavity. A pressure sensor is disposed within the cavity and configured to sense a pressure of a fluid within the fluid path. The pressure sensor includes a support structure and a sapphire isolation member bonded or coupled to the support structure to form an area between a first surface of the sapphire isolation member and the support structure. In an exemplary embodiment, the sapphire isolation member is a single crystal sapphire element. Also, in some embodiments of the present invention, the support structure is formed of sapphire or a material having similar expansion characteristics to the sapphire isolation member, such as Al2O3. A second surface of the sapphire isolation member is disposed in contact with a fluid within the fluid path. An electrical lead can extend through the support structure. A polysilicon strain gauge pattern is disposed in an area on the first surface of the sapphire isolation member and coupled to the electrical lead. The polysilicon strain gauge pattern, which may be formed as a Wheatstone bridge, is configured to generate an electrical signal indicative of the pressure of the fluid in the fluid path when the sapphire insulating member deflects in response to pressure.

[0007] In an exemplary embodiment, the region formed between the first surface of the sapphire insulating member and the support structure includes a reference pressure. The reference pressure can be a vacuum pressure. In another embodiment, the pressure sensor is configured as a gauge pressure sensor and includes a reference vent through the support structure to connect the region formed between the first surface of the sapphire insulating member and the support structure to atmospheric pressure.

[0008] In some exemplary embodiments, the pressure sensor assembly is coupled to or formed with the support structure in a region between the first surface of the sapphire insulating member and the support structure and includes a geometric protrusion that limits deflection of the sapphire insulating member during overpressure conditions.

[0009] In certain exemplary embodiments, a pressure sensor assembly is disposed on the second surface of the sapphire insulating member and includes a temperature sensor configured to measure a process temperature to compensate for process temperature transients.

[0010] In another embodiment, a method of manufacturing a pressure sensor assembly is provided that includes forming a polysilicon strain gage pattern on a first surface of a sapphire insulating member and bonding the sapphire insulating member to a support structure to form an area between the first surface of the sapphire insulating member and the support structure having the polysilicon strain gage pattern formed therein. The pressure sensor is then positioned within the cavity of the header such that the second surface of the sapphire insulating member is positioned in contact with fluid in a fluid path through the header.

[0011] In another embodiment, a process control measurement system includes a housing and a header disposed within the housing, the header including a cavity and a fluid path to the cavity. A pressure sensor is disposed within the cavity and configured to sense a pressure of a process fluid passing through the fluid path. The pressure sensor includes a support structure and a sapphire insulating member formed from a single crystal sapphire element and coupled to the support structure to define a region between a first surface of the sapphire insulating member and the support structure. A second surface of the sapphire insulating member is positioned to contact a fluid in the fluid path such that the sapphire insulating member is deflected by pressure from the fluid in the fluid path. An electrical lead extends through the support structure and couples to a polysilicon strain gauge pattern disposed in the region on the first surface of the sapphire insulating member. The polysilicon strain gauge pattern is configured to generate an electrical signal indicative of a pressure of the fluid in the fluid path when the sapphire insulating member deflects in response to pressure. In some embodiments, a geometric protrusion on the support structure in the region limits deflection of the sapphire insulating member during an overpressure condition.

[0012] This Summary is provided to introduce a selection of concepts in a simplified form that are further described in the Formulation for Carrying Out the Invention below. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended for use as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all of the shortcomings noted in the Background. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a partial cutaway cross-sectional view of an example pressure transmitter in a process control or measurement system according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a cross-sectional view of a portion of the pressure transmitter of FIG. 1 according to an embodiment of the present disclosure. [Diagram 3] FIG. 3 is a simplified cross-sectional view of a portion of a pressure sensor assembly according to an embodiment of the present disclosure for measuring absolute pressure. [Figure 4-1] FIG. 4-1 is a simplified cross-sectional view of a portion of an alternative pressure sensor assembly, according to an embodiment of the present invention, for measuring gauge pressure. [Figure 4-2] FIG. 4-2 is a diagram of a portion of the pressure sensor assembly of FIG. 4-1 illustrating the overpressure protection stop or feature. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Elements identified using the same or similar reference symbols refer to the same or similar elements. Some elements may not be shown in each of the drawings to simplify the drawings.

[0015] Various embodiments of the present disclosure may be embodied in many different forms and should not be construed as limited to the specific embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0016] Figure 1 is a partial cutaway cross-sectional view of an example process control or measurement system 100 including a pressure transmitter 102 according to an embodiment of the present disclosure. Figure 2 is a cross-sectional view of a portion of the transmitter 102 of Figure 1. The system 100 can be used to process materials (e.g., process media) to convert the materials from a less valuable state into more valuable, useful products such as oil, chemicals, paper, food, etc. For example, the system 100 may be used in facilities that perform sanitary or other types of industrial processes.

[0017] The pressure transmitter 102 may include a housing 104 that may be coupled to an industrial process 106 via a process coupling 108. The housing 104 and the process coupling 108 may be formed of stainless steel or another suitable material. The transmitter 102 includes a pressure sensor assembly 110 mounted to and / or housed within the housing 104. The assembly 110 includes a pressure sensor or pressure sensor die 112 (hereinafter, "pressure sensor") formed in accordance with one or more embodiments described herein to measure the pressure of the process. The pressure sensor assembly 110 may include a header 114 and a pedestal 116 that connects the pressure sensor 112 to the header 114, as best shown in FIG. 2 .

[0018] The process coupling 108 may be connected to the process 106 and to a pipe 118 containing a process material (e.g., a fluid) at a pressure P to be measured by the pressure sensor 112. The pressure P is communicated to the pressure sensor 112 through a fluid path 122 that extends through the pressure transmitter components, including the process coupling and header 114 in some embodiments, to a cavity 144 that houses the pressure sensor. The pressure sensor 112, embodiments of which are described in further detail with reference to FIGS. 3, 4-1 and 4-2, includes a sensor element having an electrical parameter indicative of the applied pressure P. A measurement circuit 124 may detect and process the electrical parameter of the sensor element via a suitable electrical connection 126 to establish a value of the sensed pressure P. The measurement circuit 124 may be connected to a terminal block 127 of the transmitter 102, which has a communication circuit 128 for communicating information regarding the sensed pressure P, such as the value of the pressure P, to an external computer control unit 130 via a process control loop 132, as shown in FIG. 1.

[0019] The pressure transmitter 102 may include a pathway for connecting the sensor 112 to ambient pressure or air, such as through a vent 135 in the housing 104, as shown in Figure 2. The pathway may extend through the pedestal 116.

[0020] In some embodiments, the process control loop 132 includes a physical communication link, such as a two-wire control loop as shown in FIG. 1, and / or a wireless communication link. Communication between the control unit 130, or another external computing device, and the pressure transmitter 102 may be performed via the control loop 132 according to conventional analog and / or digital communication protocols. In some embodiments, the two-wire control loop 132 includes a 4-20 milliamp control loop, and the measured pressure value may be represented by the level of loop current flowing through the two-wire control loop 132. An exemplary digital communication protocol includes modulation of a digital signal to an analog current level on the two-wire control loop 132, such as according to the HART® communication standard. Other purely digital techniques may also be used, including FieldBus and Profibus communication protocols.

[0021] Exemplary wireless versions of the process control loop 132 include, for example, a wireless mesh network protocol such as WirelessHART® (IEC 62591) or ISA 100.11a (IEC 62734), or another wireless communication protocol such as WiFi, LoRa, Sigfox, BLE, or any other suitable protocol.

[0022] Power can be provided to the pressure transmitter 102 from any suitable power source. For example, the pressure transmitter 102 may be powered entirely by the current flowing through the control loop 132. One or more power sources may also be utilized to power the pressure transmitter 102, such as an internal or external battery. A generator (e.g., solar panels, wind generators, etc.) may also be used to power the pressure transmitter or to charge a power source used by the pressure transmitter 102.

[0023] 3, a pressure sensor assembly 210 having a pressure sensor 212 is shown. The assembly 210 and pressure sensor 212 are a first exemplary embodiment of the pressure sensor assembly 110 and pressure sensor 112 described above. The pressure sensor 212 includes a support structure 220, which in an exemplary embodiment may be formed of, for example, sapphire or Al2O3. A signal lead path 222 is provided through the support structure for routing a signal lead 224 to an electrical connection 126 to establish a value of the sensed pressure P in the measurement circuit 124. A sapphire insulating member 226 configured to deflect in response to the process material pressure P is attached or bonded to the support structure 220 through a hermetic bonding material 228. The sapphire insulating member 226, the hermetic bonding portion 228, and the support structure 220 form a vacuum reference region 230 within the pressure sensor 212 to provide an absolute pressure measurement. A polysilicon layer strain gage pattern 232 is formed on the sapphire insulating member 226 in an area 230, coupled to the signal lead 224 to generate an electrical signal on the lead in response to deflection of the sapphire insulating member 226. The polysilicon resistive layer pattern may be formed as a Wheatstone bridge in some embodiments. Also shown is a process seal 234 of the pressure sensor assembly 210, which may be included to provide a seal between the transmitter surface and the sapphire insulating member 226 to prevent the passage of process fluids through the sensor assembly. In some embodiments, a sapphire etched surface 236 may be formed on the sapphire insulating member 226, although this is not required in all embodiments.

[0024] 4-1, a gauge pressure (GP) sensor assembly 310 is shown, which is a version of the pressure sensor assembly 210 shown in FIG. The pressure sensor assembly 310 has a pressure sensor 312, which is a second exemplary embodiment of the pressure sensor 112 described above. The pressure sensor 312 has the same or similar features as the pressure sensor 212, including a support structure 320, which can be formed, for example, from sapphire or Al2O3, and a signal lead path 322 is provided through the support structure to route a signal lead 324 to an electrical connection 126 and establish a value of the sensed pressure P in the measurement circuit 124. A sapphire insulating member 326 is attached or bonded to the support structure 320 through a hermetic coupling member 328. The sapphire insulating member 326, the hermetic coupling 328, and the support structure 320 form a region 330 within the pressure sensor 312. In the embodiment of the pressure sensor 312, a reference vent 340 is provided to connect the region 330 to atmospheric pressure. A polysilicon layer strain gage pattern 332 is formed on the sapphire insulating member 326 in an area 330 that is coupled to the signal lead 324 to generate an electrical signal on the lead in response to deflection of the sapphire insulating member 326. Also shown is a process seal 334 of the pressure sensor assembly 310, which may be included to provide a seal between the transmitter surface and the sapphire insulating member 326 to prevent the passage of process fluid through the sensor assembly. In some embodiments, a sapphire etched surface 336 may be formed on the sapphire insulating member 326, although this is not required in all embodiments.

[0025] FIGURE 4-2 illustrates a portion 342 of the pressure sensor assembly 310 in greater detail. As shown in FIGURE 4-2, an overpressure protection mechanism 344 may be included within region 330 to limit the deflection of the insulating member 326 during severe overpressure conditions. By acting as a stop to limit the deflection of the insulating member 326, stress on the insulating member or diaphragm is also limited to prevent damage and wear to the pressure sensor 312.

[0026] When the sapphire isolator 226 / 326 is deflected with pressure, the deflection is detected by the polysilicon strain gauge pattern 232 / 332 (as well as the temperature sensitive resistor 238 / 338) located on the back side of the isolator. The advantage of the polysilicon and associated isolating membrane layer is that a signal level as high as 18mv / v can be achieved compared to approximately 2mv / v for the nichrome layer. The high signal therefore allows for higher accuracy, range down, and stable performance. The signal is also compatible with existing strain gauge signal processing and transmitter electronics. The use of resistive elements (and protective layers) reduces the sensitivity of the detection circuit to the atmospheric reference used in the GP sensor version (discussed below and shown in Figures 4-1 and 4-2) compared to the capacitive structure.

[0027] The strength of sapphire and the high signal level of the polysilicon resistive Wheatstone bridge allows for a higher level of protection against overpressure. This robustness can be further improved by using deflection stops in the assembly, such as overpressure protection mechanism 344. Although overprotection stops are only shown with respect to pressure sensor assembly 310, it should be understood that such stops can also be included in pressure sensor assembly 210. Features of the disclosed pressure sensor, including sapphire insulating member 226 / 326 and overpressure protection mechanism 344, can enable the disclosed pressure transmitter to operate at 5 times or more the maximum working pressure (MWP), whereas conventional "oil-less" designs are often limited to 1.5 times the MWP.

[0028] In some embodiments, fabrication of the sapphire, resistive and insulating films, and backing structures can be processed at the wafer level to accommodate proven uniform batch processing. Additionally, new advances in laser cutting sapphire allow for "dicing" into the final round form without damaging the assembly. Estimated sensor diameters of 0.5 to 1.0 inches (12.7 mm to 25.4 mm) allow for small form factors and low cost.

[0029] Although embodiments of the present disclosure have been described with reference to preferred embodiments, those skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the present disclosure. Embodiments of the present disclosure include combinations of one or more of the embodiments described herein.

Claims

1. 1. A pressure sensor assembly comprising: a header defining a cavity, the pressure sensor assembly including a fluid path to the cavity; a pressure sensor disposed within the cavity and configured to sense a pressure of a fluid within the fluid path, A support structure; a sapphire insulating member coupled to the support structure and defining an area between a first surface of the sapphire insulating member and the support structure, the second surface of the sapphire insulating member being disposed in contact with fluid in the fluid path, the second surface having a sapphire etched surface formed thereon; a process seal disposed against the second surface of the sapphire insulating member to prevent fluid from passing through the pressure sensor assembly; An electrical lead; a polysilicon strain gage pattern disposed within an area on a first surface of a sapphire insulating member and coupled to electrical leads, the polysilicon strain gage pattern configured to generate an electrical signal indicative of a pressure of a fluid in the fluid path when the sapphire insulating member deflects in response to a pressure, the polysilicon strain gage pattern configured to generate an electrical signal indicative of a pressure of the fluid in the fluid path when the sapphire insulating member deflects in response to the pressure; A pressure sensor including: A pressure sensor assembly comprising:

2. 2. The pressure sensor assembly of claim 1, wherein said sapphire insulating member is a single crystal sapphire element.

3. 2. The pressure sensor assembly of claim 1, wherein the region formed between the first surface of the sapphire insulating member and the support structure contains a reference pressure.

4. 4. The pressure sensor assembly of claim 3, wherein the reference pressure is a vacuum pressure in a region formed between the first surface of the sapphire insulating member and the support structure.

5. 2. The pressure sensor assembly of claim 1, wherein the pressure sensor is configured as a gauge pressure sensor and includes a reference vent through the support structure to connect the region formed between the first surface of the sapphire insulating member and the support structure to atmospheric pressure.

6. The pressure sensor assembly of claim 1 , wherein the sapphire insulating member is bonded to the support structure using a bond material.

7. 10. The pressure sensor assembly of claim 1, further comprising a geometric protrusion formed between the first surface of the sapphire insulating member and the support structure, the geometric protrusion being coupled to the support structure in a region that limits deflection of the sapphire insulating member during an overpressure condition.

8. 10. The pressure sensor assembly of claim 1, further comprising a temperature sensor disposed on a second surface of the sapphire insulating member and configured to measure a process temperature to compensate for process temperature transients.

9. The pressure sensor assembly of claim 1 , wherein the polysilicon strain gage pattern is configured as a Wheatstone bridge.

10. The pressure sensor assembly of claim 1 , wherein the support structure comprises sapphire or Al 2 O 3 .

11. 1. A method of manufacturing a pressure sensor assembly, comprising: forming a polysilicon strain gage pattern on a first surface of a sapphire insulating member; forming a sapphire etched surface on a second surface of the sapphire insulating member; placing a process seal against the second surface of the sapphire insulating member to prevent fluid from passing through the pressure sensor assembly; bonding the sapphire insulating member to a support structure to form an area between a first surface of the sapphire insulating member and the support structure having the polysilicon strain gage pattern formed therein; positioning a pressure sensor within the cavity of the header such that the pressure sensor is positioned to interface with fluid in a fluid path to the pressure sensor assembly; method.

12. 12. The method of claim 11, wherein forming the polysilicon strain gage pattern on the first surface of the sapphire insulating member comprises forming the polysilicon strain gage pattern on a single crystal sapphire element.

13. The method of claim 12 , wherein forming the polysilicon strain gage pattern comprises forming the polysilicon strain gage pattern in a Wheatstone bridge configuration.

14. The method of claim 12 , wherein bonding the sapphire insulating member to the support structure further comprises forming the region such that the region contains a reference pressure.

15. The method of claim 14 further comprising providing a reference vent through said support structure to connect said region to atmospheric pressure such that said pressure sensor is a gauge pressure sensor.

16. The method of claim 11 , further comprising forming a geometric protrusion on the support structure in the region to limit deflection of the sapphire insulating member during an overpressure condition.

17. The method of claim 11 , wherein the support structure comprises sapphire or Al2O3.

18. Housing and a header disposed within the housing, the header including a cavity, the pressure sensor assembly including a fluid path to the cavity; and a pressure sensor disposed within the cavity and configured to sense a pressure of a process fluid passing through the fluid path, The pressure sensor includes: A support structure; a sapphire insulating member formed from a single crystal sapphire element and coupled to a support structure, the sapphire insulating member forming an area between a first surface of the sapphire insulating member and the support structure, a second surface of the sapphire insulating member being positioned in contact with fluid in the fluid path, the second surface having a sapphire etched surface formed thereon, the sapphire insulating member being configured to be deflected by pressure from fluid in the fluid path; a process seal disposed against the second surface of the sapphire insulating member to prevent fluid from passing through the pressure sensor assembly; electrical leads extending through the support structure; a polysilicon strain gage pattern disposed within an area on the first surface of the sapphire insulating member and coupled to the electrical leads, the polysilicon strain gage pattern configured to generate an electrical signal indicative of a pressure of a fluid in the fluid path when the sapphire insulating member deflects in response to a pressure; 2. A process control measurement system comprising:

19. 20. The process control measurement system of claim 18, wherein the support structure includes a geometric protrusion on the support structure in the region to limit deflection of the sapphire insulating member during an overpressure condition.

20. 20. The process control measurement system of claim 19, further comprising a reference vent extending through the support structure and connecting the region to atmospheric pressure.

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