Polysilicon on Sapphire Oil-Free Pressure Sensor

Abstract

A pressure sensor assembly includes a pressure sensor having a support structure and a sapphire isolation member. The sapphire isolation member is coupled to the support structure and forms a region between a first surface of the sapphire isolation member and the support structure. A second surface of the sapphire isolation member is positioned to engage a fluid from or coupled to a process. Electrical leads are coupled to a polysilicon strain gauge pattern positioned in the region on the first surface of the sapphire isolation member, and the polysilicon strain gauge pattern is configured to generate an electrical signal indicative of the pressure of the fluid when the sapphire isolation member deflects in response to the pressure.

Description

BACKGROUND OF THE INVENTION

[0001] Embodiments of the present disclosure relate to industrial process transmitters, and more particularly, to pressure sensor assemblies for such transmitters.

[0002] Industrial process field devices, such as process transmitters, are used in industrial process control and monitoring systems to monitor industrial process variables and transmit measurements of the process variables back to a control room in, for example, a chemical, petroleum, natural gas, pharmaceutical, or other fluid processing plant. The term "process variable" refers to the physical or chemical state of a substance or the conversion 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 can be processed by circuitry of the pressure transmitter and / or transmitted to an external control unit.

[0004] Certain pressure transmitters rely on thin (.001-.002") metal diaphragms to isolate the process fluid from the pressure sensor, where a factory-installed fill fluid transmits the pressure signal from the process to the electronic pressure sensor. These systems may not be well-suited for applications where the process is abrasive, or where the process (e.g., a sanitary process) cannot risk potential process contamination in the event of a failed isolation diaphragm. These fill systems also risk diffusion gas and / or vacuum affecting the fluid integrity.

[0005] Some pressure transmitters address these problems with "oil-free" (no fill fluid) designs that combine alumina ceramic isolation with integrated capacitance sensing. These products use alumina ceramic as the process isolation diaphragm and form part of an integrated capacitance sensor. While these pressure transmitters provide an "oil-free" feature, they may have disadvantages compared to similar metal-isolated fluid-filled devices, including reduced accuracy, rangeability, stability, and overpressure capability. Some of these limitations are inherent to the alumina material, which serves both as the isolation element and the pressure sensor deflection element in the sensor system. Additionally, the isolation / sensor ceramic has a particulate nature that is prone to impact / crack propagation failure. Moreover, when configured for instrumentation measurement, ambient air enters the capacitance detection cavity in some of these types of pressure transmitters, which can cause performance problems because the "air" dielectric may be wet / condensed and / or otherwise contaminated, resulting in measurement errors. SUMMARY OF THE INVENTION

[0006] Embodiments of the present disclosure generally relate to pressure sensor assemblies and methods of manufacturing such pressure sensor assemblies. One embodiment of a pressure sensor assembly includes a manifold forming a cavity, where the manifold provides a fluid passage to the cavity. A pressure sensor is positioned within the cavity and configured to sense the pressure of a fluid within the fluid passage. The pressure sensor includes a support structure and a sapphire isolation member bonded or coupled to the support structure to form a region 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. Moreover, in some exemplary embodiments, the support structure is formed of a material (such as sapphire or Al 2 O 3 ) having expansion characteristics similar to those of the sapphire isolation member. A second surface of the sapphire isolation member is positioned to engage the fluid within the fluid passage. Electrical leads may extend through the support structure. A polysilicon strain gauge pattern is positioned within the region on the first surface of the sapphire isolation member and coupled to the electrical leads. 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 within the fluid passage when the sapphire isolation member deflects in response to the pressure.

[0007] In an exemplary embodiment, the region formed between the first surface of the sapphire isolation member and the support structure contains a reference pressure. The reference pressure may be a vacuum pressure. In other embodiments, 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 isolation member and the support structure to atmospheric pressure.

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

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

[0010] In another embodiment, a method of manufacturing a pressure sensor assembly is provided. The method includes forming a polysilicon strain gauge pattern on a first surface of a sapphire isolation member and bonding the sapphire isolation member to a support structure to form a region between the first surface of the sapphire isolation member and the support structure, wherein the polysilicon strain gauge pattern is formed within the region. The pressure sensor is then positioned within a cavity of a manifold such that a second surface of the sapphire isolation member is positioned to engage fluid within a fluid passage through the manifold.

[0011] In another embodiment, a process control measurement system includes a housing and a manifold positioned within the housing, wherein the manifold includes a cavity and fluid passages leading to the cavity. A pressure sensor is positioned within the cavity and is configured to sense the pressure of a process fluid passing through the fluid passages. The pressure sensor includes a support structure and a sapphire isolation member formed from a single crystal sapphire element, the sapphire isolation member being coupled to the support structure to form a region between a first surface of the sapphire isolation member and the support structure. A second surface of the sapphire isolation member is positioned to engage fluid within the fluid passage such that the sapphire isolation member is deflected by the pressure of the fluid within the fluid passage. Electrical leads extend through the support structure and are coupled to a polysilicon strain gauge pattern positioned within the region on the first surface of the sapphire isolation member. The polysilicon strain gauge pattern is configured to generate an electrical signal indicative of the pressure of the fluid within the fluid passage when the sapphire isolation member deflects in response to the pressure. In some embodiments, geometric protrusions on the support structure within the region limit the deflection of the sapphire isolation member under overpressure conditions.

[0012] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the Background. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a partial cross-sectional view of an example of a pressure transmitter in a process control or measurement system according to an embodiment of the present disclosure.

[0014] Figure 2 is according to an embodiment of the present disclosure Figure 1 a cross-sectional view of a portion of a pressure transmitter.

[0015] Figure 3is a simplified cross-sectional view of a part of a pressure sensor assembly for measuring absolute pressure according to an embodiment of the present disclosure.

[0016] Figure 4-1 is a simplified cross-sectional view of a part of an alternative pressure sensor assembly for measuring gauge pressure according to an embodiment of the present invention.

[0017] Figure 4-2 is Figure 4-1 a view of a part of the pressure sensor assembly and shows an overpressure protection stop or feature. Detailed Description

[0018] Embodiments of the present disclosure are described more fully hereinafter with reference to the accompanying drawings. Elements identified by the same or similar reference numerals refer to the same or similar elements. For the sake of simplicity of illustration, some elements may not be shown in every figure.

[0019] However, the 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. On the contrary, 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.

[0020] Figure 1 is a partial cross-sectional view of an example of a process control or measurement system 100 including a pressure transmitter 102 according to an embodiment of the present disclosure. Figure 2 is Figure 1 a cross-sectional view of a part of the transmitter 102. The system 100 can be used in the processing of materials (e.g., process media) to transform the materials from a lower value state to a higher value and more useful product, such as oil, chemicals, paper, food, etc. For example, the system 100 can be used in a facility that performs a sanitary process or other types of industrial processes.

[0021] The pressure transmitter 102 can include a housing 104 that can be coupled to an industrial process 106 through a process connector 108. The housing 104 and the process connector 108 can be formed of stainless steel or another suitable material. The transmitter 102 includes a pressure sensor assembly 110 that is attached to and / or housed within the housing 104. The assembly 110 includes a pressure sensor or pressure sensor chip 112 (hereinafter referred to as "pressure sensor") formed according to one or more embodiments described herein for measuring the pressure of the process. The pressure sensor assembly 110 can include a manifold 114 and a base 116 that connects the pressure sensor 112 to the manifold 114, as Figure 2 best shown in

[0022] The process coupling 108 can be connected to a pipe 118 that is connected to a process 106 and contains process material (e.g., fluid) at a pressure P that will be measured by a pressure sensor 112. The pressure P is transmitted through a fluid passage 122 to the pressure sensor 112. The fluid passage extends through a pressure transmitter component (including the process coupling and manifold 114 in some embodiments) and into a cavity 144 that contains the pressure sensor. The pressure sensor 112 (the embodiments of which are discussed in more detail with reference to Figure 3 , 4-1 and 4-2) includes a sensor element that has an electrical parameter indicative of the applied pressure P. A measurement circuit 124 can detect and process the electrical parameter of the sensor element through suitable electrical connections 126 to establish a value for the sensed pressure P. The measurement circuit 124 can be connected to a junction box 127 of the transmitter 102, which has a communication circuit 128 for transmitting information related to the sensed pressure P (such as the value of the pressure P) to an external computer control unit 130 through a process control loop 132, as Figure 1 shown.

[0023] The pressure transmitter 102 can include a passage for connecting the sensor 112 to ambient pressure or air, such as through a vent 135 in the housing 104, as Figure 2 shown. The passage can extend through the base 116.

[0024] In some embodiments, the process control loop 132 includes a physical communication link (such as a two-wire control loop, as Figure 1 shown) and / or a wireless communication link. Communication between the control unit 130 or another external computing device and the pressure transmitter 102 can be performed over 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 mA control loop, where the measured pressure value can be represented by the level of the loop current flowing through the two-wire control loop 132. Exemplary digital communication protocols include modulating a digital signal onto the analog current level of the two-wire control loop 132 according to communication standards. Other pure digital technologies can also be employed, including FieldBus and Profibus communication protocols.

[0025] An exemplary wireless version of the process control loop 132 includes, for example, a wireless mesh network protocol such as (IEC 62591) or ISA 100.11a (IEC 62734), or another wireless communication protocol such as WiFi, LoRa, Sigfox, BLE, or any other suitable protocol.

[0026] Power can be supplied to the pressure transducer 102 from any suitable power source. For example, the pressure transducer 102 can be powered entirely by current flowing through the control loop 132. One or more power sources can also be utilized to power the pressure transducer 102, such as internal or external batteries. A generator (e.g., a solar panel, a wind turbine, etc.) can also be used to power the pressure transducer or charge the power source used by the pressure transducer 102.

[0027] Now referring to Figure 3 , a pressure sensor assembly 210 having a pressure sensor 212 is shown. The assembly 210 and the pressure sensor 212 are a first exemplary embodiment of the pressure sensor assembly 110 and the pressure sensor 112 discussed above. The pressure sensor 212 includes a support structure 220 which, in the exemplary embodiment, can be formed of, for example, sapphire or Al 2 O 3 . A signal lead channel 222 is provided through the support structure to route the signal lead 224 to the electrical connector 126 and establish the value of the sensed pressure P in the measurement circuit 124. A sapphire isolation member 226 (which is configured to deflect in response to the pressure P of the process material) is attached or coupled to the support structure 220 by an airtight bonding material 228. The sapphire isolation member 226, the airtight bond 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 gauge pattern 232 is formed on the sapphire isolation member 226 within the region 230, and the polysilicon layer strain gauge pattern is coupled to the signal lead 224 to generate an electrical signal on the lead in response to the deflection of the sapphire isolation member 226. In some embodiments, the polysilicon resistive layer pattern can be formed as a Wheatstone bridge. A process seal 234 for the pressure sensor assembly 210 is also shown, and the process seal can be included to provide a seal between the transducer surface and the sapphire isolation member 226 to prevent process fluid from passing through the sensor assembly. In some embodiments, a sapphire etched surface 236 can be formed on the sapphire isolation member 226, but is not required in all embodiments.

[0028] Now referring to Figure 4-1 , a gauge pressure (GP) sensor assembly 310 is shown, which is a version of the pressure sensor assembly 210 shown in Figure 3 . The pressure sensor assembly 310 has a pressure sensor 312 which is a second exemplary embodiment of the pressure sensor 112 discussed above. The pressure sensor 312 has the same or similar features as the pressure sensor 212, including that it can be formed of, for example, sapphire or Al 2 O 3A support structure 320 is formed, with a signal lead channel 322 provided through the support structure to route a signal lead 324 to an electrical connector 126 and establish a value of the sensed pressure P in a measurement circuit 124. A sapphire isolation member 326 is attached or coupled to the support structure 320 by an airtight bonding material 328. The sapphire isolation member 326, the airtight bond 328, and the support structure 320 form a vacuum reference region 330 within the pressure sensor 312. In an embodiment of the pressure sensor 312, a reference vent 340 is provided that connects region 230 to atmospheric pressure. A polysilicon layer strain gauge pattern 332 is formed on the sapphire isolation member 326 within region 330, and the polysilicon layer strain gauge pattern is coupled to the signal lead 324 to generate an electrical signal on the lead in response to deflection of the sapphire isolation member 326. A process seal 334 of the pressure sensor assembly 310 is also shown and may be included to provide a seal between the transmitter surface and the sapphire isolation member 326 to prevent process fluid from passing through the sensor assembly. In some embodiments, a sapphire etched surface 336 may be formed on the sapphire isolation member 326, but is not required in all embodiments.

[0029] Figure 4-2 A portion 342 of the pressure sensor assembly 310 is shown in more detail. As Figure 4-2 shown, an overpressure protection feature 344 may be included within region 330 to limit deflection of the isolation member 326 under severe overpressure conditions. By acting as a stop to limit deflection of the isolation member 326, stress on the isolation member or diaphragm is also limited to prevent damage and wear of the pressure sensor 312.

[0030] When the sapphire isolator 226 / 326 deflects under pressure, the polysilicon strain gauge pattern 232 / 332 (and temperature sensing resistor 238 / 338) located on the back of the isolator detects the deflection. The advantages of polysilicon and the associated isolation film layer are that signal levels up to 18 mv / v can be achieved compared to approximately 2 mv / v for a nickel-chrome alloy layer. Thus, a high signal enables higher accuracy, reduced range, and stable performance. The signal is also compatible with existing strain gauge signal processing and transmitter electronics. Compared to a capacitive structure, using a resistive element (and protective layer) reduces the sensitivity of the sensing circuit to atmospheric reference used in the GP sensor version (discussed below and shown in Figure 4-1 and 4-2 ).

[0031] The strength of sapphire and the high signal level of the polysilicon resistor Wheatstone bridge will allow for higher levels of protection against overvoltage. This robustness can be further enhanced by incorporating deflection stops (such as overvoltage protection feature 344) in the assembly. Although the overprotection stops are shown only with reference to pressure sensor assembly 310, it must be understood that such stops may also be included in pressure sensor assembly 210. The features of the disclosed pressure sensors (including sapphire isolation members 226 / 326 and overvoltage protection feature 344) may allow the disclosed pressure transmitters to operate at pressures five times or more the maximum working pressure (MWP), while conventional "oil-free" designs are typically limited to 1.5 times the MWP.

[0032] In some embodiments, the fabrication of the sapphire, resistor film, isolation film, and backing structure can be processed at the wafer level to accommodate proven uniform batch processing. Additionally, recent advancements in laser cutting of sapphire allow the assembly to be "cut" into its final circular shape without damage. With an estimated sensor diameter between 0.5 and 1.0 inches, a small form factor and low cost can be achieved.

[0033] 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. A pressure sensor assembly, the pressure sensor assembly comprising: a manifold forming a cavity, the pressure sensor assembly including a fluid passage leading to the cavity; a pressure sensor positioned in the cavity and configured to sense the pressure of a fluid within the fluid passage, the pressure sensor including: a support structure; a sapphire isolation member coupled to the support structure and forming a region between a first surface of the sapphire isolation member and the support structure, a second surface of the sapphire isolation member having a sapphire etched surface being positioned to engage the fluid within the fluid passage; a process seal positioned against the second surface of the sapphire isolation member to prevent fluid from passing through the pressure sensor assembly; electrical leads; and a polysilicon strain gauge pattern positioned in the region on the first surface of the sapphire isolation member and coupled to the electrical leads, wherein the polysilicon strain gauge pattern is configured to generate an electrical signal indicative of the pressure of the fluid within the fluid passage when the sapphire isolation member deflects in response to the pressure.

2. The pressure sensor assembly according to claim 1, wherein the sapphire isolation member is a single crystal sapphire element.

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

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

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

6. The pressure sensor assembly according to claim 1, wherein the sapphire isolation member is bonded to the support structure using a bonding material.

7. The pressure sensor assembly according to claim 1, further comprising a geometric protrusion coupled to the support structure within the region formed between the first surfaces of the sapphire isolation member to limit deflection of the sapphire isolation member under overpressure conditions.

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

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

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

11. A method of manufacturing a pressure sensor assembly, the method comprising: forming a polysilicon strain gauge pattern on a first surface of a sapphire isolation member; Bond the sapphire isolation member to a support structure to form a region between the first surface of the sapphire isolation member and the support structure, wherein the polysilicon strain gauge pattern is formed within the region; and Position the pressure sensor within a cavity of a manifold such that a second surface of the sapphire isolation member is positioned to engage fluid within a fluid passage leading to the pressure sensor assembly, wherein the second surface of the sapphire isolation member has a sapphire etched surface, and position a process seal against the second surface of the sapphire isolation member to prevent fluid from passing by the pressure sensor assembly.

12. The method of claim 11, wherein forming the polysilicon strain gauge pattern on the first surface of the sapphire isolation member includes forming the polysilicon strain gauge pattern on a single crystal sapphire element.

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

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

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

16. The method of claim 11, further including forming geometric protrusions on the support structure within the region to limit deflection of the sapphire isolation member under overpressure conditions.

17. The method according to claim 11, wherein the support structure comprises sapphire or Al 2 O 3 .

18. A process control measurement system, the process control measurement system comprising: a housing; a manifold positioned within the housing, the manifold including a cavity and the pressure sensor assembly including a fluid passage leading to the cavity; a pressure sensor positioned within the cavity and configured to sense a pressure of a process fluid passing through the fluid passage, the pressure sensor including: a support structure; a sapphire isolation member formed from a single crystal sapphire element, the sapphire isolation member being coupled to the support structure and forming a region between the first surface of the sapphire isolation member and the support structure, a second surface of the sapphire isolation member having a sapphire etched surface being positioned to engage fluid within the fluid passage, the sapphire isolation member being configured to be deflected by pressure of the fluid within the fluid passage; a process seal positioned against the second surface of the sapphire isolation member to prevent process fluid from passing by the pressure sensor assembly; electrical leads extending through the support structure; and a polysilicon strain gauge pattern positioned within the region on the first surface of the sapphire isolation member and coupled to the electrical leads, wherein the polysilicon strain gauge pattern is configured to generate an electrical signal indicative of the pressure of the fluid within the fluid passage when the sapphire isolation member deflects in response to the pressure.

19. The process control measurement system according to claim 18, wherein the support structure includes geometric protrusions on the support structure within the region to limit deflection of the sapphire isolation member under overpressure conditions.

20. The process control measurement system according to claim 19, further comprising a reference vent that passes through the support structure and connects the region to atmospheric pressure.

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