Flexible pH sensor and improved manufacturing method

Abstract

This paper describes a flexible pH sensor with a unique laminated structure. This sensor can be used for a variety of applications. We also explain the manufacturing method for the flexible pH sensor, including the method for supplying iridium oxide.

Description

[Technical Field]

[0001] (cross-reference to related application) This application claims the benefit of and priority to U.S. Provisional Application No. 63 / 39,046, Attorney Docket No. SENS-00301, filed in assignee 18 / 2022, and U.S. Provisional Application No. 63 / 489,580, Attorney Docket No. SENS-00600, filed in assignee 18 / 2022, the contents of which are incorporated herein by reference.

[0002] (Technical field to which the invention belongs) The present invention generally relates to flexible electronic devices and pH measurements, including flexible pH sensors, and methods for making the same. [Background technology]

[0003] Many amperometric pH sensors utilize a reference electrode to maintain a stable reference voltage, and the working or measuring electrode is held within a pH-sensitive glass bulb. The working electrode, along with the reference electrode and glass bulb, are immersed in the fluid whose pH value is to be determined. The potential across the glass bulb depends on the H+ ion concentration of the test fluid. In this way, a voltage reading can be obtained across the electrodes to determine the pH level of the fluid.

[0004] However, these types of pH sensors and their methods of operation have significant drawbacks. For example, the fragility of the glass, limitations on long-term measurements, and the requirement for repeated calibration after only a few measurements make these types of pH sensors unsuitable for many consumer, medical, and other applications. Thus, these pH sensors are unsuitable for applications that may require the pH sensor to be in contact with a patient's skin, held within a bandage, or placed within food. The fragility and / or size or configuration of these pH sensors may also make them unsuitable for applications where the sensor's configuration may need to be flexible, or where the sensor must have sufficient strength to be present in a location where changes in configuration are necessary.

[0005] Other types of pH sensors that use flexible substrates are also becoming available. However, the architecture of these pH sensors is generally limited and not easily manufactured in bulk. Therefore, these types of flexible sensors are not cost-effective for many consumer and industrial applications.

[0006] Therefore, there is a need for a pH sensor that addresses these and other shortcomings. To this end, there is a need for a flexible pH sensor that can be used in a variety of applications. There is a need for a pH sensor with a robust architecture that can withstand locations and applications that require strength. There is also a need for a pH sensor that can be manufactured efficiently and at low cost, including through manufacturing methods that use currently available manufacturing equipment. Summary of the Invention [Problem to be solved by the invention]

[0007] One aspect of the present invention includes a pH sensor having a flexible and physically stable structure.

[0008] Another aspect of the invention relates to the use of two to three electrodes.

[0009] Another aspect of the invention relates to coatings that are non-reactive with the solution whose pH is being measured.

[0010] Another aspect of the present invention relates to the use of an IrOx coating on an active or working electrode that can act as a proton conducting membrane, allowing H+ ions to pass through the coating while preventing other ions that may be present in the solution.

[0011] Other aspects of the invention are described herein. [Brief explanation of the drawings]

[0012] [Figure 1] 1A-1B show top and side views, respectively, of a pH sensor.

[0013] [Figure 2] 2A-2B show exploded side views of a pH sensor, respectively.

[0014] [Figure 3] Top and side views of a pH sensor

[0015] [Figure 4] Top view of the reference and active electrodes along with part of the pH sensor.

[0016] [Figure 5] Top view of the pH sensor

[0017] [Figure 6] Top view of the pH sensor

[0018] [Figure 7] 7A-7D show top and side views of a pH sensor.

[0019] [Figure 8] Side view of the pH sensor

[0020] [Figure 9] 9A-9D show top and side views of the pH sensor.

[0021] [Figure 10] 10A-10B show top and perspective views of a pH sensor and its packaging.

[0022] [Figure 11] 1 shows a substrate used to form a pH sensor.

[0023] [Figure 12A] ~ [Figure 13B] 12A-13B illustrate a method for manufacturing a flexible pH sensor according to an exemplary embodiment of the present disclosure.

[0024] [Figure 14] ~ [Figure 15] FIG. 1 illustrates aspects of a manufacturing apparatus that may be used to form a flexible pH sensor according to exemplary embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0025] In general, exemplary embodiments of the present specification describe pH sensors that preferably reflect a flexible and physically stable architecture, as well as other beneficial attributes. In some embodiments, the pH sensor may include a flexible polyimide sheet (or similar) with at least one surface coated with gold (or a similar transition material). Electrodes (e.g., reference and / or working) may be formed on a gold layer using appropriate metallization and / or metallization materials. For example, a reference electrode may be formed on a gold layer using silver / silver chloride (Ag / AgCl or Ag:AgCl), and / or a working electrode may be formed using iridium oxide (lrO2). An lrOx (or similar) coating on the working electrode may act as a proton transfer membrane by allowing H+ ions to pass through the lrOx coating while preventing other ions in the test solution from interacting with the measurement circuit. This can provide a true pH measurement, rather than a measurement of the total ionic potential across the test solution. In other words, the present invention preferably provides a more accurate determination of the pH level of the test solution. This represents a significant distinction from existing pH sensors that can simply measure the potential voltage across a sample solution. Other suitable metallization and / or metallization materials may also be used.

[0026] In some embodiments, the pH sensor is packaged so that at least a portion of the electrodes are exposed at regular intervals for contact with the fluid or substance to be tested. The packaging may also include electrical connectivity to external measurement equipment that can be used to measure an electrical parameter (e.g., voltage potential) across the electrodes to determine a pH level reading. The packaging may also seal the electrical connections within the pH sensor and protect the sensor from the environment.

[0027] The result is a lower-cost, more flexible pH sensor that can be incorporated into a wide variety of consumer, medical, and other applications. For example, flexible sensors could provide disposable point-of-care devices that can be incorporated into bandages to sense wound conditions, form-fitting and wearable sensors that can be incorporated into clothing to make skin contact, and sensors integrated into diapers to detect soiling and / or potential urinary tract infections. Other applications include biological media, the food industry, the nuclear field, and the oil and gas industry, to name a few.

[0028] In addition to the disclosures provided herein, the disclosure of an article, a printable and flexible iridium oxide-based pH sensor, is provided by a roll-to-roll process. https: / / doi.org / 10.3390 / chemosensors11050267 , which are incorporated by reference as if fully set forth herein.

[0029] FIG. 1A shows a top view of a flexible pH embodiment. However, the embodiment of FIGS. 1A and 1B still reflects aspects of the present invention.

[0030] In some embodiments, as shown in FIGS. 1A and 1B, the pH sensor 10 includes a reference electrode 104A and an active or working electrode 104B, each comprising a flexible polyimide sheet (or the like) coated on at least one side with a metal coating (e.g., metallization). For example, in some embodiments, the reference electrode 104A may include a metal coating comprising silver / silver chloride (Ag / AgCl), and the working electrode 104B may include a metal coating comprising iridium oxide (IrO). In use, a sample fluid whose pH level is being determined is provided across the reference electrode 104A and the working electrode 104B to complete the circuit, and a potential measurement is made between the electrodes 104A, 104B (e.g., using an external electrical measurement device) to determine the pH level of the fluid or solute. Other suitable metal coatings may also be used with any of the embodiments described herein. Also, while various substrates are described herein primarily as polyimide substrates, any suitable substrate may be used.

[0031] In some embodiments, a polyimide base sheet 100 is provided to support electrodes 104a, 104b. The base sheet 100 may include a first end 110, a second end 112 opposite the first end 110, and a top surface 114 extending between the first end 110 and the second end 112.

[0032] The reference electrode 104A and working electrode 104B may be mounted on the top surface 114 of the base sheet with their metallized surfaces facing upward and extending from the second end 112 of the sheet to an interior location L1 between the second end 112 and the first end 110; the electrodes 104A, 104B may be attached to the top surface 114 with a pressure-sensitive adhesive (PSA) 103, as described below, and may be separated side-by-side by a gap to prevent electrical shorting between the two. It is preferred that the electrodes 104A, 104B do not extend beyond the second end 112 of the base sheet and the PSA 103 to avoid excessive bending of the electrode(s) which could damage the electrode coating.

[0033] Additionally, a second polyimide sheet 102 may be attached to the upper surface 114 of the base sheet between the interior location L1 and the first end 110 of the base sheet, and as described below, the second sheet 102 may provide electrical connectivity to the reference electrode 104A and the working electrode 104B. The second polyimide sheet 102 may include a first end 116, a second end 118 opposite the first end 116, and upper and lower surfaces 120, 122 extending between the first end 116 and the second end 118, and it may be preferable for the second end 118 of the second sheet to abut both the reference electrode 104A and the working electrode 104B, respectively, at the interior location L1, as shown. Additionally, the first end 116 of the second sheet extends beyond the first end 110 of the base sheet, thereby allowing the first end 116 of the second sheet to be electrically connected to other equipment (e.g., electrical measurement equipment for taking sensor readings).

[0034] In some embodiments, the reference electrode 104A and working electrode 104B and / or the second polyimide sheet 102 may be bonded to the top surface 114 of the base polyimide sheet 100 using a pressure-sensitive adhesive (PSA) film 103, preferably containing adhesive on both sides. For example, non-limiting PSA films may include #1567 film and / or #1510 film, respectively, produced by 3M®. Other types of suitable adhesives may also be used.

[0035] As shown in FIG. 1A, it may be preferable for the width of the polyimide base sheet 100 to be wider than the width of the second polyimide sheet 102, so that the base sheet 100 extends outward (upward and downward from the perspective of FIG. 1A) on either side of the reference electrode 104A and the working electrode 104B. This may provide room for attachment and bonding of the electrodes 104A, 104B, as described herein. However, it is understood that this may not be necessary for all applications.

[0036] In some embodiments, the second polyimide sheet 102 includes one or more conductive metal paths 101, which may be printed, etched, or otherwise provided on the sheet 102, extending from a first location at or near a first end 116 of the second sheet to a second location at or near a second end 118 of the second sheet, and in some embodiments, each conductive path 101 includes a first exposed contact pad 124 at the first location and a second exposed contact pad 126 at the second location.

[0037] In some embodiments, as shown in FIG. 1A, a first conductive pathway 101-1 is arranged to provide electrical connectivity to a reference electrode 104A, and a second conductive pathway 101-2 is arranged to provide electrical connectivity to a working electrode 104B. In this configuration, the second contact pad 126 of each conductive pathway 101 is preferably adjacent to the inner end of its corresponding electrode 104A, 104B. In this manner, the electrodes 104A, 104B and their corresponding contact pads 126 may be electrically connected as described below.

[0038] In some embodiments, each conductive path 101 includes an insulating coating in the area between the first contact pad 124 and the second contact pad 126 so that the conductive path 101 is properly insulated while leaving the pads 124, 126 exposed. Insulating plastics and / or laminates may be used for this purpose. In any case, it is preferable that the second polyimide sheet 102 remain flexible.

[0039] In some embodiments, as shown in FIGS. 1A and 1B, the second contact pad 126 of the first conductive pathway 101-1 may be electrically connected to the inner end of the reference electrode 104A, and the second contact pad 126 of the second conductive pathway 101-2 may be electrically connected to the inner end of the working electrode 104B. In some embodiments, these connections may be provided using strips of conductive material, such as, but not limited to, copper tape. For example, a first strip of conductive tape 105A may be applied between the contact pad 126 of the first pathway and the reference electrode 104A, and a second strip of conductive tape 105B may be applied between the contact pad 126 of the second pathway and the working electrode 104B. It is preferred that the first and second strips 105A, 105B do not contact each other (e.g., to avoid short circuits), and that appropriate surface areas of the contact pads 126 and corresponding electrodes 104A, 104B are covered by the conductive tape to provide appropriate electrical connectivity.

[0040] Additionally, the first contact pad 124 of the conductive pathway 101 may preferably be designed to connect to an external connector, such as a zero insertion force (ZIF) connector or other connector having an appropriate attachment format (e.g., for electrically connecting the pH sensor 10 to an electrical measurement device).

[0041] The arrangement of the components described above, and the manner in which they are attached, allows the sensor 10 to be sufficiently flexible for use in a variety of applications, as described below. As also described below, this configuration of components also provides an efficient method of manufacturing the sensor 10. These advantages also apply to the embodiments described below.

[0042] 2A and 2B illustrate additional elements that may be added to the pH sensor 10 of FIGS. 1A and 1B, with FIG. 2A showing an exploded view and FIG. 2B showing the components of FIG. 2A assembled. For example, reinforcing and / or protective elements may be added to the pH sensor 10 as described herein.

[0043] In some embodiments, a small amount of adhesive 106 (e.g., epoxy or similar) can be applied to the area including the first and second strips 105A, 105B of conductive tape to effectively seal the electrical connections between the strips 105A, 105B and the respective electrodes 104A, 104B underneath, as well as the second electrical contact pads 126 underneath. In this way, the electrical connections can be protected from the external environment (e.g., from contaminants that may cause erroneous pH readings). The adhesive 106 is generally shown as a bead in FIG. 2A, which may be applied to assume the potting configuration shown in FIG. 2B; however, the adhesive 106 may be configured or applied to the sensor 10 in other ways.

[0044] An additional protective sheet 108 of polyimide material (or similar) may be adhered to the adhesive coated first and second conductive tape strips 105A, 105B using a PSA or similar intermediate layer 107. The protective sheet 108 may further protect the electrical connections by acting as a cover to protect the connections from external mechanical forces (such as abrasion).

[0045] Even with the additional protective and / or reinforcing components described in connection with FIGS. 2A and 2B, sensor 10 preferably still exhibits sufficient flexibility for a variety of applications. Moreover, these protective and / or reinforcing components may be added to sensor 10 while maintaining efficient manufacturing methods.

[0046] Another embodiment or feature of the present invention is shown in FIG. 3 (including top and side views of the sensor 10). As shown, reservoirs or wells can be formed on the top surfaces of the reference electrode 104A and working electrode 104B to hold the sample fluid to be tested. In some embodiments, a reservoir frame 109 including a central opening can be placed on the top surfaces of the electrodes 104A, 104B and sealed thereto using a PSA or the like. The frame 109 provides reservoir sidewalls, and the central opening allows the test fluid held therein to physically contact the electrodes 104A, 104B.

[0047] In some embodiments, the frame 109 comprises a flexible material, such as vinyl, polyimide, or other suitable material, and includes a height selected to meet the requirements of each particular application. Thus, flexibility of the overall sensor 10 can be maintained. While FIG. 3 shows the well or reservoir frame 109 shaped as a square, other shapes may be used. Alternatively, PSA or other suitable material may be applied in the appropriate locations and to itself form the walls of the well 109.

[0048] In some embodiments, as shown in FIG. 4, the pH sensor 10 of FIGS. 1A, 1B, 2A, and 2B may be split into two separate substrates, the first substrate including the reference electrode 104A and its associated elements, and the second substrate including the working electrode 104B and its associated elements. This results in two self-contained and fully functional connectorized electrodes 104A, 104B that can be used together to make pH readings, for example, connected to millivolt-sensing pH-calculating electronics. Having the electrodes 104A, 104B on separate substrates allows the two electrodes 104A, 104B to be positioned in different orientations relative to each other (e.g., with the reactive measurement surfaces facing away from each other, at an offset angle relative to each other, etc.), and / or otherwise configured as required for different applications.

[0049] Applicable descriptions, aspects, and / or elements of the embodiments of FIGS. 1A, 1B, 2A, and 2B described above may be applied to the embodiment of FIG. 4, and thus FIG. 4 illustrates alternatives that may be applied to various embodiments of the present invention.

[0050] Another embodiment of the present invention is shown in FIG. 5, in which the previously described pH sensor 10 may be expanded to include a third electrode 104C and its associated elements (e.g., connected to a corresponding third conductive path 101-3). The third electrode 104C may be aligned beside the first and second electrodes 104A, 104B (or in any other desired location and / or orientation) and configured to serve as an electrical ground for the pH sensor 10 and its associated electrical measurement equipment. The third electrode 104C may be metallized using a metal coating of a suitable material (e.g., Ag:AgCl). In this manner, the third electrode 104C may reduce electrical noise and / or interference associated with pH measurements that may adversely affect the accuracy of such measurements. Any of the applicable descriptions, aspects, and / or elements of the embodiments of FIGS. 1A, 1B, 2A, and 2B described above, or others, may be used. The embodiments described below may also be applied to the embodiment of FIG. 5, and thus FIG. 5 illustrates alternatives that may be applied to various embodiments of the present invention.

[0051] Another embodiment of the present invention is shown in FIG. 6, in which a thermal sensor 128 (e.g., a thermistor or other heat-sensing device) may be incorporated into the pH sensor 10, and the thermal sensor 128 may be configured to sense the temperature of the solution under test and provide or communicate the sensed temperature information to an associated measurement instrument (or controller, etc.). In this way, the effects of temperature fluctuations during the measurement process can be taken into account.

[0052] For example, in some embodiments, the measurement device may apply a temperature correction factor to account for slight or other temperature changes sensed during the measurement procedure. The temperature correction factor may be determined by calibrating the pH sensor 10 and the measurement device, by theoretical calculations, and / or by other techniques, over various temperature ranges. In this manner, the pH sensor 10 may be pre-calibrated and may not require on-site and / or in-field calibration. Other types of calibrations (e.g., other than temperature) may be performed prior to use of the pH sensor 10, and as a result, other types of correction factors may also be applied.

[0053] In some embodiments, as shown in FIG. 6, the pH sensor 10 of FIGS. 1A, 1B, 2A, and 2B may include a third conductive path 101-3 aligned adjacent to the existing paths 101-1, 101-2, or in other embodiments, may be similar to the embodiment of FIG. 5, except that the third electrode 104C and its associated bonding elements are not configured with the additional path 101-3.

[0054] In some embodiments, as shown in FIG. 6, the thermal sensor 128 comprises a two-lead device (e.g., a temperature-sensitive resistor) having a first lead electrically connected to the third conductive pathway 101-3 and a second lead electrically connected to the adjacent conductive pathway 101-2 comprised of the working electrode 104B. A thermistor or similar temperature-sensing device should be between the working electrode (IrOx) and the ground electrode (one of the Ag:AgCl electrodes). This allows a voltage to be sent from the electronics to detect the temperature-calibrated resistance of the thermistor in one operating mode and to read the difference in potential between the working and ground electrodes in the pH-reading mode. Another option is the use of an additional conductor line to isolate the thermistor and provide a separate electrical reading of the temperature.

[0055] Given this configuration, an electrical measurement device may be configured to measure the changing resistance of the thermal sensor 128 across the conductive paths 101-2, 101-3 (e.g., using the first contact pad 124), which may represent the changing temperature of the working electrode 104B and thereby the changing temperature of the pH sensor 10 itself. This temperature information may then be used to apply a correction factor to the pH reading to improve the accuracy of the measurement. It is understood that the sensor 128 may be surface mounted or otherwise mounted in place using other mounting techniques.

[0056] In some embodiments, a switching network can be used between the pH sensor 10 of FIG. 6 and the measurement equipment to switch between pH and temperature readings. For example, a switch can be controlled to first take a direct electrical measurement across the conductive paths 101-2, 101-3 to measure an electrical parameter (e.g., resistance) of the thermal sensor 128 and use this information to determine any temperature changes. The switch can then be controlled to redirect the electrical measurement across the conductive paths 101-1, 101-2 to measure an electrical parameter (e.g., potential) between the reference electrode 104A and the working electrode 104B to gather pH reading information. In some embodiments, it may be preferable for the additional conductive path 101-3 to be terminated in a properly matched impedance while the pH measurement is being taken between the electrodes 104A, 104B to avoid voltage signal leakage across the thermal sensor 128 that could affect the pH reading.

[0057] Although FIG. 6 illustrates the thermal sensor 128 as being connected between the two conductive paths 101-1, 101-3 at a slight offset distance from the working electrode 104B, it is contemplated that the thermal sensor 128 may be connected at and / or directly adjacent to the electrode 104B.

[0058] In other embodiments, a fourth conductive pathway may be added that is generally aligned with and adjacent to the third conductive pathway 101-3, and the temperature sensor 128 may be electrically connected between the third pathway and the fourth pathway, rather than between the third pathway 101-3 and the second pathway 101-2; in this manner, the working electrode 104B may be electrically isolated from the temperature sensor 128 and the measurement equipment connected thereto.

[0059] Given the above configuration including the thermal sensor 128, it is contemplated that other devices may be similarly configured with one or more conductive paths 101 on the pH sensor 10.

[0060] For example, in some embodiments, other types of sensor devices, such as pressure, orientation / motion (e.g., accelerometers, gyroscopes, etc.), shock / vibration, and / or other types of sensors, may also be configured with one or more conductive pathways 101; in some embodiments, the sensors may be configured with pathways 101 associated with electrodes 104A, 104B, while in other embodiments, the sensors may be configured with additional pathways 101 separate from electrodes 104A, 104B.

[0061] In other embodiments, one or more data chips may be configured with one or more conductive paths 101 that may provide identification information, calibration data (e.g., pre-calibration correction factors as described in other sections), and other types of information about the pH sensor 10, which may include unique identification credentials, information about the type and test range of the pH sensor 10, and / or other relevant information.

[0062] In other embodiments, additional circuitry and / or electrical components may be integrated with the pH sensor 10, for example, on the polyimide sheet 102, thereby providing data communication circuitry including signal amplifiers, thereby enabling the pH sensor 10 to operate as a wireless sensor that can communicate with other devices to provide pH data in an Internet of Things (IOT) environment.

[0063] It will be understood that in any of these embodiments, the measurement device (and / or controller) may implement one or more correction factors and / or other types of calculations using information provided by the sensor to improve the accuracy of the pH measurement and / or to facilitate use of the pH sensor 10 as an integrated sensor suite.

[0064] 7A-7D show additional embodiments of a pH sensor 10 including a rigid reference electrode 130A and a working electrode 130B mounted directly on a base substrate 1322, with FIGS. 7A-7C showing top views and FIG. 7D showing a side view.

[0065] In some embodiments, the reference electrode 130A and working electrode 130B may be fabricated using a rigid, non-flexible substrate such as a ceramic or semiconductor material (or similar). The reference electrode 130A may be coated with AgCl, and the working electrode 130B may be coated with lrOx, and both electrodes 130A, 130B may be fired to form physically and chemically stable electrode components.

[0066] In some embodiments, as shown in FIG. 7A , the base substrate 132 may comprise a rigid material (e.g., a printed circuit board (PCB), a ceramic substrate, etc.), a semi-rigid material, and / or a flexible material (e.g., a polyimide film, a plastic, etc.). As shown in FIGS. 7B and 7D , conductive pathways 134 are formed on the top surface of the substrate 132, with each pathway 134 including a first contact pad 136 at or near one end of the substrate 132 and a second contact pad 138 at or near the other end of the substrate 132. As shown in FIGS. 7B and 7D , portions of the conductive pathways 134 between the contact pads 134, 136 may be coated with an insulating layer 140, leaving the contact pads 136, 138 exposed.

[0067] In some embodiments, as shown in Figures 7C and 7D, the reference electrode 130A may be mounted directly on a first contact pad 138 with its AgCl-coated side facing upward, and the working electrode 130B may be mounted directly on an adjacent contact pad 138 with its lrO2-coated side also facing upward. In other embodiments, the reference and working electrodes 130A, 130B may be mounted face-up on the base substrate 132 directly adjacent to (e.g., in sufficient proximity to) the corresponding contact pads 138 (to be electrically connected, as described below). The electrodes 130A, 130B may be adhered and held in place using adhesive or other suitable techniques.

[0068] In some embodiments, as shown in Figures 7C and 7D, the reference electrode 130A and working electrode 130B may be electrically connected to their respective underlying contact pads 138 using conductive epoxy 142 or the like, or by using wire bonds (e.g., as used in packaging semiconductor chips). Additionally, a protective layer of epoxy or polymer material 144 may be applied to cover the conductive epoxy 142 (or wire bonds) and the surrounding areas of the contact pads 138, including the edges of the reference and working electrodes 130A, 130B (including any edges that may not be metallized). In this way, these areas may be sealed and protected from the environment. Flexible reference and / or working electrodes 104A, 104B (e.g., utilizing metallized flexible polyimide substrates as described in other sections) may also be used in the above embodiments.

[0069] Another embodiment of the present invention, shown in FIG. 8 , illustrates a base substrate 132 having conductive pathways 134 and an insulating layer 140 between contact pads 136, 138, where the reference electrode 130A and working electrode 130B may be directly attached (e.g., using adhesive, etc.) onto their respective contact pads 138 and may each include one or more electrical vias 146 from the upper metallized surface on the electrodes 130A, 130B to the underlying contact pads 138. In some embodiments, the vias 146 may be electrically connected to solder balls 148 in electrical communication with the contact pads 138 for electrical connection. Additionally, a protective layer of epoxy or polymer material 144 may be applied to cover the surrounding areas of the contact pads 138, including the edges of the reference and working electrodes 130A, 130B (including any edges that may not be metallized), to seal and protect these areas from the environment.

[0070] In another embodiment of the present invention, as shown in Figures 9A-9D, a base substrate 132 having conductive paths 134 between contact pads 136, 138 may be provided with apertures 150 that pass through the contact pads 138 and through the base substrate 132 below. All of the apertures 150 are preferably identical, although various configurations may be used. Figure 9A shows the base substrate 132 and apertures 150 from above, and Figure 9B shows the same from below.

[0071] In this embodiment, the reference electrode 130A and working electrode 130B may be mounted on respective contact pads 138 with their metallized surfaces facing downward toward the respective openings 150, as shown in FIG. 9C. In some embodiments, the downward-facing metallized surfaces of electrodes 130A, 130B may be electrically connected to the portions of contact pads 138 surrounding the openings 150 using solder or gold ball connections 152. Other types of connections may also be used, such as, but not limited to, Z-axis conductive adhesive, printed conductive adhesive, and / or other techniques.

[0072] Additionally, because the electrodes 130A, 130B face downward, the top surface of the base substrate 132, including the contact pads 138 and the electrodes 130A, 130B attached thereto, may be covered with insulating layers 140, 144 (e.g., epoxy, polymer, or similar), while leaving the input contact pads 136 exposed to allow connection to measurement equipment. This is shown in FIG. 9D

[0073] During use, the electrode ends of the pH sensor 10 may be immersed in a test fluid so that the fluid can pass through the openings 150 and interact with the metallized surfaces of the electrodes 130A, 130B.

[0074] In another embodiment of the invention, as shown in FIGS. 10A and 10B, the reference and working electrodes 130A, 130B may be packaged within a housing 154, and in some embodiments, the housing 154 may include a tray 156 designed to support and secure the electrodes 130A, 130B and a cover 158 designed to support and secure the electrical connectivity to the electrodes 130A, 130B.

[0075] In some embodiments, the tray 156 may include a track 160 (e.g., a slight recess or the like) that includes a first portion designed to secure the reference electrode 130A and a second portion designed to secure the working electrode 130B. The two portions may converge into a single track at the input to the tray 156 for connectivity. The reference electrode 130A and the working electrode 130B may be secured within the track 160 using an adhesive, and may be juxtaposed and separated by a gap for electrical isolation. As shown in FIG. 10A, the electrodes 130A, 130B may each include a non-metallized internal connection portion 162 for electrical connectivity.

[0076] In some embodiments, the cover 158 may include a channel 164 (e.g., a recess or the like) designed to support and secure an electrical wire 166 for connection to the electrodes 130A, 130B. The electrical line 166 may comprise two separate wires, a twisted pair, or the like. As shown in FIG. 10A, the channel 164 may enter the cover 158 on one side or may be split into two electrically isolated portions such that a first wire may be placed in a first portion and a second wire may be placed in a second portion. The channel 164 in the cover may generally mirror the track 160 in the tray such that the channel 164 and the track 160 may be aligned and overlay one another when the housing 154 is assembled.

[0077] In some embodiments, the ends of the electrical lines 166 (e.g., the ends of each wire in each channel portion) may be exposed (with optional insulation) and electrically connected to the exposed portions 162 of each respective electrode 130A, 130B using conductive epoxy, solder, Z-axis glue, or similar techniques.

[0078] The cover 158 may be connected and secured to the tray 156 using an adhesive sealant (preferably liquid-tight) so that test fluids or other contaminants cannot enter the combined tray 156 and cover 158 when assembled. The result is shown in Figure 10B. As shown, the portion of the tray 156 that houses the metallized electrodes 130A, 130B may extend outward from the cover 158 so that the electrodes 130A, 130B may be available to interact with the fluid under test to provide a pH measurement. In this way, the tray 156 in this region may provide base support for the electrodes 130A, 130B during use.

[0079] Although the above embodiments have been described in connection with using more rigid electrodes 130A, 130B, the more flexible electrodes 104A, 104B of other embodiments described herein may also be used in these implementations.

[0080] Various exemplary fabrication techniques for the reference and working electrodes and the overall flexible pH sensor 10 are now described with reference to FIGS. 11-15 for illustrative purposes, where the reference electrode RE may include electrodes 104A, 130A, and / or other types of reference electrodes, and the working electrode WE may include electrodes 104B, 130B, and / or other types of working electrodes.

[0081] In some embodiments, as shown in FIG. 11 , the electrodes RE, WE may be fabricated using a metallized base substrate 168, and the reference electrode RE and working electrode WE may be fabricated on a common base substrate 168, which may comprise a polyimide sheet (preferably high temperature) coated with a first layer 170 comprising copper of a thickness suitable for electrical connectivity and for providing a bonding layer for bonding additional metallization layers to the polyimide film 168 (e.g., for metallization of the reference electrode RE and working electrode RE, WE on the same common base substrate 168). Other materials, such as, but not limited to, chromium, platinum, and / or silver, may also be used (e.g., instead of copper).

[0082] The thickness of the base substrate 168 and copper layer 170 may be independent of the processing of additional layers used to form the electrode RE, WE. For example, the properties of the base sheet 168 and / or copper layer 170 may be selected based on the amount of flexibility required in the final electrode RE, WE, the ability of the polyimide base sheet 168 to withstand the processing requirements to complete electrode fabrication, and the ability to prevent any delamination, cracking, and / or other failure conditions that may affect the lifespan of the finished electrode RE, WE.

[0083] A second layer 172 comprising gold may be coated onto the first layer 170 to receive electrode metallization. The gold layer 172 may have a thickness of approximately 90 nm-150 nm to minimize thermomechanical issues with the copper layer 170 and maintain a continuous surface across the copper coating 170 without defects such as holes, delamination zones, etc.

[0084] In other embodiments, the gold layer 172 may be deposited directly onto the polyimide film 168 via the copper layer 170. This may provide a more direct conductive path that requires fewer processing steps.

[0085] In some embodiments, a third layer 174 comprising an electrode metallization layer for either or both of the reference and / or working electrodes RE, WE may be coated on top of the gold layer 172; for example, the area of ​​the substrate 168 determined to include the working electrode WE may be coated with a third layer 174 comprising lrO2 (or other suitable material). Similarly, the area of ​​the substrate 168 determined to include the reference electrode RE may be coated with a third layer 174 comprising Ag:AgCl. The lrO2 layer 174 and / or the Ag:AgCl layer are preferably uniform and may be applied by dipping, screen printing, roller printing, inkjet printing, and / or other suitable processes.

[0086] In a first example, in some embodiments, the IrO2;2 layer 174 for the working electrode WE may be fabricated via deposition of IrOx (or IrCl to form IrOx through a thermal oxidation process as described below) to create a layer thickness sufficient to cover the gold layer 172 and reach a thickness where the IrOx, when processed, crystallizes into an interlocking surface layer sufficient for proton transport capability.

[0087] In some embodiments, IrOx (or IrCl to form IrOx) can be applied using an iridium-based ink. The iridium-based ink can include iridium chloride, alcohol, and a mild acid. The alcohol is preferably high proof, e.g., 200 proof or equivalent. Preferred embodiments include ethanol, methanol, and other similar alcohols. Preferred mild acids include acetic acid, citric acid, and other similar acids, which can be 70% or higher in concentration.

[0088] The components of the iridium-based ink are preferably mixed until no solids are visible in the solution, e.g., not a suspension. The ink is preferably not heated and remains sealed during the mixing process due to the alcohol.

[0089] The relative amounts of iridium chloride powder, alcohol, and mild acid used to form the iridium-based ink may be approximately 0.75-1.5 grams of iridium chloride, 35-50 ml of alcohol, and 8-15 ml of mild acid. However, these relative amounts may vary depending on the application in which the pH sensor is used. The relative amounts may also depend on the desired viscosity of the ink, which may itself depend on the manufacturing process and equipment used to form the coating. The viscosity of the iridium-based ink may generally range around the viscosity of water. However, in some embodiments, the iridium-based ink is less viscous than water, thereby aiding in manufacturing processes involving inkjet printing. Alternatively, the viscosity of the iridium-based ink may be thicker than water, which may be preferable for manufacturing processes involving rollers, such as gravure or flexographic presses.

[0090] It is preferable that a uniform coating be formed regardless of the manufacturing process and equipment used. To print a uniform coating with iridium-based inks, the speed and pressure of the printing pad in a gravure or flexographic printing press can vary because the density of the printing pad and rollers and their materials vary depending on the machine type and manufacturer. Similarly, jet ink printing with iridium-based inks can also be sensitive to the size of the printing dot and the density of the print.

[0091] In short, it is preferable that the thickness of the coating formed on the electrode substrate be very uniform. This is because thicker areas of the coating may contain residual IrCl, which can impair the performance of the electrode.

[0092] In some embodiments, metal oxide IrOx may be formed by using a metal chloride compound, such as iridium chloride (IrCl), which, when heated to a certain temperature range, allows atmospheric oxygen to displace chlorine, thereby forming IrOx. This may be done using a single cycle and / or by using a number of cycles, such as a number of cycles corresponding to the number of coating layers used in coating gold layer 172; additionally, no inert or other process gases may be required in the heating system during the thermal process. The cycle time for the metal chloride to metal oxide thermal transition process may vary depending on the metals involved and the thickness of the coating being oxidized.

[0093] For example, a thicker monolayer of IrCl, 90 nm (nanometers)–200 urn (microns), can be heated to about 50°C–150°C for about 1–2 hours, after which the temperature is increased to about 275°C–350°C for about 4–6 hours (all in standard atmosphere) to form a thicker monolayer of IrOx. In another example, if multiple thinner layers of IrCl are applied to form an IrOx layer, the thickness of each individual layer can be in any desired range, typically from 10 nm to 200 microns. Each layer can be applied and then heated to an initial temperature of about 50°C–70°C for 2–5 minutes, after which the temperature can be increased to about 90°C–115°C for about 10–20 minutes. After this, a full oxidation process cycle, preferably used in the monolayer process, facilitates complete oxidation. In either case, the resulting IrOx layer preferably reaches a thickness appropriate for crystallization into an interlocking surface layer sufficient for proton transfer capability.

[0094] The IrO2 metallization can preferably be replaced with other metal oxides that provide a similar electrical and chemical relationship to the sample material being pH tested.

[0095] The reference electrode RE may be formed using a similar arrangement of base substrate 168, copper coating 170, and gold coating 172, and a top layer 174 of silver / silver chloride (Ag / AgCl) (or other suitable material) directed towards the reference electrode RE metallization.

[0096] The reference electrode RE and working electrode WE may also be manufactured using a flexographic or gravure type process (or similar) to print the electrodes. An anilox roller (or similar) can transfer a volume of electrode material in ink form onto a carrier with a uniform thickness.

[0097] In other embodiments, stencil printing, jet ink, or nozzle printing can be used to transfer the electrode material in ink form to the gold-coated flexible polyimide substate 168, and in some embodiments, multiple electrodes and / or electrode sets can be printed using multiple printing passes, e.g., using a sheet manufacturing process such as roll-to-roll (R2R) and / or lamination.

[0098] A generalized schematic of an exemplary manufacturing process for a batch electrode assembly is shown in Figures 12A and 12B. In some embodiments, the pH sensor 10 may be packaged by placing the electrodes RE, WE, and layers of insulating adhesive tape T between two laminate sheets LS (e.g., polyimide sheets as described herein). A mechanical punch (or similar) may be used to form holes H in one of the sheets LS (and, if necessary, adhesive tape T) to expose the sensing area of ​​each electrode RE, WE and form microwells above each electrode RE, WE to contain the fluid under test. In some embodiments, the reference electrode RE and working electrode WE may be fabricated separately and / or on a single substrate with appropriate spacing to prevent electrical shorting.

[0099] In some embodiments, the batched electrode assemblies may then be passed through a thermal laminator resulting in the laminated assembly of Figure 12B. This process is suitable for large-scale films and may be integrated with the electrode fabrication process. After batch processing, the assemblies may be cut or otherwise singulated into individual sensors 10, as shown in Figure 12C. This process may be cost-effective without requiring a vacuum environment or wafer transfer.

[0100] Figures 12C and 12D show an individual pH sensor 10 in use, and Figure 12B shows a cross-sectional view of the electrodes RE, WE. As shown, a small volume (e.g., 1 microliter - several hundred microliters) of test solution can be applied to the microwell to cover both the reference electrode RE and the working electrode WE and provide electrical connectivity between the two (to complete the circuit) for accurate pH measurement. Preferably, a layer of insulating adhesive tape T placed between the laminated sheets LS (see Figure 11a) can provide an adequate seal to prevent any test solution from shorting out the electrodes RE, WE or any connecting wires connected thereto.

[0101] The electrodes RE, WE may then be defined by scribing, cutting from bulk sheet or roll form, and / or using photolithography-printing and / or etching techniques. The cutting process may include die stamping, roll or knife cutting, and / or laser cutting.

[0102] An example of this process is shown in Figures 13A and 13B. Figure 13A shows a roll of gold-coated base sheet 168 having a gold-coated layer 172 on its inward-facing surface. As shown in Figure 13B, the rolled sheet 168 may be patterned by die cutting, laser cutting, scroll cutting, photolithographic patterning, etching, and / or other suitable techniques (preferably all computer-controlled) for processing into individual electrodes RE, WE. In the illustrated example, this may result in two opposing sections of defined electrodes RE, WE, which may be separated to form two distinct sections of bulk electrodes RE, WE. The sections of electrodes RE, WE may then be coated with an appropriate metallization M (e.g., Ag / AgCl for the reference electrode RE and / or IrO2 for the working electrode WE) and then processed accordingly (e.g., with the appropriate temperature treatment cycle for each particular metallization). The resulting electrodes RE, WE may then be Individualized and configured for use as a pH sensor 10, as described herein or otherwise (see FIG. 12B)

[0103] In some embodiments, the resulting electrodes RE, WE may be approximately 20 mm in length and approximately 2 mm in width, as shown in FIG. 12B. However, it will be understood that the electrodes RE, WE may be formed in other sizes depending on the particular application.

[0104] 13 and 14 show images of commercially available processing equipment suitable for carrying out at least some of the processing techniques described herein, with FIG. 13 showing a lab-scale version of the RK Flexible 100 printer utilizing a flexographic printing process and FIG. 14 showing an exemplary gravure printing system.

[0105] It is understood that any aspect and / or detail of pH sensor 10 and its elements described herein may be combined with any aspect and / or detail of any other embodiment of pH sensor 10 and its elements to form additional embodiments of pH sensor 10 and its elements.

[0106] While the present invention has been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

[0107] While certain presently preferred embodiments of the invention have been described herein, it will be apparent to those skilled in the art to which the invention pertains that variations and modifications of the described embodiments can be made without departing from the spirit and scope of the invention.

Claims

1. pH sensors include: a flexible base substrate including an upper base surface; and a first electrode including a first electrode surface coupled to the upper base surface and having a first metallization facing away from the upper base surface; a second electrode including a second electrode surface coupled to the upper base surface and having a second metallization facing away from the upper base surface; The first wiring includes a first line first end electrically connected to the first metallization and a first line second end adapted to be electrically connected to a separate device. The second wiring includes a second line first end electrically connected to the second metallization and a second line second end adapted to be electrically connected to a separate device. The first and second metallizations are selected to provide an indication of the pH level of a test material in electrical contact with the first and second metallizations by making an electrical measurement across the first and second conductive lines using separate instruments.

2. 10. The pH sensor of claim 1, wherein the first metallization comprises silver / silver chloride (Ag:AgCl) and the second metallization comprises iridium oxide (IrO2).

3. 10. The pH sensor of claim 1, wherein the first and second conductive traces are configured on a flexible connection substrate bonded to an upper base surface and adjacent the first and second electrodes.

4. 10. The pH sensor of claim 1, wherein the first conductive line is electrically connected to the first metallization using a first conductive tape and / or the second conductive line is electrically connected to the second metallization using a second conductive tape.

5. 5. The pH sensor of claim 4, further comprising a first adhesive layer encapsulating the first conductive line, the first metallization, and at least a portion of the first conductive tape, and / or a second adhesive layer encapsulating the second conductive line, the second metallization, and at least a portion of the second conductive tape.

6. 6. The pH sensor according to claim 5, further comprising a protective sheet covering at least a portion of the first adhesive layer and / or the second adhesive layer.

7. 10. The pH sensor of claim 1, further comprising: a third electrode including a third electrode surface coupled to the upper base surface and having a third metallization facing away from the upper base surface; The third wiring includes a third line first end electrically connected to the third metallization and a third line second end adapted to be electrically connected to a separate device.

8. 10. The pH sensor of claim 1, further comprising: The third conductive line is adjacent to the first conductive line or the second conductive line and is adapted to be electrically connected to a separate device. a thermal sensor electrically connected between the third conductive line and the first conductive line or between the third conductive line and the second conductive line;

9. pH sensors include: a flexible base sheet including an upper base surface a first conductive line configured on the upper base surface and including a first line first end and a first line second end, the first line second end adapted to be electrically connected to a separate device; a second conductive line configured on the upper base surface and including a second line first end and a second line second end, the second line second end adapted to be electrically connected to a separate device; The first electrode includes a first electrode surface electrically attached to the first conductive line at a first end of the first line, the first electrode surface facing away from the upper base surface. A second electrode including a second electrode surface is electrically attached to the second conductive line at a first end of the second line, the first electrode surface facing away from the upper base surface. The first and second metallizations are selected to provide an indication of the pH level of a test material in electrical contact with the first and second metallizations by making an electrical measurement across the first and second conductive lines using separate instruments.

10. 10. The pH sensor of claim 9, wherein the first electrode is electrically attached to the first conductive wire and the second electrode is electrically attached to the second conductive wire using a conductive adhesive or wire bonding.

11. 10. The pH sensor of claim 9, wherein the first electrode includes a first electrical via passing from the first metallization to the first conductive line, and / or the second electrode includes a second electrical via passing from the second metallization to the second conductive line.

12. A method for manufacturing a pH sensor includes: Providing a base substrate having a first surface coated with a first metallization. Coating the first metallization with a second metallization defining at least one first electrode on the third metallization; and separating at least one of the at least one defined first electrode to form at least one separate first electrode; Coating at least a portion of at least one distinct first electrode with a third metallization. The third metallization is selected to provide an indication of the pH level of a test material in electrical contact with the third metallization by making an electrical measurement between the third metallization and a corresponding electrode using a separate instrument.

13. 13. The method of claim 12, further comprising: Coating the first metallization with a fourth metallization defining at least one second electrode on the fourth metallization; and separating at least one of the at least one defined second electrode to form at least one separate second electrode; Coating at least a portion of at least one distinct second electrode with a third metallization. The third metallization is selected to provide an indication of the pH level of a test material in electrical contact with the fourth metallization and the third metallization by making an electrical measurement between the fourth metallization and the third metallization using a separate instrument.

14. 14. The method of claim 13, further comprising: providing a first laminate sheet and a second laminate sheet; providing an insulating layer; At least one distinct first electrode, at least one distinct second electrode, and an insulating layer are disposed between the first laminate sheet and the second laminate sheet to form a pH sensor assembly. Stacking the pH sensor assemblies to form at least one pH sensor

15. 15. The method of claim 14, wherein the first and second laminate sheets and the insulating layer include a first opening aligned to expose at least a portion of the first discrete electrode and a second opening aligned to expose at least a portion of the second discrete electrode.

16. 13. The method of claim 12, wherein the second metallization comprises gold.

17. The method for manufacturing a pH detection electrode includes: Providing a first substrate including a first surface Coating the first surface with a layer of iridium chloride to form a first coated substrate. and calcining the first coated substrate through at least one temperature cycle, the calcining comprising converting at least a portion of the layer of iridium chloride to a layer of iridium oxide.

18. 18. The method of claim 17, wherein the layer of iridium oxide comprises a thickness crystallized to provide sufficient interlocked surface area for proton transfer.

19. 18. The method of claim 17, wherein the coating of the first surface with a layer of iridium chloride is carried out using a single cycle and at least one The temperature cycle involves heating the first coated substrate at about 50°C-150°C for about 1-2 hours, and then at about 275°C-350°C for about 4-6 hours.

20. 18. The method of claim 17, wherein coating the first surface with a layer of iridium chloride is carried out using two or more cycles, at least one temperature cycle of each cycle comprising heating the first coated substrate to about 50°C-70°C for 2-5 minutes, and then to about 90°C-115°C for about 10-20 minutes.

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